Coupled thermal-fluid and structural analysis of a parabolic trough collector with gas as a heat transfer fluid

In a parabolic trough collector (PTC), the absorber tube is subjected to substantial temperature non-uniformity due to the concentrated solar flux, resulting in thermal stresses, strains, and high failure rates, particularly in solar-based concentrated plants operating with liquid heat transfer fluids. Most failures occur from glass envelope rupture under intense thermal stress. To address this, the present study numerically analyzes the thermo-fluid and structural behavior of a PTC's absorber tube employing a gaseous heat transfer fluid. Among the gases analyzed, carbon dioxide, air, and methane, methane exhibited the highest performance improvement. High circumferential temperature gradients cause structural deflections, especially beyond 6 m of tube length, with a maximum deflection of 6.36 mm at around 7.48 m. The substitution of stainless steel with copper markedly improves structural performance, resulting in reductions of up to 87.43% in deflection, 88.39% in stress, and 79.70% in strain. Lastly, a comparison is performed to evaluate the performance of absorber tubes with and without longitudinal rectangular fins.