Thermal performance of periodic serpentine channels with semi–circular and triangular cross–sections

Abstract

Printed Circuit Heat Exchangers (PCHE's) are very efficient compact exchangers considered as recuperators in the Brayton cycle of new generation high temperature reactor designs. The heat exchangers use multiple plate layers containing tortuous micro–channels to enhance the heat transfer between the working fluids. Understanding the flow phenomena and its effects on heat transfer inside the channels would ultimately lead to improved exchanger designs. A numerical study was conducted on the heat transfer behaviour of fully developed laminar flow in three–dimensional serpentine channels with semi–circular and equilateral triangular cross–sections. Computational Fluid Dynamics (CFD) was used to investigate the heat transfer characteristics of various physical designs under different flow conditions. The design parameters for serpentine channels were: the bend's radius of curvature (Rc )3 the channel diameter (d), the half–wavelength of the channel (L) and Reynolds number (Re). Results were obtained for a range of configurations (1.0 1.8, = 4.5) and flow conditions (50 400). Water was used as fluid and the uniform surface temperature boundary condition was applied to channel walls. Results showed a definite increase in heat transfer when Re was increased. Heat transfer enhancement due to fluid mixing was a maximum at the highest Reynolds number since the inertial effects dominated the viscous flow effects. However, a slight decrease in enhancement was noted as the bend radius of curvature increased, due to weaker mixing of the flow. In several test cases, secondary flow effects separate from main vortices and mixing were observed to influence the heat transfer. Future research topics are suggested to further clarify these phenomena.