微纳复合结构超疏水铝表面抑霜特性研究

Frost Inhibition Characteristics of Superhydrophobic Aluminum Surface of Micro-Nano Composite Structure

目的从微观上揭示超疏水表面的抑霜机理。方法运用化学刻蚀法制备微纳复合结构超疏水铝表面,在制冷实验台上对试件结霜过程进行微观可视化观测,并分析试件的霜晶演化规律。将超疏水铝片冷面温度分别设置为–5、–10、–15℃三个档次,通过对比普通铝片和超疏水铝片表面的霜晶高度与霜晶质量,结合相变动力学、经典成核理论、传热与传质理论解释相关结霜与抑霜机理。结果不同的实验阶段及不同的实验温度条件下,超疏水铝表面本身的抑霜效果虽然有差异,但是相比普通铝表面的抑霜特性,超疏水铝表面都具有一定的抑霜效果,结霜过程整体滞后,霜层高度发展相对缓慢,实验进行了10min后,超疏水表面的霜层高度只有普通表面的35%。结论由于冷凝水珠在冷表面形成Wenzel状态,水珠浸润在微细结构中,在一定的条件下,超疏水铝表面可有效延缓冷凝水珠的生成,从而抑制结霜。在结霜后期,当冷凝水珠冻结,且在表面布满霜晶后,抑霜效果相对恶化。在经月桂酸修饰后,普通铝表面也具有一定的抑霜性能,但效果明显弱于具有微纳复合结构的超疏水表面,因此建议在制作表面有抑霜需求的材料时,可以以延缓冷凝水珠的生成为技术手段,制作合适的表面微纳结构,以期达到最大程度地抑霜的目的。

The paper aims to profoundly reveal the frost inhibition mechanism of the superhydrophobic surface.The surface of superhydrophobic aluminum with micro-nano composite structure was prepared by chemical etching.The frost formation process of the specimen was observed and the frost crystal evolution of the specimen was analyzed on the refrigerating experiment table.The cold surface temperature of the super hydrophobic aluminum sheet was set at–5℃,–10℃and–15℃,respectively.The frost formation and frost inhibition mechanism were explained by comparing the frost crystal height and mass on the surface of ordinary aluminum sheet and superhydrophobic aluminum sheet in combination with phase change kinetics,classical nucleation theory,heat and mass transfer theory.It was found that the frost inhibition effect of superhydrophobic aluminum surface was different at different experimental stages and temperatures;but compared with the frost inhibition characteristics of ordinary aluminum surface,the superhydrophobic aluminum surface had a certain frost-inhibition effect,and the frost-formation process lagged behind.The frost height developed relatively slowly.After 10 minutes’of the experiment,the frost height on the superhydrophobic surface was only 35%of that of the ordinary surface.Because condensed-water beads formed Wenzel state on the cold surface,the water droplets were infiltrated in a fine structure.Under certain conditions,the formation of condensed-water beads on the ultra-hydrophobic aluminum surface could be effectively delayed,thereby the frost formation could be inhibited.At the later stage of frosting,when the condensed-water beads froze and there were full of frost crystals on the surface,the frost-inhibition effect was relatively deteriorated.Ordinary aluminum surface also has a certain frost inhibition performance after lauric acid modification,but the effect is obviously weaker than that of the superhydrophobic surface with micro-nano composite structure.It is suggested that when producing material whose surface needs the frost-inhibiting feature,delaying the generation of condensed-water beads can be used as a technological means,for producing the suitable superficial micro-nano structure,so as to achieve the frost-inhibiting purpose most effectively.