Entropy generation and thermal behavior of microchannel fitted with punched curved vortex generators

Abstract

Utilizing curved vortex generators (VGs) has emerged as a promising way to improve heat transfer in heat exchangers. However, research on the placement of punched rectangular curved winglet VGs on two opposing heat transfer surfaces of microchannel heat exchangers is limited. Through experiments and simulations, the effects of five perforation positions and three pitches on fluid flow and heat transfer were examined. This analysis is performed in the turbulent flow regime (2500 < Re < 3500) and the governing equations are solved by using SST k-ω model, assuming that the fluid is incompressible, has constant thermal properties, and ignores the effects of thermal radiation and gravity. Metrics such as the Nusselt number ratio, friction coefficient ratio, secondary flow intensity, thermal enhancement factor, and entropy generation are used to analyze the flow dynamics of mixed vortices. The results indicate that different perforation positions significantly affect the vortex characteristics, altering heat transfer and pressure loss. Furthermore, the pitch of the VGs plays a crucial role in governing heat transfer and frictional losses. Specifically, the heat transfer rate increased by 12.1 % to 61.1 % compared to empty tubes, accompanied by a rise in pressure loss ranging from 50.6 % to 115.1 %. To validate the findings, the principle of entropy generation was utilized. Notably, under conditions of a Re of 2500, a perforation position proximal to the VG's leading edge (θ = +12°), and a pitch of 15 mm, a remarkable thermal enhancement factor of 1.29 was achieved.