ALBERT

Description: In this study, the impact of Entrance Power and Silver nanofluid concentration (with base fluid ethanol and DI-water) on heat pipe thermal performance are considered. In order to reach the aim a U-shaped sintered heat pipe is utilized which causes occupied space to decline. The length of the heat pipe is 135 mm in each branch. On account of recognition the effect of working fluid on heat pipe thermal performance, thermal resistance and overall heat transfer coefficient in base working fluid and nano-colloidal silver are measured in the shape of thermosyphon. The working fluid is with volume percentages of 70 ethanol and 30 distilled water. The average size pertaining to the nanoparticle applied is 40 nm. In addition, the influences of nanofluid concentrations are measured by comparing three concentrations 0.001, 0.005, 0.1 vol%. The range of entrance power is from 10 to 40 W and the temperature of coolant has been changed from 20 to 40 °C. The results of the experiment indicate that by increasing entrance power, the temperatures of the condenser, evaporator and working temperature experience a rise. Furthermore, this causes a decrease of thermal resistance and an increase of overall heat transfer coefficient. A comparison of three concentrations reveals that in concentration of 50 ppm, thermal resistance compared to the base fluid has decreased to 42.26 % and overall heat transfer coefficient has gone up to 1883 (W/m 2 ·°K) . Also, due to unexpected changes in concentration of 1000 ppm, the existence of an optimized concentration for the silver nanofluid in this heat pipe with this geometry has been clear.

Description: The microchannels are device used to remove high heat fluxes from smaller area. In this experimental research work the heat transfer performance of nanofluids of Al 2 O 3 /water and CuO/water were compared. The important character of such fluids is the enhanced thermal conductivity, in comparison with base fluid without considerable alteration in physical and chemical properties. The effect of forced convective heat transfer coefficient was calculated using serpentine shaped microchannel heat exchanger. Furthermore we calculated the forced convective heat transfer coefficient of the nanofluids using theoretical correlations in order to compare the results with the experimental data. The heat transfer coefficient for different particle concentration and temperature were analysed using forced convection heat transfer using nanofluids. The findings indicate considerable enhancement in convective heat transfer coefficient of the nanofluids as compared to the basefluid. The results also shows that CuO/water nanofluid has increased heat transfer coefficient compared with Al 2 O 3 /water and base fluids. Moreover the experimental results indicate there is increased forced convective heat transfer coefficient with the increase in nano particle concentration.

Description: In this paper a 3-dimensional modeling of simultaneous stripping of carbon dioxide (CO 2 ) and hydrogen sulfide (H 2 S) from water using hollow fiber membrane made of polyvinylidene fluoride is developed. The water, containing CO 2 and H 2 S enters to the membrane as feed. At the same time, pure nitrogen flow in the shell side of a shell and tube hollow fiber as the solvent. In the previous methods of modeling hollow fiber membranes just one of the membranes was modeled and the results expand to whole shell and tube system. In this research the whole hollow fiber shell and tube module is modeled to reduce the errors. Simulation results showed that increasing the velocity of solvent flow and decreasing the velocity of the feed are leads to increase in the system yield. However the effect of the feed velocity on the process is likely more than the influence of changing the velocity of the gaseous solvent. In addition H 2 S stripping has higher yield in comparison with CO 2 stripping. This model is compared to the previous modeling methods and shows that the new model is more accurate. Finally, the effect of feed temperature is studied using response surface method and the operating conditions of feed temperature, feed velocity, and solvent velocity is optimized according to synergistic effects. Simulation results show that, in the optimum operating conditions the removal percentage of H 2 S and CO 2 are 27 and 21 % respectively.

Description: Infrared thermographic validation is shown for a closed-form analytical heat conduction model for non-uniformly heated, laminate bodies with an insulated domain boundary. Experiments were conducted by applying power to rectangular electric heaters and cooled by natural convection in air, but also apply to constant-temperature heat sources and forced convection. The model accurately represents two-dimensional laminate heat conduction behaviour giving rise to heat spreading using one-dimensional equations for the temperature distributions and heat transfer rates under steady-state and pseudo-steady-state conditions. Validation of the model with an insulated boundary (complementing previous studies with an infinite boundary) provides useful predictions of heat spreading performance and simplified temperature uniformity calculations (useful in log-mean temperature difference style heat exchanger calculations) for real laminate systems such as found in electronics heat sinks, multi-ply stovetop cookware and interface materials for supercooled salt hydrates. Computational determinations of implicit insulated boundary condition locations in measured data, required to assess model equation validation, were also demonstrated. Excellent goodness of fit was observed (both root-mean-square error and R 2 values), in all cases except when the uncertainty of low temperatures measured via infrared thermography hindered the statistical significance of the model fit. The experimental validation in all other cases supports use of the model equations in design calculations and heat exchange simulations.

Description: Ablation of the thermal protection material of the reentry hypersonic flight vehicle is a complex physical and chemical process. To estimate the surface heat flux from internal temperature measurement is much more complex than the conventional inverse heat conduction problem case. In the paper, by utilizing a two-layer pyrogeneration-plane ablation model to model the ablation and charring of the material, modifying the finite control volume method to suit for the numerical simulation of the heat conduction equation with variable-geometry, the CGM along with the associated adjoint problem is developed to estimate the surface heat flux. This estimation method is verified with a numerical example at first, the results show that the estimation method is feasible and robust. The larger is the measurement noise, the greater is the deviation of the estimated result from the exact value, and the measurement noise of ablated surface position has a significant and more direct influence on the estimated result of surface heat flux. Furthermore, the estimation method is used to analyze the experimental data of ablation of blunt Carbon-phenolic material Narmco4028 in an arc-heater. It is shown that the estimated surface heat flux agrees with the heating power value of the arc-heater, and the estimation method is basically effective and potential to treat the engineering heat conduction problem with ablation.

Description: In the past two decades, enhancement of heat transfer characteristics of original fluid using nanofluids has been proposed by a large number of researchers. In this paper, an experimental study was carried out to investigate effect of pulsation on heat transfer of fluid flow inside a spiral-coil tube. In order to perform the experiments, a hot water reservoir tank was prepared and the spiral-coil was immersed horizontally inside the tank. Average temperature of the hot water bath was kept constant at 60 °C to establish a quiescent region of uniform temperature. The experiments were conducted in turbulent flow regime using distilled water and Al 2 O 3 /water nanofluid at 0.5, 1, and 1.5 % particle volume concentration. Results showed that overall heat transfer coefficient of the base fluid flow increases by using nanofluid or pulsation into the base fluid flow up to 14 %. Heat transfer results also indicated that combination of the nanofluid and the pulsation into the fluid flow can increase significantly the overall heat transfer coefficient up to 23 %.

Description: Nanofluids have recently attracted researches’ attention as a new generation of heat-transferring fluids used in heat exchangers and for energy storage. Also aluminium nitride is commonly known for its considerable heat conductivity, as high as 320 W/(m K). Because of that, the compound might be a preferable dispersed phase of heat-transferring fluids. This presented studies are focused on nano-AlN–poly(propylene glycol) dispersions which can be applied as potential cooling fluids. The rheological response of the suspensions on shearing and their thermal conductivity in the function of solids concentration and temperature were measured and discussed. The most desired result of the studies is to produce dispersions with Newtonian-like flow at increased temperature and at higher shear rate. All the aforementioned parameters conjugated with significant thermal conductivity of such nanofluids could predispose them to be used as effective cooling media.

Description: This experimental study investigates the effects of vortex-generator (VG) and Cu/water nanofluid flow on performance of plate-fin heat exchangers. The Cu/water nanofluids are produced by using a one-step method, namely electro-exploded wire technique, with four nanoparticles weight fractions (i.e. 0.1, 0.2, 0.3, and 0.4 %). Required properties of nanofluids are systematically measured, and empirical correlations are developed. A highly precise test loop is fabricated to obtain accurate results of the heat transfer and pressure drop characteristics. Experiments are conducted for nanofluids flow inside the plain and VG channels. Based on the experimental results, utilizing the VG channel instead of the plain channel enhances the heat transfer rate, remarkably. Also, the results show that the VG channel is more effective than the nanofluid on the performance of plate-fin heat exchangers. It is observed that the combination of the two heat transfer enhancement techniques has a noticeably high thermal–hydraulic performance, about 1.67. Finally, correlations are developed to predict Nusselt number and friction factor of nanofluids flow inside the VG channel.

Description: Optimal design and performance of a combined infrared-convective drying system with respect to the energy issue is extremely put through the application of advanced engineering analyses. This article proposes a theoretical approach for exergy analysis of the combined infrared-convective drying process using a simple heat and mass transfer model. The applicability of the developed model to actual drying processes was proved using an illustrative example for a typical food.

Description: It is well known that dropwise condensation corresponds to a high heat transfer coefficient. The high performance enhancement of dropwise condensation in comparison to filmwise condensation is attributed to the ability of non-wetting droplets to be shed from the surface by gravity, therefore reducing the overall thermal resistance. The common treatments to carry out the hydrophobic surface for dropwise condensation are coating and structure. The improvement of heat transfer efficiency by combination of surface treatments with coating and groove structure has been proved compared of surface with single surface treatment by coating or groove structure. Based on this result, in this study presents a model developed to predict the heat transfer efficiency of dropwise condensation for surface with coating and groove structure features. The model is established by heat transfer though a single droplet with the drop size distribution. The heat transfer of single drop is not only analyzed as combination of thermal resistances, but also considered capillary effect of droplet due to groove geometry and properties of surface. In addition, the model results are validated with experimental data which is investigated by varied modification of vapor side metallic surface properties at low absolute pressure. It can be a reference to design industrial condensers of heat exchangers in the future. Further to optimize the surface properties and improve the higher heat transfer performance of dropwise condensation.

Description: The upward sub-cooled forced convection in a rectangular channel is investigated experimentally. The aim of the present work is the studying of the local heat transfer phenomena. Concerning the experimentation: the n -pentane is used as a working fluid, the independent variables are: the velocity in the range from 0.04 to 0.086 m/s and heat flux density with values between 1.8 and 7.36 W/cm 2 . The results show that the local Nusselt number distribution is not uniform along the channel; however, uniformity is observed in the mean Nusselt number for Reynolds under 1600. On the other hand, a new correlation to predict the local fluid temperature is established as a function of local wall temperature. The wall’s heat is dissipated under the common effect of the sub-cooled regime; therefore, the local heat transfer coefficient is increased. The study of the thermal equilibrium showed that for Reynolds less than 1500; almost all of the heat flux generated by the heater cartridges is absorbed by the fluid.

Description: Experimental investigation for the flow boiling of water in a vertical rectangular channel was conducted to reveal the boiling heat transfer mechanism and flow patterns map aspects. The onset of nucleate boiling went upward with the increasing of the working fluid mass flow rate or the decreasing of the inlet working fluid temperature. As the vapour quality was increased, the local heat transfer coefficient increased first, then decreased, followed by various flow patterns. The test data from other researchers had a similar pattern transition for the bubble-slug flow and the slug-annular flow. Flow pattern transition model analysis was performed to make the comparison with current test data. The slug-annular and churn-annular transition models showed a close trend with current data except that the vapor phase superficial velocity of flow pattern transition was much higher than that of experimental data.

