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final pwen absa practice exam friday 21 april > FINAL PWEN ABSA PRACTICE EXAM FRIDAY 21 APRIL > Flashcards

FINAL PWEN ABSA PRACTICE EXAM FRIDAY 21 APRIL Flashcards

1
Q

The term prime movers refers to

A

A single device that either by itself or as part of a system converts a natural source of energy into motion

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2
Q

Dry cooling towers

A

Pass the cooling water through a closed circuit of finned tubes

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3
Q

Impulse turbines

A
  • Have a velocity increase through the nozzles
  • Blades have the angle of inlet the same as the outlet
  • Could have more than one set of blades
  • May not require a trust bearing
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4
Q

In a reaction steam turbine

A

Expansion takes place in the fixed and moving blades

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5
Q

The rate of heat transfer in any cooling tower system depends on the:

A

Relative velocity of both air and water during contact
Length of contact time between the air and water
Difference between the inlet water T and the inlet air wet bulb T

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6
Q

Some of the characteristics that make the gas turbine a better choice over other prime movers are:

A

Low maintenance
Minimum cooling water
Rapid start-up and loading

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7
Q

The air side of a gas turbine regenerator is located:

A

Downstream of the compressor

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8
Q

In a compression ignition engine, the fuel is ignited by:

A

The compressed air temperature

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9
Q

A fuel injector is used to _____ the fuel in an engine:

A

Ignite

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10
Q

Cavitation of a pump refers to, when the:

A

Pump is filled with vapour

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11
Q

The capacity of a centrifugal pump should only be reduced by:

A

throttling the discharge valve

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12
Q

Which type of pump produces the greatest suction?

A

Positive displacement

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13
Q

Wear rings:

A

Are used on impellers
Are used on the casing
Reduce the maintenance costs of the pump

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14
Q

An air compressor may be automatically started and stopped by a pressure switch, which is usually found connected to the:

A

Receiver

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15
Q

Compressor unloaders:

A

Keep the suction valve open

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16
Q

Grease

A

Can be used under condition where oil may leak away and leave the bearing dry
Is less likely to drip or splash from bearings and therefore finds wide application in the textile and food industries
Serves to seal out dirt and water from bearings
Gives the working surface a permanent protective coating to prevent rusting during idle periods

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17
Q

The most common cause of lubrication problems in anti-friction bearings is:

A

over-lubrication

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18
Q

Trust bearing

A

Are used on reaction turbines
Prevent the turbine rotor from moving axially
Are lubricated with the same oil as the main bearings

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19
Q

In an equivalent circuit developed from a multi-resistor series circuit

A

The sum of voltage drops across the original resistances will be equal to the voltage drop of the equivalent circuit

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20
Q

Current flow direction and intensity will:

A

Affect magnetic field direction and intensity

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21
Q

Faraday discovered:

A

That a conductor will have a voltage induced if it cuts magnetic flux

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22
Q

Voltmeters are connected with the negative or black lead connected to the:

A

Negative side of the circuit

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23
Q

A kilowatt-hour meter has a small motor which:

A

Ha s a speed proportional to the power consumption

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24
Q

The rotating field of an alternator is obtained by exciting the windings on the rotor with

A

DC Power

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25
Q

When synchronizing an alternator; voltage, phase and frequency must all be the same as well as the:

A

Phase sequence

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26
Q

When magnetic flux produced by one coil induces an EMF in a second coil, it is called:

A

Mutual inductance

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27
Q

When AC action causes a counter current in a coil, it is termed:

A

Self inductance

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28
Q

An electrical distribution system is composed of service, feeders and:

A

branch circuits

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29
Q

A sensing element receives its signal from the:

A

Controlled variable

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30
Q

The purpose of a spiral or a helix Bourdon tube is to:

A

To provide a greater degree of rotation

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31
Q

Relative to flow, velocity is kinetic energy and when velocity increases, the:

