# Basics of Mechanical Engineering – Interview Questions Part-10

I tried to cover some basic mechanical interview question in this article. You will find more than 50 Mechanical Engineering Questions which include thermodynamics, solid mechanics, mechanics of machinery, fluid mechanics, Heat transfer, Refrigeration and Air Conditioning Viva Questions, Power Plant Questions and many more. Hope this will to improve your basics of mechanical engineering.

# 50 +Mechanical Engineering Interview Questions

These basic mechanical engineering questions with answers will help you to get a good understanding of the mechanical engineering concepts. Let’s begin.

1. What does CNC stand for? CNC Meaning / CNC definition.

Answer: CNC stands for Computer Numerical Controls.

Numeric Controls creates the automation of the machine tools. If computer program is used to make the automation then the system is called CNC system. In modern times Computer Aided designs (CADs) are used in the CNC machines for precise operation.

1. How the value of gear train is measured?

Answer: The mechanical system which engages two or more gears in such a way that their teeth meshes and provides a smooth transmission. For a successful gear power transmission the gears are designed in a way that the velocity of the pitch circles of the two gears remains the same at the time of contact.

If a Gear A (driver) and B (driven) meshes having radius Ra and Rb and angular velocity Wa and Wb then

V= RaWa = RbWb

So Wa/Wb = Rb/Ra = Na/Nb where Na = No. of teeth of driver gear A and Nb is the No. of teeth on the driven gear B.

1. Explain Stress Strain Graph / Stress Strain Curve for Mild Steel. Describe Stress Strain relationship. What are the units of stress?

Answer: Follow the link: Stress Strain Curve for Mild Steel. Units of Stresses are Pa. Most of the times GPa or Giga Pascal is used to express the units of stress for materials.

1. What is water jacket?

Answer: Water Jacket is a water filled casing. The water in the water jacket may be circulated by a pump. Water jackets are used for cooling purposes of condensers, water cooled IC engines etc.

1. What is limiting friction?

Answer: When a body tries to slide over another surface or starts sliding they experience some opposite force from the adjacent surface. Limiting friction is the maximum value of the friction force when a body just starts to slide. There are condition and laws of limiting friction.

1. Describe the co-efficient of friction formula.

Answer: Co-efficient of friction is denoted by the Greek letter µ. It is the ratio of maximum frictional force to the normal force (the force that pushes the object towards the other surface)

µ = F/R , where F = Friction Force and R= Normal force. 1. Write short notes on lathe chucks.

Answer: Chucks are the work holding devices for Lathes. Chucks are mechanical vises which hold the workpiece and transfer rotational motion of the drive motor to the work piece. Chucks are adjustable and can be of two basic types.

3 Jaw Self Centering Chuck and 4 Jaw Independent Chuck.  Please Click on the image to have a clear idea of the lathe chucks. 1. What is the value of modulus of elasticity of steel?

Answer: Up to elastic limit strain is proportional to stress. The ratio of stress to strain is known as modulus of elasticity or young’s modulus of elasticity. Modulus of elasticity for steel  is measured 210 GPa.

1. What is the bending moment equation for simple bending of beams/ Describe bending moment formula?

Answer: σ = MC/I = E/R

Here, M = bending moment, I = Moment of inertia, C = Distance of extreme fiber from the neutral axis. E= Modulus of elasticity, R = Radius of curvature, σ = Stress

1. What is the effective length of column?

Answer:  Click the image for a clear view and the end conditions. For Pinned ends L= Le , For both ends fixed Le= 0.5L , For one end fixed one end pinned Le = 0.7L, for One end free and other end fixed Le = 2L. 1. Which Equation is used to determine the critical load of a slender column? Describe Euler’s equation for column.

Answer: Euler’s Equation is used for measuring the critical load of a slender column. Here is the Euler’s Equation for slender column. C is the value for different end conditions. Please Look at question no. 48 for the values of C.

1. What is Case Hardening?

Answer: It is the process of adding carbon or nitrogen or both on to the surface of a steel object. Case hardening makes a material hard from the outside but keeps the core soft. For example gear teeth are case hardened as a result the teeth can withstand wear and tear at the same because of having soft core they can absorb shock.

