Effect of wind speed and direction on convective heat losses from solar parabolic dish modified cavity receiver

The parabolic dish collector is one of the recognized concentrated solar power systems based on point focusing, which provides high-temperature heat, high concentration ratio, and low heat loss. This system consists of a parabolic reflector and a cavity receiver situated in the focus line. In this work, the conical cavity receiver with an aperture diameter of 0.5 m is considered for a 100 m2 parabolic reflector having a focal to diameter ratio of 0.48. Due to the complexity of flow and temperature profile, the estimation of convective heat loss is a difficult task in a cavity receiver. More heat losses are associated with high temperature obtained in the cavity receiver of the parabolic dish collector. Due to diverse wind effect, the convective heat losses ramp up, which significantly influences the thermal performance of the concentrating power system. The present work aims to investigate the heat losses due to convection from the conical cavity receiver. The numerical investigation was performed using ANSYS Fluent 20R1 to calculate the convective heat losses from the conical cavity receiver of varying diameter to height ratio for varying wind speed, receiver orientation in head-on, and back-on wind flow directions. The considered influential parameters are varying from 0.5 to 1.5 for diameter to height ratio (d/h), 0° to 90° for receiver orientation (γ), 0 to 10 m/s for wind speed (V). The heat losses are highest at 60° and 75° receiver orientation for d/h = 0.5 and d/h = 1-1.5, respectively, at high wind speed in head-on condition, whereas in back-on wind condition, 30° receiver orientation has more heat losses among all the d/h values at high wind speed. The heat loss at 90° receiver orientation is low for 4-10 m/s. The trends of heat loss curve at receiver orientations for given wind conditions are similar for velocity more than 2 m/s. The result reveals that the considered influential parameters have a remarkable effect on convective heat losses from the cavity receiver.

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Comparative experimental analysis of the effect of convective heat losses on the performance of parabolic dish water heater

International Journal of Sustainable Engineering ◽

10.1080/19397038.2012.691566 ◽

2013 ◽

Vol 6 (3) ◽

pp. 258-266 ◽

Cited By ~ 5

Author(s):

Atul A. Sagade

Keyword(s):

Convective Heat ◽

Experimental Analysis ◽

Heat Losses ◽

Water Heater ◽

Parabolic Dish

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Numerical study of Flow patterns and performance of a coupled cavity-dish system under different focal lengths

Transactions of the Canadian Society for Mechanical Engineering ◽

10.1139/tcsme-2021-0110 ◽

2021 ◽

Author(s):

Muhammad Uzair ◽

Mubashir Ali Siddiqui ◽

Usman Allauddin

Keyword(s):

Heat Loss ◽

Convective Heat ◽

Numerical Study ◽

Focal Length ◽

Heat Losses ◽

Operating Conditions ◽

Convective Heat Loss ◽

Parabolic Dish ◽

And Performance ◽

Coupled Cavity

The effectiveness of the parabolic dish system (PDS) is greatly affected by the heat losses associated with high temperatures. The complexity of flow and temperature patterns in and around the cavity receiver makes it a challenging task to determine the convective heat loss from the cavity. Various studies have been carried out to determine the convection heat losses from isolated cavities of different shapes. In the presence of dish structure, the free stream wind may affect the stability of structure and the heat losses from the PDS. In this study, effect of focal length on the performance of the coupled cavity-dish system was analyzed using numerical simulations. The loading and the convective heat loss from the cavity were examined with three different cavity positions and different operating conditions in the presence of the dish. The results showed that the shallow dish experienced higher local air velocities near the cavity receiver than in the case of the deep dish. It was concluded that the heat loss is a stronger function of tilt angle rather than focal length, and in essence, the heat losses due to variation of this are negligible.

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Characterizing the convective heat exchange with plastic shading nets under natural arid conditions

International Journal of Energy Technology ◽

10.32438//ijet.11415 ◽

2019 ◽

pp. 11-20

Author(s):

Ahmed M Abdel-Ghanya ◽

Ibrahim M Al-Helal

Keyword(s):

Wind Speed ◽

Thermal Radiation ◽

Convective Heat ◽

Convective Heat Transfer Coefficient ◽

Convective Heat Exchange ◽

Radiative Properties ◽

Wooden Frame ◽

Arid Conditions ◽

Air Temperatures ◽

Radiation Fluxes

Plastic nets are extensively used for shading purposes in arid regions such as in the Arabian Peninsula. Quantifying the convection exchange with shading net and understanding the mechanisms (free, mixed and forced) of convection are essential for analyzing energy exchange with shading nets. Unlike solar and thermal radiation, the convective energy, convective heat transfer coefficient and the nature of convection have never been theoretically estimated or experimentally measured for plastic nets under arid conditions. In this study, the convected heat exchanges with different plastic nets were quantified based on an energy balance applied to the nets under outdoor natural conditions. Therefore, each net was tacked onto a wooden frame, fixed horizontally at 1.5-m height over the floor. The downward and upward solar and thermal radiation fluxes were measured below and above each net on sunny days; also the wind speed over the net, and the net and air temperatures were measured, simultaneously. Nets with different porosities, colors and texture structures were used for the study. The short and long wave’s radiative properties of the nets were pre-determined in previous studies to be used. Re and Gr numbers were determined and used to characterize the convection mechanism over each net. The results showed that forced and mixed convection are the dominant modes existing over the nets during most of the day and night times. The nature of convection over nets depends mainly on the wind speed, net-air temperature difference and texture shape of the net rather than its color and its porosity.

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