Interview Questions for ME Students

Thermodynamics

1) When a real gas behaves like ideal gas? Ans: A real gas behaves like an ideal gas in low pressure and high temperature conditions.

2). What is the significance of entropy? Ans: As per the second law of thermodynamics, any heat input to the system (Heat engine) cannot be converted completely into useful work. Some energy is lost and that is called 'unavailable work'. The amount of unavailable work increases as the entropy increases.

3). What is the difference between heat transfer and thermodynamics? Ans: Heat transfer deals with the energy analysis which in transition and depends on the modes of heat transfer like conduction, convection and radiation or combination of any modes. Heat transfer deals in non equilibrium domain and conditions while thermodynamics deals with study of system at equilibrium and does not depend on how heat transfer is calculated. Thermodynamics mainly deals with the transfer of energy in form of heat or work betweensystems and surroundings with other systems in form of either heat or work in equilibriumconditions. When there is change in one state, which was in equilibrium state and starting to change in other equilibrium state, this information helps to determine heat or work interactions due to this process. While 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.

4). At which temperature thermal radiation can become zero? Ans: Not possible. Because thermal radiation becomes only zero at absolute zero temperature which can never be attained by the third law of thermodynamics. 5) Difference between Pipe and tube

There always a debate between differentiation of pipe and tube . Pipe is always designated by its Inside Diameter (ID) because main purpose of pipe is to carry fluid, while the Tube is always designated by its Outside Diameter (OD). Pipe's thickness is sometimes called as schedule and tube's thickness is gauge. As per the tolerance basis, tubes requires higher tolerances as to that of pipe and tubes are more costlier in manufacturing compared to pipe production.

6) 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. 7) 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.

8) The by-pass factor for a cooling coil

Increases with increase in velocity of air passing through it 9) The formation of frost on cooling coils in a refrigerator

Increases power consumption

10) Defrosting of a refrigerator may be done by stopping the compressor for a short period. A:Correct

11) The relative humidity is defined as A: the ratio of actual mass of water vapour in a given volume of moist air to the mass of water vapour in the same volume of saturated air at the same temperature and pressure

12) The heat transfer by conduction through a thick sphere is same as through a thick cylinder. A:False

13) The freon group of refrigerants are A: halo-carbon refrigerants

14) What is the difference between scavenging and supercharging ? Ans: 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. 15) What are the names given to constant temperature, constant pressure, constant volume, constant internal energy, constant enthalpy, and constant entropy processes. Ans: Isothermal, isochroic, isobaric, free expression, throttling and adiabatic processes respectively.

16) In a Rankine cycle if maximum steam pressure is increased keeping steam temperature and

condenser pressure same, what will happen to dryness fraction of steam after expansion ? Ans: It will decrease.

17) Why entropy change for a reversible adiabatic process is zero ? Ans: Because there is no heat transfer in this process.

18) What are two essential conditions of perfect gas ? Ans: It satisfies equation of state and its specific heats are constant. 19) Enthalpy and entropy are functions of one single parameter. Which is that ? Ans: Temperature.

20) Why rate of condensation is higher on a polished surface compared to rusty surface ? Ans: Polished surface promotes drop wise condensation and does not wet the surface.

21) What is the difference between a 4stroke and 2stroke engine? Ans: A two-stroke, or two-cycle, engine is a type of internal combustion engine which completes a

power cycle with two strokes (up and down movements) of the piston during only one crankshaft revolution. This is in contrast to a "four-stroke engine", which requires four strokes of the piston to

complete a power cycle. In a two-stroke engine, the end of the combustion stroke and the

beginning of the compression stroke happen simultaneously, with the intake and exhaust (or scavenging) functions occurring at the same time.

Two-stroke engines often have a high power-to-weight ratio, usually in a narrow range of rotational

speeds called the "power band". Compared to four-stroke engines, two-stroke engines have a greatly reduced number of moving parts, and so can be more compact and significantly lighter.

22) How much resistance is offered to heat flow by drop wise condensation ? Ans: Nil

23) What is the relationship between COP of heating and cooling ?

