A numerical investigation of a longitudinally finned parabolic trough solar receiver tube was carried out. The main aim of this work was to analyze the impact of the fin height and location within the receiver tube. Nusselt number, friction factor, maximum temperature, and performance evaluation criterion were investigated numerically. Analyses were carried out using different heights and locations of the inner longitudinal fins with Syltherm800 as the heat transfer fluid and for Reynolds numbers ranging from 20,000 to 60,000. According to the results, fins located on the lower side significantly enhance heat transfer, while fins on the upper side drive higher velocity toward the lower section. Consequently, shorter fins in the lower section and longer fins in the upper section are recommended to optimize efficiency. For a symmetric distribution of fins, it was found that the fins should be positioned in the areas with the highest heat flux. Compared to a smooth receiver tube, the maximum temperature for the optimal cases with four and eight fins decreased by 8–25 K and 11–36 K, respectively.
