## 99+ Mechanical Engineering Important questions

• May 13, 2020

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### [Top 99+] Mechanical engineering important question for interview. Here we short list Top [100] mechanical engineering important questions.

#### 1. What is Zero Law of thermodynamics?

Ans. The zeroth law of thermodynamics states that if two thermodynamic systems are each in thermal equilibrium with a third one, then they are in thermal equilibrium with each other.

#### 2. What is First Law of thermodynamics?

The First Law of Thermodynamics states that heat is a form of energy, and thermodynamic processes are therefore subject to the principle of conservation of energy. This means that heat energy cannot be created or destroyed.

Where U = Change in internal energy,  Q = Heat , W = work done

First Law of thermodynamic state that heat and work are mutually convertible. According to first law of thermodynamic , energy can not be created or nor be destroyed.

#### 3. What is the Second law of thermodynamics?

The second law of thermodynamics introduces a new property called entropyS, which is an extensive property of a system. The entropy change of a closed system is equal to the heat added reversibly to it divided by the absolute temperature of the system.

dS = dQ/T,  Where dS = change in entropy, dQ = Change in temperature, T = Temperature.

• Second Law of Thermodynamics has two statement: –

The Kelvin-Planck Statement: It is impossible to construct a device which operates on a cycle and produces no other effect than the transfer of heat from a single body in order to produce work.

We prefer a less formal description of this statement in terms of a boat extracting heat from the ocean in order to produce its required propulsion work:

The Clausius Statement: It is impossible to construct a device which operates on a cycle and produces no other effect than the transfer of heat from a cooler body to a hotter body.

#### 3. What is the third Law of thermodynamics?

The third law of thermodynamics states that the entropy of a perfect crystal at a temperature of zero Kelvin (absolute zero) is equal to zero.

Or other way we can state as It is impossible to reach at absolute zero temperature ( 0 kelvin ) for any substance.

#### 4. what are the example mechanism?

Examples of mechanisms are the workings of a clock, a light switch, and a nail clipper.

#### 5. What Is Extruded Aluminum?

• Extrusion is the process where a metal or a metal bar is pulled through a mandrel to elongate it and/or give it a final shape.
• Extruded Aluminum is a common form of making small aluminum wire, bars or beams and many varieties of small non-structural, decorative pieces.

#### 6. What Is Knurling?

Knurling is a machining process normally carried our on a centre lathe. The act of Knurling creates a raised criss-cross pattern on a smooth round bar that could be used as a handle or something that requires extra grip.

#### 7.Why Is Over-pressurizing An Air Conditioning System Bad?

Overcharging a refrigeration or air conditioning system can result in an explosion. To avoid serious injury or death, never overcharge the system. Always use proper charging techniques. Limit charge amounts to those specified on the system equipment serial label or in the original equipment manufacturer’s service information.

Overcharging the system immerses the compressor motor, piston, connecting rods, and cylinders in liquid refrigerant. This creates a hydraulic block preventing the compressor from starting. The hydraulic block is also known as locked rotor.

Continued supply of electricity to the system causes heat to build in the compressor. This heat will eventually vaporize the refrigerant and rapidly increase system pressure. If, for any reason, the thermal protector fails to open the electrical circuit, system pressure can raise to high enough levels to cause a compressor-housing explosion.

#### 8. What Is The Difference Between An Electric Motor And An Electric Generator?

There is no fundamental difference between an electric motor and an electric generator or dynamo. In normal use, all motors behave as generators, and all generators behave as motors. DC Motors act like generators because they use less electrical energy when allowed to spin fast. DC generators act like motors because they become easier to spin when less electrical energy is drawn from their terminals.

For example, connect two small DC magnet motors together. Then if you spin the shaft of the first motor, the second motor’s shaft will start spinning too. One acts as a DC generator, and the other acts as a DC motor. Alternatively, spin the second one’s shaft, and the first one will start spinning.

Another example: If you connect a small DC motor to a small battery, then an electric current will appear in the motor’s coils, and the motor starts spinning. However, if you spin the motor’s shaft slightly faster than the normal speed, the direction of current in the circuit will reverse, and the battery starts taking in energy from the motor. The motor has become a generator, and it is recharging the battery.

#### 9. What Does Green Field Project Mean?

Green field projects are those projects, which do not create any environmental nuisance (pollution), follows environmental management system and EIA (environment impact assessment). These projects are usually of big magnitude.

#### 10. Is Pipe Round Because It Provides The Least Area To Volume Ratio?

More likely because it is easier to manufacture, much easier to put threads on, you do not have to worry about orientation when you put them together, and they have no weak spots created by corners.

My gutter pipes are rectangular because they do not stick out as far from the house as a circular one with the same area. However, they are low enough in the pressure they contain that they can be formed from sheet metal with a crimped seam. Making a water supply pipe, that way would be impossible.

In addition, it is easy to keep them aligned to the house. Running a rectangular water main under a street would be a major pain.

Mechanical Engineering Important Question