Experimental insights into the mechanism of heat losses from a cylindrical solar cavity receiver equipped with an air curtain

Abstract

We report on the effectiveness of an air curtain to mitigate convective heat losses from a heated cylindrical cavity receiver operated at fixed tilt (15°) and yaw angles (0°). The cavity was heated electrically with a controller to maintain a constant inside temperature of 300 °C, varying wind speed, air curtain velocity and discharge angle. It was found that the greatest convective heat losses occur over the lower internal surfaces of the cavity for all cases, spanning both natural and forced convection regimes, while a discharge angle of 30° relative to the face of the cavity is more effective than a parallel curtain, which was found to increase heat losses. It was also found that, for a discharge angle of 0°, increasing the velocity of the air curtain leads to higher convective heat losses. However, for a curtain discharge angle of 30°, increasing the air curtain velocity can reduce heat losses by up to 60%. The measured distribution of air temperature across the aperture plane and convective heat losses through the surface were used to provide insight into the causes of these observations. These results suggest that, for tilted, tower-mounted cavity receivers, the orientation of an air curtain should be directed with a component towards the wind, rather than parallel to the aperture plane.