# Types of Fluid – Based on Different Properties

A fluid is a substance that deforms continuously under the action of shear force. Fluid flows continuously when an external force is applied.

A fluid can be classified on the basis of the properties mentioned below:

1) Viscocity
2) Density
3) Compressibility

Types Of fluid based on Viscocity:
Based on Viscocity fluids are divided into the following types:
1) Ideal Fluid
2) Real Fluid
3) Newtonian Fluid
4) Non-Newtonian Fluid
5) Ideal Plastic Fluid
6) Thyxotropic Fluid

1) Ideal Fluid:
The ideal fluid is an incompressible fluid. This type of fluid does not have any viscosity and surface tension.
The ideal fluid is also known as a perfect fluid. In real life, no fluid has such properties so it is an imaginary fluid.
Some of the liquid can be considered ideal like water which has very low viscocity, low surface tension and high resistance to compression.
Thus water can be considered an ideal fluid for all practical purposes without incurring much appreciable error in arriving at the result.

In real life, it is impossible for any fluid to have the properties mentioned above. Every fluid has some viscosity and surface tension and also has some compressibility. So, no ideal fluid exists in real life.

2) Real Fluid:
The real fluid is a compressible fluid. Every real fluid present posses some Viscosity and Surface Tension. A real fluid is also known as practical fluid.
A fluid that possesses properties such as viscosity, surface tension, and compressibility is known as real fluid or practical fluid.
All fluid present in nature is real fluid.
Examples of real fluid: Water, petrol, kerosene, etc.

3) Newtonian Fluid:
Newtonian Fluids are the fluid that obeys Newton’s Law Of Viscocity.
In Newtonian Fluid, shear stress is directly proportional to the rate of shear strain.
Also, the viscosity totally depends upon the temperature and pressure of the fluid. Examples of Newtonian fluid are air, water, hydrogen, emulsions, kerosene, etc.

4) Non-Newtonian Fluid:
The fluids which do not obey Newton’s Law Of Viscosity are known as Non-Newtonian Fluid.
In Non-Newtonian Fluid the shear stress is not directly proportional to the rate of shear strain.
Examples Of Non-Newtonian Fluid: Blood, grease, sugar solutions, Flubber, Oobleck, etc

Non-Newtonian Fluid is further classified as:

1) Time Dependent Fluids:
In this type of non-newtonian fluid, the shear stress or viscosity changes with time.
TIme dependent fluids are divided into two types: Thixotropic and Rheotropic or Anti-thixotropic

.
Thixotropic Fluid: In thixotropic fluid, the shear stress or viscosity decreases with time due to isothermal conditions and steady shear.
Rheotropic or anti-thixotropic fluid: In rheotropic fluid, the shear stress or viscosity increases with time due to isothermal conditions and steady shear.

2) Time Independent Fluids:
In this type of new-newtonian fluid, the shear stress or viscosity remains constant and does not change with time.
Time Independent Fluids are divided into two types:
I) Fluid with yield stress
ii) Fluid without yield stress.
Fluid without yield stress is further divided into two types:
1) Pseudoplastic Fluids
2) Dilatant Fluids

5) Ideal Plastic Fluid:
The fluid in which the shear stress is proportional to the rate of shear strain i.e it follows Newton’s Law Of Viscocity and the shear stress is more than the yield value is known as ideal plastic fluid. The ideal plastic fluid is also known as Bingham Fluid.
When the ideal plastic fluid reaches a yield value of shear stress, the fluid begins to flow. The fluid flows such that the relation between the shear stress and velocity gradient is linear.

Examples of ideal plastic fluid are Water suspension Of Clay and Fly ash.

6) Thyxotropic Fluid:
Thyxotropic fluid is a fluid in which after reaching a yield value of shear stress, the fluid begins to flow. The fluid flow such that the relationship between the shear stress (T) and the velocity gradient (dy/dx) is non-linear.
The thyrxotropic fluid is similar to plastic fluid till its initial value of shear stress (T) exceeds the yield value but after that it does not follow Newton’s law during flowing.

Examples of thyxotropoic fluid are crude oil and printing ink.

Based On Density The fluids are divided into two types:
1) Gas:
Gas is a type of fluid that does not have a fixed shape and volume. Eg- hydrogen, nitrogen.

2) Liquid:
A liquid is a type of fluid that does not have a fixed shape but has a fixed volume. Eg- Water, oil.

Based on compressibility the fluid is divided into two types:
1) Compressible Fluid:
Incompressible fluid, the density of fluid changes with the application of external force.

2) Incompressible Fluid
In incompressible fluid, the density of fluid doesn’t change with the application of external force.