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02829 Granular phase changing composites for thermal energy storage
16 Fuel science and technology (fundamental science, analysis, instrumentation) standard fuel element using 3D modelling is smaller in fast energy range and higher in thermal energy range than is calculated using the 1D model for the standard cell. In the flux trap, differences of about - 4 % to 13% were found in thermal flux using the newly released libraries as compared to that obtained using 1981 WIMSD library. The major differences in the flux spectra between newly available libraries and the 1981 WIMSD library in thermal energy range are due to the differences in cross-sections of hydrogen bound-in-water, The use of only newly available cross-sections of hydrogen bound-in-water with 1981 W l M S D library resulted in significant improvement in value of keff as well as in the flux spectrum. Moreover the differences among new libraries in the thermal energy range are also due to these crosssections. Difference in fission spectra from different libraries is responsible for differences of flux spectra in the fast energy range. These differences in flux are reduced significantly in the fast energy range by only replacement of fission spectra.
05/02824 Energy and exergy of potato drying process via cyclone type dryer Akpinar, E. K. et al. Energy Conversion and Management, 2005, 46, (15-16), 2530-2552. This papel" is concerned with the energy and exergy analyses of the single layer drying process of potato slices via a cyclone type dryer. Using the first law of thermodynamics, an energy analysis was performed to estimate the ratios of energy utilization. An exergy analysis was accomplished to determine the location, type and magnitude of the exergy losses during the drying process by applying the second law of thermodynamics. It was concluded that the exergy losses took place mostly in the 1st tray where the available energy was less utilized during the single layer drying process of potato slices. It is emphasized that the potato slices are sufficiently dried in the ranges between 60 and 80°C and 20-10% relative humidity at 1 and 1.5 ms 1 of drying air velocity during 10-12 h despite the exergy losses of 01.796 kJ s -~.
05/02825 Enhanced boiling of HFE-7100 dielectric liquid on porous graphite E1-Genk, M. S. and Parker, J. L. Energy Conversion and Management, 2005, 46, (15-16), 2455-2481. Enhanced boiling of HFE-7100 dielectric liquid on porous graphite measuring 10 m m x 10 m m is investigated, and results are compared with those for smooth copper (Cu) of the same dimensions. Although liquid is out-gassed for hours before performing the pool boiling experiments, air entrapped in re-entrant type cavities, ranging in size from tens to hundreds of microns, not only enhanced the nucleate boiling heat transfer and the critical heat flux (CHF), but also, the mixing by the released tiny air bubbles from the porous graphite prior to boiling incipience enhanced the natural convection heat transfer by ~19%. No temperature excursion is associated with the nucleate boiling on porous graphite, which ensues at very low surface superheat of 0.5-0.8 K. Conversely, the temperature overshoot at incipient boiling on Cu is as much as 39.2, 36.6, 34.l and 32.8 K in 0 (saturation), 10, 20 and 30 K subcooled boiling, respectively. Nucleate boiling ensues on Cu at a surface superheat of 11.9, 10.9, 9.5 and 7.5 K in 0 (saturation), 10, 20 and 30 K subcooled boiling, respectively. The saturation nucleate boiling heat flux on porous graphite is 1700% higher than that on Cu at a surface superheat of ~10 K and decreases exponentially with increased superheat to ,.~60% higher near CHF. The CHF values of HFE-7100 on porous graphite of 31.8, 45.1, 55.9 and 66.4 W/era 2 in 0 (saturation), 10, 20 and 30 K subcooled boiling, are 60% higher and the corresponding superheats are 25% lower than those on Cu. In addition, the rate of increase in CHF with increased liquid subcooling is 50% higher than that on Cu.
