Optimizing the configuration of external fins of solar receiver tubes for the solar parabolic trough collector

• Externally finned tubes enhance thermal efficiency by up to 20% over smooth tubes. • Finned tubes maintain efficiency across varying flow rates and geometric configurations. • Small fin pitch and diameter boost efficiency and heat absorption in solar systems. • Numerical and experimental methods validate design improvements for SPTC systems. • Enhanced finned tube designs reduce costs while improving thermal and exergy efficiency. This paper aims to present a numerical study that aims to enhance the thermal efficiency of externally finned solar absorber tubes for use in the solar parabolic trough collector (SPTC). Compared to the internal finned tube, the external finned radiation absorber tube boasts an improved geometry and a simple and straightforward manufacturing process. This numerical study investigated seven absorber tube models with different finned tube characteristics. The absorber tubes, made of copper with an inner diameter of 8 mm, pitch distances of 3.63, 3.18, and 2.28 mm, and fin diameters of 22 and 32 mm, were used for comparison. A parabolic trough system with the solar absorber tube positioned at the focal point was designed and constructed to validate the model and determine thermal efficiency. These experiments used water as a heat transfer fluid, with flow rates ranging from 0.5 to 1.0 L per minute (LPM). The results show that externally finned absorber tubes are much more thermal efficiency than smooth tubes at all flow rates. Efficiency goes up as the number of fins increases. Additionally, the research found that the size of the fin diameter affects heat transfer, with finned tubes having smaller fin diameters providing higher thermal efficiency than those with larger fin diameters. The finned absorber tube, with a fin pitch of 2.28 mm and a fin diameter of 22 mm, achieved a maximum temperature rise of 9.60 °C and a thermal efficiency of 58.66 % at a flow rate of 1.0 LPM. This represents an increase of approximately 38 % and 41 %, respectively, compared to a smooth tube at the same flow rate. Additionally, it demonstrates an approximately 10 % improvement in thermal efficiency when compared to a tube with a diameter of 32 mm. The study also demonstrated the accuracy of numerical analysis, which is beneficial for shortening the design and validating prototype development.