Rheology part-1

 Rheology:

Defination:  The term  "Rheology " derived from the Greek words, Rheo means "to flow" and logos means "science" 

Rheology can be defined as the science concerened with the deformation of matter under the influence of stress,which may be applied perpendicularly to the surface of body,tangential to the surface of body or at any other angle to the surface of body.

The result of application of a stress may be divided into two types:

        (i)Elastic deformation: It is a reversible process ,deformation is recoverable when the body returns to its original position.

        (ii) Plastic deformation: It is a irreversible deformation, The work spent for the deformation is dissolute as heat.

Flow is dived into two types

(i) Newtonian: Liquids which follow Newton's law of viscous flow are known as newtonian liquid.

example: water, true solution,dilute suspensions

(ii) Non-Newtonian: Liquids which does not follow Newton's law is called as non-newtonian fluid.

      example: colloidal dispersions, emulsions,ointments,gel

Characteristics of Newtonian Fluids:

. Consider a block of liquid consisting of parallel  plates of molecules, bottom layer is considered to be fixed in place .

. If the top plane of liquid is moved at constant velocity, each lawer layer move with a velocity directly propertional to its distance from the bottom layer.

.The velocity difference between two planes is dv, velocity gradient or Rate of share is dv/dr.

.Force per unit area (F'/A) is call as Shearing stress.

The rate of share(F'/A)  is direcly proportional to Shearing stress (dv/dr)


               


 

                                Rheogram for newtonian flow


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