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

• Published in: Zhileng xuebao
• Main Authors: Zhou Shengqi, Liu Yang, Li Weizhong, Qin Yan
• Format: Article
• Language: Chinese
• Published: Journal of Refrigeration Magazines Agency Co., Ltd. 2019-01-01
• Subjects: frost; relative humidity; freezing; initial frost crystal
• Online Access: http://www.zhilengxuebao.com/thesisDetails#10.3969/j.issn.0253-4339.2019.05.143

A microscopic visualization method was applied experimentally, where comparative observations of frosting processes were conductedunder the same conditionson 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 can delay frosting for 29 min in comparison with the bare aluminum surface. When the temperature decreased to ?18 ℃, the hydrophobic surface still demonstrated a satisfactory anti-frost 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.