1. About the Capillary

As the throttling mechanism of refrigeration system, capillary is the simplest one. Because of its competitive price and flexible selection, it is widely used in small refrigeration devices ( such as mini water chillers, mobile refrigerators, wine coolers) . Recently, it is also used in large refrigeration capacity units.

Basically, the compressor-based small cooling systems consists of a mini compressor, condenser, throttling device, and evaporator.  Capillary is one of the most commonly used throttling devices in refrigeration and air conditioning systems. A capillary is a piece of copper tube with a small inner diameter. It’s long and coiled several times, so it takes up less space. Internal diameters of capillaries for refrigeration and air conditioning applications range from 0.5 to 2.28 mm (0.020 to 0.09 in). Capillaries are used as throttling devices in mini water chillers, deep coolers, water coolers, and air conditioners, etc.

When the refrigerant leaves the condenser and enters the capillary, there is a sudden drop in pressure due to the small diameter of the capillary. In the capillary, the pressure drop of the refrigerant is not due to the orifice but to the small opening of the capillary tube. The decrease in refrigerant pressure through the capillary tube depends on the diameter of the capillary tube and the length of the capillary tube. The smaller the diameter and the longer the length of the capillary tube, the greater the pressure drop as the refrigerant passes through it.

IMPORTANT: Capillary length and diameter size is very important, it directly affects the liquid refrigeration circulation and compressor refrigeration efficiency, so do not arbitrarily replace the capillary tube, if the capillary tube is bad, you should find the relevant information parameters, selection of suitable capillary tube.

2. Capillary Advantages

Here are some advantages of using capillaries as throttling devices in refrigeration and air conditioning systems:

1) Capillaries are very simple devices that are easy to make and inexpensive.

2) Because no receiver is required in these systems, capillaries limit the maximum amount of refrigerant that can be charged into the refrigeration system.

3) When the compact refrigeration unit is stopped, the pressure at both ends of the capillary becomes the same and remains constant throughout the refrigeration cycle. This means that when the equipment is stopped, the pressure on the suction side and the discharge side of the compressor are the same. 

Therefore, when the compressor restarts, it does not have much load because it does not have to overcome very high pressure. Therefore, a compressor motor with less torque can be selected to drive the compressor, thus reducing the cost of the compressor. This, together with the above two advantages, helps to reduce the overall cost of refrigeration and air conditioning systems.

3. Capillary Working Principle 

The capillary works by creating a pressure difference between the high-pressure and low-pressure sides of the compressor. The refrigerant is compressed by the compressor, which increases its temperature and pressure. The high-pressure refrigerant is then directed to the capillary tube, which is located in the evaporator section of the chiller. As the refrigerant passes through the narrow diameter of the capillary tube, the pressure drops, causing a decrease in temperature.

Under normal operating conditions of refrigeration equipment, the refrigerant pressure on both sides of the capillary decreases, but when the equipment is stopped, the refrigerant pressure on both sides of the capillary is balanced. For this reason, when the compressor is restarted, there is not much load. Also, for this reason, one could not overfill the refrigeration system with refrigerants and receivers were not used.

Capillaries are non-adjustable devices, which means that the flow of refrigerant through them cannot be controlled as in automatic throttles. Thus, the flow of refrigerant through the capillary varies as the surrounding conditions change. For example, the flow of refrigerant through the capillary changes due to increased pressure in the condenser due to high atmospheric pressure and reduced pressure in the evaporator due to a small refrigeration load. Therefore, capillaries are designed for certain environmental conditions. However, it can work well in a wide range of conditions if chosen properly.

From the physical principle, that is, industrial chiller, refrigerator, portable air conditioner and other refrigeration equipment used in the inner wall of the capillaryof water adsorption is a certain but the finer the capillary water absorption by the air pressure is less significant, so the finer the capillary perpendicular to the surface of the water under the circumstances of the degree of absorption of the stronger.

In this refrigerator is especially obvious, because the refrigerator is generally used in the capillary is very thin, if the refrigeration system or the refrigerant in the water content is too large, it is easy to ice blocking phenomenon, so the refrigerator is generally used in the refrigerator R12, R134A and other water content is relatively small refrigerant, the use of capillary in the small-scale industrial water chillers, ice and water machine, refrigerator relative to the refrigerator to be much better, because the general use of the capillary tube of the The inner diameter of the capillary tube relative to the refrigerator are relatively large.

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