The Experts below are selected from a list of 10503 Experts worldwide ranked by ideXlab platform
Lan Xiao - One of the best experts on this subject based on the ideXlab platform.
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numerical study on combined free forced Convection heat Loss of solar cavity receiver under wind environments
International Journal of Thermal Sciences, 2012Co-Authors: Lan XiaoAbstract:Abstract A numerical study has been carried out to investigate the impact of wind on combined free-forced Convection Loss from a fully open solar cavity receiver for high-temperature dish/engine system. Visualization results, i.e., velocity vector field, temperature and velocity contours are provided to reveal the wind effect. The variations of combined free-forced Convection heat Loss with wind speed, wind incidence angle as well as the receiver inclinations have been quantitatively analyzed. Results show that, the combined Convection heat Loss for some wind cases may not decrease monotonically with increasing inclinations as that of no-wind cases. Under some certain wind conditions, the combined Convection heat Loss may possibly be reduced below the natural Convection value, and there exists critical wind speed that minimizes the combined Convection heat Loss. Moreover, the combined Convection heat Loss of receiver at different inclinations becomes more and more indistinguishable as wind speed increases. Finally, a simple correlation has been proposed to estimate the Convection heat Loss variation caused by the environmental wind.
John Pye - One of the best experts on this subject based on the ideXlab platform.
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investigation of heat Loss from a solar cavity receiver
Energy Procedia, 2015Co-Authors: Ehsan Abbasishavazi, Graham Hughes, John PyeAbstract:Abstract This study examines experimentally the heat Loss from a model solar cavity receiver. For this purpose, laboratory-scale cylindrical cavity models with geometric aspect ratios (cavity length to diameter) of 1 and 2, and aperture opening ratios(aperture diameter to cavity diameter) of 0.5 and 1, were built. Each cavitywas subjected to constant boundary heat inputvia heating cables, and was operated at various downward inclinations. A carefully-applied coating of Pyromark-2500 heat resistant paint on the cavity surface, in conjunction with steady-state experimental temperatures, enabled accurate calculation of the radiative Loss from the cavities. The experimental technique allowed precise control of the operating parameters, resulting in determination of the conduction Loss, and subsequently, the Convection heat Loss.Operation at temperatures up to 650 o C allowed for a better understanding of the interaction between radiation and Convection heat Loss mechanisms. Experimental data obtained in this study are shown to be consistent with the concept of stagnation and Convection zone development in cavities, with increasing cavity inclination angle. A qualitative assessment of the impact of these zones on the cavity surface temperatures is presented. Whereas thermocouples located in stagnation region show uniform temperature distribution, the surfaces which are exposed to convective flows exhibit larger temperature variations. The temperature distribution along the cavitywalls and its effect on radiative Loss calculation is also investigated in this work. It is seen that radiative Loss predictions which consider an average cavity temperature in their model can overestimate the Losses due to this mechanism by up to 20%, in comparison to models which use experimental temperatures along the cavity interior. Convection Loss from the cavity is calculated and compared with results from correlations proposed in the literature.It is seen that correlations based on surface areas of the stagnation and Convection zones are better at predicting the experimental results.
Graham Hughes - One of the best experts on this subject based on the ideXlab platform.
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investigation of heat Loss from a solar cavity receiver
Energy Procedia, 2015Co-Authors: Ehsan Abbasishavazi, Graham Hughes, John PyeAbstract:Abstract This study examines experimentally the heat Loss from a model solar cavity receiver. For this purpose, laboratory-scale cylindrical cavity models with geometric aspect ratios (cavity length to diameter) of 1 and 2, and aperture opening ratios(aperture diameter to cavity diameter) of 0.5 and 1, were built. Each cavitywas subjected to constant boundary heat inputvia heating cables, and was operated at various downward inclinations. A carefully-applied coating of Pyromark-2500 heat resistant paint on the cavity surface, in conjunction with steady-state experimental temperatures, enabled accurate calculation of the radiative Loss from the cavities. The experimental technique allowed precise control of the operating parameters, resulting in determination of the conduction Loss, and subsequently, the Convection heat Loss.Operation at temperatures up to 650 o C allowed for a better understanding of the interaction between radiation and Convection heat Loss mechanisms. Experimental data obtained in this study are shown to be consistent with the concept of stagnation and Convection zone development in cavities, with increasing cavity inclination angle. A qualitative assessment of the impact of these zones on the cavity surface temperatures is presented. Whereas thermocouples located in stagnation region show uniform temperature distribution, the surfaces which are exposed to convective flows exhibit larger temperature variations. The temperature distribution along the cavitywalls and its effect on radiative Loss calculation is also investigated in this work. It is seen that radiative Loss predictions which consider an average cavity temperature in their model can overestimate the Losses due to this mechanism by up to 20%, in comparison to models which use experimental temperatures along the cavity interior. Convection Loss from the cavity is calculated and compared with results from correlations proposed in the literature.It is seen that correlations based on surface areas of the stagnation and Convection zones are better at predicting the experimental results.
