List of viscosities

From Wikipedia, the free encyclopedia

Dynamic viscosity is a material property which describes the resistance of a fluid to shearing flows. It corresponds roughly to the intuitive notion of a fluid's 'thickness'. For instance, honey has a much higher viscosity than water. Viscosity is measured using a viscometer. Measured values span several orders of magnitude. Of all fluids, gases have the lowest viscosities, and thick liquids have the highest. There is evidence of solid flow as result of Brownian motion in condition of extremes such as high temperature, high pressure, and extremely long time scales as theorized for the motion of the Earth's solid metal core.

The values listed in this article are representative estimates only, as they do not account for measurement uncertainties, variability in material definitions, or non-Newtonian behavior.

Kinematic viscosity is dynamic viscosity divided by fluid mass density. This page lists only dynamic viscosity.

Units and conversion factors

For dynamic viscosity, the SI unit is Pascal-second. In engineering, the unit is usually Poise or centiPoise, with 1 Poise = 0.1 Pascal-second, and 1 centiPoise = 0.01 Poise.

For kinematic viscosity, the SI unit is m^2/s. In engineering, the unit is usually Stoke or centiStoke, with 1 Stoke = 0.0001 m^2/s, and 1 centiStoke = 0.01 Stoke.

For liquid, the dynamic viscosity is usually in the range of 0.001 to 1 Pascal-second, or 1 to 1000 centiPoise. 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 0.02 centiPoise. The density is usually on the order of 0.5 to 5 kg/m^3. Consequently, its kinematic viscosity is around 2 to 40 centiStokes.

Viscosities at or near standard conditions

Here "standard conditions" refers to temperatures of 25 °C and pressures of 1 atmosphere. Where data points are unavailable for 25 °C or 1 atmosphere, values are given at a nearby temperature/pressure.

The temperatures corresponding to each data point are stated explicitly. By contrast, pressure is omitted since gaseous viscosity depends only weakly on it.

Gases

Noble gases

The simple structure of noble gas atoms makes them amenable to accurate theoretical treatment. For this reason, measured viscosities of the noble gases serve as important tests of the kinetic-molecular theory of transport processes in gases (see Chapman–Enskog theory). One of the key predictions of the theory is the following relationship between viscosity $\mu$ , thermal conductivity $k$ , and specific heat $c_{v}$ :

k=f\mu c_{v}

where $f$ is a constant which in general depends on the details of intermolecular interactions, but for spherically symmetric species is very close to $2.5$ .^[1]

This prediction is reasonably well-verified by experiments, as the following table shows. Indeed, the relation provides a viable means for obtaining thermal conductivities of gases since these are more difficult to measure directly than viscosity.^[1]^[2]

More information

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Substance	Molecular formula	Viscosity (μPa·s)	Thermal conductivity (W m⁻¹K⁻¹)	Specific heat (J K⁻¹kg⁻¹)	$f\equiv k/(\mu c_{v})$	Notes	Refs.
Helium	He	19.85	0.153	3116	2.47		^[2]^[3]
Neon	Ne	31.75	0.0492	618	2.51		^[2]^[3]
Argon	Ar	22.61	0.0178	313	2.52		^[2]^[3]
Krypton	Kr	25.38	0.0094	149	2.49		^[2]^[3]
Xenon	Xe	23.08	0.0056	95.0	2.55		^[2]^[3]
Radon	Rn	≈26	≈0.00364	56.2		T = 26.85 °C; $k$ calculated theoretically; $\mu$ estimated assuming $f=2.5$	^[4]