Description: A two-fluid model with the influence of inter-phase velocity-slip taken into account is proposed and a modified realizable k – ε turbulence model is put forward as well to make the equation set of two-fluid model closed. Based on this two-fluid model, numerical simulations are implemented on typical wet steam flow in different cases. Good consistency between numerical result and the experimental result implies that this two-fluid model is provided with high accuracy and wide applicability. The flow field analysis also shows that there exist several particular sites along the flow direction. These particular sites could illustrate the development mechanism of nucleation and droplet growing. In addition, further discussion about the flow in cascade then indicates that the presence of condensation has strong impact on the flow while the impact of inter-phase velocity-slip is relatively weaker. The composition of total pressure loss is present here, the majority of total pressure loss brought by condensation is about 8.78 % of inlet total pressure while the inter-phase velocity-slip just results in a small part of about 0.42 % of inlet total pressure, the rest of the total pressure loss is caused by pneumatic factors and this part is about 3.95 % of inlet total pressure.

Description: This paper theoretically analyzes the heat transfer characteristics associated with electroosmotic flow of blood through a micro-vessel having permeable walls. The analysis is based on the Debye–Hückel approximation for charge distributions and the Navier–Stokes equations are assumed to represent the flow field in a rotating system. The velocity slip condition at the vessel walls is taken into account. The essential features of the rotating electroosmotic flow of blood and associated heat transfer characteristics through a micro-vessel are clearly highlighted by the variation in the non-dimensional flow velocity, volumetric flow rate and non-dimensional temperature profiles. Moreover, the effect of Joule heating parameter and Prandtl number on the thermal transport characteristics are discussed thoroughly. The study reveals that the flow of blood is appreciably influenced by the elctroosmotic parameter as well as rotating Reynolds number.

Description: This paper reports the Computational Fluid Dynamics modeling studies on the effect of plasma aerodynamic actuation on combustor film cooling performance. By comparing Case (i.e. film cooling hole with plasma actuator) result to Base (i.e. film cooling hole without plasma actuator) result, the mechanism of improving film cooling performance by using plasma actuator was analyzed. The results show that the Counter Rotating Vortex Pairs in Base are weakened by a new pair of vortex in Case, which is induced by the plasma-actuator-generated arc-shape-distributed electric body force. This leads to less interaction and less mixing between the main flow and the jet flow. Then it causes enhancement of the stability and the steadiness of the jet flow. Finally the average film cooling effectiveness in Case is higher than that in Base. For Case, the uniformity of temperature distribution along spanwise wall surface is improved as the actuator electrode radian increases, so does the average film cooling effectiveness. The film cooling effectiveness is higher when actuator is closer to the exit of hole.

Description: The group method of data handling (GMDH) technique was used to predict heat transfer and friction characteristics in heat exchanger tubes equipped with wire-rod bundles. Nusselt number and friction factor were determined as functions of wire-rod bundle geometric parameters and Reynolds number. The performance of the developed GMDH-type neural networks was found to be superior in comparison with the proposed empirical correlations. For optimization, the genetic algorithm-based multi-objective optimization was applied.

Description: An inverse analysis is done to predict unknown and optimal dimensions of a fin satisfying either a given temperature or maximizing heat transfer rate. The profile simulating many geometries involves all temperature-dependent heat transfer modes. A hybrid algorithm is used to estimate relevant fin parameters. The present study shall be useful in selecting optimal dimensions to achieve either a particular temperature distribution or maximize heat transfer rate on various profiles.

Description: A numerical model has been developed to estimate the shape of the liquid cone and the resulting jet in presence of external electric field. The model estimates the liquid velocity at the cone surface to calculate the electrical current. The equations of electric potential are solved numerically with an iterative procedure and then continuity and momentum equations solved in a commercial CFD code with electrical body forces. The model is validated by comparing with experimental results.

Description: This paper focuses on improving the performance of the vertical open refrigerated display cabinets (VORDC) by optimizing the structure of deflector, which is affected by inlet velocity and velocity distribution of air curtains. The results show that the temperature of products located at the front and at the rear reduces as the increases of inlet velocity of air curtains. The increase of the inlet velocity of air curtains can strengthen the disturbance inside the VORDC, and also decrease the temperature of products inside the VORDC; the increase of the outer velocity of air curtain will exacerbate the disturbance outside the VORDC and decrease air curtain’s performance. The present study can provide a theoretical foundation for the design of VORDC.

Description: An experimental and numerical study was performed to investigate the effect of different formulas for nanofluid thermal conductivity and dynamic viscosity on natural convective heat transfer. It was found that the heat transfer across the enclosure using different models can be enhanced or deteriorated with respect to the base fluid. Also, it was found that the inconsistencies in the reported thermal conductivity and dynamic viscosity from different research groups are mainly due to the characterization of the nanofluid, including determination of colloidal stability and particle size, (i.e., aggregates size) within nanofluid.

Description: A theoretical model is developed for condensation heat transfer of binary refrigerant mixtures in mini-tubes with diameter about 1.0 mm. Condensation heat transfer of R410A and R32/R134a mixtures at different mass fluxes and saturated temperatures are analyzed, assuming that the phase flow pattern is annular flow. The results indicate that there exists a maximum interface temperature at the beginning of condensation process for azeotropic and zeotropic mixtures and the corresponding vapor quality to the maximum value increases with mass flux. The effects of mass flux, heat flux, surface tension and tube diameter are analyzed. As expected, the condensation heat transfer coefficients increase with mass flux and vapor quality, and increase faster in high vapor quality region. It is found that the effects of heat flux and surface tension are not so obvious as that of tube diameter. The characteristics of condensation heat transfer of zeotropic mixtures are consistent to those of azeotropic refrigerant mixtures. The condensation heat transfer coefficients increase with the concentration of the less volatile component in binary mixtures.

Description: An experimental study using Mach–Zehnder interferometer has been carried out to investigate the heat transfer from an isothermal horizontal circular cylinder, which is exposed to an air slot jet at different angles of jet impingement. A square edged nozzle is mounted parallel with the cylinder axis and jet flow impinges on the side of the cylinder at angles Θ = 0°, 30°, 60° and 90°. The Reynolds number varied from 240 to 1900 while the Grashof number and slot- to cylinder-spacing is kept constant at Gr = 22,300 and H/w = 7 respectively. The Richardson number varied from 0.006 to 0.4. The flow field is greatly influenced by the slot exit velocity and the buoyancy force due to density change. The local Nusselt number around the cylinder has been calculated using the infinite fringe interferograms at 10° intervals. Average Nusselt number shows that heat transfer is decreased when the angle of jet impingement is increased .

Description: This study is about the performance evaluation of a shell and tube heat exchanger operated with nanofluid. Thermal conductivity, viscosity, and density of the nanofluids were increased, but the specific heat of the nanofluids was decreased with increasing the concentrations of the particles. The convective heat transfer coefficient was found to be 2–15 % higher than that of water at 50 kg/min of both side fluid. Nevertheless, energy effectiveness has improved about 23–52 % for the above-mentioned nanofluids. As, energy effectiveness (ɛ) is strongly depends on the density and specific heat of the operating fluids therefore, maximum ɛ has obtained for ZnO–W nanofluid and lowest found for SiO 2 –W nanofluid.

Description: In the present study, structure of water drops formation, growth, coalescence and departure over a horizontal finned-tube during natural dehumidification is investigated experimentally. Starting time of repelling the drops as well as heat transfer rate and the rate of dripping condensates in quasi-steady-state conditions are presented. Furthermore, cold airflow pattern around the horizontal finned-tube is visualized by using smoke generation scheme during natural dehumidification process. The finned-tube has a length of 300 mm, and inner and outer fin diameters, fin thickness and fin spacing are 25.4, 56, 0.4 and 2 mm, respectively. The tests are conducted in an insulated control room with dimensions of 5.8 m × 3 m × 4 m. Ambient air temperature, relative humidity and fin base temperature are selected from 25 to 35 °C, from 40 to 70 % and from 4 to 8 °C, respectively. Observations show that natural condensation from humid air over the test case is completely dropwise. Droplets only form on the edge of the fin and lateral fin surfaces remain almost dry. Dehumidification process over the tested finned-tube is divided into four stages; nucleation, formation, growth and departure of drops. It is also observed that the condensate inundation leaves the tube bottom in the form of droplets. Smoke visualization depicts that humid airflows downward around the cold finned-tube surface without noticeable turbulence and separation in the initial stages of dehumidification process. But the airflow has some disturbances in the intermediate stage and especially during drop departure on the edge of the fins.

Description: Non-uniformity in electrode thickness can result in quality control defectively. To quantitatively detect the non-uniformity of electrode thickness during the manufacturing processes. A heat transfer model based on heat conduction equation has been employed to provide the computational study. The effects of boundary conditions of adiabatic and periodic walls along coating direction, electrode thickness changes from 3.9 to 30.0 %, and two types of located region in thickness changes, as well as anode and cathode material properties on temperature change percents are analyzed and discussed in detail. The relationship between thickness changes percents and temperature change percents of electrode is established. It is found that the thickness changes have a sensitivity of 1 % changes in electrode thickness will result in 1 % in temperature changes at an inherent time point. The selected time points are 0.008 or 0.01 s for cathode and 0.004 s for anode. The minimum thickness change percent 3.9 % will be detected. Further, the comparison of the computational results with experimental ones shows the validity of the heat conduction model.

Description: A new design of solar air heater simulator is presented to comply with the extensive applications inagro-industry. A wise installation of increased heat transfer surface area provided uniform and efficient heat diffusion over the duct. Nusselt number and friction factor have been investigated based on the constant roughness parameters such as relative roughness height (e/D), relative roughness pitch (P/e), angle of attack (α) and aspect ratio with Reynolds numbers ranging from 5000 to 19,000 in the fully developed region. Heat fluxes of 800, 900 and 1000 Wm −2 were provided. The enhancement in friction factor is observed to be 3.1656, 3.47 and 3.0856 times, and for the Nusselt number either, augmentation is calculated to be 1.4437, 1.4963 and 1.535 times, respectively, over the smooth duct for 800, 900 and 1000 Wm −2 heat fluxes. Thermohydraulic performance is plotted versus the Reynolds number based on the aforementioned roughness parameters at varying heat fluxes. The results show up that thermohydraulic performance is found to be maximum for 1000 Wm −2 at the average Reynolds number of 5151. Based on the results, we can verify that the introduced solar simulator can help analyzing and developing solar collector installations at the simulated heat fluxes.

Description: The main objectives of the present study were to investigate the drying characteristics and quality attributes of apple slices. The samples were dried at different air temperature levels (50, 60 and 70 °C) and a constant air velocity (1.5 m s −1 ). It was observed that the drying air temperature affected the dehydration rate significantly. The usefulness of eight different mathematical models to simulate the experimental drying curves was evaluated and the Midilli model provided the best simulation of the samples drying kinetics. The effective moisture diffusivity was determined to be 7.03 × 10 −10 , 8.48 × 10 −10 and 1.08 × 10 −9  m 2  s −1 for drying air temperatures of 50, 60 and 70 °C, respectively. The shrinkage values of the dried samples at air temperatures of 50, 60 and 70 °C were 74.70, 82.35 and 80.78 %, respectively. The maximum value of rehydration ratio (4.527) and also the minimum value of ∆E (11.27) were obtained for the slices dried at 70 °C.

