Term
18. Enthalpy is:
a. a measure of the total energy (heat content) per pound of refrigerant measured in BTUs.
b. the net heat absorbing capacity of the refrigerant after the point of expansion
c. the amount of cooling effect that can be obtained from a refrigeration system.
d. heat that cannot be measured through a change in temperature |
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Definition
| a. a measure of the total energy (heat content) per pound of refrigerant measured in BTUs 2-2 |
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Term
19. The enthalpy diagram
a. Illustrates the changes of condition and heat content of a pound of refrigerant at different points of the refrigeration cycle.
b. illustrates the total heat transfer capacity of the system from evaporators through condenser in Tons of Refrigeration.
c. Utilizes two scales, pressure and tons of refrigeration.
d. does not take into account the effect of flash gas. |
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Definition
| a. illustrates the changes of condition and heat content of a pound of refrigerant at different points of the refrigeration cycle. 2-2 |
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Term
20. The nenthalpy diagram has three regions of refrigerant condition which are:
a. solid, liquid, gas.
b. subcooled liquid, a mix of saturated liquid and vapor, superheated vapor.
c. hot, medium, cold
d. flash gas, subcooled liquid and a mixture of subcooled liquid and flash gas. |
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Definition
| b. subcooled liquid, a mixture of saturated liquid and vapor, superheated vapor.2=10 |
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Term
21. The pressure scale on an enthalpy diagram typically used in the U.S. is expressed in
a. kilopascals.
b. psig.
c. psia.
d. Newtons |
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Definition
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Term
22. In a refrigeration system (at normal refrigeration pressures), how does the heat content of a pound of saturated vapor compare to the heat content of a pound of saturated liquid?
a. the heat quantity in a pound of saturated vapor is greater than the heat quantity in a pound of saturated liquid at the same pressure.
b. the heat quantity in a pound of saturated vapor is less than the heat quantity in a pound of saturated liquid at the same pressure.
c. the heat quantity in a pound of saturated vapor is equal to the heat quantity in a pound of saturated liquid at the same pressure.
d. it is not possible to measure the heat content in a pound of saturated vapor. |
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Definition
| a. the heat quantity in a pound of saturated vapor is greater than the heat quantity in a pound of saturated liquid at the same pressure.2-10 |
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Term
23. In a refrigeration system (at normal refrigeration pressures), how does the volume of a pound of saturated vapor compare to the volume of a pound of saturated liquid?
a. a pound of saturated vapor occupies a larger volume than a pound of saturated liquid at the same pressure.
b. a pound of saturated vapor occupies a smaller volume than a pound of saturated liquid at the same pressure.
c. a pound is a pound, they take up the same volume.
d. the volume of a pound of saturated liquid depends on the pressure applied to it. |
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Definition
| a. a pound of saturated vapor occupies a larger volume than a pound of saturated liquid at the same pressure. 2-12 |
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Term
24. The temperature lines within the saturated mixture dome of an enthalpy diagram
a. are horizontal because change of state of a refrigerant at constant pressure is done at a constant temperature.
b.are vertical because change of state of a refrigerant at constant pressure is done at a constant temperature.
c. are horizontal because change of state of a refrigerant at a constant pressure results in a constantly changing temperature.
d. are vertical because change of state of a refrigerant at constant pressure results in a constantly changing temperature. |
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Definition
| a. are horizontal because change of state of a refrigerant at constant pressure is done at a constant temperature. 2-10 |
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Term
25. The boundary line between the subcooled liquid region and the saturated mixture region
a. is 100% saturated liquid
b. is 100% saturated vapor
c. represents a theoretical condition not achievable in a real system
d. represents the critical pressure of the refrigerant |
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Definition
| a. is 100% saturated liquid 2-10 |
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Term
25. The boundary line between the subcooled Vapor region and the saturated mixture region
a. is 100% saturated liquid
b. is 100% saturated vapor
c. represents a theoretical condition not achievable in a real system
d. represents the critical pressure of the refrigerant |
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Definition
| b. a 100% saturated vapor 2-10 |
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Term
27. A simple refrigeration cycle plotted on the enthalpy diagram illustrates why a condenser must reject more heat than just the heat absorbed in the evaporator because of:
a. subcooling
b. heat of compression
c. saturation
d. evaporation. |
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Definition
| b. heat of compression 2-21 |
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Term
28. a vertical change (change of pressure) in the subcooled liquid region or in the saturated mixture region ____ the enthalpy of the refrigerant at that point.
a. increases
b. decreases
c. does not change
d. multiplies |
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Definition
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Term
Superheat enters the system at
a. the condenser, high pressure receiver, and the evaporator
b. the liquid line, evaporator, and the condenser.
c. the evaporater (DX), suction lines, compressor
d. the pump accumulator package |
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Definition
| c. the evap (DX), suction lines, compressor. 2-19 |
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Term
30. In a two stage system, subcooled liquid entering the evaporator generally enhances the performance of the system because
a. it really makes no difference
b. there is less flash gas formed for the low stage compressor to handle.
c. subcooling the liquid causes the molecules to be spaced further apart which gives them a running head start toward evaporating into liquid along with the flash gas
d. subcooling of liquid entering the evaporator is never an advantage; it always reduces the performance of the evaporator |
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Definition
| b. there is less flash gas formed for the low stage compressor to handle 2-36 |
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Term
31. Using oversized figeure 2-5 Mollier Ph Diagram, solve the following problem
The single stage reciprocating ammonia compressor is operating at a suction temp of 10F from a freezer unit with an evaporating temp of 0F. The condensing temperature is 95F. What is the theoretical discharge temperature?
a. 210
b. 350
c 260
d 310 |
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Definition
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Term
33. What can be done to reduce the discharge temperature?
a. drop the suction pressure of the evaporator
b. increase suction superheat
c. decrease suction superheat
d. increase the condensing temperature |
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Definition
| c. decrease suction superheat 2-20, 21 |
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Term
34. You are the operator of a refrigeration play. the owner comes to you and sys that the power comsuption 9kWh) is up 15% over this time last year. He asks why there is this huge shift in consumption -your response is
a. the suction pressure is too high
b. we should have insulated the new suction line on the roof and kept the scale from forming on the condenser tubes
c. power consumption is not related to operating conditions
d. the price of electricity must have gone up |
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Definition
| b. we should have insulated the new suction line on the roof and kept the scale from forming on the condenser tubes 2-23, 1-13, 14 |
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Term
35. Using the Mollier Ph diagram in Figure 2-6, flash gas would be defined by
a. line (d-e)
b line (b-c)
c line (f-a)
d. line (c-b) |
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Definition
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