05•02826 Exergy analysis of flow dehumidification by solid desiccants Lior, N. and A1-Sharqawi, H. S. Energy, 2005, 30, (6), 915-931. Equations for the temporal and spatial exergy values and changes in the humid air stream and the desiccant for flow of humid air over desiccants and in desiccant-lined channels were established, and solved based on a thorough transient conjugate numerical analysis of laminar and turbulent flow, heat, and mass transfer that yielded the full velocity, temperature, and species concentration in the humid air and the solid desiccant. The desiccant was silica gel, the Reynolds number ranged from 333 to 3333, and the turbulence intensity in the turbulent flows was varied from 1% to 10%. Some of the major findings are: (1) in laminar flow, a total of ~20% of the humid air exergy is reduced in its drying, (2) in the desiccant, practically all of the exergy reduction is due to the release of absorption heat, (3) most of the exergy reduction, following the dehumidification rates, takes place in the first 1.5 s and first centimetre, (4) for the same inlet velocity, a desiccant-lined channel is more effective for dehumidification than a flat bed, and proportionally ,,~20% more exergy is expended, (5) turbulent flow
410 Fuel and Energy Abstracts
November 2005
improves dehumidification and proportionally increases exergy expenditure by 27-30%. Conclusions from these results are drawn to increase the exergy efficiency of the process.
05/02827 cracks
Explicit equations for leak rates through narrow
Beck, S. B. M. et al. International Journal of Pressure Vessels and Piping, 2005, 82, (7), 565-570. Explicit equations to describe the leak rate of a single phase fluid through a narrow crack under a low pressure gradient have been developed and are presented. Four distinct flow regimes, which change with crack opening displacement, have been previously identified and are the basis of this model. The fluid flow is governed by the pressure gradient and the tortuosity of the crack, which is particularly important when the opening displacement is small. The equations have been developed by considering the pressure forces created when the fluid flows down an idealized zig-zag channel. The nature of the flow, and hence the governing equations, change as the crack aperture increases. The power of this approach is clearly seen when the flow rates predicted using this model are compared both to the flow rates obtained from computational fluid dynamics analysis and those found by experimentation. The agreement between these sets of data is good, showing that the major effects governing the flow rate have been identified and then accounted for.
05•02828 Formulation of semi-empirical models for predicting the illuminance of light pipes Jenkins, D. et al. Energy Conversion and Management, 2005, 46, (13~I4), 2288-2300. There are now several ways of predicting the illuminance produced for different configurations of light pipe. This study is an overview of two such methods for two slightly different forms of light pipe diffuser. Both models are partly empirical in nature but have been formulated using significantly different techniques. Their outputs are also different in presentation, although both models deal with illuminance predictions (with one of the models offering luminous flux predictions also). The models have also used separately obtained measurements in their formulation and so can be seen as being two independent methods, using similar logic, to achieve similar goals. While the two sets of predictions cannot be compared to each other directly (due to the difference in diffuser in each case), the two models can be presented as an indication as to how modelling procedures of this type can be approached.
05•02829 Granular phase changing composites for thermal energy storage Zhang, D. et al. Solar Energy, 2005, 78, (3), 471480. Granular phase changing composites for thermal energy storage were made of granular porous materials and organic phase changing materials by means of vacuum impregnation method. Experimental studies on the vacuum impregnation method, phase changing behaviour, chemical compatibility between porous materials and phase changing materials, and sealing performance of coating materials arrived at the following conclusions. Firstly, the vacuum impregnation method is effective in loading porous materials with phase changing materials; and its setup is simple, cheap and easy of scale-up. Secondly, organic phase changing materials (including fatty acids and their derivatives, and paraffin) and inorganic porous materials (including expanded clay, expanded fly ash and expanded perlite) are suitable raw materials for the phase changing composites with respect to chemical compatibility, large thermal energy storage density, and feasibility of large scale processing. Thirdly, thickened latex is the best choice of coating materials for the porous material granules, whose sealing performance is about 40-fold higher than that of normal cement paste and about sevenfold higher than that of the best polymer modified cement paste in this paper.
