Wednesday, January 4, 2012



Study of fluid and its behaviour and properties is called fluid mechanics
Fluidmechanics is basically classified into two types like
1) fluid statics : study of fluid at rest
2) fluid dynamics: study of fluid at motion
Based on the shear rate fluids are classified into two types
1) Newtonian
2) non Newtonian
Based on the relation ship with temperature and pressure drop fluids are classified into two types they are
1) compressible: these fluids are sensitive to pressure and temperature drop
2) incompressible fluids: fluids which are insensitive to temperature and pressure dropn is called an incompressible fluid

Fluid properties:

Density : mass unit volume
Units kg/m3
Specific weight : weight /unit volume
Relative density :
Mass density /standard density
Surface tension :
Amount of force required to maintain a unit length of film in equilibrium
When fluid is subjected to shearstress it undergoes certain deformation offering a certain resistance called viscosity

Newtons law of viscosity
Let the area of the fluid film is a sq.m
Let the distance between the top and bottom layers be y m
Let the fluid be flowing between the two layers
Let the velocity of the fluid be v m/sec2
Let the viscosity of the fluid be u
Let the shear stress = T
T= F/A
Let the net force acting be F newtons

According to newtons law of viscosity

F∞ vA/y
F= u A dv/dy
F/A = u dv/dy

T = u dv/dy
Therefore shearstress is directly proportional to velocity gradient
Viscosity is the constant introduces
The fluids which obey the newtons law of viscosity are called Newtonian fluids
Which does not obey are considered as the no Newtonian fluid
Types of non Newtonian fluids and the graphs concerned are given as

Pseudoplastics: are those for which the viscosity decreases with the velocity gradient

Ex: blood , rubber

Bhingam plastics: these fluids undergo continuous deformation.
Ex: toothpaste , paint , jelly

Dilatant fluids : are those for which the viscosity increases with the velocity gradient
Ex: organic fluids, biological fluids

Time dependent non Newtonian fluids

Shear thinning : viscosity decreases with increase of time
Viscoplastic : acts both as elastic aswell viscous substance
Shear thickening : viscosity increases with increase of time

keywords: fluidmechanics, fluid statics, fluid dynamics, newtons law of viscosity , non newtonain fluids, graphs of non newtonain fluids,

pseudoplastics, bingham plastics, dilatent fluids , time dependent fluids

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