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Refrigeration > Regrigeration > Flashcards

Regrigeration Flashcards

1
Q

Heat will flow from a ____ surface to a _____ surface.

a. hot, cold
b. cold, hot
c. dark, light
d. large small
e. high, low

A

a. hot, cold

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2
Q

What connects the evaporator with the condenser in a “split” air-conditioning system?

A

refrigeration pipping

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3
Q

Which device in the basic compressive refrigeration cycle is used to cause a pressure drop?

A

Metering device

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4
Q

Heat flows from _____ to ____ in the condensing section of an operating refrigeration system.

A

c. Refrigerant; air

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5
Q

Heat flows from ______ to ________ in the evaporator section of operating refrigeration system.

A

d. Air; refrigerant

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6
Q

Describe refrigeration

A

Is the process of moving heat from an area where it is undesirable to an area where the heat is not objectionable. According to the second law of thermodynamics, heat always flows from a material at a high temperature to a material at a low temperature.

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7
Q

What occurs in the two sides of a refrigeration system?

A

One side of a refrigeration system decreases the temperature and pressure on the refrigerant, which causes the refrigerant to absorb heat from the medium (air to water) in the system. The air or water is cooled when heat is absorbed from the air to water. The air or water is then used for cooling building spaces. The other side of a refrigeration system increases the temperature and pressure on the refrigerant, which causes the refrigeration to reject heat to the air or water in the system. The air or water is heated and used for heating or the heat is exhausted.

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8
Q

List the main parts of a mechanical compression refrigeration system and describe their functions.

A

A mechanical compression refrigeration system consists of a compressor, refrigerant, condenser, expansion device, evaporator, refrigeration lines, and accessories.

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9
Q

Is a mechanical device that compresses refrigerant or other fluid. Increases the temperature of and pressure on refrigerant vapor and produces the high pressure side of the system.

A

Compressor

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10
Q

Is a fluid that is used for transferring heat in a refrigeration system. Have a low boiling point, which allows refrigerants to boil and vaporize at room temperature.

A

Refrigerant

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11
Q

Is a heat exchanger that removes heat from high-pressure refrigerant vapor. High-pressure refrigerant vapor flows through the condenser and the condensing medium passes across the outside of the condenser. Heat flows from the refrigerant vapor to the cold condensing medium.

A

Condenser

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12
Q

Is the fluid in the condenser of a refrigeration system that carries heat away from the refrigerant. Air and water are condensing mediums used in refrigeration systems. As refrigerant vapor gives up heat to the condensing medium, the vapor condensing to a liquid.

A

Condensing Medium

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13
Q

Is a valve or mechanical device that reduces the pressure on a liquid refrigerant by allowing the refrigerant by allowing the refrigerant by allowing the refrigerant to expand.

A

Expansion device

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14
Q

Is a heat exchanger that adds heat to low-pressure refrigerant liquid. Low-pressure refrigerant liquid. Low-pressure refrigerant liquid flows through the evaporator and an evaporating mediums passes across the outside of the evaporator. Heat flows from the hot evaporating medium to the cold refrigerant.

A

Evaporator

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15
Q

Is a fluid that is cooled when heat is transferred in the evaporator from the evaporating medium to cold refrigerant. An evaporating medium adds heat to a refrigerant because is has a higher temperature than the refrigerant. As the liquid refrigerant absorbs heat from the evaporating medium, the refrigerant boils and vaporizes.

A

Evaporating medium

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16
Q

What are the two condensing mediums used in refrigeration systems?

A

Air and water

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17
Q

What causes the temperature of refrigerant to decrease as it leaves the expansion device and enters the evaporator?

A

As the pressure in the liquid refrigerant decreases, some of the liquid refrigerant vaporizes because it has a lower boiling point. The refrigerant absorbs heat as it vaporizes, which cools the remainder of the refrigerant. The refrigeration then flows as a liquid-vapor mixture to the evaporator.

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18
Q

What instrument is used to measure atmospheric pressure?

A

A mercury Barometer is an instrument used to measured atmospheric pressure and is calibrated in inches of mercury absolute.

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19
Q

Define gauge pressure.

A

is pressure above atmospheric pressure that is used to express pressures inside a closed system. Is expressed in pounds per square inch. guage (psig or psi)

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20
Q

Explain the relationship between the boiling point of a liquid and the pressure on the liquid.

A

If the pressure on a liquid decreases, the boiling point of the liquid decreases. If the pressure on a liquid increases, the boiling point of the liquid increases.

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21
Q

Where does heat transfer occur in a mechanical compression refrigeration system?

A

In a mechanical compression refrigeration system, heat transfer occurs in the condenser and the evaporator.

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22
Q

What connects the condenser and the expansion device?

A

liquid line

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23
Q

What maintains the high pressure in the high-pressure side of a refrigeration system?

A

Compressor discharge flow maintains the high pressure in the high-pressure side of a refrigeration system.

24
Q

Describe how water provides a refrigeration effect when it vaporizes.

A

In dry climates, water soaked canvas bags are used to cool water. As the water evaporates, it absorbs heat from water inside the bag. The evaporation provides a cooling effect on the water inside the bag.

25
Q

Describe how the number assigned to a refrigerant identifies the chemical composition of the refrigerant.

A

Refrigerants are identified by numbers. The numbers are assigned according to the physical and chemical composition of a refrigerant. Numbers less that 170 are assigned to refrigerants based on the chemical composition of the refrigerant. Numbers above 170 are assigned arbitrarily.

26
Q

How has the clean air act of 1992 impacted the duties of contractors and HVAC technicians when working with refrigerants?

