Estimation of heat transfer enhancement by inserting dimple surface balls inside heat exchanger tube

Experimental and numerical analyses have been performed on the influence of inserting dimple balls inside the heat exchanger tube on the heat transfer rate. Inserting balls enhances active heat transfer and is attributed to imposed turbulence in the heat exchanger. In this paper, the challenge is to increase the heat exchanger's performance by placing more balls inside one heat exchanger tube. The current study included fixing dimple balls in the path of cool water flow with different numbers of balls, 4, 6, 8, and 10, for the range of Reynolds numbers ranging from 2950 to 13687. This increases the water velocity at the pass between the tube wall and the ends of the dimple ball, improving heat transfer. The balls were installed inside one of the tubes, so the distance between two successive balls was 10 cm. The results presented an increase in heat transfer rate at an increased number of dimple balls inside the tube from 4, 6, 8, and 10; the percentages of increased heat transfer rate are 8.3%, 11.6%, 13.6%, and 18.8%, respectively, when hot water flow rate 8 l/min. The experimental and numerical results for the thermal performance factor with Reynolds number at different conditions were compared. The different percentages of the thermal performance factor were 7.9% and 7.2% at the number of balls, 4 and 10, respectively. When the number of dimple balls within the heat exchanger pipe increases, the quantity of heat transferred is more than the increase in pressure drop as the flow velocity increases. As a result, the thermal performance factor rises to a certain point. Then the phenomenon of choked flow occurs, resulting in a reduction in flow and, as a result, a decrease in heat transfer and an increase in pressure drop. Future work will examine the influence of inserting dimple balls inside one tube of a heat exchanger on heat transfer characteristics for different conditions in moving and fixed cases.