Power Engineering 4th Class Ch 116

b

A compressor seal is required to prevent: a. Refrigerant and oil leakage into the compressor b. Refrigerant and oil leakage along the shaft c. Prevent moisture from escaping the compresor d. Prevent dirt and moisture from leaving the compressor

d

A negative factor of Hermetic Type refrigeration compressors is: Choose one answer. a. They are too large to be used in any application except large industrial plants b. The drive motor tends to overheat c. Shaft sealing is difficult d. Field servicing is not possible e. It is difficult to replace the shaft coupling

e

A rotating mechanical seal, installed on a refrigeration compressor, is held in position by: Choose one answer. a. The mating ring b. Centrifugal force c. The compressor casing d. High pressure refrigerant vapour e. A spring

c

A stationary crankshaft seal used on refrigeration compressors, which consists of a metallic bellows soldered at one end to a ring, and which presses against a shoulder on the shaft is called a: Choose one answer. a. Packing gland seal b. Diaphragm seal c. Bellows seal d. Rotating Mechanical seal e. Set screw

d

Advantages of the centrifugal compressor are? a. No moving parts b. Can be coupled to an electric motor c. Cheap d. A and B e. All of the above

d

Consider a single stage, single acting reciprocating compressor. Calculate the piston displacement in cubic metres per minute, if given the following: piston stroke 12 cm piston diameter 10 cm piston speed 1100 working strokes per minute a. 1.031 b. 1.033 c. 1.035 d. 1.037 e. 1.039

b

For a Helical Rotor Design rotary refrigeration compressor, which of the following statements is true? Choose one answer. a. The compressor consists of three opposing grooved rotors b. The driving rotor has less helical lobes than the driven rotor has flutes c. The vapour is drawn in via the closed space between the driving rotor and the casing d. The cylinders around the rotor screws must be considerably larger in diameter than the screws e. The compressor is reversible, to allow it to be used in heat pump applications

c

Helical rotors revolve at speeds up to ___ r/min a. 1550 b. 2550 c. 3550 d. 4550 e. 5550

a

In a refrigeration system, the purpose of the compressor is to a) establish two pressure levels b) reject the heat from the system c) absorb the heat into the system d) regulate the flow of the refrigerant e) heat the refrigerant

a

In a sliding vane design refrigeration compressor, a good seal is maintained between the vanes and the cylinder by: Choose one answer. a. Centrifugal force b. Lube oil c. High pressure refrigerant vapour d. Liquid refrigerant carryover e. The eccentric rotor size

c

Packing gland seals are used on what compressor? a. Open type b. Hermetic type c. Large capacity ammonia compressor d. Rotating sliding vane design e. Helical rotor design

c

Reciprocating Compressor Types are? i. Open type ii. Hermetic type iii. Semihermetic type iv. Rotating sliding vane design v. Helical rotor design a. i, ii, iv b. ii, iii, v c. i, ii, iii d. iii, iv, v e. i, iii, v

b

Refrigerant compressors: Choose one answer. a. Must have intercoolers b. Could be centrifugal type c. Use automotive-style suction and discharge valves d. Have more cooling fins than air compressors e. Discharge directly into the evaporator

a

Rotary compressor types are? i. Open type ii. Hermetic type iii. Stationary single-blade design iv. Rotating sliding vane design v. Helical rotor design a. iii, iv,v b. i, ii, iii c. ii, iv, v d. i, iii, iv e. ii, iii, iv

a

Shaft seals are used on what compressor? a. Open type b. Hermetic type c. Stationary single-blade design d. Rotating sliding vane design e. Helical rotor design

b

The function of a safety heads is to: a. Relieve the pressure of compression when the compressor cycles off b. Relieve the pressure in the cylinder if a liquid slug of refrigerant is in the cylinder c. Protect the compressor from over heating d. Protect the compressor from short cycling

c

The piston displacement of a reciprocating refrigeration compressor is defined as: Choose one answer. a. The distance along which the piston travels b. The cylinder bore c. Volume of refrigerant that can be circulated through all the cylinders per unit time d. The revolutions per minute of the compressor motor e. Piston stroke length

e

The pressure ratio of a refrigeration compressor can be calculated by dividing the: Choose one answer. a. Discharge gage pressure by the inlet gage pressure b. Swept volume of a cylinder by its clearance volume c. Absolute inlet pressure by the absolute discharge pressure d. Absolute discharge pressure by the absolute inlet pressure, and then multiplying by the number of cylinders e. Absolute discharge pressure by the absolute inlet pressure

c

The safety head of a refrigeration compressor is designed to: Choose one answer. a. Unload over-loaded cylinders b. Be installed on a hermetic compressor c. Relieve pressure due to liquid in the cylinder d. Prevent explosion damage e. Operate in place of a safety relief valve

d

The three main classifications of refrigeration compressors are: Choose one answer. a. Scroll, rotary, and positive displacement b. Axial, centrifugal, and positive displacement c. Centrifugal, dynamic, and positive displacement d. Reciprocating, rotary, and centrifugal e. Rotary, reciprocating, and lobe

a

Which of the following compressor types uses impellers to draw in vapour? a) Centrifugal compressors b) Rotary compressors c) Reciprocating Compressors d) None of the above e) All of the above

e

Which of the following is NOT a function of the refrigeration compressor? Choose one answer. a. Raises the pressure of the refrigerant b. Raises the temperature of the refrigerant c. Maintains a low pressure in the evaporator d. Circulates refrigerant through the system e. Removes energy from the vapour

d

Which of the following is NOT considered a rotary refrigeration compressor design? Choose one answer. a. Screw b. Sliding vane c. Helical rotor d. Centrifugal e. Stationary single-blade

c

Which of the following is not a function of the compressor in a refrigeration system? a) draw low pressure refrigerant out of the evaporator b) draw low temperature refrigerant out of the evaporator c) lower the temperature of the refrigerant d) maintain sufficiently low pressure in the evaporator e) raise the pressure of the refrigerant

e

Which of the following is the compressor responsible for doing? i) Maintains a high pressure in the condenser ii) Maintains a low pressure in the evaporator iii) Raises the pressure of the refrigerant a) i only b) both i and iii c) both ii and iii d) iii only e) i, ii, and iii

a

Which one is NOT true about rotating mechanical seals a. Low cost b. Less maintenance c. Reduced wear on rotating shafts d. Leakage is reduced to a minimum

a

Which part is not a part of a reciprocating compressor? a. Inlet vane b. Crankshaft c. Connecting rod d. Piston