# Fluid Definition

Fluid is a substance which can flow and deformed under a small amount of force exerted on it is called fluid.

Example of fluid – Liquid and Gas

## Types of Fluid

- Ideal Fluid
- Real Fluid
- Newtonian Fluid
- Non Newtonian Fluid

# Ideal Fluid

The Fluid which is non viscous or friction-less and in-compressible is called ideal fluid.

We assume that ideal fluid is perfect fluid but fluid without viscosity is not possible or does not exist in real world so this is only a imaginary fluid.

# Real Fluid

All fluid comes under real fluid because all the fluid having viscosity, compression and surface tension in its properties with a little amount of force.

Example of REAL FLUID: water, petrol, air etc

Before we start Newtonian and non-Newtonian fluid lets discuss Newton’s law of viscosity

# Newton’s Law of Viscosity

Newton’s law of viscosity is states that the time rate of deformation of fluid is directly proportional to the shear stress applied on it.

Shear stress ∝ time rate of deformation

F/A ∝ de/dt

F/A ∝ du/dy { time rate deformation is velocity gradient for fluid}

F/A = µ (du/dy)where F/A = Shear stress

µ = Dynamic viscosity

du/dy = velocity gradient

# Newtonian Fluid

The fluid which obey’s the Newton’s law of viscosity is called Newtonian fluid.

Newtonian fluid have constant viscosity and it does not depend upon the shear stress applied on it.

Example of Newtonian fluid: Air, water, Kerosene etc types of fluid

# Non-Newtonian Fluid

The fluid which does not follow the Newton’s law of viscosity and relationship is depend upon all the three quantity i.e. shear stress, viscosity and velocity gradient.

Example of non-Newtonian fluid: Blood, Paint, butter, ink etc types of fluid

The general equation for the non-Newtonian fluid is given by

## τ = A (du/dy)^n + B

*Image source : wikipedia*

### Types of fluid (non-Newtonian fluid)

### Dilatant Fluid

The non-Newtonian fluid which having value of B = 0 and the value of n is greater than 1 in general equation, so the graph is gradually increased.

Example of Dilatant fluid: Butter and Quick sand etc types of fluid

### Pseudoplastic Fluid

The non-Newtonian fluid which having value of B = 0 and the value of n is less than 1 in general equation, so the graph is gradually decreased.

Example of Pseudoplastic fluid: Blood, rubber and paints etc types of fluid

### Bingham Plastic

The non-Newtonian fluid which having value of B = ty and n = 1, because it having starting value of B is greater than 0, so its viscosity gradient is increased from that point.

Example of Bingham plastic is sewage slug, drilling mud

### Thixotropic Fluid

It is time dependent fluid in which velocity is depend upon shear stress and time duration of application.

The viscosity of fluid increased or decreased with time.

Example of Thixotropic Fluid: Lets take a example of paint, it takes more time of brush to uneven smoothness.