Tuesday, 27 November 2012

Interview Questions and Answers for Mechanical Engineering



1. How shear forces are incurred in fluid flow ?
Ans:  Shear forces between fluid particles and boundary walls and between the fluid particles themselves, result from the viscosity of the real fluid.

2. In laminar flow, how discharge is related to viscosity ?
Ans:  Discharge varies inversely as viscosity.

3. What is best hydraulic section ?
Ans:  Best hydraulic section is one in which for a given cross-section area, the channel section has least wetted perimeter.

4. What is best hydraulic trapezoidal section ?
Ans:  It is a half-hexagon in shape.

5. What is specific energy in a channel section ?
Ans:  It is defined as the energy head measured with respect to the channel bottom at the sec¬tion. At any section, it is equal to sum of the velocity head and the water depth at the section.

6. What is critical depth and critical flow ?
Ans:  Critical depth is the depth, at which the discharge may be delivered through the section at minimum energy.
Critical flow is the flow in open channel corresponding to critical depth.

7. What causes boundary layer separation ?
Ans:  An adverse pressure gradient.

8. What is the improtance of Nose radius ?
Ans:  Nose radius is favourable to long tool life and good surface finish. A sharp point on the end of a tool is highly stressed, short lived and leaves a groove in the path of cut.

9. At what point below free surface in a uniform laminar flow in a channel the point velocity is equal to mean velocity of flow ?
Ans:  At 0.577 depth of channel.

10. What is the value of friction factor for smooth pile when Reynolds number is approximately = 10G ?
Ans:  0.01.

11. How hydraulic grade line and free surface of open channel flow related ?
Ans:  They coincide.

12.What are the first and last elements of tool signatures ?
Ans:  Back rake angle and nose radius.

14. What is open channel flow ? Explain 4 types of open channel flows.
Ans:  Open channel flow has a free water surface which is normally subject to the atmospheric pressure.
Steady open channel flow : In this case the discharge and water depth at any section in the reach do not change with time during the period of interest.
Unsteady open channel flow : In this case the discharge and the water depth at any section in the reach change with time.
Uniform open channel flow : In this case the discharge and the water depth remain the same in energy section in the channel reach. It is mostly steady.
Varied open channel {low : In this case the water depth and/or the discharge change along the length of the channel. It may be steady (such as flow over a spillway crest) or unstgeady (as in the case of flood waves or tidal surge).

15. When does wake occur ?
Ans:  It occurs after a separation point.

16. In straight polarity, to which terminal the electrode is connected ?
Ans:  Negative.

17. What is hydraulic radius ?
Ans:  It is the ratio of fluid flow area/shear perimeter.

18. Define flow work.
Ans:  Flow work is the amount of mechanical energy required to push or force a flowing fluid across a section boundary.

19. What do you understand by dimensional analysis ?
Ans:  Dimensional analysis is the mathematics of dimensions and quantities and provides procedural techniques whereby the variables that are assumed to be significant in a problem can be formed into dimensionless parameters, the number of parameters being less than the number of variables.

20. What is hydraulic depth for open channel flow ?
Ans:  It is the ratio of area and the top width of the channel section.

21. Which welding set will you select for welding both ferrous and non ferrous materials.
Ans:  D.C. generator set.

22. Which welding process is a combination of arc welding and gas welding processes?
Ans:  Atomic hydrogen welding.

23. What is hydraulic jump ?
Ans:  It is a natural phenomenon in open channel. It is an abrupt reduction in flow velocity by means of a sudden increase of water depth in the down stream direction. Through a hydraulic jump, and high-velocity supercritical flow is changed to a low-velocity subcritical flow.

24. What is gradually varied flow ?
Ans:  The changes in water depth in the open channel take place very gradually with distance. Depending on the channel slope, the surface conditions, the sectional geometry, and the discharge, these may be classified into five categories : steep channel, critical channel, mild channel, horizontal channel, and adverse channel.

