To classify a metering valve as an actual expansion valve what must happen across the valve?

To classify a metering valve as an actual expansion valve, it is essential for several conditions to occur across the valve, which is correctly indicated by the choice provided.

Firstly, there must be a pressure drop across the valve. This drop is crucial as it indicates the reduction in refrigerant pressure as it passes through the valve and transitions into a lower pressure area. The importance of this is tied to the function of the expansion valve in a refrigeration or air conditioning system where the high-pressure liquid refrigerant is converted into a low-pressure mixture, allowing it to evaporate and absorb heat.

Secondly, a temperature drop is also expected to occur as a consequence of the pressure drop. When a refrigerant experiences a drop in pressure, it typically results in a decrease in its temperature due to the Joule-Thomson effect. This cooling effect is a defining characteristic of an expansion process, essential in the refrigeration cycle.

Finally, an increase in velocity can occur as the refrigerant moves from a high-pressure area to a low-pressure area through a constricted pathway within the valve. This increase in velocity is a result of the conservation of mass in fluid dynamics, where fluid must accelerate as it passes through a narrowing.

The inclusion of all these factors is what character