Interview Q&A in Mech Engg 2015

Interview Q&A Mechanical Engineering 2015-2016 1

Compiled by: Mr. B. Ramesh, Associate Professor in Mechanical Engineering, St. Josephs Institute of

Technology, Chennai-600119

1. What is the difference between P11 and P12 Pipes?

P11 the chromium molybdenum composition that is 1% of chromium and 1/4% of

molybdenum. P12 the chromium molybdenum composition that is 1% of chromium

and 2% of molybdenum.

2. State difference between Anti Friction Bearing and Journal Bearing?

Generally, journal bearings have higher friction force, consume higher energy and

release more heat, but they have larger contact surface, so normally used in low speed

high load applications. In anti friction bearings friction is less. One object just rolls over

each other.

3. What is Powder Technology?

Powder technology is one of the ways of making bearing material. In this method

metals like bronze, Al, Fe are mixed and compressed to make an alloy.

4. State the difference between Unilateral and Bilateral Tolerance?

A unilateral tolerance is tolerance in which variation is permitted only in one direction

from the specified direction. e.g. 1800 +0.000/-0.060

Bilateral tolerance is tolerance in which variation is permitted in both direction from the

specified direction. e.g. 1800 +0.060/-0.060

5. What is difference between Welding and Brazing?

In Welding concentrated heat (high temperature) is applied at the joint of metal and

fuse together. Brazing involves significantly lower temperatures and does not entail the

melting of base metals. Instead, a filler metal is melted and forced to flow into the joint

through capillary action.

6. The Fatigue life of a part can be improved by?

Improving the surface finish by Polishing & providing residual stress by Shot peening.

7. Poissons Ratio is Higher in, Rubber/Steel/Wood?

When a material is compressed in one direction, it usually tends to expand in the other

two directions perpendicular to the direction of compression. This phenomenon is

called the Poisson effect. Poissons ratio is a measure of the Poisson effect.

For rubber = 0.5 ; For steel = 0.288 ; For wood < 0.2

Thus Poissons ratio is higher in RUBBER.

8. What are the different types of fits? Explain?

On the basis of Indian standards fits can mainly be categorized into three groups:

Clearance Fit: These types of fits are characterized by the occurrence of a clearance

between the two mating parts. The difference between the minimum size of the hole

and the maximum size of the shaft is called the minimum clearance, the difference

between the maximum size of the hole and the minimum size of the shaft is known as




maximum clearance.

Interference Fit: In these types of fits the size of the mating parts are predefined so that

interference between them always occurs. The tolerance zone of the hole is completely

below the tolerance zone of the shaft.

Transition Fit: As the name suggests these type of fit has its mating parts size limited to

allow either clearance or interference. The tolerance zone of the hole and the shaft

overlaps in case of such fits.

9. What are the rules that must be kept in mind while designing castings?

Some of the points that must be kept in mind during the process of cast designing are as

follows:

To avoid the concentration of stresses sharp corners and frequent use of fillets should

be avoided.

Section thicknesses should be uniform as much as possible. For variations it must be

done gradually.

Abrupt changes in the thickness should be avoided at all costs.

Simplicity is the key, the casting should be designed as simple as possible.

It is difficult to create true large spaces and henceforth large flat surfaces must be

avoided.

Webs and ribs used for stiffening in castings should as minimal as possible.

Curved shapes can be used in order to improve the stress handling of the cast.

10. What are the points that should be kept in mind during forging design?

Some of the points that should be followed while forging design are:

A radial flow of grains or fibers must be achieved in the forged components.

The forged items such as drop and press forgings should have a parting line that should

divide the forging into two equal halves.

The ribs in a forging should not be high or thin.

In order to avoid increased die wear the pockets and recesses in forgings should be

minimum.

In forgings the parting line of it should lie as far as possible in a single plane.

For ease of forging and easy removal of forgings the surfaces of the metal should

contain sufficient drafts.

11. What are the different theories of failure under static load, explain briefly?

The main theories of failure of a member subjected to bi-axial stress are as follows:

Maximum principal stress theory ( Rankines theory): This theory states that failure

occurs at a point in member where the maximum principal or normal stress in a bi-axial




system reaches the maximum strength in a simple tension test.

Maximum shear stress theory ( Guests or Trescas theory): This theory states that

failure occurs when the biaxial stress reaches a value equal to the shear stress at yield

point in a simple tension test.

Maximum principal strain theory ( Saint Venant theory): This theory states that failure

occurs when bi-axial stress reaches the limiting value of strain.

Maximum strain energy theory ( Haighs theory): This theory states that failure occurs

when strain energy per unit volume of the stress system reaches the limiting strain

energy point.

Maximum distortion energy theory ( Hencky and Von Mises theory): This theory

states that failure occurs when strain energy per unit volume reaches the limiting

distortion energy.

