In order to maximize the thermal efficiency of shell and coil heat exchangers, substantial research has been done and geometrical modification is one way to improve the exchange of thermal energy between two or more fluids. One of the peculiar features of coiled geometry is that the temperature distribution is highly variable along the circumferential section due to the centrifugal force induced in the fluid. Moreover, most researchers are concentrated on using a shell and single helical coil heat exchanger to enhance the heat transfer rate and thermal efficiency at different operating parameters. Therefore, the aim of this study is to investigate temperature variation ((T-1, T-2, T-3 and T-4) across a shell and single/double coil heat exchanger at different coil pitches, hot water flow rate, and cold-water flow rate along the outer surface of the coil using experimental and numerical analysis. For single and double coil heat exchangers, Computational Fluid Dynamics (CFD) is carried out using pure water with a hot water flow rate ranging between 1-2 l/min for the coil side heat exchanger. For single coil heat exchangers, the numerical analysis findings showed a good agreement with experimental four-temperature measurement results (T-1, T-2, T-3 and T-4) with an error rate of 1.80%, 3.05%, 5.34% and 2.17% respectively. Moreover, in the current double coil analysis, the hot outlet temperature decreased by 3.07% compared to a single coil (baseline case) at a 2.5L/min hot water flow rate. In addition, increasing the coil pitch will increase the contact between the hot fluid and the coil at a constant hot water flow rate and thereby decrease the hot fluid outlet temperature. Finally, a computational analysis was carried out to examine the flow structure inside single and double coil heat exchangers, and the findings indicated that the effect of centrifugal forces in double coil heat exchangers at various coil pitches caused the secondary flow to be substantially reduced.

The goal of this work was to design a simple and cost-effective technique for improving the performance of heat exchangers, and the emphasis was on the experimental side while not neglecting the necessity of validating our findings with theoretical results using CFD. A new method was used to enhance the heat transfer inside the heat exchanger by using a coil with modified steps, as the published papers did not previously address this method, which proved its effectiveness. For varied coil pitches, the numerical findings were in good agreement with the experimentally obtained results, with an error rate of less than 8%. To compare results and confirm effective correlation between pitch changes, a double coil tube is manufactured with a fixed pitch and a double coil tube with modified pitches, while maintaining the basic design parameters of tube diameter ( ), shell diameter ( ), height of shell ( ), and coil height ( ) in order to try to increase the overall heat transfer coefficient and heat transfer. This new design enhanced heat transfer and total heat transfer coefficient at Reynolds number (400< <2000), with a 22% improvement in overall heat transfer coefficient. The new design of the coil (modified pitch) also gave an improvement in the flow distribution, which generated a higher secondary flow than the traditional pitch coil.