A comparative evaluation of double-pipe heat exchangers with enhanced mixing

Double-pipe heat exchangers have been widely used in various industries, and the efficient design of these heat exchangers has received a significant research impetus. Chaotic advection is an effective method to enhance flow mixing and convective heat transfer. In this work, we propose novel double-pipe heat exchangers with different serpentine channels to create chaotic advection. The hydrothermal characteristics of the proposed designs are numerically analysed in the laminar regime. Compared to the plain double-pipe heat exchanger, the suggested double-pipe heat exchangers present significant heat transfer enhancement performance except for the twisted in-phase and twisted out-of-phase cases. The highest overall heat transfer coefficient is found to be 679.41 W m- 2 K-1 and 677.75 W m- 2 K-1 for the case of C-shaped and enhanced C-shaped double-pipe heat exchangers at the Reynolds number of 500, respectively, due to the most intense secondary flow and mixing induced in these geometries. The performance evaluation criterion and compactness factor are considered as the metrics to compare the performance of these geometries at various Reynolds numbers. The enhanced C-shaped double-pipe heat exchanger performs better in terms of both performance evaluation criterion and compactness factor. At the Reynolds number of 500, the performance evaluation criterion and compactness factor of the enhanced C-shaped double-pipe heat exchanger are 1.3-197 % and 22.3-736 % higher than other investigated geometries, respectively. To further scrutinise the design of the enhanced C-shaped double-pipe heat exchanger, the effect of edge curvature is analysed over the performance evaluation criterion value. It is found that the curve radius of 2di/8 in the corners of the channels not only results in a higher PEC value, but also reduces the possibility of fouling in the heat exchanger.