nitrogen versus air

  • Thread starter dougparsons@ameritech.net
  • Start date
D

dougparsons@ameritech.net

Guest
Hey every 1,

A local tire company is advertising filling your tires with nitrogen
versus air says it is better for the tires they run 20 degrees
cooler etc etc. What is your theory on bouyancy? Think I should take
amphi over and ask them if it will make the car float?

Doug
 
W

WB6WSN

Guest
----- Original Message -----
From: dougparsons@ameritech.net
To: amphicar-lovers@yahoogroups.com
Sent: Friday, January 30, 2004 3:46 PM
Subject: [amphicar-lovers] nitrogen versus air


Hey every 1,

A local tire company is advertising filling your tires with nitrogen
versus air says it is better for the tires they run 20 degrees
cooler etc etc. What is your theory on bouyancy? Think I should take
amphi over and ask them if it will make the car float?

Doug




Earth's atmosphere is about 70% nitrogen, and that's free. I think nitrogen is
used (especially for aircraft) because it won't support combustion and its 100%
dry, so you don't have to worry about a lump of frost forming inside a tire
while in an un-heated wheel-well.

Since nitrogen is less dense than oxygen and carbon dioxide, I think you would
get a bit more bouyancy if a tire was filled with nitrogen. Further, the
nitrogen would be friendlier to the rubber compounds, so the tube might last
longer. Finally, I think nitrogen would carry less heat than the plain air, so
heat removal from the rear of the tread might be slightly worse with nitrogen.
So claims about cooler running tires sound suspicious.

Ed
El Cajon
67 Rust Guppy


[Non-text portions of this message have been removed]
 
B

Bill Connelly

Guest
Hey every 1,

A local tire company is advertising filling your tires with nitrogen
versus air says it is better for the tires they run 20 degrees
cooler etc etc. What is your theory on bouyancy? Think I should take
amphi over and ask them if it will make the car float?

Doug

==============

Well, Nitrogen actually makes up most of the stuff we breathe anyhow...like
78% of it, with Oxygen being about 21% of atmospheric air and Argon and
other gaseous goodies making up the rest. As for the buoyancy of pure
Nitrogen over the cocktail that is atmospheric air, since Nitrogen IS a
lighter gas than Oxygen (see "Density" listings below), pure Nitrogen would
be lighter, and hence more buoyant....But I mean, why stop there? Why not
pump up your rubber with Helium? It's almost TEN times lighter and hence
more buoyant than atmospheric air, is an inert gas that reacts with nothing
chemically (which would probably halt any dryrot of the inner inner tubes in
its tracks), and, most importantly, any leakage would make you talk like a
duck, which is, after all, sort of appropriate for us, Yes?

~Bilgey~

Basic Information

Name: Nitrogen
Symbol: N
Atomic Number: 7
Atomic Mass: 14.00674 amu
Melting Point: -209.9 ?C (63.250008 ?K, -345.81998 ?F)
Boiling Point: -195.8 ?C (77.35 ?K, -320.44 ?F)
Number of Protons/Electrons: 7
Number of Neutrons: 7
Classification: Non-metal
Crystal Structure: Hexagonal
Density @ 293 K: 1.2506 g/cm3
Color: colorless
Date of Discovery: 1772
Discoverer: Daniel Rutherford
Name Origin: Greek
Uses: forms most of atmosphere

Name: Oxygen
Symbol: O
Atomic Number: 8
Atomic Mass: 15.9994 amu
Melting Point: -218.4 ?C (54.750008 ?K, -361.12 ?F)
Boiling Point: -183.0 ?C (90.15 ?K, -297.4 ?F)
Number of Protons/Electrons: 8
Number of Neutrons: 8
Classification: Non-metal
Crystal Structure: Cubic
Density @ 293 K: 1.429 g/cm3
Color: colorless
Date of Discovery: 1774
Discoverer: Joseph Priestly
Name Origin: From the Greek words oxus (acid) and gennan (generate)
Uses: supports life

Name: Helium
Symbol: He
Atomic Number: 2
Atomic Mass: 4.002602 amu
Melting Point: -272.0 ?C (1.15 ?K, -457.6 ?F)
Boiling Point: -268.6 ?C (4.549994 ?K, -451.48 ?F)
Number of Protons/Electrons: 2
Number of Neutrons: 2
Classification: Noble Gas
Crystal Structure: Hexagonal
Density @ 293 K: 0.1785 g/cm3
Color: colorless
Date of Discovery: 1895
Discoverer: Sir William Ramsey
Name Origin: From the Greek word h?lios (sun)
Uses: balloons, deep sea diving
 
R

rogtwo@aol.com

Guest
In a message dated 1/31/04 5:08:20 AM Pacific Standard Time,
billiam@erols.com writes:
"...since Nitrogen IS a lighter gas than Oxygen...."

Yes, nitrogen is lighter, but NOT MUCH. For those of us here in the backward
US, the densities (dry, at standard temperature and pressure) are:

Air - 0.07651 lb/cu ft

Nitrogen - 0.075261 lb/cu ft

Thus, air is about 1.6% heavier. That's not much.

So how much weight of air do we actually have in our tires?

First, a quick measurement shows an Amphicar tire has a volume of somewhere
around 1 cubic foot.

Thus, if you take your spare tire, set it on the floor and remove its valve
stem core, the interior of the tire will drop to atmospheric pressure. In this
condition, the tire will have about 0.07651 pounds of air in it.*

Now, atmospheric pressure is usually taken as 14.7 psi (the actual pressure
is what we call "barometric" pressure and it varies with weather and altitude).
Anyway, if we now inflate the tire until our tire gage shows 14.7 psi, we
now have twice as much air in the tire as when it was "flat". Likewise, if you
inflate the tire to 29.4 psi, you will have 3 times the air in the tire as
when it was "flat".

