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5th Class Power Engineering > Book 2 Chapter 18: Refrigeration Compressors > Flashcards

Book 2 Chapter 18: Refrigeration Compressors Flashcards

1
Q

Which compressor type requires the use of a shaft seal?
A) Hermetic
B) Semi-hermetic
C) Serviceable
D) Open type

A

D) Open type

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2
Q

Which of the following are designs of rotary compressors?
A) Helical rotor
B) Stationary single-blade
C) Rotating vane
D) All of the above

A

D) All of the above

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3
Q

Packing gland seals are made of ________________________.
A) Metallic bellows soldered at one end to a ring bearing against a seal ring mounted on the shaft
B) Metallic bellows soldered at one end to a ring bearing against shoulder on the shaft
C) Semi-metallic material impregnated with graphite
D) A diaphragm soldered to a seal nose held between compressor body and cover plate

A

C) Semi-metallic material impregnated with graphite

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4
Q

A two cylinder compressor has an 80mm (3.15in) bore and a stroke of 110mm (4.33in). What is the volume compressed per hour if the compressor operates at 800r/min?
A) 45.25 m3/h (1553 ft3/h)
B) 53.08 m3/h (1879 ft3/h)
C) 62.75 m3/h (2216 ft3/h)
D) 88.54 m3/h (3127 ft3/h)

A

B) 53.08 m3/h (1879 ft3/h)

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5
Q

The theoretical mass of refrigerant moved in a compressor is 9.72kg/min (21.4lb/min). If the compressor has a volumetric efficiency of 65% what is the actual mass moved?
A) 6.32kg/min (13.9lb/min)
B) 5.45kg/min (12lb/min)
C) 11.25kg/min (24.8lb/min)
D) 9.84kg/min (21.7lb/min)

A

A) 6.32kg/min (13.9lb/min)

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6
Q

If a compressor discharge pressure gauge indicates 960kPa (139psi) and the suction pressure is 130kPa (18.8psi) what is the pressure ratio?
A) 3.84
B) 7.25
C) 4.59
D) 4.14

A

C) 4.59

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7
Q

Which of the following compressor types uses impellers to draw in vapour?
A) Reciprocating compressors
B) Centrifugal compressors
C) All of the above
D) Rotary compressors
E) None of the above

A

B) Centrifugal compressors

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8
Q

In a rotating vane design rotary compressor, a good seal is maintained between the vanes and the cylinder by:
A) High pressure refrigerant vapour
B) The oil
C) The eccentric rotor size
D) Low pressure suction
E) Centrifugal force

A

E) Centrifugal force

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9
Q

The safety head of a refrigeration compressor is designed to:
A) Pop when the pressure is too high
B) Prevent explosion damage
C) Relieve high-pressure gas compression
D) Operate in place of a safety relief valve
E) Relieve pressure due to liquid in the cylinder

A

E) Relieve pressure due to liquid in the cylinder

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10
Q

Rotary compressors have several different designs, some of which are:
1. Sliding vane
2. Stationary single-rotor
3. Helical rotor
4. Rotating impeller
5. Reciprocating piston

A) 2,3,4
B) 3,4,5
C) 1,3,4
D) 1,2,3
E) 1,3,5

A

D) 1,2,3

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11
Q

Pistons and connecting rods are found in which of the following types of compressors?
A) Centrifugal
B) Rotary
C) Reciprocating
D) Axial
E) Dynamic

A

C) Reciprocating

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12
Q

Piston displacement is defined as the:
A) Distance along which the compressor piston travels
B) Revolutions per minute of the compressor motor
C) Volume of refrigerant that can be circulated through all the cylinders per unit time
D) Cylinder bore of the compressor
E) Piston stroke length of the compressor

A

C) Volume of refrigerant that can be circulated through all the cylinders per unit time

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13
Q

Which of the following statements is true in regard to rotary screw refrigeration compressors?
A) The driving rotor has helical lobes and the driven rotor has flutes
B) The vapour is drawn in via the closed space between the driving rotor and the casing
C) The cylinders around the rotor screws must be considerably larger in diameter than the screws
D) All of the above
E) The compressor consists of three opposing grooved rotors

