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Middterm Review > Mechanical Final Heat Exchangers & MD Review > Flashcards

Mechanical Final Heat Exchangers & MD Review Flashcards

1
Q

An AXV works best when the evaporator load is constant.

A

True

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2
Q

The pin or valve port piston of the electronic step-motor expansion valve can move a linear motion of 300 steps per second.

A

False

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3
Q

A refrigeration system that continuously runs under high-load conditions (hot pull downs) would most likely use a thermostatic expansion valve with a vapor charged thermal bulb assembly.

A

True

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4
Q

Too high of pressure entering the compressor will cause the density of suction gases entering the compressor to increase.

A

True

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5
Q

To check the performance of a dry-type evaporator, the service technician would first make sure that the refrigerant coil is operating with enough liquid inside.

A

True

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6
Q

When condensation cannot flow directly to a drain, a condensate pump can be used to move it to the drain.

A

True

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7
Q

Some commercial refrigeration applications require that water be kept from freezing at temperatures below 32°F (0°C).

A

True

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8
Q

A PWM solenoid EEV can hold its valve at any variable position between open and closed for the purpose of modulating refrigerant flow.

A

False

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9
Q

Adsorption occurs when two substances combine to become one substance.

A

False

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10
Q

In a heat pump system with two piston-type fixed-orifice metering devices, one piston meters refrigerant flowing in one direction and allows free flow in the other direction.

A

True

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11
Q

The purpose of a capillary tube is to ____.

regulate the refrigerant flow into the evaporator

lower the pressure of the liquid refrigerant

lower the boiling point of the refrigerant

all of the above

A

d) all of the above

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12
Q

The pressure limiting TXV ____.

allows the compressor to operate at low condenser entering air temperatures

shuts off the condenser fan during hot pull down

maintains the full refrigerant flow rate during a hot pull down

limits the refrigerant flow rate to the compressor capacity

A

d) limits the refrigerant flow rate to the compressor capacity

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13
Q

Balanced port TXVs are used to ____.

feed refrigerant at a normal rate with low condenser entering air temperatures

feed refrigerant at a normal rate with high condenser entering air temperatures

stop refrigerant flow with high condenser entering air temperatures

stop refrigerant flow with low condenser entering air temperatures

A

a) feed refrigerant at a normal rate with low condenser entering air temperatures

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14
Q

When the load on the evaporator increases, the TXV ____.

increases the flow of refrigerant

decreases the flow of refrigerant

maintains constant head pressure

decreases the pressure drop across the evaporator

A

a) increases the flow of refrigerant

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15
Q

The cross liquid charge bulb at the TXV contains fluid that ____.

has similar characteristics to the system fluid to prevent liquid refrigerant from entering the suction line

has different characteristics from the system fluid

causes the valve to stay open during the off cycle

follows the typical pressure-temperature relationship

A

b) has different characteristics from the system fluid

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16
Q

If a thermostatic expansion valve’s thermal bulb came loose from the suction line at the outlet of the evaporator, which of the following could result?

The bulb pressure would increase and the thermostatic expansion valve would open.

The superheat in the evaporator would decrease.

Liquid refrigerant would flow back to the compressor.

All of the above are correct.

A

d) all of the above answers are correct

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17
Q

A thermostatic expansion valve controls refrigerant flow to the evaporator based on ____.

rate of liquid vaporization

evaporator suction line superheat

external equalizer pressure

all of the above

A

b) evaporator suction line superheat

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18
Q

The primary function of an expansion device is to ____.

produce a reduction in the pressure on the liquid refrigerant

regulate the flow of refrigerant into the evaporator

lower the boiling point of the refrigerant far enough below the temperature of the load to get the needed heat transfer rate

all of the above

A

d) all of the above

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19
Q

Which of the following can be used to maintain the head pressure of a system with an air-cooled condenser?

fan cycling

condenser flooding valve

dampers or louvers

all of the above

A

d) all of the above

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20
Q

An air-cooled condenser that is operating in a climate that has four distinct seasons must ____.

have some type of head pressure control

use a water regulating valve

have a multi-circuit evaporator

operate with zero degrees of subcooling

A

a) have some type of head pressure control

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21
Q

Condensing temperatures in an air-cooled condensing unit can be reduced by ____.

increasing the condensing surface area

increasing the cfm through the condenser

decreasing the temperature of the air entering the condenser

all of the above

A

d) all of the above

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22
Q

If an R-12 refrigeration system has its air-cooled condensing unit on a 100°F roof and the condenser outlet temperature (refrigerant) is 115°F, with how much subcooling is the condenser operating?

