Understanding Non-Newtonian Fluids: Types, Behaviors, and Applications

Non-Newtonian fluids are those whose behavior does not follow the expected behavior according to Newton's law of viscosity. In other words, the relationship between shear stress and shear rate is not linear, but rather depends on the history of the flow.

In a Newtonian fluid, the viscosity is constant and the relationship between shear stress and shear rate is linear. However, in a non-Newtonian fluid, the viscosity changes with the shear rate or the history of the flow. This means that the behavior of the fluid under different conditions of shear rate or flow history will be different from that of a Newtonian fluid.

There are several types of non-Newtonian fluids, including:

1. Shear thinning fluids: These fluids have a lower viscosity at higher shear rates. This means that they become less viscous as the shear rate increases. Examples include ketchup and paint.
2. Shear thickening fluids: These fluids have a higher viscosity at higher shear rates. This means that they become more viscous as the shear rate increases. Examples include cornstarch suspension and dilatant gels.
3. Thixotropic fluids: These fluids have a decreasing viscosity over time under constant shear stress. This means that they become less viscous as they are subjected to constant shear stress for a longer period of time. Examples include clay and gelatin.
4. Rheopectic fluids: These fluids have an increasing viscosity over time under constant shear stress. This means that they become more viscous as they are subjected to constant shear stress for a longer period of time. Examples include molten glass and some polymer solutions.

Non-Newtonian fluids exhibit a wide range of behaviors, including flow instabilities, nonlinear flow patterns, and self-healing properties. They are found in many natural and industrial applications, such as in the study of blood rheology, the behavior of suspensions and emulsions, and the flow of complex fluids in pipelines and mixing tanks.