Experimental Study And Theory Analyse On Frost Fromation

Frost is a familiar phenomenon in refrigeration, cryogenics and spaceflight, it brings many adverse affect. In this paper, frost growth was studied by experimental and theory method, the environmental factors influence frost growth was confirmed and the forecast of frost growth was given, all this work establish a foundation for restrain the frost growth and defrost.First, the experimental equipment was designed, all this system was consisted in four part:Refrigeration equipment, thermoscope, picture-collection system and temperature-humidity control system. By this system, environment temperature and humidity, cold surface temperature and contact angle can be adjusted for observing frost growth at different circumstance. The result indicate that cold surface temperature mainly influence frost height and shape; humidity have effect both on frost height and density; when copper surface was covered by wax and C 3 O3H8 layer, frost growth on both surface was delayed, frost height obviously lower than copper surface, ice crystal distribution was also thin.The study on nuclear process indicates that super saturation and contact angle has obviously influence on nuclear speed. Nuclear speed increase rapidly while super saturation was lower; and when super saturation was higher, it increase slower. The theory of hydrophilic surface restrain frost growth was that nuclear was delayed by changing local super saturation, as for hydrophobic surface, it was because high contact angle make nuclear hard to carry on.The Analyses on frost image by box-counting method express that full growth frost was a fractal structure ranging in some scale. This character implicate that frost structure was arranged, there was a scale, when measurement unit was lager than this scale, the frost was uniform; otherwise, frost was self similar, frost growth can be described by percolation model. Simulation result indicates that the conductivity increase slowly at higher porosity; it increase rapidly when porosity was near to critical value. Vapor diffusion coefficient increase slowly at low porosity; but it increase swiftly at higher porosity for one pore maybe unite...