Bubble growth inside an evaporating liquid droplet introduced in an immiscible superheated liquid

Abstract

A numerical bubble growth model for two phase droplets in an immiscible superheated liquid is developed by solving the mass and energy conservation equations. The model is applicable for concentric two-phase droplets (where the bubble is completely surrounded by the volatile liquid) like those seen during evaporation of refrigerants suspended in water. The effect of pressure driven growth in the initial phases of bubble growth is shown to be minimal and is therefore ignored to simplify the model. While previous works assumed that the droplet is initially uniformly superheated, the current model assumes a more accurate temperature profile obtained by solving the radial heat diffusion equation in the droplet and surrounding liquid. The model is validated by measuring bubble growth rate within an FC-72 droplet introduced in a water bath and it is seen that the results are in close agreement with the model predictions. Experimental results from various cases in literature are also found to be well represented by the model. The effect of the liquid superheat and initial bubble diameter on bubble growth rate is also studied. Finally, a parametric study on the effect of droplet and bulk liquid properties on bubble growth rate is conducted to highlight the relative importance of the thermal conductivity and thermal mass ratios of the two liquids.