Modelling of bubble growth and detachment in nucleate pool boiling

Abstract

A mechanistic model to study the growth of a bubble from nucleation to departure in pool boiling is proposed in this work taking into account the change in shape of a bubble as it grows. The model consists of three sub-models: (a) a heat transfer sub-model to compute the bubble growth rate based on the evaporation of the microlayer, the macrolayer, the thermal boundary layer and the bulk liquid surrounding the bubble; (b) a force sub-model to calculate the forces acting on a bubble; and (c) a contact angle and bottleneck sub-model to account for the change in shape of the bubble. Analysis of past experiments on bubble growth in nucleate pool boiling has shown that the shape of a bubble transitions from a truncated sphere to a balloon-like shape before departure. In the present work, a novel method to model this balloon-like shape of the bubble as a truncated sphere atop a conical bottleneck is presented. The model is validated against high-fidelity CFD simulations and pool boiling experiments of water and methanol from literature. In particular, the bubble departure time, wall temperature, bubble shape and microlayer profile obtained from the model are in good agreement with experimental and CFD results.