Performance analysis of receiver of parabolic trough solar collector: Effect of selective coating, vacuum and semitransparent glass cover

Abstract

Present work encompasses developing a new methodology to incorporate the heat transfer characteristics of the evacuated space (vacuum) in the annulus region between the absorber tube and glass cover and the effect of selective coatings on the steel absorber tube for a 3-dimensional computational fluid dynamics model of a parabolic trough solar collector (PTSC) receiver. In the present work, glass cover has been modeled semitransparent to the incoming solar flux, which has been applied on the glass cover. Wavelength-dependent absorption properties of glass cover material also has been modeled. In the current work, the direct normal irradiation and the mass flow rate of heat transfer fluid (HTF) has been varied to check their individual effect on the performance of PTSC absorber tube. Circumferential temperature distribution of absorber tube and glass cover has been found out; heat transfer to HTF and pressure drop of HTF in the absorber tube have also been calculated. A comparative study has been undertaken to highlight the relative contribution of the vacuum and selective coating on the receiver performance. The value of circumferential temperature difference at mid-length of absorber tube was found to be 14.78 K for 750 W/m2, which increases to 19.70 K for direct normal irradiation of 1000 W/m2. When vacuum is replaced by air in the annulus region, PTSC absorber performance decreases by 4.82%. Similarly, because of use of selective coating, the thermal efficiency of the receiver increased by 34.59%.