Vapour-compression system conceptual check Which statement about performance and components is WRONG?

Introduction / Context:
Understanding where useful cooling is produced and how operating temperatures influence performance is central to vapour-compression refrigeration. This question tests conceptual clarity about the evaporator, condenser, and the effects of subcooling and temperature levels on COP.

Given Data / Assumptions:

• Standard single-stage vapour-compression cycle.
• Useful effect is refrigeration, i.e., heat absorbed from a cold space.
• Terms: evaporating temperature (at evaporator), condensing temperature (at condenser).

Concept / Approach:
In a refrigerator, the desired effect is at the evaporator: it absorbs heat from the space being cooled. The condenser rejects heat to the surroundings and is not the source of useful refrigeration. Performance depends strongly on the temperature lift (difference between condensing and evaporating temperatures). Subcooling liquid leaving the condenser reduces flash gas after throttling, increasing net refrigerating effect and COP.

Step-by-Step Solution:
Identify the useful heat transfer: heat absorbed in the evaporator is the refrigeration effect.Check each statement against fundamentals: performance varies with operating temperatures (true); Electrolux absorption systems are heat-driven with no mechanical compressor (true); subcooling increases COP (true); reducing condensing temperature improves COP (true).Therefore, the only wrong statement is that the condenser provides the useful effect.

Verification / Alternative check:
Energy balance: Q_evap is the desired cooling; Q_cond = Q_evap + W_comp is waste heat rejection for the basic cycle.

Why Other Options Are Wrong (i.e., not the incorrect one):
Options (a), (c), (d), and (e) are consistent with standard cycle analysis and observed practice; they reinforce how COP changes with operating temperatures and subcooling.

Common Pitfalls:
Confusing “useful” effect for a heat pump (where condenser heat is useful) with a refrigerator (where evaporator heat absorption is useful).

Final Answer:
In a vapour-compression cycle, the useful heat transfer occurs at the condenser.