UNIT 3 Refrigeration and Refrigerant(Exercise tests and solutions)1st Edition 2025

1.Name three reasons why ice melts in an icebox _____,_____,_____. - answer-Heat raises off hot food being stored, heavier cold air falls out-> warm air replaces cold air, heat transfer through walls or insulation because of warmer room temperatures. 2. What are the approximate temperature ranges for low-, medium-, and high-temperature refrigeration applications? - answer-Low: -10 -> 10 degrees Medium: 35 -> 50 degrees High: 50 -> 60 degrees. 3.One ton of refrigeration is. A. 1200 Btu. B. 12,000 Btu/h. C. 120,000 Btu. D. 120,000 Btu/h - answer-B. 12000 btu/hr. 4. Describe briefly the basic refrigeration cycle. - answer-Indoor heat is pumped to the indoor coil; system heat flows from the outdoor coil to the outdoor air. 5. What is the relationship between pressure and the boiling point of liquids? - answer-They coincide. The lower the pressure the lower the boiling point and vice versa. 6. What is the function of the evaporator in a refrigeration. - answer-absorbs heat . Changes the state of the refrigerant from a liquid to a vapor/gas. It superheats the vapor. 7.What does the compressor do in the refrigeration or air conditioning system. - answer-creates Pressure - low to high pressure. The heart of the system. There is no cycle with no compressor. 8. Define a superheated vapor. - answer-Sensible heat added above a liquids boiling point. 9. The evaporating pressure is 76 psig for R-22 and the evaporator outlet temperature is 58 F. What is the evaporator superheat for this system? A. 13°F B. 74°F C. 18°F D. 17°F - answer-A. 13°F 10. If the evaporating pressure was 76 psig for R-22 and the compressor inlet temperature was 65°F, what would be the total superheat entering the compressor? A. 11°F B. 21°F C. 10°F D. 14°F - answer-D. 20°F 11. Define the term subcooled liquid. - answer-Sensible heat lost under boiling point of a liquid. 12. The condensing pressure is 260 psig and the condenser outlet temperature is 108°F for R-22. By how many degrees is the liquid subcooled in the condenser? A. 12°F B. 42°F C. 7°F D. 14°F - answer-A. 12°F 13. The condensing pressure is 260 psig and the metering device inlet temperature is 100°F for R-22. What is the total subcooling in this system? A. 15°F B. 20°F C. 25°F D. 30°F - answer-B. 20°F 14What is meant by a saturated liquid and vapor? - answer-Saturated liquid - liquid whose temperature and pressure are such that any decrease in pressure without change in temperature causes it to boil. Saturated vapor - a vapor whose temperature and pressure are such that any compression of its volume at constant temperature causes it to condense to liquid at a rate sufficient to maintain a constant pressure. Compare saturated liquid. 15. What is meant by de-superheating vapor? - answer-Bringing a substance back down to its boiling point to sub cool. 16. What happens to the refrigerant in the condenser? - answer-The refrigerant is de-superheated, sub cooled, and condensed from a vapor back to a liquid. 17. What happens to refrigerant heat in the condenser? - answer-The refrigerant heat is absorbed into the coil and through forced convection push to the outside air. 18. The metering device. A. Cycles the compressor. B. Controls subcooling. C. Stores refrigerant. D Meters refrigerant. - answer-D. Meters refrigerant 19. What is adiabatic expansion? - answer-Liquid expanding without a net loss or gain in total heat energy or enthalpy. 20. Describe flash gas, and tell how it affects system capacity - answer-Flash gas happens spontaneously when the condensed liquid is subject to boiling. The more flash gas in the system the less liquid refrigerant there is to absorb the heat. In turn reduces the efficiency of the system.