CARO Refrigeration Cycle Fundamentals 2 — Questions and Answers
Question 1: Under normal operating conditions, in what state should refrigerant leave the evaporator?
- Subcooled liquid
- Saturated liquid
- Slightly superheated vapor (Correct answer)
- Liquid-vapor mixture of about 50% quality
Correct answer: Slightly superheated vapor
A small amount of superheat ensures all liquid has boiled off before the vapor reaches the compressor.
Question 2: What type of heat does refrigerant primarily absorb as it boils in the evaporator?
- Latent heat of vaporization (Correct answer)
- Sensible heat
- Heat of compression
- Latent heat of fusion
Correct answer: Latent heat of vaporization
Boiling is a change of state, so most of the heat absorbed is latent heat of vaporization.
Question 3: If the pressure in an evaporator is lowered, what happens to the refrigerant's saturation (boiling) temperature?
- It rises
- It stays the same
- It becomes equal to the condensing temperature
- It drops (Correct answer)
Correct answer: It drops
Saturation temperature is directly tied to pressure, so lower pressure means a lower boiling point.
Question 4: How is liquid subcooling at the condenser outlet calculated?
- Discharge temperature minus condensing temperature
- Saturated condensing temperature minus actual liquid line temperature (Correct answer)
- Liquid line temperature minus ambient temperature
- Suction line temperature minus evaporator saturation temperature
Correct answer: Saturated condensing temperature minus actual liquid line temperature
Subcooling is how far the liquid has been cooled below its saturation temperature at condensing pressure.
Question 5: Refrigerant leaving the compressor discharge is best described as what?
- High-pressure, high-temperature superheated vapor (Correct answer)
- High-pressure subcooled liquid
- Low-pressure saturated vapor
- High-pressure liquid-vapor mixture
Correct answer: High-pressure, high-temperature superheated vapor
Compression raises both pressure and temperature, leaving the vapor well superheated.
Question 6: What two things happen to refrigerant as it passes through the expansion (metering) device?
- Pressure rises and the liquid subcools
- Pressure drops and all of the liquid condenses
- Pressure stays constant and temperature rises
- Pressure drops and part of the liquid flashes to vapor (Correct answer)
Correct answer: Pressure drops and part of the liquid flashes to vapor
The sudden pressure drop causes some liquid to flash, cooling the remaining liquid to evaporator temperature.
Question 7: One ton of refrigeration equals how many Btu of heat removal over 24 hours?
- 12,000 Btu
- 144,000 Btu
- 288,000 Btu (Correct answer)
- 200,000 Btu
Correct answer: 288,000 Btu
A ton is 12,000 Btu/h, which equals 288,000 Btu per 24 hours (the heat to melt one ton of ice).
CARO Refrigeration Cycle Fundamentals 2
Under normal operating conditions, in what state should refrigerant leave the evaporator?