Mechanical Engineering Sample Paper

1. The work required per cycle for a single stage reciprocating compressor with clearance volume as compared to that of ideal single compressor is
a. more
b. less
c. equal
d. none of the above
Ans: B

2. The machine which develops pressure on rotary principle is known as

a. Compressor

b. Reciprocating compressor

c. Rotary compressor

d. None of the above

Ans: C
3. In a single acting reciprocating air compressor, without clearance the compression of air may be

a. adiabatic

b. polytropicc. isothermal

d. any one of the above

Ans: D
4. Euler's equation can be used for
a. Pumps
b. Radial flow compressors
c. Axial flow compressor
d. All the above
Ans: D

5. Clearance ratio is defined as the ratio of

a. Clearance volume to the swept volume

b. Clearance volume to cylinder volume

c. Swept volume to the clearance volume

d. Cylinder volume to the clearance volume

Ans: A
6. Rotary air compressors are generally suitable for handling

a. Large discharge of air at high pressure

b. Low discharge air at high

c. pressureLarge discharge of air at low

d. pressureLow discharge of air at low pressure

Ans: C
7. The maximum speed upto which a rotary compressor can be

a. 100 rpm

b. 1000 rpm

c. 10000 rpm

d. 30000 rpm

Ans: D
8. Which one of the following is a wrong statement?

a. The volume of air sucked by the compressor during its suction stroke is known as swept volume

b. The volume of air delivered by the compressor per minute is known as the compressor capacity

c. The absolute pressure of air at outlet of a compressor is known as back pressure

d. The inlet pressure in case of a compressor is always less than the discharge pressure

Ans: C
9. The pressure rise in a non-positive displacement compressor is due to

a. Back flow action

b. Squeezing action

c. Back flow and squeezing action

d. Transfer of kinetic energy of the fluid to the pressure energy

Ans: D
10. The work done on a compressor will be minimum if air air is taken from

a. A source of high high temperature air

b. The atmosphere

c. A source at 00C

d. A source of low temperature air

Ans: D
11. In a multistage compressor, the air compression in the first stage is cooled in an intercooler at constant pressure before passing into the second stage. The cooling is said to be perfect if

a. Air is cooled to a temperature less than its original temperature

b. air is cooled to a temperature more than its original temperature

c. air is cooled to its original temperature

d. none of the above

Ans: C
12. In a centrifugal compressor, an increase in speed at a given pressure ratio causes

a. increase in flow

b. increase in flow and decrease in efficiency

c. decrease in flow

d. decrease in efficiency

Ans: B
13. A compressor is only a

a. Reciprocating

b. Centrifugalc. Rotary

d. Any one of the above

Ans: D
14. By using multistage compressor with intercooling, a large amount of work

a. will be required

b. will be saved

c. will be wasted

d. none of the above

Ans: B
15. A compressor at high altitudes will require ...... power

a. more

b. same

c. less

Ans: C
16. In a centrifugal compressor, an increase in speed at a given pressure ratio causesa. decrease in flow

b. increase in flow and decrease in efficiency

c. increase in efficiency

d. decrease in flow and increase

Ans: B
17. In case of positive displacement compressors, the pressure rise takes place due to

a. Back flow of air from receiver or by squeezing action

b. Back flow of air from receiver only

c. Squeezing action of lobes only

d. None of the above

Ans: A
18. In a centrifugal compressor, the ratio of the ........ to the blade velocity is called slip factor

a. Outlet whirl velocity

b. Outlet velocity of flow

c. Inlet velocity of flow

d. Inlet whirl velocity

Ans: A
19. The machine which provides a gas or air at high pressure is known as

a. Turbine

b. Condenser

c. Compressor

d. Steam engine

Ans: C
20. The ratio of the delivery pressure to the supply pressure of air during isothermal compression of an air compressor is known as

a. expansion ratio

b. compression ratio

c. compressor efficiency

d. volumetric efficiency

Ans: B
21. The ratio of air horse power supplied by compressor to the horse power supplied by the prime mover to the compressor, is known as

a. Mechanical efficiency

b. Volumetric efficiency

c. Overall efficiency

d. Isothermal efficiency

Ans: C
22.The compressor capacity is expressed in

a. kg/m3

b. kg/cm3

c. m3/kg

d. m3/min

Ans: D
23. Which one of the following in a positive displacement compressors?

