ALBERT

Description: After the successful construction and operation experience of the 10 MW high-temperature gas-cooled reactor (HTR-10), a high-temperature gas-cooled pebble-bed modular (HTR-PM) demonstration plant is under construction in Shidao Bay, Rongcheng City, Shandong province, China. An online gross monitoring instrument has been designed and placed at the exit of the helium purification system (HPS) of HTR-PM and is used to detect the activity concentration in the primary circuit after purification. The source terms in the primary loop of HTR-PM and the helium purification process were described. The detailed configuration of the gross monitoring instrument was presented in detail. The Monte Carlo method was used to simulate the detection efficiency of the monitoring system. Since the actual source terms in the primary loop of HTR-PM may be different than the current design values, a sensitivity analysis of the detection efficiency was implemented based on different relative proportions of the nuclides. The accuracy and resolution of the NaI(Tl) detector were discussed as well.

Description: In this study, an exergy analysis of two kinds of solar-driven cogeneration systems consisting of solar collectors and an organic Rankine cycle (ORC) is presented for series mode and parallel mode. Three kinds of solar collectors are considered: flat-plate collectors (FPC), evacuated tube collectors (ETC), and parabolic trough collectors (PTC). This study mainly compares the exergy output of the two kinds of solar cogeneration systems under different temperatures of the return heating water and different inlet temperatures of the solar collectors. This study shows that, from the perspective of or , the parallel mode is superior to the series mode. From the perspective of , the parallel mode is superior to the series mode when the solar collector is FPC; however, the series mode is superior to the parallel mode when the solar collector is PTC. When the solar collector is ETC, the result depends on the temperature of the return heating water. When the temperature of the return heating water is low (below 46°C), the series mode is better, and when the temperature of the return heating water is high (above 46°C), the parallel mode is better.

Description: The assessment of hydrogen release, distribution, and mitigation measures in the containment of a nuclear power plant is increasingly based on code calculations. These calculations require state-of-the-art experiments to benchmark the codes against them. Two of these experiments are presented in this paper. These experiments were conducted in the PANDA facility (Switzerland) in the framework of the OECD/NEA HYMERES project. The experiments consider natural circulation flow in a two-room type containment where flow loops can form between the inner and the outer zones. During normal operation these zones are separated and in the case of an accident they become either connected by the opening of rupture disks, convective foils, and dampers or connected by bursting of doors and opening of other connections between compartments. For the experiments considered here one lower PANDA-vessel represents the steam generator (SG) tower and the inaccessible area whereas the other vessel represents the outer room area. The lower vessels are isolated from one another except for a small aperture that represents the damper. The two upper vessels—representing the containment dome—are connected to the lower vessels through tubes. The scenario consisted of four phases. In phase 1, a high steam mass flow rate was injected in the vessel representing the SG tower. After the relaxation phase 2, helium (representing hydrogen) was injected in the same vessel (phase 3). Finally in phase 4 no active interventions were done until the end of the test. Two tests were conducted to evaluate the developing helium transport by the natural circulation flow: one with and one without damper (by closing the aperture). The results showed that a two-room containment (TRC) mixing scenario can be well represented with the PANDA facility. It is found that, with the mixing damper open, a global natural circulation loop develops over all four vessels, whereas with closed damper the natural circulation loop is established only between the three vessels representing the inner zone and the upper dome. It is shown that the presence of the damper has a strong effect on the resulting helium content in the inner zone with 3 times less helium at the end of the test compared with the configuration without damper. The formation of a stable helium stratification in the upper vessels was observed in the presence of the open damper.

Description: This work focuses on the impact of the devolatilization and char combustion mode modelling on the structure of a large-scale, biomass and coal co-fired flame using large eddy simulations. The coal modelling framework previously developed for the simulation of combustion in large-scale facilities is extended for biomass capabilities. An iterative procedure is used to obtain devolatilization kinetics of coal and biomass for the test-case specific fuels and heating conditions. This is achieved by calibrating the model constants of two empirical models: the single first-order model and the distributed activation energy model. The reference data for calibration are devolatilization yields obtained with predictive coal and biomass multistep kinetic mechanisms. The variation of both particle density and diameter during char combustion is governed by the conversion mode, which is modelled using two approaches: the power law using a constant parameter that assumes a constant mode during char combustion and a constant-free model that considers a variable mode during combustion. Three numerical cases are considered: single first-order reaction with constant char combustion mode, distributed activation energy with constant char combustion mode, and single first-order reaction with variable char combustion mode. The numerical predictions from the large eddy simulations are compared with experimental results of a high co-firing rate large-scale laboratory flame of coal and biomass. Furthermore, results from single particle conversion under idealised conditions, isolating the effects of turbulence, are presented to assist the interpretation of the predictions obtained with large eddy simulations. The effects of the devolatilization and conversion mode modelling on the flame lift-off, flame length, and spatial distribution and radial profiles of O2 and CO2 are presented and discussed. Both the devolatilization and conversion mode modelling have a significant effect on the conversion of particles under idealised conditions. The large eddy simulations results show that the devolatilization model has a strong impact on the flame structure, but not on the flame lift-off. On the other hand, for the tested numerical conditions, the char combustion mode model has a marginal impact on the predicted results.

Description: The LOCA (loss of coolant accident) is a kind of severe accident in the operation of PHWR (pressurized heavy water reactor) as well as other nuclear facilities, and possible cause of LOCA can be counted on the ballooning of pressure tube (PT) contacted to the outer calandria tube (CT) in the moderator system of CANDU-6 reactors. In the paper, we simulated the 150-kW experimental facility proposed by IAEA/ISCP, modeling the transient creeping behavior of pressurized tube heated with thermal radiation between the gaps of two concentric pipes. The outer boundary is simplified with a switched model that depends on the local temperature. With a multiphysical model supported by a commercial code, COMSOL multiphysics, the unsteady phenomena are simulated with models concerning various kinds of mechanics such as thermodynamics, nonlinear structural dynamics, and two-phase boiling heat transfer models.

Description: BWRs are thus far the simplest energy systems to transform fission energy into electrical power. However, there are still many aspects in their operation that, under certain conditions, may induce BWR unstable behavior. The default indicator to study BWR unstable behavior is the Decay Ratio (DR). However, due to the fact that BWRs show very complex responses under instability and responses that may even be chaotic, the DR might not be a suitable choice to rely on to accommodate for such intricate behavior. In this work a novel methodology based on the Sample entropy (SampEn) and the noise-assisted multivariate empirical mode decomposition (NA-MEMD) is introduced. Such methodology was developed thinking for a real time-implementation of a stability monitor. The proposed methodology was tested with a set of signals that stem from several nuclear power plants in operation today that have experienced in the past unstable events, each one of a different nature.

Description: Vigorously developing nuclear power is the main development direction of current renewable energy. In the nuclear environment, in order to avoid nuclear radiation damage to maintenance personnel and improve the efficiency of nuclear reaction, it is necessary and urgent to realize automatic replacement of vulnerable parts in the electron gun. As the key equipment for the generation and control of nuclear reactions in nuclear reactors, electron guns have been widely used in nuclear power plants of traveling wave reactors. However, the “high-voltage conductive ring” in electron guns is a vulnerable part. It is likely to cause nuclear reactor accidents when the vulnerable part is damaged. Automatic replacement of vulnerable parts is an important part of the entire maintenance equipment. Considering the entire maintenance equipment and the working environment, an innovative design process for vulnerable parts replacement is established. Under the guidance of the process, in order to ensure the continuity of a series of maintenance actions, the technical contradiction resolution theory is first used to conduct the overall analysis of the general direction to obtain the design layout. Then, the contradiction resolution theory and the object-field model analysis are utilized to get and improve the detailed design of the device mechanism. The theory of TRIZ can help us to get the overall mechanical structure design that meets the engineering requirements. The device is designed with a replacement part adjustment scheme to ensure the completion of the maintenance actions. Furthermore, the design provides a solution to the possible jamming phenomenon in the automatic maintenance process and achieves the maximum use efficiency of the storage and replacement of vulnerable parts.

Description: This study was carried out to examine the potential of antimony tri-iodide (SbI3) as a material for radiation detectors that operate at room temperature. SbI3 is a compound semiconductor with an AsI3-type crystal structure, high atomic number (Sb: 51, I: 53), high density (4.92 g/cm3), and a wide band-gap energy (2.2 eV). In addition, crystalline SbI3 is easy to grow by conventional crystal growth techniques from melting phase because the material exhibits a low melting point (171°C) and undergoes no phase transition in the range of its solid phase. In this study, SbI3 crystals were grown by the Bridgman method after synthesis of SbI3 from 99.9999% pure Sb and 99.999% pure I2. The grown crystals consisted of several large grains with red color and were confirmed to be single-phase crystals by X-ray diffraction analysis. SbI3 detectors with a simple planar structure were fabricated using the cleavage plates of the grown crystals, and the pulse-height spectra were recorded at room temperature using an 241Am alpha-particle (5.48 MeV) source. The detector showed response to the alpha-particle radiation.

Description: Pharmaceuticals are present in an aquatic environment usually in low (ng/L) concentrations. Their continuous release can lead to unwanted effects on the nontarget organisms. The main points of their collection and release into the environment are wastewater treatment plants. The wastewater treatment plants should be upgraded by new technologies, like advanced oxidation processes (AOPs), to be able to degrade these new pollutants. In this study, the degradation of albendazole (ALB), a drug against parasitic helminths, was investigated using four UV-based AOPs: UV photolysis, UV photocatalysis (over TiO2 film), UV + O3, and UV + H2O2. The ranking of the degradation process degree of the ALB and its degradation products for studied processes is as follows: UV photolysis 

Description: The energy scenario today is focused on the development and usage of solar cells, especially in the paradigm of clean energy. To readily create electron and hole pairs, solar cells utilize either photoactive or photosensitive components. A bulk heterojunction (BHJ) is a nanolayer consisting of donor and acceptor components with a large interpenetrated acceptor and donor contact area. In this context, a mix of P3HT and PCBM offers novelty for its use as an acceptor as well as a donor. In the work presented here, we address the mechanism of modelling and characterization of a BHJ-based polymer solar cell. Here, a new design of BHJ polymer solar cells have been designed, modelled, using Silvaco TCAD in the Organic Solar module, and matched with an already assembled device having similar features. Using this model, we have been able to estimate key parameters for the modelled devices, such as the short-circuit current density, open-circuit voltage, and fill factor with less than 0.25 error index compared to the fabricated counterpart, paving the way for fabless polymer solar cell design and optimization.

Description: This work undertakes both simulation and experimental studies of a new design of a photovoltaic thermal solar air collector (PV/T). In order to improve the thermal and electrical performances for a specific application, the analytical expressions for thermal parameters and efficiency are derived by developing an energy balance equation for each component of the PV/T air collector. This type of hybrid collector can be applied in the facades of buildings. The electricity and heat produced will satisfy the energy needs of the buildings, while ensuring an aesthetic view of its facades. A typical prototype was designed, constructed, and implemented in the applied research unit on renewable energies in Ghardaia, situated in the south of Algeria. This region has semiarid characteristics. Results obtained by an experimental test are presented and compared to those predicted through simulation. Results include the temperature of each component of the PV/T collector and air temperature at the inlet and outlet of the channel. It has been found that the theoretical results predicted by the developed mathematical model, for instance, outlet temperature, agree with those found through experimental work.

Description: Mismatching operating conditions negatively affect the extracted energy in photovoltaic (PV) systems. They may also lead to dangerous localized heating phenomena (hot spots) that can cause, in turn, accelerated ageing and reduced reliability. Since the adoption of bypass diodes or smart active switches does not prevent the occurrence of hotspots, it is necessary to investigate alternative strategies. A promising solution is represented by the proper regulation of the operating point of the PV cells in the current vs. voltage (-) or power vs. voltage (-) planes when mismatching conditions occur. In particular, in this paper, the existence of operating points allowing a suitable compromise between maximization of the extracted power and minimization of thermal stresses, due to hot spots, is experimentally evidenced. Experimental results highlighting the link existing between the operating point in the - plane and the PV cell temperature distribution under uniform and mismatching operating conditions are presented and discussed. On the basis of the obtained experimental results, it is possible to state that, when mismatching conditions occur, it is mandatory to properly choose the operating point: the global maximum power point may not be the best operating point. Hence, it is crucial to gain information about the eventual occurrence of mismatching conditions in order to be able to properly choose the best operating point. Therefore, another crucial aspect that is evidenced in this paper is represented by the fact that the detection of the occurrence of mismatching conditions, based on the analysis of the shape of the - and/or - characteristics, is effective only if the analysis is carried out for both positive and negative voltages.

