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RAC 40 > unit 3 quiz > Flashcards

unit 3 quiz Flashcards

1
Q

the ___ is another positive displacement compressor and is used for larger air conditioning and refrigeration applications

A

screw compressor

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2
Q

the 4 major components of a vapor compression refrigeration system are the compressor, condenser, evaporator, and ___

A

meter device

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3
Q

the amount of heat a refrigerant contains with -40 degree F as the 0 heat content reference point is called ___

A

enthalpy

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4
Q

from a performance standpoint, a substitute for r-12 is ___

A

r-134a

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5
Q

the ___ is referred to as a kinetic displacement compressor

A

centrifugal

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6
Q

the refrigerant vapor picks up additional heat as it flows from the evaporator to the compressor. the heat is picked up from the ___

A

suction line

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7
Q

whats the purpose of the metering device

A

meters the liquid into the evaporator

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8
Q

when the refrigerant leaves the metering device, it is not 100% liquid. why

A

refrigerant passes as 100% liquid but start to turn into 75% liquid and 25% vapor because as it starts to feed into the evaporator, ambient temp raises the refrigerants temp

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9
Q

good ventilation is important when working around refrigeration equipment because modern refrigerants ___
a. are toxic and can poison you
b. have an unpleasant odor
c. are heavier than air and may displace the oxygen around you
d. both a and c

A

c. are heavier than air and may displace the oxygen around you

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10
Q

the ___ relationship correlates the vapor pressure and the boiling point of water and is the basis for controlling the cooling systems temperature
a. boiling/pressure
b. temperature/pressure
c. boiling/vapor
d. temperature/vapor

A

b. temperature/pressure

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11
Q

which of the following refrigerants has the lowest boiling temperatures at atmospheric pressure
a. r-502
b. r-22
c. r-134a
d. r-12

A

a. r-502

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12
Q

the compressor in a refrigeration system ___
a. raises the boiling point of the refrigerant
b. pumps the refrigerant throughout the system
c. both a and b
d. none of the above

A

b. pumps the refrigerant throughout the system

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13
Q

a ton of refrigeration is equal to ___
a. 288,000 btu/24hr
b. 12,000 btu/min
c. 1 ton of ice
d. 144 btu/hr

A

a. 288,000 btu/24hr

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14
Q

the law requires technicians to recover refrigerant from all refrigeration systems so that they ___
a. will not be released into the atmosphere
b. may be used again
c. may be reclaimed for future use
d. all of the above

A

d. all of the above

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15
Q

refrigeration can be described as ___
a. the process of introducing heat to a location where it is not wanted
b. the process of removing heat from a place where it is not wanted to a place where it makes little or no difference
c. the process of making products cold
d. none of the above

A

b. the process of removing heat from a place where it is not wanted to a place where it makes little or no difference

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16
Q

the temperature inside the refrigerator fresh food section should be about ___
a. 25 degrees F
b. 30 degrees F
c. 35 degrees F
d. 40 degrees F

A

c. 35 degrees F

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17
Q

the evaporator in a refrigeration system ___
a. compress the refrigerant vapor
b. condenses the refrigerant
c. reduces the boiling point of the refrigerant
d. absorbs heat from the product to be cooled

A

d. absorbs heat from the product to be cooled

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18
Q

high temperature refrigeration is that produced by ___
a. heat from a furnace
b. the vegetable cooling system of a refrigerator
c. the freezer section of a refrigerator
d. an air conditioning system

A

d. an air conditioning system

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19
Q

reciprocating compressors have ___
a. a piston and cylinder
b. a rotor to compress the refrigerant
c. two scrolls that mesh together
d. a large fan compressor component

A

a. a piston and cylinder

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20
Q

what happens when room temperature soda is poured into a glass of ice
a. the ice melts because it is giving up the “cold” to the soda
b. the ice melts because the soda is colder than the ice
c. the ice melts because it is absorbing heat from the soda
d. the ice gets colder

A

c. the ice melts because it is absorbing heat from the soda

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21
Q

the condenser ___
a. adds superheat to the refrigerant
b. rejects the heat from the refrigerant
c. controls the refrigerant flow throughout the system
d. all of the above