A

Potential energy in the form of pressure will decrease

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32
Q

The common standard control modes for a plant control system are:

A

Derivative, proportional and integral

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33
Q

The most reliable method of checking or testing a low water fuel cutoff is to:

A

Lower the water in the boiler to the level where the burner should cut out

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34
Q

Safety devices and interlocks on boilers, when activated, shut off the:

A

Fuel

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35
Q

Digital output is put through a/an _____ before an analog control can react to the signal

A

Analog converter

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36
Q

The steam and water spaces of a cast iron sectional boiler are connected by:

A

Push nipples

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37
Q

Cast iron boiler sections maximize heat transfer by:

A

Exposing as large a surface as possible to the hot gases

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38
Q

A modulating pressure atomizer has its return oil flow regulated by:

A

A modulating valve in the return line

39
Q

Oil burners can be divided into three classes:

A

Air & steam atomizing
Atmospheric pressure burners
mechanical atomizing

40
Q

The venturi tube in the atmospheric burner mixing head has a:

A

Gradually increasing cross-sectional area

41
Q

A hydramotor valve:

A

Helps to prevent puff-backs

42
Q

According to the current code, the scale on the dial of the steam gauge for a steam heating boiler shall be graduated to not more than:

A

414 KPa

43
Q

A siphon on a boiler is necessary to:

A

?????
Prevent steam for hitting safety valve disc
Prevent water from entering a steam gauge
Drain water from a Bourdon tube
Prevent water from being siphoned out of the glass
Keep steam out of the Bourdon tube

44
Q

An expansion tank is used to

A

allow for expansion of water

45
Q

When too much air has been absorbed by water in the expansion tank of a closed, system the tank must be:

A

Drained

46
Q

If there is any question as to the accuracy indicated by a gauge glass and the true level cannot be determined:

A

The boiler should be removed from service and all water level indicating attached checked

47
Q

When air is forced through a heating coil where the fan and coil are within the same unit, the unit is known as:

A

Unit heater

48
Q

Unit heaters differ from convectors in that they use _____ to increase heat transfer.

A

Blowers

49
Q

The piping and heating units of a steam heating system must be so arranged that the:

A

Air can be expelled from the heating units and piping

50
Q

Which of the following fittings would you expect to find on a steam heating boiler?

A

Safety valve, Water gauge glass, Low water cut off

51
Q

The two pipe reverse return hot water heating system has the advantage of:

A

All circuits have the same length

52
Q

In many buildings, the hot water heating system is divided into several circuits and the flow of water is controlled by

A

A circulating pump in each heating Zone

53
Q

Air is removed from a hot water system by which of the following:

A

Air vents

Air separators

54
Q

When a closed type expansion tank on a hot water boiler is completely filled with water and the water in the system is raised in temperature so that is expands, the result will be that the:

A

Pressure builds up, lifting the safety relief valve

55
Q

One of the advantages the forced warm air heating systems has over the steam or hot water heating systems is

A

That controlled amounts of ventilation air can be admitted

The air can be humidified

56
Q

In high efficiency furnaces, if the temperature of the flue gas drops below 65°C, the:

A

water vapour will condense

57
Q

In a warm air heating system, the heated air should enter the rooms preferably via the:

A

Baseboard registers on outside walls

58
Q

Electronic filters will remove:

A

fine particles from the air

59
Q

Mechanical ventilation can be divided into which types?

A

natural air intake, mechanical exhaust
mechanical air intake, natural exhaust
Mechanical air intake, mechanical exhaust

60
Q

Which of the following is considered an advantage of a mechanical ventilation system

A

*** Controlled amounts of filtered and heated air can be supplied

61
Q

A transformer is a device that is used to change:

A

AC voltage from one value to another

62
Q

The main boiler control device used with an on/off combustion fuel control is a/an _____ sensing element

A

Pressure

63
Q

Deviation is the difference between the setpoint of a controller and the value of the controlled variable it is also called:

A

Offset

64
Q

The type of luminaire typically used in industrial warehouses and storage areas is the:

A

Open reflector

65
Q

In indirect lighting systems all or most of the luminous intensity is:

A

*** Reflected of the walls

reflected off the ceiling

66
Q

Temperature relief devices limit the temperature increase to about:

A

????

