Final answer:
The expansion device in an air conditioning or refrigeration system regulates the flow of refrigerant and reduces its pressure to allow for heat absorption in the evaporator.
Step-by-step explanation:
The expansion device in an air conditioning or refrigeration system is responsible for regulating the flow of refrigerant into the evaporator. Its primary function is to reduce the pressure of the refrigerant, which in turn cools it down before it enters the evaporator coil. This drop in pressure and temperature allows the refrigerant to absorb heat from the environment within the evaporator. There are different types of expansion devices, such as thermal expansion valves (TXVs), fixed orifice tubes, and capillary tubes, each suited to different types of systems.