Numerical investigations on optimised shell designs of a U-tube heat exchanger

Abstract

Previous researchers focused on enhancing the heat transfer rates of heat exchangers using developments on the tube-side components. Nevertheless, the performance of the shell side has been overlooked in all previous studies. Therefore, this study aims to investigate the heat transfer performance, pressure drop, friction factor, exergy, and performance enhancement criteria (PEC) of a heat exchanger due to the geometrical modification on a cylindrical shell. Three modified shell designs were proposed using SolidWorks software: Twisted-square shell model (TSSM), Mirrored-square shell model (MTSSM), and Corrugated-square shell model (CSSM). Their thermofluid performance is simulated using ANSYS-Fluent software at different Reynold's numbers (46941 ≤ Re ≤ 89616). Results have revealed that TSSM attained the highest heat transfer coefficient, with a 24.4% enhancement at Re = 55,476, followed by the MTSSM with 23.1% and TSSM with a 22.1% increment at Re = 81,081. Moreover, the MTSSM showed the most significant improvement in effectiveness, with a 24.64% advancement, followed by the TSSM with a 22.35% at Re = 81,081. Furthermore, the pressure drop experienced by the MTSSM and CSSM was found to be lower than the cylindrical shell and the TSSM at all Re, with the highest reduction of 16.25% and 15.89% by the CSSM at Re = 55,476 and 46,941, followed by the same model at Re = 72,546 and 64,011 with a 15.15% and 15.13% decrement, leading to potential cost savings in terms of lower pumping and operating expenses compared to the TSSM and cylindrical model. On the other hand, the TSSM showed an increment in the pressure drop with the highest increment of 9.94% and 8.82% at Re = 64,011 and 46,941 compared to the cylindrical model. Besides, the friction factor of both the CSSM and MTSSM was found to be much lower compared to the cylindrical shell model with the highest decrement of 16.25% and 15.98% in the CSSM at Re = 55,476 and 46,941 and 13.17% and 12.85% at Re = 81,081 & 46,941 in the MTSSM, and nonetheless increment in the TSSM with the highest increment of 9.94% and 8.82% at Re = 64,011 and 46,941 respectively. However, the TSSM still provides superior heat transfer performance even at its lowest Re = 46,941 with a lower pressure drop compared to the highest Re = 81,081 in the cylindrical shell, indicating that the TSSM can be used at Re ≤ 46,941 and still provides better heat transfer performance than the highest Re applied in the cylindrical shell, resulting in a lower operating and pumping cost to circulate the fluid through the shell. These outcomes demonstrate the positive impact of the optimised shell modifications on the overall efficiency and cost-effectivenessofthesystem.