A

Refrigerants that used chlorofluorocarbons (CFCs) and fully halogenated chlorofluorocarbons (HCFCS) such as R-11, R-12, and R-22 are believed to have deteriorated the earth’s ozone layer. The ACT banned them in 1995.

27
Q

What is retro-fitting?

A

Is the process of furnishing a system with new parts that were not available at the time the system was manufactured.

28
Q

Define saturation conditions.

A

the temperature and pressure at which a refrigerant changes state. The properties listed on a refrigerant property table are volume, density, enthalpy, and entropy.

29
Q

List the desirable refrigeration properties.

A

Low boiling point, low freezing point, nontoxic, high critical point, low specified volume, high density, high latent heat, low compression ratio, nonflammable, noncorrosive, stable, and miscible with oil.

30
Q

Why is boiling point an important property of a refrigerant?

A

A refrigerator must have a boiling point that is lower than the desired temperature of the air that leaves the evaporator.

31
Q

Differentiate between a two-stage compression system and a cascade system.

A

A two-stage compression system is a compression system that uses more than one compressor to raise the pressure of a refrigerant. The system raises the pressure above the pressure that can be achieved with a single compressor. A cascade system is a compression system that uses one refrigeration system to cool the refrigerant in another system.

32
Q

Define critical point. Why is it important?

A

Is the pressure and temperature above which a material does not change state regardless of the absorption or rejection of heat.

33
Q

What is the relationship between density and specific volume?

A

Density is the reciprocal of the specific volume at a given pressure. If the refrigerant has a low specific volume, it will have a high density.

34
Q

Why should refrigerant be noncorrosive?

A

A corrosive substance reacts chemically with materials and causes corrosion of surfaces and components.

35
Q

Define miscibility. Why is it important that a refrigerant be miscible?

A

Miscibility is the ability of a substance to mix with other substances. The oil that lubricates a compressor circulates with the refrigerant must be able to mix with oil so that refrigeration can carry the oil through the compressor.

36
Q

Compare the different classifications of refrigerant most commonly used today.

A

CFCs contain chlorine, fluorine, and carbon. They were phased out in 1995 because they contain chlorine and they decompose in the Earth’s stratosphere by reacting with the sun’s ultraviolet radiation.

37
Q

Define superheat. Explain the function of superheat in a refrigeration system.

A

Super heat is heat added to a material after it has changed state. The refrigerant leaves the evaporator at a temperature higher than the saturated temperature for its pressure. The refrigerant has more heat than if it saturated because of the superheat absorbed by the refrigerant in the evaporator.

38
Q

What is the hot gas discharge line?

A

The hot gas discharge line is the line that connects the compressor to the condenser. The hot gas discharge line contains hot gas (refrigerant vapor) that is cooled in the condenser.

39
Q

Define subcooling.

A

Is the cooling of a material such as refrigerant to a temperature that is lower than the saturated temperature of the material for a particular pressure.

40
Q

List the basic types of chillers.

A

Low-pressure single compressor centrifugal chiller, High-pressure dual compressor centrifugal chiller, Absorption chiller.

41
Q

List and describe the function of the main parts of a chiller.

A

Compressor, condensers, metering devices, Evaporators, purge units.

42
Q

The _____ is the pumping component that controls the pressure in the evaporator and condenser. This pressure corresponds to a design evaporating temperature of 38 degrees F and condensing temperature of 105 degrees F.

A

compressor

43
Q

A ____ is a heat exchanger that removes heat from high-pressure refrigerant vapor. In a water cooled system, the _________ is usually a two-pass, tube-and-shell heat exchanger. The refrigerant is in the tubes and the water surrounds the tubes. The refrigerant in the ______ transfers heat to the ________ and is circulated to a cooling tower where the water transfers its heat to the surrounding air.

A

Condenser

44
Q

Is a valve or orifice in a refrigeration system that controls the flow of refrigerant into the evaporator to maintain the correct evaporating temperature.

A

Metering Device

45
Q

Is a heat exchanger that adds heat to low-pressure refrigerant liquid. As the heat is absorbed, the refrigerant boils, creating a vapor that is carried to the compressor.

A

Evaporator

46
Q

Is a device used to maintain a system free of air and moisture.

A

Purge system.

47
Q

What are the advantages over scroll compressors over reciprocating compressors?

A

Two advantages a scroll compressor has over a reciprocating compressor are that scroll compressors run quieter and are able to handle small amounts of liquid refrigerant.

48
Q

What are the components of an absorption refrigeration system?

A

absorber, generator, condenser, evaporator, orifice, and a circulating pump.

49
Q

Is the device in an absorption system in which the refrigerant is absorbed by an absorbant substance.

A

absorber

50
Q

is a device in the chiller that adds heat to the refrigerant-absorbant solution to vaporize the refrigerant, and separate the refrigerant from the absorbant.

A

generator

51
Q

The high-pressure refrigerant vapor condenses to a liquid as heat is removed from it by the condenser eat exchange.

A

Condenser

52
Q

The low-pressure, low-temperature refrigerant evaporates as it absorbs heat from the evaporating medium.

A

Evaporator.

53
Q

Is located in the refrigerant-absorbant line between the absorber and generator. The _______ moves the refrigeration from the absorber to the generator.

A

Circulating pump

54
Q

Is a restriction in the refrigerant line between the condenser and the evaporator. ___ causes a pressure decrease in the refrigerant as it flows through the line.

A

Orifice

55
Q

Includes the orifice between the condenser and the evaporator, the evaporator, the absorber, and the refrigerant-absorbant solution line that leads to the inlet of the circulating pump.

A

low-pressure system

56
Q

Includes the circulating pump (solution pump) discharge line, the generator, the condenser, and the refrigerant line that leads to the inlet of the orifice.

A

High pressure system

Refrigeration (1 decks)

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