Description: In this paper, two accurate methods for determining the transient fluid temperature were presented. Measurements were conducted for boiling water since its temperature is known. At the beginning the thermometers are at the ambient temperature and next they are immediately immersed into saturated water. The measurements were carried out with two thermometers of different construction but with the same housing outer diameter equal to 15 mm. One of them is a K-type industrial thermometer widely available commercially. The temperature indicated by the thermometer was corrected considering the thermometers as the first or second order inertia devices. The new design of a thermometer was proposed and also used to measure the temperature of boiling water. Its characteristic feature is a cylinder-shaped housing with the sheath thermocouple located in its center. The temperature of the fluid was determined based on measurements taken in the axis of the solid cylindrical element (housing) using the inverse space marching method. Measurements of the transient temperature of the air flowing through the wind tunnel using the same thermometers were also carried out. The proposed measurement technique provides more accurate results compared with measurements using industrial thermometers in conjunction with simple temperature correction using the inertial thermometer model of the first or second order. By comparing the results, it was demonstrated that the new thermometer allows obtaining the fluid temperature much faster and with higher accuracy in comparison to the industrial thermometer. Accurate measurements of the fast changing fluid temperature are possible due to the low inertia thermometer and fast space marching method applied for solving the inverse heat conduction problem.

Description: A 2-D numerical simulation is carried out to investigate the effect of two adiabatic square ribs on laminar flow and heat transfer in an asymmetrically heated channel. The two ribs are symmetrically located on each wall, exactly above the heating zone. The computational procedure is made by solving the unsteady bi-dimensional continuity, momentum and energy equations with the finite volume method. The investigations focused more specifically on the influence of ribs sizes on the flow structure and heat transfer enhancement. The results showed that the variation of ribs sizes significantly alters the heat transfer and fluid flow distribution along the channel, especially in the vicinity of protrusions. Also, the results show that streamlines, isotherms, and the number, sizes and formation of vortex structures inside the channel strongly depend on the size of protrusions. The changes in heat transfer parameters have also been presented.

Description: A grooved heat pipe (GHP) is an important device for managing heat in space applications such as satellites and space stations, as it works efficiently in the absence of gravity. Apart from the above application, axial GHPs are used in many applications, such as electronic cooling units for temperature control and permafrost cooling. Improving the performance of GHPs is essential for better cooling and thermal management. In the present study, the effect of anodization on the heat transfer characteristics of a GHP is studied with R600a as a working fluid. In addition, the effects of fill ratio, inclination angle and heat inputs on the heat transfer performance of a GHP are studied. Furthermore, the effect of heat flux on dimensional numbers, such as the Webber, Bond, Kutateladze and condensation numbers, are studied. The inclination angle, heat input and fill ratio of GHPs are varied in the range of 0°–90°, 25–250 W and 10–70 % respectively. It is found that the above parameters have a significant effect on the performance of a GHP. Due to the anodisation, the maximum enhancement in heat transfer coefficient at the evaporator is 39 % for a 90° inclination at a heat flux of 11 kW/m 2 . The reported performance enhancement of a GHP may be due to the large numbers of nucleation sites created by the anodisation process and enhancement in the capillary force due to the coating.

Description: A hot stainless steel (SS-304) surface of 450 ± 10 °C initial temperature is cooled with a normally impinging round water jet. The experiments have been performed for the surface of different thickness e.g. 1, 2, 3 mm and jet Reynolds number in the range of Re  = 26,500–48,000. The cooling performance of the hot test surface is evaluated on the basis of wetting front velocity. The wetting front velocity is determined for 10–40 mm downstream spatial locations away from the stagnation point. It has been observed that the wetting front velocity increase with the rise in jet flow rate, however, diminishes towards the downstream spatial location and with the rise in surface thickness. The proposed correlation for the dimensionless wetting front velocity predicts the experimental data well within the error band of ±30 %, whereas, 75 % of experimental data lies within the range of ±20 %.

Description: This paper presents a numerical analysis by using the finite difference method to describe the steady and unsteady state thermal behavior of triple concentric-tube heat exchanger with parallel flow and counter flow arrangements. One gives the temperature variations of the three fluids and three walls with time along the triple concentric-tube heat exchanger. The fluids have a time lag and the response of triple concentric-tube heat exchanger in parallel flow configuration is faster than those of a counterflow arrangement, its performances are always lower than those of a counterflow triple concentric-tube heat exchanger. The heat transfer coefficients by convection of the three fluids vary with time in addition to the temperature and the heat exchanger performances are lower in unsteady state than the steady state case.

Description: The present study reports the heat-transfer performance of a two-phase closed thermosyphon (TPCT) equipped with a novel condenser. Distillated water was used as working fluid, with a volumetric liquid filling ratio of 75 %. An increase in heat flux was used to measure the response of the TPCT, including variations in temperature distribution, thermal resistance, average temperature of each section of TPCT and overall thermal difference. Results show that for various power inputs from 71 to 960 W, the TPCT with the novel condenser had a lower wall-temperature difference between the evaporator and condenser sections than did the unmodified TPCT. Given the experimental data for heat-transfer performance, it was found that the thermal resistance in the TPCT equipped with the proposed condenser was between 10 and 17 % lower than in the one without.

Description: This paper presents the experimental heat transfer coefficient and pressure drop measured during R-134a saturated vapour condensation inside a small brazed compact plate fin heat exchanger with serrated fin surface. The effects of saturation temperature (pressure), refrigerant mass flux, refrigerant heat flux, effect of fin surface characteristics and fluid properties are investigated. The average condensation heat transfer coefficients and frictional pressure drops were determined experimentally for refrigerant R-134a at five different saturated temperatures (34, 38, 40, 42 and 44 °C). A transition point between gravity controlled and forced convection condensation has been found for a refrigerant mass flux around 22 kg/m 2 s. In the forced convection condensation region, the heat transfer coefficients show a three times increase and 1.5 times increase in frictional pressure drop for a doubling of the refrigerant mass flux. The heat transfer coefficients show weak sensitivity to saturation temperature (Pressure) and great sensitivity to refrigerant mass flux and fluid properties. The frictional pressure drop shows a linear dependence on the kinetic energy per unit volume of the refrigerant flow. Correlations are provided for the measured heat transfer coefficients and frictional pressure drops.

Description: High heat transfer performance of spray cooling on structured surface might be an additional measure to increase the safety of an installation against any threat caused by rapid increase in the temperature. The purpose of present experimental study is to explore heat transfer performance of structured surface under different spray conditions and surface temperatures. Two cylindrical stainless steel samples were used, one with pyramid pins structured surface and other with smooth surface. Surface heat flux of 3.60, 3.46, 3.93 and 4.91 MW/m 2 are estimated for sample initial average temperature of 600, 700, 800 and 900 °C, respectively for an inlet pressure of 1.0 MPa. A maximum cooling rate of 507 °C/s was estimated for an inlet pressure of 0.7 MPa at 900 °C for structured surface while for smooth surface maximum cooling rate of 356 °C/s was attained at 1.0 MPa for 700 °C. Structured surface performed better to exchange heat during spray cooling at initial sample temperature of 900 °C with a relative increase in surface heat flux by factor of 1.9, 1.56, 1.66 and 1.74 relative to smooth surface, for inlet pressure of 0.4, 0.7, 1.0 and 1.3 MPa, respectively. For smooth surface, a decreasing trend in estimated heat flux is observed, when initial sample temperature was increased from 600 to 900 °C. Temperature-based function specification method was utilized to estimate surface heat flux and surface temperature. Limited published work is available about the application of structured surface spray cooling techniques for safety of stainless steel structures at very high temperature scenario such as nuclear safety vessel and liquid natural gas storage tanks.

Description: In this work, the macro adsorption characteristic of water vapor by the allochroic silica gel and the zeolite 5A and ZSM-5 were investigated experimentally. BET analysis method presented the difference of the porosity, the micro pore volume, and the specific surface area of the material. The dynamic and the equilibrium characteristics of the sample were measured thermo-gravimetrically in the moist air. In general, the ZSM-5 zeolite showed an inferior feature of the adsorption speed and the equilibrium concentration to the others. By comparison to the result of SAPO-34 zeolite in the open literature, the 5A zeolite showed some superiorities of the adsorption. The equilibrium concentration of the ZSM-5 zeolite was higher than that of the SAPO-34 calcined in the nitrogen, whereas it was lower than that calcined in the air. The adsorption isotherm was correlated and the relation of the isotherm to the microstructure of the material was discussed. With more mesopore volume involved, the zeolite presented an S-shaped isotherm in contrast to the exponential isotherm of the silica gel. In addition, the significance of the S-shaped isotherm for the application in adsorption heat pump has also been addressed.

Description: In this study, a detailed exergy analysis of an industrial-scale ultrafiltrated (UF) cheese production plant was conducted based on actual operational data in order to provide more comprehensive insights into the performance of the whole plant and its main subcomponents. The plant included four main subsystems, i.e., steam generator (I), above-zero refrigeration system (II), Bactocatch-assisted pasteurization line (III), and UF cheese production line (IV). In addition, this analysis was aimed at quantifying the exergy destroyed in processing a known quantity of the UF cheese using the mass allocation method. The specific exergy destruction of the UF cheese production was determined at 2330.42 kJ/kg. The contributions of the subsystems I, II, III, and IV to the specific exergy destruction of the UF cheese production were computed as 1337.67, 386.18, 283.05, and 323.51 kJ/kg, respectively. Additionally, it was observed through the analysis that the steam generation system had the largest contribution to the thermodynamic inefficiency of the UF cheese production, accounting for 57.40 % of the specific exergy destruction. Generally, the outcomes of this survey further manifested the benefits of applying exergy analysis for design, analysis, and optimization of industrial-scale dairy processing plants to achieve the most cost-effective and environmentally-benign production strategies.

Description: In the present study, it was aimed to produce a fundamental i nformation and to investigate the effects of various design parameters on tube performance characteristics by setting up vortex tube experimental system in order to study the parameters predetermined for the design of vortex tubes and by conducting thermodynamic analysis. According to the findings of experiments, as the mass flow rate of cold flow increases (y c ) temperature of cold flow also increases, while the temperature of warm flow increases approximately to y c  = 0.6 and then decreases. Increases in inlet pressure, inlet nozzle surface and diameter of the cold outlet orifice increased temperature differences between cold and warm flows. Tube with L/D = 10 showed better performance than with L/D = 20. The finding that irreversibility parameter is very close to critical threshold of irreversibility proved that process in vortex tube is considerably irreversible. Coefficient of performance (COP) values in vortex tube were much lower than other heating and cooling systems. This situation may show that vortex tubes are convenient in the processes where productivity is at the second rate compared to other factors.

Description: Molecular dynamic simulations are performed to study the effects of nanostructure on rapid boiling of water that is suddenly heated by a hot copper plate. The results show that the nanostructure has significant effects on energy transfer from solid copper plate to liquid water and phase change process from liquid water to vapor. The liquid water on the solid surface rapidly boil after contacting with an extremely hot copper plate and consequently a cluster of liquid water moves upward during phase change. The temperature of the water film when it separates from solid surface and its final temperature when the system is at equilibrium strongly depend on the size of the nanostructure. These temperatures increase with increasing size of nanostructure. Furthermore, a non-vaporized molecular layer is formed on the surface of the copper plate even continuous heat flux is passing into water domain through the plate.

