Heat transfer characteristics of Taylor flow in a bottom-heated square microchannel: A 3D conjugate heat transfer numerical study

Abstract

The heat transfer mechanisms of Taylor flow in rectangular microchannels under asymmetric heating conditions remain incompletely understood. In this work, a three-dimensional conjugate heat transfer numerical simulation method is developed, which can achieve different Taylor flow distribution characteristics by modulating the second-phase volume fraction at the inlet boundary. Using this method, the heat transfer characteristics of gas–liquid Taylor flow in a rectangular channel under asymmetric bottom heating conditions were systematically studied for the first time. The simulation results show good agreement with our previous experimental results, verifying the reliability of the model. Heat transfer paths within bubbles and liquid slugs under bottom heating conditions were analyzed in detail based on three-dimensional velocity and temperature fields. The local Nusselt number distributions for single-phase flow and Taylor flow at various typical locations within the rectangular microchannel are compared, and it is found that the heat transfer enhancement effect of Taylor flow is evident throughout the entire channel. The heat transfer associated with leakage flow at channel corners has been investigated, revealing that the leakage flow in gas–liquid systems is characterized by low velocity and non-uniform distribution. The formation mechanism of the localized vortex at the tail of the bubble and its impact on heat transfer in the entire liquid film region were analyzed. A comprehensive investigation was conducted on the three-dimensional recirculation flow field distribution characteristics of Taylor flow in rectangular microchannels and the intrinsic mechanisms of heat transfer enhancement by short slugs. It was found that the velocity distribution within the short slug no longer conforms to the classical Poiseuille-flow profiles, and the “stagnant heat zone” in the bubble region disappears. Under the conditions of constant void fraction and mixture velocity, reducing the slug length by 60% decreases the average absolute recirculation time within the slug by approximately 53.2 % and increases the Nusselt number by 34 %.