Description: Highly light scattering structures have been generated in a poly(ethylene terephthalate) (PET) film using a CO2 laser. The haze, and in some cases the transparency, of the PET films have been improved by varying the processing parameters of the laser (namely, scanning velocity, laser output power, and spacing between processed tracks). When compared with the unprocessed PET, the haze has improved from an average value of 3.26% to a peak of 55.42%, which equates to an absolute improvement of 52.16% or a 17-fold increase. In addition to the optical properties, the surfaces have been characterised using optical microscopy and mapped with an optical profilometer. Key surface parameters that equate to the amount and structure of surface roughness and features have been analysed. The CO2 laser generates microstructures at high speed, without affecting the bulk properties of the material, and is inherently a chemical-free process making it particularly applicable for use in industry, fitting well with the high-throughput, roll to roll processes associated with the production of flexible organic photovoltaic devices.

Description: This study is aimed at providing a comparison between fuzzy systems and convectional P&O for tracking MPP of a PV system. MATLAB/Simulink is used to investigate the response of both algorithms. Several weather conditions are simulated: (i) uniform irradiation, (ii) sudden changing, and (iii) partial shading. Under partial shading on a PV panel, multipeaks appeared in - characteristics of the panel. Simulation results showed that a fuzzy controller effectively finds MPP for all weather condition scenarios. Furthermore, simulation results obtained from the FLC are compared with those obtained from the P&O controller. The comparison shows that the fuzzy logic controller exhibits a much better behavior.

Description: This paper presents capacity of the passive decay heat removal system (DHRS) operated under the natural circulation conditions to remove decay heat inside the main vessel of the Lead-bismuth eutectic cooled Fast Reactor (LFR). The motivation of this research is to improve the inherent safety of the LFR based on the China Accelerator Driven System (ADS) engineering project. Usually the plant is damaged due to the failure of the main pumps and the main heat exchangers under the Station Blackout (SBO). To prevent this accident, we proposed the DHRS based on the diathermic oil cooling for the LFR. The behavior of the DHRS and the plant was simulated using the CFD code STAR CCM+ using LFR with DHRS. The purpose of this analysis is to evaluate the heat exchange capacity of the DHRS and is to provide the reference for structural improvement and experimental design. The results show that the stable natural circulations are established in both the main vessel and the DHRS. During the decay process, the heat exchange power is above the core decay heat power. In addition, in-core decay heat and heat storage inside the main vessel are efficiently removed. All the thermal-hydraulics parameters are within a safe range. Moreover, the highest temperature occurs at the upper surface of the core. A swirl occurs at the corner of the lateral core surface and some improvements should be considered. And the natural circulation driving force can be further increased by reducing the loop resistance or increasing the natural circulation height based on the present design scenario to enhance the heat exchange effect.

Description: There has been considerable progress in the area of fuel surrogate development to emulate gasoline fuels’ oxidation properties. The current paper aims to review the relevant hydrocarbon group components used for the formulation of gasoline surrogates, review specific gasoline surrogates reported in the literature, outlining their utility and deficiencies, and identify the future research needs in the area of gasoline surrogates and kinetics model.

Description: Source term analysis is important in the design and safety analysis of advanced nuclear reactor and also provides a radiation safety analysis basis for Modular High-Temperature Gas-Cooled Reactor (HTR). High-Temperature Gas-Cooled Reactor-Pebble-bed Modules (HTR-PM) design by China is a typical Gen-IV and due to different safety concepts and systems, the implements of source term analysis in light water reactors are not entirely applicable to HTR-PM. To solve this problem, HTR-PM Source Term Analysis Code (HTR-STAC) has been developed and related V&V has been finished. HTR-STAC consists of five units, including LOOP (Primary Circuit Source Term Analysis Code), NORMAL (Normal Condition Airborne Source Term Analysis Code), ARCC (Accident Release Category Calculation code), CARBON (C-14 Source Term Analysis Code), and TRUM (Tritium Source Term Analysis Code). LOOP and NORMAL may be used as calculating primary circuit coolant radioactivity and the release of airborne radioactivity to the environment under normal operating conditions of HTR-PM, respectively. The code ARCC composed of several source term analysis programs in the different typical accidents scenario, including SGTR (Steam Generator Tube Rupture), LOCA (Loss of Coolant Accident), and the Transient Process, is compiled based on the results given by LOOP and NORMAL. CARBON and TRUM are developed to calculate the productions of C-14 and H-3 through a different mechanism. Furthermore, the V&V has been performed and show some positive results.

Description: A 2 inch, cold-leg loss-of-coolant accident (LOCA) in a 900 MWe generic Western PWR was simulated using ASTEC 2.1.1 and MAAP 5.02. The progression of the accident predicted by the two codes up to the time of vessel failure is compared. It includes the primary system depressurization, accumulator discharge, core heat-up, hydrogen generation, core relocation to lower plenum, and lower head breach. The purpose of the code comparison exercise is to identify modelling differences between the two codes and the user choices affecting the results. The two codes predict similar primary system depressurization behaviour until the accumulation injection, confirming similar break flow and primary system thermal-hydraulic response calculations between the two codes. The choice of the accumulator gas expansion model, either isentropic or isothermal, affects the rate and total amount of coolant injected and thereby determines whether the core is quenched or overheated and attains a noncoolable geometry during reflooding. A sensitivity case was additionally simulated by each code to allow comparisons to be made with either accumulator gas expansion models. The two codes predict similar amount of in-vessel hydrogen generated and core quench status for a given accumulator gas expansion model. ASTEC predicts much larger initial core relocation to lower plenum leading to an earlier vessel failure time. MAAP predicts more gradual core relocation to lower plenum, prolonging the lower plenum debris bed heat-up and time to vessel failure. Beside the effect of the code user in conducting severe accident simulations, some discrepancies are found in the modelling approaches in each code. The biggest differences are found in the in-vessel melt progression and relocation into the lower plenum, which deserve further research to reduce the uncertainties.

Description: In order to study the evolution process and hydraulic characteristics of pressurizer insurge in CPR1000 pressurized water reactor (PWR), the computational fluid dynamics (CFD) of three-dimensional unsteady heat transfer was used to capture the temperature and velocity fluctuation intensity of the mixing of the hot and cold. The results show that Realizable k–ε Turbulence Model combined with VOF multiphase heat transfer model can effectively predict the development trend of pressurizer insurge process. The small diameter pressurizer surge line of CPR1000 enhances the intensity of velocity fluctuation. From the essence of flow and heat transfer, it is concluded that buoyancy force can increase the degree of fluctuation and make an accelerated effect on the influx cold fluid. The electric heater inside the pressurizer should be arranged as far as possible in z0.45m; it is beneficial to improve its harsh operating environment. This research can provide reference for the structural design of pressurizer and the layout optimization of the electric heater.

Description: Nonuniform distribution of tri-structural-isotropic (TRISO) fuel particles in a spherical fuel element (SFE) may increase the failure probability of the SFE in the high-temperature gas-cooled reactor, leading to the release of fission products. To evaluate the uniformity of the TRISO particles nondestructively, 3-dimensional cone-beam computed tomography is used to image the SFE, and TRISO particles are segmented. After TRISO particle positions are identified, the Voronoi tessellation and Delaunay triangulation are used to extract several geometric metrics. Results indicate that both the Voronoi volume distribution and the nearest neighbor-distance distribution follow the log-normal distributions, which provide strong evidence that the TRISO particles are approximately randomly uniformly distributed. Further study will be focused on validating the conclusion with more SFE data.

Description: Flame stability and pollution control are significant problems in the design and operation of any combustion system. Real-time monitoring and analysis of these phenomena require sophisticated equipment and are often incompatible with practical applications. This work explores the feasibility of model-based combustion monitoring and real-time evaluation of proximity to lean blowout (LBO). The approach uses temperature measurements, coupled with Chemical Reactor Network (CRN) model to interpret the data in real-time. The objective is to provide a computationally fast means of interpreting measurements regarding proximity to LBO. The CRN-predicted free radical concentrations and their trends and ratios are studied in each combustion zone. Flame stability and a blowout of an atmospheric pressure laboratory combustor are investigated experimentally and via a phenomenological real-time Chemical Reactor Network (CRN). The reactor is operated on low heating value fuel stream, i.e., methane diluted with nitrogen with N2/CH4 volume ratios of 2.25 and 3.0. The data show a stable flame-zone carbon monoxide (CO) level over the entire range of the fuel-air equivalence ratio (Φ), and a significant increase in hydrocarbon emissions approaching blowout. The CRN trends agree with the data: the calculated concentrations of hydroxide (OH), O-atom, and H-atom monotonically decrease with the reduction of Φ. The flame OH blowout threshold is 0.025% by volume for both fuel mixtures. The real-time CRN allows for augmentation of combustion temperature measurements with modeled free radical concentrations and monitoring of unmeasurable combustion characteristics such as pollution formation rates, combustion efficiency, and proximity to blowout. This model-based approach for process monitoring can be useful in applications where the combustion measurements are limited to temperature and optical methods, or continuous gas sampling is not practical.

Description: The Fukushima accident has reiterated that the seismic safety is a clear necessity in the design of nuclear power plants. To overcome the weaknesses of the plant design, appropriate measures or interventions have thus to be put in place to improve the nuclear safety. In this study, seismic isolation, widely adopted for conventional constructions, is considered as retrofit measure to provide superior performance of plant itself, even when exceptional events occur. In this paper, we numerically investigate the dynamic behaviour of a Small Modular Reactor (SMR) plant subjected to 0.6g PGA; in doing that time-history analysis has been performed assuming the reactor building with and without isolators. For that purpose, a suitable FEM model has been implemented to provide in-structure response spectra at safety relevant locations and subsystem supports. Adequate steel and concrete properties as well as isolators properties, experimentally determined, have been assumed. Results have shown the benefits of seismic isolation for NPP that can so sustain levels of loading beyond the design input and demonstrated that failure of an isolation system cannot occur before failure of the isolated structure. However, the large horizontal displacements of the structure require appropriate considerations in the layout and interfaces for interconnected systems.

Description: Ionization in flames is of interest in the design and development of modern combustion devices. The identity and concentration of various charged species in reacting mixtures can play an important role in the diagnostics and control of such devices. Simplified chemistry computations that provide good estimates of ionic species in complex flow-fields can be used to model turbulent reacting flows in various combustion devices, greatly reducing the required computational resources for design and development studies. A critical assessment of the use of the equilibrium chemistry method to compute charged species concentration in combusting mixtures under various temperatures, pressures, and thermal disequilibrium conditions is presented. The use of equilibrium chemistry to compute charged species concentrations in propane-air mixtures performed by Calcote and King has been extended. A more accurate computational methodology that includes the effect of negative ions, chemi-ions (H3O+ and CHO+), and thermal nonequilibrium was investigated to evaluate the suitability of equilibrium computations for estimating charged species concentrations in reacting mixtures. The results show that equilibrium computations which include the effects of H3O+ and elevated electron temperatures can indeed explain the levels of ion concentrations observed in laboratory flame experiments under lean and near-stoichiometric conditions. Furthermore, under engine-like conditions at higher temperatures and pressures, equilibrium computations can be used to obtain useful estimates of charged species concentrations in modern combustion devices.

