Numerical modelling of convective heat losses of a real scale cavity receiver used in solar thermal power towers

Kurzfassung

Using cavity receivers in the solar thermal towers as a solution to reduce the radiation losses from receiver was always a point of interest in the CSP (concentrating solar power) researches. Although the radiative losses could be reduced significantly by cavity receivers, the convective heat losses remain as a crucial factor on the efficiency of the receiver and overall system. However, the influence of wind on these losses has not been studied sufficiently for large scale commercial cavity receivers. In the present study, the influence of wind with Reynolds numbers in the range of Re = [2.82×10^6, 1.07×10^7] on a cavity receiver with inclination of phi = 60° and a Grashof Number of Gr = 1.85×10^13 has been investigated and analyzed numerically. This study has tried to investigate convective heat losses from a real scale cavity receiver with the nominal thermal power of 75 MWth. Results of this study shows that the convective heat loses in this scale and inclination level is highly related to forced convection induced by wind and can significantly affects the efficiency of the receiver. The results show an almost linear relation between the convective heat losses and wind velocity. Shrinkage of the stagnation zone has been observed with all wind velocities and stagnation zone become smaller with higher wind speeds. As the convective heat losses in the stagnation zone are very small, the shrinkage of the stable stagnation zone and consequently a bigger convective zone with lower temperature and natural and forced convective flows in it, has been recognized as the main reason for the increase of the convective heat losses from the cavity.