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M. Prakash - One of the best experts on this subject based on the ideXlab platform.
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Numerical Study of Natural Convection Heat Loss from Cylindrical Solar Cavity Receivers
International Scholarly Research Notices, 2014Co-Authors: M. PrakashAbstract:The numerical study of the natural convection Loss occurring from cylindrical solar cavity receivers is reported in this communication. These cavity receivers can be used with solar dish concentrators for process heat applications at medium temperature levels. Three cylindrical cavity receivers of diameter 0.2, 0.3, and 0.4 m with aspect ratio equal to one and opening ratios of 1 and 0.5 are used for the analysis. Fluent CFD software is used for the analysis of the three-dimensional (3D) receiver models. In this study the receiver tubes within the cylindrical cavity are modeled as a helical coil similar to those existing in actual systems. The flow of the working fluid within the helical coil is also modeled. The simulations are performed for fluid inlet temperatures of 150°C and 250°C and for receiver inclination angles of 0 (sideways-facing cavity), 30, 45, 60, and 90 degree (vertically downward-facing receiver). It is found that the Convective Loss increases with increasing mean fluid temperature and decreases with, increase in receiver inclination. The Convective Loss is found to increase with, opening ratio. These observations are true for all cavity receivers analysed here. A Nusselt number correlation involving Rayleigh numbers, receiver inclinations, and opening ratios is proposed for the Convective Loss.
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Numerical Studies on Natural Convection Heat Losses from Open Cubical Cavities
The Journal of Engineering, 2013Co-Authors: M. PrakashAbstract:The natural convection heat Losses occurring from cubical open cavities are analysed in this paper. Open cubical cavities of sides 0.1 m, 0.2 m, 0.25 m, 0.5 m, and 1 m with constant temperature back wall boundary conditions and opening ratio of 1 are studied. The Fluent CFD software is used to analyse the three-dimensional (3D) cavity models. The studies are carried out for cavities with back wall temperatures between 35°C and 100°C. The effect of cavity inclination on the Convective Loss is analysed for angles of 0° (cavity facing sideways), 30°, 45°, 60°, and 90° (cavity facing vertically downwards). The Rayleigh numbers involved in this study range between 4.5 × 105 and 1.5 × 109. The natural convection Loss is found to increase with an increase in back wall temperature. The natural convection Loss is observed to decrease with an increase in cavity inclination; the highest Convective Loss being at 0° and the lowest at 90° inclination. This is observed for all cavities analysed here. Nusselt number correlations involving the effect of Rayleigh number and the cavity inclination angle have been developed from the current studies. These correlations can be used for engineering applications such as electronic cooling, low- and medium-temperature solar thermal systems, passive architecture, and also refrigeration systems.
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Numerical study of natural convection Loss from open cavities
International Journal of Thermal Sciences, 2012Co-Authors: M. Prakash, Shireesh B. Kedare, J.k. NayakAbstract:Abstract In this paper, the natural convection occurring from open cavities is analysed. Three different cavity shapes are studied namely cubical, spherical and hemispherical geometries having equal heat transfer area. The numerical analysis is performed on three dimensional (3-D) cavity models using the Fluent CFD software. The studies are performed for cavities having isothermal wall temperatures of 100 °C, 200 °C and 300 °C. The effect of opening ratios ( d / D or a / H ) of 1, 0.5 and 0.25 on the Convective Loss is studied for the cubical and hemispherical cavity shapes while the spherical cavity is analysed for opening ratios of 0.5 and 0.25. The effect of inclination of the cavity on the natural convection is studied for five inclinations; 0° (aperture facing sideways), 30°, 45°, 60° and 90° (aperture facing vertically downwards). The natural convection Loss is found to increase with an increase in opening ratio. The increase in natural convection Loss for different inclinations is found to vary between 30% and 80% when the opening ratio is increased from 0.25 to 0.5 for all cavity shapes. A similar increase in natural convection Loss is observed when the opening ratio is increased from 0.5 to 1 for the cubical and hemispherical cavities. The natural convection Loss increases with increase in cavity wall temperature. A decrease in Loss is observed with increase in cavity inclination; the highest Convective Loss being at 0° inclination and the lowest at 90°. For all the cavity shapes analysed with opening ratios of 0.5 and 0.25, it is observed that the hemispherical open cavity has the highest natural convection Loss when compared to cubical and spherical cavities. The hemispherical cavity has higher Convective Loss than the cubical cavity for an opening ratio of 1. A Nusselt number correlation involving the effect of cavity shape, Rayleigh number, inclination angle and the opening ratio has been developed from this study.