05•02830 Heat transfer by free convection from the inside surface of the vertical and inclined elliptic tube Elshazly, K. et al. Energy Conversion and Management, 2005, 46, (9 10), 1443-1463. Free convection from the inside surface of vertical and inclined elliptic tubes of axis ratio (a:b) 2:1 with a uniformly heated surface (constant heat flux) is investigated experimentally. The effects of orientation angle (c0 and inclination angle (4~) on the heat transfer coefficient were studied. The orientation angle (o0 is varied from 0 ° (when the major axis is horizontal) to 90 ° (when the major axis is vertical) with steps of 15°. The inclination angle (qS) is measured from the horizontal and varied from 15° to 75 ° with steps of 15°. The vertical position is considered as a special case of the inclined case when 0 = 90. The experiments covered a range of Rayleigh number, Ra from 2.6 x 106 to 3.6 x 10~. The local and average Nusseh numbers are estimated for different orientation angles and inclination angles at different Rayleigh numbers. The results obtained showed that the local Nu increased with the increase of axial distance from the lower end of the elliptic tube
05/02824 Energy and exergy of potato drying process via cyclone type dryer Akpinar, E. K. et al. Energy Conversion and Management, 2005, 46, (15-16), 2530-2552. This papel" is concerned with the energy and exergy analyses of the single layer drying process of potato slices via a cyclone type dryer. Using the first law of thermodynamics, an energy analysis was performed to estimate the ratios of energy utilization. An exergy analysis was accomplished to determine the location, type and magnitude of the exergy losses during the drying process by applying the second law of thermodynamics. It was concluded that the exergy losses took place mostly in the 1st tray where the available energy was less utilized during the single layer drying process of potato slices. It is emphasized that the potato slices are sufficiently dried in the ranges between 60 and 80°C and 20-10% relative humidity at 1 and 1.5 ms 1 of drying air velocity during 10-12 h despite the exergy losses of 01.796 kJ s -~.
05/02825 Enhanced boiling of HFE-7100 dielectric liquid on porous graphite E1-Genk, M. S. and Parker, J. L. Energy Conversion and Management, 2005, 46, (15-16), 2455-2481. Enhanced boiling of HFE-7100 dielectric liquid on porous graphite measuring 10 m m x 10 m m is investigated, and results are compared with those for smooth copper (Cu) of the same dimensions. Although liquid is out-gassed for hours before performing the pool boiling experiments, air entrapped in re-entrant type cavities, ranging in size from tens to hundreds of microns, not only enhanced the nucleate boiling heat transfer and the critical heat flux (CHF), but also, the mixing by the released tiny air bubbles from the porous graphite prior to boiling incipience enhanced the natural convection heat transfer by ~19%. No temperature excursion is associated with the nucleate boiling on porous graphite, which ensues at very low surface superheat of 0.5-0.8 K. Conversely, the temperature overshoot at incipient boiling on Cu is as much as 39.2, 36.6, 34.l and 32.8 K in 0 (saturation), 10, 20 and 30 K subcooled boiling, respectively. Nucleate boiling ensues on Cu at a surface superheat of 11.9, 10.9, 9.5 and 7.5 K in 0 (saturation), 10, 20 and 30 K subcooled boiling, respectively. The saturation nucleate boiling heat flux on porous graphite is 1700% higher than that on Cu at a surface superheat of ~10 K and decreases exponentially with increased superheat to ,.~60% higher near CHF. The CHF values of HFE-7100 on porous graphite of 31.8, 45.1, 55.9 and 66.4 W/era 2 in 0 (saturation), 10, 20 and 30 K subcooled boiling, are 60% higher and the corresponding superheats are 25% lower than those on Cu. In addition, the rate of increase in CHF with increased liquid subcooling is 50% higher than that on Cu.
05•02826 Exergy analysis of flow dehumidification by solid desiccants Lior, N. and A1-Sharqawi, H. S. Energy, 2005, 30, (6), 915-931. Equations for the temporal and spatial exergy values and changes in the humid air stream and the desiccant for flow of humid air over desiccants and in desiccant-lined channels were established, and solved based on a thorough transient conjugate numerical analysis of laminar and turbulent flow, heat, and mass transfer that yielded the full velocity, temperature, and species concentration in the humid air and the solid desiccant. The desiccant was silica gel, the Reynolds number ranged from 333 to 3333, and the turbulence intensity in the turbulent flows was varied from 1% to 10%. Some of the major findings are: (1) in laminar flow, a total of ~20% of the humid air exergy is reduced in its drying, (2) in the desiccant, practically all of the exergy reduction is due to the release of absorption heat, (3) most of the exergy reduction, following the dehumidification rates, takes place in the first 1.5 s and first centimetre, (4) for the same inlet velocity, a desiccant-lined channel is more effective for dehumidification than a flat bed, and proportionally ,,~20% more exergy is expended, (5) turbulent flow
410 Fuel and Energy Abstracts
November 2005
improves dehumidification and proportionally increases exergy expenditure by 27-30%. Conclusions from these results are drawn to increase the exergy efficiency of the process.