12. How many Laws of Thermodynamics are there?

There are three laws of the thermodynamics.

First Law: Energy can be neither created nor destroyed. It can only change forms. In any

process in an isolated system, the total energy remains the same. Heat and mechanical

work are mutually convertible.

Second Law: When two isolated systems in separate but nearby regions of space, each

in thermodynamic equilibrium in itself, but not in equilibrium with each other at first,

are at some time allowed to interact, breaking the isolation that separates the two

systems, and they exchange matter or energy, they will eventually reach a mutual

thermodynamic equilibrium. The sum of the entropies of the initial, isolated systems is

less than or equal to the entropy of the final exchanging systems. In the process of

reaching a new thermodynamic equilibrium, entropy has increased, or at least has not

decreased. The entropy of the universe increases over time and moves towards a

maximum value.

Third Law: As temperature approaches absolute zero, the entropy of a system

approaches a minimum.

13. State Laws of conservation of energy?

According to the laws of conservation of energy, energy can neither be created nor be

destroyed. It can only be transformed from one form to another.

14. Is the boiler a closed system?

Yes definitely the boiler is a closed system.




15. What is Carnot engine?

It was being designed by Carnot and let me tell you that Carnot engine is an imaginary

engine which follows the Carnot cycle and provides 100% efficiency.

16. Which has more efficiency: Diesel engine or Petrol engines?

Of course Diesel engine has the better efficiency out of two.

17. Compare Brayton Cycle and Otto Cycle?

The heat addition and rejection processes in Otto cycle are of constant volume, whereas

in Brayton cycle, they are of constant pressure.

-Otto cycle is the ideal cycle for spark ignition engines.

-Brayton cycle is the ideal cycle for gas power turbines.

18. What is DTSI Technology?

DTSI stands for Digital Twin Spark Plug Ignition. The vehicles with DTSI Technology

use 2 spark plugs which are controlled by digital circuit. It results in efficient

combustion of air fuel mixture.

Digital - Since the spark generation will be initiated by a microchip.

Twin - Since two spark plugs will be used.

Spark ignition - Since the ignition will be done via a spark.

19. What is the difference between Speed and Economic Speed?

The rated speed tells us about the maximum speed which can be achieved by a vehicle

or some other machine but the economical speed means the speed limit at which the

machine works efficiently with least consumption of fuel.eg-in normal bikes(not

racing),the max.speed limit shown on speedometer is upto 120 kmph but companies

always advice their customers to drive such bikes at around 60 kmph to have maximum

mileage.

20. What is meant by One Tonn Air-Conditioner?

1 tonn refrigeration means it extracts 210 kJ/min of heat from the system.

21. If you heat a steel pipe with the hole at center, does heat affects the hole

diameter?

It gets bigger.

22. Why Entropy decreases with increase in temperature?

ds=dQ/T Entropy is inversely proportional to the temperature so, as temp. increases,

entropy decreases.

23. Why different types of sound are produced in different bikes, though they run on

SI Engines?




Engine specifications are different in different manufactures like as Bore Diameter (CC),

Ignition timing. Also the exhaust passage takes more responsible for sound.

24. How much Watt means 1Hp?

746.2 Watt

25. Explain Bicycle Rear Wheel Sprocket working?

Rear wheel sprocket works under the principle of ratchet and pawl.

26. Definition of Octane Number and Cetane Number?

Octane No.- Octane number is defined as the percentage, by volume, of iso octane in the

mixture of iso octane and h-heptane. It is the measure of rating of SI engine.

Cetane No.- Cetane number is defined as the percentage, by volume, of n-cetane in the

mixture of n-cetane and alpha methyl naphthalene. It is the measure of rating of CI

engine.

27. What is the difference between Critical Speed and Whirling Speed?

In Solid mechanics, in the field of rotor dynamics, the critical speed is the theoretical

angular velocity which excites the natural frequency of a rotating object, such as a shaft,

propeller or gear. As the speed of rotation approaches the objects natural frequency, the

object begins to resonate which dramatically increases system vibration. The resulting

resonance occurs regardless of orientation. Whirling Speed is due to the unbalanced

forces acting on a rotating shaft.

28. What is the difference between Technology and Engineering?

Engineering is application of science. Technology shows various methods of

Engineering. A bridge can be made by using beams to bear the load, by an arc or by

hanging in a cable; all shows different technology but comes under civil engineering

and science applied is laws of force/load distribution. Application of engineering for

sophistication/modernization is also called as technology.

29. What is Hydrostatic System?

Hydrostatics is the study of uid bodies that are

At rest

Moving suciently slowly so there is no relative motion between adjacent parts

of the body

For hydrostatic situations

There are no shear stresses

There are only pressure forces that act perpendicular to any surface.

