Mark Browne wrote:

I believe that what you are neatly trying to side-step in your consideration
is the presence of liquid water. If all we were talking about is water
vapor, even at 100% humidity, then I would completely agree that you are
right.

Unfortunately there *can* be liquid water trapped inside the tire. Some of
this comes from tire mounting compound, some from air compressors without
suitable dryers, some from water inside the tire. This trapped water inside
the tire can be standing on the surface, or inside the rubber.

Wasn't this discussion about using nitrogen in the tires? If the racers
are so particular why are they using wet air from a cheap air compressor
and still worry about the effects of moisture? Why are they using
practices and processes that are known to add worrisome quantities of
liquid water to a component that is so sensitive to moisture?

Which way do you guys want this? Perfectly predictable tire pressures
will be impossible to obtain when the mounting is done with shade tree
techniques as you describe.

If there is so much water in a tire despite the best efforts of "real
physicists and engineers on their staff (who)go to considerable effort
to control the presence of water inside the tire" then something is
missing in this equation.

In a Formula or NASCAR setting moisture can raise tire pressure
about 4 PSI in the corners.

I find this a bit hard to believe. If it is water vapor it will
respond exactly like the nitrogen or air and the pressure rise is due to
the temperature increase of the tire. That is one of the gas laws that
no one seems to want to follow. If there is liquid water in the tire a
whole new set of conditions exist that are still unlikely to produce the
effect you describe.

Look at it another way. If you can attribute that 4 psi increase to
moisture then why not control the amount of moisture in the tire ... dry
the tire and add a measured amount of water so that you can predict the
pressure increase and regulate accordingly? But if you can dry the tire
then why worry about moisture? If you cannot dry the tire then you can
measure the dew point of the filling gas and calculate the weight of the
water in the tire and predict accordingly. It sounds to me like you guys
are just using "rules of thumb" and are surprised when you get surprised.

What is the normal tire pressure on one of those cars? Thirty - forty
psig? Let's say the tire started out at 35 psi, for the water to boil
away and increase the pressure of the tire to 39 psi its temperature
would have to increase to somewhere around 285 degrees F. Do you run
your tires at those temperatures? For the tires to increase 4 psi in the
second or two of cornering due to boiling water the carcass temperature
of the tire would have to be damn near glowing since heat does not
transfer instantaneously to the water, nor does it cool instantaneously
as the car leaves the corner.

If the starting temperature and pressure of the tire in the pits was 35
psig at 80 degrees F and it heated up to 200 degrees in the corner its
pressure would raise to around 46 psig ... at that pressure any water
would still be water until it reached over 290 degrees ...

I have not even mentioned the fact that the heat to vaporize the water
comes from the tire and the other gases filling the tire. The transfer
of that heat actually cools the tire and the gas ... a minute amount,
yes, but the effect of water has to be an equally minute amount and I
have yet to be shown the mechanism whereby "normal" amounts of water in
a tire will produce the effect you describe in the conditions in which
tires operate.

If you can explain how race car tires somehow work differently than
other machines I would love to hear it. I am very open minded but this
smacks of voodoo engineering to me.

Rick

"basskisser" wrote in message
om...


Again, unless introduced under ideal conditions, there WILL be water
vapor.

Key word "vapor". It obeys the ideal gas law as long as you stay away from
the condesation points.

If you had inflated the tire from an air compressor that included a storage
tank then the air had originally been at a much higher pressure. The higher
pressure increases the "dew point" considerably which usually results in
water condensing in the tank of the air compressor. A high quality air
compressor will provide for an automatic water drain, cheaper units simply
provide a drain valve at the bottom. Either way, the air that travels down
the air hose ends up drier than the air that was originally pumped into the
tank.

Assuming that you aren't pumping your trailer tires up to a couple hundred
PSI, the air in the tires will be significantly less than the air in the
storage tank was. At the lower pressure, the dew point will be
significantly higher, making it much less likely that you will condense any
of the vapor back into liquid.

You could create a sceanario where you could end up with enough water vapor
pumped into the tire so that at some realistic temperature there would be
enough condensation to create a measurable change in pressure. If a fraction
of a PSI matters that much to you then it would be trivial to avoid such a
sceanario at far less cost than dealing with nitrogen.

Which gas are you saying doesn't obey the gas laws: air or nitrogen?

Niether.


This is an interesting statement. Are you saying that the ideal gas laws
are wrong, or that for some reason nitrogen is not an ideal gas? Do you
think there are no ideal gases at all?