25. Explain 5 types of channels.
Ans:  Steep channel : In this case normal depth < critical depth.
Critical channel   : In this case normal depth = critical depth.
Mild channel       : In this case, normal depth > critical depth.
Adverse channel    : In this case, the slope of channel bed < 0
Horizontal channel : In this case, the slope of channel bed = 0.

26. Mention two major differences between shaper and planer ?
Ans:            Shaper                                   Planer
(a)    The cutting tool reciprocates     (a) Work reciprocates
(b)    The work is stationary              (b) Tool is stationary
(c)    Meant for small work pieces     (c) Meant for large work pieces
(d)    Only lighter cut can be taken    (d) Heavy cuts can be taken
(e)    Tools are smaller in size           (e) Tools are bigger in size

27. Differentiate between drilling and reaming ?
Ans:              Drilling                                                              Reaming
(a)    It is the operation of initiating hole                (a)  Reaming is the operation of finishing and
                                                                             sizing a drilled/bored hole
(b)    It can be done at relatively high speeds        (b)  It should be done only at slow speeds
(c)    Larger chips are produced                          (c)   Less chips are produced
(d)     Drill has only two flutes                              (d)   Reamer has more than 4 flutes
(e)     Drill has chisel edge                                    (e)   Reamer has a bevel edge

28. What is similarity between normal shock wave and hydraulic jump ?
Ans:  Both are analogous and irreversible.

29. For what purpose chills are used in moulds ?
Ans:  Chills are used to achieve directional solidification.

30. What is tumbler gear mechanism ?
Ans:  Tumbler gear mechanism is a mechanism consisting of number of different sized gears keyed to the driving shaft in the form of cone and is used to give the desired direction of motion of the lathe spindle.

31. What is relative roughness of pipe ?
Ans:  It is the ratio of the size of the surface imperfections to the inside diameter of the pipe.

32. What is conicity ?
Ans:  The ratio of the difference in diameter of the taper to its length is termed conicity.

33. Under what condition the effect of compressibility of fluid can be neglected ?
Ans:  When Mach number is less than 0.4.

34. For which type of flow the velocity distribution in a pipe is parabolic.
Ans:  For uniform laminar flow.

35. What is the relationship between center line velocity and average velocity for a laminar flow in a pipe ?
Ans:  Average velocity = 1/2 centre line velocity.

36. On which factor the friction factor for a smooth pipe in turbulent flow depends ?
Ans:  Reynolds number.

37. What do you understand by pipe branchings ?
Ans:  When water is brought by pipes to a junction where more than two pipes meet, them the total amount of water brought by pipes to a junction must always be equal to that carried away from the junction by other pipes, and all pipes that meet at the junction must share the same pressure at the junction.

38. What is pipe networks and what are the condition for network ?
Ans:  Pipe network comprises a number of pipes connected together to form loops and branches. For a network,
(i) at any junction, Y.Q = 0 and
(ii) between any two junctions the total head loss is independent of the path taken.

39. What is Hardy-Cross Method ?
Ans:  It is a commonly used computer program for a pipe network.

40. Explain water hammer.
Ans:  The force resulting from changing the speed of the water mass (say in a pipe due to sudden change of flow rate) may cause a pressure rise in the pipe with a magnitude several times greater
than the normal static pressure in the pipe. Pressure head caused by water hammer = C (V - velocity in pipe, C = celerity).

41. What happens to impurities in centrifugal casting ?
Ans:  They get collected at the center of the casting.

42. Define the terms hydraulic similitude and dimensional analysis.
Ans:  Hydraulic similitude is the principle on which the model studies are based.
Dimensional analysis is the analysis of the basic relationship of the various physical quantities involved in the static and dynamic behaviors of water flow in a hydraulic structure.