05/02827 cracks
Explicit equations for leak rates through narrow
Beck, S. B. M. et al. International Journal of Pressure Vessels and Piping, 2005, 82, (7), 565-570. Explicit equations to describe the leak rate of a single phase fluid through a narrow crack under a low pressure gradient have been developed and are presented. Four distinct flow regimes, which change with crack opening displacement, have been previously identified and are the basis of this model. The fluid flow is governed by the pressure gradient and the tortuosity of the crack, which is particularly important when the opening displacement is small. The equations have been developed by considering the pressure forces created when the fluid flows down an idealized zig-zag channel. The nature of the flow, and hence the governing equations, change as the crack aperture increases. The power of this approach is clearly seen when the flow rates predicted using this model are compared both to the flow rates obtained from computational fluid dynamics analysis and those found by experimentation. The agreement between these sets of data is good, showing that the major effects governing the flow rate have been identified and then accounted for.
05•02828 Formulation of semi-empirical models for predicting the illuminance of light pipes Jenkins, D. et al. Energy Conversion and Management, 2005, 46, (13~I4), 2288-2300. There are now several ways of predicting the illuminance produced for different configurations of light pipe. This study is an overview of two such methods for two slightly different forms of light pipe diffuser. Both models are partly empirical in nature but have been formulated using significantly different techniques. Their outputs are also different in presentation, although both models deal with illuminance predictions (with one of the models offering luminous flux predictions also). The models have also used separately obtained measurements in their formulation and so can be seen as being two independent methods, using similar logic, to achieve similar goals. While the two sets of predictions cannot be compared to each other directly (due to the difference in diffuser in each case), the two models can be presented as an indication as to how modelling procedures of this type can be approached.
05•02829 Granular phase changing composites for thermal energy storage Zhang, D. et al. Solar Energy, 2005, 78, (3), 471480. Granular phase changing composites for thermal energy storage were made of granular porous materials and organic phase changing materials by means of vacuum impregnation method. Experimental studies on the vacuum impregnation method, phase changing behaviour, chemical compatibility between porous materials and phase changing materials, and sealing performance of coating materials arrived at the following conclusions. Firstly, the vacuum impregnation method is effective in loading porous materials with phase changing materials; and its setup is simple, cheap and easy of scale-up. Secondly, organic phase changing materials (including fatty acids and their derivatives, and paraffin) and inorganic porous materials (including expanded clay, expanded fly ash and expanded perlite) are suitable raw materials for the phase changing composites with respect to chemical compatibility, large thermal energy storage density, and feasibility of large scale processing. Thirdly, thickened latex is the best choice of coating materials for the porous material granules, whose sealing performance is about 40-fold higher than that of normal cement paste and about sevenfold higher than that of the best polymer modified cement paste in this paper.
05•02830 Heat transfer by free convection from the inside surface of the vertical and inclined elliptic tube Elshazly, K. et al. Energy Conversion and Management, 2005, 46, (9 10), 1443-1463. Free convection from the inside surface of vertical and inclined elliptic tubes of axis ratio (a:b) 2:1 with a uniformly heated surface (constant heat flux) is investigated experimentally. The effects of orientation angle (c0 and inclination angle (4~) on the heat transfer coefficient were studied. The orientation angle (o0 is varied from 0 ° (when the major axis is horizontal) to 90 ° (when the major axis is vertical) with steps of 15°. The inclination angle (qS) is measured from the horizontal and varied from 15° to 75 ° with steps of 15°. The vertical position is considered as a special case of the inclined case when 0 = 90. The experiments covered a range of Rayleigh number, Ra from 2.6 x 106 to 3.6 x 10~. The local and average Nusseh numbers are estimated for different orientation angles and inclination angles at different Rayleigh numbers. The results obtained showed that the local Nu increased with the increase of axial distance from the lower end of the elliptic tube