Thin liquid film boiling on micro-nano composite structures fabricated by laser direct writing and low-temperature sintering

Vapor chambers (VCs) achieve efficient directional heat transport and dissipation through the synergistic effect of liquid capillary and thin liquid film boiling. For the micro-nano composite wick structures of VC, the understanding of bubbles evolution, liquid-vapor interface oscillation, liquid film rupture behavior, and directional capillary liquid replenishment remains challenging. In this work, the micro-nano composite structures were fabricated using laser direct writing and low-temperature sintering technique. The experimental investigations were conducted on the heat flux, heat transfer coefficient, and bubble evolution of thin liquid film boiling on the fabricated surfaces. The results of micro structures (microporous, microchannel and micropillar) show that, under high heat flux, the high-frequency bubble rupture induces rapid vapor escape from the liquid surface, accompanied by the formation of an unstable liquid ring at the edge, which in turn triggers liquid film instability, resulting in vapor jet and droplet splashing. A continuous “nucleation-growth-vapor jet/droplet splashing-liquid replenishment” cycle is proposed to explain the physical mechanism behind the improved heat transfer performance and reduced wall superheat. Subsequently, the experiments were carried out on the micro-nano composite structure. It is found that the micropillar composite porous (MPCP) structure with high porosity and abundant fluid storage achieves the highest critical heat flux of 86.41 W/cm 2 , which is 4.1% and 17.6% higher than that of the micropillar-groove composite porous (MPGCP) structure and the micropillar structure, respectively. During the vapor jet and droplet splashing stages, the heat transfer coefficient is 19.4% higher than that of the MPGCP structure.