Thermal performance improvement using unilateral spiral ribbed absorber tube for parabolic trough solar collector

Enhancing the heat transfer in the absorber tube improves effectively both the thermal efficiency and the structural safety of the parabolic trough receiver (PTR). This study proposed a novel unilateral spiral ribbed PTR (USR-PTR) for enhancing the heat transfer inside the absorber. The flow and heat transfer performance of the proposed USR-PTR was studied numerically using CFD tool coupled with Monte Carlo Ray Tracing (MCRT). A detailed comparison between the USR-PTR and the conventional straight and smooth PTR (CSS-PTR) was conducted in terms of both thermal and hydraulic performance, revealing that fluid disturbance, rotational flow and local longitudinal vortexes induced by the discontinuous spiral ribs are the three main causes of heat transfer enhancement in the USR-PTR. In most cases of the discussed flow rates, the overall performance of the USR-PTR is better than that of the CSS-PTR. The circumferential temperature difference of the USR-PTR can be reduced by up to 25% compared to the CSS-PTR. The structural parameters of the spiral rib influence greatly the performance of the USR-PTR. It is revealed that the improvement of the overall performance of the USR-PTR by changing individually the rib structural parameters, including pitch interval, rib height, corner radius and spiral angle, can be up to 12.5%, 9.8%, 10.8% and 30.1% respectively.