Exploring Impacts of Using Porous Media on Heat Transfer in Helical Coils: A Comprehensive Numerical Study

This research investigates the thermal performance of a helically coiled tube filled with a porous material. The study uses numerical simulations over a wide range of Reynolds and Darcy numbers. The porous materials used are steel, aluminum, and copper. To determine the contribution of porous material as well as the spiraling effects of the pipe to increased heat transfer, the simulations were also run for a helical coil without porous material and a porous-filled straight tube. The pitch and radius of the coil were varied, resulting in different coil turns for a given length of the pipe. The rate of exergy destruction in different states was calculated to determine the optimal operating point of the system. The study reveals that porous material significantly improves heat transfer in both straight and helical tubes. The optimal performance is achieved at higher Darcy numbers, with heat transfer being independent or dependent on Re. The highest Nu value is around 450 at Da=0.1 and Re=2000, about 103 times and 17 times the Nu in the straight and helical tubes without porous material, respectively. However, the peak value of PEC is 2 and 17 with respect to porous-filled straight tubes and non-porous helical coils. The main achievement of this study is that it shows that porous media can be applied to amplify heat transfer beside the secondary flow in helical tubes under specific conditions. This enhancement occurs when using porous media with high Da numbers, such as Da ~ 0.1. In contrast, the study shows that using porous media with low permeability (Da ~ 0.0001) surpasses secondary flows effects where the thermal performances of porous filled helical tubes and straight t