Refrigerants can be divided into three categories: sing […]
Refrigerants can be divided into three categories: single working fluid refrigerants, non-azeotropic mixed refrigerants, and azeotropic mixed refrigerants.
No matter whether the single-working-substance refrigerant is gaseous or liquid, its composition will not change, so it can be charged into gaseous state when charging refrigerant.
Although the composition of the azeotropic refrigerant is different, because the boiling point is the same, the composition of the gas and liquid is the same, so it can be charged into gas;
Non-azeotropic refrigerants have different boiling points, so liquid refrigerants and gaseous refrigerants are actually different in composition. At this time, if gas is added, it will inevitably lead to different refrigerant components, such as only a certain gaseous state. Refrigerant, so only liquid can be added.
In other words, non-azeotropic refrigerants must be added with liquid, and non-azeotropic refrigerants start with R4. This type of liquid must be added. Common non-azeotropic refrigerants are: R40, R401A, R403B, R404A, R406A , R407A, R407B, R407C, R408A, R409A, R410A, R41A.
As for other common refrigerants, such as: R134a, R22, R23, R290, R32, R500, R600a, no matter how to add gas or liquid, it will not affect the composition of the refrigerant, so how convenient it is to come.
We need to understand that if the refrigerant charge in the refrigeration system is too low, the cooling capacity will decrease, the input power will decrease, the EER will decrease, and the equipment life will be shortened. If the refrigerant is charged too much, the cooling capacity will decrease, the input power will increase, the EER will decrease, and the equipment life will be shortened.
This method does show that there are bubbles that indicate a lack of refrigerant, but we must understand that the pressure loss of the liquid pipe can also cause bubbles. If the pressure loss of the liquid pipe is large, the liquid refrigerant will flash into a gas, and the flash gas will reduce the flow of the refrigerant when flowing through the expansion valve and will also corrode the expansion valve. If the subcooling of the system is small, the pressure loss can easily produce bubbles seen in the sight glass. Remember, if there is no liquid but steam, it will be transparent when seen in the sight glass.
If you have experience or careful observation of refrigeration engineers, you will find that when the system is charged correctly, bubbles or flashes can also be seen in the sight glass. This is because the resistance in the liquid pipe in front of the sight glass causes a pressure drop, causing the refrigerant to flash. If the expansion valve is unstable or fluctuates with liquid, the expansion valve opens sharply, and the flow rate increases to produce enough pressure drop to cause the outlet of the liquid reservoir to flash. The sharp change in condenser pressure is also the cause of flash.
For example: suddenly changing the fan speed in a cold storage can easily change the condensing temperature from 5.5°C to 8°C. At this time, the liquid temperature in the liquid reservoir will be higher than the saturation temperature corresponding to the changed condensation pressure, and evaporation will occur at this time, and the evaporation will not end until the liquid temperature drops below the saturation temperature again.
This method is believed to be frequently used by many refrigeration practitioners. However, we should note that if the condensing air volume and evaporating air volume are not satisfied, the test refrigerant pressure will be affected. If the condensing air volume is insufficient, the high pressure will be very high, and if the evaporation air volume of the expansion valve system is insufficient, the low pressure will be very low.