A refrigerant capillary, also known as a capillary tube or simply capillary, is a narrow and long tube used in refrigeration and air conditioning systems as a metering device. It is an essential component of systems that use the vapor compression cycle to transfer heat and cool spaces.
The primary function of the refrigerant capillary is to control the flow of high-pressure liquid refrigerant from the condenser to the evaporator. It serves as a restriction in the system, causing a pressure drop and enabling the refrigerant to change phase from a high-pressure liquid to a low-pressure, low-temperature mixture of liquid and vapor as it enters the evaporator.
The capillary tube is usually made of copper or another metal with good thermal conductivity and flexibility. Its inner diameter is very small, typically ranging from 0.5 to 2.28 millimeters (0.02 to 0.09 inches) and can be several meters (feet) in length, depending on the specific application and the refrigerant used.
The capillary tube works passively without any moving parts, and the amount of refrigerant flow is determined by its length and internal diameter. It provides a simple and cost-effective method of metering the refrigerant and controlling the cooling capacity of the system.
Though capillary tubes are widely used in smaller refrigeration systems and window air conditioners, larger systems often use more complex metering devices like expansion valves to control the refrigerant flow and system performance more precisely.