Description: A new method based on shifted Chebyshev series of the first kind is introduced to solve stiff linear/nonlinear systems of the point kinetics equations. The total time interval is divided into equal step sizes to provide approximate solutions. The approximate solutions require determination of the series coefficients at each step. These coefficients can be determined by equating the high derivatives of the Chebyshev series with those obtained by the given system. A new recurrence relation is introduced to determine the series coefficients. A special transformation is applied on the independent variable to map the classical range of the Chebyshev series from to . The method deals with the Chebyshev series as a finite difference method not as a spectral method. Stability of the method is discussed and it has proved that the method has an exponential rate of convergence. The method is applied to solve different problems of the point kinetics equations including step, ramp, and sinusoidal reactivities. Also, when the reactivity is dependent on the neutron density and step insertion with Newtonian temperature feedback reactivity and thermal hydraulics feedback are tested. Comparisons with the analytical and numerical methods confirm the validity and accuracy of the method.

Description: The subcooling effect on pool boiling heat transfer using a copper microporous coating was experimentally studied in water for subcoolings of 10 K, 20 K, and 30 K at atmospheric pressure and compared to that of a plain copper surface. A high-temperature thermally conductive microporous coating (HTCMC) was made by sintering copper powder with an average particle size of 67 μm onto a 1 cm × 1 cm plain copper surface with a coating thickness of ~300 μm. The HTCMC surface showed a two times higher critical heat flux (CHF), ~2,000 kW/m2, and up to seven times higher nucleate boiling heat transfer (NBHT) coefficient, ~350 kW/m2K, when compared with a plain copper surface at saturation. The results of the subcooling effect on pool boiling showed that the NBHT of both the HTCMC and the plain copper surface did not change much with subcooling. On the other hand, the CHF increased linearly with the degree of subcooling for both the HTCMC and the plain copper surface. The increase in the CHF was measured to be ~60 kW/m2 for every degree of subcooling for both the HTCMC and the plain surface, so that the difference of the CHF between the HTCMC and the plain copper surface was maintained at ~1,000 kW/m2 throughout the tested subcooling range. The CHFs for the HTCMC and the plain copper surface at 30 K subcooling were 3,820 kW/m2 and 2,820 kW/m2, respectively. The experimental results were compared with existing CHF correlations and appeared to match well with Zuber’s formula for the plain surface. The combined effect of subcooling and orientation of the HTCMC on pool boiling heat transfer was studied as well.

Description: An investigation of ultralean stratified, disk stabilized, propane flames operated with acoustic modulation of the inlet velocity and fuel-air mixture profiles is presented. Transverse acoustic forcing was applied to the air, upstream of a double-cavity premixer section, formed along three concentric disks, which fueled the stabilization region with a radial mixture gradient. Measurements and supporting Large Eddy Simulations with a nine-step mechanism for propane combustion were performed to evaluate variations in the ultralean flame characteristics under forced and unforced conditions. The effects of forcing on the heat release profiles and on the interaction of the toroidal flame with the recirculation region are examined and discussed. The impact of the acoustic excitation of inlet conditions on the local extinction behavior is, also, assessed by monitoring a local stability criterion and by analyzing phase-resolved chemiluminescence images.

Description: One of the severe accident management strategies for nuclear reactors is the melted corium retention inside the reactor pressure vessel. The work presented in this article investigates the application of in-vessel retention (IVR) severe accident management strategy in a BWR reactor. The investigations were performed assuming a scenario with the large break LOCA without injection of cooling water. A computer code RELAP/SCDAPSIM MOD 3.4 was used for the numerical simulation of the accident. Using a model of the entire reactor, a full accident sequence from the large break to core uncover and heat-up as well as corium relocation to the lower head is presented. The ex-vessel cooling was modelled in order to evaluate the applicability of RELAP/SCDAPSIM code for predicting the heat fluxes and reactor pressure vessel wall temperatures. The results of different ex-vessel heat transfer modes were compared and it was concluded that the implemented heat transfer correlations of COUPLE module in RELAP/SCDAPSIM should be applied for IVR analysis. To investigate the influence of debris separation into oxidic and metallic layers in the molten pool on the heat transfer through the wall of the lower head the analytical study was conducted. The results of this study showed that the focusing effect is significant and under some extreme conditions local heat flux from reactor vessel could exceed the critical heat flux. It was recommended that the existing RELAP/SCDAPSIM models of the processes in the debris should be updated in order to consider more complex phenomena and at least oxide and metal phase separation, allowing evaluating local distribution of the heat fluxes.

Description: Uncertainty of a severe accident code output needs to be handled reliably considering its use in safety regulation of nuclear industry. In particular, severe accident codes are utilized for probabilistic safety assessment (PSA), where the uncertainty of severe accident progress should be considered carefully due to its influence on human reliability analysis. Therefore, in this study, the uncertainty analysis of severe accident progress was performed using MELCOR code, and a total of 200 data sets of in-vessel uncertainty parameters were generated by Latin hypercube sampling method. The rank regression analysis was also performed to investigate the effect of uncertainty parameters on the severe accident progress. Sensitivity coefficients (SCs) in MELCOR such as molten clad drainage rate and zircaloy melt breakout temperature showed significant influence on relocation time and dryout time of lower plenum. However, the influence of uncertainty parameter diminished as the accident progressed.

Description: Compression ratio has very important influence on fuel economy, emission, and other performances of internal combustion engines. Application of variable compression ratio in diesel engines has a number of benefits, such as limiting maximal in cylinder pressure and extended field of the optimal operating regime to the prime requirements: consumption, power, emission, noise, and multifuel capability. The manuscript presents also the patented mechanism for automatic change engine compression ratio with two-piece connecting rod. Beside experimental research, modeling of combustion process of diesel engine with direct injection has been performed. The basic problem, selection of the parameters in double Vibe function used for modeling the diesel engine combustion process, also performed for different compression ratio values. The optimal compression ratio value was defined regarding minimal fuel consumption and exhaust emission. For this purpose the test bench in the Laboratory for Engines of the Faculty of Engineering, University of Kragujevac, is brought into operation.

Description: The discrete ordinates method (SN) is one of the mainstream methods for neutral particle transport calculations. Assessing the quality of the numerical solution and controlling the discrete error are essential parts of large-scale high-fidelity simulations of nuclear systems. Three error estimators, a two-mesh estimator, a residual-based estimator, and a dual-weighted residual estimator, are derived and implemented in the ARES transport code to evaluate the error of zeroth-order spatial discretization for SN equations. The difference in scalar fluxes on coarse and fine meshes is adopted to indicate the error in the two-mesh method. To avoid zero residual in zeroth-order discretization, angular fluxes within one cell are reconstructed by Legendre polynomials. The error is estimated by inverting the discrete transport operator using the estimated directional residual as an anisotropic source. The inner product of the forward directional residual and the adjoint angular flux is employed to quantify the error in quantities of interest which can be denoted by a linear functional of forward angular flux. Method of Manufactured Solutions (MMS) is adopted to generate analytical solutions for SN equation with scattering and the determined true error is used to evaluate the effectivity of these estimators. Promising results are obtained in the numerical results for both homogeneous and heterogeneous cases. The larger error region is well captured and the average effectivity index for the local error estimation is less than unity. For the series test problems, the estimated goal quantity error can be contained within an order of magnitude around the exact error.

Description: The essential power supply system is important for the nuclear safety and accident mitigation of the currently operating nuclear power plants. This system provides electrical power to the essential instrumentation and control systems of the nuclear power plant when all alternate current power sources are lost. This event is known as station blackout (SBO) event. Operational events of failure or deficiency of the essential power supply system are analyzed in this paper. The relevant events were searched and identified in four databases of operational events. The report includes events identified in French SAPIDE and German VERA operational events records for the time period 1996 to 2015. The International Atomic Energy Agency (IAEA) IRS and Nuclear Regulatory Commission (NRC) LER operational events databases were screened for relevant events that occurred in the period between 2000 and 2016. In total, 308 relevant events are identified in the SAPIDE, 103 in VERA, 56 in LER, and 15 in IRS operational events database. Classification and in-depth analysis were done on the identified events considering the following predefined categories: the plant status during the event, circumstances, affected equipment, cause of the event (direct and root), and implications of the event on plant safety. Main findings from the evaluation of the events are presented. Observations of the causes resulting in the events and potential actions that can decrease the number and consequences of the events are presented.

Description: Closed supercritical carbon dioxide (S-CO2) Brayton cycle is a promising alternative to steam Rankine cycle due to higher cycle efficiency at equivalent turbine inlet conditions, which has been explored to apply to nuclear, solar power, waste heat recovery, and coal-fired power plant. This study establishes 300MW S-CO2 power system based on modified recompression Brayton cycle integrated with coal-fired circulating fluidized bed (CFB) boiler. The influences of two stages split flow on system performance have been investigated in detail. In addition, thermodynamic analysis of critical operating parameters has been carried out, including terminal temperature difference, turbine inlet pressure/temperature, reheat stages, and parameters as well as compressor inlet pressure/temperature. The results show that rational distribution of split ratio to the recompressor (SR1) achieves maximal cycle efficiency where heat capacities of both sides in the low temperature recuperator (LTR) realize an excellent matching. The optimal SR1 decreases in the approximately linear proportion to high pressure turbine (HPT) inlet pressure due to gradually narrowing specific heat differences in the LTR. Secondary split ratio to the economizer of CFB boiler (SR2) can recover moderate flue gas heat caused by narrow temperature range and improve boiler efficiency. Smaller terminal temperature difference corresponds to higher efficiency and brings about larger cost and pressure drops of the recuperators, which probably decrease efficiency conversely. Single reheat improves cycle efficiency by 1.5% under the condition of 600°C/600°C/25Mpa while efficiency improvement for double reheat is less obvious compared to steam Rankine cycle largely due to much lower pressure ratio. Reheat pressure and main compressor (MC) inlet pressure have corresponding optimal values. HPT and low pressure turbine (LPT) inlet temperature both have positive influences on system performance.

Description: A steam explosion in a reactor cavity makes a mechanical load of the pressure pulse, which can result in a failure of the containment isolation. To prove the integrity of the containment during the ex-vessel steam explosion, the effects of water conditions on a steam explosion have to be identified, and the impulse of a steam explosion has to be exactly assessed. In this study, the analyses for steam explosions were performed for the conditions of a partially flooded cavity and a submerged-vessel in a pressurized water reactor. The entry velocity of a corium jet for the scale of the test facility was varied to simulate the two plant conditions. The TEXAS-V code was used for simulating the phases of premixing and explosion, and the load of a steam explosion was estimated based on the pressure variation. The impulse of a steam explosion under the condition of a corium jet falling into water without a free-fall height is bigger than that under a free-fall height. The fragmented mass of corium in an explosion phase and the distribution of steam fraction are the main parameters for the total load of the steam explosion. This study is expected to contribute to analyses of a steam explosion for a severe accident management strategy.

Description: Liquid annular seals are primarily used to control the leakage in high-speed turbomachinery, especially in nuclear and petrochemical pumps. In this paper, a theoretical analysis method for dynamic characteristics of liquid seals with herringbone grooves on the stator is proposed based on bulk-flow theory. Steady-state velocities and leakage rates within the upstream and downstream spiral parts and the middle plain part taking account of the pumping effects are figured out first with the inertia term of the fluid within the whole seal. Then, the dynamic characteristics of the whole seal are solved based on Childs’ finite-length solutions and verified by comparing with experimental hydraulic forces. Moreover, characteristic coefficients and instability parameters of the herringbone-grooved teeth-on-stator (TOS) seals and teeth-on-rotor (TOR) seals of the same size under different pressure differences are predicted and compared in detail. The influences of the lengths of constituent parts on the dynamic characteristics and instability parameters of the model seals are theoretically investigated. The results show that the stability of the TOS seal is much better than that of the TOR seal under most operating conditions. And the lengths of the middle plain part significantly affect the dynamic characteristics and the stability parameter.

Description: Recompression supercritical carbon dioxide (SCO2) Brayton Cycle for the Chinese Initiative Accelerator Driven System (CiADS) is taken into account, and flexible thermodynamic modeling method is presented. The influences of the key parameters on thermodynamic properties of SCO2 Brayton Cycle are discussed and the comparative analyses on genetic algorithm and pattern search algorithm are conducted. It is shown that the cycle parameters such as turbine inlet temperature, pressure ratio, outlet temperature at the hot end of condenser, and terminal temperature difference of regenerator 1 and regenerator 2 have significant effects on the cycle thermal efficiency. The calculation results indicate that pattern search algorithm has better optimization performance and quicker calculating speed than genetic algorithm. The result of optimization of the parameters for CiADS with supercritical carbon dioxide Brayton Cycle is 35.97%. Compared with other nuclear power plants of SCO2 Brayton Cycle, CiADS with SCO2 Brayton Cycle does not have the best thermal efficiency, but the thermal efficiency can be improved with the reactor outlet temperature increases.

