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https://www.sstubecn.com/stainless-steel-tubing/stainless-steel-capillary-tubes.html

Capillary refers to a tube with a very small inner diameter. In an industrial chiller system, a capillary refers to a copper tube within 1-2 mm. What is the role of the capillary in the chiller?

The metal capillary tube is one of the throttling devices of the chiller. The role of the capillary in the chiller is to throttle. The principle is simple, in order to increase the "flow resistance of the liquid flowing through the capillary". The ultimate goal is to control the amount of liquid supplied. However, while increasing the resistance to liquid flow and controlling the amount of liquid supplied, the capillary also has a depressurizing effect. When the high pressure refrigerant flows through the capillary, it changes from a high pressure liquid to a low-pressure high-temperature gas.

Specifically, the inner diameter and total length of the chiller throttling capillary and the nominal pressure difference between the inlet and outlet are all factors influencing the chiller throttling capillary. However, specific calculations require integrated cooling temperatures as well as evaporation temperatures, evaporation pressures, and the like. The evaporation pressure should be the same as the capillary outlet pressure.

By obtaining the pressure difference between the inlet and outlet, it is possible to obtain the values of the inner diameter and the length of the capillary, and then select the corresponding capillary. In most cases, this calculation does not have a fixed value, and the experimental values obtained by each chiller manufacturer may be different and complicated.

The capillary can adjust the amount of liquid supplied as well as throttling and depressurization. However, before the chiller leaves the factory, the length and inner diameter of the capillary should be determined and configured, rather than the customer's own calculation and installation, so the customer does not have to worry. However, when the first actual use and trial operation of the machine, it can also be slightly adjusted to meet the actual needs.

In addition, the stainless steel capillary tube is mainly used in a small chiller system with a small cooling capacity. The selected capillary has a small inner diameter and a long length, and the flow rate of the refrigerant flowing through the capillary is naturally small and the pressure is lower. The opposite is true. The value of the capillary inner diameter (diameter) and the length are determined according to the actual needs of the chiller.

Most of the chillers with large cooling capacity use expansion valves as throttling devices, and the expansion valves are installed between the refrigerant tank and the evaporator to throttle and reduce the pressure. The expansion valve allows the refrigerant that has been returned to the chiller system and has a relatively high temperature and relatively high pressure to become a low-temperature low-pressure refrigerant vapor through the expansion valve, and then enters the evaporator to absorb heat to achieve a cooling effect.