Difficulty: Medium
Correct Answer: Increases C.O.P.
Explanation:
Introduction / Context:Superheating in vapour-compression systems can occur intentionally in the evaporator or unintentionally in the suction line. Its effect on performance depends on how it influences refrigerating effect and compressor work.
Given Data / Assumptions:
Concept / Approach:Superheating generally increases the refrigerant enthalpy at the compressor inlet, thereby increasing the refrigerating effect per kg (h1 − h4) because h1 rises while h4 (post-expansion enthalpy) is almost unchanged. Compressor work per kg (h2 − h1) also rises, but in many refrigerant–condition combinations the percentage increase in refrigerating effect is greater than the percentage increase in work, leading to a net increase in C.O.P. = (refrigerating effect)/(compressor work).
Step-by-Step Solution:
Define RE = h1 − h4 and W = h2 − h1.Introduce superheat: h1 increases; for similar pressure ratio, h2 increases but not as much proportionally.Compute C.O.P. = RE / W → often rises with moderate, controlled superheat.Conclusion: C.O.P. generally increases, especially when superheat is created in the evaporator adding useful capacity.Verification / Alternative check:Plot points on a p-h diagram for a common refrigerant (e.g., R-134a). Moving the suction point into the superheat region increases the area representing RE more than the increase in W for many practical cases.
Why Other Options Are Wrong:
No change: contradicts enthalpy changes.Decreases: can happen for extreme suction-line superheat with large pressure drops, but not as a general rule under controlled evaporator superheating.“Work to zero” is impossible; compression requires work.
Common Pitfalls:Confusing evaporator superheat (beneficial capacity gain) with suction-line heat pickup (which may hurt C.O.P.). Proper design ensures controlled superheat at the evaporator outlet with minimal suction-line heat gain.
Final Answer:
Increases C.O.P.
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