自然对流条件下冷表面结霜的实验研究

Experimental Investigation on Frost Formation on Cold Surface under Natural Convection Conditions

本文利用微观可视化观测方法,实验对比研究了裸铝(接触角78°)、疏水(接触角141°)和亲水(接触角26°)3种特性表面结霜过程。结果表明,当相对湿度为26%,表面温度为-10℃时,相比于裸铝表面,疏水表面可以延迟结霜29 min;当温度降至-18℃,疏水表面仍具有较好的抑霜效果。1 h后,疏水表面上的霜层高度仅为裸铝表面上霜层高度的68%。当表面温度为-26℃时,3种不同接触角的表面上初始霜晶的形态差异较大,疏水表面倾向于形成更加稠密的沿水平方向生长的枝状霜晶并向片状转变,而亲水表面则倾向于形成沿竖直方向生长的稀疏的针状霜晶,随着空气中水蒸气向霜晶扩散凝华,针状霜晶从顶部向底部逐渐向片状霜晶转变。

A microscopic visualization method was applied experimentally,where comparative observations of frosting processes were conducted under the same conditions on bare aluminum and hydrophobic surface with contact angles of 78°and 141°,respectively.The hydrophilic surface with a contact angle of 26°,whose initial ice crystal shapes were observed and contrasted,was also included.Results showed that under the condition of low relative humidity at a surface temperature of-10℃,the hydrophobic surface was delayed frosting for 29 min in comparison with the bare aluminum surface.When the temperature was decreased to-18℃,the hydrophobic surface was still demonstrated a satisfactory antifrost effect.After an hour,the frost height on the surface of the hydrophobic surface was only 68%of the frost height on the bare aluminum surface.Furthermore,at the surface temperature of-26℃,there were relatively large differences in the shapes of initial ice crystals for the three surfaces that had different contact angles.The hydrophobic surface tended to form denser dendritic frost crystals,which grew horizontally and transformed to plates,whereas the hydrophilic surface was inclined to form sparse needle-like crystals that grew in the vertical direction.As the water vapor in the air diffused into the frost crystals,then needle-crystals gradually transformed to sheet forms from top to bottom.