The condensation point for nitrogen at any reasonable pressure is damn cold!
The rubber on the tire will get hard and brittle long before you got
anywhere close to the condensation point of nitrogen!

Your understanding of thermodynamics is simply wrong!
Do a web search on "ideal gas" or "PV=nRT" or "boyles law". There are
plenty of sites from major universities that will educate you on this.

Rod

"Rod McInnis" wrote in message ...
"basskisser" wrote in message
om...


Again, unless introduced under ideal conditions, there WILL be water
vapor.

Key word "vapor". It obeys the ideal gas law as long as you stay away from
the condesation points.

If you had inflated the tire from an air compressor that included a storage
tank then the air had originally been at a much higher pressure. The higher
pressure increases the "dew point" considerably which usually results in
water condensing in the tank of the air compressor. A high quality air
compressor will provide for an automatic water drain, cheaper units simply
provide a drain valve at the bottom. Either way, the air that travels down
the air hose ends up drier than the air that was originally pumped into the
tank.

Assuming that you aren't pumping your trailer tires up to a couple hundred
PSI, the air in the tires will be significantly less than the air in the
storage tank was. At the lower pressure, the dew point will be
significantly higher, making it much less likely that you will condense any
of the vapor back into liquid.

You could create a sceanario where you could end up with enough water vapor
pumped into the tire so that at some realistic temperature there would be
enough condensation to create a measurable change in pressure. If a fraction
of a PSI matters that much to you then it would be trivial to avoid such a
sceanario at far less cost than dealing with nitrogen.

Which gas are you saying doesn't obey the gas laws: air or nitrogen?

Niether.


This is an interesting statement. Are you saying that the ideal gas laws
are wrong, or that for some reason nitrogen is not an ideal gas? Do you
think there are no ideal gases at all?

Nope, never said either. And I never said that either air, or nitrogen
"doesn't obey the gas laws."

The condensation point for nitrogen at any reasonable pressure is damn cold!
The rubber on the tire will get hard and brittle long before you got
anywhere close to the condensation point of nitrogen!

That has absolutely nothing to do with the fact that that nitrogen
doesn't expand at the same rate as oxygen for any given temperature
change. Do you deny this?

Your understanding of thermodynamics is simply wrong!
Do a web search on "ideal gas" or "PV=nRT" or "boyles law". There are
plenty of sites from major universities that will educate you on this.

Rod

No, it's not. You simply don't understand my position.

(Steven Shelikoff) wrote in message ...
On 29 Oct 2003 04:33:04 -0800, (basskisser) wrote:

"Rod McInnis" wrote in message
It is generally accepted that all gases obey the ideal gas law if you stay
away from their condensation temperature.

Not true. Unless you introduce nitrogen to the tire under ideal
conditions, which would entail a vacuum process first. Do you really
think that people are going to do that, when all they need is a larger
tire?

Air is mostly nitrogen, then
oxygen, carbon dioxide, and traces of many other gases including water.

Bingo, you're starting to get it. Water.

It's water VAPOR you moron, a gas. It obeys the gas laws until it
condenses or sublimates. Are you saying that's what happens inside a
hot tire?

Unless you have artificially introduced liquid water into the tire, or
inflated the tire with air super saturated with moisture, the typical
operating temperature of the tire will sufficienty above the dew point of
the air inside such that the air (complete with water vapor) will obey the
ideal gas law.

Again, unless introduced under ideal conditions, there WILL be water
vapor.

Proof you don't know the first thing about high school physics if you
think water vapor in air causes it not follow the gas laws. You do
realize tha if you put nitrogen in a tire, chances are you'll have some
water vapor in there also.

Steve

Bull****. Pure and simple. Again, your obsession with me has blinded
you so much that you fail to read for content.

(Steven Shelikoff) wrote in message ...
On 29 Oct 2003 04:27:31 -0800, (basskisser) wrote:

Please refute my statements, or shut up. Quit stalking me.

lol. Stalking you? I didn't even respond to you. You're so stupid you
can't even follow a thread.

Steve

Idiot. If you aren't stalking me, why did you bother to refer to me in
a response that had NOTHING to do with the topic?

snip

That has absolutely nothing to do with the fact that that nitrogen
doesn't expand at the same rate as oxygen for any given temperature
change. Do you deny this?

snip
Now you have my curiosity!

I understand all gases to expand about 1/270 per degree C at room
temperature.

Please explain how now nitrogen and oxygen differ?

