In the current work, a substantial research and cost-effective strategy has been conducted to enhance the thermal efficiency of shell and coil heat exchangers, and geometrical modifica-tion is one technique to improve the exchange of thermal energy between two or more fluids. Therefore, experimental and numerical analysis across a shell and single/double coil heat ex-changer at constant temperatures of 36 °C for cold water and 65 °C for hot water are studied. Various coil pitches (baseline pitch, P-2P-P and 2P-P-2P) and mass flow rates (1 L/min for hot water and 2, 4, 6, and 8 L / min for cold water) were studied. The present experimental results for single and double coil heat exchangers were in good agreement with previous research’s numerical study, with an error rate of 9% and 5%, respectively. Moreover, the numerical find-ings revealed that modifying the double coil pitch improves the heat transfer rate by 10% com-pared to a baseline case. Following the encouraging simulation findings, improving the heat exchanger’s performance by utilizing more than one pitch for the same coil is a novel method that has not yet been reported. Therefore, when comparing the modified pitch of a double coil
heat exchanger to a conventional coil under the same conditions (400