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Investigations on heat Losses from a solar cavity receiver
Solar Energy, 2009Co-Authors: M. Prakash, Shireesh B. Kedare, J.k. NayakAbstract:Abstract Thermal as well as optical Losses affect the performance of a solar parabolic dish-cavity receiver system. Convective and radiative heat Losses form the major constituents of the thermal Losses. In this paper, an experimental and numerical study of the steady state Convective Losses occurring from a downward facing cylindrical cavity receiver of length 0.5 m, internal diameter of 0.3 m and a wind skirt diameter of 0.5 m is carried out. The experiments are conducted for fluid inlet temperatures between 50 °C and 75 °C and for receiver inclination angles of 0° (side ways facing cavity), 30°, 45°, 60° and 90° (vertically downward facing receiver). The numerical study is performed for fluid inlet temperatures between 50 °C and 300 °C and receiver inclinations of 0°, 45° and 90° using the Fluent CFD software. The experimental and the numerical Convective Loss estimations agree reasonably well with a maximum deviation of about 14%. It is found that the Convective Loss increases with mean receiver temperature and decreases with increase in receiver inclination. Nusselt number correlations are proposed for two receiver fluid inlet temperature ranges, 50–75 °C and 100–300 °C, based on the experimental and predicted data respectively. Besides no-wind tests, investigations are also carried out to study the effects of external wind at two different velocities in two directions (head-on and side-on). The wind induced Convective Losses are generally higher than the no-wind Convective Loss (varying between 22% and 75% for 1 m/s wind speed and between 30% and 140% for the 3 m/s wind speed) at all receiver inclination angles, the only exception being the Loss due to side-on wind at 0° receiver inclination angle. This is because the wind acts as a barrier at the aperture preventing the hot air to flow out of the receiver. The head-on wind causes higher Convective Loss than the side-on wind. Nusselt number correlations proposed in this work are compared with the existing correlations in the literature. It is found that the correlations available in literature under-predict the Convective Losses at mean receiver temperatures between 100 °C and 300 °C. This is due to the fact that the correlations are developed for certain receiver geometries having the ratio of aperture diameter to receiver diameter equal to or lesser than one.
J.k. Nayak - One of the best experts on this subject based on the ideXlab platform.
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Investigation on Convective Heat Losses from Solar Cavities under Wind Conditions
Energy Procedia, 2014Co-Authors: Ravindra Jilte, Shireesh B. Kedare, J.k. NayakAbstract:Abstract Numerical three dimensional studies of forced Convective heat Loss from cavity receiver of different shapes have been investigated under wind conditions. The cavity shapes used are: cylindrical, conical (frustum of a cone), cone-cylindrical (combination of frustum of cone and cylindrical shape), dome-cylindrical (combination of hemispherical and cylindrical shape) and hetro-conical. These studies are carried out for three isothermal wall temperatures (523, 723 and 923 K) and five inclinations: θ = 0° (cavity aperture facing sideways), 30°, 45°, 60° and 90° (cavity aperture facing down). Besides, effects of mouth blockage (mouth blockage area 36% and 64%) on forced Convective heat Loss are also investigated. Three wind directions viz., head-on, side-on and back-on and wind speed of 1 to 5 m/s are considered. The ratio of Convective Losses occurring under wind and no-wind conditions shows minimum value θ = 0° and it increases with cavity inclination. As expected, the Convective heat Loss under wind conditions is higher than the no-wind case. The Convective heat Losses are higher for head-on wind condition for all shapes in the range (1 to 5 m/s) of wind speed considered. Among the different shapes under study, conical cavity yields the lowest Convective Losses for both categories of cavities (with and without mouth blockage). Under wind condition, Convective Losses reduce marginally with mouth blockage. Increase of mouth blockage from 36% (D ap = 0.4 m) to 64% (D ap = 0.3 m) does not significantly alter the magnitude of Convective Loss. The mouth blockage is found to be more effective for conical cavity where reduction in Convective heat Loss is observed to be 7 and 16% respectively for wind speed of 1 and 5 m/s as compared to fully open conical cavity (D ap = 0.5 m). Generalized Nusselt number correlation is proposed based on the forced Convective heat Loss data from cavities of different shapes and sizes with and without mouth blockage for head-on wind condition. It correlates 83% of data within ±11%, 95% of data within ±15% and 100% of data within ±21%.
