Numerical investigation of the hydrothermal performance of convergent solar absorber with various corrugations fitted in a parabolic trough collector

Parabolic trough collectors (PTCs) are becoming widely used in various industries for thermal and power generation purposes. Despite the proposal of multiple techniques to significantly improve the performance of PTCs, amelioration of the heat transfer rate inside the absorber tube has proven to be highly impactful. Yet, it is accompanied by an immense pressure drop so the search for an optimized internal geometry is necessary. In this study, for the first time, four different corrugation shapes (circular, rectangular, triangular, and trapezoidal) have been tested with convergent absorber tube collectors for various diameter ratios (DR = 1, 1.25, 1.5, 1.75, and 2) at a wide range of Reynolds number from 20k to 100k. These geometric alterations are investigated numerically using solar tracking and finite volume simulation tools (TracePro and Ansys Fluent, respectively). Its hydrothermal performance, including the Nusselt number ( N u ) and friction coefficient ( f ) is then compared against the standard absorber tube collector. This study identifies an optimal absorber tube configuration that resolves the classic trade-off between heat transfer enhancement and pressure drop in PTCs. Among all designs tested, the convergent tube with circular corrugations at a diameter ratio of 1.5 (CirCorrugs-DR = 1.5) provided the best overall hydrothermal performance. It achieved a superior and stable thermal enhancement factor ( T E F ) of 1.30–1.45 across the operational range. This was accomplished by boosting heat transfer by 50–100 %, while limiting the pressure drop penalty to only 2–3.5 times that of a standard tube. This optimal design outperforms all previously reported geometric modifications by at least 10 %, establishing a new benchmark for efficient solar thermal collector design.