ALBERT

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〉