Non Newtonian fluids

what is a non Newtonian fluid

a fluid in which shear stress is not proportional to rate of shear

Non-Newtonian phenomena may be

1. time dependent

• thixotropy

• rheopexy

2. time independent

• plastic flow

• pseudoplastic flow

• dilatant flow

plastic flow

• the substance initially behaves like an elastic body and fails to flow when less amount of stress is applied. further increase in shear stress leads to increase in shear rate which progressively gets linearized.

• the amount of shear stress required to break the interparticle behaves individually is called yield value.

• follows Newtonian flow above yield

Dilatant

viscosity of fluid increases when shear is applied

example corn flour, wet beach sand, potassium silicate in water and starch in water

pseudoplastic

viscosity of the fluid decreases when shear is applied

eg. ketchup, polymer solution , grease

rheopectic

viscosity of the fluid increases when shear is applied

the difference from dilatant is that in rheopectic viscosity increase is time dependent

thixotropic