Description: The code assessment typically comprises basic tests cases, separate effects test, and integral effects tests. On the other hand, the thermal hydraulic system codes like RELAP5/MOD3.3 are primarily intended for simulation of transients and accidents in light water reactors. The plant measured data come mostly from startup tests and operational events. Also, for operational events the measured plant data may not be sufficient to explain all details of the event. The purpose of this study was therefore besides code assessment to demonstrate that simulations can be very beneficial for deep understanding of the plant response and further corrective measures. The abnormal event with reactor trip and safety injection signal actuation was simulated with the latest RELAP5/MOD3.3 Patch 05 best-estimate thermal hydraulic computer code. The measured and simulated data agree well considering the major plant system responses and operator actions. This suggests that the RELAP5 code simulation is good representative of the plant response and can complement not available information from plant measured data. In such a way, an event can be better understood.

Description: The purpose of this paper is to conduct an experimental research on the impact of mixing ratio of biodiesel from waste cooking oil and an innovative diesel fuel (in which a renewable component is contained) on the emissions of an up-to-date light and compact small engine that has a leading role in city cars and urban vehicles. Two blends’ mixing ratios (20% and 40% by volume) were tested and the results were compared to those obtained when the engine was operated with low sulfur diesel (ULSD) and ULSD blended with 15% by volume of renewable diesel. The results indicate that diesel+ enhances CO and HC emissions in the exhaust as regards ULSD. Blending diesel+ with WCO causes a further reduction for most of the engine operative field. Concerning particulate emission, accumulation mode dominates for all fuels. Diesel+ is always characterized by lower mean diameters as regards ULSD. The addition of WCO further reduces the court mean diameter. Particle number concentration obtained by fuelling the engine with B40 is the lowest as regards all the other tested fuels. Concerning , a moderate increase of the emission was observed when fuelling the engine with diesel+, net or in blends.

Description: The Separation and Safeguards Performance Model (SSPM) uses MATLAB/Simulink to provide a tool for safeguards analysis of bulk handling nuclear processing facilities. Models of aqueous and electrochemical reprocessing, enrichment, fuel fabrication, and molten salt reactor facilities have been developed to date. These models are used for designing the overall safeguards system, examining new safeguards approaches, virtually testing new measurement instrumentation, and analyzing diversion scenarios. The key metrics generated by the models include overall measurement uncertainty and detection probability for various material diversion or facility misuse scenarios. Safeguards modeling allows for rapid and cost-effective analysis for Safeguards by Design. The models are currently being used to explore alternative safeguards approaches, including more reliance on process monitoring data to reduce the need for destructive analysis that adds considerable burden to international safeguards. Machine learning techniques are being applied, but these techniques need large amounts of data for training and testing the algorithms. The SSPM can provide that training data. This paper will describe the SSPM and its use for applying both traditional nuclear material accountancy and newer machine learning options.

Description: The growth of soot volume fraction and aggregate size was studied in burner-stabilized premixed C2H4/air flames with equivalence ratios between 2.0 and 2.35 as function of height above the burner using laser-induced incandescence (LII) to measure soot volume fractions and angle-dependent light scattering (ADLS) to measure corresponding aggregate sizes. Flame temperatures were varied at fixed equivalence ratio by changing the exit velocity of the unburned gas mixture. Temperatures were measured using spontaneous Raman scattering in flames with equivalence ratios up to = 2.1, with results showing good correspondence (within 50 K) with temperatures calculated using the San Diego mechanism. Both the soot volume fraction and radius of gyration strongly increase in richer flames. Furthermore, both show a nonmonotonic dependence on flame temperature, with a maximum occurring at ~1675 K for the volume fraction and ~1700 K for the radius of gyration. The measurement results were compared with calculations using two different semiempirical two-equation models of soot formation. Numerical calculations using both mechanisms substantially overpredict the measured soot volume fractions, although the models do better in richer flames. The model accounting for particle coagulation overpredicts the measured radii of gyration substantially for all equivalence ratios, although the calculated values improve at = 2.35.

Description: A depressurization accident is the design-basis accidents of a gas turbine high temperature reactor, GTHTR300, which is JAEA’s design and one of the Very-High-Temperature Reactors (VHTR). When a primary pipe rupture accident occurs, air is expected to enter the reactor core from the breach and oxidize in-core graphite structures. Therefore, it is important to know a mixing process of different kinds of gases in the stable and unstable density stratified fluid layer. In order to predict or analyze the air ingress phenomena during the depressurization accident, we have conducted an experiment to obtain the mixing process of two component gases and the characteristics of natural circulation. The experimental apparatus consists of a storage tank and a reverse U-shaped vertical rectangular passage. One side wall of the high temperature side vertical passage is heated and the other side wall is cooled. The other experimental apparatus consists of a cylindrical double coaxial vessel and a horizontal double coaxial pipe. The outside of the double coaxial vessel is cooled and the inside is heated. The results obtained in this study are as follows. When the primary pipe is connected at the bottom of the reactor pressure vessel, onset time of natural circulation of air is affected by not only molecular diffusion but also localized natural convection. When the wall temperature difference is large, onset time of natural circulation of air is strongly affected by natural convection rather than molecular diffusion. When the primary pipe is connected at the side of the reactor pressure vessel, air will enter the bottom space in the reactor pressure vessel by counter-current flow at the coaxial double pipe break part immediately. Afterward, air will enter the reactor core by localized natural convection and molecular diffusion.

Description: A 2D dynamic model for a bubbling fluidized bed (BFB) combustor has been developed for simulating the coal and biomass cofiring process under 21% O2/79% CO2 atmosphere in a 6 kWth bubbling fluidized bed, coupled with the Euler-Euler two-phase flow model. The kinetic theory of binary granular mixtures is employed for the solid phase in order to map the effect of particle size and density. The distribution of temperature, volume fraction, velocity, gas species concentration, and reaction rates are studied with numerical calculations. The simulated temperature distribution along the height of the combustor and outlet gas concentrations show good agreement with experimental data, validating the accuracy and reliability of the developed cofiring simulation model. As indicated in the results, there are two high temperature zones in the combustor, which separately exist at the fuel inlet and dilute phase. The reaction rates are related to the species concentration and temperature. The higher concentration and temperature lead to the larger reaction rates. It can be seen that all of the homogeneous reaction rates are larger at the fuel inlet region because of rich O2 and volatiles. High mass fraction of volatile gas is found at the fuel inlet, and the main reburning gas at the dilute phase is CH4. The mass fraction distribution of CO is related to the volume fraction of fuel which is due to the fact that the source of CO is not only from the devolatilization but also from the gasification. On the basis of this theoretical study, a better understanding of flow and combustion characteristics in biomass and coal cofiring under oxy-fuel atmospheres could be achieved.

Description: The paper studies structure, phase composition, and thermophysical properties (TPP) (specific heat capacity, thermal diffusivity, and heat conductivity) of a prototype corium of a fast nuclear reactor (melt of core materials of nuclear reactor produced under out-of-pile conditions). The obtained data will be used to get more accurate understanding of main regularities of actual interaction of core materials of a nuclear reactor under a severe accident.

Description: Design of nuclear power plant shall provide an adequate margin to protect items ultimately necessary to prevent an early large radioactive release in the case of earthquakes exceeding those considered in the design. An essential question is how large the margin should be to be accepted as adequate. In the practice, depending on the country regulation, a plant margin of at least 1.4 or 1.67 times the design basis peak ground acceleration is required to be demonstrated. The catastrophe at the Fukushima Daiichi Nuclear Power Plant revealed the fundamental experience that the plants designed in compliance with nuclear standards can survive the effects of the vibratory ground motion due to disastrous earthquake but may fail due to effects of phenomena accompanying or generated by the earthquakes. Liquefaction is one of those secondary effects of beyond-design basis earthquakes that should be investigated for NPPs at soil sites. However, the question has not been investigated up to now, whether a “margin earthquake”, vibratory effects of which the plant can withstand thanks to design margin, will not induce liquefaction at soil sites and will not result in loss of safety functions. In the paper, a procedure is proposed for calculation of the probability and margin to liquefaction. Use of the procedure is demonstrated on a case study with realistic site-plant parameters. Criteria for probability for screening and acceptable probabilistic margin to liquefaction are proposed. The possible building settlement due to margin earthquake is also assessed.

Description: Three tests were carried out with the ROSA/LSTF (rig of safety assessment/large-scale test facility), which simulated accident management (AM) measures during station blackout transient with loss of primary coolant under assumptions of nitrogen gas inflow and total failure of high-pressure injection system in a pressurized water reactor. As the AM measures, steam generator (SG) secondary-side depressurization was done by fully opening the relief valves in both SGs, and auxiliary feedwater was injected into the secondary-side of both SGs simultaneously. Conditions for the break size and the onset timing of the AM measures were different among the three LSTF tests. In the three LSTF tests, the primary pressure decreased to a certain low pressure of below 1 MPa with or without the primary depressurization by fully opening the relief valve in a pressurizer as an optional AM measure, while no core uncovery took place through the whole transient. Nonuniform flow behaviors were observed in the SG U-tubes under natural circulation (NC) with nitrogen gas depending probably on the gas accumulation rate in the two LSTF tests that the gas accumulated remarkably. The RELAP5/MOD3.3 code predicted most of the overall trends of the major thermal hydraulic responses observed in the three LSTF tests. The code, however, indicated remaining problems in the predictions of the primary pressure, the SG U-tube collapsed liquid levels, and the NC mass flow rate after the nitrogen gas ingress as well as the accumulator flow rate through the analyses for the two LSTF tests, where the remarkable gas accumulation occurred.

Description: The combustion kinetic characteristics of wood powder and pellet were investigated within thermogravimetric analyser (TGA) and tube furnace system. The kinetic parameters of these two different forms of woody fuel were measured and derived by double-step-and-double-equal and isothermal method, respectively. The results showed that the combustion mechanisms of wood powder kept consistent through the whole process, while the combustion mechanisms of wood pellet differed significantly between the volatile and char combustion stages. The most probable mechanism functions of the two different forms of woody fuel were not the same due to the differences in internal heat and mass transfer properties. In addition, activation energy values varied from 92.33 kJ·mol−1 for wood powder to 71.20 kJ·mol−1 for wood pellet, while the preexponential factor value of wood powder (2.55×108 s−1) was far greater than the one of the wood pellet (78.55 s−1) by seven orders of magnitude.

Description: Supercritical CO2 Brayton cycle is a good choice of thermal-to-electric energy conversion system, which owns a high cycle efficiency and a compact cycle configuration. It can be used in many power-generation applications, such as nuclear power, concentrated solar thermal, fossil fuel boilers, and shipboard propulsion system. Transient analysis code for Supercritical CO2 Brayton cycle is a necessity in the areas of transient analyses, control strategy study, and accident analyses. In this paper, a transient analysis code SCTRAN/CO2 is developed for Supercritical CO2 Brayton Loop based on a homogenous model. Heat conduction model, point neutron power model (which is developed for nuclear power application), turbomachinery model for gas turbine, compressor and shaft model, and PCHE type recuperator model are all included in this transient analysis code. The initial verifications were performed for components and constitutive models like heat transfer model, friction model, and compressor model. The verification of integrated system transient was also conducted through making comparison with experiment data of SCO2EP of KAIST. The comparison results show that SCTRAN/CO2 owns the ability to simulate transient process for S-CO2 Brayton cycle. SCTRAN/CO2 will become an important tool for further study of Supercritical CO2 Bryton cycle-based nuclear reactor concepts.