43. Explain the difference between geometric similarity, kinematic similarity and dynamic similarity.
Ans:  Geometric similarity : It implies similarity of form. The model is a geometric reduction of the prototype and is accomplished by maintaining a fixed ratio for all homologous lengths between the model and the prototype.
Kinematic similarity : It implies similarity in motion. Kinematic similarity between a model and the prototype is attained if the homologous moving particles have the same velocity ratio along geometrically similar paths. It involves the scale of time as well as length.
Dynamic similarity : It implies similarity in forces involved in motion.

44. Define Reynolds law ?
Ans:  When the inertial force and the viscous force are considered to be the only forces governing the motion of the water, the Reynolds number of the model and the prototype must be kept at the same value.

45. When a built up edge is formed while machining ?
Ans:  While machining ductile materials at high speed.

46. On what factor the friction factor for a rough pipe in turbulent flow depends ?
Ans:  Relative roughness.

47. What is unit power of a turbine ?
Ans:  PHP12.

48. How cavitation causes damage ?
Ans:  In a a closed system (pipelines, or pumps), water vaporises rapidly in regions where the pressure drops below the vapour pressure. This phenomenon is called cavitation. The vapour bubbles formed in cavitation usually collapse in a violent manner, which may cause considerable damage to the system.

49. In milling process, how the arbor torque can be smoothend ?
Ans:  Arbor torque can be smoothened by increasing number of teeth, using higher spiral angle of teeth, using higher cutting depth.

49. What are webs in a twist drill ?
Ans:  Webs are the metal column in the drill which separates the flutes.

50. What is bluff body ?
Ans:  It is a body with such shape that the flow is separated much ahead of its rear end resulting in a large wake, the pressure drag being much greater than the friction drag.

51. What is bulk modulus ?
Ans:  It is the ratio of hydrostatic stress to volumetric strain within the elastic limits.

52. Define boundary layer.
Ans:  It is the fluid layer in the neighborhood of a solid boundary where the effects of fluid friction are predominant.

53. What is creep flow ?
Ans:  It is flow at very low Reynolds number where viscous forces are larger than the inertia forces.

54. What is Torricellis theorem ?
Ans:  According to it velocity of jet flowing out of a small opening is proportional to the square root of head of liquid above it.

55. How does cavitation manifest itself in a centrifugal pump ?
Ans:  Usual symptoms of cavitation of pump are noise, vibration, a drop in head and capacity with a decrease in efficiency, accompanied by pitting and corrosion of the impeller vanes.

56. What happens if centrifugal pump is operated at excessive speeds ?
Ans:  When a pump is operated at excessive speeds, the differential pressure developed increases and causes a powerful pulsating vacuum on the underside of the blade tips and each particle of water is pulled away from the blade, taking away with it a small particle of metal, producing pitting/grooved effect. Repeated erosive action results in complete honey combing and total destruction of blade, with resultant loss in pump performance.

57. On what parameters the head developed by a centrifugal pump depends ?
Ans:  It depends upon the impeller diameter and its rotative speed.

58. Which factors determine the selection of electrolyte for electrochemical machining process ?
Ans:  Electrolyte should be chemically stable and have high electrical conductivity.

59. What is the disadvantages of centrifugal pump having very low specific speed ?
Ans:  For a.centrifugal pump having very low specific speed, the impeller diameter is large and narrow having excessively high disc friction and excessive hydraulic losses.

60. On what factors the efficiency of pump depends ?
Ans:  Efficiency of a pump (centrifugal) depends on the size, speed, and proportions of the impeller and casing.

61. On what factors the cavitation in centrifugal pumps is dependent ?
Ans:  Cavitation in centrifugal pumps depends on the velocity of water entering tne impeller and on the relatiave velocity of the impeller blades where the water is picked up.

62. What are the losses in a centrifugal pump ?
Ans:  The losses in a centrifugal pump are : Friction losses due to eddies in flow, leakage, friction loss due to rotation of impeller in chamber of water, gland and bearing power losses.