30°F

15°F

100°F

130°F

A

b) 15F

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23
Q

A normally operating water-cooled condenser is operating with a 10° differential between water in and water out. If the amount of 85°F water going through the condenser is reduced, which of the following is a possible temperature of the water leaving the condenser?

75°F

0°F

95°F

105°F

A

d) 105F

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24
Q

What can be used to maintain the head pressure of a system with a water-cooled condenser?

fan cycling

dampers or louvers

water regulating valve

all of the above

A

c) water regulating valve

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25
Q

In a water-cooled condenser, a regulating valve is used to control the ____.

refrigerant flow through the pressure reducing device

refrigerant condensing temperature

suction pressure

water temperature

A

b) refrigerant condensing temperature

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26
Q

The shell-and-tube condenser is cleaned ____.

with a brush after removing the end caps

only with chemicals

with compressed air

with a vacuum cleaner

A

a) with a brush after removing the end caps

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27
Q

The water circuit in shell and coil and coil-type tube-in-a-tube condensers must be cleaned ____.

by removing the end caps

with a brush

chemically

by air pressure

A

c) chemically

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28
Q

In a water-cooled condenser with dirty condenser tubes, the temperature difference between the refrigerant and the leaving water will be ____ when the tubes are clean.

less than

greater than

the same as

slightly lower than

A

greater than

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29
Q

Mineral deposits in the water portion of a water-cooled condenser act as ____.

a conductor of heat

an insulator

a cleaning solution

They have no effect on the operation of the condenser.

A

an insulator

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30
Q

A normally operating water-cooled condenser is operating with a 10° differential between water in and water out. If scale forms on the water tubes and the entering water is 85°F, which of the following is possible?

The outlet water temperature will be lower than expected.

The system head pressure will rise.

The water regulating valve will close.

Both a and b are correct.

A

Both A and B are correct

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31
Q

The condenser in a refrigeration system ____.

desuperheats the vapor from the compressor

condenses the vapor from the compressor

subcools the liquid refrigerant before it leaves the condenser

all of the above

A

all of the above

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32
Q

The refrigerant in a condenser in a refrigeration system ____.

absorbs heat

rejects heat

changes to a vapor

is under lower pressure than the evaporator

A

rejects heat

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33
Q

A typical superheat for an evaporator operating under normal conditions would be ____.

4 to 6°F

6 to 8°F

8 to 12°F

14 to 16°F

A

8 to 12F

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34
Q

____ is the best method of checking to see when a refrigerant coil has a proper level of refrigerant.

Boiling temperature

Superheat

Dryheat

Vapor temperature

A

b) superheat

35
Q

A direct expansion-type evaporator is also called a ____.

flooded evaporator

dry-type evaporator

multi-circuit evaporator

stamped evaporator

A

dry-type evaporator

36
Q

The ____ of the liquid refrigerant determines the coil operating temperature.

freezing point

melting point

transition temperature

boiling temperature

A

boiling temperature

37
Q

A typical evaporator operating temperature in an air-conditioning system is ____.

40°F

55°F

75°F

200°F

A

40F

38
Q

The boiling temperature and its relationship to the system exist in the ____.

coil

thermostat

condenser

evaporator

A

evaporator

39
Q

The ____ in a refrigeration system is responsible for absorbing heat into the system from whatever medium is to be cooled.

evaporator

thermostat

compressor

condenser

A

evaporator

40
Q

The household refrigerator fresh-food compartment is a good example of ____ refrigeration.

low-temperature

medium-temperature

high-temperature

average-temperature

A

medium-temperature

41
Q

The superheating done by a suction line-liquid line heat exchanger helps prevent ____.

liquid slugging in the compressor

frozen drain pans

frosted evaporators

tripped thermal overloads

A

liquid slugging in the compressor

42
Q

A suction line-liquid line heat exchanger ____.

superheats liquid refrigerant on the high side

superheats vapor refrigerant in the suction line

promotes a steady column of liquid in the suction line

All of the above.

A

superheats vapor refrigerant in the suction line

43
Q

A tank connected between the outlet of a condenser and a liquid line that is used for refrigerant storage is a(n) ____.

reclaim tank

liquid receiver

accumulator

All of the above.

