Gt6steve@aol.com wrote:
>
> Certainly wouldn't (or couldn't) dispute any of the science in this
> interesting topic but I believe the advantage of Nitrogen over air in a race
> tire comes from it being well dried and consistent as opposed to the vapor
> laden air from our garage compressors.
> Steve
>
> << FOTers
>
> The volume within a tire is not constant. Otherwise one would not
> have
> centerline wear in an over-inflated tire.
>
> I can attest that Nitrogen does result in less changes in tire
> pressure during racing. If the tire pressure change is lower as others and I
> have observed, it reflects less heat transfer from the tire body to the
> Nitrogen inside. I graduated from ChemE so long ago and used it so little
> that I can not explain the exact science.
Steve is probably onto something here, but it's not water vapor in air
from home garage compressors. It's more likely liquid water droplets
going into the tire with the compressed air. Newton's heat transfer
equation depends upon the value of h, the heat transfer coefficient. For
gases, the forced convection coefficient (which might be produced in a
rapidly rolling tire) is about 100. For materials which change state
from liquid to vapor (boiling), the value of h is about 20,000. If the
interior of a tire is hotter than its exterior (likely), there would be
a noticeable change in both pressure and volume if liquid water were to
boil off inside the tire.... (!)
Cheers, all.
--
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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