1. What is modulus of resilience?

Answer: It is the energy absorbed per unit volume within the elastic limit in the stress strain curve.

1. What are the thermal conductivity of different metals?

Answer: Thermal conductivity charts for different materials. It has a unit of Watt per Meter-Kelvin W/(m K)

 Materials Thermal Conductivity, W/(m K) at 25 degress Air, atmosphere 0.024 Aluminum 205 Copper 401 Water 0.58

1. What are the different types of boilers?

Answer: Classification of the boiler is done by considering different aspects.

According to the tube content boilers are classified as

1. Fire Tube Boiler also known as smoke boiler and
2. Water Tube Boiler

According to the furnace position

1. Externally Fired Boiler
2. Internally Fired Boiler

With respect to the axis of the boiler shell boiler is classified as

1. Vertical boiler and
2. Horizontal boiler

According to the number of tubes 1. Single tube boiler 2. Multitube boiler

By the method of water and steam circulation 1. Natural circulation 2. Forced Circulation.

By use or application 1. Stationary and 2. Mobile.

The boiler are also classified by the method of heating source. They are named after the type of fuel.

1. What is slenderness ratio? Show the slenderness ratio formula.

Answer: The ratio of the length of a column to the least radius of gyration is known as the slenderness ratio.

Slenderness ratio = l/k; l = length of the column, k = least radius of gyration.

1. What is Bending Moment? Describe the term bending moment diagram.

Answer:  Most of the time the bending moment is associated with the beams. Beams carry loads perpendicular to its axis and also withstand bending moment. When some external forces or moments are applied on a structural element, it can bend. The reaction to this applied forces and moments are known as the bending moment.

If we have a structural element, suppose a beam and some forces are applied on it and we want to determine the bending moment in every point then we have to use the bending moment diagram. Watch this video tutorial on how to draw bending moment diagram for a beam.

1. What is spring constant? Describe spring constant formula.

Answer: According to Newton’s third law of motion, if a force is applied to a spring it will apply a restoring force opposite in direction. We get hook’s law from this Newtonian physics which involves the term spring constant. According to Hook’s law-

F= – kx

F = restoring force, x = displacement, k = spring constant. The negative sign indicates the opposite direction of the force.

From the above equation we get, spring constant, k = – F/x. The unit of the spring constant is Newton per meter , N/m

Every spring has its own spring constant which shows the stiffness and strength of the spring.

1. Give thermal conductivity definition.

Answer: Thermal Conductivity can be explained as the heat conducted in unit time, through the unit area of a substance of unit thickness when the difference of temperature between the opposite faces of the object is unity.

1. What is boundary layer thickness?

Answer: It is the distance from the wall / plate across the boundary where the velocity of the flow has become free stream velocity. Watch this video on how to calculate boundary layer thickness

1. What is Reynolds Number?

Answer: Reynolds Number is the ratio of viscous force to the inertia force. Mathematically

Reynolds Number , Nre = ρvd/µ

For further studies of dimensionless numbers go to this link : Dimensionless Groups in fluid mechanics

1. What is heat transfer co-efficient? What is the value of heat transfer coefficient of air?

Answer: Heat Transfer Co-efficient is the parameter used to measure the heat transfer rate in convective heat transfer. Convective Heat Transfer Rate,

Q = h.A. (T2-T1)

Here, Convection heat transfer coefficient is h. It is the rate of heat transfer occurred between solid and liquid surfaces through unit surface area when the temperature difference is unity. It has a SI unit of W/m2 K.

Value of heat transfer coefficient of air can be 10-100 W/m2 K.

1. Describe vapor compression refrigeration cycle.

Answer: In vapor compression refrigeration cycle a compressor is used to produce extra work. It compresses the working fluid or the refrigerants and increases the pressure.

