Simulation of Single Bubble Growth in a Planar Microchannel With Temperature Recovery Model

Abstract

In the study numerical simulations are performed to investigate the saturated fluid flow through a two dimensional microchannel (1000μm×200μm, with a superheated bottom wall) by building a comprehensive physical method and updating the standard solver in the OpenFOAM software package. On basis of previous numerical study, most of the numerical methods for the micro-scale flow boiling emphasizes the mass transfer and interfacial heat exchange. Simultaneously, geometric reconstruction technology for liquid-vapor interface is widely used, which evidently captures the interfacial boundary characteristic accurately but costs lots of computational resources. In the present study, the temperature recovery model is adopted to maintain the liquid-vapor interface temperature, and an interface-cell searching algorithm is added into the model, while the geometric interface reconstruction technology is abandoned. For the validation of the new codes developed in OpenFOAM, 1-d Stefan Problem and the experimental results of Mukherjee are both utilized to compare with our simulation results. The growth process of a single bubble in the laminar flow regime is studied in order to explore the underlying mechanism of flow boiling in microchannels. The qualitative investigation for effects of wall superheat, Reynolds number, contact angle and surface tension on heat transfer are comprehensively discussed. In general, heat flux of the bottom wall increases because of the motion of liquid-vapor interface. Wall superheat determines the rate of bubble growth on the heated wall, which is roughly proportional to wall heat flux due to the Fourier’s Law. The distribution of velocity and temperature fields in the channel refresh progressively with increasing inflow Reynolds number, which speeds up the evolution of interface position and augments the wall heat flux significantly. Furthermore, the area of thin liquid film between the wall and the bubble is enlarged by reducing the contact angle, thus augmenting the wall heat flux by several times compared with the single phase microchannel flow. However, surface tension and gravitational acceleration are found to be negligible in the present study.