Thermal efficiency enhancement of parabolic trough collectors: a review

The parabolic trough collectors are the most widely used linear concentrators for the thermodynamic conversion of solar energy, especially in industrial and domestic fields which require an operating temperature between 80 and 160 °C. The importance of these devices has led the various researchers to study the improvement of their performances in both experimental and numerical approach. A typical parabolic trough collector is mainly composed of the cavity collector, the tube receiver, the heat transfer fluid and the energy storage system. However, enhancing the global performance of these systems requires improving the performance of their main parts. For example, for many research studies in the literature, the use of nanofluids in normal tube receiver enhanced the efficiency up to 10%, while using tube receiver with insertion enhanced the global efficiency up to 10% in many research studies. Consequently, coupling of both nanofluids with insertion is surely enhancing the global efficiency. On the other hand, every improvement is accompanied with such a default to be minimized as much as possible, such as increasing of pressure drop which means increasing in the operating power. In this work, a global review of previous studied the enhancement of these kind of concentrators in terms of heat transfer as well as optical performance is presented; this investigation pays more attention to the works that dealt with the subject through numerical methods. Finally, probable further developments of these devices were outlined as well as the different points missed attention and more investigation.