Which statement about capillary tube metering devices is correct?

The statement about capillary tube metering devices that is correct is that they are simple in design. Capillary tubes operate based on the principles of fluid dynamics and are essentially just narrow tubes that allow refrigerant to flow at a controlled rate. Their straightforward construction means they do not involve complex components or moving parts, which makes them easy to manufacture and install.

In addition, while capillary tubes do help regulate refrigerant flow, they function best at consistent load conditions and are more suited for smaller systems rather than maintaining a constant evaporator temperature across large variations in load. They are primarily used in systems where the flow rates are controlled by the characteristics of the capillary tube itself, rather than through sophisticated means, which enhances their simplicity and reliability.

Their simplicity often limits their application to smaller refrigeration units or systems rather than large commercial setups, which typically require more advanced metering devices for handling variable loads and higher efficiency needs. Consequently, while they perform their intended function effectively in appropriate contexts, they are not meant for high flow rates or large systems where complex demands cannot be met by their simple design.