Description: The heat transfer properties of different cooling systems dealing with Poly-Ethylene-Terephthalate (PET) bottles were investigated. The heat transfer coefficient (U g ) was measured in various fluid dynamic conditions. Cooling media were either air or water. It was shown that heat transfer coefficients are strongly affected by fluid dynamics conditions, and range from 10 W/m 2  K to nearly 400 W/m 2  K. PET bottle thickness effect on U g was shown to become relevant under faster fluid dynamics regimes.

Description: Nano-fluids are used to improve the heat transfer rates in heat exchangers, especially; the shell-and-tube heat exchanger that is considered one of the most important types of heat exchangers. In the present study, an experimental loop is constructed to study the thermal characteristics of the shell-and-tube heat exchanger; at different concentrations of Al 2 O 3 nonmetallic particles (0.0, 2, 4, and 6 %). This material concentrations is by volume concentrations in pure water as a base fluid. The effects of nano-fluid concentrations on the performance of shell and tube heat exchanger have been conducted based on the overall heat transfer coefficient, the friction factor, the pressure drop in tube side, and the entropy generation rate. The experimental results show that; the highest heat transfer coefficient is obtained at a nano-fluid concentration of 4 % of the shell side. In shell side the maximum percentage increase in the overall heat transfer coefficient has reached 29.8 % for a nano-fluid concentration of 4 %, relative to the case of the base fluid (water) at the same tube side Reynolds number. However; in the tube side the maximum relative increase in pressure drop has recorded the values of 12, 28 and 48 % for a nano-material concentration of 2, 4 and 6 %, respectively, relative to the case without nano-fluid, at an approximate value of 56,000 for Reynolds number. The entropy generation reduces with increasing the nonmetallic particle volume fraction of the same flow rates. For increase the nonmetallic particle volume fraction from 0.0 to 6 % the rate of entropy generation decrease by 10 %.

Description: Auto-refrigerating cascade (ARC) systems possess many advantages comparing with traditional cascade refrigeration systems. This work proposed a novel ternary mixture, R600a/R23/R14, for ARC systems for 190 K applications. The performance of the ternary mixture and the influences of compositional ratio and bypass scheme were assessed in a modified domestic cooler. The results demonstrated the feasibility of the proposed R600a/R23/R14 ternary mixture as an environmental benign alternative for ARC systems. The performance varied little within a certain composition range and a mass ratio of 35/30/35 for R600a/R23/R14 mixture was recommended. It also showed that the two bypass schemes, which can regulate more effectively the refrigerant compositions, were better than the conventional hot-gas bypass approach. The variation of the evaporator temperature suggested the presence of local dryout at high heat loads (i.e., larger than the design value), which should be carefully prevented.

Description: The flexibility of vanadium nitrate makes it a good constituent for emerging superconductors. Its thermal instability engenders a disordered structure when doped by insulating constituents. The physics of the heat source i.e. the probe laser was theoretical derived to avoid deficiency of the superconducting material at low laser energy density. The mathematical experimentation was accomplished by queering the energy balance and heat conductivity of the individual constituents of the reagent. In-depth analysis of the layered distribution of laser induced temperature fields was carried out by cooling the compound via the forced convective cooling technique to about 150 °C. The material was gradual heated via the laser probe to its superconducting state. The structural defect which explained different state of the thermal outcomes were explained and proven to correspond with experimental outcomes. The temperature distribution under the irradiating laser intensity (0.45 W) shows an effective decay rate probability density function which is peculiar to the concept of photoluminescence. The dynamics of the electronic structure of thermally-excited superconducting materials is hinged on the complementary stoichiometry signatures, thermal properties amongst others. The maximum possible critical temperatures of the inter-layer were calculated to be about 206 K.

Description: Micro heat pipes (MHPs) with excellent heat transfer performance have been the ideal radiating components to meet increasingly higher requirements posed by high heat-flux products. Based on MHPs’ working principle, this study deduced capillary limit of a novel MHP with compound structure of sintered wick on grooved substrate, and probed into its forming mechanism: first, high-speed oil-filled spinning was applied to fabricating micro grooves, with optimal spinning and drawing speeds determined; then a mini-type vibration machine was used to help fill copper powders fast and uniformly, with appropriate sintering temperature and time fixed; the manufacturing method that integrates vacuum-pumping–cold-welding with secondary-degassing–cold-welding to increase vacuumizing efficiency. The results of experiments on its heat transfer performance show that the MHPs with sintered-wick-on-grooved-substrate structure fabricated through the proposed forming method can not only acquire much better heat transfer performance, but have advantages such as higher productivity and lower cost.

Description: In this paper steady state two-dimensional mixed convection heat transfer problem in a lid-driven cavity heated via an uniformly distributed heat flux on the bottom wall is investigated numerically. The lid moves with constant velocity and is kept at low constant temperature, between two ideally thermally insulated vertical walls. A wide range of Prandtl Pr and Richardson Ri number is examined to study their effects on heat transfer rate and fluid flow. Governing parameters are 0.001 ≤ Ri ≤ 1.0 and 0.71 ≤ Pr ≤ 56.00. Grashof number Gr is fixed at 10 4 . The results are presented in the form of isotherms and streamlines plots. Also, local and mean Nusselt number are depicted on charts. Numerical values of the surface averaged Nusselt number are also presented. Results show that increase of Prandtl number strongly influences enhancement of heat transfer rate and that decreasing of Richardson number increases surface averaged Nusselt number. Mechanisms responsible for intensification of heat transfer are identified and physical explanation of this phenomenon are also given.

Description: Closed form approximate solutions to nonlinear heat (mass) diffusion equation with power-law nonlinearity of the thermal (mass) diffusivity have been developed by the integral-balance method avoiding the commonly used linearization by the Kirchhoff transformation. The main improvement of the solution is based on the double-integration technique and a new approach to the space derivative. Solutions to Dirichlet and Neumann boundary condition problems have been developed and benchmarked against exact numerical and approximate analytical solutions available in the literature.

Description: The permanent magnet synchronous motor (PMSM) is widely used in ships under frequency conversion control system. The fluid flow performance and temperature distribution of the PMSM are difficult to clarify due to its complex structure and variable frequency control condition. Therefore, in order to investigate the fluid and thermal characteristics of the PMSM, a 50 kW PMSM was taken as an example in this study, and a 3-D coupling analysis model of fluid and thermal was established. The fluid and temperature fields were calculated by using finite volume method. The cooling medium’s properties, such a velocity, streamlines, and temperature, were then analyzed. The correctness of the proposed model, and the rationality of the solution method, were verified by a temperature test of the PMSM. In this study, the changing rheology on the performance of the cooling medium and the working temperature of the PMSM were revealed, which could be helpful for designing the PMSM.

Description: Temperature uniformity after a mixing process plays a very important role in many applications. Non-uniform temperature at the entrance of the turbine in gas turbine systems has an adverse effect on the life of the blades. These temperature non-uniformities cause thermal stresses in the blades leading to higher maintenance costs. This paper presents experimental and numerical results for mixing process in coaxial ducts. The effect of increased jet-to-mainstream momentum flux ratio on the temperature uniformity of the exit flow was analyzed. It was found that better mixing of primary (or hot) stream and dilution (or cold) stream was achieved at higher flux ratio. Almost 85 % of the equilibrium mixture fraction was achieved at flux ratio of 0.85 after which no significant improvement was achieved while the exergy destruction kept on increasing. A new parameter, ‘Cooling Rate Number’, was defined to identify the potential sites for presence of cold zones within the mixing section. Parametric study reveals that the cooling rate numbers were higher near the dilution holes which may result in rapid cooling of the gases.

Description: In the present study, the lamination effect in a micro T-mixer with non-aligned inputs on the mixing index has been investigated numerically in four different cases. The multi-block lattice Boltzmann method has been implemented for the flow field simulation and the second order upwind finite difference scheme has been used to simulate mass transfer. Reynolds numbers includes in the range of 10 ≤  Re  ≤ 70. The simulation results show that the lamination effect in the mixer inputs, despite of its simple design, causes the interface of two fluids to increase and also to make the vortex effect stronger in the confluence of two fluid streams that increases the mixing index considerably. Of four lamination cases included for the mixing input, the maximum mixing index is for the vertical and asymmetrical lamination at the Reynolds number of 70 that is equal 0.689 and the minimum mixing index is for the horizontal and asymmetrical lamination at the Reynolds number of 10 that is equal 0.198.

Description: This work is focused on the analysis of various computed terms of entropy generation rate in the gaseous combustion processes at different inlet temperatures of air and CH 4 . Therefore, the expression of the entropy generation rate includes the effect of the viscosity friction, the thermal diffusion, the species diffusion and the chemical reaction. The expressions have been used for each term of entropy generation in order to examine the influence of each one in the overall system.

Description: The experimental conductive heat transfer results for flow through inserted perforated twisted tapes in a horizontal tube during condensation of pure R-245fa vapor. The test section consisting of two separate coaxial double pipes assembled in series, acted like a counter flow heat exchanger, where the refrigerant condensed inside the inner tube by rejecting heat to the cooling water flowing inside the outer tube in reversed direction. Data for three perforated twisted tapes having constant twist ratio of 7.1 mm and pitch of perforation as 12.5, 25.0 and 37.5 mm, inserted one by one in full length of test condenser by varying refrigerant mass flux from 100 to 200 kg/m 2  s in steps of 50 kg/m 2  s for the range of vapor quality from 0.1 to 0.9, were collected together with flow and without insert (plain tube). It has been found that the perforated twisted tape insert having pitch of perforation equal to in order of 12.5 mm gives the highest value of average heat transfer coefficient and is of the order of 37.5 % more than that of the plain one and the correlation predicts the experimental data within an error band of ±15 %.

Description: A new model which includes liquid molecule nanolayer, aggregation and nanoconvection is developed to discuss the enhanced thermal conductivity of nanofluids. Dimensionless numbers (particle size and thermal conductivity) are firstly defined, and it is confirmed that the particle size including powder and aggregate sizes is one of the key parameters to affect the thermal conductivity. It is found that the maximum enhancement of thermal conductivity is to be 64.4 %.

Description: A numerical study was conducted to investigate the performance of film cooling injection from a row of multiple square holes spaced laterally across a flat plate. LES with the standard Smagorinsky–Lilly model was used to investigate the dynamic mixing process between the coolant jet stream and the mainstream flows. The finite volume method and the unsteady PISO algorithm on a non-uniform staggered grid were applied. The values of rotation number (Ro) examined were 0.0, 0.03021, 0.06042, and 0.12084, jet spacing to jet width ratio (P/D) was 3.0, and a jet Reynolds number (Re) of 4700, which based on the hole width and the jet exit velocity. The effects of the coolant to mainstream density ratio (DR) on the film cooling effectiveness were investigated by injecting either nitrogen (DR = 0.98) or carbon dioxide (DR = 1.55) as the coolant streams. The effect of DR on the film-cooling effectiveness is coupled with varying velocity ratio (VR = 0.5 and 1.0). The coolant gas was injected at 90° to the mainstream flow. The flow fields of the present study were compared with experimental data in order to validate the reliability of the LES technique. It was shown that rotation has a strong impact on the jet trajectory behaviour and the film cooling effectiveness. In all cases, as the rotation number increases, the film effectiveness increases; this effect is increased as the velocity ratio increases. The results also showed the strong influence of velocity ratio on the flow field behaviour and the film cooling where the jet penetrates further into the cross flow as VR increases and the wake region increases with increasing VR. Furthermore, it was concluded that DR has only a minor effect on flow field and heat transfer at a constant velocity ratio.

