Different Types of Fluids

Fluid:

Fluid is one which cannot remain at rest under the action of shear force or fluid is the one which can flow and deforms under the action of shear stress or external force.

Fluid can be categorized based on following properties:

• Viscosity
• Conductivity
• Density
• Compressibility
• Temperature
• Pressure etc.

Types of Fluid:

Fluid can be classified as:

• Ideal Fluid
• Real Fluid
• Compressible Fluid
• Non-Compressible Fluid
• Newtonian Fluid
• Non-Newtonian Fluid

Ideal Fluid:

An imaginary fluid which is incompressible and having no viscosity.

e.g.: This fluid does not exist.

Real Fluid:

An actual fluid which possesses viscosity is known as real fluid. (All the fluids, in actual practice, are real fluids).

e.g.: Water, Air etc.

Compressible Fluid:

A fluid in which the density of fluid changes with the change in external force or by applying some pressure.

e.g.: All the gases.

Non-Compressible Fluid:

A fluid in which the density of fluid does not change with the change in external force or by applying some pressure.

e.g.: All the liquids.

Newtonian Fluid:

A real fluid in which shear stress is directly proportional to the rate of shear strain or velocity gradient.

e.g.: Water, Benzene etc.

Non-Newtonian Fluid:

A real fluid in which shear stress is not directly proportional to the rate of shear strain or velocity gradient.

e.g.: Plaster, Honey, Ketchup etc.

There are three categories of Non-Newtonian Fluid:

·         Time Dependent Fluid.

·         Time Independent Fluid.

·         Visco-Plastic Fluid.

1. Time Dependent Fluid:

The fluids whose apparent viscosity changes with time as the fluid is continuously sheared are time dependent fluids.

      a) Thixotropic Fluids

·         b) Rheopectic Fluids

Thixotropic Fluids:

The fluids whose apparent viscosity decreases with time when sheared continuously.

These fluids are thick under normal condition but when shaken, agitated, sheared or stressed they will start to flow. It will take some time to become viscous again.

e.g.: The best example of thixotropic fluids is tomato ketchup.

Rheopectic Fluids:

 The fluids whose apparent viscosity increases with time when continuously stress is applied.

e.g.: The examples of such fluids are gypsum paste and printer ink.

2. Time Independent Fluid:

The fluids whose apparent viscosity does not change with time as the fluid is continuously sheared are time dependent fluids.

·         a) Dilatant Fluid.

·         b) Pseudo plastic Fluid.

Dilatant Fluid.

The type of fluid whose viscosity increases when shear stress is applied on it independent of time which mean that in no time the fluid will become viscous when stress is applied and in no time, it will return to its non-viscous condition when stress is removed.

e.g.: The best example of dilatant fluids is Corn Flour-Water Solution.

Pseudo Plastic Fluids:

The type of fluid whose viscosity decreases when stress is applied irrespective to time are known as pseudo plastic fluids.

e.g.: The best example of pseudo plastic fluids is Paint.

3. Visco-Plastic Fluid:

a) Bingham Plastic Fluid.

Bingham Plastic Fluid.

For some fluid, when the stress is moderate or low it acts as solid but on applying stress more than its yield stress the viscosity decreases and the fluid started to flow.

e.g.: The best example of Bingham Plastic Fluid is Toothpaste.

Diagrams

Graphical Representation for the understanding of different types of fluids