Thermodynamic Mechanical Interview Questions And Answers

Thermodynamic Questions with answer for mechanical engineering students
1.          Why Entropy decreases with increase in temperature?
Ans.      ds=dQ/T Entropy is inversely proportional to the temperature so, as temp. Increases, entropy decreases.
2.           Why different types of sound are produced in different bikes, though they run on SI Engines?
Ans.       Engine specifications are different in different manufactures like as Bore Diameter (CC), Ignition timing. Also the exhaust passage takes more responsible for sound.
3.           How much Watt means 1Hp?
Ans.       746.2 Watt
4.           Explain Bicycle Rear Wheel Sprocket working?
Ans.      Rear wheel sprocket works under the principle of ratchet and pawl.
5.          Definition of Octane Number and Cetane Number?
Ans.     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.
6.         Which Mechanism is used in Automobile gearing System?
Ans.     Differential mechanism
7.            When Crude Oil is Heated, Which Hydro Carbon comes first?
Ans.       Natural gas (Gasoline)… at 20 Celsius
8.           How to calculate Bearing number ti Diameter of the inner and outer?
Ans.      Divide the shaft diameter size by 5, it will give last two digit of the bearing no. and according to type of load we have to choose the type of bearing and that will give prior number of the bearing.
9.           The Fatigue life of a part can be improved by?
Ans.       Improving the surface finish by Polishing & providing residual stress by Shot peening.
10.          What happens if gasoline is used in a Diesel Engine, Siesel 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 & it may blast.
11.          Poissons Ratio is Higher in, Rubber/Steel/Wood?
Ans.       When a material is compressed in one direction, it usuallytends to expand in the other two directions perpendicular tothe direction of compression. This phenomenon is called thePoisson effect. Poisson’s ratio is a 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.
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