So, lets assume we inflate all 5 tires to 29.4 psi (with air). The total
weight of air in the tires will be -- 5 X 3 X 0.07651 this equals 1.1 pounds!
Or, if compared to Nitrogen, air will weigh about 1/4 ounce more. Take a
quarter out of your pocket and toss it overboard -- this will save you the same
1/4
ounce of weight that using nitrogen instead of air will.

About heat transfer, here the difference will be even less. The only way the
wheel and tire can loose heat is outward into the atmosphere or to the
pavement. As the tire heats up, the air in the tire will heat up of course; but
the
only way the heat can escape the air in the tire is to go back out through
the tire or the rim. Now, even IF nitrogen did transfer heat better, it could
transfer a bit more of the heat of the tire to the inside of the rim, thus
cooling the tire a bit more. But, this effect will be small. On top of this,
as
previously noted, most of the atmosphere is nitrogen. Thus, heat transferred
by air or by nitrogen is going to be extremely close to the same. There will
be no measurable difference in the temperature of the tires if you change to
nitrogen. **

As was mentioned, nitrogen is used in airplane tires. This is to avoid
explosions when the tires get VERY hot (over 250 F -- Do your Amphi tires sizzle
and steam when you first hit the water? :) ). With the high pressures used
(over 150 psi), and the extreme heat that can occur on landing, the rubber
compounds in aircraft tires can actually spontaneously combust if there is too
much
oxygen in the tires. Your Amphicar is not going to have this problem!

Roger
White '63
Seattle

* Do not confuse the pressure of air in your tire with the weight of air in
your tire. People often say "I put 30 pounds of air in my tire." This is NOT
the weight of air you put in the tire. The "pounds" is short for "pounds per
square inch - psi, this is a pressure not a weight. As shown above, at 30
psi, an Amphi sized tire will have less than 1/4 pound (weight) of air in the
tire. If you don't believe this, then put your spare tire on a scale and let
the
air out to see how much lighter it gets.


** Higher tire pressures will decrease the running temperature of tires
significantly. Thus, the tire store you are referring to could lower your tire
temps by simply inflating the tires to a higher pressure when they switch to
nitrogen.


[Non-text portions of this message have been removed]
 
A

Al Heath

Guest
Doug querried:
>>What is your theory on bouyancy? Think I should take
>>amphi over and ask them if it will make the car float?
Bilgey added:
>>pure Nitrogen would be lighter, and hence more buoyant....But I mean, why
stop there? >>Why not pump up your rubber with Helium? It's almost TEN
times lighter and hence
>>more buoyant than atmospheric air

Hey Doug, I got a suggestion for you. Stop just off the end of the ramp
and just let the air outa your tires ... 4 tires and you could easily lose
60-80 pounds of air....just don't let water back in! Maybe you could
customize the rims like the Hummer's with inflator/deflators and onboard
air. <g> Come to think of it, up there where are there's a lot of cold,
dense air, perhaps you should relocate further south where there is more
hot air!

Al

[Non-text portions of this message have been removed]
 
R

rogtwo@aol.com

Guest
Here's some additional information

I found the conductivity of different gases in one of my reference books. It
lists the value for air and nitrogen as exactly the same (k = 0.0140 for
both).

Thus, nitrogen is not going to make your tires run cooler! The tire store is
probably just repeating what they were told, but they are not correct.

An interesting trend is that generally lighter gases conduct heat better.
For example helium has a k value of 0.0818. It conducts heat 5.8 times better
than air. If I remember correctly, the explanation for this is that lighter
gas molecules move faster than heavy ones, and thus transfer heat from one place
to another faster.

Before you decide that helium is just what you need in your tires, consider
that those fast little molecules also escape much faster. You can see this
with balloons. Latex balloons filled with helium go flat much faster than ones
filled with air. The helium literally leaks out through the latex material. I
don't know how fast it will leak out of tires, but if you use it, I'd keep an
eye on the pressure.

Roger
White '63
Seattle


[Non-text portions of this message have been removed]
 
N

nelson625@aol.com

Guest
Roger,

From your dissertation and statistics concerning the weights and heat
conductivity of ordinary air vs Nitrogen, you must be a scientist. In that case,
the following will certainly not be news to you. However, many of you other
web toed members might find it interesting to try the following yourselves. A
few years ago, I owned a full sized van and had occasion to be transporting a
couple of Helium filled party balloons which were riding against the ceiling in
the middle of the van (not over the front or back seats.) Though the
following is perfectly logical, I was not expecting it and was mildly surprised
until
I mulled the physics of it over a bit. When you are driving along at a
constant speed - at almost any speed you might choose, apply your brakes (it
need
not be a hard braking, just a normal stop.) I think most people would expect,
based on experience with anything else they might have ever had in the car such
as a bag of groceries or you name it, that the balloons would "naturally"
come forward - probably pretty rapidly if you brake at all hard. As science and
logic will show, upon braking, the balloons head toward the back of the van
as the air with which they are surrounded pushes forward, displacing the
lighter balloons. It is sort of a neat and easy demonstration of the fact that
the
air around us is indeed, though invisable, exerting an effect on the things it
surrounds, much the same as the lift created by the reduced pressure of the
air on top of an airplane's wing, even though we cannot see the air. When I
posed the subject to my brother who is a research scientist, he immediately said
the balloons would go rearwards while asking me "what would I expect?"
Vic "Splash" Nelson with the "Split Pesonality" near
Daytona.


[Non-text portions of this message have been removed]
 
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