Refrigerant selection: Which high property is generally undesirable for a good refrigerant due to increased pumping losses and poorer heat transfer?

Introduction / Context:
Choosing a refrigerant involves balancing thermophysical properties for efficiency, safety, and practicality. Some properties should be high (e.g., latent heat), while others are preferably low (e.g., viscosity) to minimize irreversibilities and parasitic loads in compressors and pumps.

Given Data / Assumptions:

• Focus on property impact on circulation and heat exchange.
• Comparison is qualitative and broadly valid across common refrigerants.
• System operates in typical ranges for HVAC/R or process refrigeration.

Concept / Approach:

High viscosity increases pressure drop in pipes and heat exchangers, raises pumping power, and degrades convective heat transfer coefficients. Conversely, high latent heat reduces mass flow required for a given cooling duty, improving COP. Low specific vapor volume is desirable to reduce compressor size; excessively high specific volume is undesirable for machinery sizing. Between the listed choices, high viscosity is the unambiguously undesirable attribute across most designs.

Step-by-Step Solution:

Verification / Alternative check:

Empirical correlations for friction factor and Nusselt number show adverse dependence on viscosity, confirming the design penalty.

Why Other Options Are Wrong:

High latent heat is typically favorable; specific vapor volume is ideally low (but the prompt asks for a single most generally undesirable property—viscosity is the clear choice). Specific heat and thermal conductivity can aid heat transfer in secondary loops.

Common Pitfalls:

Confusing refrigerant property desirability with secondary coolant properties; misreading 'specific volume' versus 'density' effects.

Final Answer:

viscosity