Description: The paper discusses about thermal management of PEM fuel cells. The objective is to define criteria and guidelines for the design of the air flow cooling system of fuel cells stacks for different combination of power density, bipolar plates material, air flow rate, operating temperature It is shown that the optimization of the geometry of the channel permits interesting margins for maintaining the use of separate air flow cooling systems for high power density PEM fuel cells.

Description: Combustion of hydrocarbon fuel is accompanied with the formation of nitric oxide (NO) amongst other harmful emissions. In this work, a numerical investigation has been made for understanding the effect of radiative heat transfer on temperature distribution and formation of thermal NO in a methane–air diffusion flame under different reduced gravity environments. Conservation equations of overall mass, species concentration, momentum and energy for the reactive flows have been numerically solved with the use of finite difference scheme. In addition to that a semi-empirical soot model and an optically thin radiation model have been incorporated in the simulation. Gravity level is varied by the changed values of acceleration due to gravity. A thermal NO model incorporated accounts for the NO formation process which is decoupled from the hydrocarbon combustion. The relevant conservation equations have been solved as a post combustion reaction process. The flame height drops marginally with the reduction of gravity. Temperature becomes more uniformly distributed at lower gravity. NO formation boosts up with the fall of gravity below normal level when no radiation effect is considered. However, when radiation is considered, NO formation declines marginally with the reduction of gravity levels. Also in this case, concentration values of NO compare substantially lower with those without radiation. The upsurge of NO formation due to decline in gravity; and on the other hand, a shrinkage in concentration values of NO due to radiation effect can be attributed mainly to the rise and fall of temperature respectively in the computational zone.

Description: Herein, a systematic investigation was carried out to reach a rational understanding and to provide information concerning the possible causes for a significant influence of pressure variation in the underlying processes of mass transport in polycrystalline materials. The authors focused their research in solid-state diffusion, a part of the subject “Mass Transport in Solids”. Theories on diffusion are the subject by itself which exists as a latent fingerprint in every text of higher learning in interdisciplinary science. In this research, authors prepared sandwich samples of titanium alloy and stainless steel using nickel as an intermediate metal. The samples were processed at three different levels of bonding pressure (3, 4 and 5 MPa) while bonding temperature and bonding time was maintained at 750 °C and 1 h, respectively, throughout the experiments. It was observed that the net flux of atomic diffusion of nickel atoms into Ti-alloy at TiA/Ni interface increased by ~63 % with the rise in the bonding pressure from 3 to 4 MPa, but decreased by ~40 % with the rise in the bonding pressure from 4 to 5 MPa. At the same time, the net flux of atomic diffusion of nickel atoms into stainless steel at Ni/SS interface increased by ~19 % with the rise in the bonding pressure from 3 to 4 MPa, but increased by ~17 % with the rise in the bonding pressure from 4 to 5 MPa. Here authors showed that the pressure variations have different effects at the TiA/Ni interface and Ni/SS interface, and tried to explain the explicit mechanisms operating behind them. In general for sandwich samples processed irrespective of bonding pressure chosen, the net flux of Ni-atoms diffused into SS is greater than that of the net flux of Ni-atoms diffused in Ti-alloy matrix by four orders of magnitude. The calculated diffusivity of Ni-atoms into Ti-alloy reaches its highest value of ~5.083 × 10 −19  m 2 /s for the sandwich sample processed using 4-MPa bonding-pressure, whereas the diffusivity of Ni-atoms into SS reaches its peak value of ~1.615 × 10 −14  m 2 /s for the sample bonded using 5-MPa bonding-pressure.

Description: In this study, the effect of drying temperature on drying behaviour and mass transfer parameters of lemon slices was investigated. The drying experiments were conducted in a laboratory air ventilated oven dryer at temperatures of 50, 60 and 75 °C. It was observed that the drying temperature affected the drying time and drying rate significantly. Drying rate curves revealed that the process at the temperature levels taken place in the falling rate period entirely. The usefulness of eight thin layer models to simulate the drying kinetics was evaluated and the Midilli and Kucuk model showed the best fit to experimental drying curves. The effective moisture diffusivity was determined on the basis of Fick’s second law and obtained to be 1.62 × 10 −11 , 3.25 × 10 −11 and 8.11 × 10 −11  m 2  s −1 for the temperatures of 50, 60 and 75 °C, respectively. The activation energy and Arrhenius constant were calculated to be 60.08 kJ mol −1 and 0.08511 m 2  s −1 , respectively. The average value of convective mass transfer coefficient for the drying temperatures of 50, 60 and 75 °C was calculated to be 5.71 × 10 −7 , 1.62 × 10 −6 and 2.53 × 10 −6  m s −1 , respectively.

Description: A unique experimental set-up was fabricated to carry out axial heat flow steady state experiments for the assessment of thermal contact conductance (TCC) at the interface of two materials. Three different materials (copper, brass and stainless steel) were selected for the experiments considering their mechanical and thermal properties. Heat transfer experiments were performed in vacuum environment (0.045 torr) to find out solid spot contact conductance for nominally flat surfaces with different surface roughness (1–5 μm) for each specimen under several load conditions (0.6–15 MPa). A precise estimation of TCC for the interface of sets of similar materials was one of the most important results of this research. The effects of the surface roughness, the material properties and the load conditions (nominal interface pressure) have been studied and documented. Furthermore, the experimental results of solid spot contact conductance were compared with four theoretical models, showing their limitations to make a precise estimation of the TCC in the range of the used parameters.

Description: Convective heat transfer in the flow of silver nanofluid through a straight tube with twisted tape inserts was investigated experimentally. This straight tube was used as absorber/receiver tube in parabolic trough collector. The experiments were conducted for Reynolds number range 500 〈 Re 〈 6000 with twisted tape inserts of different twist ratio range 0.577 〈 H/D 〈 1.732. This experimental study shows that twisted tape inserts enhances heat transfer rate in the tube. The heat transfer coefficient and friction factor in the flow of silver nanofliud with 5 % volume fraction (concentration) are higher compared to the flow of water. From this study, Nusselt number, friction factor and enhancement factor are found as 2.0–3.0 times, 10–48.5 and 135–175 %, respectively with silver nanofliud. Finally new possible correlations for predicting heat transfer and friction factor in the flow of silver nanofliud through the straight tube with twisted tape inserts are proposed.

Description: In recent years, there is an increased demand on the international market of dried fruits and vegetables with significant added value. Due to its important production, consumption and nutrient intake, drying of tomato has become a subject of extended and varied research works. The present work is focused on the drying behavior of thin-layer tomato and its mathematical modeling in order to optimize the drying processes. The moisture desorption isotherms of raw tomato were determined at four temperature levels namely 45, 50, 60 and 65 °C using the static gravimetric method. The experimental data obtained were modeled by five equations and the (GAB) model was found to be the best-describing these isotherms. The drying kinetics were experimentally investigated at 45, 55 and 65 °C and performed at air velocities of 0.5 and 2 m/s. In order to investigate the effect of the exchange surface on drying time, samples were dried into two different shapes: tomato halves and tomato quarters. The impact of various drying parameters was also studied (temperature, air velocity and air humidity). The drying curves showed only the preheating period and the falling drying rate period. In this study, attention was paid to the modeling of experimental thin-layer drying kinetics. The experimental results were fitted with four different models.

Description: Torrefaction, a thermal treatment process of biomass, has been proved to improve biomass combustible properties. Torrefaction is defined as a thermochemical process in reduced oxygen condition and at temperature range from 200 to 300 °C for shorter residence time whereby energy yield is maximized, can be a bridging technology that can lead the conventional system (e.g. coal-fired plants) towards a sustainable energy system. In efforts to develop a commercial operable torrefaction reactor, the present study examines the minimum input condition at which biomass is torrefied and explores the heat transfer mechanisms during torrefaction in poplar wood samples. The heat transfer through the wood sample is numerically modeled and analyzed. Each poplar wood is torrefied at temperature of 250, 270, and 300 °C. The experimental study shows that the 270 °C-treatment can be deduced as the optimal input condition for torrefaction of poplar wood. A good understanding of heat transfer mechanisms can facilitate the upscaling and downscaling of torrefaction process equipment to fit the feedstock input criteria and can help to develop treatment input specifications that can maximize process efficiency.

Description: Convective heat transport in a relatively thin porous layer of monosized particles is here modeled. The size of the particles is only one order of magnitude smaller than the thickness of the layer. Both a discrete three-dimensional system of particles and a continuous one-dimensional model are considered. The methodology applied for the discrete system is Voronoi discretization with minimization of dissipation rate of energy. The discrete and continuous model compares well for low velocities for the studied uniform inlet boundary conditions. When increasing the speed or for a thin porous layer however, the continuous model diverge from the discrete approach if a constant dispersion is used in the continuous approach. The new result is thus that a special correlation must be used when using a continuous model for flow perpendicular to a thin porous media in order to predict the dispersion in proper manner, especially in combination with higher velocities.

Description: To improve heat transfer performance of the shell side of a double-pipe heat exchanger enhanced by helical fins, triangle-winglet-pair vortex generators (VG) were installed along the centerline of the helical channel with rectangular cross section. The effects of the arrangement of the triangle-winglet-pair VG, such as the geometry, the angle of attack and the quantity on heat transfer performance and pressure drop characteristics have been investigated experimentally to find out the optimal design of the VG. Air was used as working fluid within the range of Re from 680 to 16,000. The results show that, the heat exchange effectiveness of the shell side with VG is 16.6 % higher than that without VG. The vortices and the unsteadiness of the flow introduced by the VG make a great contribution to the increase. Under identical pressure drop condition, the angle of attack of 30° is the best choice compared with 45° and 60°. Under the three constraints, i.e., identical mass flow rate, identical pressure drop and identical pumping power, the largest VG size can achieve the best enhancement effect. Installation of three pairs of VG within one pitch is an optimal design for the shell side used in the present experiments. The enhancement effect of isosceles right triangle is better than that of right triangle in which one acute angle is 30°.

Description: This study investigates how fusel oil affect the thermal performance of a two-phase closed thermosyphon (TPCT) at various states of operation. The present study experimentally demonstrated the effect of using fusel oil comprised of various types of alcohols (1.1 % ethyl alcohol, 74.7 % amyl alcohol, 11.3 % isobutyl alcohol, 4.9 % butyl alcohol and 3.8 % propyl alcohol and 4 % water) in varying ratios on improving the performance of the TPCT. Fusel oil has been obtained from fermentation plants as a by product. A straight copper tube with an inner diameter of 13 mm, outer diameter of 15 mm and length of 1 m was used as the TPCT. The fusel oil was filled up 33.3 % (44.2 ml) of the volume of the TPCT. Three heating power levels (200, 300 and 400 W) were used in the experiments with three different flow rates of cooling water (5, 7.5 and 10 g/s) used in the condenser for cooling the system. An increase of 17.64 % was achieved in efficiency of TPCT when fusel oil was used to replace deionized water at a heat load of 200 W and with a cooling water flow rate of 10 g/s.

