Experimental Study of Frost Crystal Dendrite Growth On a Cryogenic Cold Surface Under Natural Convection Conditions

Quantitative measurements were carried out of the dendrite frost crystal growth under natural convection conditions on a frozen water drop sitting on a cold surface whose temperature is as low as-190 degrees C to study the effects of cold surface temperature, wet air state and original water drop size. In order to classify the influences of different cold surface temperature regions, the frost crystal dendrite growth of both ordinary-low and cryogenic cold surface temperatures were investigated. It was found that the cold plate surface temperature has a direct influence on frost formation mechanism. Decreasing the cold surface temperature for ordinary-low cold surface temperatures will enhance and for cryogenic cold surface temperatures will suppress the frost crystal dendritic growth of the frozen water drop. The measurements disclosed that the length of the longest frost crystal dendrite grows almost linearly with time, esp. in the early stage. The effects of the water drop sizes on the longest frost crystal dendrite growth become more and more obvious as the cold surface temperature decreases. The influence of air relative humidity on the frost crystal dendrite growth is something similar to that of air temperature under given conditions, since their change both changes the absolute air humidity. A very peculiar phenomenon, i.e. the influence of wet air state on frost crystal dendrite growth is not monotonous, was observed. These findings are important for understanding and studying the frost formation and growth, especially the initial frost formation period, on low temperature surfaces.