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In a non-Newtonian fluid, the relation between the shear stress and the shear rate is different. The fluid can even exhibit time-dependent viscosity. Therefore, a constant coefficient of viscosity cannot be defined. Although the concept of viscosity is commonly used in fluid mechanics to characterize the shear properties of a fluid, it can be ...
This mathematical relationship is useful because of its simplicity, but only approximately describes the behaviour of a real non-Newtonian fluid. Power-law fluids can be subdivided into three different types of fluids based on the value of their flow behaviour index: pseudoplastic, Newtonian fluid, and dilatant.
The large class of fluids whose viscosity changes with the strain rate (the relative flow velocity) are called non-Newtonian fluids. Rheology generally accounts for the behavior of non-Newtonian fluids by characterizing the minimum number of functions that are needed to relate stresses with rate of change of strain or strain rates.
When a material exhibits a linear response it is categorized as a Newtonian material. In this case the stress is linearly proportional to the strain rate. If the material exhibits a non-linear response to the strain rate, it is categorized as non-Newtonian fluid. There is also an interesting case where the viscosity decreases as the shear ...
Classification of fluids with shear stress as a function of shear rate: Pseudoplastic, Bingham plastic and Bingham pseudoplastic all show reduction in apparent viscosity with increasing shear rate. In rheology , shear thinning is the non-Newtonian behavior of fluids whose viscosity decreases under shear strain .
Such a shear thickening fluid, also known by the initialism STF, is an example of a non-Newtonian fluid. This behaviour is usually not observed in pure materials, but can occur in suspensions. A dilatant is a non-Newtonian fluid where the shear viscosity increases with applied shear stress.
Let’s talk science: A non-Newtonian fluid is defined as a liquid that does not follow Newton’s law of viscosity. Ultimately, a non-Newtonian fluid will change under force to be either more ...
Alternatively, stirring a non-Newtonian fluid can cause the viscosity to decrease, so the fluid appears "thinner" (this is seen in non-drip paints). There are many types of non-Newtonian fluids, as they are defined to be something that fails to obey a particular property—for example, most fluids with long molecular chains can react in a non ...