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Mahagenco Mechanical Engg questions with answers for practice, Mahagenco technical questions and answers

1. What is the importance of the Thermodynamics in the field of Mechanical Engineering?All the mechanical engineering systems are studied with the help of thermodynamics. Hence it is very important for the mechanical engineers.

2. 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.

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, entropyhas increased, or at least has not decreased.

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

3. 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.

4. Is the boiler a closed system?Yes definitely the boiler is a closed system.

5. 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.

6. Which formula forms a link between the Thermodynamics and Electro chemistry?

Gibbs Helmholtz formula is the formula which forms the link between the thermodynamics and electromagnetism.?Hs/R = [? lnp /? (1/T)]xwhere: x mole fraction of CO2 in the liquid phasep CO2 partial pressure (kPa)T temperature (K)R universal gas constanta mole ratio in the liquid phase (mole CO2 per mole of amine)

7. Which is the hardest compound known?Diamond.

8. What is Hess Law?

According to the Hess law the energy transfer is simply independent of the pathbeing followed. If the reactant and the product of the whole process are the same then same amount of energy will be dissipated or absorbed.

9. Which has more efficiency: Diesel engine or Petrol engines?Off course Diesel engine has the better efficiency out of two.

10. A Bearing is designated as 6205 , what is its bore diameter?Bore diameter is equal to : last two digit multiplied by 5.In case of 6205 , the bore diameter =05 x 5 = 5 x 5 =25 mm


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1.The third and fourth digits indicate the bore size in millimeters. Except for0 through 3, the bore size is simply five times the third and fourth digits together. 0 through 3, however, are different:00 10mm01 12mm02 15mm03 17mm2.Bearing number starts from a number means it is a metric series bearing.3.Type 6, single-row deep groove, is perhaps the most common type of bearing.4.The second digit is the series reflects the robustness of the bearing.In 6205 .>second digit is 2 and it is a light series.

11. Advantages and Disadvantages of using LPG in car?

Advantages

1. Complete combustion

2. Fuel saving

3. Homogenous combustion

Disadvantages

1. As complete combustion is occurring ,more heat liberated,not advised for longjourney, engine will be over heated

2. Installation is difficult

3. Reduce engine life efficiency

12. All Reactor or Exchanger have Spherical/Hemispherical end Why?

Its in order to reduce the internal stress of the working substance.

For eg., If Water Vapour Dry is the working substance in the reactor or boiler a

nd if the ends are square, at the corners there are possibilities of pressure shoot up and also possibility of more pressure concentration at those points. in order to avoid that, Spherical/Hemispherical Vessels are used. Spherical head isthe only remaining option because it is stronger.

One more place where Spherical vessels are used for storage is LPG Storage Containers

13. Compare Brayton 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.

14. Current rating of a 3 phase DG set is 20 Amps, but what will be the per phase current for single phase supply.

Amps means product of voltage and current. For 3 phase generator, its Amps = (1.732 X (Line Voltage) X Current)/1000.

substitute the value and you get the answer.


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15. Define Overall Heat transfer coefficient.

The overall heat transfer coefficient U is a measure of the overall ability of aseries of conductive and convective barriers to transfer heat. It is commonly applied to the calculation of heat transfer in heat exchangers, but can be applied equally well to other problems.

1 / U A = 1 / h1 A1 + dxw / k A + 1 / h2 A2 (1)

where

U = the overall heat transfer coefficient (W/m2K)

A = the contact area for each fluid side (m2)

k = the thermal conductivity of the material (W/mK)

h = the individual convection heat transfer coefficient for each fluid (W/m2K)

dxw = the wall thickness (m)

The thermal conductivity k - for some typical materials: .

Polypropylene PP 0.12 W/mKStainless steel 21 W/mKAluminum 221 W/mK

16. Does Is 2062 Specifies Only Seamless Pipes Or ERW Pipe Is Also Covered UnderIs 2062

IS:2062 Steel is a hot rolled structural steel that comes in three grades- low,medium and high tensile strengths. So its only applied for Seamless pipe.

ERW (Electric Resistance Welding) pipe is manufactured by rolling metal and thenwelding it longitudinally across its length. Seamless pipe is manufactured by e

xtruding the metal to the desired length, hence ERW pipe has a welded joint in its cross-section, while seamless pipe does not have any joint in its cross-section through-out its length.

17. During Steam Blowing of Pipe Line, A Bluish Color Conical Pattern Is Observed At The End. Why?

Flames are blue because of the molecules that are produced during combustion. CHand C2 radicals give off light in the green to blue region of the visible spectrum.

Fire needs oxygen to burn, and since the bottom of a flame does not get much oxygen, it is the hottest spot in the flame and is blue in color.

18. Even though LPG is economical than petrol,why we are not promoting LPG usage?

Because its not an alternating source.

Its exhaust emissions contain a large number of harmful substances, these substances emitted to the atmosphere, in a free state, ready for human and biologicalabsorption affected by .


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19 LPG does not have as many BTUs per gallon as petrol. That means an engine running on LPG will not have as much power as the same engine running on petrol.1. Pick up the wrong statement? A refrigent should have

a. Low specific heat of liquid

b. High boiling point

c. High latent heat of vaporization

d. Higher critical temperature

e. Low specific volume of vapour

Answer:

High boiling point

20. The property of a material which enable it to resist fracture due to high impact loads is known as

a. Elasticity

b. Endurance

c. Strength

d. Toughness

e. Resilience

Answer:Toughness

21. Spring index is

a. Ratio of coil diameter to wire diameter

b. Load required to produce unit deflection

c. Its capability of storing energy

d. Indication of quality of spring

e. Nothing

Answer:Ratio of coil diameter to wire diameter

22. Nodular iron has

a. High machinability

b. Low melting point

c. High tensile strength

d. Good fluidity

e. All of the above

Answer:All of the above


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23 Six isometric views are given below along with 3 set of orthographic views. Please correlate the orthographic views with their isometric view and write the answer in the box given below with a-f.

Answer:

D, A, B1. The purpose of jigs and fixtures are to

a. Increased production rate

b. Increased machining accuracy

c. Facilitate interchangeable manufacturing

d. Enable employ less skilled operators

e. All of the above

Answer:All of the above

24. Which one of the following methods produces gear by generating process

a. Hobbing

b. Casting

c. Punching

d. Milling

e. Broaching

Answer:Hobbing

25 . Tool life of the cutting tool is most affected by

a. Cutting speed

b. Tool geometry

c. Cutting feed and depth

d. Microstructure of material being cut

e. Not using coolant and lubricant

Answer:Cutting speed

26 Metal in machining operation is removed by

a. Tearing chips

b. Distortion of metal

c. Shearing the metal across a zone

d. Cutting the metal across a zone


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e. Pushing the metal with tool

Answer:Shearing the metal across a zone

27. A feeler gauge is used to check

a. Radius

b. Screw pitch

c. Surface roughness

d. Unsymmetrical shape

e. Thickness of clearance

Answer:Thickness of clearance

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