Mark Browne

Mark Browne wrote:


Now you have my curiosity!

I understand all gases to expand about 1/270 per degree C at room
temperature.

Please explain how now nitrogen and oxygen differ?

This should be a good one ... but don't hold your breath waiting for a
response. I am just amazed that he doesn't just look up the gas laws and
see for himself. Bizarre.

Bass posted this and I haven't heard from him since I answered him, so
if you attempt to explain it to him maybe he will finally just go away.

You apparently don't know squat about the Laws of Gases.
Now, Im again telling you that the ONLY reason is that
the pressure to temperature ratio is more linear.
Do you refute that? If so, do tell why. Now, I suspect that
you don't UNDERSTAND my answer, and that is the reason that
you don't think it's correct. So, allow me to explain.
The nitrogen doesn't expand as much as air, for a given
temperature change.

The level of scientific illiteracy in this country is frightening when
you see it defended so hotly by those with the smallest armory.

Rick

"Mark Browne" wrote in message
news:qv8ob.62616$Tr4.167581@attbi_s03...

snip

That has absolutely nothing to do with the fact that that nitrogen
doesn't expand at the same rate as oxygen for any given temperature
change. Do you deny this?

snip
Now you have my curiosity!

I understand all gases to expand about 1/270 per degree C at room
temperature.

Please explain how now nitrogen and oxygen differ?

Mark Browne

Nitrogen has an atomic weight of 14 and oxygen is 16? I can live on pure
oxygen, but pure nitrogen will kill me?

By the way, is is more like 1/300 at room temperature unless you live in a
very cold room.... :-)

PV=nRT or PV=NkT

del cecchi

"basskisser" wrote in message
om...

That has absolutely nothing to do with the fact that that nitrogen
doesn't expand at the same rate as oxygen for any given temperature
change. Do you deny this?

Yes. I deny this.

Mr. Boyle denies this. Mr. Charles denies this. Mr. Gay and Mr. Lussac
deny this. They wrote laws of physics about it. Every chemistry, physics and
thermodynamics class uses these laws. Here, don't take my word for it, let's
take a look at some of the information available from the net.

As an example:

Department of Chemistry
California State University, Sacramento
http://kekule.chem.csus.edu/gaslaws

Boyle's Law
Simply stated, Boyle's Law indicates that for a fixed amount of gas (fixed
number of moles) at a fixed temperature, the pressure and the volume are
inversely proportional.
pV = constant or p1V1 = p2V2


In other words, as the pressure increases, the volume decreases. (When you
squeeze on a balloon to increase the pressure, the volume of the balloon
goes down.)



Charles' Law
Simply stated, Charles' Law indicates that for a fixed amount of gas (fixed
number of moles) at a fixed pressure, the volume is proportional to the
temperature.

V/T = constant or V1/T1 = V2/T2


In other words, as the temperature increases, the volume increases. (When
you heat a balloon the volume of the balloon goes up.)



Gay-Lussac's Law
Simply stated, Gay-Lussac's Law indicates that for a fixed amount of gas
(fixed number of moles) at a fixed volume, the pressure is proportional to
the temperature.
p/T = constant or p1/T1 = p2/T2


In other words, as the temperature increases, the pressure increases. (When
you put a pickle jar in the refridgerator, the drop in pressure from the
trapped air becoming colder makes it hard to open the jar later!)





Note that there is no factor in these equations for the type of gas. If you
take a rigid container that contains a gas, any gas and heat it up the
pressure will increase a known and predictable amount. You double the
temperature, you double the pressure.

These three laws combine together to create the "ideal gas" law, whihc is
PV=nRT. This law relates Pressure, Volume and Temperature. Give me the
starting values, how much you changed the other two variable and I can tell
you exactly what the third variable will be. I don't need to know what the
gases are involved.

The only time that you deviate from the ideal gas law is if you reach a
pressure/temperature point where the gas might change state into a liquid.
You had some basis for an argument with water at room temperatures, but
oxygen and nitrogen are not ever going to be liquid at any pressure you are
likely to have in your tires. Air will obey the ideal gas law as long as it
isn't saturated with water vapor, and as I pointed out earlier you would
have to try hard to get saturated air into the tires.

Rod

Rod McInnis wrote:

Mr. Gay and Mr. Lussac deny this.

I don't know what those two guys contributed to the gas laws but maybe
they were related to Joseph Gay-Lussac and helped out with his balloons
or something. 8-)

Rick