Experimental study on heat transfer enhancement of parabolic trough solar collector using a rectangular channel receiver

Abstract

BackgroundThe solar receiver design plays a vital role in exchanging solar radiation into heat transfer fluids in concentrated solar collectors. The solar receiver's heat absorption rate in a parabolic trough collector depends on the heat transfer surface area, the fluid flow residence time, and turbulence in the fluid flow. The rectangular channel solar receiver with dual-functional fins is selected as an alternative receiver to increase the heat transfer area and fluid flow path. MethodsThe staggered arrangement of thin fins at the rectangular channel receiver's bottom deviates the fluid in zig-zag directions, confirming more physical contact with the absorber for a more extended period and enhanced flow turbulence. The outdoor tests are conducted on modified and conventional solar receivers. The experimental results are compared with the conventional tubular solar receiver at flow rates of 0.05, 0.13, and 0.2 kg/s. Significant findingsThe proposed rectangular receiver results in higher water outlet temperature with lesser receiver surface temperature and heat loss. A rectangular surface absorbs concentrated solar radiation more effectively than a circular surface. An average convective heat transfer coefficient and Nusselt number are higher by 45.4 and 136% than the circular receiver at a fluid flow rate of 0.2 kg/s. The average thermal and exergy efficiency is higher by 48.1 and 73.7% than the circular receiver at 0.2 kg/s. Maximum thermal and exergy efficiency is 78.5 and 4.4% at higher flow rates.