A review on passive methods for thermal performance enhancement in parabolic trough solar collectors

Summary Among the diverse renewable energy sources available, solar energy harnessing has become very common in most countries. Various collectors were developed, built and checked to work in various temperature ranges. The parabolic trough solar collector is found to be the most common among the other collectors in applications such as the distribution of process heat and the production of steam. The heat collector part known as receiver tube is one of the key practical devices of parabolic trough solar collector. Numerous research studies have centered on receiver tube to raise its thermal potential. The usage of passive techniques such as provision of inserts in the receiver tube and geometrical changes of receiver tube are efficient strategies for increasing thermal performance. Detailed review of the numerical and experimental studies conducted on heat transfer enhancement strategies that rely on the use of inserts with the use of different working fluids in a parabolic trough solar collector's receiver tube is described in this article. Additionally heat transfer enhancement due to geometrical modification of receiver tube is also presented. Further, on the basis of literature survey, a comparison among various strategies is outlined. These studies show that future work in this area, that is, usage of passive techniques in parabolic trough solar collector will offer further growth. The passive techniques such as provision of inserts and geometrical changes of receiver tube are efficient strategies for increasing thermal performance. The thermal and fluid flow properties of various insert geometries have been studied for different parameters such as insert height, insert thickness, insert orientation, insert shape, number of inserts on receiver tube, porosity, twist ratio, pitch value, length etc. The passive method of heat transfer enhancement helps in uniform distribution of heat flux on absorber tube surface.