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The density is usually on the order of 1000 kg/m^3, i.e. that of water. Consequently, if a liquid has dynamic viscosity of n centiPoise, and its density is not too different from that of water, then its kinematic viscosity is around n centiStokes. For gas, the dynamic viscosity is usually in the range of 10 to 20 microPascal-seconds, or 0.01 to ...
Viscosity is a measure of a fluid's rate-dependent resistance to a change in shape or to movement of its neighboring portions relative to one another. [1] For liquids, it corresponds to the informal concept of thickness; for example, syrup has a higher viscosity than water. [2]
In fluid dynamics, inviscid flow is the flow of an inviscid fluid which is a fluid with zero viscosity. [1] The Reynolds number of inviscid flow approaches infinity as the viscosity approaches zero. When viscous forces are neglected, such as the case of inviscid flow, the Navier–Stokes equation can be simplified to a form known as the Euler ...
This transfer of momentum can be thought of as a frictional force between layers of flow. Since the momentum transfer is caused by free motion of gas molecules between collisions, increasing thermal agitation of the molecules results in a larger viscosity. Hence, gaseous viscosity increases with temperature.
In condensed matter physics and physical chemistry, the terms viscous liquid, supercooled liquid, and glass forming liquid are often used interchangeably to designate liquids that are at the same time highly viscous (see Viscosity of amorphous materials), can be or are supercooled, and able to form a glass.
For instance, it is 0 in a monatomic gas at low density (unless the gas is moderately relativistic [3]), whereas in an incompressible flow the volume viscosity is superfluous since it does not appear in the equation of motion. [4] Volume viscosity was introduced in 1879 by Sir Horace Lamb in his famous work Hydrodynamics. [5]
The dilute gas viscosity contribution to the total viscosity of a fluid will only be important when predicting the viscosity of vapors at low pressures or the viscosity of dense fluids at high temperatures. The viscosity model for dilute gas, that is shown above, is widely used throughout the industry and applied science communities.
Newtonian fluids are the easiest mathematical models of fluids that account for viscosity. While no real fluid fits the definition perfectly, many common liquids and gases, such as water and air, can be assumed to be Newtonian for practical calculations under ordinary conditions.