A Review on Solar Line Concentrator to Improve Its Performance by Varying Concentration Ratio

Presently, constant diameter receivers are used for line concentrating systems. This gives constant concentrating ratio. The concentrating ratio (CR) is selected depending upon the outlet temperature of the fluid/receiver. There are many industrial requirements which have a large difference in outlet and inlet temperature of the heating fluid. Using a constant C.R. for such a system reduces its efficiency. The intercept factor (energy intercepted) depends upon diameter of the receiver. Higher the diameter, higher is the energy intercepted by the receiver. While, the heat loss from the receiver, for a given receiver temperature increases with receiver diameter. To optimize the concentrator system, it is necessary to balance energy intercepted and the heat loss. This can be done by using lower concentrator ratio (higher receiver diameter) at the initial portion of the concentrator where the fluid temperature is low. Further portion of the concentrator where fluid temperature is higher, a high concentrator ratio can be used to reduce the loss of heat through reduction of area of the receiver tube (smaller diameter receiver). Thus, the concentrator system will have different diameter receivers offering variable concentration ratio system. This concept is confirmed with the help of G.O. Lof, Fester and Duffie Beck paper. The authors (Lof et al) have evaluated performance of two receivers having diameter of 0.060 m and 0.027m. In this attempt the authors of present paper have superimposed the two graphs presented by G.O.Lof and Duffie Beck. The superimposition shows that the receiver tube with 0.060 m diameters gives higher efficiency up to 170?C receiver temperature and further the receiver tube of 0.027m diameter offers higher temperature performance. Therefore, it is promising to use reduced diameter receivers in steps offering varying CR to enhance the performance of line concentrator.