Radiation Heat Exchange in a Solar Cavity-type Receiver at Various Times

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Abstract
Steady-state solar and infrared radiation heat exchange in the cavity receiver of a solar tower is presented in the form of a mathematical model. The inside cavity walls consist partly of tubes containing air as a heat carrier. The distribution of tube wall temperatures, air temperature, and the heat flux density along the tubes are calculated at different times of day for different seasons. The efficiency of solar and infrared radiation exchange in the cavity is determined, as well as cosine losses of the heliostat Held. The receiver layout is based on maximum gain on 21 June, 12 O'clock noon. With a fixed value of 800 °C for the air outlet temperature and a constant air inlet temperature of 352 °C, the air mass flow-rate must be controlled within a wide range in order to compensate for the varying irradiation conditions. On 21 June, e.g., during an operation time between 9 a.m. and 3 p.m. the range is between 70 and 100% while operation between 6 a.m. and 6 p.m. requires a range of 15 to 100%. The reduced irradiance in December aggravates the problems of partial load characteristics.