Term
93. A pumped liquid recirculation system sends 15F liquid ammonia out to the system. The piping goes up to and over the roof, 21 feet above the pump outlet. The pump discharge pressure is 45psig. The pressure of the liquid in the pipe at the roof is:
a. approx 45psig
b. approx 39psig
c. approx 51psig
d. Saturated |
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Definition
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Term
94. Carry over to the compressor is minimized in the pumped liquid overfeed system because:
a. of the low side float
b. of the liquid line design
c. of the recirculator
d. of the liquid pup |
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Definition
| C. of the recirculator 6-4 |
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Term
95. Liquid is forced out of the drum of gas 'double pumper drum' system to the evap by means of
a. high pressure vapor
b. bulb pressure in the power element
c. evap pressure
d. liquid line pressure |
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Definition
| A. High pressure vapor 6-21 |
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Term
96. In a double pumper drum system, when one drum is filling, the other drum is
a. also filling
b. venting
c. developing gas pressure
d. being emptied |
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Definition
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Term
97. If the gas pressure in the vessel increases 2 psig when the liquid feed valve on a recirculator vessel opens. The effect of the feeding liquid on the pump is
a. to reduce the pump capacity because of flash gas
b. it increases the temp of the liquid at the pump immediately
c. to possible enhance the performance because of the increased NPSH available
d. to cavitate the pump because of the sudden pressure increase |
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Definition
| c. to possibly enhance the performance because of the increased NPSH available. |
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Term
98. When oil and liquid refrigerants separate, the characteristics are that:
a. oil settles to the bottom with ammonia and rises to the top with the halocarbons
b. oil migrates towards high pressure with ammonia and low pressure with halocarbons
c. oil migrates towards low pressure with ammonia and high pressure with halocarbons
d. oil rises toward the top with ammonia and settles to the bottom with halocarbons. |
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Definition
| A. oil settles to the bottom with ammonia and rises to the top with the halocarbons. 6-48 |
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Term
99. A 3:1 recirculation ratio means that the wet suction return line contains
a. 3 parts liquid, 1 part vapor
b. 1 part liquid, 3 parts vapor
c. 2 parts liquid, 1 part vapor
d. 4 parts liquid, 1 part vapor |
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Definition
| C. 2 parts liquid, 1 part vapor 6-4, 5 |
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Term
100. Compared with top fed evaporators, the overfeed ratio for bottom feed evaporators is
a. greater
b. the same
c. lower
d. none |
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Definition
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Term
101. Recirculator sizing is important to prevent
a. suction line superheat
b. liquid in the suction line from the evaporator to the receiver
c. liquid in the suction line to the compressor
d. vapor in the suction evaporator |
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Definition
| c. liquid in the suction line to the compressor 6-37 |
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Term
102. Liquid refrigerant pump suction line velocity should not exceed
a. 3fps
b. 5fps
c. 6fps
d. 10fps |
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Definition
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Term
103. The ratio of the amount of liquid entering the evaporator (by weight) to the amount of vapor formed (by weight) in the evaporator during the heat transfer process is the definition of which of the following?
a. liquid to vapor ratio
b. cooling ratio
c. recirculation ratio
d. refrigeration ratio |
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Definition
| C. Recirculation ratio 6-4 |
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Term
104. Given a 33F cold room that has liquid overfeed evaporators (a recirculation ratio of 4:1) and is used to maintain the temp of precooled product, what would happen to the recirculation ratio if the manager decided to load the room with hot product for cooling?
a. the recirculatio nratio does not change.
b. the recirculation ratio rises
c. The recirculation ratio drops.
d. the TXV compensates to maintain standard recirculation ratio |
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Definition
| c. the recirculation ratio drops 6-4 |
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Term
105. Which evaporator the requires the highest recirculation ratio?
a. Liquid recirculation bottom feed
b. Liquid recirculation top feed
c. Gravity flooded top fed
d. DX |
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Definition
| b. Liquid recirculation top feed. 6-31 |
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Term
106. A plat freezer that requires a recirculation ratio of 6:1 will return ____ to the low temp recirculated suction line for each pound of liquid refrigerant evaporated when operating at design conditions.