67
Q

A code requirement for all facilities is to include a ______________ to prevent supply system contamination:

A

Back flow preventor

68
Q

Which of the following statements about footing drains is true?

A

Installed to prevent an accumulation of ground water around the building foundations
Used to reduce the hydrostatic pressure on the walls below ground level
Perforated or poroud pipe is used to collect the water near the footings
The collected water is drained to a remote area or into a sump

69
Q

Which of the following statements about low-side pressure and temperature is false?

A

The evaporation temperature of the refrigerant should be 5-10°C higher than that of the cooled medium.

70
Q

A liquid evaporating is an example of a:

A

Gain of latent heat

71
Q

The amount of heat given up by a refrigerant to the evaporator is equal

A

Latent heat of vaporization

72
Q

Which of the following is not a physical property of a refrigerant

A

Entropy

73
Q

Raising the condensing point (saturation temperature) of the refrigerant vapour above the temperature of the cooling medium is the function of the:

A

Compressor

74
Q

Which of the following compressor types uses rotating vanes to regulate vapour flow?

A

Rotary***

75
Q

Which of the following compressor types is not typically used for refrigeration systems?

A

Lobe***

76
Q

The purpose of the condenser in a refrigeration system is to:

A

Remove of latent heat from the refrigerant

77
Q

Refrigerant evaporators are:

A

Used to transfer heat

78
Q

In many cases evaporator pressure must not be allowed to drop below a certain level to prevent which of the following results?

A

Frosting of coils..***

o Overheating of the evaporator

79
Q

The automatic expansion valve operates on the principle of balancing:

A

The volumetric expansion of a fluid against a return spring

80
Q

The automatic expansion valve operates on the principle of balancing:

A

Evaporator pressure against a return spring

81
Q

Which of the statements about automatic expansion valves is false?

A

The control may be used with multiple cooling coils

connected to the same compressor.

82
Q

The Dryer for a refrigeration systems is typically fitted:

A

Just before the compressor***

83
Q

High head pressure in a refrigeration system usually indicates:

A

Air or NCG in the system

84
Q

If the chilled water temperature drops approximately 2.5-3°C below the set point of the control thermostat, the chilled water low temperature cut out will:

A

Shut down the compressor

85
Q

When some refrigeration systems are to be shut down for a prolonged period of time they should be “pumped down” and the refrigerant stored in the:

A

Receiver

86
Q

In an absorption refrigeration system the compressor is eliminated and its functions are performed by the

A

absorber, generator, and the generator pump

87
Q

During seasonal start-up, when should the purge pump be started?

A

About one half hour after the absorption unit is started.

88
Q

Which of the following is not a result of having non-condensable gases in the absorption systems?

A

Lower than normal chilled water temperature leaving the evaporator.

89
Q

Damper designs include:

A

Opposed, parallel and single blade types

90
Q

Dampers in air handling systems may only be:

A

Manual, modulating and 2 position

91
Q

The types of humidifiers used for residential purposes are:

A

Pan
Wetted Element
Atomizing

92
Q

Some systems use “Free Cooling” to maintain 12.5°C air. What is “Free Cooling”?

A

*** On cooler days manipulating mixed air dampers to reduce the amount of mechanical cooling needed

93
Q

To maintain space conditions during heating this system zone thermostat reduces the air flow to a minimum of 20% before modulating the output of the heat supply

A

Variable air volume system

94
Q

Advantages of the runaround heat recovery system include:

A
  1. no cross contamination is likely
  2. exhaust and ventilation streams can be remote
  3. many exhaust ducts can be grouped on the same system

final pwen absa practice exam friday 21 april (1 decks)

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