Description: This paper investigates the enhancement of convective heat transfer within a sub-millimetre diameter copper tube using Al 2 O 3 , Co 3 O 4 and CuO microparticle suspensions. Experiments are conducted at different particle concentrations of 1.0, 2.0 and 5.0 wt% and at various flow rates ranging from 250 to 1000 µl/min. Both experimental measurements and numerical analyses are employed to obtain the convective heat transfer coefficient. The results indicate a significant enhancement in convective heat transfer coefficient due to the implementation of microparticle suspensions. For the case of Al 2 O 3 microparticle suspension with 5.0 wt% concentration, a 20.3 % enhancement in convective heat transfer coefficient is obtained over deionised water. This is comparable to the case of Al 2 O 3 nanofluid at the same concentration. Hence, there is a potential for the microparticle suspensions to be used for cooling of compact integrated systems.

Description: This paper explores the mathematical formulations of Fick and Maxwell–Stefan diffusion in the context of polymer electrolyte membrane fuel cell cathode gas diffusion layers. The simple Fick law with a diagonal diffusion matrix is an approximation of Maxwell–Stefan. Formulations of diffusion combined with mass-averaged Darcy flow are considered for three component gases. For this application, the formulations can be compared computationally in a simple, one dimensional setting. Despite the models’ seemingly different structure, it is observed that the predictions of the formulations are very similar on the cathode when air is used as oxidant. The two formulations give quite different results when the Nitrogen in the air oxidant is replaced by helium (this is often done as a diagnostic for fuel cells designs). The two formulations also give quite different results for the anode with a dilute Hydrogen stream. These results give direction to when Maxwell–Stefan diffusion, which is more complicated to implement computationally in many codes, should be used in fuel cell simulations.

Description: Nanofluid is the colloidal suspension of nanosized solid particles like metals or metal oxides in some conventional fluids like water and ethylene glycol. Due to its unique characteristics of enhanced heat transfer compared to conventional fluid, it has attracted the attention of research community. The forced convection heat transfer of nanofluid is investigated by numerous researchers. This paper critically reviews the papers published on experimental studies of forced convection heat transfer and pressure drop of Al 2 O 3 , TiO 2 and CuO based nanofluids dispersed in water, ethylene glycol and water–ethylene glycol mixture. Most of the researchers have shown a little rise in pressure drop with the use of nanofluids in plain tube. Literature has reported that the pumping power is appreciably high, only at very high particle concentration i.e. more than 5 %. As nanofluids are able to enhance the heat transfer at low particle concentrations so most of the researchers have used less than 3 % volume concentration in their studies. Almost no disagreement is observed on pressure drop results of different researchers. But there is not a common agreement in magnitude and mechanism of heat transfer enhancement. Few studies have shown an anomalous enhancement in heat transfer even at low particle concentration. On the contrary, some researchers have shown little heat transfer enhancement at the same particle concentration. A large variation (2–3 times) in Nusselt number was observed for few studies under similar conditions.

Description: In this work, the heat transport phenomena coupled with melting process are studied by using the enthalpy-based lattice Boltzmann method (LBM). The proposed model is a modified version of thermal LB model, where could avoid iteration steps and ensures high accuracy. The Bhatnagar–Gross–Krook (BGK) approximation with a D1Q2 lattice was used to determine the temperature field for one-dimensional melting by conduction and multi-distribution functions (MDF) with D2Q9 lattice was used to determine the density, velocity and temperature fields for two-dimensional melting by natural convection. Different boundary conditions including Dirichlet, adiabatic and bounce-back boundary conditions were used. The influence of increasing Rayleigh number (from 10 3 to 10 5 ) on temperature distribution and melting process is studied. The obtained results show that a good agreement with the analytical solution for melting by conduction case and with the benchmark solution for melting by convection.

Description: An experimental investigation, coupled with theoretical modeling of CaCO 3 fouling in plate-and-frame type heat exchangers (PHEs) have been conducted. Four different plates, made of SS-304, are used in two different surface patterns (chevron and zig-zag) of varying corrugation severity (waviness depth and pitch) and area enhancement. They were further characterized in clean, non-fouled convection by their measured heat transfer coefficients and friction factors in the Reynolds number range of 600–6000. The flow-fouling experiments delineate the effects of temperature and plate-surface geometry on growth rates and stabilization of fouling resistance, along with the anti-fouling behavior of plates coated with a hydrophobic PTFE (Teflon) film. Moreover, the microscopic structure of fouling deposits is mapped in a scanning-electron microscope. Corrugated plates with the largest height-to-pitch ratio and hydraulic diameter are found to have the lowest fouling growth rate and resistance; Teflon-film coating of plate surface is also found to mitigate fouling relative to the performance of bare stainless steel plates. Finally, a semi-empirical fouling model, based on the Prandtl–Taylor analogy, has been devised to describe the experimental data and provide a predictive tool.

Description: Hydrogels of poly(acrylic acid) crosslinked with trimethylolpropane triacrylate (TMPTA) were produced through solution polymerization. After these hydrogels were loaded with insulin solution, they evidenced swelling. Experiments of controlled release of insulin through the hydrogels were performed in acidic and basic media in order to evaluate the rates of release of this protein provided by the referred copolymer. Additionally, a mathematical description of the system based on differential mass balance was made and simulated in MATLAB. The model consists of a system of differential equations which was solved numerically. As expected, the values of swelling index at the equilibrium and the rates of insulin release were inversely proportional to the degree of crosslinking. The mathematical model provided reliable predictions of release profiles with fitted values of diffusivity of insulin through the hydrogels in the range of 6.0 × 10 −7 –1.3 × 10 −6 cm 2 /s. The fitted and experimental values of partition coefficients of insulin between the hydrogel and the medium were lower for basic media, pointing out good affinity of insulin for these media in comparison to the acidic solutions.

Description: Transverse twisted-baffles (T-TBs) and transverse baffles (TBs) were employed for heat transfer enhancement in circular tubes. The experimental and numerical studies were carried out to investigate heat transfer, friction loss and thermal performance factor associated with the use of the baffles (T-TBs/TBs). The studies encompass three different baffle width ratios ( w / D  = 0.1, 0.2 and 0.3, for TBs and T-TBs), three baffle twist ratios ( y / w  = 2.0, 3.0 and 4.0, for T-TBs) and Reynolds numbers from 6000 to 20,000. The experimental results reveal that at similar conditions, thermal performance factors of the tubes with the T-TBs are consistently higher than those of the ones with the TBs. This is attributed to the superior heat transfer enhancement with lower pressure drop penalty as the beneficial effects given by the T-TBs, as compared to those given by the TBs. For T-TBs, thermal performance factor increases as baffle width ratio ( w / D ) increases and twist ratio ( y / w ) decreases. The T-TBs with the smallest twist ratio ( y / w  = 2.0) give higher thermal performance factors than the ones with 3.0 and 4.0 by around 4.7–6.1 and 10.2–15 %, respectively. For the studied range, the T-TBs with the optimal geometric parameters, ( y / w  = 2.0 and w / D  = 0.3), give the thermal performance factors in a range of 1.46–1.69.

Description: Effective thermal conductivity including radiation is analyzed using a homogenization method. This method can precisely represent the microstructure of a porous medium with ellipsoidal pores. Here, the effects of parameters such as porosity, pore shape, pore distribution, and temperature of the porous medium on the conductivity are estimated to clarify the mechanisms in complex pore structures. For example, heat transfer by radiation does not dominate if the medium has pores of less than 1 mm in size. Moreover, the anisotropy of the effective thermal conductivity is found to depend on temperature, pore shape, pore size, and pore distribution.

Description: This work analytically investigates the problem of steady film condensation along a vertical surface embedded in an anisotropic porous medium filled with a dry saturated vapor. The porous medium is anisotropic in permeability whose principal axes are oriented in a direction which is oblique to the gravity vector. On the basis of the generalized Darcy’s law and within the boundary layer approximations, similar solutions have been obtained for the temperature and flow patterns in the condensate. Moreover, closed form solutions for the boundary layer thickness and heat transfer rate have been obtained in terms of the governing parameters of the problem.

Description: An experimental and numerical investigation of the flow field of variable density turbulent offset jet is presented. The velocity measurements are performed using a Velocimetry Laser Doppler technique for an offset height h. Three cases of variable-density turbulent plane jets discharging from a rectangular nozzle into a quiescent medium are studied. The variation density jets considered were revealed at different Reynolds numbers. In the second step of this work, a numerical three-dimensional model of the problem is simulated through the resolution of the Navier–Stokes equations by means of the finite volume method and the Reynolds stress model second-order turbulent closure model. A non-uniform mesh system tightened close to the emitting nozzle and both the vertical and horizontal walls is also adopted. A good level of agreement was achieved, between the experiments and the calculations. Once the model validated, our model allowed the evaluation of the influence of the variation density on the characterizing features of the resulting flow filed. It is found that the centerline velocity and concentration of the heavier jet decays much faster than in the two other jets, and a similar behavior for the vertical profiles in the three variable-density jets is well reproduced in the simulation.

Description: In this study a new approach for radiation heat flux calculations by coupling the discrete ordinates method with the Leckner global model is introduced. The aim is to analyze the radiative heat transfer problem within a three-dimensional enclosure filled with non-gray gas mixture of \(\hbox {H}_{2}\hbox {O}\) and \(\hbox {C}\hbox {O}_{2}\) . A computer code developed by this approach is applied to radiative calculations in three groups of well-known test cases published previously; considering homogeneous and inhomogeneous isothermal and non-isothermal participating media. All results are compared with well-known calculations based on statistical narrow band model. Also a new series of predictions for a medium with non-black walls and various mixture of \(\hbox {H}_{2}\hbox {O}\) and \(\hbox {C}\hbox {O}_{2}\) is performed to demonstrate the applicability of the Leckner model. The effect of different compositions of \(\hbox {H}_{2}\hbox {O}\) and \(\hbox {C}\hbox {O}_{2}\) on the radiative transfer within modern combustors is also examined. Based on the results obtained, it is believed that the discrete ordinates method coupled with the Leckner global model despite of its inherent simplicity and low computational cost is sufficiently accurate. For its convenient use, this method is suitable for a wide range of engineering calculations of participating media as well as for its link to previously written computational fluid dynamics codes.

Description: The heat transfer coefficient at the casting-die interface is the most important factor on the solidification process. With the 75-ton hydraulic press machine and P20 steel die mold, 5-step castings of magnesium alloy AM60 with different wall-thicknesses (3, 5, 8, 12, 20 mm) were poured under various hydraulic pressures (30, 60, and 90 MPa) using an indirect squeeze casting process. Thermal histories throughout the die wall and the casting surface have been recorded by fine type-K thermocouples. The in-cavity local pressures measured by pressure transducers were explored at the casting-die interfaces of 5 steps. The casting-die interfacial heat transfer coefficients (IHTC) initially reached a maximum peak value followed by a gradually decline to the lower level. Similar characteristics of IHTC peak values can be observed at the applied pressures of 30, 60 and 90 MPa. With the applied pressure of 90 MPa, the peak IHTC values from steps 1 to 5 varied from 5623 to 10,649 W/m 2  K. As the applied hydraulic pressure increased, the IHTC peak value of each step was increased accordingly. The wall thickness also affected IHTC peak values significantly. The peak IHTC value and heat flux increased as the step became thicker. The empirical equations relating the IHTCs to the local pressures and the solidification temperature at the casting surface were developed based on the multivariate linear and polynomial regression.

