Effect of micro-cavities structured surfaces on bubble dynamics and pool boiling heat transfer enhancement

This paper presents pool boiling experiments on copper surfaces with micron-scale inverted truncated pyramid (ITP) using deionized water and FCM-47 fluorocarbon-based coolants. The dynamic behavior of bubbles on these micro-cavity structures is observed using a high-speed visualization system. Our study focuses on the impact of micro-cavity diameter, wettability, surface tension, and bubble behavior on boiling heat transfer. The findings show that, in comparison to smooth surfaces, surfaces with micro-cavity pit structures perform noticeably better in high heat flux regions. The enhancement effect of identical structural surfaces on boiling varies with different working fluids. The maximum critical heat flux (CHFmax) and heat transfer coefficient (HTCmax) for the water-cooled micro-cavities with 200-micrometer side lengths are 117.36% and 162.1% of that for smooth surface, respectively. Correspondingly,in the fluorinert-cooled experiment are CHFmax in the micro-cavities with 300-micrometer side lengths and HTCmax in the micro-cavities with 200-micrometer side lengths. The substantial increase in the density of active nucleation sites within the micro-cavities leads to a superior heat transfer coefficient, surpassing that of smooth surfaces. For larger micro-cavities, the primary driver behind the enhanced nucleate boiling at low heat fluxes is the expanded effective heat transfer area. At high heat flux, microstructures preventing the formation of vapor films and then reducing wall superheating and enhancing critical heat flux.