What is a capillary tube in refrigeration systems?

A capillary tube in refrigeration systems is indeed a passive device that drops pressure in the system. It functions as a metering device that allows the refrigerant to expand and reduce pressure as it flows through the tube, which is typically made of a small-diameter, long length of tubing. This pressure drop is essential for the refrigeration cycle, as it enables the refrigerant to change from a high-pressure liquid to a low-pressure vapor, facilitating the absorption of heat from the surrounding environment.

In specific applications, the capillary tube is used in systems with low cooling capacities and operates without the need for external control mechanisms. The design of the capillary tube allows the refrigerant to flow at a controlled rate, maintaining the proper balance of refrigerant needed for efficient operation, while the temperature and pressure decrease naturally due to the physical properties of the tube and the refrigerant.

This distinguishes it from other options like a device that actively controls pressure or a gauge for measuring refrigerant flow, which play different roles in the refrigeration system. A capillary tube does not actively manage pressure but allows pressure drops solely through its design. Additionally, it is not a gauge, as it does not measure flow but rather facilitates the flow and pressure drop of refrigerant.