Thermal performance improvement for parabolic trough solar collectors integrated with twisted fin and nanofluid: Modeling and validation

The low thermal efficiency of parabolic trough solar collectors (PTSCs) is a major drawback that has hindered their development as a viable renewable energy resource. Among the available methods to enhance the thermal performance of PTSCs, installing internal fins within the collector tube is one of the most reliable, economical, and straightforward passive techniques. However, while internal fins can significantly improve thermal performance in turbulent flows, they also lead to a substantial increase in pumping work. Here, we demonstrate that with an optimal design of helical fins, the thermal efficiency of PTSCs can be improved without causing significant pressure losses through the receiver tube. The results proved that higher thermal efficiency and lower pressure losses were achieved when annular fins are replaced by an axial helical insert. Installation of a helical fin with 4 turns and a height of 4 mm led to a 4.5 % increase in thermal efficiency (η) while raising the friction factor (f) by 30 %. Optimal performance was observed with helical fins having 10 turns. For instance, at Re = 105, switching from 16 to 4 turns of 8 mm helical fins resulted in η and Nu enhancements, and f reduction of 1.6 %, 33 % and 64 %, respectively. While these changes were 2.0 %, 55 % and 54 % when n reduced from 16 to 10.