The refrigerant is compressed in the compressor and then the superheated refrigerant is passed through the condenser. The condenser liquefies the refrigerant and this high pressure liquid is received in a tank. The liquid passes a throttling device and the pressure drops. The low pressure saturated vapor refrigerant passes the evaporator and produces cooling effect. Have a look at the schematic diagram of vapor compression refrigeration cycle. 1. What is fire tube boiler and water tube boiler?

Answer: In fire tube boiler the hot combustion products (gases and flames) runs through the tubes and the tube is surrounded by the water. Example of fire tube boiler is : Simple vertical boiler, Cochran Boiler, Lancashire Boiler and Locomotive boiler.

In Water Boilers the water runs through the tubes and the combustion products surround the tubes. Example of water tube boiler is : Babcock & Wilcox Boiler, Stirling Boiler, La-monte Boiler etc.

1. What is boiler accessory and mounting? Give example.

Answer: Mountings are the parts or the devices which are mounted on the boiler for the proper and safe functioning of the boiler. Example of boiler mountings: Pressure gage, safety valve, Water Level Indicator, Steam Stop Valve, Feed check valve and fusible plugs etc.

Accessories are the parts which are additionally attached to the boiler for the increased efficiency. Accessories include economizer, superheater and feed pumps.

1. What is boiler water treatment?

Answer: Boiler water treatment is the process of reducing or removing the impurities from the boiler feed water. It is done externally and internally.

1. What is log mean temperature difference? Why it is used?

Answer: Log mean Temperature Difference (LMTD) is a mathematical term which is used to measure the temperature difference of the two opposite parts of a heat exchanger. This data can be used to determine the heat transfer rate.

1. What is lateral torsional buckling?

Answer: When a load carrying member is unstable due to its slenderness and load, the buckling can happen. Beams undergo Lateral torsional buckling (LTB). It happens due to the buckling of the compression flange of the beam. The web of the beam supports the beam from LTB. But if there is no lateral support and enough force is applied then both the web and the flange can buckle. The torsion flange remains stable and restrains the compression flange and web causing the beam to twist. As a result lateral torsional buckling happens. Watch this video to understand lateral torsional buckling.

1. What is latent heat of condensation and latent heat of evaporation?

Answer: Latent heat is the heat required to change a material from one state to another.

Latent heat of condensation is the heat released while water vapor condenses into liquid.

Latent heat of evaporation is the heat required to change the liquid in to vapor.

1. What is shear force?

Answer: The definition of shear force: Shear forces are generally unaligned forces which pushes one part of the body in a certain direction and the other part of the body in opposite direction. 1. What is multistage centrifugal pump?

Answer: Multistage Centrifugal pump is a device in which more than one impeller is engaged in the same shaft or on different shaft. The main reason for constructing these type of pumps is to create more pressure on the same pump casing. A centrifugal pump having single impeller cannot produce a pressure between suction and discharge side which is equivalent to 150 psid. It will be very costly to build such a pump with single impeller system. That’s why multistage centrifugal pumps are introduced. For producing higher heads impellers are connected in series and to get more discharge impellers are connected in parallel connections.

1. What is priming of centrifugal pump?

Answer: When the impeller rotates it adds Kinetic Energy to the adjacent fluid. As a result the pressure of the adjacent fluid increases. At the same time negative pressure is developed at the suction side. Because of this pressure differential fluid flows through the impeller. If the impeller is filled air rather than water then the pressure differential will be small and no fluid will flow. So to eliminate that phenomenon the pump flow path is filled with water. This is known as priming.

1. What is Engine Governor? What is its functions?

Answer: A governor is a device attached in the engine to control the speed. It is actually a speed limiter. It can measure the speed and can regulate it.

Governor’s function is to keep the speed stable in different loads. If the load is lighter, less fuel supply is needed to keep a stable speed. But if the load increases more fuel supply is needed. Governor controls the fuel supplies.

1. What is draft tube? Why it is used?

Answer: Draft Tubes are used at the exit of the runner of the turbines. These are pipes of gradually increasing area. The draft tube at the exit of the turbine increases pressure of the exiting fluid by reducing its velocity. It converts waste kinetic energy of the exit fluid into useful pressure energy.

