UNIT 3 Refrigeration and Refrigerant

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

A. 12°F

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

A. 13°F

3.One ton of refrigeration is. A. 1200 Btu. B. 12,000 Btu/h. C. 120,000 Btu. D. 120,000 Btu/h

B. 12000 btu/hr.

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

B. 20°F

15. What is meant by de-superheating vapor?

Bringing a substance back down to its boiling point to sub cool.

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

D. 20°F

18. The metering device. A. Cycles the compressor. B. Controls subcooling. C. Stores refrigerant. D Meters refrigerant.

D. Meters refrigerant

24. Define enthalpy.

Describes how much he a substance contents with respect to an accepted reference point.

26. Define net refrigeration effect as it applies to the refrigeration cycle.

Expressed in BTU/LBS and is the quantity of heat that the refrigerant absorbs from the refrigerated space to produce useful cooling.

20. Describe flash gas, and tell how it affects system capacity

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.

1.Name three reasons why ice melts in an icebox _____,_____,_____.

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.

4. Describe briefly the basic refrigeration cycle.

Indoor heat is pumped to the indoor coil; system heat flows from the outdoor coil to the outdoor air.

25.Define a pure compound refrigerant, and give two examples.

It is an azotroptic refrigerant blend that has negligible temperature glide and behaves like a pure compound.

19. What is adiabatic expansion?

Liquid expanding without a net loss or gain in total heat energy or enthalpy.

2. What are the approximate temperature ranges for low-, medium-, and high-temperature refrigeration applications?

Low: -10 -> 10 degrees Medium: 35 -> 50 degrees High: 50 -> 60 degrees.

23. List the cylinder color codes for R-12, R-22, R-502, R-134a, R-11, R-401A, R-402B, R-410A, R-404A, and R-407C.

R-12 - white R-22- green R-502 - orchid R-134a - light blue R-11 - orange R- 401A - light brown R- 402B - green-brown R-410A - rose R- 404A - orange R- 407C - chocolate

22. Describe the difference between a reciprocating compressor and a rotary compressor.

Reciprocating compressor is a compressor that uses a piston in a cylinder and back and forth motion to compress vapor. Rotary compressor that uses rotary motion to pump fluids. It is a positive displacement pump. It has fewer parts. Smaller units than reciprocating compressor and more efficient.

14What is meant by a saturated liquid and vapor?

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.

8. Define a superheated vapor.

Sensible heat added above a liquids boiling point.

11. Define the term subcooled liquid.

Sensible heat lost under boiling point of a liquid.

29. Define temperature glide as it pertains to a refrigerant.

Temperature glide is when the refrigerant blend has many temps as it evaporates and or condenses at a given pressure.

27. Define heat of compression, and explain how it is computed.

The heat content at the outlet of the compressor, point E, is 136Btu/lb. Since the refrigerant entered the compressor with heat content of 113 Btu/lb, the amount of heat added to the refrigerant during the compression process is 23 Btu/lb ( 136Btu /lb) . This is referred to as heat of compression (HOC) for the compressor.

17. What happens to refrigerant heat in the condenser?

The refrigerant heat is absorbed into the coil and through forced convection push to the outside air.

16. What happens to the refrigerant in the condenser?

The refrigerant is de-superheated, sub cooled, and condensed from a vapor back to a liquid.

5. What is the relationship between pressure and the boiling point of liquids?

They coincide. The lower the pressure the lower the boiling point and vice versa.

21. Quality means when referring to a refrigerant.

Vapor percentage

6. What is the function of the evaporator in a refrigeration.

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.

creates Pressure - low to high pressure. The heart of the system. There is no cycle with no compressor.

28. Define flash gas, and explain how it applies to the net refrigeration effect of the refrigeration cycle.

flash gas occurs because the refrigerant entering the evaporator from the metering device must be cooled to the evaporating temp, before the remaining liquid can evaporate in the evaporator and produce useful cooling as part of the net refrigeration effect. The heat absorbed in the flash gas does not contribute to the net refrigerating effect because it comes from the liquid as it partially phase changes to liquid/vapor mixture.

31. Define a near-azeotropic refrigerant blend, and give two examples.

is a blend of two or more refrigerants that have a small change in temp and volumetric composition as they evaporate or condense at a constant pressure. Their temp glide and fractionation is sometimes unnoticeable = R404a R410a.

30. Define a zeotropic refrigerant blend and give an example.

is a blend of two or more refrigerants that will change in temp and volumetric composition as they evaporate or condense at a constant pressure. Zeotropic blends have a very large temp glide = R407c.