a. 6lbs of vapor
b. 5lbs of liquid
c. 1lbs of liquid
d. the same amount of liquid under all loads |
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Definition
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Term
107. Why d pumps used for ammonia require less power per ton than halocarbons?
a. ammonia requires more power per ton.
b. Halocarbons have lower liquid density.
c. ammonia has higher latent heat capabilities.
d. ammonia has higher liquid density. |
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Definition
| c. Ammonia has higher latent heat capabilities 6-33 |
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Term
108. The term "constant pressure liquid recirculation system" refers to maintaining constant pressure at the :
a. compressor suction inlet.
b. evap outlet
c. liquid compressor inlet
d. CPR outlet |
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Definition
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Term
109. How does the recirculator that is located above the pumper drums maintain its level in a double pumper drum system (fig 6-7)
a. it is connected to the recirculator.
b. it is constantly supplied by a pump
c. The level control allows the high pressure liquid flow directly into the pumper drum
d. The level control allows the high pressure liquid flow into the recirculator. |
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Definition
| d. The level control allows the high pressure liquid flow into the recirculator. 6-18 |
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Term
110. In a double pumper drum system, what happens when the pumper drum is filled?
a. liquid stops returning to the recirculator.
b. flow is stopped from the high pressure receiver.
c. the compressor shuts down.
d. flow from the recirculator stops |
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Definition
| d. flow from the recirculator stops 6-20, 21 |
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Term
111. What happens to flash gas in a pumped liquid overfeed system?
a. it goes through the recirculator to the compressor
b. it goes directly to the evap
c. there is no flash gas in an overfeed system.
d. it is used to power the pumper drum to circulate liquid ammonia |
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Definition
| a. it goes through the recirculator to the compressor. 6-49 |
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Term
112. Why does the liquid overfeed system require less evap surface than a DX evaporator of the same capacity?
a. less refrigerant passes throug hthe evap
b. the evap tubes are smaller
c. the evap tubes are larger
d. more of the evap surface is kept wet |
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Definition
| d. More of the evap surface is kept wet 6-49 |
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Term
113. What does a liquid overfeed system have that is not common to a DX system?
a. two phase flow from the evap
b. an evap
c. a liquid solenoid valve
d. a receiver |
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Definition
| a. two phase flow from the evap 6-3 |
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Term
114. The pressure of the -20F liquid supplied to the orifices of an evap's finned tube circuits is roughly 16psig. The pressure after the orifice is about 3.5psig. How much flash gas was formed by the pressure drop?
a. the amount that would evaporate from 0- -20F as the pressure drops on the liquid passing through the orifice.
b. Approximately 4% of each pound of liquid fed to the evp coils
c. No flash gas because there is no change in refrigerant temp
d. more when the orifice diameter is increased |
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Definition
| c. No flash gas because there is no change in refrigerant temp 6-51 |
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Term
115. Given a system that is an ammonia pumped liquid overfeed system where the evap are bottom fed, operating at 20F with hot gas defrost entering the evap at the top, where would you drain the oil that accumulates?
a. the recirculator
b. the oil separator
c. the suction line accumulator
d. the condenser outlet |
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Definition
| A. The recirculator. 6-48 |
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Term
116. Which of the following is not a problem associated with migrating oil in a system?
a. inefficient operation of evaporators
b. loss of lubrication in the compressor
c. Reduction of system capacity
d. Low condensing pressures |
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Definition
| c. Reduction of system capacity 6-48 |
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Term
117. What precaution must be exercised in placing a check valve in any liquid line?
a. the check valve should be at least one line size larger
b. the check valve must have a bypass line
c. Positive closing of the down stream line must be possible
d. That no liquid refrigerant can be trapped. |
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Definition
| d. That no liquid refrigerant can be trapped 6-44 |
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Term
118. What is not a requirement of a properly sized recirculator?
a. it must be able to hold all surges from the evaporator(s)
b. it must be able to hold all of the system's refrigerant.
c. it must keep the pup suction flooded.
d. it must prevent liquid from passing through to the compressor |
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Definition
| b. it must be able to hold all of the system's refrigerant 6-37, 38 |
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