Refrigeration Fundamentals & Thermodynamics Flashcards

What is the critical point of a refrigerant?

Answer: The temperature and pressure above which no distinction exists between liquid and vapour phases

The critical point is the specific temperature and pressure above which a refrigerant exists as a supercritical fluid and cannot be liquefied by pressure alone.

What does a high suction pressure reading typically indicate in a refrigeration system?

Answer: High heat load or overcharge of refrigerant

High suction pressure usually indicates an excessive heat load on the evaporator or a refrigerant overcharge, both of which cause more refrigerant vapour to enter the compressor suction.

What is the purpose of a liquid receiver in a refrigeration system?

Answer: To store liquid refrigerant and ensure a steady supply to the expansion device

A liquid receiver stores a reserve of liquid refrigerant on the high side of the system, ensuring a continuous and bubble-free supply of liquid to the expansion device under varying load conditions.

What does enthalpy represent in refrigeration thermodynamics?

Answer: The total heat content of the refrigerant per unit mass

Enthalpy (kJ/kg) represents the total heat content of the refrigerant, including internal energy and flow work, and is used to calculate heat transfer in each component of the cycle.

What is the purpose of the oil separator in a refrigeration system?

Answer: To separate compressor oil from the discharge gas and return it to the compressor crankcase

An oil separator is installed in the compressor discharge line to capture oil entrained in the hot gas and return it to the compressor crankcase, preventing oil loss and maintaining lubrication.

In a refrigeration system, what causes flash gas to form in the liquid line?

Answer: Pressure drop or insufficient subcooling causing partial vaporization before the expansion device

Flash gas forms when liquid refrigerant loses pressure or gains heat in the liquid line, causing some of it to vaporize before reaching the expansion device, which reduces system efficiency.