铝表面结霜现象的实验研究

Experimental study of frost phenomena on aluminum plate

实验研究了自然对流时水平铝表面上的结霜现象.实验中空气温度25 ℃、湿度50%,冷面温度-40～0 ℃.与先前的铜表面实验结果类似,在冷面温度高于-38 ℃时,结霜前铝面上首先出现水珠;冷面温度越低,过冷水珠存续的时间越短,冻结温度也越低;冷面温度较高时,水珠冻结时引起的壁温回升较明显;不同冷面温度对应的初始霜晶形状不同;结霜过程中霜层表面新形成的霜晶形状随时间变化.将冷面温度降至-38 ℃后再与湿空气接触时,发现直接出现霜晶而未经过结露阶段.

The process of frost formation on horizontal aluminum surface in natural convection was experimentally studied. Tests were conducted at 25℃ atmospheric temperature and 50 % relative humidity, the cold surface temperature was changed from - 40 to 0 ℃. Similar to the results obtained for the copper surface, for aluminum surface at temperature above -38℃, super-cooled water droplets were observed before frost crystal formed on the surface; the lower the surface temperature, the shorter the life time of the super-cooled water droplets and the lower the freezing temperature; the recovery of the cold surface temperature caused by the freezing of the super-cooled water droplets became more conspicuous for higher surface temperature; frost crystals of different shapes were observed for different surface temperatures at the initial stage of the frost formation; the frost crystals newly formed on the surface of the frost layer changed with time during the frost formation process. For the case that the cold surface was maintained in no contact with the moisture air until its temperature reached -38℃, the frost crystals formed directly, no super-cooled water droplets appeared on the surface before the frost formation.