Mechanical engineering Interview Question an Answer for experienced/Engineering Interview Questions and Answers for Freshers & Experienced

Why gas turbine power plant needs efficient compressor ?

Because a large portion of turbine work is eaten away by compressor and its inefficiency will affect net power output and cost of generation.

Posted Date:- 2022-06-25 13:18:36

How the thickness of thermal boundary layer and thickness of hydrodynamic boundary layer related ?

Ratio of their thickness
(Prandtl number)-1/3.

Posted Date:- 2022-06-25 13:17:40

Why supercritical boilers use less amount of steel compared to non-supercritical boilers ?

Supercritical boilers do not head heavy drum for separation of steam from mixture of water and steam.

Posted Date:- 2022-06-25 13:16:08

How engine design needs to be changed to burn lean mixture ?

Engine to burn lean mixture uses high compression ratio and the highly turbulent movement of the charge is produced by the
geometry of the combustion chamber.

Posted Date:- 2022-06-25 13:15:06

As compression ratio increases, thermal n increases. How is thermal n affected by weak and rich
mixture strength?

Thermaln is high for weak mixture and it decreases as mixture strength becomes rich.

Posted Date:- 2022-06-25 13:14:41

Why consumption of lubricating oil is more in two-stroke eycle petrol engine than four-stroke cycle
petrol engine ?

In two-stroke engine lub oil is mixed with petrol and thus some lub oil is blown out through the exhaust valves by scavenging
and charging air. There is no such wastage in four stroke petrol engine.

Posted Date:- 2022-06-25 13:14:17

In some engines glycerine is used in place of water for eooling of engine. Why ?

Glycerine has boiling point of 90°C which inereases its heat carrying capacity. Thus weight of coolant gets reduced and smaller
riadiator can be used.

Posted Date:- 2022-06-25 13:13:35

Which impurities form hard scale and which impurities soft seale ?

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

Posted Date:- 2022-06-25 13:12:45

What is caustic embrittlement ?

It is the actual physical change in metal that makes it extremely brittle and filled with minute eracks. It occurs particularly in
the seams of rivetted joints and around the rivet holes.

Posted Date:- 2022-06-25 13:11:23

What is pitting ? How it is caused ?

Non uniform corrosion over the entire metal surface, but occurring only in smalls pits is called pitting. It is caused by lack of
uniformity in metal.

Posted Date:- 2022-06-25 13:10:50

Why the work per kg of air flow in axial flow compressor is less compared to centrifugal compressor for same pressure ratio ?

Isentropic efficiency of axial flow compressor is higher.

Posted Date:- 2022-06-25 13:09:39

Why the electric motor of a fan with backward curved blades is never got overloaded under any condition ?

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.

Posted Date:- 2022-06-25 13:09:16

What is the difference between stalling and surging in rotary compressions ?

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.

Posted Date:- 2022-06-25 13:07:19

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

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

Posted Date:- 2022-06-25 13:06:46

When maximum discharge is obtained in n0zzle ?

At the critical pressure ratio.

Posted Date:- 2022-06-25 13:05:37

How much is the work done in isochoric process ?


Posted Date:- 2022-06-25 13:05:18

What is the relationship between COP of heating and cooling ?

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

Posted Date:- 2022-06-25 13:05:00

Why rate of condensation is higher on a polished surface compared to rusty surface ?

Polished surface promotes drop wise condensation and does not wet the surface.

Posted Date:- 2022-06-25 13:04:28

What are two essential conditions of perfect gas ?

It satisfies equation of state and its specific heats are constant.

Posted Date:- 2022-06-25 13:03:56

Why entropy change for a reversible adiabatic process is zero?

Because there is no heat transfer in this process.

Posted Date:- 2022-06-25 13:03:33

What is the difference between scavenging and supercharging ?

Seavenging is process of flushing out burnt gases from engine cylinder by introducing freslh air in the cylinder before exhaust stroke ends. Supercharging is the process of supplying higher mass of air by compressing the atmospheric air.

Posted Date:- 2022-06-25 13:02:10

In which process fluid expands but does no work ?

Throttling process.

Posted Date:- 2022-06-25 13:01:35

Whether entropy is intensive property or extensive property ?

Entropy is extensive property.

Posted Date:- 2022-06-25 13:00:49

Whether superheated steam can be treated like ideal gas ?


Posted Date:- 2022-06-25 12:59:55

Which parameter remains constant in isochoric process ?


Posted Date:- 2022-06-25 12:59:32

Define the terms free energy and free enthalpy. What is their significance and importance?

