A. Overview
Due to the frost on the surface of the evaporator in the cold storage, it prevents the conduction and dissemination of the cold capacity of the refrigeration evaporator (pipeline), and ultimately affects the refrigeration effect. When the thickness of the frost layer (ice) on the surface of the evaporator reaches a certain extent, the refrigeration efficiency even drops to less than 30%, resulting in a large waste of electric energy and shortening the service life of the refrigeration system. Therefore, it is necessary to carry out cold storage defrost operation in the appropriate cycle.
B. The purpose of defrosting
1, improve the refrigeration efficiency of the system;
2. Ensure the quality of frozen products in the warehouse;
3, save energy;
4, extend the service life of cold storage system.
C. defrosting methods
Cold storage defrosting methods: hot gas defrosting (hot fluorine defrosting, hot ammonia defrosting), water defrosting, electrical defrosting, mechanical (artificial) defrosting, etc.
1, hot gas defrost
Suitable for large, medium and small cold storage pipe defrosting:
The hot high-temperature gaseous condensate is directly entered into the evaporator without interception, and the temperature of the evaporator rises, which causes the frost layer and the cold discharge joint to dissolve or then peel off. Hot gas defrosting is economical and reliable, convenient for maintenance and management, and its investment and construction difficulty is not large.
2, water spray defrost
It is widely used in defrosting of large and medium chiller:
Periodically spray the evaporator with room temperature water to melt the frost layer. Although the defrosting effect is very good, it is more suitable for air coolers, and it is difficult to operate for evaporation coils. It is also possible to spray the evaporator with a solution with a higher freezing temperature, such as 5% to 8% concentrated brine, to prevent frost formation.
3, electric defrost
The electric heat pipe is mostly used for medium and small chillers:
The electric heating wire is mainly used for defrosting of aluminum row tube electric heating in medium and small cold storage, which is simple and easy to use for chiller; However, for the case of aluminum tube cold storage, the construction difficulty of aluminum fin installation of electric heating wire is not small, and the failure rate is relatively high in the future, the maintenance and management is difficult, the economy is poor, and the safety factor is relatively low.
4, mechanical artificial defrosting
Small cold storage pipe defrosting application:
Cold storage pipe manual defrosting is more economical, the original defrosting method. Large cold storage with artificial defrosting is not realistic, the operation of the head is difficult, physical consumption is too fast, the retention time in the warehouse is too long and harmful to health, defrosting is not easy to be thorough, may cause the evaporator deformation, and may even break the evaporator leading to leakage accidents.
D. fluorine system defrosting method selection
According to the different evaporator of the cold storage, choose a relatively suitable defrosting method. A small number of micro cold stores use the shut-off door to naturally defrost using air heat. Some high temperature library chillers choose to stop the refrigerator, open the chiller fan separately, use the fan to circulate air to defrost, and do not enable the electric heat pipe to achieve the purpose of energy saving.
1, the defrosting method of the cooler:
(1) There are electric tube defrosting and water defrosting can be selected, areas with more convenient water can prefer to choose water defrosting chiller, water shortage areas prefer to choose electric tube defrosting chiller.
(2) electric tube defrosting is mostly used in small air cooler defrosting; Water flushing frost chiller is generally configured in large air conditioning, refrigeration system.
2. Defrosting method of steel row:
There are hot fluorine defrosting and artificial defrosting options.
3. Defrosting method of aluminum tube:
There are thermal fluoride defrosting and electric thermal defrosting options.
E. cold storage defrosting time
Now most cold storage defrosting is controlled according to defrosting temperature probe or defrosting time. The defrosting frequency, time, and defrosting stop temperature should be adjusted according to the quantity and quality of the stacked goods.
At the end of the defrosting time, and then to the drip time, the fan starts. Be careful not to set the defrosting time too long and try to achieve a reasonable defrosting. (The defrosting cycle is generally based on the power supply time or the compressor startup time.)
F. Analysis of causes of excessive frost
There are many reasons that affect frost formation, such as: evaporator structure, atmospheric environment (temperature, humidity) and air flow rate. The effects on frost formation and air cooler performance are as follows:
1, the temperature difference between the inlet air and the cold storage fan;
2, the humidity of the inhaled air;
3, fin spacing;
4, inlet air flow rate.
When the storage temperature is higher than 8℃, the normal cold storage system almost does not frost; When the ambient temperature is -5℃ ~ 3℃ and the relative humidity of the air is large, the air cooler is easy to frost; When the ambient temperature is lowered, the frost formation speed decreases because the moisture content in the air is reduced.
Post time: Dec-12-2023