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## Power-law fluidA where: *K*is the*flow consistency index*(SI units Pa⋅s^{n}),- ∂
*u*/∂*y*is the shear rate or the velocity gradient perpendicular to the plane of shear (SI unit s^{−1}), and *n*is the*flow behaviour index*(dimensionless).
The quantity represents an Also known as the Ostwald–de Waele power law, this mathematical relationship is useful because of its simplicity, but only approximately describes the behaviour of a real non-Newtonian fluid. For example, if Power-law fluids can be subdivided into three different types of fluids based on the value of their flow behaviour index: *n*Type of fluid <1 Pseudoplastic 1 Newtonian fluid >1 Dilatant (less common)
## Pseudoplastic fluidsPseudoplastic, or A common household example of a strongly shear-thinning fluid is styling gel, which primarily composed of water and a fixative such as a vinyl acetate/vinylpyrrolidone copolymer (PVP/PA). If one were to hold a sample of hair gel in one hand and a sample of corn syrup or glycerine in the other, they would find that the hair gel is much harder to pour off the fingers (a low shear application), but that it produces much less resistance when rubbed between the fingers (a high shear application). ## Newtonian fluidsA Newtonian fluid is a power-law fluid with a behaviour index of 1, where the shear stress is directly proportional to the shear rate: These fluids have a constant viscosity, ## Dilatant fluidsDilatant, or While not strictly a dilatant fluid, Silly Putty is an example of a material that shares these viscosity characteristics. Another use is in a viscous coupling in which if both ends of the coupling are spinning at the same (rotational) speed, the fluid viscosity is minimal, but if the ends of the coupling differ greatly in speed, the coupling fluid becomes very viscous. Such couplings have applications as a lightweight, passive mechanism for a passenger automobile to automatically switch from two-wheel drive to four-wheel drive such as when the vehicle is stuck in snow and primary driven axle starts to spin due to loss of traction under one or both tires. ## See also |
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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Power-law_fluid". A list of authors is available in Wikipedia. |