A refrigerant capillary, also known as a capillary tube or expansion capillary, is a type of throttling device used in refrigeration and air conditioning systems. Its primary function is to regulate the flow of refrigerant from the high-pressure side to the low-pressure side of the system. This controlled flow creates a pressure drop, which enables the refrigerant to undergo a phase change (from liquid to vapor) and absorb heat from the surrounding environment.
The capillary tube is a small-diameter, thin-walled tube typically made of copper. Its internal diameter can range from a few millimeters to a few tenths of a millimeter, depending on the specific application and system requirements. The length of the capillary tube also varies based on the refrigeration system's design and the desired operating characteristics.
As the high-pressure liquid refrigerant passes through the capillary tube, it experiences a drop in pressure due to the tube's small diameter and length. This pressure drop causes the refrigerant to expand and evaporate, converting it into low-pressure, low-temperature vapor. This cold refrigerant then enters the evaporator coil, where it absorbs heat from the surrounding air or the targeted space, thereby providing cooling.
The capillary tube is a simple and cost-effective method of controlling the flow of refrigerant in small-scale refrigeration and air conditioning systems, especially in domestic refrigerators and window air conditioners. However, in larger commercial systems, other types of expansion devices like thermostatic expansion valves (TXVs) are often preferred due to their ability to provide more precise control over the refrigerant flow based on system conditions.