Free energy (or Helmholtz function) is defined as/= u -Ts.
It is equal to the work during a constant-volume isothermal reversible nonflow process.
Free enthalpy (or Gibbs function) is defined asg =h
(where u = internal energy, h= enthalpy, T= temperature, s = entrop)
Gibbs function is of particular importance in processes where chemical changes occur. For reversible isothermal steady-flow
processes or tor reversible constant-pressure isothermal nonflow processes, change in free energy is equal to net work.

Posted Date:- 2022-06-25 12:51:44

What do you understand by latent heat ? Give four examples of latent heats.

For pure substances, the heat effects accompanying changes in state at constant pressure (notemperature change being
evident) are known as latent heats. Examnples of latent heats are : heat of fusion, vaporisation, sublimation, and change in
erystal form.

Posted Date:- 2022-06-25 12:34:06

Explain the rule to find specific heat of aqueous solutions.

For aqueous solutions of salts, the specific heat can be estimated by assuming the specific heat of the solution equal to that of
the water alone. Thus, for a 15% by weight solution of sodiunm chloride in water, the specific heat would be approximately o. 85.

Posted Date:- 2022-06-25 12:33:22

What is the difference between heat capacity and specific heat of a material ?

• The heat capacity of a material is the amount of heat transformed to raise unit mass of a material 1 degree in temperature.
• The specific heat of a material is the ratio of the amount of heat transferred to raise unit maSs of a material 1 degree in temperature to that required to raise unit mass of water 1 degree of temperature at some specified temperature.
• For most engineering purposes, heat capacities may be assumed numerically equal to;specifie heats.

Posted Date:- 2022-06-25 12:32:55

What is Bauschinger effect?

According to Bauschinger, the limit of proportionality of material does not remain constant but vaies aceording to the direction
of stress under cyclic stresses.

Posted Date:- 2022-06-25 12:32:03

What are whiskers ?

Whiskers are very small crystals which are virtually free from imperfections and dislocations.

Posted Date:- 2022-06-25 12:31:43

What is temper embrittlement in alloy steels and what are its effects ?

Embrittlement attack is usually intergranular in metals, i.e. cracks progress between the grains of the polycrystalline material.
It imparts a tendency to fail under a static load after a given period of time in those alloy steels which are susceptible to

Posted Date:- 2022-06-25 12:30:43

In which process internal energy remnains constant ?

Isothermal process.

Posted Date:- 2022-06-25 12:30:25

Name the strongest and weakest type of atomic bonds.

Metallic bond is strongest and molecular bond also known as Vander Waals bond is weakest.

Posted Date:- 2022-06-25 12:29:04

List two effects of manganese in plain carbon steels.

Manganese increases tensile strength and hardness. It decreases weldability.

Posted Date:- 2022-06-25 12:27:40

Which factors influence the type of fracture in failure of a material ?

Seven factors influencing type of failure are:
1. Type of material (inherent structure properties),
2. Manner of loading (Static versus dynamic),
3. Range of imposed stress,
4. Strain rate (static, dynamic, impact),
5. Stress distribution (discontinuity in material/shape),
6. temperature, and
7. surtace treatment.

Posted Date:- 2022-06-25 12:25:34

What for zinc finds applications ?

Galvanizing consumes the largest proportion of zinc. Zinc is resistant to corrosion but is attacked by acids and alkalies. Zine alloys are suited for making die casting since the melting point is reasonably low.

Posted Date:- 2022-06-25 12:25:12

What is the maximum use of magnesium ?

Magnesium is used to alloy with aluminium and as an additive for making SG (Spheroidal Graphite) iron.

Posted Date:- 2022-06-25 12:24:46

What for admiralty brass used ?

Admirality brass with 296 zinc and 1% tin has good corrosion resistance and is used for condenser and feed heater tubes.
Aluminium is also added to brass to improve corrosion resistance.

Posted Date:- 2022-06-25 12:24:29

What is the effect of addition of zinc in copper? What is the use of 7o/30 brass ?

By addition of zinc in copper, both tensile strength and elongation increases. The 70/3o brass has excellent deep drawing property and is used for making radiator fins.

Posted Date:- 2022-06-25 12:23:46

What is the different between brass and bronze ?

Brass is an alloy of copper with zinc; and bronze is alloy of copper with tin.

Posted Date:- 2022-06-25 12:22:52

What do you understand by sulphur print ?

Sulphides, when attached with dilute acid, evolve hydrogen sulphide gas which stains bromide paper and therefore can be
readily detected in ordinary steels and cast irons. While sulphur is not always as harmful as is sometimes supposed, a sulphur
print is a ready guide to the distribution of segregated impurities in general.

Posted Date:- 2022-06-25 12:22:07

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