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Numerical Investigation of Natural Convection Loss From Cavity Receivers in Solar Dish Applications
Journal of Solar Energy Engineering-transactions of The Asme, 2011Co-Authors: Sawat Paitoonsurikarn, Keith Lovegrove, Graham HughesAbstract:In open cavity receivers employed in solar paraboloidal dish applications, natural Convection occurs and contributes a significant fraction of energy Loss. Its characteristics hence need to be clarified so that it can be effectively minimized in order to improve the system efficiency. The investigation of natural Convection Loss from cavity receivers was undertaken numerically and was validated using the published experimental results for four different receiver geometries. A good agreement between experimental and numerical results was obtained. Furthermore, the numerical results of all receivers were qualitatively comparable to the predictions by other available correlations hitherto, although it was found that each correlation has a limited range of applicability arising from the particular cavity geometry and experimental conditions used to derive it. To address this shortcoming, a new correlation based on the numerical results for three of the above four receivers has been proposed. The correlation employs a new concept of an ensemble cavity length scale, to take into account the combined effects of cavity geometry and inclination. Despite a wide variety of cavity geometries and operating conditions, the proposed correlation predicts approximately 50% of the data within ±20% and 90% of the data within ±50%. This is better than any of the other correlations published to date. The new correlation is also simpler to use than the most accurate of those previously published.
Keith Lovegrove - One of the best experts on this subject based on the ideXlab platform.
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Numerical Investigation of Natural Convection Loss From Cavity Receivers in Solar Dish Applications
Journal of Solar Energy Engineering-transactions of The Asme, 2011Co-Authors: Sawat Paitoonsurikarn, Keith Lovegrove, Graham HughesAbstract:In open cavity receivers employed in solar paraboloidal dish applications, natural Convection occurs and contributes a significant fraction of energy Loss. Its characteristics hence need to be clarified so that it can be effectively minimized in order to improve the system efficiency. The investigation of natural Convection Loss from cavity receivers was undertaken numerically and was validated using the published experimental results for four different receiver geometries. A good agreement between experimental and numerical results was obtained. Furthermore, the numerical results of all receivers were qualitatively comparable to the predictions by other available correlations hitherto, although it was found that each correlation has a limited range of applicability arising from the particular cavity geometry and experimental conditions used to derive it. To address this shortcoming, a new correlation based on the numerical results for three of the above four receivers has been proposed. The correlation employs a new concept of an ensemble cavity length scale, to take into account the combined effects of cavity geometry and inclination. Despite a wide variety of cavity geometries and operating conditions, the proposed correlation predicts approximately 50% of the data within ±20% and 90% of the data within ±50%. This is better than any of the other correlations published to date. The new correlation is also simpler to use than the most accurate of those previously published.
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A New Correlation for Predicting the Free Convection Loss from Solar Dish Concentrating Receivers
2006Co-Authors: Sawat Paitoonsurikarn, Keith LovegroveAbstract:The study of free Convection Loss from an open-cavity receiver used in solar dish application has been undertaken by many researchers. Various correlations for free Convection prediction have been proposed, e.g., by Stine & McDonald (1989), and Leibfried & Ortjohann (1995). Nonetheless, it was found that each correlation has a limited range of applicability, which is inherently based on the particular cavity geometry and experimental condition used in each of those work (Paitoonsurikarn & Lovegrove, 2002).