Description: The safe introduction of Generation IV (Gen IV) reactor concepts into operation will require extensive testing of their components. This must be performed under neutronic conditions representative of those expected to prevail inside the new reactor cores when in operation. In a thermal Material Testing Reactor (MTR) such neutronic conditions can be achieved by tailoring the prevailing neutron spectrum with the utilization of a device containing appropriate materials. In this work various materials are investigated as candidate components of a device that will be required in case that a thermal MTR neutron energy spectrum must be locally transformed, so as to imitate Sodium cooled Fast Reactor (SFR). Many nuclides have been examined with respect to only their neutronic behavior, providing thus a pool of neutronically appropriate materials for consideration in further investigation, such as regarding reactor safety and fabrication issues. The nuclides have been studied using the neutronics code TRIPOLI-4.8 while the reflector of the Jules Horowitz Reactor (JHR) was considered as the hosting environment of the transforming device. The results obtained suggest that elements with important inelastic neutron scattering could be chosen at a first level as being able to modify the prevailing neutron spectrum towards the desired direction. The factors which are important for an effective inelastic scatterer comprise density and inelastic microscopic cross section, as well as the energy ranges where inelastic scattering occurs. All the above factors have been separately examined in order to suggest potential device materials, able to locally produce SFR neutron spectrum imitation in a thermal MTR.

Description: Construction of a stable flame is one of the critical design requirements in developing practical combustion systems. Flames stabilised by a bluff-body are extensively used in certain types of combustors. The design promotes mixing of cold reactants and hot products on the flame surface to improve the flame stability. In this study, bluff-body stabilised methane-hydrogen flames are computed using the steady laminar flamelet combustion method in conjunction with the Reynolds-averaged Navier-Stokes (RANS) approach. These flames are known as Sandia jet flames and have different jet mean velocities. The turbulence is modelled using the standard k-ϵ model and the chemical kinetics are modelled using the GRI-mechanism with 325 chemical reactions and 53 species. The computed mean reactive scalars of interest are compared with the experimental measurements at different axial locations in the flame. The computed values are in reasonably good agreement with the experimental data. Although some underpredictions are observed mainly for NO and CO at downstream locations in the flame, these results are consistent with earlier reported studies using more complex combustion models. The reason for these discrepancies is that the flamelet model is not adequate to capture the finite-rate chemistry effects and shear turbulence specifically, for species with a slow time scale such as nitrogen oxides.

Description: A large number of carbon materials are adopted in high-temperature gas-cooled reactor (HTGR). These carbon materials mainly include graphite IG-110 and boron-containing carbon material (BC), both of which are typical porous materials and normally absorb moisture. In order to inhibit the chemical corrosion reaction between core internals materials and moisture, the core needs to be strictly dehumidified before the reactor is put into operation. This paper mainly analyzed the moisture transfer mechanism in these carbon materials. Moisture transfer models were developed, and the dehumidification process of HTR-PM core was simulated. In addition, the influence of working temperature and system pressure on dehumidification was studied as well.

Description: Water tank is one important component of passive containment cooling system (PCS) of nuclear island building. The sloshing frequency of water is much less than structure frequency and large-amplitude sloshing occurs easily when subjected to seismic loadings. Therefore, the sloshing dynamics and fluid-structure interaction (FSI) effect of water tank should be considered when the dynamic response of nuclear island building is analyzed. A 1/16 scaled model was designed and the shaking table test was done, in which the hydrodynamic pressure time histories and attenuation data of wave height were recorded. Then the sloshing frequencies and 1st sloshing damping ratio were recognized. Moreover, modal analysis and time history analysis of numerical model were done by ADINA software. By comparing the sloshing frequencies and hydrodynamic pressures, it is proved that the test method is reasonable and the formulation of potential-based fluid elements (PBFE) can be used to simulate FSI effect of nuclear island building.

Description: Multiphase flow measurements have become increasingly important in a wide range of industrial fields. In the present study, a dual needle-contact capacitance probe was newly designed to measure local void fractions and bubble velocity in a vertical channel, which was verified by digital high-speed camera system. The theoretical analyses and experiments show that the needle-contact capacitance probe can reliably measure void fractions with the readings almost independent of temperature and salinity for the experimental conditions. In addition, the trigger-level method was chosen as the signal processing method for the void fraction measurement, with a minimum relative error of −4.59%. The bubble velocity was accurately measured within a relative error of 10%. Meanwhile, dynamic response of the dual needle-contact capacitance probe was analyzed in detail. The probe was then used to obtain raw signals for vertical pipe flow regimes, including plug flow, slug flow, churn flow, and bubbly flow. Further experiments indicate that the time series of the output signals vary as the different flow regimes and are consistent with each flow structure.

Description: A simple method using the time-dependent Monte Carlo (TDMC) neutron transport calculation is presented to determine an effective detector position for the prompt neutron decay constant () measurement through the pulsed-neutron-source (PNS) experiment. In the proposed method, the optimum detector position is searched by comparing amplitudes of detector signals at different positions when their estimates by the slope fitting are converged. The developed method is applied to the Pb-Bi-zoned ADS experimental benchmark at Kyoto University Critical Assembly. The convergence time estimated by the TDMC PNS simulation agrees well with the experimental results. The convergence time map and the corresponding signal amplitude map predicted by the developed method show that polyethylene moderator regions adjacent to fuel region are better positions than other candidates for the PNS measurement.

Description: Environmental problems related to the generation of wastewater contaminated with organic compounds and the emissions of pollutants from fuel burning have become major global problems. Thus, there is a need for the development of alternative and economically viable technologies for the remediation of the affected ecosystems. Therefore, this work describes the preparation and characterization of a Ti(OH)4 catalyst with the modified surface for application in the photodegradation of organic compounds (methylene blue (MB) dye and the drug amiloride (AML)) and in the artificial photosynthesis process. Characterization results reveal that peroxo groups on the surface of the catalyst had a great influence on the optical properties of the Ti(OH)4 and consequently in its photocatalytic property. This catalyst showed a high photocatalytic activity for the degradation of organic pollutants under visible radiation, reaching approximately 98% removal of both the dye and the drug in 150 min of reaction. In addition, the catalyst presented a great potential for the reduction of CO2 under ultraviolet (UV) radiation when compared to P25, which is a classic catalyst used in photocatalytic processes. The highest photocatalytic activity can be attributed to the strong visible light absorption, due to the narrow band gap, and the effective separation of photogenerated electron-hole pairs caused by the peroxo groups on the Ti(OH)4 surface.

Description: Copper Indium Gallium Selenide- (CIGS-) based solar cells have become one of the most promising candidates among the thin film technologies for solar power generation. The current record efficiency of CIGS has reached 22.6% which is comparable to the crystalline silicon- (c-Si-) based solar cells. However, material properties and efficiency on small area devices are crucial aspects to be considered before manufacturing into large scale. The process for each layer of the CIGS solar cells, including the type of substrate used and deposition condition for the molybdenum back contact, will give a direct impact to the efficiency of the fabricated device. In this paper, brief introduction on the production, efficiency, etc. of a-Si, CdTe, and CIGS thin film solar cells and c-Si solar cells are first reviewed, followed by the recent progress of substrates. Different deposition techniques’ influence on the properties of molybdenum back contact for CIGS are discussed. Then, the formation and thickness influence factors of the interfacial MoSe2 layer are reviewed; its role in forming ohmic contact, possible detrimental effects, and characterization of the barrier layers are specified. Scale-up challenges/issues of CIGS module production are also presented to give an insight into commercializing CIGS solar cells.

Description: The photocatalyzed water splitting reaction in aqueous methanol solution is an efficient preparation method for hydrogen and methanal under mild conditions. In this work, metal sulfide-loaded TiO2 photocatalysts for hydrogen and methanol production were synthesized by hydrothermal method (180°C/12 h) and characterized by X-ray diffraction (XRD), UV-visible diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The crystal structures of the samples are the typical anatase phase of TiO2 and exhibit a spherical morphology. When TiO2 was loaded with CoS, ZnS, and Bi2S3, respectively, the resulting catalysts showed photocatalytic activities for water decomposition to hydrogen in aqueous methanol solution under 300 W Xe lamp irradiation. Among the photocatalysts with various compositions, the 20 wt% CoS/TiO2 sample with a 2.1 eV band gap showed the maximum photocatalytic activity for the photocatalytic reaction, which indicated that CoS improved the separation ratio of photoexcited electrons and holes. The enhanced activity can be attributed to the intimate junctions that are formed between CoS and TiO2, which can reduce the electron-hole recombination. The production rate of hydrogen with 20 wt% CoS/TiO2 photocatalyst was about 5.6 mmol/g/h, which was 67 times higher than that of pure TiO2. The formation rate of HCHO was 1.9 mmol/g/h with 98.7% selectivity. Moreover, the CoS/TiO2 photocatalyst demonstrated good reusability and stability. In the present study, it is demonstrated that CoS can act as an effective cocatalyst to enhance the photocatalytic hydrogen and methanal production activity of TiO2. The highly improved performance of the CoS/TiO2 composite was mainly ascribed to the efficient charge separation.

Description: The demand for clean and sustainable energy has spurred research in all forms of renewable energy sources, including solar energy from photovoltaic systems. Grid-connected photovoltaic systems (GCPS) provide an effective solution to integrate solar energy into the existing grid. A key component of the GCPS is the inverter. The inverter can have a significant impact on the overall performance of the GCPS, including maximum power point (MPP) tracking, total harmonic distortion (THD), and efficiency. Multilevel inverters are one of the most promising classes of converters that offer a low THD. In this paper, we propose a new multilevel inverter topology with the motivation to improve all the three aforementioned aspects of performance. The proposed topology is controlled through direct model predictive control (DMPC), which is state of the art in control techniques. We compare the performance of the proposed topology with the topologies reported in literature. The proposed topology offers one of the best efficiency, MPP tracking, and voltage THD.

Description: In this work, thin CdS films have been deposited using the chemical bath deposition technique (CBD). Different synthesis parameters, such as number of runs, deposition time, and postannealing temperature, are studied and optimized in order to avoid the supersaturation phenomenon and to achieve a low-temperature growth. CdS thin films, of cubic structure, oriented along the (111) direction with homogenous and smooth surface, have been deposited by using the CBD growth process without any annealing treatment. Based on a set of experimental observations, we show that the solution saturation phenomenon can be avoided if the deposition is performed in several runs at a short deposition time. Throughout the CBD technique, it is then possible not only to overcome any film thickness limitation but also to grow the CdS films in a single technological step at a low temperature and without any postdeposition annealing treatment. CdS films with excellent structural quality and a controllable thickness are obtained when the deposition bath temperature is fixed at 65°C. In addition, deposited films exhibit an optical transmittance ranging from 70 to 95% depending on the synthesis parameters, with band gap energy around 2.42 eV. The process developed in this work might be useful for depositing CdS films on flexible substrates.

Description: This paper deals with the analysis and interpretation of flow visualization and residence time distribution (RTD) in a compound parabolic concentrator (CPC) reactor using computational fluid dynamics (CFD). CFD was calculated under turbulent flow conditions solving the Reynolds averaged Navier–Stokes (RANS) equation expressed in terms of turbulent viscosity and the standard k−ε turbulent model in 3D. A 3D diffusion-convection model was implemented in the CPC reactor to determine the RTD. The fluid flow visualization and RTD were validated with experimental results. The CFD showed that the magnitude of the velocity field remains almost uniform in most of the bulk reactor, although near and inside the 90° connectors and the union segments, the velocity presented low- and high-speed zones. Comparisons of theoretical and experimental RTD curves showed that the k−ε model is appropriate to simulate the nonideal flow inside the CPC reactor under turbulent flow conditions.

Description: Recently, binary metal oxides have been proven to be the most investigated semiconductors due to their high activity for the removal of organic pollutants. In this paper, to improve the photocatalytic efficiency of MgFe2O4, a MgFe2O4/reduced graphene oxide (MFO/rGO) photocatalyst was synthesized by a facile generalized solvothermal method. The morphology, structure, and photocatalytic activities in the degradation of methyl orange (MO) reaction were systematically characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and UV-vis absorption spectroscopy, respectively. The results showed that the MFO/rGO composite exhibited enhanced photocatalytic performance in the photodegradation of MO under visible-light irradiation and reached a maximum degradation rate of 99% within 60 min of irradiation. This excellent photocatalytic performance is attributed to the introduction of rGO in the composite, which can effectively reduce the photoproduction of the electron-hole pair recombination rate. The excellent photocatalytic activity reveals that the MFO/rGO composite photocatalyst is a promising photocatalyst with good visible-light response and has potential applications in the field of water treatment.

