Numerical and experimental study of enhancement heat exchanger performance by inserting a dimple surface ball inside the tubes

Heat exchangers are available in various types and are widely used in engineering and industrial applications. Many techniques, including passive methods, were used to enhance heat exchanger performance. These methods include surface treatment, rough surfaces, increasing surface areas, swirl flow devices, twisted pipes, flow enhancement devices, additives for gases, and additives for liquids. Several studies have initially analyzed the effect of stationary balls inside the tube with a similar arrangement of distances between the balls on pressure drop and heat performance. Other researchers have applied this evaluation method to study heat transfer through the tubes with tabulators. Unfortunately, limited literature resources are devoted to ball inserts. In this work, 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. 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.