Dependence of pressure on viscosity of air

[vantveen]

Hi all,

I'm looking for a formula, graph or explanation which describes the viscosity of air depending on the pressure (1 atm until vacuum). Can anyone join this information?

With kind regards,
ME

 

[iainuts]

There's almost no variation. At 0.01 psia and 70 F, air viscosity is .04410 lb/ft-hr. At 15 psia and 70 F, air viscosity is .04415 lb/ft-hr. Those values are from a computer data base I use, so the number of significant digits may be questionable also.

 

[vantveen]

Thanks for your quick respons. Actually I'm looking for the viscosity of air from 1 atm (1000 mBar = 15 psi) until vacuum (10^-6 mBar = 15*10^-8 psi). Probably the viscosity will be reduced strongly.

 

[25362]

At these low pressures

http://webbook.nist.gov/chemistry/

gives for nitrogen an oxygen at 25 deg C, 17.8 and 20.4 [μ]Pa, respectively.

Besides, your conversion from mBar to psi has an error by a factor of 10.

 

[iainuts]

At 10^-6 mbar (1.5E-8 psi), the database I have still shows .04410 lb/ft-hr.

 

[iainuts]

Try graphing the results below. The graph seems to indicate that viscosity curve is going to flatten out at low pressure.
P (psia) Viscosity (lb/ft-hr
1.5E-08 0.04410
0.001 0.04410
1 0.04411
3 0.04412
5 0.04412
10 0.04414
20 0.04417
50 0.04425
100 0.04438
200 0.04467
500 0.04567
1000 0.04771
2000 0.05287
3000 0.05901
5000 0.07238
8000 0.09182

 

[25362]

I should have written [μ]Pa.s. The link I gave above gives the viscosities for nitrogen and oxygen over the full range of pressures and temperatures.

As indicated by iainuts, it appears that -at constant temperature- the required high vacuum diminishes the dynamic viscosity at atmospheric pressure by about 1%.

 

[25362]

The kinematic viscosity, on the other hand, being the ratio of the dynamic viscosity (kg/m.s) to density (kg/m³), and expressed in m²/s (or cSt), changes a lot with pressure.