| An attempt was made to clarify the fundamental nature of the crystal growth period of frost formation phenomena. Experimental observations show that frost formation during the crystal growth period is best characterized by linear crystal growth. A suitable theory was developed by using the principles of crystallization and nucleation theory. The agreement of this theory with experiment was demonstrated.;During the crystal growth period, vapor diffusion through the void portions of the frost layer is found to be less than 10% of the total mass flux through the air boundary layer in most cases except for very low plate temperatures.;An expression for the initial volumetric ratio of frost columns, which is the only empirical coefficient used in the analysis, was developed based on the experimental results.;The temperature variation inside the frost layer is calculated by using the heat flux problem solution. The frost surface temperature tends to rise rapidly with respect to time and then slows down while asymptotically approaching the melting point.;The effects of four dominant parameters on frost formation, namely plate tem-perature, air temperature, air humidity ratio and Reynolds Number, are demonstrated through several frost formation properties such as frost surface temperature, frost height, frost deposition rate, frost density, heat flux during frost formation, effective frost thermal conductivity, vapor diffusion in the frost layer and the volumetric ratio of frost columns.;Instead of using the experimental and empirical correlations of frost density found in the literature, ice crystal density results under different ambient conditions measured by cloud physicists are found to be more suitable to be used in the theory of crystal growth period of frost formation. Frost column density is found to closely follow the sublimation density of ice crystals at the frost surface temperature.;Effective frost thermal conductivity that was developed depends not only on frost density but also on the water vapor diffused through the void portions of the frost layer. |