30. What is Cotter joint?




A cotter joint is used to connect rigidly two co-axial rods or bars which are subjected to

axial tensile or compressive forces.

31. What is the difference between Strainer and Fitler?

Strainer for coarse size, Filter is more accurate than Strainer.

32. Why the Centrifugal Pump is called High Discharge pump?

Centrifugal pump is a kinetic device. The centrifugal pump uses the centrifugal force to

push out the fluid. So the liquid entering the pump receives kinetic energy from the

rotating impeller. The centrifugal action of the impeller accelerates the liquid to a high

velocity, transferring mechanical (rotational) energy to the liquid. So it discharges the

liquid in high rate. It is given in the following formulae:

Centrifugal force F= (M*V2)/R.

Where, M-Mass, V-Velocity, R-Radius

33. Which Pump is more Efficient Centrifugal Pump or Reciprocating Pump?

Centrifugal pump. Because flow rate is higher compared to reciprocating pump. Flow is

smooth and it requires less space to install. Lower initial cost and lower maintenance

cost.

34. Which Mechanism is used in Automobile gearing System?

Differential mechanism

35. When Crude Oil is Heated, Which Hydro Carbon comes first?

Natural gas (Gasoline) at 20 degree Celsius.

36. What is heat treatment and why is it done?

Heat treatment can be defined as a combination of processes or operations in which the

heating and cooling of a metal or alloy is done in order to obtain desirable

characteristics without changing the compositions. Some of the motives or purpose of

heat treatment are as follows:

In order to improve the hardness of metals.

For the softening of the metal.

In order to improve the machinability of the metal.

To change the grain size.

To provide better resistance to heat, corrosion, wear etc.

Heat treatment is generally performed in the following ways:

Normalizing, Annealing, Spheroidising, Hardening, Tempering, Surface or case

hardening

37. How many governors are needed for safe turbine operation? Why?




Two independent governors are needed for safe turbine operation. One is an over speed

or emergency trip that shuts off the steam at 10 percent above running speed

(maximum speed). The second, or main governor, usually controls speed at a constant

rate; however, many applications have variable speed control.

38. Besides lubrication, what are two functions of lubricating oil in some turbines?

In larger units, lube oil cools the bearings by carrying off heat to the oil coolers. Lube oil

in some turbines also acts as a hydraulic fluid to operate the governor speed-control

system.

39. What are the assumptions made in simple theory of bending?

The assumptions made in the theory of simple bending are:

The material of the beam is homogeneous this implies that it is uniform in density,

strength and have isotropic properties meaning possessing same elastic property in all

directions.

Even after bending the cross section of the beam remains constant.

During the initial stages the beam is straight and unstressed.

All the stresses in the beam are within the elastic limit of its material.

The layers of the beam are free to contract and expand longitudinally and laterally

On any cross section the perpendicular resultant force of the beam is zero.

Compared to the cross-sectional dimension of the beam the radius of curvature is very

large.

40. What kind of materials should be used for shafts manufacturing?

Some of the qualities that should be present in materials for shafts are as follows:

The material should have a high index of strength.

Also it should have a high level of machinability.

The material should possess a low notch sensitivity factor.

The material must also have wear resistant properties.

Good heat treatment properties should also be present.

The common material used to creates shafts of high strengths an alloy of steel like nickel

is used. The shafts are manufactured by hot rolling processes and then the shaft is

finished using drawing or grinding processes.

41. Why should a chain drive be used over a belt or rope driven drive? State pro`s and

con`s?

The advantages of using a chain drives are:

In a chain drive no slip occurrence takes place.

The chains take less space as compared to rope or belts as they are made of metal and




offer much strength.

The chain drives can be used at both short and long ranges and they offer a high level of

transmission efficiency.

Chain drives can transmit more load and power as compared to belts.

A very high speed ratio can be maintained in one step of chain drives.

Some of the cons of using a chain drive are:

The cost of producing chain drives is higher as compared to that of belts.

The chain drives must be serviced and maintained at regular intervals and henceforth

their cost of ownership is high comparatively.

42. What are the different types of springs and explain them briefly?

Springs can be broadly classified into the following types:

Helical Springs: These springs as their name suggests are in coil form and are in the

shape of helix. The primary purpose of such springs are to handle compressive and

tensile loads. They can be further classified into two types: compression helical spring

and tension helical spring each having their own unique areas of application./

Conical and volute springs: Both these spring types have specialized areas of usage

where springs with adaptable rate according to the load is required. In case of conical

springs they are wound so as to have a uniform pitch while on the other hand volute

springs are wound in a slight manner of a parabloid.

Torsion Springs: The characteristics of such springs is that they tend to wind up by the

load. They can be either helical or spiral in shape. These types of springs are used in

circuit breaker mechanisms.