A

A) The driving rotor has helical lobes and the driven rotor has flutes

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14
Q

A typical stationary crankshaft seal consisting of metallic bellows soldered at one end to a ring (seal nose) which bears either against a shoulder on the shaft or against a seal ring on the shaft is called a:
A) Diaphragm seal
B) Setscrew seal
C) Bellows seal
D) Packing gland seal
E) Rotating mechanical seal

A

C) Bellows seal

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15
Q

Which of the following are functions of a refrigeration compressor?
1. Maintain a high pressure in the condenser
2. Maintain a low pressure in the evaporator
3. Raise the pressure of the refrigerant

A) 3
B) 1
C) 1,3
D) 2,3
E) 1,2,3

A

E) 1,2,3

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16
Q

A disadvantage of hermetic type refrigeration compressors is:
A) The motor is cooled by the low-pressure, low-temperature vapour drawn into the housing
B) Shaft sealing is not required
C) The compressor is driven by an electric motor
D) Field servicing is not possible
E) The compressor and motor are mounted within the same housing

A

D) Field servicing is not possible

17
Q

An advantage of centrifugal refrigeration compressors is:
A) Small pistons
B) High velocity, high pressure
C) Positive displacement
D) No valves or pistons
E) High outlet pressure

A

D) No valves or pistons

18
Q

Packing gland seals are made of ___________.
A) Metallic bellows soldered at one end to a ring bearing against a shoulder on the shaft
B) Semi-metallic material impregnated with graphite
C) A mating ring and sealing ring
D) A diaphragm soldered to a seal nose held between compressor body and cover plate
E) Metallic bellows soldered at one end to a ring bearing against a seal ring mounted on the shaft

A

B) Semi-metallic material impregnated with graphite

19
Q

The female (driven) rotor in the helical screw compressor usually has _________ helical grooves or flutes along the length of the rotor
A) Two
B) Four
C) Five
D) Six
E) Three

A

D) Six

20
Q

The theoretical mass of refrigerant moved in a compressor is 8.65kg/min (19lb/min). If the compressor has a volumetric efficiency of 70%, what is the actual mass moved?
A) 9.84kg/min (21.7lb.min)
B) 12.35kg/min (27.19lb/min)
C) 6.21kg/min (13.7lb/min)
D) 6.32kg/min (13.9lb/min)
E) 6.06kg/min (13.3lb/min)

A

E) 6.06kg/min (13.3lb/min)

21
Q

One of the main classifications of refrigeration compressors is the _______ compressor.
A) Piston
B) Vane
C) Reciprocating
D) Screw
E) Axial

A

C) Reciprocating

22
Q

One of the functions of the compressor in a refrigeration system is to draw the:
A) High-temperature, low-pressure vapour from the evaporator
B) Low-temperature, low-pressure vapour from the condenser
C) Low-temperature, high-pressure vapour from the evaporator
D) Low-temperature, low-pressure liquid from the evaporator
E) Low-temperature, low pressure vapour from the evaporator

A

E) Low-temperature, low-pressure vapour from the evaporator

23
Q

The flexible reed and disc valves in the reciprocating compressor consist of a thin flexible piece of spring steel part of which covers the suction or discharge port in the valve plate and are opened by:
A) Low temperature
B) Differential temperature
C) Push rods
D) Low pressure
E) Differential pressure

A

E) Differential pressure

24
Q

Which compressor type requires the use of a shaft seal?
A) Open type
B) Serviceable
C) Closed
D) Hermetic
E) Semi-hermetic

A

A) Open type

25
Q

One of the functions of the compressor in a refrigeration system is to raise the __________ pressure and temperature.
A) High-temperature, low-pressure liquids
B) Low-temperature, low-pressure liquids
C) High-temperature, low-pressure vapours
D) Low-temperature, low-pressure vapours
E) Low-temperature, high-pressure vapours

A

D) Low-temperature, low-pressure vapours

26
Q

The main parts of a refrigerant reciprocating compressor includes all except the:
A) Suction and discharge valves
B) Safety head
C) Pistons and connecting rods
D) Compressor body
E) Rotor

A

E) Rotor

27
Q

The rotary design of refrigeration compressors includes all of the following except:
A) Rotating vane
B) Helical screw
C) Piston
D) Stationary single blade
E) Helical rotor

A

C) Piston

5th Class Power Engineering (75 decks)

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