Description: In the present study, reduced graphene oxide (rGO) is synthesized from graphite using modified Hummer and chemical reduction methods. Various characterizations techniques are carried out to study the in-plane crystallite size, number of layers, presence of functional groups and surface morphology. Different concentrations of 0.01, 0.1, and 0.3 g/l of rGO/water nanofluids are prepared by dispersing the flakes in DI water. The colloidal stability of 0.3 g/l concentration is measured after 5 days using Zetasizer and found to be stable. The rGO/water nanofluids are then used to study the effect on the enhancement of critical heat flux (CHF) in pool boiling heat transfer. Results indicate an enhancement in CHF ranging from 145 to 245 % for the tested concentrations. The mechanisms of CHF enhancement are analyzed based on surface wettability, surface roughness, and porous layer thickness. The macrolayer dryout model sufficiently supports the mechanism of CHF enhancement of thin wire with rGO deposits, which is not reported yet.

Description: This paper applies the model including back-propagation network (BPN) and principal component analysis (PCA) to estimate the effective viscosity of carbon nanotubes suspension. The effective viscosities of multiwall carbon nanotubes suspension are examined as a function of the temperature, nanoparticle volume fraction, effective length of nanoparticle and the viscosity of base fluids using artificial neural network. The obtained results by BPN–PCA model have good agreement with the experimental data.

Description: Closed form approximate solutions to nonlinear transient heat conduction with linearly temperature-dependent thermal diffusivity have been developed by the integral-balance integral method under transient conditions. The solutions uses improved direct approaches of the integral method and avoid the commonly used linearization by the Kirchhoff transformation. The main steps in the new solutions are improvements in the integration technique of the double-integration technique and the optimization of the exponent of the approximate parabolic profile with unspecified exponent. Solutions to Dirichlet and Neumann boundary condition problems have been developed as examples by the classical Heat-balance integral method (HBIM) and the Double-integration method (DIM). Additional examples with HBIM and DIM solutions to cases when the Kirchhoff transform is initially applied have been developed.