63. What should be done to avoid cavitation in pumps ?
Ans:  In order to avoid cavitation, the suction lift and the operating speed must be carefully chosen.

64. What will happen if speed of reciprocating pump is increased ?
Ans:  If speed of a reciprocating pump is increased beyond a limit, then atmospheric pressure would be insufficient to force water into the pump at the same speed as the piston. This would a break in the continuity of the water in suction pipe (cavitation) and give rise to vibration, noise, and chemical attack by any dissolved gases which may be released from the water owing to the high vacuum and the breaking of the water column.

65. What is the order of efficiency of cenetrifugal and reciprocating pumps ?
Ans:  The efficiency of centrifugal pump is of the order of 45% whereas that of reciprocting pump is around %.

66. What are the basic operations performed in a slotter ?
Ans:  The different operations done in slotter are :
1. Machining grooves   
2. Machining cylindrical surface      
3. Machining irregular profiles.

67. How the positive displacement is obtained in rotary pumps ?
Ans:  Positive displacement in rotary pumps is achieved in two ways :
(i) A rotor carries radially adjustable vanes, the outer tips of which are constrained by a circular casing, whose centre is remote from that of the rotor.
(ii) Various combinations of gears, lobes, helices, etc. within a casing arranged so that the lobes or teeth attached to each rotor pass in sequence through the same pumping space.

68. How a slotter differs from shaper ?
Ans:          Slotter                                        Shaper
(a)  Ram reciprocates vertically          (a) Ram reciprocates horizontally
(b)  It has a circular table                  (b) It has a rectangular table
(c)  Suited for machining internal surfaces   (c) Suited for machining external surfaces
(d)  Table can take less load                  (d) Table can take much load

69. Under what condition the flow and power of pump vary as square of the size ?
Ans:  The flow and power vary as size2 when the geometric size changes as inverse of change of speed.

70. How the incidence of cavitation detected ?
Ans:  The incidence of cavitation is detected by the following in order of appearance.
(i)   stroboscopic observation of bubble appearance and size
(ii)  sensitive acoustic tests of cavitation noise
(iii) reduction of efficiency and/or head of 3%.

71. How cavitation erosion is assessed ?
Ans:  Cavitation erosion is assessed by depth of attack or weight of metal removed.

72. At which temperature the cavitation erosion is negligible and why ?
Ans:  Cavitation erosion is negligible at above 300°C because the water and steam have same densities at critical temperature of 374°C and thus there is no volume change or bubble collapse in the vicinity of this range.

73. What is an arbor ?
Ans:  An arbor is an accurately machined shaft for holding and driving the arbor type cutter. It is tapered at one end to fit the spindle nose and has two slots to fit the nose keys for locating and driving it.

74. For a body to float in stable equilibrium where the e.g. should be located w.r.t. metacentre ?
Ans:  e.g. should be below metacentre.

75. What is the condition for a flow to be fully developed through a pipe ?
Ans:  Ratio of maximum velocity to average velocity should be 2.

76. When a fluid is moving with uniform velocity, whether the pressure of fluid will depend on its depth and orientation ?
Ans:  No.

77. How much is the vertical component of force on a curved surface submerged in a static liquid ?
Ans:  It is equal to weight of the liquid above the curved surface.

78. On which factors depends the friction factor in a rough turbulent flow in a pipe?
Ans:  It depends on pipe diameter and the condition of the pipe.

79. What does the realisation of velocity potential in fluid flow indicate ?
Ans:  It indicates that flow is irrotational.

80. What is the difference between potential flow and creep flow ?
Ans:  Potential flow assumes viscous forces to be zero but same is considered larger than inertia forces in creep flow.

81. For which application Mach number and Froude numbers are significant ?
Ans:  Mach no. is significant in the study of projectiles and jet propulsion. Froude number is significant in the study of ship hulls.

