Wednesday, 18 April 2012

Latest Mechanical Engineering Interview Questions with Answers

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1. A Bearing is designated as 6205 , what is it’s 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
1.The third and fourth digits indicate the bore size in millimeters. Except for                  0 through 3, the bore size is simply five times the third and fourth digits together. 0 through 3, however, are different:
00 10mm
01 12mm
02 15mm
03 17mm
2.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.
2. Advantages and Disadvantages of using  LPG in car?
1. Complete combustion
2. Fuel saving
3. Homogenous combustion
1. As complete combustion is occurring ,more heat liberated,not advised for long journey, engine will be over heated
2. Installation is difficult
3.  Reduce engine life efficiency
3. 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 and 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 is the only remaining option because it is stronger.
One more place where Spherical vessels are used for storage is LPG Storage Containers
4. 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.
5. 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.
6. Define Overall Heat transfer coefficient.
The overall heat transfer coefficient U is a measure of the overall ability of a series 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)
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/mK
  • Stainless steel – 21 W/mK
  • Aluminum – 221 W/mK
7. Does Is 2062 Specifies Only Seamless Pipes Or ERW Pipe Is Also Covered Under Is 2062
IS:2062 Steel is a hot rolled structural steel that comes in three grades- low, medium and high tensile strengths. So it’s only applied for Seamless pipe.
ERW (Electric Resistance Welding) pipe is manufactured by rolling metal and then welding it longitudinally across its length. Seamless pipe is manufactured by extruding 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.
8. 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. CH and 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.
9. Even though LPG is economical than petrol,why we are not promoting LPG usage?
Because it’s 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 biological absorption affected by .
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.

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