Description: Luminous efficacy model uses solar radiation data to generate illuminance data, and its performance also depends on the quality of solar radiation data. Various luminous efficacy models are reviewed and evaluated to select a universal luminous efficacy model. Since most luminous efficacy models are fitted with specific local climate characteristics, the model that has the least locality as well as accuracy is a mandatory requirement. Three representative luminous efficacy models are selected and evaluated with measured solar radiation and illuminance data from four worldwide cities. It was found that all the evaluated models provide good predictions (over 0.96 value) for both global and diffuse illuminance. Among them, the Perez luminous efficacy model shows the highest performance in terms of accuracy and bias. However, illuminance data prediction based on estimated solar radiation data is more common practice rather than those from measured solar data. The performance of the selected luminous efficacy models is evaluated when recently proposed universal solar radiation model supplies predicted solar radiation data. The result indicates that the quality of estimated solar radiation data has a much deeper impact on the performance of the luminous efficacy model. Within the current limited technology and measured data resource, the consecutive processing of the modified Zhang and Huang solar model and Perez luminous efficacy model could provide the best option to predict both global and diffuse solar radiation and illuminance. But, users of the model-based illuminance data should interpret their simulation results with the error (30%~40% in RMSE and ±6% in MBE) in predicting global and diffuse illuminance.

Description: The outdoor operating photovoltaic arrays have two different shading conditions, shadowing and covering. The shading causes a decrease in output power of photovoltaic system and may bring hot spots which causes physical damage to the array. This paper studies the electrical parameter distribution feature of photovoltaic array under different shading conditions by means of analog simulation and empirical testing. Through introducing theoretical computational method of the electrical parameters, it describes the distribution features of the electrical parameters of photovoltaic array. The results indicate that the influence of local shadowing on the current of array can be neglected. Shadowing decreases the optimal operating voltage while covering leads to a decrease in the optimal operating voltage and the open-circuit voltage. The drop magnitude of voltage is associated with the number of the shaded cell strings and the string voltage. The two shading types can be identified on the basis of distribution rules of open-circuit voltage and optimal operating voltage. Simulations and experiments verify the consistency of the rules. Relevant conclusions provide a reference for modeling, online fault diagnosis, and optimization design of the maximum power tracking algorithm of photovoltaic array under different shading conditions.

Description: Wickless gravity loop thermosiphons (LTs) have been widely used in heat collection for distances up to several meters. This two-phase closed device, which is operating under reduced pressure, is useful in solar water heating (SWH) systems because it could address the freezing problem during winter. Compared to the normal type, forced-circulation wickless LTs have significant advantages in the long-distance heat transfer and installation freedom of condensation section. In this study, a pump-forced wickless LT-SWH system with a remolded flat-plate solar collector was put forward. Solar collector acted as the evaporation section of the wickless LT, while the spiral heat exchanger in the water tank acted as the condensation section. R600a was employed as the working fluid, and long-term outdoor experiments were carried out. Results show that the instantaneous and daily average photothermal efficiency of the proposed system can reach 69.54% and 58.22%, respectively. Temperature differences between the top and bottom and the middle and bottom of the evaporation section of the wickless LT were small, and it usually ranged between 1.1 and 3.9°C. Linear fittings of the collector and system overall performance of the pump-forced wickless LT-SWH system demonstrate the promising potential application of the system.

Description: In this paper, two main contributions are presented to manage the power flow between a wind turbine and a solar power system. The first one is to use the fuzzy logic controller as an objective to find the maximum power point tracking, applied to a hybrid wind-solar system, at fixed atmospheric conditions. The second one is to respond to real-time control system constraints and to improve the generating system performance. For this, a hardware implementation of the proposed algorithm is performed using the Xilinx System Generator. The experimental simulation results show that the suggested system presents high accuracy and acceptable execution time performances. The proposed model and its control strategy offer a proper tool for optimizing the hybrid power system performance which we can use in smart house applications.

Description: A series of three-dimensional microflower-like Ag/Bi2WO6 composites were synthesized through a simple and practical photoreduction process with different photoreduction times. The UV-visible diffuse reflectance spectra indicate that the spectrum of Ag/Bi2WO6 is significantly red-shifted compared to pure Bi2WO6 microspheres in the visible light region. The photocatalytic activities of the as-prepared samples were evaluated by the decolorization of rhodamine B under visible light irradiation. The photocatalytic reaction rate constants of the Ag/Bi2WO6 with a photoreduction time of 20 min was 3.60 times bigger than those of pure Bi2WO6. The enhanced photocatalytic activity could be attributed to the synergistic effect of increased light absorption range and the effective separation of photogenerated carriers caused by Ag nanoparticles.

Description: Anatase TiO2 presents a large bandgap of 3.2 eV, which inhibits the use of visible light radiation ( 〉 387 nm) for generating charge carriers. We studied the activation of TiO2 (101) anatase with visible light by doping with C, N, S, and F atoms. For this purpose, density functional theory and the Hubbard approach are used. We identify two ways for activating the TiO2 with visible light. The first mechanism is broadening the valence or conduction band; for example, in the S-doped TiO2 (101) system, the valence band is broadened. A similar process can occur in the conduction band when the undercoordinated Ti atoms are exposed on the TiO2 (101) surface. The second mechanism, and more efficient for activating the anatase, is to generate localized states in the gap: N-doping creates localized empty states in the bandgap. For C-doping, the surface TiO2 (101) presents a “cleaner” gap than the bulk TiO2, resulting in fewer recombination centers. The dopant valence electrons determine the number and position of the localized states in the bandgap. The formation of charge carriers with visible light is highly favored by the oxygen vacancies on TiO2 (101). The catalytic activity of C-doping using visible radiation can be explained by its high absorption intensity generated by oxygen vacancies on the surface. The intensity of the visible absorption spectrum of doped TiO2 (101) follows the order: C 〉 N 〉 F 〉 S dopant.

Description: The focus of this paper is to predict the transient response of a nanoengineered photovoltaic thermal (PV/T) system in view of energy and exergy analyses. Instead of a circular-shaped receiver, a trapezoidal-shaped receiver is employed to increase heat transfer surface area with photovoltaic (PV) cells for improvement of heat extraction and thus achievement of a higher PV/T system efficiency. The dynamic mathematical model is developed using MATLAB® software by considering real-time heat transfer coefficients. The proposed model is validated with experimental data from a previous study. Negligible discrepancies were found between measured and predicted data. The validated model was further investigated in detail using different nanofluids by dispersing copper oxide (CuO) and aluminum oxide (Al2O3) in pure water. The overall performance of the nanoengineered PV/T system was compared to that of a PV/T system using water only, and optimal operating conditions were determined for maximum useful energy and exergy rates. The results indicated that the CuO/water nanofluid has a notable impact on the energy and exergy efficiencies of the PV/T system compared to that of Al2O3/water nanofluid and water only cases.

Description: The existence of H2S has limited the biogas energy promotion. The traditional photodegradation of H2S is usually conducted in the presence of O2, yet this is unsuitable for biogas desulfurization which should be avoided. Therefore, the ultraviolet degradation of H2S in the absence of O2 was investigated for the first time in the present study from a mathematical point of view. Light wavelength and intensity applied were 185 nm and 2.16 × 10−12 Einstein/cm2·s, respectively. Firstly, the mathematical model of H2S photodegradation was established with MATLAB software, including the gas flow distribution model and radiation model of photoreactor, kinetics model, mass balance model, and calculation model of the degradation rate. Then, the influence of the initial H2S concentration and gas retention time on the photodegradation rate were studied, for verification of the mathematical model. Results indicated that the photodegradation rate decreased with the increase in initial H2S concentration, and the maximum photodegradation rate reached 62.8% under initial concentration of 3 mg/m3. In addition, the photodegradation rate of H2S increased with the increase in retention time. The experimental results were in good accordance with the modeling results, indicating the feasibility of the mathematical model to simulate the photodegradation of H2S. Finally, the intermediate products were simulated and results showed that the main photodegradation products were found to be H2 and elemental S, and concentrations of the two main products were close and agreed well with the reaction stoichiometric coefficients. Moreover, the concentration of free radicals of H• and SH• was rather low.

Description: The objective of this paper is to establish the performance of 8 kWp grid-connected photovoltaic (PV) power systems based on different PV module technologies in Nanjing, China. Nanjing has a hot summer and a cold winter which are considered based on monthly average solar irradiation and ambient temperature specifically for the deployment of grid-connected PV systems. The study focuses on performance assessment of grid-connected PV systems using typical PV modules made of monocrystalline silicon (m-Si), polycrystalline silicon (p-Si), edge-defined film-fed growth silicon (EFG-Si), cadmium telluride (CdTe) thin film, copper indium selenide (CIS) thin film, heterojunction with intrinsic thin layer (HIT), and hydrogenated amorphous silicon single-junction (a-Si:H single-PV) installed on location. The yearly average energy output, PV module and system efficiency, array yield, final yield, reference yield, performance ratio, monthly average array capture losses, and system losses of seven PV module technologies are all analyzed. The results show that grid-connected PV power system performance depends on geographical location, PV module types, and climate conditions such as solar radiation and ambient temperature. In addition, based on energy output and efficiency, the HIT PV power technology can be considered as the best option and CdTe and p-Si as the least suitable options for this area. The monthly average performance ratio of the CdTe technology was higher than those of other technologies over the monitoring period in Nanjing.

Description: In this work, the seasonal and yearly optical performance of supported catalyst CPC solar photocatalytic reactors has been theoretically analyzed. A detailed model for the optical response of the anatase catalyst films is utilized, based on the characteristic matrix method, together with Monte Carlo ray tracing simulations. The catalyst is supported over glass tubes contained inside a larger glass tube that functions as receiver of the CPC reflector. Arrangements with four, five, and six tubes are considered. Overall, the four-tube scenario presents the worst performance of all, followed by the five-tube case. In general, the six-tube configuration is better. Nevertheless, important differences can be observed depending on the specific arrangement of tubes. The six-tube case surpasses the absorption rate of all the other configurations when the distance between tubes is extended. This configuration exhibits 27% increased yearly energy absorption with respect to the reference case and 47% with respect to the worst case scenario.

Description: Effects of polysilane additions on CH3NH3PbI3 perovskite solar cells were investigated. Photovoltaic cells were fabricated by a spin-coating method using perovskite precursor solutions with polymethyl phenylsilane, polyphenylsilane, or decaphenyl cyclopentasilane (DPPS), and the microstructures were examined by X-ray diffraction and optical microscopy. Open-circuit voltages were increased by introducing these polysilanes, and short-circuit current density was increased by the DPPS addition, which resulted in the improvement of the photoconversion efficiencies to 10.46%. The incident photon-to-current conversion efficiencies were also increased in the range of 400~750 nm. Microstructure analysis indicated the formation of a dense interfacial structure by grain growth and increase of surface coverage of the perovskite layer with DPPS, and the formation of PbI2 was suppressed, leading to the improvement of photovoltaic properties.

Description: Photochromic 5-phenylpyrazolidin-3-one-based azomethine imines containing 2-((1H-imidazol-2-yl)methylene) 1, 2-(pyridin-2-ylmethylene) 2, 2-(quinolin-2-ylmethylene) 3, and 2-((8-hydroxyquinolin-2-yl)methylene) 4 substituents were synthesized. All the compounds exist in the ring-opened O forms. Under irradiation with light of 365 nm, compounds 1–4 undergo thermally reversible isomerization into ring-closed bicyclic diaziridine isomers C. Azomethine imines 1–3 exhibit properties of ion-active molecular “off-on” switches of fluorescence when interacting with F− or AcO− anions. Compound 4 represents a bifunctional chemosensor demonstrating a colorimetric “naked-eye” effect for Ni2+ cation and complete fluorescence quenching in the presence of H+, F−, and CN− ions.

