Heat transfer enhancement, thermodynamic and numerical optimisation of complex solar energy systems-parabolic trough collector systems

In this paper, heat transfer enhancement, thermodynamic, and numerical optimization using both the entropy generation minimization method and multi-objective optimization for parabolic trough solar collector systems is presented. Due to the non-uniform heat flux distribution across the receiver tube's circumference, accurate determination of the heat flux profile is crucial for the prediction of the thermal and thermodynamic performance. Firstly, the Monte Carlo ray tracing techniques are used to obtain the realistic optical performance of the system. Then, the thermal and thermodynamic performances are investigated by coupling the obtained realistic heat flux profiles with a finite volume based computational fluid dynamics tool. The parabolic trough systems considered have concentration ratios from 57 - 143, rim angles between 40^o and 120^o, inlet temperatures from 400 - 650 K and flow rates from 1.22 m³ h^-1 to 134.73 m³ h^-1. Following the thermal and thermodynamic performance studies, the potential for improved performance using centrally placed perforated plate inserts and twisted tape inserts was investigated. For some range of Reynolds numbers, the studies showed significant improvements in both the thermal and thermodynamic performance with heat transfer enhancement. Both the thermal and thermodynamic performance were improved appreciably. The heat transfer performance increased by about 134% and 169% where as the entropy generation rate reduced by 53% and 68% for the respective heat transfer enhancement techniques. Moreover, the use of the entropy generation minimization method and multi-objective optimisation gave the optimal parameters for each of the enhancement techniques considered.