Investigation Of The Frosting Performance And Improvement Of The Defrosting Method For An Air-cooler Under Low Temperature Condition

The mathematical model was proposed in this paper on the frosting performance of an air-cooler in one freezing room of a poultry enterprise in Huazhong area. To improve the working performance of the air-cooler, further studies were carried out on the factors that affecting the area of heat transfer, the coefficient of heat transfer and air side pressure drop during a frosting process. The characteristics of frost growth were analyzed under different inlet air temperature, relative humidity and velocity. The comparison of the calculated thickness of the frost layer shows good agreement with the experimental date. The calculated results show that the inlet air temperature and the relative humidity of the inlet air have obvious influence on the frosting process. Based on the investigation, the disadvantages of present defrosting method (Hot Ammonia-Water Defrosting) were analyzed.The energy consumption of the refrigeration system has a strong connection with the cost of a large-scale enterprise. In order to insure the air-cooler running economically under the frosting condition, the defrosting method of the air-cooler in the freezing room was studied in this paper. An improved way was proposed which can make the refrigeration system running at higher efficency with lower first cost and energy consumption. The defrosting device installed at the return vent of the air-cooler was described in detail. It was proved that the improved defrosting method is feasible and effective. It would be helpful to solve the problem of non-continuous freezing, cut down defrosting time, and increase the efficiency of refrigeration equipment. Results from the study prove that the improved defrosting method can save 80505 Yuan RMB of electricity charge each year for one freezing room, and cause smaller variations on the evaporating temperature and coefficient by 1 ～2%. With the improved defrosting method, the refrigeration capacity and electricity charge per piece of production would decreased by 8.33% and 10.18%, respectively. Moreover, it can be concluded that with the improved defrosting method the heat transfer coefficient of the investigated air cooler and its refrigeration capacity are increased after analyzing the dates from practice running and adjusting. The research on the frosting performance of low-temperature air-cooler and improvement of its defrosting method would be of important guidance for design and maintenance. It would be helpful to discuss energy-saving measures for the refrigeration system. In addition, cold-storage enterprise would benefit a lot from lowering the first cost, enhancing economy profits and saving energy.