Impact of Flow Blowing and Suction strategies on the establishment of an aerodynamic barrier for solar cavity receivers

Abstract

This study compares two aerodynamic approaches to minimize convective losses from cavity receivers, namely blowing and suction. A laboratory-scale cavity receiver was operated in a large wind tunnel at varying wind speed and tilt angle. The inner surface of the cavity was heated to a constant temperature of 300 °C by finely controlled electrical heaters. The measured electric energy required to maintain the heaters at the same temperature was used to provide a direct measure of losses from the receiver. An air curtain was engineered to provide curtain of air blown either downward or upwards across the aperture. Suction was alternatively applied through a nozzle positioned below the aperture for a series of suction flowrates. A numerical study was also conducted using a commercial CFD package and validated with available data. It was found that the upward blowing air curtain performs better than the downward curtain for the buoyancy dominant conditions. Moreover, the measured effectiveness of the downward blowing air curtain at tilt angle of the cavity of 45° showed that the application of air curtain with higher velocities increases the convective heat losses over the case with no air curtain. When comparing the performance of air curtain with air suction, it was found that for the low range of relative momentum ratio of curtain to wind flow, suction performs better than blown air. Finally, this study highlights the need for adaptable strategies, based on operating condition, to minimize heat losses and improve the thermal efficiency of cavity receivers.