Theoretical analysis of bubble nucleation in liquid film boiling

Abstract

Many industrial applications such as electronic cooling and thermal desalination have adopted the heat dissipation technologies of capillary evaporation and liquid film boiling, with bubble nucleation being the transition criterion between them. In this paper, a theoretical model for bubble nucleation in liquid film boiling is developed, which mainly considers three aspects: transient heat conduction inside the liquid film supported with porous wick, evaporation at the liquid-vapor interface, and superheat requirement for the stable existence of a bubble nucleus. The criterion for the onset of nucleate boiling (ONB) in liquid film boiling is established, and size range of active microcavities for bubble nucleation is obtained, as well as comparisons being made with that during pool boiling and flow boiling. The results indicate that the size range of active microcavities in liquid film boiling is narrower with the minimum size being several times larger, and bubble nucleation in liquid film boiling is much more difficult. Although superhydrophilic surface with small contact angle is disadvantageous to bubble nucleation, it will decrease the minimum size of effective microcavities radius within the size scope of a few micrometers, which is beneficial for ONB in liquid film boiling. Moreover, critical thickness to trigger ONB in liquid film boiling is found to decrease with increasing contact angle, augmenting superheat and strengthening effective thermal conductivity of the wick, and its theoretical prediction is validated with experimental data in the literature. Our model offers a new avenue for understanding the ONB in liquid film boiling, and therefore can serve as a guideline for future enhancement design.