82. What is the difference between geometric, kinematic, and dynamic similarities between model and prototype ?
Ans:  Geometric similarity is mainly for same shape for model and prototype, kinematic similarity is concerned with stream line pattern, whereas dynamic similarity concerns the ratio of forces.

83. A body is floating in water. If it is displaced slightly then about which point it will oscillate.
Ans:  It will oscillate about centre of buoyancy.

84. Why uniform ramming is considered desirable in green sand moulding process ?
Ans:  Uniform ramming results in greater dimensional stability of a casting.

85. On what account the friction drag is experienced ?
Ans:  Friction drag is experienced on separation of boundary layer.

86. What is the characteristic of centrifugally cast components ?
Ans:  These have fine grain structure with high density.

87, Under what condition the separation of flow occurs ?
Ans:  When pressure gradient changes abruptly.

88. What is the criterion for shaping of streamlined body ?
Ans:  It is shaped to suppress the flow separation about the body and to shift the boundary layer separation to near most part of body to reduce the wake size.

89. What do you understand by entrance length and what is its value for turbulent flow in smooth pipe ?
Ans:  Entrance length of flow is the initial length in which the flow develops fully such that the velocity profile remains unchanged downstream. For turbulent flow in smooth pipe, entrance length is taken as 50 x diameter of pipe.

90. Explain the difference between friction drag and pressure drag.
Ans:  Friction drag is the drag force exerted by a fluid on the surface due to friction action when
the flow occurs past a flat surface at zero incidence. Pressure drag is the additional drag force on
account of the differences of pressure over the body surface when flow occurs past a surface which is
not everywhere parallel to the fluid stream. Pressure drag depends upon separation of bondary layer
and the size of wake. Friction drag is due to shear stresses generated due to viscous action.

91. What do you understand by choking in pipe line ?
Ans:  When specified mass flow is not able to take place in a pipe line.

92. What is the difference between streamline body and bluff body ?
Ans:  In streamline body the shape is such that separation in flow occurs past the nearmost part of the body so that wake formed is small and thus friction drag is much greater than pressure drag. In bluff body the flow gets separated much ahead of its rear resulting in large wake and thus pressure drag is much greater than the friction drag.

93. What is the difference between dressing and trueing of a grinding wheel ?
Ans:  Dressing is the process used to clear the cutting surface of the grinding wheel of any dull grits and embedded swarf in order to improve the cutting action. Trueing is the process employed to bring the wheel to the required geometric shop and also to restore the cutting action of a worn wheel.

94. Whether hard grade or softer grade is required for internal grinding than external grinding?
Ans:  Softer graders of wheel are required for internal grinding than for external grinding.

95. How is the velocity profile and stress distribution due to laminar flow of an incompressible flow under steady conditions in a circular pipe.
Ans:  Velocity profile is parabolic with zero velocity at boundary and maximum at the centre. Shear stress distribution is linear, being maximum at boundary and zero at centre.

96. Where the maximum velocity occurs in open channels ?
Ans:  Near the channel bottom.

97. Define hydraulically efficient channel cross section.
Ans:  The shape of such section is that which produces minimum wetted perimeter for a given area of flow and carries maximum flow.

9. What is follower rest ?
Ans .For slender work a travelling or follower rest is used. This fits on the lathe - saddle and travels to and fro with it. By this means support is constantly provided at the position of cut. Thus the work piece being turn is rigidly held against the tool.

99. What is the meaning of the term sensitive drill press ?
Ans:  A sensitive drilling press is a light, simple, bench type machine for light duty working with infinite speed ratio.

100. Why carburised machine components have high endurance limit ?
Ans:  In carburised machine components, the process of carburisation introduces a compressive layer on the surface and thus endurance limit is increased.

2 comments:

ANUJ MISHRA on 22 October 2013 at 07:37 said...

best question for basic knowledge as well as interview

ANUJ MISHRA on 22 October 2013 at 07:38 said...

best question

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