Description: 〈h3〉Abstract〈/h3〉 〈p〉The intensification of energy claim and inadequate fossil fuel wealth instruct the way to renewable-based energy development that is to say vegetable oils, seed oils, plants oil and animal fats and etc. The experimental study investigated the significance of biodiesel replaced for diesel. The biodiesel is obtained by two intrinsic methods from 〈em〉Citrullus colocynthis〈/em〉, one with methyl ester and other with enzymatic lipase-based methyl ester transesterification process. The process involves Fe〈sub〉3〈/sub〉O〈sub〉4〈/sub〉+ thermomyces lanuginosus lipase as a catalyst for transesterification. The fuel extruded from these methods is tested with a single cylinder four stroke DI diesel engine to investigate the performance emission and combustion parameters. Initially, Novel immobilization-based lipase transesterification method was involved in the extrusion of oil from 〈em〉Citrullus colocynthis〈/em〉 seed and a yield of 90% with a time frame of 0 to 73 h, the extrusion was also escalated with conventional transesterification. The investigation shows that the fuel undergoes good combustion and the performance parameters were improved which in turns reflects the reduction of emission. The brake thermal efficiency of lipase immobilized biodiesel (Blend-L) is 29.86% at full load condition which is fairly less than diesel (31.33%) followed by a value of 28.93% at full load condition for conventional transesterified biodiesel. When the fuels are combusted the heat release rate and peak pressure is quite less than diesel fuel for Blend-L. The emission parameters such as PM and NO〈sub〉x〈/sub〉 are comparatively high than diesel and the remaining emission showed significantly reduced values.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Structuring of surfaces increases the efficiency of heat exchangers, but influences the deposition of particles suspended in the fluid. It is assumed, that spherical dimples suppress the deposition of particles or even induce a permanent cleaning of the occupied surface. In this study the self-cleaning mechanism of dimpled surfaces in heat exchangers is investigated to describe the influencing factors and mechanisms of particulate fouling. To get a detailed insight into fundamental deposition mechanisms, experiments on different dimpled surfaces have been carried out. According to conditions of industriell problems, e.g. cooling water fouling using river or sea water, concentrations of particles (spherical glas, d〈sub〉p,50〈/sub〉 = 3 μm) of c = 2 g/l to c = 10 g/l were used. Influences of enforced turbulence due to structuring of surface with dimples or increasing fluid velocity were investigated and visualialized with μPIV technique. Furthermore, different test durations and number as well as the geometry of the dimples were considered and evaluated with specially developed analytical methods. In extension of preceding studies on the effect of a single dimple the influencing parameters were quantified and the effect of multiple dimples in a row were investigated experimentally. A repeatable fouling pattern was observed for the different structured surfaces. The quantitative results show that the surface coverage is generally decreased downstream of the dimples. Therefore, the results confirm earlier findings suggesting an advantage of dimpled surfaces against other surface structures with respect to thermo-hydraulic efficiency as well as reduced fouling propensit. Thus, this study has shown the occurrence of self-cleaning mechanisms of the surface downstream of the dimple and provides the possibility to estimate values for the reduction of particulate depositions on dimpled surfaces. All results presented were obtained by analyzing the surface around the dimple.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Subcooled boiling of alcohol flowing through micro-cylinder-groups with different heights in aligned arrangement was investigated. Meanwhile, the outlet temperature and Nusselt number of the working fluid were obtained when the heating power was 80 W, 60 W and 40 W respectively. Subcooled boiling is divided into two parts: the partially developed stage and fully developed stage. The result showed that the outlet temperature of the fully developed stage in subcooled boiling changed rarely as the Reynolds number decreased. At the same heating power, the heights of the micro-cylinders had little effects on the outlet temperature of working fluid in the fully developed stage. However, for the same height of micro-cylinder, the fully developed stage of subcooled boiling came earlier as the heating power increased. And the Nusselt number in the fully developed stage was greater than that in the partially developed stage. Based on the regression analysis of experimental data, a correlation formula of Nusselt number for subcooled boiling in micro-cylinder-groups was established and made comparison with existing correlation.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The sorption isotherms of di-calcium phosphate (DCP) were determined using the gravimetric method at four temperatures. The sorption curves were fitted by the Guggenheim-Anderson-deBoer (GAB) model. The dehydration process was studied by means of X-ray diffraction. Thermo-gravimetric /differential thermal analyses (TGA / DTA) were used to record the loss of water and the nature of the products was studied by Fourier Transform Infrared Spectroscopy. The morphology of DCP was tested using the electronic scanning morphology (SEM). The thermal conductivity was determined using Hot Disk method. DCP convective drying kinetics modeling was conducted by the experimental study of the aero-thermal condition effects. The drying characteristic curves were then modeled using the nonlinear regression functions of MATLABR2013a. The curves predicted by the GAB model coincide well with the majority of the experimental points of the sorption isotherms. The net isosteric heat is mathematically expressed by second-order exponential function of the water content. SEM shows the presence of anhydrate and di-hydrate forms of DCP. DCP loses molecules of water when heated in two stages. Hot Disk method shows that the thermal conductivity depends heavily on the drying temperature and the product moisture. Midilli-kucuk is considered the most suitable model for the experimental results.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉In order to investigate the flow characteristics and film cooling performance of novel merged holes cooling method, merged cylindrical holes structures have been applied on a flat plate with three merging ratios under three blowing ratios. Single cylindrical hole film cooling structure is also established as a benchmark structure. The numerical results of the single cylindrical hole are validated with the experimental results available in open literatures. The discharge coefficient, aerodynamic loss, tangential velocity vectors and total vorticity distributions are studied and compared. The spanwise averaged film cooling effectiveness and adiabatic temperature contours are studied and compared. Results show that the development of the kidney vortex is impeded and the film cooling performance is promoted in merged holes cooling cases. The blowing ratio and merging ratio both affect the cooling performance of merged holes cooling cases. In this paper, the best film cooling performance is obtained at the biggest merging ratio.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The solid-liquid phase change processes are very sensitive to thermal boundary conditions. The phase change processes are also dominated by the shape of the cavity and thermo-physical properties of phase change materials. The transient experimental studies of unconstrained phase change processes are very difficult. Therefore, the numerical simulation is chosen to study the solidification phase change process in a rectangular and a spherical cavity. In this work, the solidification process of paraffin wax is simulated in a spherical cavity and a rectangular cavity for different thermal boundary conditions. The different sizes of cavities are taken to show the impact of shape on the solidification process. The simulations results are obtained using enthalpy-porosity model for free surface solidification process. The commercial software Ansys-fluent 16.2 is used to solve the numerical model. The model used for simulation is validated in previous work for melting in a spherical cavity [1] The result shows the solidification time is minimum for highest Stefan number. It also reveals that the solidification process is slow as the thickness of the solid zone increases. This is because of decreasing effect of natural convection and increasing effect of conductive resistance of solidified phase change material. The conduction dominated process makes the solidification slower as the thermal conductivity of paraffin wax is low. Different shapes of cavity, effects the solidification time. This research shows that though the size of spherical cavity is higher than that of rectangular cavity, the solidification time is much lower for spherical cavity.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉An analytic model that describes the kinetics of the process of gas hydrate film growth along the gas–water interface is presented. This model is based on the assumption that this process is controlled only by the mass transfer of gas molecules dissolved in water to the moving front of the gas hydrate film. In the presented model, the driving force of the process of gas hydrate film growth along the gas–water interface is the concentration driving force. The calculated data obtained in the framework of the presented model are compared with the available experimental data on the kinetics of methane hydrate film growth on a planar water surface and on the surface of a methane bubble suspended in water. Moreover, the calculated data obtained in the framework of the presented model are compared with the available experimental data on the kinetics of carbon dioxide hydrate film growth on the surface of a carbon dioxide bubble suspended in water. As a result of this comparison, the dependence of the thickness of carbon dioxide hydrate film on the concentration driving force was determined.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The effect of spacer orientation on flow behavior is studied at different spacer filament spacings using Computational Fluid Dynamics (CFD) technique. At high inlet velocity / Reynolds number the flow becomes transient and vorticity magnitude increases in a major portion of the two channels. The temperature and heat flux in this case also vary in time. The comparison of various spacer geometrical arrangements/orientations shows that the arrangements in which the spacer filaments are opposite to the membrane layers are more suitable due to higher heat transfer rates. Further appropriate turbulence models for predicting flow and heat transfer behavior in membrane channels are also proposed.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Local measurements along the boiling curve of heat flux, surface temperature and void data from fiber-optic microprobes are presented for vertical subcooled flow boiling of refrigerant Novec 649. Experiments were conducted in a square flow channel with a cross section of 40mm by 40mm. Mass flux varied between 1000kgm〈sup〉− 2〈/sup〉s〈sup〉− 1〈/sup〉 and 2000kgm〈sup〉− 2〈/sup〉s〈sup〉− 1〈/sup〉 and subcooling ranged from 9K to 24K. Two heaters of technically relevant thickness made of two different materials but with identical surface characteristics were investigated: a wall-mounted copper heater and a single-rod copper-coated stainless steel heater. Boiling curves for both heater configurations are provided with data on void fraction, bubble detection frequency and bubble length obtained from fiber-optic microprobes placed at a distance of 100μm relative to the heater surface. A comparison of the void morphology along the boiling curve between the two heater configurations is presented. The data is discussed with respect to recent advancements in identifying the governing parameters for boiling heat transfer in pool boiling. It was found that the entire boiling curve correlates well with the triple-phase contact line density on the heater surface. A common stability limit for the boiling process for the two heater configurations was identified based on the fiber-optic microprobe data. It was found that the boiling process becomes unstable when the thermal diffusivity time of the heater substrate becomes much longer than the void interaction time at the heater surface.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉In this work, an experimental study has been carried out to analyse the effect of wavy delta winglets on Nusselt number (〈em〉Nu〈/em〉) and friction factor (〈em〉f〈/em〉) in solar air passage for a specified range of system and operating parameters. The geometrical parameters considered are the number of waves (〈em〉ϕ〈/em〉)=3 to 7, the relative longitudinal pitch (〈em〉P〈/em〉/〈em〉H〈/em〉)=3 to 6, and the angle of attack (〈em〉α〈/em〉) = 30° to 75°. A fixed values of relative winglet chord length (〈em〉c/H〈/em〉 = 1.4) and relative blockage height (b/H = 0.5) are considered in the present study. The experimental data are generated for Nusselt number and friction factor for different combinations of geometrical and flow parameters and correlations for 〈em〉Nusselt number〈/em〉 and friction factor are also developed. Further, the developed correlations are deployed for the parametric optimization based on effective efficiency.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The effects of various factors of the pulsed electric field (PEF) as an apple osmotic dehydration (OD) preprocess by using response surface methodology (RSM) are investigated and optimized in this paper. Electric field strength, pulse numbers and pulse duration were considered as PEF pretreatment effective factors in constant osmotic dehydration conditions such as concentration and temperature. After 4 h of osmosis, the results indicate decrease in amounts of water loss (WL) and solid gain (SG) by increasing field strength from 1 to 2 kV/cm and decreasing pulse duration from 0.5 to 0.02 s, respectively. The effect of increasing the pulse numbers from 8 to 16 give rise to the increase in amounts of water loss and solid gain at first and then by increasing to 24 pulses, the decrease in these amount has been evident. The ratio of water loss to solid gain (WL/SG) and response surface methodology (RSM) were used for optimization effects of PEF factors on the OD process. In optimal values of electric field strength, pulse numbers and pulse duration, the WL/SG ratio provided highest reduction sample mass.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉In the present work, the heat transfer through a solar thermal collector (STC) provided with jet air impingement on the absorbent plate fitted with multi V-shaped protrusion ribs is investigated experimentally. The investigation is carried out for geometric parameters such as Relative width ratio (〈em〉W〈/em〉〈sub〉〈em〉PR〈/em〉〈/sub〉/〈em〉W〈/em〉〈sub〉〈em〉APR〈/em〉〈/sub〉), Relative protrusion rib height (〈em〉h〈/em〉〈sub〉〈em〉PR〈/em〉〈/sub〉/〈em〉d〈/em〉〈sub〉〈em〉PR〈/em〉〈/sub〉), Relative pitch ratio (〈em〉P〈/em〉〈sub〉〈em〉PR〈/em〉〈/sub〉/〈em〉h〈/em〉〈sub〉〈em〉PR〈/em〉〈/sub〉), Angle of attack (〈em〉α〈/em〉〈sub〉〈em〉PR〈/em〉〈/sub〉) respectively. The values of the streamwise pitch ratio (〈em〉X〈/em〉〈sub〉〈em〉SW〈/em〉〈/sub〉/〈em〉d〈/em〉〈sub〉〈em〉h〈/em〉〈/sub〉) = 0.40, spanwise pitch ratio (〈em〉Y〈/em〉〈sub〉〈em〉SW〈/em〉〈/sub〉/〈em〉d〈/em〉〈sub〉〈em〉h〈/em〉〈/sub〉) = 0.85 and jet diameter ratio (〈em〉d〈/em〉〈sub〉〈em〉j〈/em〉〈/sub〉/〈em〉d〈/em〉〈sub〉〈em〉h〈/em〉〈/sub〉) = 0.064 are kept constant. The overall performance of STC is effectively evaluated by varying Reynolds number (〈em〉Re〈/em〉) in the range 2500–35,000. The results obtained from the experiments shows that the impingement jets flow on multi V-shaped protrusion ribs absorber plate accelerated the heat transfer through the solar collector channel. The optimal augmentation is obtained at 〈em〉W〈/em〉〈sub〉〈em〉PR〈/em〉〈/sub〉/〈em〉W〈/em〉〈sub〉〈em〉APR〈/em〉〈/sub〉= 5, 〈em〉h〈/em〉〈sub〉〈em〉PR〈/em〉〈/sub〉/〈em〉d〈/em〉〈sub〉〈em〉PR〈/em〉〈/sub〉= 0.9, 〈em〉P〈/em〉〈sub〉〈em〉PR〈/em〉〈/sub〉/〈em〉h〈/em〉〈sub〉〈em〉PR〈/em〉〈/sub〉 = 8 and 〈em〉α〈/em〉〈sub〉〈em〉PR〈/em〉〈/sub〉 = 65° respectively. Thermal-hydraulic performance parameter ( 〈em〉η〈/em〉〈sub〉〈em〉PR〈/em〉〈/sub〉) has also been investigated and the maximum value of 3.44 is obtained for the range of parameters studied.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉In this manuscript, the heat transfer coefficient of de-ionized water based nanofluid’s containing 〈em〉Al〈/em〉〈sub〉〈em〉2〈/em〉〈/sub〉〈em〉O〈/em〉〈sub〉〈em〉3〈/em〉〈/sub〉 nanoparticles under natural convection is experimentally investigated. The thermophysical properties of the prepared nanofluid samples which have great roles in the heat transfer process such as the thermal conductivity and viscosity are experimentally measured and their effects are discussed. Furthermore, the transient temperature of the hot and cold walls and the other sides of the container enclosure are measured and the variation of heat transfer coefficient with the volume fraction of the nanoparticles is shown. According to our results, the heat transfer coefficient of nanofluids enhanced at low volume fractions while with further increase in the volume fraction of nanoparticles it decreased as a result of the increase in viscosity. The results show that in comparison with de-ionized water the heat transfer coefficient of nanofluids containing 0.1% volume fraction nanoparticles had a 16.0% enhancement but for a 3.0% volume fraction it had a 24.0% decrease.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The steady state heat transfer and flow resistance performance in cosine style runners with different amplitudes are studied numerically and experimentally in this paper. The results show that: When the Reynolds numbers (〈em〉Re〈/em〉) range from 1210 to 5080, the core volume goodness factor (〈em〉η〈/em〉〈sub〉o〈/sub〉〈em〉h〈/em〉〈sub〉std〈/sub〉〈em〉α〈/em〉) is used to compare the overall heat transfer performance of the two runners, and the 〈em〉η〈/em〉〈sub〉o〈/sub〉〈em〉h〈/em〉〈sub〉std〈/sub〉〈em〉α〈/em〉 value in the cosine style runner is 7–25% larger than that of the equal cross section runner, so that the cosine style runner has better overall heat transfer enhancement performance. When the amplitudes (2〈em〉A〈/em〉) range from 5 to 9 mm, with the decrease of amplitude, the overall heat transfer performance is getting better. At the same amplitude, the convective heat transfer performance gradually increases as the inlet height (〈em〉F〈/em〉〈sub〉〈em〉h〈/em〉〈/sub〉) decreases; with the increase of 〈em〉Re〈/em〉, the thickness of the thermal and velocity boundary layers are both decreasing. Based on the field synergy principle, the heat transfer enhancement mechanisms with different parameters are evaluated, and we conclude that the smaller the amplitude is, its field synergy is better.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉A simplified and efficient hydrothermal model was adapted and validated with both the experiment and literature data to further investigate the mechanism and influence of different columns on thermal performance of the vapor chamber (VC). The experiment was conducted by testing a T-shaped VC under different heat loads, and the maximum error with the numerical model was about 2 K. Factors including column dimension, column number and column structures were analyzed. Results show that sintered wick ring layer could provide auxiliary liquid circulation paths, reduce the pressure drop in the fluid circulation, and provide additional heat conductive passages. The column dimension shows enhancement on heat transfer capability of VC as the area ratio in the range of 0~0.5, with a maximum decrease by about 6.45% of the thermal resistance compared with the void VC. By comparing with other column structures, copper columns with sintered wick rings were found to the optimal type for enhancing the thermal performance of VC.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉Thermoacoustic engines have been recently regarded and developed as reliable, long-life, and environment-friendly engines by using experiments or mathematical models. Thermoacoustic mathematical models can be divided into two categories of linear and nonlinear. This paper introduces a coupled 1D-2D computational nonlinear model of heat and flow fields inside loaded standing-wave thermoacoustic engines. On the one hand, the computational cost of the present model is much lower than that of full CFD models whose computational domain contains the entire engine. On the other hand, it does not have the limitation of uniform global cross section as the simplified numerical models do. In addition to the coupled nonlinear model, another simulation based on linear thermoacoustic theory (LTA) has been performed. The model has been well validated using previous experimental data and compared with the results of LTA. Subsequently, the temperature and pressure distributions, the mean acoustic power, and heat transfer and volume flow rate distributions have been presented and discussed. This model is extendable to many other systems whose some parts have negligible multidimensional effects and the other parts have considerable ones.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The requirement of fresh drinking water is one of the most severe problems all over the globe. The humidification dehumidification systems have shown promising outcomes while being used for water desalination. The performance of humidification-dehumidification water desalination systems is generally presented in the form of productivity of the humidifier or dehumidifier. Humidification being the predecessor process plays a crucial role in the performance of the Humidification - Dehumidification system. This work presents the theoretical and experimental investigation of bubbler humidifier. The performance of the bubbler humidifier is studied under various operation conditions such as: hole diameter, bubble column height, air mass flow rate, temperature of air and temperature of water inside the humidification chamber. A mechanistic model for bubbler humidifier is presented and validated with the experimental results. The Relative Humidity (RH) of air was achieved in the range of 68% to 97% for various operation conditions while the highest RH of air was recorded 97% for 1 mm of hole diameter, 7 g/s of mass flow rate of air, 60 °C of temperature of water, 48 °C of temperature of air, 7 cm of Height of water Column.〈/p〉

Description: 〈h3〉Abstract〈/h3〉 〈p〉The effect of the addition of different concentrations of Cu〈sup〉2+〈/sup〉, Fe〈sup〉2+〈/sup〉, and Fe〈sup〉3+〈/sup〉 on the micromorphology and crystalline structure of CaCO〈sub〉3〈/sub〉 fouling was studied using the VHX-500FE digital microscope and X-ray diffraction. Results indicate that the fouling morphology becomes stubby and forms a cluster and the fouling color deepens with the increase in the concentration of metal ions. Furthermore, the relative content of aragonite increases and that of calcite decreases. Fe〈sup〉2+〈/sup〉 plays a more important role in the inhibition of calcite than Fe〈sup〉3+〈/sup〉 when scaling occurs in the boiling system under the condition of atmospheric environment. The reason may be that O〈sub〉2〈/sub〉 participates in the inhibition process. Fe〈sup〉2+〈/sup〉 and Fe〈sup〉3+〈/sup〉 promote atomic transition and crystal defects, and this condition changes the absorption wavelength of fouling. Carbon steel and copper samples were immersed in test solution for 28 h as a comparative experiment. This experiment indicates that corrosion may release metal ions, which further affect the fouling morphology and phase component content in the long-term fouling process. In conclusion, fouling weight method for measuring anti-fouling property can only be used to compare materials with similar anti-corrosion property.〈/p〉