A

liquid receiver

44
Q

Counterflow in a tube-within-a-tube condenser allows ____.

the warmest water to be adjacent to the warmest refrigerant

the coolest refrigerant to be next to the coolest water

a steady transfer of heat throughout the entire condenser

All of the above.

A

d) all of the above

45
Q

A condenser that consists of an inner tube through which water flows in one direction and a surrounding outer tube through which refrigerant flows in the opposite direction of the water flow is a ____.

shell-and-tube

shell-and-coil

tube-within-a-tube

All of the above.

A

tube-within-a-tube

46
Q

A condenser in which a water tubing winds around the inside of a metal refrigerant shell is called a(n) ____ condenser.

air-cooled

shell-and-coil

shell-and-tube

tube-within-a-tube

A

shell-and-coil

47
Q

A condenser that is composed of a long refrigerant cylinder filled with straight copper tubes filled with cooling water is called a ____ condenser.

shell-and-tube

shell-and-coil

tube-within-a-tube

All of the above.

A

shell-and-tube

48
Q

A condenser that uses only water as the medium into which system heat is expelled is a(n) ____ condenser.

air-cooled

water-cooled

evaporative

All of the above.

A

all of the above

49
Q

A condenser that uses only the air movement of either natural convection or forced drafts to remove heat from a system’s refrigerant is a(n) ____ condenser.

water-cooled

evaporative

air-cooled

All of the above.

A

air cooled

50
Q

In a hot-gas defrost system, the evaporator is defrosted by ____.

refrigerant vapor from the discharge line

suction vapor from the low side

warm liquid refrigerant from the high side

hot exhaust fumes from a gas or diesel engine

A

refrigerant vapor from the discharge line

51
Q

Since a compressor continues to operate after a pump-down solenoid closes, ____.

refrigerant from the evaporator and low side is pumped down

refrigerant collects in the evaporator and accumulator

high-side pressure drops

a high-pressure control is used to turn off the compressor

A

refrigerant from the evaporator and low side is pumped down

52
Q

In what type of defrost system is hot refrigerant gas diverted to the evaporator to expedite the defrosting process?

Off-cycle defrost system.

Pump-down defrost system.

Electric heat defrost system.

None of the above.

A

none of the above

53
Q

Which of the following statements regarding off-cycle defrost systems is false?

Frost accumulates during the On cycle.

The evaporator fans continue to circulate air during the Off cycle.

The heat in the air circulated during the Off cycle melts the frost.

It can only be used in very-low-temperature systems.

A

It can only be used in very-low-temperature systems.

54
Q

In what type of defrost system is air from the conditioned space circulated over the evaporator when the compressor is not running?

Off-cycle defrost system.

Pump-down defrost system.

Electric heat defrost system.

None of the above.

A

off-cycle defrost system

55
Q

An electric heat defrost system ____.

energizes electric heating coils

applies an electric voltage directly to the frost-covered coil

uses illuminated heat lamps

None of the above.

A

energies electric heating coils

56
Q

Which of the following statements regarding water defrost systems is false?

Water delivery may be dripped through a pan located over the evaporator.

Water delivery may be through a spray.

Water delivery may be done during a cooling cycle with the compressor running.

The water running over the evaporator is warm enough to melt the ice.

A

Water delivery may be done during a cooling cycle with the compressor running.

57
Q

In a nonfreezing solution defrost system, ____.

the nonfreezing solution may be heated by hot gas

the system’s nonfreezing solution is usually stored in a heat exchanger

the nonfreezing solution may be heated by electric heat

All of the above.

A

all of the above

58
Q

A condensate pump is used to ____.

remove the moisture that builds up from defrosting and condensation

move water to a cooling tower’s gravity flow basin

provide water pressure for an evaporative condenser

All of the above.

A

remove the moisture that builds up from defrosting and condensation

59
Q

A defrost timer that turns on defrost operations at a preset time and turns it off when a preset pressure is reached is a ____ defrost timer.

time-initiated, temperature-terminated

time-initiated, pressure-terminated

time-initiated, time-terminated

None of the above.

A

time-initiated, pressure-terminated

60
Q

A defrost timer that turns on defrost operations at a preset time and ends the defrost operation at a preset time is a ____ defrost timer.

time-initiated, temperature-terminated

time-initiated, pressure-terminated

time-initiated, time-terminated

None of the above.