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Estimation of Convection Loss from Paraboloidal Dish Cavity Receivers
2004Co-Authors: Sawat Paitoonsurikarn, Tua Taumofeloau, Keith LovegroveAbstract:In general, cavity receivers employed in the sun-tracking paraboloidal dish concentrator are subjected to various modes of heat Loss. Among these, Convection is the most complicated phenomenon and yet also a major contributor of the total energy Loss. Hence, its characteristics need to be clarified such that it can be effectively minimized for the improvement of system efficiency. This study undertakes the numerical investigation of natural and combined Convection Loss from cavity receivers employed in solar paraboloidal dishes. Three different receiver geometries have been considered. One of these is the experimental model receiver for validating the numerical results. The other two are essentially the ones currently used in ANU 20 m 2 and 400 m 2 dishes. For natural Convection study, two simple models that can estimate heat Loss with reasonable accuracy are proposed. On the combined Convection Loss study, several cases of varying wind speeds and directions are considered and some typical results are presented in graphical form. They clearly show a general relationship of wind characteristics and heat Loss. The range of wind speed in which force Convection dominates can be clarified.
Ranjeet Agarwala - One of the best experts on this subject based on the ideXlab platform.
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Effects of circumsolar radiation on the optimal performance of a Stirling heat engine coupled with a parabolic dish solar collector
Applied Thermal Engineering, 2019Co-Authors: Praveen D. Malali, Ranjeet AgarwalaAbstract:Abstract This paper investigates the effects of circumsolar radiation on the optimal performance of a coupled parabolic dish and a Stirling heat engine, referred to as the Dish/Stirling system. The presence of circumsolar radiation results in the widening of the solar cone in which the solar beam (direct) radiation is received by the parabolic dish. This beam radiation cone enlargement effectively degrades the collector performance, especially for the very high concentration ratio collectors such as the parabolic dish. The enlarged solar beam radiation cone angular width results in enhanced solar radiation flux spillage at the receiver due to the inability of the parabolic dish reflector surface to focus a significant fraction of incoming beam radiation. This reduces both the energy input as well as the maximum temperature of the Stirling heat engine cycle and causes a reduction in the overall thermal efficiency of the Dish/Stirling system. The present study analyzes this effect by considering various levels of circumsolar radiation, characterized by a parameter known as the circumsolar ratio. The data for the intercept factor of the parabolic dish collector is based on the circumsolar radiation measurements obtained by researchers at the Lawrence Berkeley Laboratory, and the results of analysis reported by researchers at the Solar Energy Research Institute (currently the National Renewable Energy Laboratory). For the present analysis, this intercept factor data is curve-fitted for different circumsolar ratio, mirror optical errors and the concentration ratio using a MATLAB® program. The overall thermal efficiency of the Dish/Stirling system is maximized with respect to the concentration ratio of the parabolic dish and the maximum temperature ratio of the Stirling heat engine using the first law of thermodynamics. This optimization process is performed using a MATLAB® program. Optimal values of concentration ratio for the parabolic dish collector, and the maximum temperature ratio of the Stirling cycle are obtained corresponding to the maximum overall thermal efficiency of the Dish/Stirling system. The study shows that, for a parabolic collector with low mirror optical error and rim angle of 60°, an increase in circumsolar ratio from 0.02 to 0.2 reduces the maximum overall thermal efficiency, optimal concentration ratio and optimal temperature ratio by about 13%, 18% and 7% respectively. In the case of parabolic collectors with high mirror optical error and rim angle of 60°, an increase in circumsolar ratio from 0.02 to 0.2 reduces the maximum overall thermal efficiency, optimal concentration ratio and optimal temperature ratio by about 10%, 11% and 5% respectively. Similar trends are observed for parabolic dish collectors with rim angle of 40°. Results from this study are presented in the form of performance charts that show the effects of varying circumsolar ratios, mirror optical errors, rim angles, non-dimensional radiation flux and non-dimensional Convection Loss parameters on the maximum overall thermal efficiency of the Dish/Stirling system.