In a standard vapor-compression refrigeration cycle, the highest refrigerant temperature occurs at which point of the cycle?
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AImmediately after the evaporator (compressor inlet)
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BImmediately after the compressor (compressor discharge, before the condenser)
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CMidway through the condenser
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DImmediately after the expansion device
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EUniform temperature throughout the cycle
Answer
Correct Answer: Immediately after the compressor (compressor discharge, before the condenser)
Explanation
Introduction / Context:Understanding state points in a vapor-compression cycle is foundational in refrigeration and air-conditioning. Identifying where the refrigerant reaches its highest temperature helps with diagnosing discharge overheating, sizing condensers, and ensuring compressor safety.
Given Data / Assumptions:
- Cycle components: evaporator → compressor → condenser → expansion device.
- Compression is non-isothermal; it raises both pressure and temperature.
- No abnormal subcooling/flash-gas issues overriding basic trends.
Concept / Approach:The compressor takes low-pressure vapor from the evaporator and compresses it to a high-pressure, high-temperature superheated vapor. This discharge state is the cycle’s maximum temperature. The condenser then rejects heat, decreasing refrigerant temperature toward saturation and subcooling levels.
Step-by-Step Solution:
1) Evaporator exit: low-pressure superheated vapor at relatively low temperature.2) Compressor: adds work → temperature rises sharply.3) Condenser: rejects heat at nearly constant pressure → temperature falls.4) Expansion device: throttling reduces temperature further before evaporator.Verification / Alternative check:On a T–s diagram, the peak temperature is at the end of the compression line (compressor discharge) before the condensation curve.
Why Other Options Are Wrong:
- (a) Evaporator outlet is the coolest vapor state, not the hottest.
- (c) In the condenser, temperature is dropping as heat is rejected.
- (d) After throttling, temperature decreases substantially.
- (e) Temperature varies throughout the cycle.
Common Pitfalls:Confusing “after evaporation” with “after compression.” The maximum temperature is not at evaporator exit; it is at compressor discharge.
Final Answer:Immediately after the compressor (compressor discharge, before the condenser)