An adaptive aerodynamic approach to mitigate convective losses from solar cavity receivers

We explore the potential for adaptive air barriers to mitigate convective heat losses from cavity receivers, especially at large tilt angles, using both suction and blowing nozzles. A heated scaled-down cylindrical cavity receiver was fitted with nozzles on four sides of the aperture, at 30 degrees to the aperture plane. The tilted cavity receiver was mounted in a large wind tunnel to allow systematic variation of wind speed and direction. The effectiveness of different nozzle arrangements was calculated from the measured convective heat losses for a series of different mitigation strategies. The results reveal that a suction nozzle mounted at the bottom of the aperture is more effective than a blowing nozzle mounted at the top of aperture for tilt angles of theta = 45 degrees, and under different wind speeds. The effectiveness ranged from 0 at a low suction flow rate to similar to 80% at a high suction flow rate. With the use of three suction nozzles, at the bottom and both sides of aperture, the effectiveness decreased markedly for both tilt angles and all wind speeds. For more challenging conditions of a 45 degrees tilt angle and 45 degrees yaw angle, the most effective approach is the use of suction through nozzles aligned diametrically opposite to the wind, while other nozzle combinations were ineffective in mitigating losses. Finally, the results highlight the need to apply an adaptive aerodynamic strategy that can respond to measured changes in the environmental conditions to achieve the highest thermal efficiency.