Experimental investigation and model prediction of sliding bubble dynamics in vertical subcooled boiling flow

Abstract

In the subcooled flow boiling, the behavior of sliding bubbles significantly affects the partition of wall heat flux, especially the transient heat flux in the sliding area. Therefore, an experimental investigation was conducted to examine sliding bubble characteristics in subcooled flow in a vertical rectangular channel in this paper. The characteristics of sliding bubbles have been recorded and analyzed from size and velocity distribution, growth rate, sliding velocity, velocity-diameter dependence, and coalescence critical velocity in detail. By comparing experimental data and growth models, we found that all the bubble growth model at the thermal control stage overestimates the growth rate of sliding bubble. During the sliding phase, the effect of condensation gradually increases and the contribution of the microlayer evaporation to the bubble growth is negligible. In addition, based on the force balance model, the differential equation of motion describing the sliding bubble is developed. The model considers the effects of buoyancy, flow drag, bubble volume expansion, and additional mass effects brought about by pressure gradients. With near-wall drag coefficient and local liquid velocity correction, the model agrees well with the experimental data and predicts diameter-velocity correlations well.