Leaf springs: These types of springs are comprised of metal plates of different lengths

held together with the help of bolts and clamps. Commonly seen being used as

suspensions for vehicles.

Disc Springs: As the name suggests such types of springs are comprised of conical discs

held together by a bolt or tube.

Special Purpose Springs: These springs are all together made of different materials

such as air and water.

43. What are the different types of brakes and explain them briefly?

Brakes can be classified on the basis of their medium used to brake, they are as follows:

Hydraulic Brakes: These brakes as their name suggest use a fluid medium to push or

repel the brake pads for braking.

Electric Brakes: These brakes use electrical energy to deplete or create a braking force.

Both the above types of breaks are used primarily for applications where a large




amount of energy is to be transformed.

Mechanical Brakes: They can be further classified on the basis of the direction of their

acting force: Radial Brakes: As their names suggests the force that acts on the brakes is

of radial direction. They can further be classified into internal and external blades. Axial

Brakes: In these types of brakes the braking force is acting in an axial direction as

compared to radial brakes.

44. On what basis can sliding contact bearings be classified? Explain?

Sliding contact bearings can be classified on the basis of the thickness of the lubricating

agent layer between the bearing and the journal. They can be classified as follows:

Thick film bearings: These type of bearings have their working surface separated by a

layer of the lubricant. They are also known as hydrodynamic lubricated bearings.

Thin film bearings: In this type of bearings the surfaces are partially in direct contact

with each other even after the presence of a lubricant. The other name for such type of

bearings is boundary lubricated bearings.

Zero Film Bearings: These type of bearings as their name suggests have no lubricant

present between the contact layers.

Externally or hydrostatically pressurized lubricated bearings: These bearings are able

to without any relative motion support steady loads.

45. Briefly explain the advantages of Cycloidal and Involute gears?

The advantages of the Cycloidal gears are as follows:

Having a wider flank as compared to Involute gears they are considered to have more

strength and hence can withstand further load and stress.

The contact in case of cycloidal gears is between the concave surface and the convex

flank. This results in less wear and tear.

No interference occurs in these types of gears.

The advantages of Involute gears are as follows:

The primary advantage of involute gears is that it allows the changing of the centre

distance of a pair without changing the velocity ratio.

The pressure angle remains constant from start to end teeth, this results in less wear and

smooth running of the gears.

The involute gears are easier to manufacture as they can be generated in a single curve (

the face and flank ).

46. What are Bevel Gears and what are its types?

Bevel gears are the type of gears in which the two shafts happen to intersect. The gear

faces which are tooth bearing are conical in shape. They are generally mounted on




shafts which are 90 degrees apart but they can be made to work at other angles as well.

The bevel gears are classified into the following types on the basis of pitch surfaces and

shaft angles:

Mitre Gears: These types of gears are similar to each other ie. they have the same pitch

angles and contain the same number of teeth. The shaft axes intersect at 90 degrees

angle.

Angular bevel gears: When two bevel gears connect at any angle apart from 90 degrees.

Crown bevel gears: When the two shaft axes intersect at an angle greater than 90 and

one of the bevel gears have a pitch angle of 90 degrees they are known as crown bevel

gears.

Internal bevel gears: In these type of gears the teeth on the gears is cut on the inside

area of the pitch cone.

47. What are the different values that need to be determined in order to design a

cylinder for an ICE?

The following values are needed to be determined:

Thickness of the cylinder wall: The cylinder walls in an engine is made witness to gas

pressure and the side thrust of a piston. This results in two types of stresses:

longitudinal and circumferential stress. Both the types of stresses are perpendicular to

each other and hence it is aimed to reduce the resulting stress as much as possible.

Length and bore of the cylinder: The length of the cylinder and the length of the stroke

is calculated on the basis of the formula: length of cylinder L = 1.15 times the length of

the stroke (l). L = 1.15(l)

Cylinder flange and studs: The cylinders are always cast integral as a part of the upper

crankcase or in some cases attached to it by means of nuts and bolts. The flange is

integral to a cylinder and henceforth its thickness should be greater than that of the

cylinder wall. The thickness of flange should generally be between 1.2t-1.4t where t is

the cylinder thickness.

The stud diameter is calculated by equating gas load ( due to max pressure ) to the

grand total of all the resisting forces of the studs.

48. What are considerations taken into account while creating a piston head?

The piston head is designed on the basis of the following considerations:

The crown should have enough strength to absorb the explosion pressure inside the

engine cylinder.

The head must always dissipate the heat of the explosion as quickly as possible to the

engine walls.




The temperature at the center and edges of the head.

The thickness of the piston head is calculated on the basis of the Grashoff`s formula

which takes into consideration the maximum gas pressure of an explosion , the

permissible bending and the outside diameter of the piston.

