Why vacuum the refrigeration system? How to vacuum?
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Why does the refrigeration system emphasize vacuuming? Let's start with the composition of the air, as shown in the figure below: nitrogen takes up 78% of the air; Oxygen: 21%; Other gases are 1%. Now let's analyze, what is the influence of the composition of these gases on the refrigeration system after entering the refrigeration system?
1. Nitrogen effect on refrigeration system
The first thing we need to know is that nitrogen is an incondensable gas. The so-called non-condensable gas refers to the gas circulation in the system with the refrigerant, does not condense with the refrigerant, also does not produce the refrigeration effect.
The existence of non-condensable gas will do great harm to the refrigeration system, which is mainly manifested in the increase of system condensing pressure, condensing temperature, compressor exhaust temperature and power consumption. Nitrogen goes into the evaporator and cannot evaporate with the refrigerant; It also occupies the heat transfer area of the evaporator, making the refrigerant unable to fully evaporate and reducing the refrigeration efficiency. At the same time, too high exhaust temperature may lead to the carbonization of lubricating oil, affect the lubrication effect, and seriously burn down the refrigeration compressor motor.
2. The effect of oxygen on the refrigeration system
Oxygen and nitrogen are also non-condensable gases. We have analyzed the hazards of non-condensable gases above, and we will not repeat them here. However, it is worth noting that compared with nitrogen, if oxygen enters the refrigeration system, there are also these hazards:
1). The oxygen in the air will react with the frozen oil in the refrigeration system to form organic compounds, which will eventually form impurities and enter the refrigeration system, causing fouling and other adverse consequences.
2), oxygen and refrigerant, water vapor and other easy to produce acid chemical reaction, so that the oxidation of frozen oil, the acid will damage each component of the refrigeration system, damage the insulation layer of the motor; At the same time, these acid products will remain in the refrigeration system, without any problems at first, and eventually lead to compressor damage over time. The picture below illustrates these problems very well.
3. Effects of other gases (water vapor) on refrigeration systems
Water vapor affects the normal operation of refrigeration system. The solubility of freon liquid is the smallest, and the solubility decreases as the temperature decreases. The most direct impact of water vapor on the refrigeration system is shown in the following three aspects:
1) There is water in the refrigeration system, and the first effect is the throttle structure. When the water vapor enters the throttle structure, the temperature rapidly decreases and the water reaches the freezing point, resulting in icing and blocking the fine through-hole of the throttle structure, resulting in the fault of ice blocking.
2) Corrosive pipe steam enters the refrigeration system, increasing the water content of the system and causing corrosion and blockage of pipes and equipment.
3) Produce sludge deposits. In the process of compressor compression, water vapor encounters high temperature and frozen oil, refrigerant, organic matter, etc., resulting in a series of chemical reactions, resulting in motor winding damage, metal corrosion and sludge deposition.
To sum up, in order to ensure the effect of refrigeration equipment and extend the life of refrigeration equipment, it is necessary to ensure that there is no non-condensable gas in refrigeration, and vacuum the refrigeration system.
4. Operation method of pumping vacuum in refrigeration system
Here we will talk about the method and process of vacuuming. Since only the materials for vacuuming of household air conditioners are available, the vacuuming equipment below takes household air conditioners as an example. In fact, the vacuuming operation of other refrigeration equipment is similar, and the principle is the same.
1) Before operation, check that the vacuum pump sealant pad is not damaged and the vacuum gauge pressure gauge is reset to zero. The fluoridated tube, vacuum gauge and vacuum pump are combined together.
2) Unscrew the nut from the valve at the fluoridated orifice and the fluoridated tube to the fluoridated orifice. Turn on the vacuum gauge, then turn on the power switch of the vacuum pump and start pumping. The vacuum degree of normal system should be below -756mmhg. Vacuum pumping time should be determined according to the size of the refrigeration system and the size of the vacuum pump.
3) After the pumping operation, quickly remove the fluorimeter and vacuum gauge, and then fully open the valve.