Heat transfer and entropy generation in a parabolic trough receiver with wall-detached twisted tape inserts

Abstract

In this paper, heat transfer enhancement in a parabolic trough receiver using wall-detached twisted tape inserts was numerically investigated. The resulting heat transfer, fluid friction and thermodynamic performance were determined and presented. The flow was considered fully developed turbulent, with Reynolds numbers in range 10 260 ≤ Rep ≤ 1 353 000 depending on the fluid temperature. The twisted tape's twist ratio and width ratio vary in the range 0.50–2.00 and 0.53–0.91, respectively. The numerical investigations are based on a finite volume method, with the realisable k–ɛ model for turbulence closure. The study shows considerable increase in heat transfer performance of about 169%, reduction in absorber tube's circumferential temperature difference up to 68% and increase in thermal efficiency up to 10% over a receiver with a plain absorber tube. An entropy generation analysis shows the existence of a Reynolds number for which there is minimum entropy generation for each twist ratio and width ratio. The optimal Reynolds number increases with increasing twist ratio and reducing width ratios. The maximum reduction in the entropy generation rate was about 58%. Correlations for heat transfer and fluid friction performance for the range of parameters considered were also derived and presented.