49. Which is the hardest material on earth?

Diamond is currently the hardest material, made up of carbon atoms which cannot

move. Carbon is the only atom that can have four electrons in the second shell

surrounding the carbon nucleus, precisely why making a diamond the hardest material.

However, there also are claims by a few to a new rare material called Wurtzite Boron

Nitride which has a structure similar to a diamond but has some other atoms in place of

carbon.

50. One unit of BTU is how many Joules?

1 BTU=1055.06 Joules

51. What does a pump develop? Give reason to support your answer.

Pump is a device that is used to transfer fluid from one place to another place which

means it develops flow not pressure.

52. Explain the difference between pipe and a tube.

A pipe is measured based on its inner diameter (ID) whereas a tube is measured based

on the outer diameter (OD). Other than the dimensions there is no major difference

between the two.

53. Explain the formula of heat loss in a pipe.

In order to find total heat loss through the pipes it is imperative to know the thermal

conductivity and the differing thicknesses of each layer. The ground that surrounds the

pipe also acts as a layer of insulation. Considering this, the thermal properties of the

stoneless sand is included in the heat loss calculation.

54. What kind of pipes are used for steam lines?

Pressure and temperature are two of the most important factors to be considered before

selecting the type of material to be used. Steam is a compressible gas due to which the

capacity of the pipe line depends on the size of the pipes and pressure of the steam.

Since steam at even low pressure can be dangerous, extra care is to be taken.

Galvanized pipes are usually not used for steam. Pipes made of mild steel with welded

fittings are instead largely used.

55. Who invented the four stroke engine? According to you which one is more

efficient, four stroke engine or a two stroke engine and why?




Nikolaus Otto invented the four stroke engine. Both, two stroke and four stroke have

their own advantages and disadvantages. 4 stroke is more fuel efficient. However, 2

stroke produces more power.

56. Explain what is torque

Torque is the force that causes rotation. It is a measure of how much force is acting on

an object making it rotate.

57. What is the difference between torque and power?

While power determines the speed of a vehicle, torque determines the time in which

that speed can be reached. The greater the torque figure, the faster the acceleration. The

more torque in the engine, the faster you accelerate. Power is the rate at which work is

done, so it is basically the potential of the engine.

58. Explain why diesel engine is known as high torque and petrol engine as high

speed engine?

Each power stroke in a petrol engine releases more heat and is converted into

mechanical energy due to a higher rate of burning. This is the reason petrol engine has

higher power and acceleration.

Diesel engine is a compression ignition engine with higher compression ratio, therefore

extreme pressure is high. Since the piston of a diesel engine is larger, more torque is

delivered in produced.

59. Why do heavy vehicles use diesel engine?

The compression ratio of diesel engine is higher than the petrol engine, the reason for

producing higher torque. The efficiency of diesel engine increases with load. Diesel

produces slow energy on burning of fuel and the efficiency of the engine increases with

load which is why diesel engine is suitable and largely used for heavy vehicles.

60. Between steel, copper and brass, which conduct faster heat.

Copper conducts heat faster than steel or brass. In most cases, material that is good for

conducting heat is also good for electricity.

61. What are the advantage and disadvantage of using LPG in a car?

Advantages:

The high octane rate enables it to blend better with air and to burn completely,

generating less carbon. With less carbon buildup, spark plugs often last longer and oil

changes are needed less frequently.

Since it burns in the gaseous phase, it results in less corrosion and engine wear.

In case of a spill, LPG evaporates quickly.

Disadvantages:

The LPG requires servicing at approximately once a year.




Since complete combustion occurs, more heat is liberated which is not advised for a

long journey as the engine will get over heated.

Installation of LPG is rather difficult.

62. Why gas containers are mostly in a cylindrical shape?

The ideal shape would be a sphere. The container must have the capacity to withstand

the extremely high pressure of liquefied gas. A spherical shape helps in distributing

these forces uniformly.

63. Why DTSI is used in motor bikes?

DTSI is used for a better fuel combustion in the cylinder head which helps provide

better efficiency and optimum use of fuel.

64. What are the advantages of DTSI over normal engines?

The cylinder head has two spark plugs, instead of the usual one. When two sparks are

generated at either ends of the combustion chamber, the air-fuel mixture is ignited in a

way that creates two flame fronts. A higher rate of combustion is achieved leading to

higher rise in pressure. The outcome of this is more torque, better fuel efficiency and

lower emissions.

65. What is the difference between scavenging and supercharging ?

Scavenging is process of flushing out burnt gases from engine cylinder by introducing

fresh air in the cylinder before exhaust stroke ends. Supercharging is the process of

supplying higher mass of air by compressing the atmospheric air.

66. What are the names given to constant temperature, constant pressure, constant

volume, constant enthalpy, and constant entropy processes.

Isothermal, isochroic, isobaric, throttling and adiabatic processes respectively.

