ATP Cooling Cycle & Heat Transfer Principles 2

Question 1

In a vapor-compression refrigeration cycle, what happens to refrigerant temperature during the throttling process through an expansion valve?

Accepted Answer

Temperature decreases as enthalpy remains nearly constant

Answer

The expansion valve is an isenthalpic device, so enthalpy stays approximately constant while pressure and temperature both drop.

Question 2

Which heat transfer mode is primarily responsible for heat exchange inside a fin-and-tube evaporator coil?

Accepted Answer

Forced convection on the air side and conduction through the tube wall

Answer

Forced convection moves air over the fins while conduction transfers heat through the tube wall to the refrigerant.

Question 3

What does the coefficient of performance (COP) of a refrigeration system represent?

Accepted Answer

The ratio of cooling effect to the net work input

Answer

COP = Q_evaporator / W_compressor, expressing how much useful cooling is obtained per unit of work consumed.

Question 4

A technician notices that the condenser outlet temperature is 10°F above the ambient temperature. This condition is known as:

Accepted Answer

Approach temperature

Answer

Approach temperature is the difference between condenser leaving liquid temperature and the entering ambient (or cooling medium) temperature.

Question 5

Which law governs the rate of conductive heat transfer through a flat wall?

Accepted Answer

Fourier's Law of Heat Conduction

Answer

Fourier's Law states Q = -kA(dT/dx), relating heat flux to thermal conductivity, area, and temperature gradient.

(ATP) Accredited Tier Professional Certification (Cooling & Refrigeration) Practice Test