Refrigerant selection — identify the undesirable property For a refrigerant used in vapor-compression systems, which of the following is an undesirable thermophysical or safety property for practical HVAC/R applications?

Introduction / Context:
Refrigerant choice affects efficiency, component size, environmental impact, and safety. Key properties include normal boiling point, flammability, toxicity, chemical stability, and compatibility with materials.

Given Data / Assumptions:

• Comparing single properties in isolation for typical HVAC/R equipment.
• Focus on practical desirability in compressors, condensers, and evaporators.

Concept / Approach:
A desirable refrigerant should boil at a low temperature at near-atmospheric pressure to achieve evaporating temperatures below ambient while keeping suction pressures moderate. Safety attributes (non-toxic, non-flammable, non-explosive) and chemical stability are also desirable. Therefore, a high boiling point is undesirable because it forces high evaporator pressures and limits low-temperature operation.

Step-by-Step Solution:

Verification / Alternative check:
Examine pressure-temperature charts: refrigerants with low boiling points achieve sub-zero evaporator temperatures without extreme suction pressures; high-boiling fluids would require impractical conditions.

Why Other Options Are Wrong:

Non-toxic, non-flammable, non-explosive, and chemically stable are all desirable safety and reliability attributes.

Common Pitfalls:
Confusing normal boiling point with critical temperature; both matter, but the normal boiling point directly relates to evaporator operating ranges.

Final Answer:

high boiling point