BillDentin@aol.com wrote:
>
> In a message dated 07/23/2002 7:43:54 AM Central Daylight Time,
> cartravel@pobox.com writes:
>
> > Subj:Re: Tyre Pressure/Temperature
> > Date:07/23/2002 7:43:54 AM Central Daylight Time
> > From:<A HREF="mailto:cartravel@pobox.com";>cartravel@pobox.com</A>
> > CC:<A HREF="mailto:fot@autox.team.net";>fot@autox.team.net</A>
> > Sent from the Internet
> >
> >
> >
> > Ok, I tried to be quiet, but my chemical engineering background won't let
> > me.
> > Air in your tires (or nitrogen, argon, hydrogen, hellium, whatever) obeys
> > the
> > ideal gas law, PV=nRT. The tire volume is fixed, so the absolute pressure
> > increases in direct proportion to the absolute temperature.
> Bill Dentinger replies:
> Amici:
>
> This stuff is great. I am memorizing it verbatim, and plan to use it a
> cocktail parties. While I am totally unqualified, I love to talk Hi Tech.
> Can anyone tell me how VIAGRA works. Someone told me it was 2% nitrogen, .5%
> argon, 3% hydrogen, 6% helium and 88.5% Fix-a-Flat.
<smile> Yup, very much like that. Actually, it does involve nitrogen
(promotes nitrogen oxides in the bloodstream, which dilate arteries, I
believe).
> Seriously, I appreciate this thread. We've been playing with tire pressures
> for years, and while we look really cool with our clip boards, pyrometers,
> and tire gauges.....truth be told..... we're still just 'playing with tire
> pressures'.
There may be some small advantage to using pure nitrogen in the tires,
but, as Larry Young says, it has nothing to do with the ideal gas law.
All gases behave the same with regard to temperature and pressure. What
benefit nitrogen may provide is in its room temperature
characteristics--at lower temperatures (below, say, 1200 deg F) as a
free gas, it's inert, and its molecular size and chemical inertness at
tire temperatures may make it less permeable through rubber and
therefore, may make for more predictable pressures than using compressed
air.
Tires grow with heat and the increased pressure created by that heat,
and this likely stretches the links in the rubber, making it easier for
atmospheric monoatomic gases to permeate the rubber and escape the tire
(and, likely, some of the oxygen and CO2 in air would be combining with
materials in the tire at elevated temperatures). If that's so, then pure
nitrogen would offer more consistency of gas _volume_ in the tire over
running time, which would result in more predictable pressures.
Cheers.
--
Michael D. Porter
Roswell, NM (yes, _that_ Roswell)
[mailto:mporter@zianet.com]
The gulf between content and substance continues to widen....
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