Refrigeration Flashcards
In a shell-and-tube type heat exchanger, the most common cause of decreased performance is __________ .
fouling on the seawater side
The degree to which the viscosity of an oil will change with a change in temperature is indicated by the __________ .
viscosity index
The meat box temperature control circuit, as used in the ship service refrigeration system, is an example of __________ .
two position control (ON or OFF)
Which of the gage types listed is shown in the illustration? GS-0114
Simplex Bourdon tube type
Which of the following instruments can be used to measure the rate of air flow? A Thermometer B Anemometer C Psychrometer D Aerometer
B Anemometer
What is the function of a heat interchanger used in a refrigeration system?
A lower the temperature of liquid refrigerant before entering the expansion valve
B reduce the possibility of liquid refrigerant from flooding? back to the compressor
C minimize sweating of the suction line
D All of the above.
D All of the above.
What is the principal purpose of subcooling liquid refrigerant prior to its entering the expansion valve?
increase the refrigeration effect by decreasing the amount of flash gas
The pressure difference between the system cut-in and cut-out pressures of a refrigeration unit low pressure cutout device is known as what?
differential
In a small appliance using HFC-134a you would expect to see the greatest temperature drop across what system component?
condenser
A liquid line to suction line heat interchanger in a refrigeration system using a reciprocating compressor serves what function?
reduce the possibility of liquid refrigerant slugging the compressor
The process of removing moisture from air is known as what?
dehumidification
Vapor barrier seals used in the insulation on refrigerated space boundaries serve what function?
they reduce the possibility of moisture laden warm air from outside the refrigerated space from entering the insulation
A pressure drop in the liquid line of a refrigeration system may cause what condition?
flash gas to form in the liquid line
Subcooling is a method of reducing the temperature of the liquid refrigerant below what temperature or point?
condensing temperature
In a small refrigeration appliance using HFC-134a you would expect to see the greatest temperature drop across which system component?
thermal expansion valve
The low-pressure refrigerant leaves the evaporator of a refrigeration system in what condition?
superheated vapor
Which chemical symbol represents ammonia?
NH3
A compound gauge is used to measure _________.
pressure and vacuum
Under normal conditions, the refrigerant enters the compressor in an operating refrigeration system in what condition and/or state?
superheated vapor
In a refrigeration system, the heat normally producing the flash gas at the thermostatic expansion valve, is obtained by what means?
the portion of liquid refrigerant which does not flash
An increase in the heat load subjected to a refrigeration system will cause what to happen?
the compressor suction pressure to increase
The only means of removing the latent heat of condensation from a refrigerant in the normal refrigeration cycle is by performing what process?
condensing refrigerant in the system condenser
Which of the listed statements describes specific heat?
A The amount of heat required to change the temperature of one pound of a material, one degree Fahrenheit.
B The amount of heat required to change one pound of a solid material to a liquid or vice versa.
C The amount of heat required to change one pound of a liquid material to a vapor or vice versa.
D The amount of heat required to change one pound of solid material to a vapor or vice versa.
A The amount of heat required to change the temperature of one pound of a material, one degree Fahrenheit.
The temperature at which water vapor in the atmosphere begins to condense is called what?
dew point temperature
When used as a refrigerant, ammonia containing moisture will act as a corrosive mixture to what metal or metals?
brass and bronze
Which of the following statements is correct concerning a typical shipboard multi-coil refrigeration system?
Refrigerant temperature in an evaporator is directly related to refrigerant pressure.
As the amount of moisture in the air increases, what will happen to the difference between the dry bulb and wet bulb temperatures?
decrease
What condition listed would be associated with an excessively high suction temperature as a result of excessive superheating which produces no useful cooling?
decreased capacity of the compressor
Which of the listed types of refrigeration compressors can be designed with very short, very large diameter suction lines?
centrifugal
Increasing the moisture content of conditioned air is known as what?
humidification
The temperature of the refrigerant in the evaporator coil depends mostly upon what factor?
refrigerant pressure in the evaporator
In a vapor compression refrigeration cycle, the temperature of the liquid refrigerant experiences its greatest decrease flowing through what component?
expansion valve
In which of the listed refrigeration system components does superheating of the refrigerant take place?
evaporator
In the order of the direction of flow, which of the listed components is considered to separate the high pressure side of a refrigeration cycle from the low pressure side of the cycle?
