The viscosity of fluid

The viscosity of a fluid is defined as follows:

Viscosity is a parameter of the internal frictional force of a fluid. This friction occurs when the liquid layers move against each other. The frictional force is greater, the force that causes the movement the greater. This slip occurs when there is any mechanical movement of fluids such as spray, flow, sweep... It means that the high viscosity fluid will need a stronger force than the fluid with a low viscosity.

Movement of fluid *


The viscosity is shown by Newton through the following equation:

µ = γτ = shear stress/shear rate (Pa.s)

The liquid is divided into Newton liquid and Non-Newtonian liquid

Newton liquid *
Non-Newtonian liquid *

The Newton liquid is a liquid in which the change between shear stress and shear rate is linear. That means at the same temperature, the viscosity value will not change when any related factors are changed.

The non-Newtonian liquid is a liquid in which the change between shear stress and shear rate is not linear. Liquids will have different viscosities at different rates. It is divided into two groups:

Time Independent non-Newtonian

Pseudoplastic: This material will display a decreasing viscosity with an increasing shear rate (rpm). If the rotation speed is changed from small to large and vice versa, the corresponding values ​​will be equal.

Plastic: This material shows the properties of Newtonian, Pseudoplastic, or Dilatant

Dilatant: This material displays increasing viscosity with increasing shear rate (rpm).

Time-Dependent non-Newtonian

Thixotropic: A material has a gradual decrease in viscosity while the shear rate (rpm) remains constant.

Rheopectic: A material has a gradual increase in viscosity while the shear rate (rpm) remains constant.

(*) Picture reference from the book "MORE SOLUTIONS TO STICKY PROBLEMS"