What type of device controls the flow of refrigerant in a refrigeration system based on an electric signal?

A solenoid valve is the correct answer because it operates by using an electric signal to open or close the valve, controlling the flow of refrigerant in a refrigeration system. When the coil of the solenoid is energized, it generates a magnetic field that moves a plunger, thereby changing the valve's state to either allow or restrict the flow of refrigerant. This ability to respond to electric signals makes solenoid valves ideal for applications requiring precise control over fluid dynamics based on system conditions or operational commands.

In contrast, a pressure relief valve operates based on system pressure, opening to release excess pressure without being controlled by an electric signal. A ball valve uses a spherical obstruction to manage the flow but typically requires manual operation or a mechanical actuator rather than an electrical signal. A capillary tube is a passive device that aids in refrigerant flow regulation through friction and does not actively respond to electric signals at all.