Study the effect of adding rectangular fins along the riser pipe on the thermal performance of the flat-plate solar water heater system

The earlier studies investigated many parameters affecting the flat plate solar collectors (FPSCs) while employing an active approach to transmit the heat transfer fluid and running under a constant heat flux. In contrast, the presented study investigates enhancing the thermal performance through added fins with different heights and numbers to FPSC in a changing heat-flux condition and relies on a passive technique. Thus, Models A, B, and C included adding five fins along the riser-pipe with heights of 5, 7.5, and 10 mm, respectively, while Models D and E used four and three fins of 10 mm height, and the numerical calculations were conducted using ANSYS Fluent 2022R1. Then, the experimental work was done for the traditional model in Baghdad City, Iraq, to validate the results of numerical work, and the numerical and experimental work difference was found to be 10.17% for the tank's average temperature and the heat transfer liquid's temperature at the riser outlet is 10.14%. The numerical results indicate that the thermal efficiency of the system in all test models (A, B, C, D, and E) is enhanced than the classical model regarding the water's temperature in the tank and the working liquid's temperature at the pipe's outlet. In addition, the study concluded that Model C achieved a greater overall thermal efficiency than the traditional model by 38.59% and higher than Models A, B, D, and E by 11.77%, 6.65%, 8.19%, and 18.09%, respectively.