In a vapor compression cycle, the refrigerant condition immediately downstream of the expansion valve is___________________?
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Answer: D. wet vapour
Explanation
Immediately downstream of the expansion valve, the refrigerant flashes into a low pressure wet vapor. The sudden pressure drop causes a fraction of the liquid refrigerant to evaporate rapidly. This flashing process absorbs latent heat and drops the temperature of the remaining liquid mixture. Expansion valves act as throttling devices that drop high pressure liquid to low pressure conditions. The resulting mixture consists of both saturated liquid and saturated vapor phases coexisting together. Quality of the vapor fraction depends on the enthalpy values entering and leaving the valve.
This cold wet vapor mixture enters the evaporator to absorb heat from the refrigerated space. Proper expansion valve operation ensures that the refrigerant enters the evaporator at optimal conditions. Refrigeration technicians monitor expansion valve performance to verify correct system charge levels. Sub-cooled liquid describes the high-pressure refrigerant state exiting the condenser before the valve. Saturated liquid condition exists just before the expansion valve inlet, not immediately downstream. Dry vapor condition is achieved only after complete evaporation inside the downstream evaporator coils.
- Subject
- Engineering
- Category
- Mechanical Engineering
- Topic
- —
- Difficulty
- medium
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