Enhancing the Heat Transfer Performance in Double-Pipe Heat Exchanger by Passive Swirl Flow: An Experimental Investigation

The conventional heat exchanger requires improvement in its heat transport capabilities to achieve the desired rate while simultaneously reducing costs and size. Utilizing swirl flow is a promising method among various approaches to enhance heat transfer rates. However, it should be noted that this technique can sometimes result in increased friction losses. In this study, a new technique for creating swirl flow by a passive method, without using twisted baffles or fins, is experimentally investigated to enhance heat transfer rate and pressure drop among a pipe-in-pipe heat exchanger. Experiments were conducted, involving the injection of hot water at various angles (30°, 60°, and 90°) and Reynolds (Re) numbers ranging from 6000 to 11000 to simulate turbulent flow. According to the experimental results, it was observed that lower Re numbers yielded the highest heat transfer rate and the factor of thermal performance, whereas increasing Re values resulted in a decrease in the friction factor (f). Compared to the heat exchanger of a plain pipe, at an injection angle of 90° and a Re number of 6000, the Nusselt (Nu) number exhibited a 25.9% increase, while the f experienced a 14.83% increase. Additionally, the thermal performance factor was 1.199 under the same working conditions. Predicted correlations of Nu number and f as a function of Re were developed for various tested injection angles.