# pressure variations in low vacuum (10e-3 to 1 bar)

 Register Blogs Members List Search Today's Posts Mark Forums Read

 November 26, 2001, 13:08 pressure variations in low vacuum (10e-3 to 1 bar) #1 cecile baril Guest   Posts: n/a Hello, I have to lead a project about low vacuum, and I don't really know what are the differences between the equations in case of high pressures and the equations in case of vacuum. Do you have informations about that and do you know the way to calculate the variation of pressure along a 40mm diameter pipe ? My study concerns only air. I don't know the pump flow and the applications ? Thank you for your help, Cecile

 November 27, 2001, 03:50 Re: pressure variations in low vacuum (10e-3 to 1 #2 P.Fonteijn Guest   Posts: n/a At high pressure the gas molecules will interact heavily and you will have to use rho=p*M/(z*R*T) with z=z(T,p,.....whatsoever). The lower the pressure, the easier it will be. Then you can easily treat air as an ideal gas, so rho=p*M/(R*T). As far as I know all continuum and NS-equations are applicable. Good luck, Pascale.

 November 27, 2001, 12:12 Re: pressure variations in low vacuum (10e-3 to 1 #3 Johan Larsson Guest   Posts: n/a The Navier-Stokes and continuity equations are derived by using the continuum approximation, which means that the mean free path of the molecules has to be much, much shorter than any physically relevant dimension. I'm not very familiar with the area of vacuum, but I would assume that your pressure (0.001 bar) would be high enough for the Navier-Stokes equations to be valid. You should, however, check this in any basic fluid mechanics book! /Johan

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post a.lynchy FLUENT 3 March 23, 2012 14:45 engahmed FLUENT 0 July 6, 2010 17:19 haykozoom FLUENT 0 July 13, 2009 08:34 DS & HB Main CFD Forum 0 January 8, 2000 16:00 subodh kumar Main CFD Forum 1 November 20, 1999 23:23

All times are GMT -4. The time now is 07:57.