Vapour-compression basics: Just before entering the expansion (throttle) valve, the refrigerant in a standard vapor-compression system is typically in which state?

Introduction / Context:
Understanding the state points around the throttling device clarifies the energy flows in the vapor-compression cycle and aids in diagnosing subcooling and flashing issues.

Given Data / Assumptions:

• Condenser rejects heat to ambient and delivers liquid at condenser pressure.
• Some designs add subcooling, but baseline condition remains near saturated liquid.
• Pressure drop across the liquid line and valve is significant; across the condenser it is small.

Concept / Approach:
The condenser condenses refrigerant vapor to liquid at high pressure. Ideally, the exit is saturated liquid or slightly subcooled liquid to avoid premature flashing before the expansion valve. This state is the proper inlet to the throttling device to ensure controlled two-phase formation in the evaporator.

Step-by-Step Solution:

Verification / Alternative check:
On a pressure–enthalpy diagram, the condenser outlet lies on or just to the left of the saturated liquid line at the condenser pressure.

Why Other Options Are Wrong:

• Wet vapour / very wet vapour: indicates two-phase mixture inappropriate for the liquid line ahead of the valve.
• Dry vapour: would imply incomplete condensation, causing poor evaporator performance and valve instability.

Common Pitfalls:
Confusing evaporator outlet (superheated vapor) with condenser outlet (liquid). Keep the cycle sequence clear.

Final Answer:
High-pressure saturated liquid