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| Re: [GMCnet] Tire size and blowputs [message #96724 is a reply to message #96694] |
Sat, 21 August 2010 18:52   |
Dave Mumert
Messages: 272
Registered: February 2004
Location: Olds, AB, Canada
Karma: 0
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Hi All
If you want to slow down the leaks with a larger molecule maybe one should
try argon (.98pM) or krypton (1.12pM) instead of the puny nitrogen molecule
(.75pM).
Argon is readily available. When I looked after scoreboards we specified
the bulbs use krypton fill, of course now they use LEDs instead of
incandescent bulbs.
Dave
> Molecular size a bit tricky. As a quick comparison, one can use the
covalent
> radius defined as 1/2 the distance between two identical covalently
bonding
> nuclei. This is measured in picometers (1 pm= 1x 10-12 m). Nitrogen's
> covalent radius is 75pm so the length of a nitrogen (N2) molecule ought to
be
> 4 X 75pm or 300 pm. A molecule of oxygen (O2) ought to be just a shade
> smaller 4 X 73pm or 292pm. So an oxygen molecule is a little less than 3%
> smaller than a nitrogen molecule.
>
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| Re: [GMCnet] Tire size and blowputs [message #96731 is a reply to message #96694] |
Sat, 21 August 2010 20:42 |
John Sharpe
Messages: 489
Registered: February 2006
Location: Texas
Karma: 1
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| Quote: |
Emery wrote:....Molecular size a bit tricky. As a quick comparison, one can use the covalent radius defined as 1/2 the distance between two identical covalently bonding nuclei. This is measured in picometers (1 pm= 1x 10-12 m). Nitrogen's covalent radius is 75pm so the length of a nitrogen (N2) molecule ought to be 4 X 75pm or 300 pm. A molecule of oxygen (O2) ought to be just a shade smaller 4 X 73pm or 292pm. So an oxygen molecule is a little less than 3% smaller than a nitrogen molecule.
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I've been telling my wife this for years. She just gives me a look and says, 'I knew that'.
John Sharpe
Humble,TX
'78 Eleganza TBI
'89 Spectrum 2000 MPI V-10
'40 Ford Panel Delivery TPI
johnasharpe@gmail.com
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| Re: [GMCnet] Tire size and blowputs [message #96833 is a reply to message #96683] |
Sun, 22 August 2010 16:52 |
kingd
Messages: 592
Registered: June 2004
Karma: 2
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Senior Member |
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Regarding Nitrogen in tires. As Emery says, anyone who says it's better because the nitrogen molecule is bigger is splitting hairs. 3% geesh, I bet most peoples tires that haven't been checked in a month aren't with-in 3% of the pressure they think they are. However, there may be some advantages to Nitrogen(remeber ordinary air is approx 78% Nitrogen already.) If the Nitrogen comes from a compressed gas cylinder there is probably very little water/vapour in it. I am lead to believe that the water vapour ups the pressure in a HOT tire when used in competition(tread temperatures of 200 Degrees F)
I think the current push in Nitrogen filling is it's another thing to sell you.
DAVE KING
DAVE KING
lurker, wannabe
Toronto, Ontario, Canada
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| Re: [GMCnet] Tire size and blowputs [message #124659 is a reply to message #96683] |
Thu, 05 May 2011 08:55 |
Gary Casey
Messages: 448
Registered: September 2009
Karma: 0
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Senior Member |
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The nitrogen vs. air in tires has been discussed many times before. However, I
am surprised (I take that back, maybe not so surprised) that a rag like Popular
Mechanics would publish so much folklore and misleading information. First, any
gas, whether nitrogen, oxygen or water vapor will change pressure in exactly the
same way when the temperature changes. At these pressures, the Perfect Gas Law
is, well, nearly perfect. As for migration through the rubber, that is a
function of molecular weight. Oxygen has a molecular weight of 32 and nitrogen
28. Therefore, using their theory nitrogen is MORE likely to permeate through
the rubber than oxygen. Interestingly, water vapor has a molecular weight of
18, just a bit more than half the other constituents: Therefore, it could
indeed permeate through the rubber and cause a loss of pressure. Certainly,
their argument that a combination of water and oxygen will promote corrosion is
true and that is a big reason to get rid of the water vapor. Another thing -
saturated water vapor (vapor with some liquid present) will change pressure with
changes in temperature, as more of the liquid water will evaporate, but that
effect isn't large. I haven't run the numbers, but I would guess it would be
less than 1 psi.
Conclusion? Filling with nitrogen is better than with air - especially humid
air - but not enough to go out of your way to do it. Certainly not worth
anything close to the $30 someone reported.
Gary Casey
Here's a pretty good read on nitrogen versus air in tires for anyone
interested.
http://www.popularmechanics.com/cars/how-to/repair-questions/4302788
Gord :)
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| Re: [GMCnet] Tire size and blowputs [message #124668 is a reply to message #124659] |
Thu, 05 May 2011 09:32 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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Sorry, Gary, but your theory that migration through rubber is a
function of molecular WEIGHT is incorrect. It is actually a function
of molecular SIZE.