67. Enthalpy and entropy are functions of one single parameter. Which is that ?

Temperature.

68. Which impurities form hard scale and which impurities soft scale ?

Sulphates and chlorides of lime and magnesium form hard scale, and carbonates of lime

and magnesium form soft scale.

69. What is the difference between hard water and soft water ?

Hard water contains excess of scale forming impurities and soft water contains very

little or no scale forming substances.

70. Why large boilers are water tube type ?

Water tube boilers raise steam fast because of large heat transfer area and positive water

circulation. Thus they respond faster to fluctuations in demand. Further single tube

failure does not lead to catastrophy.




71. Low water in boiler drum is unsafe because it may result in overheating of water

tubes in furnace. Why it is unsafe to have high water condition in boiler drum ?

High drum level does not allow steam separation to be effective and some water can be

carried over with steam which is not desirable for steam turbine.

72. What is the principle of mechanical refrigeration ?

A volatile liquid will boil under the proper conditions and in so doing will absorb heat

from surrounding objects.

73. In some engines glycerine is used in place of water for cooling of engine. Why ?

Glycerine has boiling point of 90C which increases its heat carrying capacity. Thus

weight of coolant gets reduced and smaller riadiator can be used.

74. What is the effect of friction on flow of steam through a nozzle ?

To decrease both mass flow rate and wetness of steam.

75. What is the purpose of biological shield in nuclear plants ?

Biological shield of heavy concrete prevents exposure to neutrons, beta rays and

gamma rays which kill living things.

76. What is heavy water and what is its use in nuclear plants ?

Water containing heavy isotopes of hydrogen (Deuterium) is known as heavy water.

Heavy water is used as a moderator. Heavy water slows down the fast neutrons and

thus moderates the chain reaction.

77. Explain nuclear reactor in brief.

A plant which initiates, sustains, controls and maintains nuclear fission chain reaction

and provides shielding against radioactive radiation is nuclear reactor.

78. Disposal of radioactive waste materials and spent fuel is a major and important

technology. How the waste radioactive material is disposed off ?

Non usable fission products are radioactive and take short/medium/long time for

radioactive decay to reach safe level of radioactivity. Accordingly three methods of

disposal are :

(a) Zero or low radioactivity material is dispersed or stored without elaborate shielding.

(b) Medium radioactivity material is stored for short duration of about 5 years to allow

decay of radioactivity.

(c)High radioactive material. They are stored in water for several months to permit

radioactive decay to an acceptable low level.

79. What is the difference between Fan and Blower?

Fan moves the air in low pressure at all directions. Blower directs the air in a single path

with high pressure.




80. What is Heat Rate of Power Plant?

Heat rate is a measure of the turbine efficiency. It is determined from the total energy

input supplied to the Turbine divided by the electrical energy output.

81. What is Difference between Hardness and Toughness?

Toughness is the ability of a material to absorb energy.

Hardness is the ability of a material to withstand wear.

82. What is the hottest part of Refrigerant in Refrigeration?

Compressor

83. What does pump develop:- (a) Flow (b) Pressure

A pump does not create pressure, it only creates flow. Pressure is a measurement of the

resistance to flow.

84. Difference between Performance and Efficiency?

The accomplishment of a given task measured against preset known standards of

accuracy, completeness, cost, and speed is called as Performance.

Efficiency is defined as the input given and the work obtained from that input like

money, time, labour etc. Its the main factor of productivity.

85. What is the difference between Specification, Codes, Standards?

Specification is describing properties of any type of materials.

Code is procedure of acceptance and rejection criteria.

Standard is accepted values and compare other with it.

86. Which is heavier 1kg Cotton or 1kg Iron?

Both of them have same weight.

87. What is the difference between Sudden Force and Impact Force?

An impact is a high force or shock applied over a short time period when two or more

bodies collide. A force which applies on the body (material) suddenly is known as

sudden force.

88. What is difference between Corrective actions and Preventive actions?

Corrective actions are taken on discrepancies noticed during inspection of

products/documents/process whereas preventive actions are taken to eliminate the

possibility of discrepancy in future.

89. Difference between 'Thermodynamics and Heat Transfer'

Heat transfer deals with non equilibrium heat exchange or transfer due to temperature

gradient while in thermodynamics, during thermal equilibrium (No temperature

gradient) no heat exchange is possible. Heat never transfer when there is no

temperature gradient.




90. Difference between Flywheel and Governor.

The function of flywheel is to store the energy/power produced during the power

stroke of an engine and this stored energy is used during remaining stroke to make

piston up and down during working of engine while governor tries control the speed of

an engine due to variation in load. It does this work by reducing or increasing the

amount of fuel passing to the engine.