Ans: COP of heating is one(unity) more than COP of cooling.

24) How much is the work done in isochoric process ? Ans: Zero.

25) When maximum discharge is obtained in nozzle ?

Ans: At the critical pressure ratio.

26) Under what condition the work done in reciprocating compressor will be least ?

Ans: It is least when compression process approaches isothermal. For this purpose, attempts are made to cool the air during compression.

27) What is the difference between stalling and surging in rotary compressions ? Ans: Stalling is a local phenomenon and it occurs when How breaks away from the blades. Surging causes complete breakdown of flow and as such it affects the whole machine.

28) Why the electric motor of a fan with backward curved blades is never got overloaded under

any condition ? Ans: The maximum power is consumed at about 70% of maximum flow in case'of fan with backward blades. For higher flow, power consumption gets lower.

29) Why the work per kg of air flow in axial flow compressor is less compared to centrifugal

compressor for same pressure ratio ? Ans: Isentropic efficiency of axial flow compressor is higher.

30) What is the name given to portion of thermal energy to be necessarily rejected to environment ? Ans: Anergy.

31) What is pitting ? How it is caused ? Ans: Non uniform corrosion over the entire metal surface, but occuring only in small pits is called pitting. It is caused by lack of uniformity in metal.

32) What is caustic embrittlement ? Ans: It is the actual physical change in metal that makes it extremely brittle and filled with minute cracks. It occurs particularly in the seams of rivetted joints and around the rivet holes.

33) Which impurities form hard scale and which impurities soft scale ?

Ans: Sulphates and chlorides of lime and magnesium form hard scale, and carbonates of lime and magnesium form soft scale.

34) What is the difference between hard water and soft water ? Ans: Hard water contains excess of scale forming impurities and soft water contains very little or no scale forming substances.

35) Which two elements in feed water can cause corrosion of tubes and plates in boiler ? ' Ans: Acid and oxygen in feed water lead to corrosion.

36) What should be done to prevent a safety valve to stick to its seat ? Ans: Safety valve should be blown off periodically so that no corrosion can take place on valve and valve seat.

37) Why large boilers are water tube type ?

Ans: 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.

38) What type of boiler does not need a steam drum ?

Ans: Super-critical pressure boiler.

39) Why manholes in vessels are usually elliptical in shape ?

Ans: Elliptical shape has minimum area of opening and thus plate is weakened the least. Further it is very convenient to insert and take out the cover plate from elliptical opening.

40) 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 ? Ans: 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.

41) Why boiler is purged everytime before starting firing of fuel ? Ans: Purging ensures that any unburnt fuel in furnace is removed, otherwise it may lead to explosion.

42) What is the principle of mechanical refrigeration ? Axis. A volatile liquid will boil under the proper conditions and in so doing will absorb heat from surrounding objects.

43) Why high latent heat of vaporisation is desirable in a refrigerant ? Ans: A high latent heat of vaporisation of refrigerant results in small amount of refrigerant and thus lesser circulation system of refrigerant for same tonnage.

44). Which are the reference fuels for knock rating of S.I. engines ?

Ans: n-heptane and ISO-octane.

45) When effect of variations in specific heats is considered then how do maximum temperature

and pressure vary compared to air standard cycle ?

Ans: Temperature increases and pressure decreases.

46) Quantities like pressure, temperature, density, viscosity, etc. are independent of mass. What

are these called ?

Ans: Intensive properties.

47) What is the difference between petrol & diesel engines?

There are differences between the two engines due to the difference between the way fuels burn.

Petrol is a volatile fuel, is readily evaporates, so it gets mixed with the air efficiently. As a result, just a spark is sufficient to produce smooth combustion in a well pre-mixed petrol engine. petrol has a very low flash point. Flash point is the minimum temperature required for a liquid fuel to

form a spontaneously combustible mixture. On the other hand, diesel being a less volatile fuel does not properly mix with air. You can note that diesel has such a high flash point value. However, if atomized diesel is sprayed into high-temperature air, spontaneous combustion will occur. This means that in petrol engines, the fuel and air should be pre-mixed, while in diesel

engines, mixing happens only during the combustion. Due to this reason diesel engines use a fuel injector while petrol engines use a spark plug.