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Comparison of Cavity Receivers with and without Mouth-Blockage of Different Shapes and Sizes Used in Paraboloid Dish Applications
Journal of Fundamentals of Renewable Energy and Applications, 2012Co-Authors: Ravindra Jilte, Shireesh B. Kedare, J.k. NayakAbstract:Numerical three-dimensional studies of the nat- ural convection and radiative heat Loss from cavity receiver of different shapes with and without mouth-blockage have been investigated under isothermal wall condition. Convective heat Loss is found to decrease for cavities having mouth blockage created by reducing aperture area (case I) whereas it enhances when mouth blockages are introduced by increasing the cavity dimensions and keeping the same aperture area (case II). Convective Loss is characterized by using the Convective zone area (Acb � ). Conical cavity yields the lowest Convective Loss whereas hetro-conical cavity gives the highest Convective Loss among different shapes investigated. Radiative Loss is independent of cavity inclination and is found to be nearly constant for all cavity shapes and cavity configurations (with or without mouth blockage) so long as the aperture area remains the same; it is proportional to the aperture area. However, investigations on decrease in heat Loss of mouth-blocked cavities needed to be coupled with the estimation of concentrated flux.
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Numerical study of natural convection Loss from open cavities
International Journal of Thermal Sciences, 2012Co-Authors: M. Prakash, Shireesh B. Kedare, J.k. NayakAbstract:Abstract In this paper, the natural convection occurring from open cavities is analysed. Three different cavity shapes are studied namely cubical, spherical and hemispherical geometries having equal heat transfer area. The numerical analysis is performed on three dimensional (3-D) cavity models using the Fluent CFD software. The studies are performed for cavities having isothermal wall temperatures of 100 °C, 200 °C and 300 °C. The effect of opening ratios ( d / D or a / H ) of 1, 0.5 and 0.25 on the Convective Loss is studied for the cubical and hemispherical cavity shapes while the spherical cavity is analysed for opening ratios of 0.5 and 0.25. The effect of inclination of the cavity on the natural convection is studied for five inclinations; 0° (aperture facing sideways), 30°, 45°, 60° and 90° (aperture facing vertically downwards). The natural convection Loss is found to increase with an increase in opening ratio. The increase in natural convection Loss for different inclinations is found to vary between 30% and 80% when the opening ratio is increased from 0.25 to 0.5 for all cavity shapes. A similar increase in natural convection Loss is observed when the opening ratio is increased from 0.5 to 1 for the cubical and hemispherical cavities. The natural convection Loss increases with increase in cavity wall temperature. A decrease in Loss is observed with increase in cavity inclination; the highest Convective Loss being at 0° inclination and the lowest at 90°. For all the cavity shapes analysed with opening ratios of 0.5 and 0.25, it is observed that the hemispherical open cavity has the highest natural convection Loss when compared to cubical and spherical cavities. The hemispherical cavity has higher Convective Loss than the cubical cavity for an opening ratio of 1. A Nusselt number correlation involving the effect of cavity shape, Rayleigh number, inclination angle and the opening ratio has been developed from this study.
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Investigations on heat Losses from a solar cavity receiver
Solar Energy, 2009Co-Authors: M. Prakash, Shireesh B. Kedare, J.k. NayakAbstract:Abstract Thermal as well as optical Losses affect the performance of a solar parabolic dish-cavity receiver system. Convective and radiative heat Losses form the major constituents of the thermal Losses. In this paper, an experimental and numerical study of the steady state Convective Losses occurring from a downward facing cylindrical cavity receiver of length 0.5 m, internal diameter of 0.3 m and a wind skirt diameter of 0.5 m is carried out. The experiments are conducted for fluid inlet temperatures between 50 °C and 75 °C and for receiver inclination angles of 0° (side ways facing cavity), 30°, 45°, 60° and 90° (vertically downward facing receiver). The numerical study is performed for fluid inlet temperatures between 50 °C and 300 °C and receiver inclinations of 0°, 45° and 90° using the Fluent CFD software. The experimental and the numerical Convective Loss estimations agree reasonably well with a maximum deviation of about 14%. It is found that the Convective Loss increases with mean receiver temperature and decreases with increase in receiver inclination. Nusselt number correlations are proposed for two receiver fluid inlet temperature ranges, 50–75 °C and 100–300 °C, based on the experimental and predicted data respectively. Besides no-wind tests, investigations are also carried out to study the effects of external wind at two different velocities in two directions (head-on and side-on). The wind induced Convective Losses are generally higher than the no-wind Convective Loss (varying between 22% and 75% for 1 m/s wind speed and between 30% and 140% for the 3 m/s wind speed) at all receiver inclination angles, the only exception being the Loss due to side-on wind at 0° receiver inclination angle. This is because the wind acts as a barrier at the aperture preventing the hot air to flow out of the receiver. The head-on wind causes higher Convective Loss than the side-on wind. Nusselt number correlations proposed in this work are compared with the existing correlations in the literature. It is found that the correlations available in literature under-predict the Convective Losses at mean receiver temperatures between 100 °C and 300 °C. This is due to the fact that the correlations are developed for certain receiver geometries having the ratio of aperture diameter to receiver diameter equal to or lesser than one.
