EXPLORING IMPACTS OF USING POROUS MEDIA ON HEAT TRANSFER IN HELICAL COILS : A COMPREHENSIVE NUMERICAL STUDY

The advantages of porous media in enhancing heat transfer have been well established. Similarly, the benefits of helical tubes in generating secondary flows, promoting flow mixing, and improving heat transfer are also recognized. However, previous studies have not thoroughly examined the combined effects of using porous media and helical tubes to enhance heat transfer. This study aims to demonstrate that careful selection of porous media can leverage both the heat transfer enhancements provided by porous structures and the secondary flow effects induced by helical tubes, thereby improving overall heat transfer performance. The key findings are that porous material significantly improves heat transfer, with the highest Nusselt number reaching around 450 in a straight tube filled with porous material at Da = 0.1 and Re = 2000-about 103 and 17 times higher than the Nusselt number in the straight and helical tubes without porous material, respectively. The rate of exergy destruction was calculated to determine the optimal operating point of the system. The peak values of the performance evaluation criterion (PEC) were 2 times greater in the helical tube filled with porous material compared to straight tubes filled with porous material, and 17 times greater compared to nonporous helical coils, indicating significant enhancement. The study also reveals that porous media with high permeability (Da similar to 0.1) can amplify heat transfer alongside the secondary flow in helical tubes, while low-permeability porous media (Da similar to 0.0001) diminish the impact of secondary flow, resulting in similar thermal performance between helical tubes and straight tubes filled with porous material. The main achievement of this work is demonstrating that porous media can be applied to amplify heat transfer in helical tubes under specific conditions, providing a viable method to enhance thermal efficiency and minimize exergy destruction.