纳米孔链双层复合表面过冷池沸腾传热特性

Heat transfer characteristics of subcooled pool boiling on two-layer composite surface with nano-porous chain

微纳复合多孔结构对相变换热的强化是能源化工领域的重要主题。基于气液协同输运的概念,通过飞秒激光正交扫描加工,在硅片上生成二维嵌套的纳米孔链双层复合多孔结构,实验研究了其对HFE-7100过冷池沸腾传热特性的影响。实验结果表明,相比于光滑表面,多孔表面在35K过冷池沸腾条件下的起始过热度从16.7K下降到12.3K,降低26.3%,最大临界热通量提高128.7%。同时利用高速摄影观察气泡行为来研究强化沸腾传热机理。研究发现,双层多孔结构表面和内部形成的大量连通孔穴大幅度增加了有效成核位点,纳米孔和双层连通结构提供垂直和水平方向的液体补充通道,在高热通量下气泡尺寸更小,脱离更快。有效汽化核心密度增加以及气液自适应协同输运增强了多孔网络中的微液膜蒸发和微对流作用,从而有效提升沸腾换热能力和临界热通量。

The heat transfer enhancement of phase change by composite porous structure is an important topic in the fields of energy and chemical industry.Based on the concept of vapor-liquid synergetic transport,two-layer hierarchical structure nested with two-dimensional nano-porous chain on the silicon substrate was processed by femtosecond laser orthogonal scanning method.The subcooled pool boiling heat transfer performance of the porous structure was experimentally investigated.The experimental medium was HFE-7100.Compared with a smooth surface,the wall superheat of the two-layer porous structure at the onset of nucleate boiling was reduced from 16.7K to 12.3K at liquid subcooling of 35K,and the ratio is 26.3%.The maximum critical heat flux was increased by 128.7%.At the same time,the enhancement mechanism of boiling heat transfer was studied by observing bubble behaviors with a high-speed camera.It was found that a large number of interconnected cavities formed on the surface and inside the porous structure increase the effective nucleation site density.And nano-pores and two-layer structure provided vertical and horizontal liquid replenishment.The bubble size was smaller,and the departure frequency was faster under high heat flux.The increased nucleation site density and the vapor-liquid synergetic transport enhanced the micro convection and the thin liquid film evaporation,which effectively enhanced the boiling heat transfer coefficient and critical heat flux.