Effect of evaporator temperature on performance: If condenser temperature is held constant, how does the refrigeration cycle COP change as the evaporator temperature increases?
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AYes
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BNo
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CCOP remains exactly the same
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DCOP first decreases then increases
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ECOP reduces to zero
Answer
Correct Answer: Yes
Explanation
Introduction / Context:The coefficient of performance (COP) of a vapour-compression system depends strongly on the evaporating and condensing temperatures. Understanding these trends informs set-point selection and defrost strategies.
Given Data / Assumptions:
- Condenser temperature (or pressure) is fixed.
- Evaporator temperature is increased (warmer evaporator).
- Same refrigerant and general cycle configuration.
Concept / Approach:For idealized cycles, COP_R increases as the temperature lift (T_cond − T_evap) decreases. Raising the evaporator temperature reduces this lift and increases the ratio of cooling effect to compressor work.
Step-by-Step Solution:
Let T_H be condenser temperature, T_L be evaporator temperature.Temperature lift = T_H − T_L; increasing T_L reduces lift.Lower lift → lower compressor work per unit cooling → higher COP.Verification / Alternative check:For a simple ideal cycle, COP_R ≈ T_L / (T_H − T_L) on absolute scale. Increasing T_L while T_H constant increases COP_R.
Why Other Options Are Wrong:
“No/unchanged” contradicts the standard dependence on temperature lift.Non-monotonic or zero COP outcomes do not apply here.
Common Pitfalls:Comparing COP across different refrigerants or mixing Celsius and absolute temperatures; always use absolute temperatures in theoretical relations.
Final Answer:
Yes