In a standard vapor-compression refrigeration system, what is the thermodynamic state of the refrigerant immediately before it enters the condenser (i.e., at the compressor discharge)?

Introduction / Context:
Identifying the correct state of the refrigerant at key points in the vapor-compression refrigeration cycle is fundamental for design, control, and diagnostics. The point immediately before the condenser is the compressor discharge, and understanding this state helps explain why condensers are sized for both desuperheating and condensation duties.

Given Data / Assumptions:

• Cycle sequence: evaporator → compressor → condenser → expansion device.
• Compressor handles low-pressure vapour and delivers high-pressure vapour.
• Real compressors add sensible superheat to the discharge stream.

Concept / Approach:
During compression, work input raises both pressure and temperature of the refrigerant. Because the gas is compressed from an evaporator outlet state (usually slightly superheated to avoid liquid slugging) to a higher pressure, the discharge temperature exceeds the saturation temperature corresponding to the condenser pressure. Therefore, the refrigerant at the condenser inlet is superheated vapour, not saturated vapour or liquid.

Step-by-Step Solution:

Verification / Alternative check:
A temperature–entropy (T–s) or pressure–enthalpy (p–h) diagram shows the maximum temperature at compressor discharge, located to the right of the saturation dome (superheated region) at condenser pressure.

Why Other Options Are Wrong:

• Saturated liquid (a) and subcooled liquid (e) occur after condensation, not before the condenser.
• Wet vapour (b) is two-phase; discharge lines do not contain two-phase under normal operation.
• Dry saturated vapour (c) would mean no superheat; real compressors deliver superheat due to inefficiencies and work input.

Common Pitfalls:
Confusing the point “before the condenser” with “after the condenser.” Remember, the condenser handles hot, high-pressure superheated vapour first, not liquid.

Final Answer:
Superheated vapour