Viscosity – The Physics Hypertextbook
The viscosity of a fluid is the measure of its resistance to gradual deformation by shear stress or . In Cartesian coordinates, the general relationship can then be written as . In fluid dynamics, it is common to work in terms of the kinematic viscosity . Nonstandard units include the reyn, a British unit of dynamic viscosity . A discussion about the differences and application of Dynamic and Kinematic Viscosity. The kinematic viscosity is highly dependent on temperature. Kinematic Viscosity is the ratio of absolute or dynamic viscosity to density - a quantity in which the.
One of the most common instruments for measuring kinematic viscosity is the glass capillary viscometer. In coating industries, viscosity may be measured with a cup in which the efflux time is measured.
There are several sorts of cup — such as the Zahn cup and the Ford viscosity cup — with the usage of each type varying mainly according to the industry. The efflux time can also be converted to kinematic viscosities centistokes, cSt through the conversion equations.
The viscosity is reported in Krebs units KUwhich are unique to Stormer viscometers. Vibrating viscometers can also be used to measure viscosity. Resonant, or vibrational viscometers work by creating shear waves within the liquid. In this method, the sensor is submerged in the fluid and is made to resonate at a specific frequency.
As the surface of the sensor shears through the liquid, energy is lost due to its viscosity. This dissipated energy is then measured and converted into a viscosity reading.
A higher viscosity causes a greater loss of energy. Volume viscosity can be measured with an acoustic rheometer. Apparent viscosity is a calculation derived from tests performed on drilling fluid used in oil or gas well development.
Kinematic Viscosity Formula
Now it ceases to behave like a solid and starts to act like a thick liquid. You don't have to worry about it flowing off the brush as you raise it to your mouth. Shear-thinning fluids can be classified into one of three general groups.
A material that has a viscosity that decreases under shear stress but stays constant over time is said to be pseudoplastic. A material that has a viscosity that decreases under shear stress and then continues to decrease with time is said to be thixotropic.
If the transition from high viscosity nearly semisolid to low viscosity essentially liquid takes place only after the shear stress exceeds some minimum value, the material is said to be a bingham plastic. Materials that thicken when worked or agitated are called shear-thickening fluids.
Kinematic Viscosity Formula
An example that is often shown in science classrooms is a paste made of cornstarch and water mixed in the correct proportions. The resulting bizarre goo behaves like a liquid when squeezed slowly and an elastic solid when squeezed rapidly.
Ambitious science demonstrators have filled tanks with the stuff and then run across it. As long as they move quickly the surface acts like a block of solid rubber, but the instant they stop moving the paste behaves like a liquid and the demonstrator winds up taking a cornstarch bath. The shear-thickening behavior makes it a difficult bath to get out of. The harder you work to get out, the harder the material pulls you back in.
Kinematic Viscosity is the ratio of absolute or dynamic viscosity to density - a quantity in which the force is external and independent of the mass of the fluid. Kinematic viscosity can be obtained by dividing the dynamic viscosity of a fluid by its density. It is also expressed in terms of centistokes cSt or ctsk.
Difference Between Kinematic and Dynamic Viscosity
The kinematic viscosity can also be called diffusivity of momentum since it has the same dimensions as the diffusivity of heat and diffusivity of mass concentration. The transport of momentum is analogous to the transport of other properties of a fluid. This also means that it can be used in many dimensionless numbers to compare ratios of diffusivities, and hence the relative importance of different physical processes. Bookmark this page in your browser using Ctrl and d or using one of these services: