Effects of surface wettability on bubble departure and critical heat flux: A parametric study based on 3-D dynamic force analysis model

Abstract

To investigate the effect of bubble dynamics on boiling heat transfer, and provide theoretical support for the design of enhanced structured heating surfaces, a 3-D dynamic model is established for predicting the bubble behaviors and the critical heat flux (CHF) on hydrophilic surfaces. Instead of assuming a force equilibrium state for the bubble attached to the surface, a dynamic model comparing the instantaneous bubble interface expansion with the bubble upwards movement under non-static state captures the departure diameter well, leading to an approximation to the realistic boiling process with a maximum error of 15%. The CHF prediction is then acquired based on the bubble dynamics analysis. According to the model analysis, increasing bubble base wetting reduces bubble departure diameter and leads to higher CHF. On superhydrophilic microstructured surfaces with thorough wetting, the CHF is approximately 153 W cm−2 for pure water as working fluid, which represents the maximum contribution of two key surface parameters including the contact angle and the bubble base wetting ratio. Further exceeding the critical value, the CHF enhancement is merely attributed to the improved convective heat transfer. This study focuses on the bubble departure mechanism and quantifies the contribution of key parameters towards the CHF enhancement, which provides a new idea for the structural design of enhanced surface from the perspective of controlling of bubble behaviors.