Research On Pneumatic Defrosting Of Air Cooler

In this paper, according to relevant literatures, the author reviewed theories of recent years about frosting, anti-frosting and defrosting of air cooler and came to the following conclusions: 1. The frosting of air cooler is owed to the joint effects of surface growth of frost and deposition of floating ice crystal; 2. Because of the larger contact angle 9 of low-energy surface, the phase transformation energy barrier of vapor is higher than those of high-energy surface, and the frosting of air cooler is effectively restrained; 3. Since frosting is inevitable so long as some physical factors are satisfied, it will enlarge the resistance of airflow, cut down the airflow rate of air cooler and reduce the coefficient of heat transfer. In order to keep the refrigeration system run smoothly, frost must be removed.The traditional defrosting method of air cooler is to "melt" frost. In this paper, based on my experiments, the mechanism of pneumatic defrosting of air cooler was studied through the application of Thermodynamics, Heat and Mass Transfer, Classical Theory of Nucleation, Boundary-layer Theory, the Theory on Gas Dynamics. And the author pointed out that frost would be eliminated when the drives of airflow was greater than the adhesion work of frost, rather than the result of the stagnant heat of airflow "melted" frost. Those drives include:1. Head on impact of airflow.2. Superficial friction of airflow.3. The strike of condensed ice crystal.Besides, low temperature and high-speed air stream would heat frost with higher temperature.In this paper, the contrast experiments and theoretical researches on frosting and defrosting on low-energy surface and common metal surface are carried out simultaneously. Low-energy surface restrains the frosting of air cooler, and the adhesion work of unit-area frost on low-energy surface is smaller than that on common metal surface, so pneumatic defrosting becomes easier.In the end, the economic viability and feasibility of pneumatic defrosting are demonstrated, and the application prospect is forecasted. Pneumatic defrosting is a brand new kind of defrosting method. In order to apply this method into reality, further research is needed.