Refrigeration and p-h chart basics Which of the following statements is WRONG for a standard vapour-compression refrigerator?

Introduction / Context:
Engineers must distinguish universally true principles from convenient rules of thumb. This question checks your understanding of coefficient of performance (C.O.P.), refrigerant state at compressor inlet, and interpretation of the pressure–enthalpy (p–h) diagram for a vapour-compression system.

Given Data / Assumptions:

• Standard single-stage vapour-compression refrigerator.
• Idealized discussions use dry saturated vapour at compressor inlet; practical systems may use slight superheat.
• C.O.P. definitions: C.O.P._R = Q_L / W, C.O.P._HP = Q_H / W.

Concept / Approach:
C.O.P._R can be less than, equal to, or greater than 1 depending on conditions. While good refrigerators normally achieve C.O.P. greater than 1, the statement “always greater than 1” is not a law. Meanwhile, the ideal inlet condition to a compressor is dry saturated vapour (or slightly superheated) to avoid wet compression. On a p–h chart, the space between saturated liquid and saturated vapour lines is indeed the two-phase region.

Step-by-Step Solution:
Identify the claim that overstates reality: “C.O.P. is always > 1.”Recall definition: C.O.P._R = Q_L / W. With very poor heat exchangers or extreme temperature lifts, W can approach or exceed Q_L, making C.O.P._R ≤ 1.Confirm other statements: dry saturated (or slightly superheated) inlet is standard; the region between saturation lines is the wet-vapour dome.Therefore, the WRONG statement is that C.O.P. is always > 1.

Verification / Alternative check:
Compare with the Carnot refrigerator: C.O.P._Carnot = T_L / (T_H − T_L). As T_L approaches T_H (favorable), C.O.P. becomes large; for very large temperature lifts, it can be close to or below 1 in real systems.

Why Other Options Are Wrong:
Option B reflects the ideal inlet condition; Option C correctly describes the two-phase region; Option E is a common practical design choice for reliability.

Common Pitfalls:
Assuming a performance metric that is “usually > 1” is “always > 1.” Real plants deviate from ideal behavior due to irreversibilities.

Final Answer:
The value of C.O.P. is always greater than 1.