1. What is Break Specific fuel Consumption, bsfc?

Answer: Break Specific fuel Consumption, BSFC is a ratio of the rate of fuel consumption to the power produced. So it is the measurement of the efficiency of the fuel of any prime mover which produces power.

bsfc =  fuel consumption/ Power Produced. The unit of fuel consumption is gm/s and the unit for power is watt.

1. What is third law of thermodynamics?

Answer: The entropy of a perfect crystal approaches to zero, when it approaches to absolute zero temperature.

1. What is Bernoulli equation for ideal and real fluid?

Answer: When a fluid is flowing in a continuous stream its energy remains constant for all the points. The flow must be incompressible and Newtonian fluid.

According to bernoulli’s equation the sum of pressure head, velocity head and datum head for a incompressible newtonian fluid remain constant.  Mathematical expression of Bernoulli equation: 1. Show the rheological properties of materials with the help of a graph.

39. What are the different unit of viscosity?

Answer: SI unit of Dynamic Viscosity is Poiseuille (Pl). CGS unit is Poise.

1 Poiseuille = 1 Pa-s or 1 (N-s)/mor kg (m-s).

The SI unit for kinematic viscosity is m2 /s.  CGS unit is stokes.

1. What is Stress Concentration? What you know about stress concentration factor?

Answer: Stress Concentration is the localized stress. When a stress is distributed over a material , it remains strong. But concentrated stress can cause serious damage to a material. Stress concentration is also known as stress raisers or stress risers. The effect of stress concentration can be easily identified by the term stress concentration factor. Stress Concentration factor is the ratio is average stress by the maximum stress. 1. What is Gear Module? What its importance?

Answer: The ratio of pitch circle diameter to the number of teeth in gears are known as Gear module. It is generally denoted as m. Gear module m = D/ T.

For two gears to be meshed their module must be equal.

1. What is Combined Cycle Power Plant?

Answer: A combined cycle power plant is one which uses both gas turbine and steam turbine to produce more electricity. By using CCPP the efficiency and the electrical power output both can be increased.

In a combined cycle power plant the gas turbine runs by the combustion products of the compressed air fuel mixture. It produces electricity by moving a generator. The waste gases from the gas turbine is then utilized in a heat recovery steam generator (HRSG). It produces steam and runs the steam turbine. Thus steam turbine produces some additional electricity. Here’s a schematic representation of CCPP. Click on the image for better view. 1. What is Pressure and Velocity Compounding for Impulse Turbine? Draw the velocity and pressure graphs for reaction and impulse turbines. / Describe Rateau and Curtis stages of impulse turbine.

1. What is sub-cooling and superheating in refrigeration system? Describe sub-ccoling and Superheating with T-s and P-h diagram.

1. Describe Gas Turbine Cycle with Regeneration, Intercooling and Reheating.

1. What is Herringbone Gear?

Answer: Herringbone is a pattern which resembles fish bone structure. Herringbone gear is a type of gear which is consist of two helical gears of opposite hand side. These are assembled side by side rather than face to face. As a result a fishbone structure is developed which is known as the herringbone gear. The gear creates a V shaped pattern. 1. Describe the relation between actual and theoretical COP in a refrigeration system.

Answer: The ratio of actual COP to theoretical COP is known as Relative COP.

1. What are the different end conditions of the column?

In Euler Formula, C is used to describe the end condition of the column

If the both ends of the column is hinged then C= 1

If the both ends of the column is fixed C= ¼

If the one end of the column is fixed and other is hinged C = ½

If the one end of the column is fixed and other is free, C = 4

1. What are the differences between beams and columns?

Answer: Beams are horizontal structural elements which experiences loads perpendicular to its axis and also withstands bending moments. Columns are the vertical members which have to withstand compressive loads which can be parallel to their axis.

1. What is Poison’s Ratio?

Answer: It is the ratio of lateral to linear strain.

1. What is section modulus? What is plastic section modulus?

Answer: The ratio of the moment of inertia of a cross sectional area to the distance of the highest point of the fiber from the neutral axis is known as the section modulus. Mathematically section modulus , z = I/C .