Observations of early-stage frost formation on a cold plate in atmospheric air flow

The present study is conducted to investigate the frost formation on a cold plate in atmospheric air flow by means of experimental and theoretical methods. In order to provide observations for the early stage of the frost growth process, a microscopic image system is used to record the pattern and the thickness of the frost layer per five seconds after the onset of frost formation. In this study, a multiple-step ascending frost growth pattern caused by melting of frost crystals at the frost surface has been observed. Effects of velocity, temperature and relative humidity of air (V, T_a and φ) are studied, and the surface temperature of the cold plate (T_w) is also varied. The considered ranges of these dominant variables are: 2≤V≤13 m/s. 20≤T_a≤35°C, 40 percent ≤φ≤80 percent, and -13≤T_w≤-2°C. The theoretical model presented by Cheng and Cheng [22] for predicting the frost growth rate during the frost layer growth period is verified. Results show that the predictions of frost growth rate by the model agree with the experiment data, especially for the frost layer growth period.