ASHRAE Refrigeration Principles and Applications 2

Question 1

In an ideal vapor-compression cycle, the process across the expansion valve is best described as:

Accepted Answer

Isenthalpic

Answer

Throttling through an expansion device occurs at constant enthalpy because no work or heat transfer takes place.

Question 2

What is the primary benefit of subcooling liquid refrigerant before it enters the expansion device?

Accepted Answer

It increases the refrigerating effect per unit mass of refrigerant

Answer

Subcooling lowers the enthalpy entering the evaporator, so each pound of refrigerant absorbs more heat.

Question 3

With evaporating temperature held constant, raising the condensing temperature will typically:

Accepted Answer

Decrease COP and increase compressor work per unit of cooling

Answer

A higher temperature lift raises compression work and reduces refrigerating effect, lowering COP.

Question 4

A reversed Carnot refrigerator operates between an evaporator at 250 K and a condenser at 300 K. What is its COP?

Accepted Answer

5.0

Answer

Carnot COP = Te/(Tc − Te) = 250/50 = 5.0.

Question 5

One ton of refrigeration is equivalent to:

Accepted Answer

12,000 Btu/h

Answer

One ton equals 12,000 Btu/h, derived from melting one ton of ice in 24 hours (288,000 Btu/day).

ASHRAE - American Society of Heating, Refrigeration and Air Conditioning Engineers Certification Practice Test