Cooling Cycle & Heat Transfer Principles Flashcards
7 cards from real ATP practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Cooling Cycle & Heat Transfer Principles flashcards as text
In a vapor-compression refrigeration cycle, what happens to refrigerant temperature during the throttling process through an expansion valve?
Answer: Temperature decreases as enthalpy remains nearly constant
The expansion valve is an isenthalpic device, so enthalpy stays approximately constant while pressure and temperature both drop.
Which heat transfer mode is primarily responsible for heat exchange inside a fin-and-tube evaporator coil?
Answer: Forced convection on the air side and conduction through the tube wall
Forced convection moves air over the fins while conduction transfers heat through the tube wall to the refrigerant.
What does the coefficient of performance (COP) of a refrigeration system represent?
Answer: The ratio of cooling effect to the net work input
COP = Q_evaporator / W_compressor, expressing how much useful cooling is obtained per unit of work consumed.
A technician notices that the condenser outlet temperature is 10°F above the ambient temperature. This condition is known as:
Answer: Approach temperature
Approach temperature is the difference between condenser leaving liquid temperature and the entering ambient (or cooling medium) temperature.
Which law governs the rate of conductive heat transfer through a flat wall?
Answer: Fourier's Law of Heat Conduction
Fourier's Law states Q = -kA(dT/dx), relating heat flux to thermal conductivity, area, and temperature gradient.
In a refrigeration system, flash gas in the liquid line before the expansion valve causes:
Answer: Reduced capacity and possible expansion valve hunting
Flash gas reduces the density of refrigerant entering the expansion valve, starving the evaporator and causing erratic valve operation.
The latent heat of vaporization of a refrigerant is best described as:
Answer: Heat required to change liquid refrigerant to vapor at constant pressure
Latent heat of vaporization is absorbed during the phase change from liquid to vapor at constant temperature and pressure.