Numerical simulation of growth of a vapor bubble during flow boiling of water in a microchannel

Abstract

The present study is performed to numerically analyze growth of a vapor bubble during flow of water in a microchannel. The complete Navier-Stokes equations along with continuity and energy equations are solved using the SIMPLER method. The liquid vapor interface is captured using the level set technique. The microchannel is 200 microns in square cross-section and the bubble is placed at the center of the channel with superheated liquid around it. The results show steady initial bubble growth followed by a rapid axial expansion after the bubble fills the channel with a thin liquid film around it. The bubble then rapidly turns into a plug and fills up the entire channel. A trapped liquid layer is observed between the bubble and the channel as the plug elongates. The bubble growth rate increased with the incoming liquid superheat and formation of vapor patch at the walls is found to be dependent on the bubble growth rate. The upstream interface of the bubble is found to exhibit both forward and reverse movement during bubble growth. Results show little effect of gravity on the bubble growth rate under the specified conditions. The bubble growth features obtained from numerical results are found to be qualitatively similar to experimental observations.