Description: Photocatalytic materials based on silica-titania (SiO2-TiO2) were synthesized by sol-gel and dip-coating method. TEOS and titanium butoxide were used as precursors of the silica-titania, respectively. A thin film with anatase phase was obtained on the surface of the support. The effect of variables as dispersion mechanism, immersion time, and number of treatment cycles were studied. The materials were characterized using X-ray diffraction, scanning electron microscopy, energy dispersion scanning, and N2 adsorption-desorption. The highest crystallinity of TiO2 on silica, high specific surface area in TiO2-SiO2 materials, and thin film formation were obtained by using a stirring plate and minimum immersion time. The so synthesized catalyst allowed the production of formaldehyde from the photocatalyzed methanol oxidation in a packed-bed reactor.

Description: The shape and connection type of MOx are critical to the physical and chemical properties. A series of new material Sr2-xNaxNbO4 containing NbO4 tetrahedra was prepared by controlling the ratio of SrCO3 to sodium niobate under ambient air. With increasing the content of Sr in the sample, the MOx shape will change from NbO6 octahedra to NbO4 tetrahedra, which is confirmed by the Raman scattering spectra. With increasing the content of NbO4 in the sample, the lattice parameter increases, optical band gap becomes larger, and the surface changes to be more active for oxygen adsorption, resulting in a higher photocatalytic activity.

Description: This experimental research comparatively investigates the Escherichia coli (E. coli) bacterial inactivation of the TiO2 photocatalytic thin films fabricated by the sol–gel dip-coating (SG) and low-temperature spray-coating (SP) techniques, with low-intensity (12 μW·cm−2) UVA-light-emitting diodes (UVA-LED) as the light source. The bacteriostatic experiments were undertaken using the nutrient broth (NB) and 0.85% NaCl with the initial E. coli concentrations of 102, 104, 106, and 108 CFU·mL−1. Moreover, the essential physical characteristics of the SG-TiO2 and SP-TiO2 photocatalytic thin films were determined prior to the experimental bacterial inactivation. The findings showed that both photocatalytic thin films possessed the ideal physical characteristics, especially the SP-TiO2 thin film. In addition, the viable cell counts, the cell morphology, and the bioluminescence-based adenosine triphosphate (ATP) indicated that both SG-TiO2 and SP-TiO2 thin films under UVA could effectively inhibit the proliferation of the E. coli cells in both NB and 0.85% NaCl.

Description: Three kinds of anthracene-based organic dyes for dye-sensitized solar cells (DSSCs) were studied, and their structures are based on a push–pull framework with anthracenyl diphenylamine as the donor connected to a carboxyphenyl or carboxyphenyl-bromothiazole (BTZ) as the acceptor via an acetylene bridge. The photoelectric properties of the three dyes were investigated using density functional theory (DFT). The simulations indicate that the improvement of anthracene-based dyes (the addition of BTZ and the change of alkyl groups to alkoxy chains) can reduce the energy gap and produce a red shift. This structural modification also improves the light capturing and the electron injection capability, making it excellent in photoelectric conversion efficiency (PCE). In addition, twelve molecules have been designed to regulate photovoltaic performance.

Description: An interconnect electrode called conductive belt was applied to modules instead of interconnection ribbons. The conductive belt has multiple wires and can achieve a multibusbar structure by forming ohmic contacts with the cell electrodes. The following problems were studied with innovative approaches to optimize the multibusbar modules: the shading rate and the contact resistance of the conductive belts, the relationship between the finger series resistance and the wire number, and the influence of the series resistance variation on the maximum power output. Furthermore, the wire number and diameter were optimized according to the following conditions: the cell sizes were full, half, and one-third, and the finger wet weights of a full cell were 80 mg, 40 mg, and 20 mg. The result showed that multibusbar and half-cell structures could achieve the maximum power output, the wire number was 16 and the wire diameter was 200 μm, and the finger wet weight was reduced to 20 mg. Finally, the reliability of the modules made with conductive belts was tested and was qualified according to International Electrotechnical Commission standards.

Description: In recent years, research on noncatalytic methods for biodiesel production has increased, mainly processes under supercritical conditions that allow the processing of waste vegetable oils (WVO) without the need to use catalysts, where the absence of catalyst simplifies the processes of purification of biodiesel. The high consumption of alcohol and energy to maintain the appropriate conditions of pressure and temperature of the reaction has turned the processes of supercritical conditions into an unfeasible method. However, the stages of biodiesel purification and methanol recovery are more straightforward, allowing the reduction of the total energy consumption by 25% compared to alkaline methods. Therefore, the present work describes a study through Aspen Plus® of the production of biodiesel by a process in supercritical conditions with WVO as raw material. Also, a solar collector arrangement was structured using the TRNSYS® simulator to supply energy to the process. To evaluate the economic feasibility of the proposed process, the installation of a pilot plant in Mexicali, Baja California, was considered. The internal rate of return (IRR) and the net present value (NPV) were determined for ten-year period. The planned system allows supplying solar energy, 69.5% of the energy required by the process, thus reducing the burning of fossil fuels and the operation cost. Despite the additional investment cost, for the solar collectors, the process manages to maintain a competitive production cost of USD 0.778/l of biodiesel. With an IRR of 31.7%, the investment is recovered before the fifth year of operation. The integration and implementation of clean technologies are vital in the development of the biofuels.

Description: This paper presents a comparative study of “life cycle cost” or LCC of a building school rooftop element in Jakarta. The simulation applied two different types of roof: a concrete roof and a PV rooftop. The aim of this study is to investigate the electricity production of the solar panels, the saving to investment ratio or SIR, and the total life cycle cost of each rooftop element. To accommodate those objectives, the calculation utilized a software called “Building Life Cycle Cost (BLCC) version 5” which is a product of the US Department of Energy. The simulation results showed that the LCC can be improved by 27.6%, and the “discounted payback” is reached at year 15. Indeed, this indicates that a roof made of solar panels is promising to replace the existing concrete roof.

Description: TiO2/carbon fiber composite is achieved by loading TiO2 nanoparticles on biomass carbon fiber, which originates from the carbonized natural bast. The carbonized process and the loading amount of TiO2 are researched in detail. It is found that the carbonized bast fiber shows robust adsorption characteristics for TiO2 nanoparticles in aqueous dispersion, and TiO2 nanoparticles with ~15 wt.% in total weight are uniformly loaded onto the fiber surface. The photocatalytic properties of TiO2/carbon fiber composite are evaluated by photocatalytic degradation of rhodamine B and water splitting for hydrogen production. The results indicate that 90% RhB molecules could be attacked in 60 min under UV light irradiation, and the hydrogen production rate of water splitting is up to 338.51 μmol/h. The highlight is that TiO2/carbon fiber composite is easy to be recycled due to the incorporation of macroscopical biomass carbon fiber.

Description: As the need to use green chemistry routes increases, environmentally friendly catalytic processes are a demand. One of the most important and abundant naturally occurring catalysts is chlorophyll. Chlorophyll is the first recognized catalyst; it is a reducing agent due to its electron-rich structure. The effects of spinach on the preparation of zinc oxide nanoparticles and the photocatalytic degradation of methyl orange and paraquat in sunlight and under a UV lamp and photocatalytic degradation in sunlight were studied. Different parameters of the catalytic preparation process and photocatalytic degradation process were studied. Characterization of differently prepared samples was carried out using different analytical techniques such as XRD, SEM, and EDX and finally the photocatalytic activity towards decomposition of methyl orange and paraquat.

Description: The photocatalytic degradation of 4-chlorophenol in water using Ru-doped ZnO mixed oxides (0, 0.5, 1, and 3 wt% RuO2) synthesized by the one-pot homogeneous coprecipitation method is reported. ZnO with wurtzite structure was present in the mixed oxide as corroborated by Raman spectroscopy and X-ray diffraction analysis. All the samples showed nanorod morphological features. The presence of Ru6+/Ru4+ couples on ZnO modified the band gap of the mixed oxides and led to a shift of the band gap energy from 3.20 eV to 3.07 eV. Ru addition increased the surface area and significantly promoted the formation of active surface oxygen species such as hydroradicals evidenced by the fluorescence spectroscopy measurement. In the photodegradation of 4-chlorophenol solution under UV irradiation, a notable increase in photoactivity was obtained as the amount of RuO2 in the mixed oxides increased to 3 wt%. The charge transfer between Ru6+/Ru4+ couples and ZnO nanoparticles together with the formation of free radical oxidant species effectively inhibits electron-hole recombination rate, thus favoring the photodegradation of 4-chlorophenol.

Description: When light water reactor (LWR) is subject to a cold shutdown, it needs to be cooled with pure water or seawater to prevent the core melting. To precisely evaluate the cooling characteristics in the fuel assembly, a measurement method capable of installing to the fuel assembly structure and determining the temperature distribution with high temporal resolution, high spatial resolution, and in multidimension is required. Furthermore, it is more practical if applicable to a pressure range up to the rated pressure 16 MPa of a pressurized water reactor (PWR). In this study, we applied the principle of the wire-mesh sensor technology used in the void fraction measurement to the temperature measurement and developed a simulated fuel assembly (bundle) test loop with installing the temperature profile sensors. To investigate the measurement performance in the bundle test section, it was confirmed that a predetermined temperature calibration line with respect to time-average impedance was calculated and became a function of temperature. To evaluate the followability of measurement in a transient temperature change process, we fabricated a 16 × 16 wire-mesh sensor device and measured the hot-water jet-mixing process into the cold-water pool in real time and calculated the temperature profile from the temperature calibration line obtained in advance from each measurement point. In addition, the sensors applied to three-dimensional temperature distribution measurement of a complex flow field in the bundle structure. The axial and cross-sectional profiles of temperature were quantified in the forced flow field with nonboiling when the 5×5 bundle was heated by energization.

Description: Delayed postoperative infection is known as a major complication after bone surgeries using osteosynthetic biomaterial such as titanium (Ti) and bioresorbable organic materials. However, the precise cause of this type of infection is still unclear and no effective prevention has been established. The purpose of this study is to investigate the effect of irradiation with a 405 nm blue-violet laser on the bacteria adhered on the Ti and hydroxyapatite-poly-L-lactic acid- (HA-PLLA) based material surfaces and to verify the possibility of its clinical application to prevent the delayed postoperative infection after bone surgeries using osteosynthetic biomaterial. The suspension of Staphylococcus aureus FDA 209P was delivered onto the surface of disks composed of Ti or HA-PLLA. Bacterial adhesion on each disk was observed using a scanning electron microscope (SEM). After thorough washing with distilled water, the growth of bacteria attached to the material surfaces was examined with an alamar blue-based redox indicator. Moreover, a bactericidal effect of 405 nm blue-violet laser irradiation on residual bacteria on both materials was investigated using colony-forming assay. As a result, there was no significant difference in the bacterial adhesion between Ti and HA-PLLA materials. In contrast, 45 J/cm2 of irradiation with 405 nm blue-violet laser inhibited the bacterial growth at approximately 93% on Ti disks and at approximately 99% on HA-PLLA disks. This study clearly demonstrated the possibility that the irradiation with a 405 nm blue-violet laser is useful as an alternative management strategy for the prevention of delayed postoperative infection after bone surgeries using osteosynthetic biomaterials.

Description: In this study, laser-treated polycrystalline Si (pc-Si) wafers, fabricated by wire sawing of hot-pressed ingots sintered from Si powder, have been investigated. As-cut wafers and those with high-quality thin Si layers deposited on top of them by e-beam have been subjected to laser irradiation to clarify typical trends of structural modifications caused by laser treatments. Moreover, possibility to use laser-treated Si powder-based substrates for fabrication of advanced Si structures has been analysed. It is established that (i) Si powder-based wafers with thicknesses ~180 μm can be fully (from the front to back side) or partly (subsurface region) remelted by a diode laser and grain sizes in laser-treated regions can be increased; (ii) a high-quality top layer can be fabricated by crystallization of an additional a-Si layer deposited by e-beam evaporation on top of the pc-Si; and (iii) silicon nanowires can be formed by metal-assisted wet chemical etching (MAWCE) of polished Si powder-based wafers and as-cut wafers irradiated with medium laser power, while a surface texturing on the as-cut pc-Si wafers occur, and no nanowires can form in the region subject to a liquid phase crystallization (LPC) caused by high-power laser treatments.

