Numerical simulation of single bubble growth in vertical rectangular narrow flow channels

Abstract

The narrow rectangular channels of compact type reactors rely on boiling to generate bubbles to transfer a large amount of heat. On the one hand, the growth behavior of bubbles is closely related to the heat-mass conversion efficiency. On the other hand, the resulting flow instability and critical heat flow also affect operation safety. We set up a test bench with a visible flow channel to investigate the bubble growth in vertical rectangular narrow channels. The bubbles at the ONB (Onset of Nucleate Boiling) site were observed at 1 atm in subcooled flow boiling water. Two typical bubble growth processes were picked out to simulate numerically. A high-speed camera and thermocouples were used to record bubble contours and wall temperatures in the experiment. The heat flow was obtained based on assumptions and theoretical analysis. A numerical simulation of the whole process was conducted, where the bubble contours and temperature fields can be obtained. According to the simulation results of two examples, the microlayer evaporation at the bubble bottom accounts for about 30% of the total evaporation amount.