Refrigeration cycles comparison: The coefficient of performance (COP) of a vapour-compression refrigeration system is generally __________ than that of an air (gas) refrigeration system operating between similar temperature limits.

Introduction / Context:
Vapour-compression systems (using phase change) are the workhorse of refrigeration. Air refrigeration (reversed Brayton) relies on gas expansion without phase change. COP comparisons are a staple concept in refrigeration engineering.

Given Data / Assumptions:

• Similar evaporator and condenser (or sink/source) temperatures.
• Idealized cycles for conceptual comparison.
• Neglecting pressure losses and non-idealities for clarity.

Concept / Approach:
COP = refrigeration effect / work input. Two-phase systems exploit large latent heat at near-constant temperature, yielding high refrigeration effect per unit work. Gas cycles produce smaller temperature drops and refrigeration effects for the same work, so COP is typically lower than vapour-compression.

Step-by-Step Solution:

Verification / Alternative check:
Textbook examples show typical COPs: domestic vapour-compression refrigerators often achieve COP 2–4+, while simple air cycles are lower under similar spans.

Why Other Options Are Wrong:
“Low/about the same/zero/indeterminate” contradict fundamental thermodynamic behaviors and practical performance data.

Common Pitfalls:
Comparing COPs without holding temperature limits roughly similar; ignoring non-ideal compressor efficiencies that still do not reverse the general trend.

Final Answer:
high