The compressor and the expansion valve
The EPA allows a large low pressure system to be brought to atmopsheric pressure during non-major repairs by what means?
adding heat with controlled hot water
Refrigerant enters the condenser in what condition?
high pressure vapor
The component of a refrigerating system in which the refrigerant vaporizes and absorbs heat is known as what?
evaporator
In a mechanical refrigeration system, in addition to the high and low side pressure differential, what is the amount of refrigerant admitted to the evaporator directly related to?
the degree of opening of the expansion valve
A purge-recovery unit is used in a centrifugal air conditioning or refrigeration system for what purpose?
purge non-condensable gases while minimizing the loss of refrigerant
refrigerant is circulated through a refrigeration system by the action of what component?
compressor
Which of the following terms represents the form of heat removed from the refrigerant in the condenser of a refrigeration system? A Latent heat of vaporization B Heat of compression C Superheat D All of the above
D All of the above
The refrigerant gas returning to the compressor should be in what condition?
superheated
In a typical refrigeration system, refrigerant leaving the receiver will then flow to what system component?
liquid line strainer
During the operation of a large multi-box refrigeration system, using a fixed capacity compressor, only two of the five boxes are in the process of actively being cooled. If two additional boxes were to be brought into the cooling process simultaneously, how would the system react?
low side pressure would temporarily increase
Pure anhydrous ammonia is considered noncorrosive to what metal or metals?
iron, steel, and copper- bearing metals
Refrigerants that experience fractionation when changing state are characterized as what?
zeotropic blend of refrigerants
In the order of the direction of flow, the low pressure side of a refrigeration system is considered to exist between what two components?
expansion valve to the compressor
One of the primary steps in assisting someone who has been overcome by ammonia vapors is to do what?
give the patient plenty of fresh air
In a refrigeration system, at what component does the refrigerant absorb the latent heat of vaporization?
evaporator
The high pressure cut-out switch used on centrifugal low pressure refrigeration units using R-123 would be set to shut off the compressor at approximately what pressure?
10 psig
Which of the following devices is the safest to use when locating ammonia leaks? A Litmus paper B Sulphur candle C Halide torch D All of the above are recommended.
A Litmus paper
Which of the following refrigerants will normally require a compressor that is water cooled?
ammonia
Which of the listed valves should be closed when charging refrigerant into a refrigeration system?
King valve
In a typical refrigeration system, where is the temperature of the refrigerant gas at the highest?
at the compressor discharge
The inlet of the purge-recovery units used with some compressors in low pressure refrigeration systems is connected to the top of what system component?
condenser
HCFC-22 has been recovered from a refrigeration system prior to and in preparation for condenser replacement. What is true concerning the recovered refrigerant?
it may be returned to the system for re-use
Which of the refrigerants listed is considered as a suitable and limited ozone producing alternative for R-11?
R-123
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In terms of the conditions associated with the boiling process, what impact does oil in solution mixed with the liquid refrigerant have?
higher boiling temperature for a given pressure than does a pure refrigerant
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One refrigeration ton is equal to which of the following heat removal rates? A 180 BTU/hr B 2,000 BTU/hr C 12,000 BTU/hr D 2,880,000 BTU/day
C 12,000 BTU/hr
Which of the fluids listed is normally used to condense the primary refrigerant in an indirect shipboard central air conditioning system? A Engine jacket water B Seawater or Fresh water. C Sodium Nitrate brine. D Calcium Sulfate brine.
B Seawater or Fresh water.
Which of the following represents the chemical formula for ozone?
O3
The rupture disc used on low pressure refrigerant storage containers is set for what pressure?
15 psig
Which of the listed statements is correct concerning refrigeration systems?
A Dehydrators must be used continuously in a refrigeration system.
B A 25 ton refrigeration system has the same cooling effect as melting 25 tons of ice in 24 hours.
C A thermostatic expansion valve is used to control? refrigerated space temperature.
D The liquid receiver functions to collect and remove noncondensable gases.
B A 25 ton refrigeration system has the same cooling effect as melting 25 tons of ice in 24 hours.
Which chemical, when released into the atmosphere, has been found to eventually reach the stratosphere and react unfavorably with the earths ozone layer?
chlorine
What is one benefit of maintenance of proper air circulation in an air conditioned cargo space? A reduced slime and mold B increased moisture content C increased density of the air D more temperature differential
A reduced slime and mold
Which group of three refrigerants are considered low pressure refrigerants under the Clean Air act rules? A CFC-11, CFC-113 and R- 502 B CFC-11, CFC-113 and HCFC-123 C CFC-11, R-502 and HCFC-123 D CFC-11, CFC-114 and R 502
B CFC-11, CFC-113 and HCFC-123
In general, the thermal bulb for a thermal expansion valve used in a reciprocating air conditioning system is usually charged with what substance?
the same refrigerant as the system
Large quantities of halogenated chlorofluorocarbons when released from refrigeration systems, will contribute to ozone depletion in which region of the atmosphere?
stratosphere
Flash gas formed in the liquid line of a direct reciprocating air conditioning system may cause what condition?
expansion valve pins and seats to erode
Most freon refrigerants are originated primarily from which of the following base molecules?
ethane and methane
For the proper control of the air temperature in an air conditioning system using chilled water circulation, which of the listed conditions should remain constant regardless of load changes?