91. Difference between tempering and annealing.

Annealing is a process in which workpiece is heated up to certain temperature to get

desired changes in grain or micro-structure and then allowed to cool slowly in order to

relieve the stresses during work treatment. While tempering is a process wherein

hardness and elasticity or ductility can be regain by use of heating and cooling cycle till

desired properties can be obtained.

92. What is added in LPG to detect leakage?

- Methyl Mercaptan

93. Pascal law ? Applications?

Pascal's law or the Principle of transmission of fluid-pressure states that "pressure

exerted anywhere in a confined incompressible fluid is transmitted equally in all

directions throughout the fluid such that the pressure ratio (initial difference) remains

the same.

Application- Hydraulic jacks, Car lifts, Fork Lifts

94. Can you transfer the heat energy from cold body to hot body?

- Yes, with external work. Eg : Air conditioner

95. What is hogging and sagging?

- Hogging and sagging describe the shape of a beam or similar long object when

loading is applied. Hogging describes a beam which curves upwards in the middle, and

sagging describes a beam which curves downwards.

96. What Bernoullis Principle?

In fluid dynamics, Bernoulli's principle states that for an inviscid flow, an increase in

the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in

the fluid's potential energy.

97. Difference between single acting and double acting pump?

In single-acting machines the compression takes place on only one side of the piston;

double-acting machines use both sides of the cylinder for compression. The flow is

continuous in double acting and in single acting the flow is not continuous unless there

is a surge vessel.




98. What is conduction, convection and radiation? Give Examples?

Conduction or diffusion

The transfer of energy between objects that are in physical contact

Convection

The transfer of energy between an object and its environment, due to circular fluid

motion.

Radiation

The transfer of energy to or from a body by means of the emission or absorption of

electromagnetic radiation

99. Classify Carbon Steels on basis of carbon content?

Low-carbon steels contain up to 0.30% C. The largest category of this class of steel is

flat-rolled products (sheet or strip), usually in the cold-rolled and annealed condition.

The carbon content for these high-formability steels is very low, less than 0.10% C, with

up to 0.4% Mn. Typical uses are in automobile body panels, tin plate, and wire

products.

For rolled steel structural plates and sections, the carbon content may be increased to

approximately 0.30%, with higher manganese content up to 1.5%. These materials may

be used for stampings, forgings, seamless tubes, and boiler plate.

Medium-carbon steels are similar to low-carbon steels except that the carbon ranges

from 0.30 to 0.60% and the manganese from 0.60 to 1.65%. Increasing the carbon content

to approximately 0.5% with an accompanying increase in manganese allows medium

carbon steels to be used in the quenched and tempered condition. The uses of medium

carbon-manganese steels include shafts, axles, gears, crankshafts, couplings and

forgings. Steels in the 0.40 to 0.60% C range are also used for rails, railway wheels and

rail axles.

High-carbon steels contain from 0.60 to 1.00% C with manganese contents ranging

from 0.30 to 0.90%. High-carbon steels are used for spring materials and high-strength

wires.

Ultrahigh-carbon steels are experimental alloys containing 1.25 to 2.0% C.

100. What are ISO-9000 standards?

ISO-9000 standards are made up of five parts namely ISO-9000, ISO-9001, ISO-9002,

ISO-9003 and ISO-9004. ISO-9000 and ISO-9004 are advisory documents. For instance,

ISO-9000 contains guidelines for using the standards. The standards are contained in

ISO-9001, 9002 and 9003.




101. Which ISO standard would be applicable if the product or the service involved

design and development?

It would involve ISO-9001 which is the model for quality assurance in design,

development, production, installation and servicing.

102. Can you tell us about ISO-9002 and 9003 also?

ISO-9002 is for quality assurance in production, installation and servicing and

ISO-9003 is for quality assurance in final inspection and test.

103. What are the common profiles used for splines in machine elements?

The profiles used for splines in machine elements are straight sided splines, triangular

splines and involute splines.

104. What type of threads are used for pressure tight joints and for power

transmission?

Pipe threads are used for pressure tight joints and square threads for power

transmission.

105. How computer helps in designing?

Computer is able to store lot of information and same can be retrieved fast. It performs

calculations very fast. The design can be visualized on screen and any alterations made

and its effects clearly seen. Thus optimum designs can be achieved much faster and

these are thoroughly tested from all angles.

106. Can you tell something about Hazop study?

In Hazop (Hazards and operatibility) study each and every conceivable process

deviation from normal operating condition of a system having identical design

intention, is thoroughly analysed for causes and consequence and required action plan

to mitigate hazard/operability problems are suggested on the basis of available

protective system.

107. Why slenderness ratio is considered in design of members?

When length of the member is increased, the member may fail due to buckling even

though the member is symmetrical in all respects and the load is concentric.

108. A wire rope is designated as 6 x 19 standard hoisting. What do the numbers 6 x 19

represent?

Number of strands x number of wires in each strand.