A

b. rejects the heat from the refrigerant

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22
Q

when a refrigerant enters the compressor, it is a ___ and when it leaves the compressor, it is a ___
a. high pressure superheated vapor, low pressure superheated vapor
b. low pressure low temperature subcooled liquid, high pressure high temperature superheat vapor
c. low pressure low temperature superheated vapor, high pressure high temperature superheated vapor
d. low pressure low temperature superheated vapor, low pressure low temperature subcooled vapor

A

c. low pressure low temperature superheated vapor, high pressure high temperature superheated vapor

23
Q

the ___ are used to change the vapor to a liquid and the liquid form back into a vapor the refrigeration
a. condenser and compressor
b. compressor and expansion device
c. expansion device and evaporator
d. condenser and evaporator

A

d. condenser and evaporator

24
Q

ice melts in iceboxes because___
a. heat enters when the door is opened
b. heat flows through the insulated walls
c. heat enters when warm food is placed in the icebox
d. all of the above

A

d. all of the above

25
Q

t/f if a cylinder of r-22 is moved from a 100F truck body into and 80F shop, the quantity of liquid refrigerant in the cylinder will remain the same

A

false

26
Q

t/f modern refrigerators have become state of the art appliances and some models even include automatic beverage and ice dispensers, built in television screens and connections to the world wide web

A

true

27
Q

the boiling point of a refrigerant should be low enough at atmospheric pressure to keep the system pressure above 0 psig when operating at low temperatures

A

true

28
Q

the discharge gas from the compressor is a high pressure, high temperature, superheated vapor

A

true

29
Q

an expansion valve is the pressure reducing device that controls the flow of liquid refrigerant into the evaporator

A

true

30
Q

the evaporator can be thought of as a “heat sponge”

A

true

31
Q

vapor is more dense than liquid and, as the liquid refrigerant boils, it has a tendency to sink

A

false

32
Q

only liquid refrigerant should enter the metering device

A

true

33
Q

the only location where the refrigerant vapor is superheated is in the evaporator

A

false

34
Q

the evaporator in a refrigeration system must be colder than the refrigerated space in order to absorb heat

A

true

35
Q

the halide leak detector should be used in well ventilated areas the resulting blue or green flame indicates that phosgene gas is being produced

A

true

36
Q

what is another word for flash gas

A

adiabatica

37
Q

what is the meaning of THOR

A

total heat of rejection

38
Q

how will discharge temperatures affect your compressor

A

cause oil to break down, acid will form

39
Q

name 3 positive displacement compressors

A

scroll, rotary, screw, reciprocating

40
Q

when engineers design air conditioning units what parameters are used

A

outside/inside temp
evap temp
evap coil temp

41
Q

what temperature will the hawaii health department use to gauge med temp chill boxes and low temp freezer

A

0F-10F

42
Q

how are refrigeration compressor rated

A

kwh/hp/ton/btu

43
Q

where are evaporators fed from and why

A

bottom of evaps

44
Q

what type of equipment will you find r410a refrigerant in

A

high temp
a/c, ductless, chillers, package units, heat pumps

45
Q

what type of equipment will you find r404a

A

low temp, med temp

46
Q

what type of equipment will you find r407c refrigerant in

A

chillers, walk in chillers

47
Q

what type of equipment will you find r-134a refrigerant in

A

med temp, car a/c, chill boxes

48
Q

what type of equipment will you find r32 refrigerant in

A

water chill systems

49
Q

what is system subcooling

A

15-20 subcooling, total rejection of heat from condenser

50
Q

___ ensures that no liquid returns to the compressor
a. constant heat
b. miami heat
c. latent heat
d. super heat

A

d. superheat

51
Q

t/f 404a and 410a are known as near orangetropics blend

A

false

52
Q

how would you calculate standard condenser efficiency

A

ambient + 30 degrees

53
Q

___ and ___ are responsible for naming refrigerants and identifying there characteristics

A

ASHRAE, ANSI

RAC 40 (10 decks)

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