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Dependence of pressure on viscosity of air

Dependence of pressure on viscosity of air

Dependence of pressure on viscosity of air

(OP)
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

RE: Dependence of pressure on viscosity of air

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.  

RE: Dependence of pressure on viscosity of air

(OP)
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.

RE: Dependence of pressure on viscosity of air


At these low pressures http://webbook.nist.gov/chemistry/ gives for nitrogen an oxygen at 25 deg C, 17.8 and 20.4 μPa, respectively.

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

RE: Dependence of pressure on viscosity of air

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

RE: Dependence of pressure on viscosity of air

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

RE: Dependence of pressure on viscosity of air


I should have written μPa.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%.

RE: Dependence of pressure on viscosity of air


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.

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