Dynamic interaction of growing bubble and microlayer: Need for reconciliation of experiments and theory in flow boiling

Abstract

The bubble growth and its corresponding microlayer dynamics are strongly coupled from the point of bubble inception to its eventual liftoff. This paper discusses the complex and interesting interaction between a bubble and a microlayer through high-speed photography and thin-film interferometry in vertical flow boiling conditions. We analyzed existing force balance models and bubble growth rate models using experimental data. Our analysis revealed that the existing force balance models show severe limitations in predicting bubble dynamics, and the success of models reported by researchers is mainly due to over-parametrization and over-fitting. We show through our experimental results that the movement of the bubble in the flow direction and depletion of the upstream microlayer are strongly correlated with bubble diameter and growth rate. We discuss a non-dimensional approach based on forces acting on the bubble to predict the bubble movement in the flow direction. Furthermore, we report an interesting stage of the bubble ebullition cycle, where the bubble does neither liftoff nor contact the heater surface.