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1-Fluid

Fluid is a substance that is capable of flowing. It has no definite shape of its own. It assumes the shape of its container.

Liquids and gases are fluids.

2-Types of Fluids

Fluids can be classified into four basic types

1- Ideal Fluid

2- Real Fluid

3- Newtonian Fluid

4-Non-Newtonian Fluid

1- Ideal Fluid: is a fluid that has no viscosity. It is incompressible in nature.

Practically, no ideal fluid exists.

2- Real Fluid:are compressible in nature. They have some viscosity.

Examples: Kerosene, Petrol, Castor oil

3- Newtonian Fluid:Fluids which obey the Newton's law of viscosity are called as Newtonian fluids.

Newton's law of viscosity is given by

(t = m dv / dy )

where

(t = shear stress)

(m = viscosity of fluid)

(dv/dy = shear rate, rate of strain or velocity gradient)

All gases and most liquids which have simpler molecular formula and low molecular weight

such as water, benzene, ethyl alcohol, CCl4, hexane

and most solutions of simple molecules are Newtonian fluids.

4-Non-Newtonian Fluid:are only type of fluid which do not obey Newton’s law of viscosity

There are four main types of non-Newtonian fluids

1-Bingham plastic:

Fluids that have a linear shear stress/shear strain relationship require a finite yield stress before they begin to flow

(the plot of shear stress against shear strain does not pass through the origin).

These fluids are called Bingham plastics.

Several examples are clay suspensions, drilling mud, toothpaste, mayonnaise, chocolate, and mustard.

The surface of a Bingham plastic can hold peaks when it is still.

By contrast Newtonian fluids have flat featureless surfaces when still.

2-Shear thinning (pseudoplastic)

is an effect where a fluid's viscosity—the measure of a fluid's resistance to flow—decreases with an increasing rate of shear strain.

Another name for a shear thinning fluid is a pseudoplastic.

This property is found in certain complex solutions, such as lava, ketchup, whipped cream, blood, paint, and nail polish.

It is also a common property of polymer solutions and molten polymers.

Pseudoplasticity can be demonstrated by the manner in which squeezing a bottle of ketchup, a Bingham plastic,

causes the contents to undergo a change in viscosity. The force causes it to go from being thick like honey to flowing like water.

The study of such phenomena is called rheology.

3-Shear thickening (dilatant):

the shear rate is increased, the viscosity of the system also increases.

This behavior is observed because the system crystallizes under stress and behaves more like a solid than a solution.

[4] Thus, the viscosity of a shear-thickening fluid is dependent on the shear rate.

The presence of suspended particles often affects the viscosity of a solution.

In fact, with the right particles, even a Newtonian fluid can exhibit non-Newtonian behavior.

An example of this is cornstarch in water and is included in the Examples section below.

The parameters that control shear thickening behavior are: particle size and particle size distribution, particle volume fraction,

particle shape, particle-particle interaction, continuous phase viscosity, and the type, rate, and time of deformation.

In addition to these parameters, all shear thickening fluids are stabilized suspensions and have a volume fraction of solid that is

relatively high.[5]

Viscosity of a solution as a function of shear rate is given via the Power Law equation,

where η is the viscosity, K is a material-based constant, and γ̇ is the applied shear rate.

Dilatant behavior occurs when n is greater than 1.[7]

Below is a table of viscosity values for some common materials.

3-Rheopectic

A rheopectic liquid exhibits a behavior opposite to that of a thixotropic liquid, i.e.

the apparent viscosity of the liquid will increase over time at a constant shear rate.

Once the shear stress is removed, the apparent viscosity gradually decreases and returns to its original value.

Rheopectic fluids are rare. Examples include specific gypsum pastes and printers inks.

4-Thixotropic

A thixotropic liquid will exhibit a decrease in apparent viscosity over time at a constant shear rate.

Once the shear stress is removed, the apparent viscosity gradually increases and returns to its original value.

When subjected to varying rates of shear, a thixotropic fluid will demonstrate a "hysteresis loop".

Drilling mud and cement slurries are among the many materials which can exhibit thixotropic behavior.

Example.http://upload.wikimedia.org/wikiversity/en/thumb/4/4b/Rheological-fluids-1.png/400px-Rheological-fluids-1.png

Material 	Viscosity (cP) Benzene 	0.60 Carbon Tetrachloride 	0.88 Ethanol 	1.06 Water 	1 to 5 Mercury 	1.55 Pentane 	2.24 Blood 	10 Anti-Freeze 	14 Sulfuric Acid 	27 Maple Syrup 	150–200 Honey 	2,000–3,000