Let's Prepare for Technical Interview (Part-6)

Mechanical engineering interview questions:

Que: What is bending moment?
Ans: When a moment is applied to bend an element, a bending moment exists in the element.

Que: What are the points in the Stress Strain curve for Steel?
Ans: Proportional limit, elastic limit or yield point, ultimate stress and stress at failure.

Que: Define Reynolds number?
Ans: Reynolds number is the ratio of inertial force and viscous force. It is a dimensionless number. It determines the type of fluid flow.

Que: What is a Newtonian fluid?
Ans: A Newtonian fluid possesses a linear stress strain relationship curve and it passes through the origin. The fluid properties of a Newtonian fluid do not change when any force acts upon it.

Que: How many Joules is 1 BTU?
Ans: 1 BTU is equal to 1055.056 joules.

Que: What is PS?
Ans: PS is Pferdestarke, the German unit for Horsepower.

Que: Explain Otto cycle?
Ans: Otto cycle can be explained by a pressure volume relationship diagram. It shows the functioning cycle of a four stroke engine. The cycle starts with an intake stroke, closing the intake and moving to the compression stroke, starting of combustion, power stroke, heat exchange stroke where heat is rejected and the exhaust stroke. It was designed by Nicolas Otto, a German engineer.

Que: Explain the nomenclature of a 6203-ZZ bearing?
Ans: 6 is the type code, which shows it is a single-row ball bearing, 2 is the series, means light, 03 is the bore, which is 17 mm and ZZ is the suffix meaning double shielded bearing.

Que: What is Gear ratio?
Ans: It is the ratio of the number of revolutions of the pinion gear to one revolution of the idler gear.

Que: What is Annealing?
Ans: It is a process of heating a material above the re-crystallization temperature and cooling after a specific time interval. This increases the hardness and strength if the material.

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Let's Prepare for technical interview (Part-4)

Mechanical engineering interview questions:

Que:What is the importance of thermodynamics in the field of mechanical engineering ?
Ans:All the mechanical engineering systems are studied with the help of thermodynamics. Hence it is very important for the mechanical engineers.

Que: How many laws of thermodynamics are there?
Ans: 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.

Second Law: When two isolated systems in separate but nearby regions of space, each in thermodynamic equilibrium in itself, but notin 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.

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

Que: State law of conservation of energy ?
Ans: 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.”

Que: Is boiler a closed system ?
Ans: yes, boiler is definitely a closed system.

Que: What is carnot engine?
Ans: 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.

Que:which formula forms a link between thermodynamics and electro-magnetism?
Ans: Gibbs Helmholtz formula is the formula which forms the link between the thermodynamics and electromagnetism.
ΔHs/R = [∂ lnp /∂ (1/T)]x

Que:Which is the hardest compound known?
Ans: diamond.

Que:What is hess law?
Ans:According to the Hess law the energy transfer is simply independent of the path being followed. If the reactant and the product of the whole process are the same then same amount of energy will be dissipated or absorbed.

Que: Which engine is more efficient diesel engine or petrol engine?
Ans: Diesel engine

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Let's Prepare for technical interview (part-3)

Mechanical engineering interview questions:
Que: What is the difference between generator and invertor ?
Ans: An inverter is only effective if there is already a source of electrical energy. It cannot generate
its own. It can simply convert electrical energy that is already there. On the other hand, a traditional generator cannot make AC current into DC current.

Que: What is the difference between qualitative and quantitative research ?
Ans: Quantitative research involves gathering data that is absolute, such as numerical data, so that it can be examined in as unbiased a manner as possible.
Qualitative research may yield stories, or pictures, or descriptions of feelings and emotions. The interpretations given by research subjects are given weight in qualitative research, so there is no seeking to limit their bias. At the same time, researchers tend to become more emotionally attached to qualitative research, and so their own bias may also play heavily into the results.

Que: Difference between adsorption and absorption ?
Ans: In absorption, one substance (matter or energy) is taken into another substance. But in adsorption only the surface level interactions are taking place.

Que: Difference between liquid and aqueous ?
Ans:

• Liquid is a state of matter, while aqueous is a special type of liquid formed by dissolving a compound in water.
• All aqueous solutions are liquids, but not all liquids are aqueous solutions.

Que: Difference between gas and vapor ?
Ans:

• Vapour can turn back and forth into liquid and solid states but a gas cannot.
• Gases cannot be see while vapours are visible.
• Vapours settle down on ground while gases do not.

Que: Difference between boiling and melting point ?
Ans:

• The melting point is a defined for solids when it transfers from solid state to liquid state.
• The boiling point is defined for liquids for a state change from liquid to gas.
• Boiling point is highly dependent on the external pressure whereas the melting point is independent of the external pressure.

Que: why sound is faster in warm air ?
Ans: The speed of sound in air cair = 331.3 + (0.66 x T) m/s, where T is the temperature in °C.
         The speed of sound is proportional to gas temperature and inversely proportional to its
molar mass.
 Sound is transferred by collisions of molecules. Therefore sound waves will travel faster on warm air because collisions of molecules of air in warm air is greater.

Que: How Cavitation can be eliminated in a pump ?
Ans: Cavitation means bubbles are forming in the liquid.

• To avoid Cavitation, we have to increase the Pump size to One or Two Inch;
• To increase the pressure of the Suction Head, or
• Decrease the Pump Speed.

Que: Which pump is more efficient centrifugal pump or reciprocating pump?
Ans: 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.

Que: Why centrifugal pump not called positive displacement type of pump ?
Ans: The centrifugal has varying flow depending on pressure or head, whereas the Positive Displacement pump has more or less constant flow regardless of pressure.

