A complete collection of important Basic Mechanical Engineering viva questions and short answers from Unit 1, Unit 2, and Unit 3. Covers thermodynamics, engines, turbines, boilers, pumps, and refrigeration concepts in simple and exam-oriented format.
Basic Mechanical Engineering Viva Questions and Short Answers
Unit I
1. List Energy Resources
Energy resources are broadly classified as renewable and
non-renewable. Renewable sources include solar, wind, hydro, biomass, and
geothermal energy. Non-renewable sources include coal, petroleum, natural gas,
and nuclear fuels.
2. What is the use of
surge tank in hydroelectric power plant?
A surge tank is provided in a hydroelectric plant to control
pressure variations in the penstock. It protects the pipeline from water hammer
effects caused by sudden load changes. It also stabilizes the flow of water to
the turbine.
3. Define System,
Boundary, Surroundings
A system is a defined quantity of matter or region selected
for study. The boundary is the real or imaginary surface separating the system
from surroundings. Everything outside the boundary is called surroundings.
4. Define closed, open
and isolated system
A closed system allows energy transfer but not mass transfer
across its boundary. An open system permits both mass and energy transfer. An isolated
system allows neither mass nor energy exchange.
5. Difference between
intensive and extensive properties
Intensive properties do not depend on the quantity of
matter, such as temperature and pressure. Extensive properties depend on the
mass of the system, such as volume and energy. Extensive properties change with
system size, while intensive ones remain constant.
6. Difference between
diathermic and adiabatic process
In a diathermic process, heat transfer between system and
surroundings is allowed. In an adiabatic process, no heat transfer occurs
across the boundary. Adiabatic processes are usually well insulated.
7. Difference between
pump and turbine
A pump converts mechanical energy into fluid energy to
increase pressure. A turbine converts fluid energy into mechanical work. Pumps
require external power, whereas turbines produce power.
8. State Zeroth law of
thermodynamics
The Zeroth law states that if two systems are each in
thermal equilibrium with a third system, they are in thermal equilibrium with
each other. This law forms the basis for temperature measurement.
9. State First law of
thermodynamics
The First law states that energy cannot be created or
destroyed, only transformed. For a closed system, heat added equals the
increase in internal energy plus work done. It represents conservation of
energy.
10. Second law of
thermodynamics – Clausius and Kelvin-Planck statements
Clausius statement says heat cannot flow spontaneously from
a colder body to a hotter body. Kelvin-Planck statement says no heat engine can
convert all heat into work in a cycle. Both statements express limitations on
energy conversion.
Unit II
1. Define Heat Engine
A heat engine is a device that converts thermal energy into
mechanical work. It operates between a high temperature source and a low temperature
sink. It works on a thermodynamic cycle.
2. List components of
Heat Engine
The main components are a heat source, working substance,
heat sink, and mechanical output device. The working substance absorbs heat and
produces work. The sink receives the rejected heat.
3. What is TDC and BDC?
TDC (Top Dead Centre) is the highest position of the piston
inside the cylinder. BDC (Bottom Dead Centre) is the lowest position of the
piston. These positions define the piston stroke length.
4. What is clearance volume?
Clearance volume is the space remaining in the cylinder when
the piston is at TDC. It prevents mechanical contact between piston and
cylinder head. It also influences compression ratio.
5. List performance
parameters of engine
Common performance parameters include indicated power, brake
power, mechanical efficiency, and thermal efficiency. Specific fuel consumption
and mean effective pressure are also important. These parameters evaluate
engine efficiency and output.
6. Difference between
air cooling and water cooling
Air cooling uses air flow to remove engine heat directly
from fins. Water cooling uses circulating coolant to absorb and carry away
heat. Water cooling provides better temperature control than air cooling.
7. List properties of
lubricant
Lubricants should have suitable viscosity, high flash point,
and low pour point. They must resist oxidation and prevent corrosion. Good
lubricants reduce friction and wear.
8. Define boiler and
classify them
A boiler is a closed vessel in which water is converted into
steam by heating. Boilers are classified as fire-tube and water-tube types.
They can also be classified based on pressure and circulation method.
9. List boiler mountings
and accessories
Boiler mountings include safety valve, pressure gauge, water
level indicator, and stop valve. Accessories include economizer, superheater,
and air preheater. Mountings ensure safety, while accessories improve
efficiency.
10. Difference between
impulse and reaction turbine
In an impulse turbine, water pressure remains constant across
the runner. In a reaction turbine, pressure changes as water flows through the
blades. Impulse turbines use high velocity jets, while reaction turbines use
pressure energy.
Unit III
1. What is a centrifugal
pump?
A centrifugal pump is a hydraulic machine that increases
fluid pressure using centrifugal force. It consists of an impeller rotating
inside a casing. It is widely used for water supply and irrigation.
2. What is a Pelton
turbine?
A Pelton turbine is an impulse turbine used for high head
applications. It uses water jets striking bucket-shaped blades. It converts
kinetic energy of water into mechanical energy.
3. Use of braking jet in
Pelton turbine
The braking jet is used to stop the runner quickly during
shutdown. It directs a jet opposite to the rotation direction. This reduces
stopping time and improves safety.
4. Applications of
Pelton turbine
Pelton turbines are used in high head, low discharge
hydroelectric plants. They are suitable for mountainous regions. They are
commonly installed in small and medium hydro projects.
5. What is a Kaplan
turbine?
A Kaplan turbine is a reaction turbine used for low head and
high flow conditions. It has adjustable blades for better efficiency. It
operates similar to a propeller.
6. Difference between
Kaplan and Francis turbine
Kaplan turbine is used for low head and high discharge
conditions. Francis turbine is used for medium head applications. Kaplan has
adjustable runner blades, while Francis has fixed blades.
7. Define Refrigerant
A refrigerant is a working fluid used in refrigeration
systems. It absorbs heat at low temperature and pressure and releases it at
high temperature. It undergoes phase change during the cycle.
8. Define One Ton of
Refrigeration
One ton of refrigeration is the cooling effect required to freeze one ton of water into ice in 24 hours. It is equal to 3.517 kW of cooling capacity. It represents the rate of heat removal.