CRST Refrigerants & Thermodynamics Flashcards
6 cards from real CRST practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 CRST Refrigerants & Thermodynamics flashcards as text
What is 'superheat' in a refrigeration system?
Answer: The temperature of suction vapor above the saturation temperature at suction pressure
Superheat is the number of degrees that suction vapor exceeds the saturation temperature at the measured suction pressure, ensuring only dry vapor enters the compressor.
Per EPA Section 608, what is the maximum allowable leak rate for refrigeration equipment with a charge of 50 lbs or more used in commercial processes before repair is required?
Answer: 30% per year
EPA Section 608 requires owners of commercial refrigeration equipment with charges of 50 lbs or more to repair leaks when the annual leak rate exceeds 30%.
When recharging a system with an HFC blend refrigerant (such as R-410A), how must the refrigerant be added from the cylinder?
Answer: As a liquid (cylinder inverted or using a liquid valve)
HFC blends like R-410A must be charged as liquid to maintain the correct blend ratio, as vapor-charging can cause fractionation and alter the refrigerant composition.
What happens to the pressure-temperature relationship of a refrigerant mixture that 'glides'?
Answer: The temperature changes during phase change at constant pressure
Zeotropic refrigerant blends exhibit temperature glide, meaning the evaporation or condensation temperature shifts (slides) across a range during phase change at constant pressure.
What is the primary purpose of a refrigerant receiver in a commercial refrigeration system?
Answer: Store liquid refrigerant to accommodate system demand changes and ensure liquid feed to the expansion device
A liquid receiver stores excess refrigerant charge, provides a stable liquid supply to the expansion device, and accommodates load variations without flooding or starving the system.
Which pressure-enthalpy diagram characteristic indicates a refrigeration system is operating with excessive head pressure?
Answer: The condensing process line moves to the right (higher enthalpy/temperature) at elevated pressure
High head pressure shifts the condensing portion of the P-H diagram to the right and upward, indicating the refrigerant must be cooled to a higher temperature before condensing, which reduces system efficiency.