Numerical investigation on radiative heat loss of a direct absorption solar collector using the discrete ordinates method

Direct-absorption solar collectors have the potential to be highly efficient and exhibit a uniform temperature distribution. However, the standard numerical model simplifies radiation and heat loss, which require further consideration at high temperatures. Thus, a novel self-programming model for photothermal conversion in a direct-absorption solar collector was developed based on the discrete ordinates method. This novel model contains further details on radiative transfer and specular reflection boundary conditions. This study compared the results of the two models at high temperatures. With an inlet temperature of 500℃ and a solar concentration ratio of 100, the standard model overestimated outlet temperature and conversion efficiency by 27.6℃ and 18.9%, respectively. This study investigated radiative heat loss at different temperatures, solar concentration ratios, and incident angles. The results showed that radiative heat loss will exceed 5% with a fluid temperature exceeding 600℃. Furthermore, efficiency decreases significantly at incident angles exceeding 30°. The proposed model expands the range of applications of numerical models of solar collectors to high temperatures. These results provide a reference for improving the conversion efficiency of solar collectors at high temperatures, which is regarded as an urgent problem.