Thermodynamics Flashcards

What happens to entropy in a truly reversible process?

Answer: It remains constant

In a perfectly reversible (ideal) process, total entropy change is zero; real processes always increase entropy.

The heat rejection rate of a condenser equals the:

Answer: Sum of evaporator heat absorption plus compressor work input

By energy conservation (First Law), the condenser must reject the heat absorbed in the evaporator plus the work added by the compressor.

What is the dew point temperature in the context of refrigerant pressure-temperature relationships?

Answer: Temperature at which refrigerant starts to condense from 100% vapor

The dew point is the saturation temperature at which the last bit of vapor begins to condense when cooling a refrigerant mixture.

Why is it important to avoid liquid refrigerant entering the compressor suction?

Answer: Liquid is incompressible and can cause mechanical damage (slugging)

Liquid refrigerant cannot be compressed and can cause catastrophic compressor damage known as liquid slugging.

In a heat pump operating in heating mode, which component acts as the heat absorber from outdoor air?

Answer: Outdoor coil (acting as evaporator)

In heating mode, the outdoor coil absorbs heat from outdoor air (even cold air) acting as an evaporator to deliver heat indoors.

What does a higher EER (Energy Efficiency Ratio) value indicate about an air conditioning system?

Answer: More cooling output per watt of electricity consumed

EER = BTU/hr of cooling divided by watts of input; a higher EER means more efficient cooling at a single operating condition.

Which thermodynamic cycle forms the theoretical basis for the vapor-compression refrigeration system used in most HVAC equipment?

Answer: Reversed Rankine (vapor-compression) cycle

The reversed Rankine cycle, using a working fluid that changes phase, is the thermodynamic model for vapor-compression refrigeration.