48) what is gasoline direct injection?

Ingasoline direct injection (GDI), the combustion does not happen during the fuel injection

process. Even for a direct injection engine a spark plug is needed. The direct injection technology is just an another way of producing a fine petrol-air mixture. Instead using a carburetor to mix air and fuel these technologies use a fuel injector. The biggest advantage of direct injection method is that the fuel to be sprayed can be controlled very accurately. This will result in great fuel

savings.

49) Why Diesel Engines are Heavier ?

petrol engines are less noisy and vibrate less compared to diesel engines. This is because the

combustion process in a pre-mixed mixture is smooth and propagates well.But in a diesel engine,

the combustion could begin anywhere in the combustion chamber, and it turns out to be an

uncontrolled process. For this reason, to reduce the excessive vibration and noise problem, diesel

engines require a more rugged structural design than petrol engines. To normalize the heavy

unbalanced power production of diesel engines a heavy fly wheel is often required. This is why

petrol engines are always preferred for light-weight applications, such as in 2-wheeler or portable

devices.

50) what will happen if petrol is put in diesel engine or vice versa?

Diesel in Petrol Engine

Diesel in a petrol engine will not even cause firing. The reason is simple. Diesel is less volatile and

will not mix with the air properly. In fact you will find it is impossible to make a good diesel-air

mixture using carburetor or direct injection technology. This means if you apply spark to such a

poor quality mixture, it will not initiate any combustion.

Petrol in Diesel Engine

On the other hand, if you put petrol in a diesel engine, you are spraying a highly volatile fuel into

a chamber of highly compressed and hot air. This will lead to detonations rather than smooth

combustion. Eventually, the engine components will get damaged. Moreover diesel generally acts

a good lubricant for the fuel pump and the injection system. When you put petrol (which does not

have any lubrication property) into a diesel car your are actually making the intricate components

to wear down over the time. So that’s a big no for petrol in a diesel engine. The reason why your

diesel car gives more mileage than a petrol car is due to the difference in the compression ratio.

The higher the compression ratio, the better is the efficiency of the cycle. This is the reason why

diesel engines have better fuel economy as compared to petrol engines.

51) why diesel engines are more fuel economical?

Since the diesel engine is compressing only the air, it can achieve a good compression ratio

without risk of self-ignition. But, in a pre-mixed petrol engine, such a high compression ratio is

not possible. As we increase compression ratio of petrol engine the mixture becomes more prone

to self ignition. This is known as knocking. Over the period of operation knocking badly damages

the engine.

Production Engg.

1) Define the following metal properties (a) Machinability (b)Malleability Machinability is the property of metal due to which a metal can easily be cut by cutting tools

to obtain good surface finish. E.g.: Brass, Mild steel. Malleability is the property of the metal on account of which it can be extended in all directions by hammering or rolling. E.g.: Tin, Lead

2) Define Hardness of the metal ?

It is the property of the metal which makes a metal capable to resist surface penetration by other metals .Hard metals are High carbon steel and High speed steel.

3) What is the Toughness of metal ? Toughness is the property of metal due to which without fracture a metal is able to withstand

bending or torsion. Mild steel and wrought iron are tough metals. 4) Define the following properties of metal : (a) Fusibility (b) Stiffness (c) Ductility

Fusibility. It is the property of metal due to which a metal becomes fluid when it is heated.

Stiffness. It is the property of metal due to which a metal is capable of resisting deflection due to an externally applied load.

Ductility. It is the property of metal due to which a metal can be drawn into the form of wires without rupture.

5) Why are cast iron seasoned before machining ? For easy machining and saving the cutting edge of the tool.

6) How does carbon affects the properties of steel ?

If carbon content is higher the degree of hardness is more and the melting point is lower, If carbon percentage is lower it is easy to forging and forge welding.

7) Why are machine beds made of cast iron ?

