A solar parabolic trough is one of the types of solar thermal collector used to harness sunlight and convert it into usable heat energy. Solar parabolic trough collector demonstrates reduced efficiency compared to point-focusing types of concentrating solar collectors when it comes to converting solar energy into thermal energy. This disparity arises due to its operation within the medium temperature range of 100–400 °C. The enhancement of efficiency is achievable through the utilization of several passive heat transfer augmentation methods within the receiver tube. Among these approaches, the implementation of conical strip inserts stands out as a particularly promising method in the receiver's design because of their straight-forward construction, simple design and wide range of geometric customization options. The present study examines how the solar parabolic trough receiver performs when passive heat augmentation approaches are used in the receiver. The evaluation involved testing using perforated conical strips with pitch ratios (P*) of 0.5, 1.0, 1.5, 2.0, twist angle (φ) of 6°, 8°, 10°, 12°, and geometry angle (θ) as 60°, 70°, 80°, and 90° for Reynolds number (Re) in the range of 3000–21,000. Air is used as working fluid inside the solar parabolic trough receiver tube. The results demonstrate that modified receiver tube geometry significantly enhances the Nusselt number (Nu) and friction factor (ff) by 4.26 and 7.29 times as compared to the plain receiver tube respectively. This indicates an improvement in heat transfer characteristics of solar parabolic trough collector in term of thermo-hydraulic performance (). The maximum () of 2.94 is received by using twisted perforated conical strips at pitch ratio (P*) = 1, twist angle (φ) = 6° and geometry angle (θ) = 60° at the Re = 21,000. Correlations for Nu and ff of twisted perforated conical strips have also been established, demonstrating accuracy within the range of ±5.0% for Nu and ±4.5% for ff.
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