Description: Solar energy is the most abundant renewable energy and it has a great potential for development. There are two ways to transfer solar energy to electricity: photovoltaic power generation (PV) and concentrated solar power (CSP). CSP-PV hybrid system can be fully integrated with the advantages of the two systems to achieve low cost, stable output, and manageable to generate electricity. In this paper, the operation strategy of the CSP-PV system is proposed for parabolic trough CSP system and PV system which are now commercially operated. Genetic algorithm is used to optimize the design of the system and calculate PV-installed capacity, battery capacity, and storage capacity of CSP system, making the system to achieve the lowest cost of electricity generation. The results show that the introduction of the CSP system makes it possible to ensure the stability of the output power of hybrid system when the battery capacity is small, which greatly improves the annual utilization time of the PV and reduces solar abandonment. When the system is optimized by operation characteristics of Spring Equinox, the lowest LCOE is 0.0627 $/kWh, the rated capacity of PV and CSP system are 222.462 MW and 30 MW, respectively, and the capacity of heat storage and battery are 356.562 MWh and 14.687 MWh. When the system is optimized by the operation characteristics of the whole year, the lowest LCOE is 0.0555 $/kWh, the rated capacity of PV and CSP system are 242.954 MW and 30 MW, respectively, and the capacity of heat storage and battery are 136.059 MWh and 8.977 MWh. The comparison shows that the power generation curves of the hybrid system are similar in the two optimization-based methods—Spring Equinox based and annual based, but LCOE is lower when optimized by the annual operation characteristic, and the annual utilization rate of the system is higher when optimized by Spring Equinox based.

Description: This article presents the validation of the Code for Thermal-hydraulic Evaluation of Nuclear Reactors with Plate Type Fuels (COTENP), a subchannel code which performs steady-state thermal-hydraulic analysis of nuclear reactors with plate type fuel assemblies operating with the coolant at low pressure levels. The code is suitable for design analysis of research, test, and multipurpose reactors. To solve the conservation equations for mass, momentum, and energy, we adopt the subchannel and control volume methods based on fuel assembly geometric data and thermal-hydraulic conditions. We consider the chain or cascade method in two steps to facilitate the analysis of whole core. In the first step, we divide the core into channels with dimensions equivalent to that of the fuel assembly and identify the assembly with largest enthalpy rise as the hot assembly. In the second step, we divide the hot fuel assembly into subchannels with size equivalent to one actual coolant channel and similarly identify the hot subchannel. The code utilizes the homogenous equilibrium model for two-phase flow treatment and the balanced drop pressure approach for the flow rate determination. The code results include detailed information such as core pressure drop, mass flow rate distribution, coolant, cladding and centerline fuel temperatures, coolant quality, local heat flux, and results regarding onset of nucleate boiling and departure of nucleate boiling. To validate the COTENP code, we considered experimental data from the Brazilian IEA-R1 research reactor and calculated data from the Chinese CARR multipurpose reactor. The mean relative discrepancies for the coolant distribution were below 5%, for the coolant velocity were 1.5%, and for the pressure drop were below 10.7%. The latter discrepancy can be partially justified due to lack of information to adequately model the IEA-R1 experiment and CARR reactor. The results show that the COTENP code is sufficiently accurate to perform steady-state thermal-hydraulic design analyses for reactors with plate type fuel assemblies.

Description: The falling liquid flow rate under flooding conditions is limited at a square top end of a vertical pipe in the pressurizer surge line with the diameter of about 300 mm that consists of a vertical pipe, a vertical elbow, and a slightly inclined pipe with elbows. In this study, therefore, we evaluated effects of diameters on countercurrent flow limitation (CCFL) at the square top end in vertical pipes by using existing air-water data in the diameter range of D = 19-250 mm. As a result, we found that there was a strong relationship between the constant and the slope m in the Wallis-type correlation where the Kutateladze parameters were used for the dimensionless gas and liquid velocities. The constant and the slope m increased when the water level is increased in the upper tank h. CCFL at the square top end of the vertical pipes could be expressed by the Kutateladze parameters with = 1.53±0.11 and m = 0.97 for D ≥ 30 mm. The values were smaller for D = 19-25 mm than those for D ≥ 30 mm.

Description: Photocatalytic processes are present in natural biochemical pathways as well as in the organic synthetic ones. This minireview will cover the field of photocatalysis that uses both the free-base and specially metallated porphyrins as catalysts. While free-base porphyrins are valuable sensitizers to output singlet oxygen, metalloporphyrins are even more adjustable as photocatalysts because of their coordination capacity, generating a wider range of oxidation reactions. They can be applied in autooxidation reactions, hydroxylations, or direct oxygen transfer producing epoxides. This review will mainly focus on how manganese and some iron porphyrins can be utilized for the functionalization of compounds that have a polycyclic skeleton in their structure. These kinds of compounds are notoriously taxing to obtain and difficult to further functionalize by conventional organic synthetic methods. We have focused on photocatalytic oxygenation reactions in mild conditions with the use of water-soluble porphyrins, as this has been proven to be a good tool for these transformations. In the photocatalytic reactions of some polycyclic heteroaromatic compounds, new polycyclic epoxides, enediones, ketones, alcohols, and/or hydroperoxides are yielded, depending on the catalyst applied. The application of anionic and cationic Mn(III) porphyrins under different reaction parameters results in different reaction pathways generating a vast number of photocatalytic products. Recently, Co and Ni complexes have been also photophysically investigated and confirmed as potential photocatalysts for the functionalization of organic substrates.

Description: The forecast for photovoltaic (PV) power generation is of great significance for the operation and control of power system. In this paper, a short-term combination forecasting model for PV power based on similar day and cross entropy theory is proposed. The main influencing factors of PV power are analyzed. From the perspective of entropy theory, considering distance entropy and grey relation entropy, a comprehensive index is proposed to select similar days. Then, the least square support vector machine (LSSVM), autoregressive and moving average (ARMA), and back propagation (BP) neural network are used to forecast PV power, respectively. The weights of three single forecasting methods are dynamically set by the cross entropy algorithm and the short-term combination forecasting model for PV power is established. The results show that this method can effectively improve the prediction accuracy of PV power and is of great significance to real-time economical dispatch.

Description: A tetra-n-butoxy zinc phthalocyanine (n-BuO)4ZnPc has been synthesized in a single step, starting from commercial precursors, and easily purified. The molecule can be solution processed to form an effective and inexpensive hole transport layer for organic and perovskite solar cells. These appealing features are suggested by the results of a series of chemical, optical, and voltammetric characterizations of the molecule, supported by the results of ab initio simulations. Preliminary measurements of (n-BuO)4ZnPc-methylammonium lead triiodide perovskite-based devices confirm such suggestion and indicate that the interface between the photoactive layer and the hole transporting layer is characterized by hole-extracting and electron-blocking properties, potentially competitive with those of other standards de facto in the field of organic hole transport materials, like the expensive Spiro-OMeTAD.

Description: Computed Tomography of Chemiluminescence (CTC) was used to reconstruct the instantaneous three-dimensional (3D) chemiluminescence field of a high-power industrial flame, which was made optically accessible, for the first time. The reconstruction used 24 projections that were measured simultaneously, in one plane and equiangularly spaced within a total fan angle of 172.5°. The 3D results were examined by plotting both vertical and horizontal slices, revealing highly wrinkled structures with good clarity. The results presented are one of a series of experimental demonstrations of CTC applications to turbulent gaseous flames. The work reveals the potential to use any kind of luminescence measurement, such as emission from heated particles in coal-fired flames, for analysis of the flame shape directly in 3D.

Description: Photoconductivity is a fundamental and highly applicable phenomenon for semiconductor oxide-based devices, and the presence of defects plays a significant role in this mechanism. Here, we present an investigation based on different atmospheres and light excitation (above and below bandgap) dependences of zinc oxide thin film grown by spray-pyrolysis. As-grown ZnO presents a representative Urbach tail associated to the presence of localized levels in the bandgap. Photoconductivity response and decay times are investigated for air and inert atmospheres as well as under vacuum conditions with significant features due to light excitation conditions. The observed characteristics are explained based on oxygen photodesorption when excitation is above bandgap while this process is suppressed when excitation is below bandgap.

Description: In this work, we synthesized Ag nanoparticles on TiO2 thin films deposited on soda lime glass substrates. Ag nanoparticles were synthesized by photoreduction under UV irradiation silver nitrate solution. X-ray diffraction, Raman spectroscopy, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) measurements were used for physicochemical characterization. The structural study showed that all samples were polycrystalline, main phases were anatase and rutile, and no additional signals were detected after surface modification. Raman spectroscopy suggested that silver aggregates deposited on the TiO2 films could exhibit the surface plasmon resonance (SPR) phenomenon; XPS and SEM analysis confirmed TiO2 film morphological modification after photoreduction process. Photocatalytic degradation of methylene blue (MB) was studied under UV irradiation in aqueous solution, and, besides, pseudo-first-order model was used to obtain kinetic information about photocatalytic degradation. Results indicated that Ag-TiO2 showed an important increase in photocatalytic activity under UV (from 20% to 35%); finally, Ag-TiO2 thin films had value 2.4 × 10−3 ± 0.003 min−1 of 1.8 times greater than the value 1.3 × 10−4 ± 0.0004 min−1 of TiO2 thin films.

Description: The regular performance deterioration of P-type crystalline silicon solar modules and module strings caused by potential-induced degradation in a photovoltaic power plant was found in the field. The PID-affected solar modules dismounted from the photovoltaic power plant were further investigated systematically in the laboratory. For the first time, we found that the neutral point of voltage in a module string moved forward to the positive pole for a PID-affected module string as time goes on. Even if low positive voltage is applied to a PID-prone module, it could cause PID. The thermographic and electroluminescence (EL) images of a PID-affected module string also exhibit a regular degradation pattern. This is in good agreement with the measured power loss of the dismounted solar modules under standard test conditions. The results obtained in this paper show that the maximum power degradation rate of solar modules was as high as 53.26% after only one year of operation because of PID in the field. Due to the vast amount of solar modules and incomplete recovery, this is a terrible catastrophe for the owner of a power plant and module producer.

Description: In the deep geological repository of nuclear waste, the corrosion of waste generates gas, which increases the storage pressure, changes the properties of the rock strata, and affects the stability of nuclear waste repository. Therefore, it is of great importance to understand the gas migration in the engineering barrier and the potential impact on its integrity for the safety assessment of nuclear waste repository. A hydro-mechanical-damage model for analyzing gas migration in sedimentary rocks is established in this paper. On the basis of which, a set of coupled formulas for the coupling of gas migration in rock mass is established. The model considers the characteristics of gas migration in sedimentary rock, especially the microcracks caused by the degradation of elastic modulus and damage, and the coupling between the rock deformation and failure of fractures. The numerical simulation of gas injection test is beneficial to understand the mechanism of gas migration process in sedimentary rock.

Description: At present, the Tokamak has become a mainstream form of the magnetic confinement fusion device. The toroidal field (TF) magnet in the Tokamak system is required to generate a high-steady field to confine and shape the high temperature plasma. To secure high current density and high thermal stability, the no-insulation (NI) winding technique is used in the fabrication of the TF magnet. During plasma operation, heat is generated in the TF magnet caused by the interaction with central solenoid (CS) coils, poloidal field (PF) coils, and the plasma current. The heat generated in NI coils is complex owing to the existence of current flow between adjacent turns. Thus, it is necessary to calculate the thermal problems. Taking into consideration the effect of turn-to-turn contact resistance, this paper presents the thermal behavior of a NI toroidal magnet under different operating conditions. The NI toroidal magnet is composed of 10 double-pancake (DP) coils wound with BSCCO tapes. The analysis procedure combines the finite element method (FEM) with an equivalent circuit model. This analysis has applicability and practical directive to the design of cryogenic cooling system for NI toroidal magnet.