RACT Unit 21 Review questions/Practice test Flashcards
What is the function of the evaporator in the refrigeration system?
A) to add heat to the space or product being coole
B) to add humidity to the space being refrigerated
C) It condenses superheated refrigerant vapour to a liquid
D) absorbs heat into the refrigeration system
D) absorbs heat
Refrigerant in the evaporator;
A) changes from vapour to liquid
B) changes from liquid to vapour
C) stays in vapour state
B) changes from liquid to vapour
The sensible heat that is added to a saturated vapour after all of the liquid has boiled away is referred to as;
A) superheat
B) Latent heat
C) Sub-cooling
D) Specific heat
superheat
What determines the pressure on the low pressure side of the system?
A) the condensing temp of the refrigerant in the condenser
B) the length of the liquid line feeding the TXV
C) The boiling temperature of the refrigerant in the evap
the boiling point of the refrigerant in the evaporator
A refrigeration systems evaporator typically runs at about ________ of super heat
8 to 12F
What does a high evaporator
superheat indicate?
A) flooded evap
B) starved evap
C) proper system operation
starved evaporator
A low evaporator superheat may indicate;
A) undercharge
B) system restriction
C) overcharge
D) high heat load
overcharge
Why is a multi circuit evaporator used?
A) to reduce pressure drop through larger evaporators
B) To ensure proper compressor operation
C) to prevent ice build on the fine
D) easily defrosted in low temp applications
to reduce pressure drop
Flooded evaporators typically use a __________ type of expansion device
a) automatic
b) float
c) TXV
d) fixed bore
float
An evaporator that does not operate flooded is thought of as what type of evaporator?
A) A dry type
B) a starved type
C) a float type
D) a low pressure type
A dry type
When an evaporator experiences a heat load increase, the suction pressure
a) remains constant
b) decreases
c) varies up and down
d) increases
increases
What is commonly used to defrost the ice from a low temp evaporator?
A) random or off-cycle defrost
B) hot gas or electric resistance heat defrost
C) Off-cycle or manual defrost
D) Low temperature evaporators do not require a defrost
hot gas or electrical heaters
A medium temperature refrigeration box typically operates within what temperature range?
A) 28 to 40
B) 40 to 60
C) 0 to 220
D) 0 to 50
28 to 40F
The greater the difference in temperature between the evaporator and the air being cooled;
A) the less moisture will be removed from the air
B) The less moisture will be added to the air
C) The more moisture will be added to the air
D) The more moisture will be removed from the air
The more moisture will be removed
A finned tube evaporator equipped with fans is called a _______ evaporator
A) bare tube
B) stamped
C) induced or forced draft
D) liquid cooling
bare pipe
Which of the following is not a function of an evaporator efficiency control?
A) minors evap efficiency and
performance
B) Initiates a defrost when coil efficiency drops below 90%
C) Contains an ethernet network device that supports industry standard protocols
D) regulates condensate removal by activating condensate pump
C)
A medium temperature evaporator uses a _________ defrost method
A) hot gas
B) random or off cycle
C) electric resistance heat
D) liquid injection
B) random or off-cycle
The difference in the amount of heat (in btu/lb) that the refrigerant contains at the point where it enters the evaporator and the point at which it leaves the evaporator is known as
A) mass flow rate
B) total heat of rejection
C) the net refrigeration effect
D) The heat of compression
The net refrigeration effect
Low temperature refrigeration systems typically operate at what temperature range?
0 to -20F
high temp refrigeration systems typically operate at?
47 to 60F
The difference in temperature between the boiling refrigerant temperature and the evaporator is known as ____________
a) evaporator superheat
b) delta T
c) suction line superheat
d) temperature difference
a) evaporator superheat
Low temperature food storage applications typically have a temperature range of __________
a) 0 to -32F
b) 0 to -20F
c) -20F to -32F
d) 0 to 32F
b) 0 to -20F
When the evaporator removes heat from the air and lowers the temperature of the air, ___________
a) sensible heat is removed from the air
b) moisture is added to the air
c) refrigerant vapour condenses to a liquid
d) latent heat is added to the air
a) sensible heat is removed from the air
When moisture is removed from the air, latent heat is removed
True or False
True
Natural-convection evaporators use a blower to force or induce air over the coil to improve the efficiency of the heat exchange
false
When a refrigerated space has been allowed to warm up considerably, the system must ___________
a) be overcharged to remove the excess heat
b) be defrosted at regular intervals
c) go through a hot pull down
d) turned off and the product being cooled moved to another cooler
c) go through a hot pull down
Flooding the compressor crankcase with liquid refrigerant can cause _________
a) oil foaming
b) excessive superheat
c) starved evaporator
d) moisture to accumulate in the compressor oil
a) oil foaming
Low-temperature evaporator coils ___________
a) operate the same as medium temperature evaporator coils
b) have fewer fins per inch than medium temperature evaporator coils
c) require more oil circulation that medium temperature evaporator coils
d) have more fins per inch than medium temperature evaporator coils
b) have fewer fins per inch than medium temp evaporator coils
Two common methods for defrosting a low temperature evaporator are _____________
a) off-cycle and got gas
b) reverse cycle and hot gas
c) off-cycle and electric heat
d) hot gas and electric heat
d) hot gas and electric heat
When liquid refrigerant floods the compressor crankcase, the oil level in the crankcase can drop causing ________
a) condenser flooding
b) excessive superheat
c) bearing washout
d) valve damage
c) bearing washout
