Thermo-hydraulic assessment of flat-tube parabolic trough receivers under realistic non-uniform solar flux

This study analyzes the thermo-hydraulic performance of parabolic trough collector (PTC) systems using novel flat tube absorbers. Two absorber configurations—horizontal and vertical flat tubes—are evaluated against conventional circular tubes across three base diameters (15 mm, 30 mm, and 70 mm). Realistic, non-uniform solar heat-flux distributions are obtained using SolTrace-based Monte Carlo Ray Tracing (MCRT), and the resulting flux is applied in a 3D finite element method (FEM)-based thermo-fluid model (COMSOL Multiphysics). The analysis covers Reynolds numbers from 20,000 to 80,000 and heat transfer fluid (HTF) inlet temperatures ranging from 150 °C to 350 °C. Performance metrics include Nusselt number, friction factor, and thermal efficiency. Results show that horizontal flat tubes deliver the highest thermal efficiency in all cases, with improvements of 9% at 15 mm, 0.5% at 30 mm, and 0.3% at 70 mm compared to circular tubes. Vertical flat tubes outperform circular tubes at 15 mm (∼5%) but show marginal or lower performance at larger diameters. These efficiency gains are associated with increased pumping power, particularly at smaller diameters. Overall, flat tube geometries, especially the horizontal type demonstrate strong potential for enhancing PTC performance, provided the associated pressure drop is carefully managed.