Abstract: The frosting behavior in the cooling process of the copper flake specimen as cold surface was observed microscopically. In order to avoid the obstacle of the frost layer growth at the specimen edge to the observing area, the specimen was bent to an arch to observe the frosting phenomena at the arch apex. The experiments showed that the initial rate of the frost layer formation is different from the subsequent growth rate. In the frost layer growth process, in addition to the melt-back phenomenon of the surface frost branches, there were periodic overall collapse of the outer frost layer. Analysis suggested that the breeding point distribution and density of the initial frost layer are the origins of difference of the frost layer growth rates, and the collapse of the frost layer is the result of the melt-back and recomposition of the initial loose frost layer.

Key words: heat and mass transfer, cold surface, frost formation, growth rate, microscopic observation