H Ohtsuka - One of the best experts on this subject based on the ideXlab platform.
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Convective Loss in tokamaks
Nuclear Fusion, 1993Co-Authors: H OhtsukaAbstract:Large scale, DC type plasma convection is investigated in the JFT-2M tokamak. In the plasma edge region, E*B type Convective flows are observed, which are caused by interactions with both a poloidal limiter and an RF wave injection. Observation of changes in the edge potential during lower hybrid (LH) wave injection indicated that the confinement improvement in the LH phase is due to the reduction of an intrinsic E*B type convection. These results are used in the construction of a model that explains both the L and H modes found in the tokamak NBI experiments. The model consists of both a deterioration mechanism based on the obstacle induced convection and a recovery due to the increase of the electric conductivity along the magnetic field. Agreement between the model and typical experimental results is shown
Shireesh B. Kedare - One of the best experts on this subject based on the ideXlab platform.
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Investigation on Convective Heat Losses from Solar Cavities under Wind Conditions
Energy Procedia, 2014Co-Authors: Ravindra Jilte, Shireesh B. Kedare, J.k. NayakAbstract:Abstract Numerical three dimensional studies of forced Convective heat Loss from cavity receiver of different shapes have been investigated under wind conditions. The cavity shapes used are: cylindrical, conical (frustum of a cone), cone-cylindrical (combination of frustum of cone and cylindrical shape), dome-cylindrical (combination of hemispherical and cylindrical shape) and hetro-conical. These studies are carried out for three isothermal wall temperatures (523, 723 and 923 K) and five inclinations: θ = 0° (cavity aperture facing sideways), 30°, 45°, 60° and 90° (cavity aperture facing down). Besides, effects of mouth blockage (mouth blockage area 36% and 64%) on forced Convective heat Loss are also investigated. Three wind directions viz., head-on, side-on and back-on and wind speed of 1 to 5 m/s are considered. The ratio of Convective Losses occurring under wind and no-wind conditions shows minimum value θ = 0° and it increases with cavity inclination. As expected, the Convective heat Loss under wind conditions is higher than the no-wind case. The Convective heat Losses are higher for head-on wind condition for all shapes in the range (1 to 5 m/s) of wind speed considered. Among the different shapes under study, conical cavity yields the lowest Convective Losses for both categories of cavities (with and without mouth blockage). Under wind condition, Convective Losses reduce marginally with mouth blockage. Increase of mouth blockage from 36% (D ap = 0.4 m) to 64% (D ap = 0.3 m) does not significantly alter the magnitude of Convective Loss. The mouth blockage is found to be more effective for conical cavity where reduction in Convective heat Loss is observed to be 7 and 16% respectively for wind speed of 1 and 5 m/s as compared to fully open conical cavity (D ap = 0.5 m). Generalized Nusselt number correlation is proposed based on the forced Convective heat Loss data from cavities of different shapes and sizes with and without mouth blockage for head-on wind condition. It correlates 83% of data within ±11%, 95% of data within ±15% and 100% of data within ±21%.
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Comparison of Cavity Receivers with and without Mouth-Blockage of Different Shapes and Sizes Used in Paraboloid Dish Applications
Journal of Fundamentals of Renewable Energy and Applications, 2012Co-Authors: Ravindra Jilte, Shireesh B. Kedare, J.k. NayakAbstract:Numerical three-dimensional studies of the nat- ural convection and radiative heat Loss from cavity receiver of different shapes with and without mouth-blockage have been investigated under isothermal wall condition. Convective heat Loss is found to decrease for cavities having mouth blockage created by reducing aperture area (case I) whereas it enhances when mouth blockages are introduced by increasing the cavity dimensions and keeping the same aperture area (case II). Convective Loss is characterized by using the Convective zone area (Acb � ). Conical cavity yields the lowest Convective Loss whereas hetro-conical cavity gives the highest Convective Loss among different shapes investigated. Radiative Loss is independent of cavity inclination and is found to be nearly constant for all cavity shapes and cavity configurations (with or without mouth blockage) so long as the aperture area remains the same; it is proportional to the aperture area. However, investigations on decrease in heat Loss of mouth-blocked cavities needed to be coupled with the estimation of concentrated flux.