Because it has more compressive strength and negligible shrinkage. It can easily cast into

any integral shape, wear resisting and can absorb vibrations. 8) What is the difference between Wrought iron, Cast iron and Pig iron ?

Wrought iron contains less than 0.1% carbon and this is a product of puddling furnace. Cast iron is produced from cupola furnace. It contains 33.5% carbon in combined or free state. Pig iron is

an iron carbon alloy contains 35% carbon along with impurities like manganese, sulphur and phosphorous. It is a product of blast furnace. 9) How is steel classified ?

Low carbon steel : Less than 0.25% carbon Medium carbon steel: 0.25%0.7% carbon

High carbon steel: 0.7%1.5% carbon 10) What do you mean by Stainless Steel ?

It is an alloy steel which contains mainly 8% Nickel and 18% Chromium. Stainless steel main applications in measuring and surgical instruments

11) What are the differences between Brass and Bronze ?

Brass is an alloy of copper and zinc. Generally brass contains 60% copper and 40% zinc. These

are used for making bearings, pump fittings, bushes and utensils. Bronze contains copper and tin. It is comparatively hard, surface wear is less, can be remolded

into any shape like wires, sheets, rods etc. 12) How will you identify cast iron, mild steel and high carbon steel ?

By spark: When a metal is held against grinding wheel it gives sparks. Cast iron gives thick and short sparks. Mild steel gives medium and dense sparks and High carbon steel gives long and

dense sparks. By hammering : When a blow of hammer is given with these metals there will be a deep spot on mild steel, less deep spot on high carbon steel and cast iron may break.

13) What is Heat treatment ? Heat treatment is an operation involving heating and cooling of metals to change its properties.

14) What do you mean by Brazing ?

Brazing is the process through which metal pieces are jointed by means of alloy of copper and

zinc called spelter. The metal pieces to be joined should be heated instead of using a soldering iron bit. For this muffle as well as Smith’s furnaces are used. it provide much stronger joint as

compared to soft soldering 15) Why cast iron cannot be forged ?

Because it will break if heated and beaten by hammer.

16) What are the advantages of forging ?

Metal can be forged to any shape.

Metal can be forged in short time without wasting. The strength of steel as well as granular structure can be improved. The manufacturing cost is lesser than machining.

17) Which type of grains formed after hardening the steel ?

Hardened steel have contains fine grains. 18) What is Soldering ?

It is a process of joining two or more metal pieces by using solder.

19) What is the material of gears ? The material of gears should be selected according to the capacity and nature of work. Gears are generally made of cast iron, bronze, tool steel, chromium steel , alloy steel etc.

20) Why new files should not be used on castings and forgings ?

Because they have hard outer surface, when new files are used on these over sides the teeth either break or get blunt easily.

21) For machining cast iron which rake angle is given on shaper tool ? Negative rake angle

22) What is the material of shaper tool ? Generally used HSS(High Speed Steel),sometimes satellite, carbide tipped tools may also be

used.

23) What is runner? Connecting member between gate and sprue bush.

24) What is gate? Connecting member between impression and runner.

25) What do you meant flash ? If the parting surfaces are not properly matched, the molding material from the impression will

escape through the gap. This escaped melt is called the flash.

26) Why do we provide vent in mold? Vents are provided in the mold to allow such air to escape freely. The vent is a shallow slot not more than 0.05 mm deep and 3mm wide. If the depth is more, the plastic material can pass

through the slot and leave a flash mark.

27)What are the types of die casting defects ?

Cold defects Hot defects

Miscellaneous defects

28) What do you mean Blanking ? In this operation, cut out material or slug will be the component.

29) What is piercing?

Process of making opening on sheet metal is called piercing. The cut out material will be waste. 30) What is called cutting off ?

Material is going to cut in a single line, there won’t be any waste.

31) What is trimming ? Removing large amount of material from the edge of the piece part.

32)What do you understand shaving ? Removing small amount of material from the previously blanked part.

33)What is broaching ? Series of teeth profile removes metal from blanked part.

34) Describe bending?

Bending can be explained as shaping of material around straight line axis. Result is a new plane which is at an angle to the mother plane.