a. Roots blower

b. Centrifugal compressor

c. Axial compressor

d. None of the above

Ans: A
24.The roots efficiency is defined as

a. Actual work done divided by isentropic work done

b. Isentropic work done divided by actual work done

c. Actual work done divided by isentropic work done

d. None of the above

Ans: B
25.The compression ratio for the compressor is alwaysa. less than oneb. equal to onec. more than oned. none of the aboveAns: C
26. Rotary compressors are used to handle

a. Large quantities of air at high pressure

b. Small quantity of air at high pressure

c. Large quantities of air at low pressure

d. Small quantity of air at low pressure

Ans: C
27. Stagnation temperature is equal to

a. Static temperature only

b. Static temperature - temperature equivalent to kinetic head

c. Static temperature + temperature equivalent to kinetic energy head

d. None of the above

Ans: C
28. In case of a compressor, isothermal compression in practice is not possible because the compressor in that case should run

a. at high speed

b. at very high speed

c. at very slow speed

d. at zero speed

Ans: C
29. A compressor is having a capacity of 5m3/min. This means that the compressor

a. delivers 5m3/ min of compressed air

b. compresses 5m3/min of standard air

c. compresses 5m3/min of free air

d. delivers 5m3/min of free air

Ans: C
30. A jet engine has

a. no propeller

b. propeller in front

c. propeller on the top

d. propeller at back

Ans: A
31. For a two stage compressor for maximum efficiency, the intermediate pressure is

a. Arithmetic mean of the initial and final pressure

b. Geometric mean of the initial and final pressure

c. One plus arithmetic mean of initial and final pressure

d. None of the above

Ans: B
32. At the outlet of a compressor, the absolute pressure is known asa. Back pressure

b. Critical pressure

c. Discharge pressure

d. None of the above

Ans: C
33. The pressure rise in positive displacement compressor takes place due to

a. Squeezing action only

b. Back flow of air from receiver only

c. Back flow of air from receiver or squeezing action

d. None of the above

Ans: C
34. For the highest capacity of a compressor, the intake temperature should be

a. atmospheric

b. highest

c. lowest

d. none of the above

Ans: C
35. In case of centrifugal compressor, the slip is defined as

a. Sum of velocity of whirl at outlet under ideal and actual conditions

b. Difference of velocity of whirl at outlet under ideal and actual conditions

c. Ratio of velocity of whirl at outlet under ideal and actual conditions

d. None of the above

Ans: B
36. The rotary compressor runs at a speed

a. Equal to that of a reciprocating compressor

b. Less than that of reciprocating compressor

c. More than that of reciprocating compressor

d. None of the above

Ans: C
37. In a multistage compressor, the gas after being compressed in one cylinder

a. is heated before it enters the next cylinder

b. is cooled before it enters the next cylinder

c. is cooled back to initial temperature before it enters the next cylinder

d. is cooled 50C less than the initial temperature

Ans: C
38. In a compressor, the shut off pressure is corresponding to

a. Zero discharge

b. Maximum discharge

c. Average discharge

d. None of the above

Ans: A
39. The volume of air sucked by the compressor during its suction stroke is known asa. Compressor capacityb. Free air deliveryc. Swept volumed. None of the aboveAns: C
40. If no cooling device is used in rotary compressor, then the index of compression may be as high as

a. 1.2

b. 1.3

c. 1.7

d. 1.5

Ans: C
41. If the degree of reaction of a compressor is 0.5 then the compressor will have

a. Symmetrical blades

b. Flat blades

c. Unsymmetrical blades

d. None of the above

Ans: A
42. With the increase of pressure ratio, the volumetric efficiency of an air compressora. decreases

b. increases

c. remains constant

d. none of the above

Ans: A
43. Which of the following is a correct statement?

a. The work done by the prime mover to run a compressor is minimum if compression follows adiabatic law

b. Compressor is a machine which provides a gas at a very high temperature

c. The clearance ratio is defined as the ratio of clearance volume to cylinder volume

d. The compressor capacity is expressed as m3/min

Ans: D
44. The performance of air compressor at high altitudes will be ...... as compared to that at sea level

a. lower

b. higher

c. same

d. sometimes higher

Ans: A
45. In case of a compressor

a. Supply pressure is less than delivery pressure

b. Supply pressure is more than delivery pressure

c. Supply pressure is same as delivery pressure

d. None of the above

Ans: A
46. Which one of the following is a non-positive displacement compressors?

a. Screw compressor

b. Vane blower

c. Roots blower

d. Centrifugal compressor

Ans: D
47. If the flow of air through the compressor is perpendicular to its axis, then it is a

a. Turbo compressor

b. Axial flow compressor

c. Reciprocating compressor

d. Centrifugal compressor

Ans: D
48. Which one of the following is a correct statement?
a. A compressor at high altitudes will require more power
b. The volumetric efficiency of a compressor increases with the increase of compression ratio
c. The ratio of the volume of free air delivery per stroke to the swept volume of the piston is known as isothermal efficiency
d. Inter cooling in multistage compressors is done to minimize the work of compression
Ans: D

49. The degree of reaction in axial flow compressor is equal to

a. Pressure rise in the stage

b. Ratio of pressure rise in rotor blades to pressure rise in the stage

c. Ratio of pressure rise in stage to pressure rise in rotor blades

d. Pressure rise in rotor blades

Ans: B
50. The positive displacement compressor, in which the pressure rise takes place due to back flow of high pressure air from the receiver is known as
a. Screw compressor
b. Vane blower
c. Roots blower
d. None of the above
Ans: C