Fluid Mechanics: Definition & Study of Fluids

A substance that flows is called as fluid. 

All liquid and gaseous
substances are considered to be fluids. 

Water, oil, and others are very
important in our day-to-day life as they are used for various
applications. For instance water is used for generation of electricity in
hydroelectric power plants and thermal power plants, water is also
used as the coolant in nuclear power plants, oil is used for the
lubrication of automobiles etc.
Fluid Mechanics is the branch of science that studies the behavior of
fluids when they are in state of motion or rest.
 Whether the fluid is at
rest or motion, it is subjected to different forces and different climatic
conditions and it behaves in these conditions as per its physical
properties. Fluid mechanics deals with three aspects of the fluid:
static, kinematics, and dynamics aspects:

1) Fluid statics: The fluid which is in state of rest is called as static
fluid and its study is called as fluid statics.

2) Fluid kinematics: The fluid which is in state of motion is called as
moving fluid. The study of moving fluid without considering the effect
of external pressures is called as fluid kinematics.

3) Fluid dynamics: The branch of science which studies the effect of
all pressures including the external pressures on the moving fluid is
called as fluid dynamics.

Why Study Fluid Mechanics

What is the necessity of studying fluids as an aspect of engineering?
Fluids are already an integral part of our day-to-day life. Engineering
allows us to explore the potential of fluids for a number of new
applications and various functions. Some of these include:

1) There are number of fluids that when burnt, produce lots of heat,
which can be used for various applications. Examples of these fluids
includes petrol and diesel for vehicles.

2) There are some fluids like oil that have a tendency to exert very
high pressure or force. These fluids can be used for lifting various
heavy loads. The fluids used in hydraulic machines and hydraulic
lifters are an example.

3) Some fluids have excellent flow properties which can be used for
the lubrication of various machines.

4) Fluids like water posses kinetic and potential energy, which is used
for generation of electricity as in hydroelectric power plants.
Fluid mechanics helps us understand the behavior of fluid under
various forces and at different atmospheric conditions, and to select
the proper fluid for various applications.

This field is studied in detail within Civil Engineering and also to great
extent in Mechanical Engineering and Chemical Engineering. It is in
these branches of engineering where there is maximum use of the
fluids.
Common Applications of Fluids

1) Hydroelectric Power Plants

In hydroelectric power plants, water is used to generate electricity on
a large-scale basis. Water stored in the dam possesses potential
energy, which is converted into the electrical energy in the power
generation unit of the plant. Hydroelectric power plants are one of the
major suppliers of power throughout the world. In some countries
power requirements are fulfilled entirely by these plants.

2) Hydraulic machines

Machines that operate on a fluid like water and oil are called hydraulic
machines. The fluid as the capacity to lift heavy loads and exert
extremely high pressures. Some hydraulic machines are used to
perform various machining operations. In most of these machines, oil
is used as the fluid. The oil is passed through the hydraulic motor
which transfers large amounts of energy to the fluid. This high energy
fluid enters the piston and cylinder arrangement where it can be used
to lift heavy loads or apply large forces.

3) Automobiles

No automobile can run without fluid. Fluids perform three crucial
operations in automobiles: generation of power, lubrication, and
cooling of the engine. Petrol or diesel generates power on
combustion in the engine. This is commonly referred to as fuel. Oil is
used for the lubrication of the engine and the gearbox and also
various other moving parts of the vehicle. In larger automobiles like
cars, buses and trucks, water is used for cooling the engine.

4) Refrigerators and Air Conditioners

This is another important area where fluids play a crucial role. In
refrigerators and air-conditioners, the fluids are known as
refrigerants. The refrigerant absorbs the heat from whatever is being
kept in the chiller or evaporator, which is at a low temperature, and
delivers that heat to the atmosphere, which is at a high temperature.
In air conditioners, the refrigerant absorbs room heat and throws it in
to the atmosphere, thereby keeping the room cool. The entire
operation of refrigerators and air-conditioners depends on the use of
a refrigerant.

5) Thermal Power Plants

In thermal power plants, water is used as the working fluid. After
getting heated in a boiler, water is converted into super heated steam
which is passes through the blades of turbines, thus rotating them.
The shaft of the turbine rotates in the generator, where electricity is

produced. Thermal power plants are one of the major suppliers of
power in various parts of the world, and water working as the fluid is
their most important component.

6) Nuclear power plants

Water is again a crucial power plant component. Here it is both the
working fluid and a coolant. In some nuclear power plants, heat
produced within the nuclear reactor is used to directly heat water,
which is converted into steam. This steam is passed through the
turbines similar to thermal power plants, rotating turbine blades to
generate power. This is an application of water as the working fluid.
In other nuclear power plants, the heat from nuclear reactors is not
used to generate steam directly. Heat is first used to heat the water,
which acts as the coolant. This coolant then transfers the heat to a
secondary coolant or the working fluid, which is again water and it is
passed through the turbine to generate electricity.

7) Fluids as a Renewable Energy Source

There are number of fluids that are being used as a renewable energy
source. Air or wind is one of the most popular sources of renewable
energy. Wind is used for generation of electricity on a small as well as
large scale basis. Water is used in tidal power plants to generate
electricity on a small scale basis. Ocean waves are used to rotate
turbine blades within the power generation unit. Bio diesel, a type of
the vegetable oil, is used as a fuel for vehicles along with traditional
diesel.

8) Operating Various Instruments

Compressed air is used for the operation of various types of
instruments and automatic valves. These valves can be activated and
deactivated by applying the pressure of compressed air. The
pneumatic tools which work on compressed air are used for various
applications like grinding, screwing and unscrewing various machinery
parts, etc.

9) Heat Engines

In previous heat engine designs, air was used as a fluid to generate
power in automobiles. Earlier it was thought that the efficiency of an
engine is dependent on the type of fluid used, but later it was shown
by Sadi Carnot, that the efficiency of an engine is not dependent on
the type of the fluid, but rather, the temperature of the fluid.
Fluids are used in a wide range of applications, often playing a vital
role, without which, these applications will just cease to exist. The
important thing to note is that most of the crucial applications of
fluids are for generation of electricity or power. In hydroelectric power
plants and automobiles, fluids are directly used to generate power or
electricity. In thermal and nuclear power plants, fluids are indirectly
used for generation of power, and still they are the dominant parts of
these applications. It is not an overstatement to say that without
fluids, the progress of the human race would stop.