Chapter 18 Refrigeration Compressors

Question 1

1. A bellows seal consists essentially of a 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 mounted on the shaft and the other end is:
   A. A mating ring
   B. A diaphragm soldered to a seal nose held between compressor body and cover
   plate
   C. Fastened to a flange which is tightly held against the housing by a cover plate
   D. A sealing ring
   E. A metallic bellows soldered at one end to the shaft

Answer 1

C. Fastened to a flange which is tightly held against the housing by a cover plate

Question 2

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

Answer 2

B. Low-temperature, low-pressure vapours

Question 3

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

Answer 3

B. Piston

Question 4

4. The male (driving) rotor in the helical screw compressor usually has \_\_\_\_\_ helical
lobes along the length of the rotor.
A. Five
B. Two
C. Four
D. Six
E. Three

Answer 4

C. Four

Question 5

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

Answer 5

C. Reciprocating

Question 6

6. A two cylinder compressor has a 90 mm bore and a stroke of 115 mm. Calculate
   the volume compressed per hour if the compressor operates at 400 r/min.
   A. 35.12 m³/h
   B. 79.62 m³/min
   C. 17.56 m³/min
   D. 79.62 m³/h
   E. 19.91 m³/h

Answer 6

A. 35.12 m³/h

Question 7

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

Answer 7

B. 6.06 kg/min (13.3 lb/min)

Question 8

8. If the refrigerant is R-12 and the evaporator operates at -15°C (5°F) the specific
   volume of the vapour is 0.09102 m³/kg. Calculate the mass of refrigerant per
   minute if the volume compressed is 45.24 m³/h (1600 ft³/h):
   A. 497 kg/min (1093 lb/min)
   B. 8.28kg/min (18.22 lb/min)
   C. 4.12 kg/min (9.06 lb/min)
   D. 0.069 kg/min (0.15 lb/min)
   E. 17.56 kg/min (0.15 lb/min)

Answer 8

B. 8.28kg/min (18.22 lb/min)

Question 9

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

Answer 9

D. Six

Question 10

10.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. Semi-metallic material impregnated with graphite
C. Metallic bellows soldered at one end to a ring bearing against a shoulder on the
shaft
D. A diaphragm soldered to a seal nose held between compressor body and cover
plate
E. A mating ring and a sealing ring

Answer 10

B. Semi-metallic material impregnated with graphite

Question 11

11.In terms of energy transformation in the centrifugal compressor the kinetic energy
of the \_\_\_\_\_ is transformed into potential energy in the high-pressure, low-velocity
compressed vapour.
A. Low-pressure, low-velocity vapour
B. High-pressure, high-velocity vapour
C. Low-pressure, high-velocity liquid
D. Low-pressure, low-velocity liquid
E. Low-pressure, high-velocity vapour

Answer 11

E. Low-pressure, high-velocity vapour

Question 12

12.In terms of energy transformation, the kinetic energy of the low-pressure, highvelocity vapour is transformed into potential energy in the\_\_\_\_\_ compressed
vapour.
A. High-pressure, low-velocity
B. Low-pressure, low-velocity
C. High-pressure, High-velocity
D. High-pressure, low-temperature
E. High-Temperature, low-velocity

Answer 12

E. High-Temperature, low-velocity

Question 13

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

Answer 13

B. Low-temperature, low-pressure vapours

Question 14

14.To prevent damage to the reciprocating compressor by the _____ compressors
are often fitted with a safety head.
A. Hydraulic pressure resulting from trapped liquid at the end of the compression
stroke
B. Hydraulic temperature resulting from trapped liquid at the end of the compression
stroke
C. Hydraulic pressure resulting from trapped vapour at the end of the compression
stroke
D. Hydraulic temperature resulting from trapped vaopur at the end of the compression
stroke
E. Hydraulic pressure resulting from trapped liquid at the end of the intake stroke

Answer 14

A. Hydraulic pressure resulting from trapped liquid at the end of the compression
stroke

Question 15

15.One of the main classifications of refrigeration compressors is the \_\_\_\_\_
compressor.
A. Screw
B. Axial
C. Piston
D. Rotary
E. Vane

Answer 15

D. Rotary