HVAC Thermodynamics 5

Question 1

What happens to entropy in a truly reversible process?

Accepted Answer

It remains constant

Answer

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

Question 2

The heat rejection rate of a condenser equals the:

Accepted Answer

Sum of evaporator heat absorption plus compressor work input

Answer

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

Question 3

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

Accepted Answer

Temperature at which refrigerant starts to condense from 100% vapor

Answer

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

Question 4

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

Accepted Answer

Liquid is incompressible and can cause mechanical damage (slugging)

Answer

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

Question 5

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

Accepted Answer

Outdoor coil (acting as evaporator)

Answer

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

HVAC Practice Test