A design method and numerical study for a new type parabolic trough solar collector with uniform solar flux distribution

The non-uniform concentrated solar flux distribution on the outer surface of the absorber tube can lead to large circumferential temperature difference and high local temperature of the absorber tube wall, which is one of the primary causes of parabolic trough solar receiver (PTR) failures. In this paper, a secondary reflector used as a homogenizing reflector (HR) in a conventional parabolic trough solar collector (PTSC) was recommended to homogenize the solar flux distribution and thus increase the reliability of the PTR. The design method of this new type PTSC with a HR was also proposed. Meanwhile, the concentrated solar flux distribution was calculated by adopting the Monte Carlo ray-trace (MCRT) method. Then, the coupled heat transfer process within the PTR was simulated by treating the solar flux calculated by the MCRT method as the heat flux boundary condition for the finite volume method model. The solar flux distribution on the outer surface of the absorber tube, the temperature field of the absorber tube wall, and the collector efficiency were analyzed in detail. It was revealed that the absorber tube could almost be heated uniformly in the PTSC with a HR. As a result, the circumferential temperature difference and the maximum temperature could be reduced significantly, while the efficiency tended to decrease slightly due to the inevitably increased optical loss. Under the conditions studied in this paper, although the collector efficiency decreased by about 4%, the circumferential temperature difference was reduced from about 25 to 3 K and the maximum temperature was reduced from 667 to 661 K.