Experimental Study and Fractal Analysis of Frost Crystals During Frost Formation Process

摘要

The frost crystals present needle-like shapes and dendrite growth patterns at the initial period of the frost formation on cold surfaces. They gradually turn into plane-like shapes with time disappear. After frost crystals cover the whole cold surface, the frost formation steps into the frost layer growth period. During this period, as the frost layer becomes thicker, its surface temperature can be high enough to result the frost crystals melt and fall down periodically. It is the growth pattern of the frost crystals that results in a multiple-step ascending tendency of the fractal dimension with time. The physical meaning of the fractal dimension and the volume fraction in describing the frost layer characteristics are also discussed in this paper and it is pointed out that it is necessary to introduce a fractal parameter in modeling frost formation process. The fractal dimension may well define the frost crystal shape and structure features; the volume fraction is directly proportional to the frost layer density, and has a very weak relation with the frost crystal shape and structure features.