35) What is lancing ? Combination of cutting and bending.

36) What is forming ? Press tool non cutting operations in which material is formed into different shapes.

37) What do you mean drawing ?

Process of making cup or vessel is called drawing. 39) What is swaging?

Opposite of bilge. External forming operation also called as necking.

40) What is extrusion ? Operation to produce collapsible tubes, shell etc.

SOM & Machine Design

1)Define Ductility.

Answer:

It is the property of the material enabling it to be drawn into wire, with the application of tensile

force. It must be both strong and plastic. It is usually measured in terms of percentage

elongation and reduction in area, (e.g.) Ni, Al, and Cu.

2)Define fatigue.

Answer:

When a material is subjected to repeated stress, it fails at stresses below the yield point stress;

such type of failure of the material is called fatigue.

3)Define: Factor of safety.

Answer:

The ratio between maximum stresses to working stress is known as factor of safety.

Factor of safety = Maximum stress /Working stress

4)Define endurance limit. Answer:

Endurance limit is the maximum value of completely reversed stress that the standard specimen can sustain an infinite number (106) of cycles without failure. 5) What is impact load? Answer: If the time of load application is less than one third of the lowest natural period of vibration of the part, it is called an impact load. 6)What are the various phases of design process? Answer: The various phases of design process are:

1. Recognition of need. 2. Definition of problem 3. Synthesis 4. Analysis and optimization 5. Evaluation 6. Presentation

7) What are the different types of loads that can act on machine components? Answer: Different loads on machine components are:

1. Steady load. 2. Variable load. 3. Shock load 4. Impact load.

8) What are the factors affecting endurance strength. Answer: Factors affecting endurance strength are

1. Load ii. Surface finish 2. Size 3. Temperature 4. Impact 5. Reliability

9) What are the types of variable stresses? Answer: Types of variable stresses are:

1. Completely reversed or cyclic stresses 2. Fluctuating stresses 3. Repeated stresses

10) Differentiate between repeated stress and reversed stress. Answer: Repeated stress refers to a stress varying from zero to a maximum value of same nature. Reversed stress of cyclic stress varies from one value of tension to the same value of compression. 11) What are the types of fracture? Answer: The two types of fracture are

1. Ductile fracture 2. Brittle fracture

12)Distinguish between brittle fracture and ductile fracture. Answer: In brittle fracture, crack growth is up to a small depth of the material. In ductile fracture large amount of plastic deformation is present to a higher depth. 13) Define stress concentration and stress concentration factor. Answer:

Stress concentration is the increase in local stresses at points of rapid change in cross section or discontinuities. Stress concentration factor is the ratio of maximum stress at critical section to the nominal stress 14) Explain size factor in endurance strength. Answer: Size factor is used to consider the effect of the size on endurance strength. A large size object will have more defects compared to a small one. So, endurance strength is reduced. If K is the size factor, then Actual endurance strength = Theoretical endurance limit x K

15) Explain Griffith theory. (Or) State the condition for crack growth. Answer: A crack can propagate if the energy release rate of crack is greater than crack resistance. 16) What are the modes of fracture? Answer: The different the modes of fractures are:

1. Mode I (Opening mode) – Displacement is normal to crack surface. 2. Mode II (Sliding mode) – Displacement is in the plane of the plate. 3. Mode III (Tearing mode) – Out of plane shear.

17) What are the factors to be considered in the selection of materials for a machine element? Answer: While selecting a material for a machine element, the following factors are to be considered

1. Required material properties 2. Manufacturing ease 3. Material availability 4. Cost

18) What are various theories of failure? Answer: The failure theories are:

1. Maximum principal stress theory. 2. Maximum shear stress theory. 3. Maximum principal strain theory.

19) List out the factors involved in arriving at factor of safety. Answer: The factors involved in arriving at factor of safety are:

1. Material properties 2. Nature of loads 3. Presence of localized stresses 4. Mode of failures

20) Give some methods of reducing stress concentration. Answer: Some of the methods are:

1. Avoiding sharp corners. 2. Providing fillets. 3. Use of multiple holes instead of single hole 4. Undercutting the shoulder parts.

