A heat exchanger is a device that transfers heat between two media. It is widely applied in various Industrial processes and power plants. Most previous studies relied either on CFD without experimental validation or on limited diameters, while this work integrates both experiments and CFD and compares three diameters. An experimental study on a counter-flow double-pipe heat exchanger with a 12 mm inner pipe was conducted to validate the CFD model. The validated model was then used to assess the effects of inner pipe diameter (12, 15, and 18 mm), flow rate, and temperature on thermal performance. For validation purposes, the experimental data were compared with simulation results for the overall heat transfer coefficient and effectiveness. The results show that the percentage error ranges between (0–12.95) % and (0–11.63) % for both the overall heat transfer coefficient and effectiveness, respectively. This, in turn, indicated an acceptable and accurate simulation model that can be reliably used for further numerical studies. In general, the findings show that the coefficients of overall heat transfer (Ui) and effectiveness (ϵ) can be controlled by selecting an appropriate inner pipe diameter and carefully managing the flow rate and temperatures. The results indicated that a 188% increase in the overall heat transfer coefficient and a 177% increase in the effectiveness can be achieved at the same flow rate and temperatures by reducing the inner pipe diameter from 18 mm to 12 mm. Finally, the study underscores the critical roles of the inner pipe dimensions as a passive technique in optimizing heat exchanger efficiency.
Salih et al. (Mon,) studied this question.