Experimental investigation of the secondary flow influencing on two-phase heat transfer and pressure drop characteristics in curved micro-tube

Abstract

This study investigates the flow behavior, heat transfer, and pressure drop in a helically coiled microchannel exposed to a range of heat flux levels. The analysis focuses on the effects of secondary flow and two-phase (phase-change) flow of R134a refrigerant under vertically upward conditions. The experiment involved fabricating a helically coiled channel with a 1 mm inner diameter. Experiments were conducted with a mass flux of 636 kg/m²·s, a saturation pressure of 0.9 MPa, and heat fluxes ranging from 0.1 to 10 kW/m². The experimental results demonstrated that the helical tubes enhance heat transfer through secondary flows and Dean vortices, which increase turbulence and disrupt the thermal boundary layer.