Currently the major refrigerants that are used includes HCFC gas: refrigerant R22. HFC gas: refrigerant R134a, R410a,R290,etc. As far as air conditioning is concerned, the principle of system circulation is generally the same as that of refrigerator freezer. The symptoms of air conditioning system lacking fluoride are similar to those of refrigerator freezer. Many people say that air conditioning lacks fluoride and the thick tube (return pipe) will frost. Under rated air-conditioning operating conditions, the lack of fluorine in the air-conditioning system and the frost phenomenon of the return air pipe are not easy to occur. After the lack of fluorine, the temperature of the return air pipe will only be higher than normal, that is, the temperature of the return air superheat is higher than normal. At this time, common sense of the refrigeration cycle principle, It is certain that the fluorine return air pipe can still frost. The indoor temperature is low or the ventilation of the internal machine is poor; the ambient temperature is low and the machine is running for a long time. It is possible to fill the evaporator up to the air return tube, but it is not always true that the lack of fluorine will cause frost.
How does the air return pipe of the refrigeration appliance frost? Under what circumstances will frost? Scientific ethics and logic must be used to explain this problem.
1. Household air conditioner
Taking R22 refrigerant as an example, its saturation gauge pressure at 0 degrees is 0.399MPa. When this pressure is lower than the corresponding temperature of 0 degrees, that is, the crystallization point (freezing point) of water, the outer surface of the tube will of course first Frosted after condensation, this is normal physical response and changes. Therefore, after the low pressure of the household air conditioner is lower than 0.399MPa, the connecting pipe will start to frost.
2. Household refrigerator
The refrigerant used in the freezer is R12, R134a, R600a, etc. When the saturation pressure of R12 refrigerant is less than 2.11kg, the saturation pressure of R134a refrigerant is less than 0.193MPa, and the saturation pressure of R600a refrigerant is less than 0.058MPa gauge pressure, The saturation temperature is at or below 0 degrees. When the temperature is below 0 degrees, if more refrigerant is added to the system at this time, the refrigerant in the evaporator cannot be sufficiently heat exchanged (endothermic) to produce boiling (evaporation), If the superheat of the return air is too small, the liquid refrigerant will enter the return air pipe and even the compressor, which will inevitably cause frosting on the return air pipe and the compressor.
3. Cold storage
The difference between the cold storage is that, according to the thermodynamic properties (physical and chemical properties) of the refrigerant used, as well as the evaporating temperature and return superheat specified by the system, when the superheat is too small, such as the opening of the expansion valve is too large, or the system When there is too much refrigerant and the liquid level in the evaporator is too high (too much), excessive moisture and moisture will be entrained in the return air, and the compressor may cause liquid shock and frost.
These are different systems. Under different refrigerants and different corresponding pressures and temperatures, different reactions occur, which are also specific thermal conditions of the refrigeration system. This is a basic problem that is easy to understand. Don't misunderstand and confuse!