Thermodynamics Flashcards

Which thermodynamic property measures the total heat content of a substance, including both sensible and latent heat?

Answer: Enthalpy

Enthalpy (H) represents the total heat content and is used on pressure-enthalpy (P-H) diagrams to analyze refrigeration cycles.

Superheat in the suction line of a refrigeration system indicates that the refrigerant is:

Answer: Fully vaporized with additional heat above saturation

Superheat means the vapor has absorbed heat beyond its saturation point, ensuring no liquid enters the compressor.

What is the primary reason that refrigerant vapor is compressed in the refrigeration cycle?

Answer: To raise its pressure and temperature so it can reject heat at a higher temperature

Compression raises the refrigerant pressure and temperature, enabling heat rejection to the warmer outdoor environment in the condenser.

On a pressure-enthalpy (P-H) diagram, the area inside the saturation curve represents:

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

The two-phase region under the saturation dome is where refrigerant exists as a mixture of liquid and vapor.

If an HVAC system has a higher outdoor ambient temperature, what typically happens to the condensing pressure?

Answer: It increases

Higher ambient temperatures reduce the temperature difference available for heat rejection, requiring higher condensing pressure and temperature.

The term 'flash gas' in refrigeration refers to:

Answer: Instantaneous vaporization of refrigerant as pressure drops through the expansion device

Flash gas forms when refrigerant passes through the expansion valve and some liquid instantly vaporizes due to the pressure drop.

Which value represents the theoretical maximum efficiency a heat engine can achieve between two temperature reservoirs?

Answer: Carnot efficiency

Carnot efficiency = 1 - (Tc/Th) and represents the theoretical upper limit of efficiency for any heat engine operating between two temperatures.