The elliptic cavity tube absorber is used in the parabolic trough solar collectors to increase the optical efficiency and decrease the thermal loss. But the non-uniform heat flux distribution on the tube receiver will cause non-uniform temperature distribution, thus leading to asymmetric thermal stress and deformation of the tube receiver. In this paper, the geometric as well as thermal parameters of the elliptical cavity tube receiver are analysed through numerical simulation. The temperature distribution of the tube receiver in the single-phase liquid zone, viz. the water zone and the vapour zone, is analysed. It is found from this study that there are two extreme temperature areas in the elliptical cavity tube receiver. When the major semi-axis of the elliptical cavity is 63mm, the maximum temperature of the water zone is the largest, which occurs at (-35mm, 0mm) of the tube receiver. When the major semi-axis of the elliptical cavity is 67mm, the maximum temperature appears at (-9mm, 0mm) in the vapour zone, and the minimum temperature rise appears at (-13.88mm, 0mm).

The solar trough concentrator is used to increase the solar radiation intensity on absorbers for water heating, desalination, or power generation purposes. In this study, optical performances of four solar trough concentrators, viz. the parabolic trough concentrator (PTC), the compound parabolic concentrator (CPC), the surface uniform concentrator (SUC), and the trapezoid trough concentrator (TTC), are simulated using the Monte Carlo Ray Tracing method. Mathematical models for the solar trough concentrators are first established. The solar radiation distributions on their receivers are then simulated. The solar water heating performances using the solar trough concentrators are finally compared. The results show that, as a high-concentration ratio concentrator, the PTC can achieve the highest heat flux, but suffers from the worst uniformity on the absorber, which is only 0.32%. The CPC can generate the highest heat flux among the rest three low-concentration ratio solar trough concentrators. Compared with the PTC and the CPC, the TTC has better uniformity, but its light-receiving ratio is only 70%. The SUC is beneficial for its highest uniformity of 87.38%. Thermal analysis results show that the water temperatures inside the solar trough concentrators are directly proportional to their wall temperature, with the highest temperature rise in the PTC and the smallest temperature rise in the TTC. The solar trough concentrators’ thermal deformations are positively correlated to their wall temperatures. The radial deformation of the SUC is much larger than those of other solar trough concentrators. The smallest equivalent stress is found in the SUC, which is beneficial to the long-term operation of the solar water heating system.