Optimum number of internal fins in parabolic trough collectors

Parabolic trough collectors are among the most mature solar concentrating technologies which are applied in numerous applications. The enhancement of their performance is a crucial issue in order to be established as a feasible technology. The use of internal fins is one of the most interesting techniques for enhancing the heat transfer phenomena in the flow as well as for increasing the collector's performance. However, their utilization leads to higher pressure losses. The objective of this paper is to investigate the optimum number and location of the internal fins in the absorber of a parabolic trough collector. The examined fins have 10 mm length and 2 mm thickness, while their shape is rectangular. Various numbers of fins are investigated in various locations inside the absorber and in every case, the collector's performance is investigated by taking into account the increase of the Nusselt number and of the friction factor. According to the final results, the internal fins have to be placed in the lower part of the absorber where the higher amount of the solar heat flux is concentrated. A multi-objective procedure proved that the absorber with three fins in the lower part is the optimum case with 0.51% thermal efficiency enhancement.