21) Explain notch sensitivity. State the relation between stress concentration factor and

notch sensitivity. Answer: Notch sensitivity (q) is the degree to which the theoretical effect of stress concentration is actually reached. The relation is, Kf = 1 + q (Kt-1)

22) What are the factors that affect notch sensitivity? Answer: The factors effecting notch sensitivity are:

1. Material 2. Notch radius 3. Size of component 4. Type of loading 5. Grain Structure

23) What is the use of Goodman & Soderberg diagrams? Answer: They are used to solve the problems of variable stresses. 24) Define machinability Answer: It is the property of the material, which refers to a relative ease with which a material can be cut. It is measured in a number of ways such as comparing the tool life for cutting different material 25) What is an S-N Curve? Answer: An S- N curve has fatigue stress on ‘Y ’ axis and number of loading cycles in ‘X’ axis. It is used to find the fatigue stress value corresponding to a given number of cycles. 26) What is curved beam? Answer: In curved beam the neutral axis does not coincide with the centroidal axis. 27) Give some example for curved beam. Answer: C frame, crane hook 28) What is principle stress and principle plane? Answer: A plane which has no shear stress is called principle plane the corresponding stress is called principle stress. 29) Write the bending equation. Answer: The bending moment equation is, M/I = f/y= E/R, Where, M – Bending moment (M is in N-mm) I - Moment of inertia about centroidal axis (I is in mm⁴) f – Bending Stress (f is in N/mm²) y - Distance from neutral axis (y is in mm) E - Young’s modulus (E is in N/mm²) R - Radius of curvature (R is in mm) 30) Write the torsion equation. Answer: The torsional equation is, T/J = q/r = GӨ/L Where, T – Torsional moment (T is in N-mm) J - Polar moment of inertia (J is in mm⁴) q – Shear stress in the element (q is in N/mm²) r - Distance of element from centre of shaft (r is in mm) G- Modulus of Rigidity (G is in N/mm²) Ө – Angle of twist (Ө is in radians)

L – Length of the shaft (L is in mm)

What are the different methods of dimensioning?

Ans6:-There are two methods of dimensioning.

1) Aligned Method: – In aligned system, the dimensions are placed parallel to the dimension lines, preferably

in the middle and not by interrupting the dimension lines. All the dimensions are placed as per orientation of

all other lines in the drawing.

2) Unidirectional Method: – In this system dimensions shall be horizontally in respective of the orientation of

the line in the drawing.

What are various types of scales used in drawing?

There are three types of scales used in drawings.

1) Full size scale:-The scale in which the actual measurements of the object are drawn to same size on the

drawing is known as full size scale. For example 1:1

2) Reducing scale: – The scale in which the actual measurements of the object are reduced to some proportion

is known as reducing scale. For example 1:4

3) Enlarging scale: – The scale in which the actual measurements of the object are increased to some

proportion is known as enlarging scale. For example 2:1

What is the principle of projection?

Ans:-Straight lines are drawn from various points on the contours of an object to meet at points on the plane

of projection. There points when joined form a shadow of the object on that plane. This shadow is called the

projection of the object on that plane. The object is said to be projected on that plane.

Q 5 What are the different methods of projections?

Ans: There are two methods of projections namely orthographic and isometric projections.

Q 6 What is meant by orthographic projections?

Ans: The projections on planes perpendicular to each other are called orthographic projections. Front view,

top view and side view of an object are called Orthographic projections.

Differentiate first and third angle projection. Ans i.) Object is placed in first and third quadrant in first and third angle projection respectively. ii.)Object is in between POP and observer in first

angle projection, whereas in third angle projection POP is in between object and observer. iii.)In first angle projection, Plan (Top View) is below the Elevation (Front View).Right side view is on

the left of elevation and Left side view is on the right of the elevation. iv) In third angle projection , Plan (Top View) is above the Elevation (Front View).Right side view is on the right of front view (elevation) and Left side view is on the left of the elevation