Interview Questions For Mechanical Freshers – Part 7
11) : 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.”
12) : Is the boiler a closed system?
Yes definitely the boiler is a closed system.
13) : 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.
14) : 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.
ΔHs/R = [∂ lnp /∂ (1/T)]x
where: x – mole fraction of CO2 in the liquid phase
p – CO2 partial pressure (kPa)
T – temperature (K)
R – universal gas constant
α – mole ratio in the liquid phase (mole CO2 per mole of amine)
15) : Which is the hardest compound known?
Diamond.
16) : Which has more efficiency: Diesel engine or Petrol engines?
Off course Diesel engine has the better efficiency out of two.
17) : How many Laws of Thermodynamics are there?
There are four laws of the thermodynamics.
Zeroth law of thermodynamics: If two systems are in thermal equilibrium with a third system, they must be in thermal equilibrium with each other. This law helps define the notion of temperature.
First law of thermodynamics: Because energy is conserved, the internal energy of a system changes as heat flows in or out of it. Equivalently, machines that violate the first law (perpetual motion machines) are impossible. Heat is the flow of thermal energy from one object to another.
Second law of thermodynamics: The entropy of any isolated system cannot decrease. Such systems spontaneously evolve towards thermodynamic equilibrium — the state of maximum entropy of the system. Equivalently, machines that violate the second law (perpetual motion machines) are impossible.
Third law of thermodynamics: The entropy of any pure substance in thermodynamic equilibrium approaches zero as the temperature approaches zero. The entropy of a system at absolute zero is typically zero, and in all cases is determined only by the number of different ground states it has.
19) : What is the difference between Critical Speed and Whirling Speed?
In Solid mechanics, in the field of rotor dynamics, the critical speed is the theoretical angular velocity which excites the natural frequency of a rotating object, such as a shaft, propeller or gear. As the speed of rotation approaches the objects natural frequency, the object begins to resonate which dramatically increases system vibration. The resulting resonance occurs regardless of orientation.Whirling Speed is due to the unbalanced forces acting on a rotating shaft.
20) : What is Hess Law?
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.
21) : Explain Second Law of Thermodynamics?
The entropy of the universe increases over time and moves towards a maximum value.
21) : Compare Brayton Cycle 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.
22) : What is the purpose of Scrapper Ring?
Scrap the excess lube oil from the cylinder walls. there by preventing oil from entering combustion zone.
23) : What is DTSI Technology?
DTSI stands for Digital Twin Spark Plug Ignition. The vehicles with DTSI Technology use 2 spark plugs which are controlled by digital circuit. It results in efficient combustion of air fuel mixture.
• Digital – Since the spark generation will be initiated by a microchip.
• Twin – Since two spark plugs will be used.
• Spark ignition – Since the ignition will be done via a spark.
24) : How to Find, Ductile-Brittle Transition Temperature in Metals?
The point at which the fracture energy passes below a pre-determined point for a standard Impact tests. DBTT is important since, once a material is cooled below the DBTT, it has a much greater tendency to shatter on impact instead of bending or deforming.
25) : What is the importance of Thermodynamics?
All the mechanical engineering systems are studied with the help of thermodynamics. Hence it is very important for the mechanical engineers.
26) : How a Diesel Engine Works as Generator?
Diesel engine is a prime mover, for a generator, pump,and for vehicles etc. generator is connected to engine by shaft. mostly in thermal power plat ,there is an engine is used to drive generator to generate power.
27) : State difference between AnitiFriction Bearing and Journal Bearing?
Generally, journal bearings have higher friction force, consume higher energy and release more heat, but they have larger contact surface, so normally used in low speed high load applications. In anti friction bearings friction is less. One object just rolls over each other.
28) : What is the difference between Technology and Engineering?
Engineering is application of science. Technology shows various methods of Engineering. A bridge can be made by 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 laws of force/load distribution.
29) : What are the 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 long journey, engine will be over heated
2. Installation is difficult
3. Reduce engine life efficiency
30) : What is the difference between Speed and Economic Speed?
The rated speed tells us about the maximum speed which can be achieved by a vehicle or some other machine but the economical speed means the speed limit at which the machine works efficiently with least consumption of fuel.eg-in normal bikes(not racing),the max.speed limit shown on speedometer is upto 120 kmph but companies always advice their customers to drive such bikes at around 60 kmph to have maximum mileage