Mechanical Final Heat Exchangers & MD Review Flashcards by Kyle Halverson

An AXV works best when the evaporator load is constant.

True

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

False

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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.

True

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

True

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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.

True

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

True

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

True

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

False

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Adsorption occurs when two substances combine to become one substance.

False

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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.

True

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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

d) all of the above

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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

d) limits the refrigerant flow rate to the compressor capacity

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

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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) increases the flow of refrigerant

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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

b) has different characteristics from the system fluid

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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.

d) all of the above answers are correct

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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

b) evaporator suction line superheat

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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

d) all of the above

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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

d) all of the above

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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) have some type of head pressure control

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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

d) all of the above

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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

b) 15F

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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

d) 105F

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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

c) water regulating valve

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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

b) refrigerant condensing temperature

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) with a brush after removing the end caps

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

c) chemically

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

greater than

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.

an insulator

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.

Both A and B are correct

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

all of the above

The refrigerant in a condenser in a refrigeration system ____. absorbs heat rejects heat changes to a vapor is under lower pressure than the evaporator

rejects heat

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

8 to 12F

____ is the best method of checking to see when a refrigerant coil has a proper level of refrigerant. Boiling temperature Superheat Dryheat Vapor temperature

b) superheat

A direct expansion-type evaporator is also called a ____. flooded evaporator dry-type evaporator multi-circuit evaporator stamped evaporator

dry-type evaporator

The ____ of the liquid refrigerant determines the coil operating temperature. freezing point melting point transition temperature boiling temperature

boiling temperature

A typical evaporator operating temperature in an air-conditioning system is ____. 40°F 55°F 75°F 200°F

40F

The boiling temperature and its relationship to the system exist in the ____. coil thermostat condenser evaporator

evaporator

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

evaporator

The household refrigerator fresh-food compartment is a good example of ____ refrigeration. low-temperature medium-temperature high-temperature average-temperature

medium-temperature

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

liquid slugging in the compressor

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.

superheats vapor refrigerant in the suction line

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.

liquid receiver

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.

d) all of the above

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.

tube-within-a-tube

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

shell-and-coil

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.

shell-and-tube

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.

all of the above

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.

air cooled

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

refrigerant vapor from the discharge line

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

refrigerant from the evaporator and low side is pumped down

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.

none of the above

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.

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

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.

off-cycle defrost system

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.

energies electric heating coils

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.

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

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.

all of the above

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.

remove the moisture that builds up from defrosting and condensation

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.

time-initiated, pressure-terminated

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.

time-initiated, time-terminated

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

baffles

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

fin-and-tube

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.

all of the above

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.

pressure transducer

The minimum ____ setting is the point that causes the least sensing bulb temperature change while the system is running. stable signal superheat subcooling surging

stable signal

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.

overcharge

Electronic expansion valves (EEVs) use a ____-operated assembly. spring diaphragm bellows None of the above.

none of the above

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.

increases

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

binding

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.

oil

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.

rises

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

solenoid valve

Low-side float (LSF) metering devices control the flow of liquid refrigerant into the ____. sensing bulb compressor evaporator suction line

evaporator

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 layer of gas adheres over the surface of a solid substance

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

slugging

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.

idle

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.

none of the above

A thermostatic expansion valve should reduce its flow rate as its evaporator ____. warms cools starves None of the above.

cools

TXVs have a sensing bulb mounted on the ____ of the evaporator. inlet inside outlet Any of the above.

outlet

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

compressor

To help prevent contaminants from entering the capillary tube, a(n) ____ is usually installed at its inlet. accumulator condenser filter-drier sight glass

filter-drier

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

condenser

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.

all of the above

The primary purpose of a metering device is to produce ____. a pressure drop a temperature drop subcooling superheat

a pressure drop