109. Why a sleeve is fitted on a ball bearing?

To prevent relative axial movement between the shaft and the bearing.

110. What is the main purpose of a gear box in a vehicle?

To vary the torque at the road vehicles.

111. What is endurance limit?




Endurance limit or fatigue limit is the maximum stress that a member can withstand for

an infinite number of load applications without failure when subjected to completely

reversed loading.

112. The designation M 33 x 2 of a bolt means

Metric threads of 33 mm outside diameter and 2 mm pitch.

113. Say the use of some couplings.

Oldhams coupling is used to connect two shafts which have lateral misalignment.

Universal coupling is used to join two shafts whose axes intersect at a small angle.

Bushed pin flexible coupling is used to join two shafts which are not in exact alignment.

Sleeve or muff coupling is the simplest type of rigid coupling.

114. What type of cam follower is generally used in automobiles?

Spherical type cam follower.

115. Say some types of cam.

S.H.M. cam is used in order to minimize jerks.

Harmonic cam is used for low and moderate speed engine.

Cycloidal cam is used for high speed engine.

116. How do you define a spring?

A spring is an elastic member which stores energy and provides a force over a distance

by elastic deflection.

117. How do you define a shaft?

A shaft is a rotating member, usually of circular cross-section (either solid or hollow),

transmitting power.

118. What is a flywheel?

A flywheel is a heavy rotating body which acts as reservoir for absorbing and

redistributing kinetic energy. The function of a flywheel is to keep the speed of machine

between given limits while the machine is doing work or receiving energy at a variable

rate.

119. What is a design?

Creating a plan or drawings for a product using intellectual ability and scientific

knowledge is called design. A product so designed should permit economical

manufacture, and it should meet the specification requirements.

120. What are the different types of design?

Adaptive design Adaptation of the existing design

Development design Improvement of the existing design

New design Design of an entirely new product

121. What is engineering design?




Iterative decision making process to conceive and implement optimum systems to solve

problems and needs of society.

122. What is machine design?

A process of achieving a plan for the construction of a machine.

123. What is modeling?

Representation of the real world on desk in symbolic form or in the laboratory.

124. What are preferred numbers?

A general basis for standardizing and grading a series of similar dimensions,

characteristics, etc.

125. What is resilience? What is proof resilience?

Strain energy stored per unit volume is resilience. The maximum strain energy which

can be stored in a material per unit volume is called as proof resilience.

126. What is creep?

The slow and progressive deformation of a material with time under a constant stress.

127. What is cam?

A plate or cylinder which communicates motion to a follower by means of its edge or a

groove cut in its surface.

128. What is coupling?

Coupling makes a semi permanent connection between two shafts.

129. What are clutches?

Couplings which permit the disengagement of the coupled shafts during rotation.

130. What is shot peening?

Shot peening is a cold working process used to produce a compressive residual stress

layer and modify the mechanical properties of metals. It entails impacting a surface

with shot (round metallic, glass, or ceramic particles) with a force sufficient to create

plastic deformation. Peening a surface spreads it plastically, causing changes in the

mechanical properties of the surface.

The main benefit of shot peening is the delay or prevention of cracks in highly tensile

stressed alloy components.

131. What is poissons ratio?

The ratio of the relative contraction strain (or transverse strain) normal to the applied

load - to the relative extension strain (or axial strain) in the direction of the applied load.

132. What is enthalpy and entropy?

Enthalpy describes the energy it takes for a substance to change from one phase to

another (i.e. solid to liquid.) Entropy deals with the actual disorder of particles and

substances (i.e. more disorder of the particles as a solid substance is heated to a liquid.)




In short, enthalpy looks at the energy needed whereas entropy looks at the organiztion

of the particles themselves.

133. What is the difference between helical and spiral?

A helix is a curve in 3-d space with an axis, where the tangent line makes a constant

angle with the axis. Spirals on the other hand do not need to have that property, and are

typically curves in a 2-d plane.

134. What is mechanical engineering?

Mechanical engineering is the discipline that applies the principles

of engineering, physics, and materials science for the design, analysis,manufacturing,

operation and maintenance of machines/machines tools.

135. What is the difference between heat and temperature?

Important Questions:

3, 4, 5, 7, 15, 16, 17, 19, 20, 22, 23, 24, 26, 28, 31, 33, 35, 36, 41, 42, 45, 46, 49, 50, 51, 52, 55,

58, 59, 61, 62, 64, 65, 66, 67, 68, 69, 72, 73, 75, 76, 78, 79, 81, 82, 84, 85, 86, 88, 89, 90, 91, 92,

93, 99, 108, 110, 111, 112, 113, 115, 116, 118, 119, 120, 125, 126, 127, 128, 129, 130, 131, 132,

133, 134, 135.

Documents

Interview Q&A in Mech Engg 2015