When the evaporation temperature of the cold storage refrigeration system is lower than 0 ° C, a frost layer will appear on the surface of the evaporator, affecting the heat transfer efficiency. Therefore, regular defrosting is also a very important part of cold storage maintenance. There are many ways to defrost. At present, cold storage construction manufacturers mainly use five methods: artificial defrosting, electric defrosting, hot air defrosting, water defrosting, hot air water defrosting.
1. Manual defrosting is to manually remove the frost layer on the surface of the evaporator discharge tube. This method can be carried out without stopping the refrigeration equipment. This method is time-consuming and laborious, and the defrosting effect is poor.
2. Electric defrosting is to install an electric heater on the evaporator to defrost with electric heating. During defrosting, stop the compressor or stop feeding liquid to the evaporator. Electric defrosting has the advantages of low cost and easy control, but the operation cost is high. Generally used for defrosting of cold storage equipment, not for defrosting of refrigeration equipment. For different temperatures, the requirements for insulation skills must be different, and the required cooling capacity must also be different. The establishment of cold storage needs to be customized according to the customer’s actual application environment and application, unless there is no special need to take the road of standardization.
3. Hot gas defrosting is the use of superheated refrigerant steam discharged by the compressor to release heat in the evaporator and melt the frost layer on the surface of the evaporator. Hot gas defrosting system is complicated and cost is high. But the defrosting effect is better. When used in the ammonia system, the oil accumulated in the evaporator can also be discharged into the drain or low pressure circulation reservoir. In the process of hot gas defrosting, the pressure is generally controlled at 0.6MPa. Try to use high-pressure gas discharged from a single stage compressor for defrosting. Winter can be appropriate to reduce the cooling water or reduce the number of condensers, increase the exhaust temperature, shorten the defrosting time. For ammonia systems, hot ammonia for defrosting should be connected to the exhaust pipe of the oil separator.
4. Water defrosting is to spray water on the surface of the evaporator with a sprinkler device to melt the frost layer. Water defrosting system has complex structure and high cost, but good effect and low cost. Water defrosting can only remove the frost layer on the outer surface of the evaporator, and can not solve the adverse effect of oil accumulation in the evaporator on heat transfer. The most important thing is the cold storage board, which is usually produced in advance by the cold storage board manufacturer and has a fixed length, width and thickness. 100mm thick cold storage board is usually used for high and medium temperature cold storage, 120mm or 150mm thick cold storage board is usually used for low temperature storage and freezing storage.
5. Hot air water defrosting is the two methods of hot defrosting and water defrosting used at the same time, which concentrate the advantages of both, and can quickly and effectively remove the frost layer on the surface of the evaporator and eliminate the accumulation of oil inside the evaporator. When defrosting, the hot gas is first sent into the evaporator to separate the frost layer from the surface of the evaporator, and then the water is sprayed to quickly wash off the frost layer. After the water supply is cut off, the surface of the evaporator is “dried” by hot air to prevent the surface water film from freezing and affecting the heat transfer. In the past, cold storage board manufacturers mainly used polyethylene and polystyrene as materials. Now there is a better performance of polyurethane sandwich board. Polystyrene foam insulation material density is low, can not be insulated. They are usually used in special equipment. Polyethylene is a good raw material. Through a certain ratio, can be foamed out of the appropriate density, insulation effect is good, strong bearing capacity of the insulation material. Polyurethane plate is better, has better insulation function and does not absorb moisture, but this cold storage price is slightly higher.
Post time: Dec-08-2023