A MICROSCOPIC OBSERVATION OF TRANSIENT FROST FORMATION PROCESSES AND THEIR ANALYSIS BY USE OF PHASE CHANGE DYNAMICS

摘要

Frost formation is a common phenomenon under cryogenic conditions. Without effective control, frost deposition may result in serious malfunction of cryogenic equipment and systems. In this paper, an experimental study on the initial period of frost deposition, the crystal morphology and its variation with time of frost ice are carried out of frost formation on a vertical plate by microphotographics. The phase change, the initiation of frost formation and the different shapes of frost crystal at various time stages are described. It is proved from the present study that the main factors that affect frost formation in natural convection are plate temperature, air humidity and air temperature. In order to explain the frost thickness difference under various conditions, a frost thickness growth driving force is defined and compared with the experimental results. Hydrophobic surfaces are used to release frost formation on cold surfaces and the results show that these surfaces can retard the formation and growth of frost significantly.