You point out that oxygen has a molecular weight of 32 and nitrogen is
28.
However nitrogen gas has a larger molecular size than oxygen gas so it
will permeate through rubber less than oxygen.
I will do a quick search on the Internet to find a better explanation
than I could write myself and post it later.
Emery Stora
On May 5, 2011, at 7:55 AM, Gary Casey <casey.gary@yahoo.com> wrote:
> The nitrogen vs. air in tires has been discussed many times before.
> However, I
> am surprised (I take that back, maybe not so surprised) that a rag
> like Popular
> Mechanics would publish so much folklore and misleading
> information. First, any
> gas, whether nitrogen, oxygen or water vapor will change pressure in
> exactly the
> same way when the temperature changes. At these pressures, the
> Perfect Gas Law
> is, well, nearly perfect. As for migration through the rubber, that
> is a
> function of molecular weight. Oxygen has a molecular weight of 32
> and nitrogen
> 28. Therefore, using their theory nitrogen is MORE likely to
> permeate through
> the rubber than oxygen. Interestingly, water vapor has a molecular
> weight of
> 18, just a bit more than half the other constituents: Therefore, it
> could
> indeed permeate through the rubber and cause a loss of pressure.
> Certainly,
> their argument that a combination of water and oxygen will promote
> corrosion is
> true and that is a big reason to get rid of the water vapor.
> Another thing -
> saturated water vapor (vapor with some liquid present) will change
> pressure with
> changes in temperature, as more of the liquid water will evaporate,
> but that
> effect isn't large. I haven't run the numbers, but I would guess it
> would be
> less than 1 psi.
>
> Conclusion? Filling with nitrogen is better than with air -
> especially humid
> air - but not enough to go out of your way to do it. Certainly not
> worth
> anything close to the $30 someone reported.
>
> Gary Casey
>
>
> Here's a pretty good read on nitrogen versus air in tires for anyone
> interested.
>
> http://www.popularmechanics.com/cars/how-to/repair-questions/4302788
>
> Gord :)
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> GMCnet mailing list
> Unsubscribe or Change List Options:
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| Re: [GMCnet] Tire size and blowputs [message #124677 is a reply to message #124668] |
Thu, 05 May 2011 10:24 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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Here is one site I found that discusses molecular size vs molecular
weight and even has a reference to rubber permeability.
http://www.getnitrogen.org/pdf/graham.pdf
Emery Stora
On May 5, 2011, at 8:32 AM, Emery Stora <emerystora@mac.com> wrote:
> Sorry, Gary, but your theory that migration through rubber is a
> function of molecular WEIGHT is incorrect. It is actually a function
> of molecular SIZE.
>
> You point out that oxygen has a molecular weight of 32 and nitrogen is
> 28.
>
> However nitrogen gas has a larger molecular size than oxygen gas so it
> will permeate through rubber less than oxygen.
>
> I will do a quick search on the Internet to find a better explanation
> than I could write myself and post it later.
>
> Emery Stora
>
> On May 5, 2011, at 7:55 AM, Gary Casey <casey.gary@yahoo.com> wrote:
>
>> The nitrogen vs. air in tires has been discussed many times before.
>> However, I
>> am surprised (I take that back, maybe not so surprised) that a rag
>> like Popular
>> Mechanics would publish so much folklore and misleading
>> information. First, any
>> gas, whether nitrogen, oxygen or water vapor will change pressure in
>> exactly the
>> same way when the temperature changes. At these pressures, the
>> Perfect Gas Law
>> is, well, nearly perfect. As for migration through the rubber, that
>> is a
>> function of molecular weight. Oxygen has a molecular weight of 32
>> and nitrogen
>> 28. Therefore, using their theory nitrogen is MORE likely to
>> permeate through
>> the rubber than oxygen. Interestingly, water vapor has a molecular
>> weight of
>> 18, just a bit more than half the other constituents: Therefore, it
>> could
>> indeed permeate through the rubber and cause a loss of pressure.
>> Certainly,
>> their argument that a combination of water and oxygen will promote
>> corrosion is
>> true and that is a big reason to get rid of the water vapor.
>> Another thing -
>> saturated water vapor (vapor with some liquid present) will change
>> pressure with
>> changes in temperature, as more of the liquid water will evaporate,
>> but that
>> effect isn't large. I haven't run the numbers, but I would guess it
>> would be
>> less than 1 psi.
>>
>> Conclusion? Filling with nitrogen is better than with air -
>> especially humid
>> air - but not enough to go out of your way to do it. Certainly not
>> worth
>> anything close to the $30 someone reported.
>>
>> Gary Casey
>>
>>
>> Here's a pretty good read on nitrogen versus air in tires for anyone
>> interested.
>>
>> http://www.popularmechanics.com/cars/how-to/repair-questions/4302788
>>
>> Gord :)
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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