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Numerical study of natural convection Loss from open cavities
International Journal of Thermal Sciences, 2012Co-Authors: M. Prakash, Shireesh B. Kedare, J.k. NayakAbstract:Abstract In this paper, the natural convection occurring from open cavities is analysed. Three different cavity shapes are studied namely cubical, spherical and hemispherical geometries having equal heat transfer area. The numerical analysis is performed on three dimensional (3-D) cavity models using the Fluent CFD software. The studies are performed for cavities having isothermal wall temperatures of 100 °C, 200 °C and 300 °C. The effect of opening ratios ( d / D or a / H ) of 1, 0.5 and 0.25 on the Convective Loss is studied for the cubical and hemispherical cavity shapes while the spherical cavity is analysed for opening ratios of 0.5 and 0.25. The effect of inclination of the cavity on the natural convection is studied for five inclinations; 0° (aperture facing sideways), 30°, 45°, 60° and 90° (aperture facing vertically downwards). The natural convection Loss is found to increase with an increase in opening ratio. The increase in natural convection Loss for different inclinations is found to vary between 30% and 80% when the opening ratio is increased from 0.25 to 0.5 for all cavity shapes. A similar increase in natural convection Loss is observed when the opening ratio is increased from 0.5 to 1 for the cubical and hemispherical cavities. The natural convection Loss increases with increase in cavity wall temperature. A decrease in Loss is observed with increase in cavity inclination; the highest Convective Loss being at 0° inclination and the lowest at 90°. For all the cavity shapes analysed with opening ratios of 0.5 and 0.25, it is observed that the hemispherical open cavity has the highest natural convection Loss when compared to cubical and spherical cavities. The hemispherical cavity has higher Convective Loss than the cubical cavity for an opening ratio of 1. A Nusselt number correlation involving the effect of cavity shape, Rayleigh number, inclination angle and the opening ratio has been developed from this study.
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Investigations on heat Losses from a solar cavity receiver
Solar Energy, 2009Co-Authors: M. Prakash, Shireesh B. Kedare, J.k. NayakAbstract:Abstract Thermal as well as optical Losses affect the performance of a solar parabolic dish-cavity receiver system. Convective and radiative heat Losses form the major constituents of the thermal Losses. In this paper, an experimental and numerical study of the steady state Convective Losses occurring from a downward facing cylindrical cavity receiver of length 0.5 m, internal diameter of 0.3 m and a wind skirt diameter of 0.5 m is carried out. The experiments are conducted for fluid inlet temperatures between 50 °C and 75 °C and for receiver inclination angles of 0° (side ways facing cavity), 30°, 45°, 60° and 90° (vertically downward facing receiver). The numerical study is performed for fluid inlet temperatures between 50 °C and 300 °C and receiver inclinations of 0°, 45° and 90° using the Fluent CFD software. The experimental and the numerical Convective Loss estimations agree reasonably well with a maximum deviation of about 14%. It is found that the Convective Loss increases with mean receiver temperature and decreases with increase in receiver inclination. Nusselt number correlations are proposed for two receiver fluid inlet temperature ranges, 50–75 °C and 100–300 °C, based on the experimental and predicted data respectively. Besides no-wind tests, investigations are also carried out to study the effects of external wind at two different velocities in two directions (head-on and side-on). The wind induced Convective Losses are generally higher than the no-wind Convective Loss (varying between 22% and 75% for 1 m/s wind speed and between 30% and 140% for the 3 m/s wind speed) at all receiver inclination angles, the only exception being the Loss due to side-on wind at 0° receiver inclination angle. This is because the wind acts as a barrier at the aperture preventing the hot air to flow out of the receiver. The head-on wind causes higher Convective Loss than the side-on wind. Nusselt number correlations proposed in this work are compared with the existing correlations in the literature. It is found that the correlations available in literature under-predict the Convective Losses at mean receiver temperatures between 100 °C and 300 °C. This is due to the fact that the correlations are developed for certain receiver geometries having the ratio of aperture diameter to receiver diameter equal to or lesser than one.
Tim Lindley - One of the best experts on this subject based on the ideXlab platform.
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Reduction of Convective Losses in solar cavity receivers
2016Co-Authors: Graham Hughes, Martin Kaufer, Ehsan Abbasi-shavazi, Jack Zhang, Adam Mcintosh, Tim LindleyAbstract:Two design innovations are reported that can help improve the thermal performance of a solar cavity receiver. These innovations utilise the natural variation of wall temperature inside the cavity and active management of airflow in the vicinity of the receiver. The results of computational fluid dynamics modelling and laboratory-scale experiments suggest that the Convective Loss from a receiver can be reduced substantially by either mechanism. A further benefit is that both radiative and overall thermal Losses from the cavity may be reduced. Further work to assess the performance of such receiver designs under operational conditions is discussed.