A

time-initiated, time-terminated

61
Q

Surfaces in and along air ducts that direct airflow through the evaporator and throughout the cabinet are called ____.

off-center plates

fittings

wet plates

baffles

A

baffles

62
Q

Heat exchangers featuring metal fins of various styles and types connected to evaporator tubing are ____ evaporators.

baffle-tube

fin-and-tube

plate

shell-and-sheet

A

fin-and-tube

63
Q

A liquid-cooling evaporator ____.

uses a cooled liquid that acts as the primary heat transfer medium

can be immersed or tube-within-a-tube

is designed to cool a liquid rather than air

All of the above.

A

all of the above

64
Q

The pressure reading in a system using an EEV is supplied from a ____ connected to the suction line.

temperature sensor

pressure gauge

pressure transducer

All of the above.

A

pressure transducer

65
Q

The minimum ____ setting is the point that causes the least sensing bulb temperature change while the system is running.

stable signal

superheat

subcooling

surging

A

stable signal

66
Q

On a capillary tube system, severe frosting of the suction line during compressor start-up indicates a(n) ____.

overcharge

undercharge

refrigerant leak

None of the above.

A

overcharge

67
Q

Electronic expansion valves (EEVs) use a ____-operated assembly.

spring

diaphragm

bellows

None of the above.

A

none of the above

68
Q

To maintain a constant pressure in the evaporator when the system is running, an AXV ____ refrigerant flow when the evaporator pressure drops.

decreases

stabilizes

increases

None of the above.

A

increases

69
Q

In a float-operated system, oil ____ occurs when oil forms a layer on the surface of the liquid refrigerant in the evaporator instead of returning to the compressor.

flooding

adsorption

absorption

binding

A

binding

70
Q

In evaporators equipped with a float pan, the suction line extends down into the float pan for the purpose of circulating ____.

liquid refrigerant

oil

liquid moisture

None of the above.

A

oil

71
Q

When the low-side pressure ____ in a low-side float system, a pressure control activates the compressor motor.

vents to atmosphere

falls

rises

All of the above.

A

rises

72
Q

Pulse width-modulating (PWM) solenoid EEVs are refrigerant metering devices that use a pulse width modulation signal to control the operation of a ____ for variable refrigerant flow.

stepper motor

diaphragm or bellows

solenoid valve

bleed valve

A

solenoid valve

73
Q

Low-side float (LSF) metering devices control the flow of liquid refrigerant into the ____.

sensing bulb

compressor

evaporator

suction line

A

evaporator

74
Q

Adsorption occurs when ____.

a layer of gas adheres over the surface of a solid substance

a chemical combination between the gas and the solid substance occurs

two liquid substances combine into one substance

All of the above.

A

a layer of gas adheres over the surface of a solid substance

75
Q

A condition in which too much refrigerant is in the evaporator and can be drawn into the compressor is referred to as liquid ____.

starving

chugging

slugging

hunting

A

slugging

76
Q

If a TXV is adjusted correctly, it will close and remain closed whenever the compressor is ____.

running normal operation

idle

running hot-gas defrost

All of the above.

A

idle

77
Q

Which of the following statements regarding TXVs with bleed ports is true?

They cannot be used in systems with compressors using motors that have low starting torque.

They are not equipped with sensing bulbs.

They allow high-side and low-side pressures to equalize when the compressor is running.

None of the above.

A

none of the above

78
Q

A thermostatic expansion valve should reduce its flow rate as its evaporator ____.

warms

cools

starves

None of the above.

A

cools

79
Q

TXVs have a sensing bulb mounted on the ____ of the evaporator.

inlet

inside

outlet

Any of the above.

A

outlet

80
Q

Extra refrigerant in a system using a capillary tube will increase the risk that liquid refrigerant could cause damage by being drawn into the ____.

capillary tube

filter-drier

compressor

evaporator

A

compressor

81
Q

To help prevent contaminants from entering the capillary tube, a(n) ____ is usually installed at its inlet.

accumulator

condenser

filter-drier

sight glass

A

filter-drier

82
Q

When a capillary tube serves the function of both the liquid line and the metering device, it is connected between the evaporator and the ____.

suction line

condenser

compressor

accumulator

A

condenser

83
Q

The ____ of the capillary tube determines how much the pressure drops between the condenser and evaporator.

length

inside diameter

number of turns

All of the above.

A

all of the above

84
Q

The primary purpose of a metering device is to produce ____.

a pressure drop

a temperature drop

subcooling

superheat

A

a pressure drop

Middterm Review (4 decks)

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