结霜前期纳米结构超疏水表面的凝结-冻结特性

研究结霜前期水蒸气在超疏水表面的凝结-冻结特性,有利于揭示超疏水表面的抑霜机理以及加深对结霜过程的认知。利用溶液刻蚀-沸水法制备了具有纳米结构的铝基表面,水滴与其形成的接触角达161.1°。通过微细观可视化观测,揭示结霜前期纳米结构超疏水表面的凝结-冻结特性,并与接触角为86.5°的裸露铝表面进行了对比分析。结果表明,超疏水表面凝结液滴的形状、尺寸和分布密度与裸露表面均存在差异,且液滴的冻结时间和冻结速率也不同。超疏水表面的液滴从17 min开始冻结,直到26 min才全部冻结,而裸露表面的液滴在4 min内就全部冻结。超疏水表面的纳米结构导致其与凝结液滴间的热阻增大,导热过程被削弱,从而抑制了液滴的生长与冻结。

Condensation and Freezing Characteristics of Nano-structured Superhydrophobic Surface in Early Frosting Stage

The characteristics of water vapor condensation and condensate droplet freezing in the early frosting stage is helpful for knowing the anti-frosting mechanism of superhydrophobic surface and the process of frost formation. A nano-structured superhydrophobic surface with aluminum substrate was prepared by solution etching and water boiling. The contact angle of the water droplet on the surface was 161.1°. The effects of the nano-structured surface on the condensation and freezing processes in the early frosting stage were observed and analyzed, and the results were compared with the bare aluminum whose surface contact angle was 86.5°. The experiments show that the shape, size and distribution density of the water condensate droplets on the nano-structured surface are different from those on the bare surface. The freezing time and freezing rate of the water condensate droplets are also different. The droplets on the nano-structured surface begin to freeze after 17 min and totally freeze after 26 min, while they totally freeze only within 4 min on the bare surface. The nanostructures increase the thermal resistance between the water condensate droplet and the superhydrophobic surface, and then weaken the heat conduction between them, which effectively delaying the droplet growth and freezing.