Improvement in the photothermal conversion performance of a solar cavity receiver with concave spherical windows

Photothermal conversion parameters are key indicators for measuring the operational performance of solar cavity receivers. By utilizing the redistributive ability of a functional surface in an optical concave lens to transmit solar radiation, previous studies have shown that installing a concave spherical quartz window at the front end of a solar cavity receiver can homogenize the flux distribution on the receiver wall. On this basis, research has been conducted on the impact of solar cavity receivers with concave spherical windows on their photothermal conversion performance. Based on the finite volume method, a coupling model for photothermal conversion in the receiver is established to calculate the heat transfer efficiency and temperature distribution of the receiver for different windows. The results indicate that, compared with a receiver with a flat quartz window, a receiver with a concave spherical quartz window can significantly reduce the peak temperature and peak temperature gradient of the spiral tube in the receiver, effectively improving the temperature distribution of the tube. When DNI = 1000 W/m2, the flow velocity at the inlet is 2.5 m/s, and the temperature at the inlet is 650 K. The receiver with a concave spherical quartz window has a reduced temperature peak from 868.09 K to 834.23 K and a temperature gradient from 2.46 K/mm to 1.27 K/mm relative to the receiver with a flat quartz window. This study provides ideas for the design of cavity receivers and improves their photothermal conversion performance.