In a standard vapour-compression refrigeration cycle, what is the thermodynamic state of the refrigerant immediately after passing through the condenser (i.e., at the condenser outlet before the expansion device)?

Difficulty: Easy

Correct Answer: Saturated liquid

Explanation:


Introduction / Context:
Recognizing refrigerant states at key points in the vapour-compression cycle is vital for sizing heat exchangers and protecting the compressor. After compression, the hot superheated vapour enters the condenser, where it is first desuperheated and then condensed to liquid before throttling.


Given Data / Assumptions:

  • Ideal cycle description without deliberate subcooling.
  • Condenser rejects heat to ambient until condensation is complete.
  • Pressure is approximately constant across the condenser.


Concept / Approach:
Within the condenser, three regions may exist: desuperheating, condensation (phase change at essentially constant temperature for a pure refrigerant), and sometimes subcooling. The minimum requirement before the expansion device is liquid at saturation; subcooling is beneficial but not mandatory in the idealized description.


Step-by-Step Solution:

1) Compressor discharge is superheated vapour at high pressure.2) Desuperheating region lowers temperature to the saturation temperature at condenser pressure.3) Phase change region removes latent heat → saturated liquid at outlet (ideal case).4) Optional subcooling further lowers liquid temperature below saturation.


Verification / Alternative check:
On a p–h diagram, the condenser outlet lies on the saturated liquid line (or slightly to the left if subcooled). The expansion valve requires liquid to avoid flash-gas before the evaporator inlet.


Why Other Options Are Wrong:

  • Wet vapour and dry saturated vapour describe states before full condensation.
  • Superheated vapour is the condenser inlet, not outlet.
  • Subcooled liquid may occur by design, but “always subcooled” is not universally true.


Common Pitfalls:
Confusing the condenser outlet with the compressor discharge, or assuming subcooling without checking system design.


Final Answer:
Saturated liquid

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