A Compressor discharge temperature.
B Chilled water system return temperature.
C Compressor suction pressure.
D Chilled water system supply temperature.
D Chilled water system supply temperature.
The refrigerants referred to as CFC’s are considered to be what?
fully halogenated
In an air conditioning system, moisture is removed from the air by what means?
cooling coils
To add small amounts of refrigerant to the low side of an air conditioning system, the refrigerant should be introduced through a particular valve and in a particular state. What valve and state combination is correct? A suction service valve as a vapor B discharge service valve as a vapor C discharge service valve as a liquid D suction service valve as a liquid
A suction service valve as a vapor
Which refrigerant listed is considered to have the highest ozone depletion potential?
R-12
Industrial process and commercial CFC type refrigeration equipment with annual leak rates of 35% or more, require leak repair of the system if it contains a refrigerant charge of more than what quantity?
50 pounds (22.6 kg)
What is the purpose of the low pressure cut-out switch as used as a primary controller for a refrigeration system or unit?
start and stop the compressor as needed
What is he primary purpose of the thermostatic expansion valves in a typical multi-box shipboard refrigeration system?
they regulate the amount of refrigerant superheat leaving the individual evaporators
The receiver used in a refrigeration system performs what function?
stores liquid refrigerant and acts as a surge tank to compensate for changes in system load
A one ton air conditioning system has which of the listed operating characteristics?
A It forces 2,000 lbs. of refrigerant through the evaporator coil per day.
B It forces 2,000 lbs. of air per hour across the evaporator coils.
C It has the cooling capacity equivalent to melting 2,000 lbs. of ice per day.
D It has the cooling capacity equivalent to melting 2,000 lbs. of ice per hour.
C It has the cooling capacity equivalent to melting 2,000 lbs. of ice per day.
HCFC-123 presents health threats to service technicians, which may include which of the following?
A flammability as a liquid
B freezing in the compressor
C toxic threat
D being caustic and strong offensive odor
C toxic threat
In a vapor compression type refrigeration cycle, the refrigerant temperature decreases the most when passing through which system component? A evaporator B condenser receiver C compressor D expansion valve
D expansion valve
CFC refrigerants exposed to high temperature or direct flame, will decompose and may produce what chemical substance?
hydrofluoric acid
To add refrigerant to the high side of an air conditioning system, you should close the king valve and introduce the refrigerant through what valve in what state?
charging valve as a liquid
The safety heads of most large reciprocating compressors used in refrigeration systems are held in place by what means?
heavy coil springs
What characteristic can be applied to Refrigerant 134a when compared to R-12?
It is not compatible with mineral based lubricants.
When pumping down an air conditioning system to test the low pressure cutout switch, assuming that the compressor is running, what should be done to initiate the test?
close the ‘king’ valve
In multi-box refrigeration systems, the sensing bulb of the thermostatic expansion valves used on the refrigerated boxes with elevated temperatures should be located where?
before the back pressure regulating valve
In a refrigeration system, silica gel is found in what component?
dehydrator or combination filter/drier
To service a 60 ton air conditioning package, what is the easiest way to determine the type of refrigerant that the unit is charged with?
look at the unit name plate
In an air conditioning system, low discharge head pressure associated with a reciprocating compressor can be the result of what condition?
A leaky suction valves
B insufficient cooling water to the condenser
C air in the condenser
D air in the evaporator coils
A leaky suction valves
Sludge may form in the crankcase of an air conditioning compressor as a result of what condition?
overheating and carbonization of the oil in the crankcase
What parameter is the thermostatic expansion valve designed to maintain constant?
evaporator superheat
Besides the evaporator pressure, the thermal expansion valve reacts directly to changes in what parameter?
temperature of the evaporator coil outlet
A multiple evaporator system is equipped with a evaporator back pressure regulating valve on the warmer of the two boxes. This valve must be bypassed when pumping down the system for repairs because reduction of suction pressure would cause the valve to do what?
close
In a large refrigeration system having more than one evaporator, a king solenoid valve should be installed in what location?
just after the receiver
In a multi-evaporator refrigeration system, a solenoid valve is installed in the liquid line prior to what device?
each expansion valve
The individual box temperatures of a multi-box refrigeration system are directly controlled by what means?
thermostatically controlled solenoid valves!!
NOT the TXV!
When starting a reciprocating refrigeration compressor that has been shut down for a period of time, you should manually throttle which valve?
suction valve
In which of the following lines is an oil separator most likely to be?
discharge line
In a refrigeration system, the condenser cooling water regulating valve is directly controlled by changes in what parameter or condition?
compressor discharge pressure
The pressure in the part of a high pressure refrigeration system about to be opened for a non-major repair should be brought to what value?
0 psig
Which recovery procedure should be used to minimize the loss of oil from the system during the recovery of refrigerant from small appliances such as a water cooler?
vapor recovery