         Likewise viscosity is constant for positive displacement pump where centrifugal pump have up and down value because the higher viscosity liquids fill the clearances of the pump causing a higher volumetric efficiency. When there is a viscosity change in supply there is also greater loss in the system. This means change in pump flow affected by the pressure change.

        One more example is, positive displacement pump has more or less constant efficiency, where centrifugal pump has varying efficiency rate.

Que: Why centrifugal pump is called high discharge pump ?
Ans: 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

Que: why cavitation will occur in centrifugal pump and not in displacement pump ?
Ans: The formation of cavities (or bubbles) is induced by flow separation, or non-uniform flow velocities, inside a pump casing. In centrifugal pumps the eye of the pump impeller is smaller
than the flow area of pipe. This decrease in flow area of pump results in increase in flow rate. So pressure drop happened between pump suction and the vanes of the impeller. Here air bubbles or cavities are formed because of liquid vapour due to increase in temperature in impeller. This air bubbles are transmitted to pump which forms cavitation.

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Let's prepare for technical interview (part-2)

Mechanical engineering interview questions:
Que: what is the other name of micrometer and vernier caliper?
Ans: micrometer's other name is screw gauge & vernier caliper's other name is slide caliper.

Que: what is flash-point?
Ans: flash-point is the lowest temperature at which the vapor of combustible liquid can be ignited in air.

Que: what is the difference between impulse turbine and reaction turbine?
Ans: » In impulse turbine, jet is used to create impulse on blades which rotates the turbine and in reaction turbine, no jet is used pressure energy is converted into kinetic energy.
» In impulse turbine fluid enter & leaves with same energy, but in reaction turbine fluid enter with pressure energy and leaves with kinetic energy.

Que: What is the difference between BSP thread and BSW thread?
Ans: The British Standard Pipe thread (BSP thread) is a family of standard screw thread types that has been
adopted internationally for interconnecting and sealing pipe ends by mating an external (male) with an internal
(female) thread. British Standard Whit-worth (BSW) is one of a number of imperial unit based screw thread standards which use the same bolt heads and nut hexagonal sizes.

Que: What is refrigerant?
Ans: Any substance that transfers heat from one place to another, creating a cooling effect. water is the refrigerant in absorption machines.

Que: The amount of carbon present in cast Iron?
Ans: Carbon is basically present in the form of cementite in cast iron.Its percentage lies in the range of 2.03-6.67(% by weight of cementite for Cast Iron.If the amount is less than the above range than it is stainless steel.

Que: What loads are considered while designing nuts and bolts ?
Ans: Shear loads and crushing loads.

Que: What is the effect of reheat on rankine cycle?
Ans: Its efficiency increases.

Que: Why are the head gaskets blown ?
Ans: Normally head gasket blows, when the engine overheats and they can also blow from incorrect installation or poor design. Head gaskets expand and contract according to engine temperature, these cycles may happen after a long period of time, causes the gasket to fail. If you’re replacing the gasket, check the engine block, and head for warping. Follow proper cleaning and torque specifications during assembly.

Que: What is the difference between humidifier and vaporizer ?
Ans: The basic difference between humidifiers and vaporizers is that humidifiers disperse cool mist
 into the air, and vaporizers heat the water to disperse hot steam. Humidifiers are normally used in cooler climates, when due to the usage of heater, the air in the house becomes too dry for comfort and also, it becomes very difficult to breathe. Humidifiers release cool moisture droplets into the air.
    Vaporizers also help in moistening the dry air in the house, but vaporizers release hot vapor into the air. There is a heating element in the vaporizers, which help in releasing steam. Vaporizers heat the water and then release vapors.
    The basic difference between them is that one emits cold vapors, while the other one emits hot vapors.

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Let's prepare for technical interview( part-1)

Mechanical engineering interview questions:
Q. What if the gasoline is used in diesel engine? Diesel engine will work?
Ans. No, it will not work, as the compression ratio of petrol engine is 6 to 10 & that of diesel engine is 15 to 22. Thus on such high compression, gasoline gets highly compressed and it may blast.
Q. Which mechanism is used in automobile gearing system?
Ans. Differntial mechanism.
Q. Why different types of sound are produced in different bikes though they all ran on SI engine?
Ans. Engine specifications are different in different manufacturer like bore diameter(cc), ignition timing. Also the exhaust passage take more responsible for sound.
Q. 1HP= how much watt ?
Ans. 746.2 watt.
Q. How to calculate bearing number to diameter of inner and outer?
Ans. Divide shaft diameter size by 5, it will give last two digits of the bearing number and according to type of load we have to choose the type of bearing and that will give prior no. Of the bearing .
Q. Define octane and cetane number?
Ans. Octane number: 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 number: cetane number is defines as the percentage, by volume, of n-cetane in the mixture of n-cetane and alpha methyl naphthaline. It is measure of rating of CI engine.
Q. Poissons ratio is higher in rubber/steel/wood ?
Ans. When 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 poissons effect. Poisson's ratio is measure of the poisson effect.
For rubber= 0.5
For steel = 0.288
For wood < 0.2
Thus poisson's ratio is higher in rubber.
Q. The fatigue life of the part can be improved by?
Ans. Improving the surface finish by polishing and providing residual stress by shot peening.
Q. When crude oil is heated which hydro-carbon comes first.?
Ans. Natural gas ( gasoline) i.e. at 20 degree celsius.
Q. Difference between technology and engineering?
Ans. Engineering is application of science. Technology shows various methods of engineering. A bridge can be made 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 law of force/load distribution.

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