Term
79. Why is a DX coil considered dry expansion?
a. because it has no liquid in it
b. because the condition of the refrigerant leaving the coil is a 'dry' vapor
c. because they always operate in a dry environment
d. because they do not form condensation on their surface and therefore do not dehumidify the air passing over them |
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Definition
| b. because the condition of the refrigerant leaving the coil is a 'dry' vapor 5-1, 2 |
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Term
80. In steady state operation approximately how far through the coil circuit path does liquid refrigerant travel in a properly adjusted DX coil?
a. 25%.
b. 50%
c. 75%
d. 100% |
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Definition
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Term
81. Where does the flash gas go after the expansion valve in a DX coil system?
a. through the coil with the liquid refrigerant
b. Around the coil straight to the suction line.
c. A DX coil has no flash gas
d. The flash gas is eliminated in the surge drum before it enters the coil |
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Definition
| a. through the coil with the liquid refrigerant 5-2 |
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Term
82. What is liquid carry over?
a. when liquuid carries over from a liquid overfeed coil to its recirc receiver
b. when liquid is drawn into the TXV equalizing line.
c. when the TXV is seeking and liquid travels further through the coil before becoming fully evaporated
d. When liquid refrigerant gets into the dry suction line. |
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Definition
| d. when liquid refrigerant gets into the dry suction line. 5-3, 4 |
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Term
83. What is a common cause of liquid carry over?
a. Oil in the evap
b. too much tension on the TXV superheat spring
c. Loss of charge in the TXV sensing bulb
d. a sudden reduction in suction pressure |
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Definition
| D. a sudden reduction in suction pressure 5-5 |
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Term
84. If you are only concerned about protecting your compressors from liquid carry over, which of the following vessels would you have installed:
a. a suction line accumulator
b. a flash intercooler
c. a sub cooler
d. a larger high pressure receiver |
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Definition
| a. a suction line accumulator 5-9, 10 |
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Term
85. One characteristic of a DX feed air unit is
a. flash gas flows through the coil
b. it requires a pump to operate
c. it must be located near a surge drum
d. the typical expansion device used for DX coils must be manually adjusted to keep up with changing load |
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Definition
| a. flash gas flows through the coil. 5-2, 4, 9 |
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Term
86. As defined in the text, liquid slugs (in DX coils) result from
a. high velocity vapor pushing liquid ahead of it.
b. a TXV closing abruptly
c. a compressor unloading rapidly
d. oil accumulating in the bottom of a coil |
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Definition
| a. High velocity vapor pushing liquid ahead of it 5-10 |
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Term
87. Which of the following is not true about suction line accumulators in a plant?
a. they may be emptied by allowing the liquid to evaporate from the accumulator.
b. they may be emptied by automatic pumps.
c. they may be emptied automatically with a transfer system.
d. they are intended to maintain a constant level and therefore do not need to be emptied |
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Definition
| d. they are intended to maintain a constant level and therefore do not need to be emptied 5-10 |
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Term
88. How much liquid (by volume) is in a properly operating dry expansion evaporator?
a. there is no liquid in a dry expansion evaporator. it is all vapor
b. these evaporators average about 1/4 full of liquid refrigerant by volume during operation
c. these evaporators average about 1/2 full of liquid refrigerant by volume during operation
d. these evaporators average about 3/4 full of liquid refrigerant by volume during operation |
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Definition
| b. these evaporators average about 1/4 full of liquid refrigerant by volume during operation. 5-1 |
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Term
89. As defined in the text, what other names are dry expansion evaporators called?
a. DX coils or direct expansion evaporators
b. Air coils or DX coils
c. Direct expansion evaporators or flash gas coils
d. Suction evaporators or flash gas coils |
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Definition
| a. DX coils or direct expansion evaporators 5-1 |
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Term
90. Which statement is not true regarding refrigerant passing through a dry expansion evaporator?
a. It is completely changed to vapor before leaving the coil to enter the compressor.
b. Part of the liquid vaporizes instantly when leaving the expansion valve.
c. it "boils"
d. It is subcooled as it enters the evaporator. |
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Definition
| d. It is subcooled as it enters the evaporator. 5-2 |
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Term
91. Which of the following does not happen when the cooling load is increased on a system using a dry expansion evap?
a. the boiling rate increases
b. the rate at which vapor is produced increases
c. the compressor will have to move more vapor or the pressure in the evaporator will rise
d. the TXV will respond by reducing the refrigerant flow to the coil. |
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Definition
| d. the TXV will respond by reducing the refrigerant flow to the coil. 5-4,5 |
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Term
92. What is the purpose of a suction line accumulator?
a. Suction line accumulators store refrigerant for using the in evaporator when the receiver is off line
b. Accumulators reduce pressure fluctuations in the evap coils
c. Accumulators collect lequid that passes through ha dry expansion evaporator
d. Accumulators return oil directly to the compressor crankcase? |
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Definition
| c. Accumulators collect liquid that passes through a dry expansion evaporator 5-9, 10 |
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