Refrigeration Fundamentals & Thermodynamics Flashcards

On a pressure-enthalpy (P-h) diagram, what does the area under the saturation dome represent?

Answer: The two-phase (liquid-vapour) mixture region

The area under the saturation dome on a P-h diagram represents the two-phase region where both liquid and vapour coexist at saturation conditions.

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

Answer: The ratio of refrigeration effect to the work input to the compressor

COP is defined as the useful refrigeration effect (heat absorbed at the evaporator) divided by the compressor work input, indicating system efficiency.

What happens to the boiling point of a refrigerant as pressure increases?

Answer: It increases

As pressure increases, the boiling (saturation) temperature of a refrigerant also increases, which is why high-side pressure corresponds to higher condensing temperatures.

In a standard vapour-compression cycle, which process occurs in the compressor?

Answer: Isentropic compression of refrigerant vapour

The ideal compressor process is isentropic (adiabatic and reversible) compression, raising both the pressure and temperature of the refrigerant vapour.

What is sensible heat?

Answer: Heat that changes the temperature of a substance without changing its phase

Sensible heat is heat energy that causes a measurable temperature change in a substance without changing its physical state.

What is the purpose of calculating the refrigeration effect in system design?

Answer: To determine how much heat the evaporator can absorb per kilogram of refrigerant

The refrigeration effect (kJ/kg) tells the designer how much heat each kilogram of refrigerant absorbs as it passes through the evaporator, which is used to size the system for the required cooling load.