HAHAHAHAHA! Great post^^^
Nitrogen Tire Fill
- Thread starter carguy996
- Start date
- Status
Originally Posted By: edhackett
Let's also take a quick look at the "doesn't expand with temperature" claim. All gasses behave according to the ideal gas law, pv=nRt. They expand when heated, and if the volume stays the same, the pressure will go up.
Now lets take a look at individual gas constants.
Nitrogen is 296.8 J/kg K
Oxygen is 259.8 J/kg K
Air is 286.9 J/kg K
Water vapor is 461.5 J/kg K
Oops. Physics says nitrogen actually expands more than air with a given temperature input.
Take a look at the value for water vapor. It's easy to see why dry nitrogen is better than un-dried air straight from a compressor. They used a water based lube to mount your tires, you say? Oops again.
Ed
It doesn't. R is a constant for each gas. If you do the pv=nRt math for each gas, you will see that they all change pressure the same amount for the same temperature change.
It does require a different amount of thermal energy to raise the temperatures of the gases, but the mass of the gas is so small compared to the tire and energy source that it doesn't make a difference you could detect with a tire gauge and a stop watch.
Let's also take a quick look at the "doesn't expand with temperature" claim. All gasses behave according to the ideal gas law, pv=nRt. They expand when heated, and if the volume stays the same, the pressure will go up.
Now lets take a look at individual gas constants.
Nitrogen is 296.8 J/kg K
Oxygen is 259.8 J/kg K
Air is 286.9 J/kg K
Water vapor is 461.5 J/kg K
Oops. Physics says nitrogen actually expands more than air with a given temperature input.
Take a look at the value for water vapor. It's easy to see why dry nitrogen is better than un-dried air straight from a compressor. They used a water based lube to mount your tires, you say? Oops again.
Ed
It doesn't. R is a constant for each gas. If you do the pv=nRt math for each gas, you will see that they all change pressure the same amount for the same temperature change.
It does require a different amount of thermal energy to raise the temperatures of the gases, but the mass of the gas is so small compared to the tire and energy source that it doesn't make a difference you could detect with a tire gauge and a stop watch.
That's precisely my point.
For any normal consumer there is no detectable benefit to Nitrogen fill over dry air.
For any normal consumer there is no detectable benefit to Nitrogen fill over dry air.
XS650, you are thinking of R as the universal gas constant describing a perfect gas. In that case they all do change at the same rate. That's how the equation was used in basic classes. In that case the R in pv=nRt should be more properly denoted as Ru or R with a bar over it.
The values for the gasses I posted are the value of R for that individual gas. If R is larger, any change in T must result in a larger value for p.
I checked my somewhat fuzzy recollection here:
http://www.engineeringtoolbox.com/ideal-gas-law-d_157.html
Take a look and see if I'm looking at it correctly. Wouldn't be the first time I've gotten something bassackwards.
Ed
The values for the gasses I posted are the value of R for that individual gas. If R is larger, any change in T must result in a larger value for p.
I checked my somewhat fuzzy recollection here:
http://www.engineeringtoolbox.com/ideal-gas-law-d_157.html
Take a look and see if I'm looking at it correctly. Wouldn't be the first time I've gotten something bassackwards.
Ed
Replying to my own post. I see that when using individual constants, n should be m. Old brains, old eyes, and computer screens don't mix.
Ed
Ed
Originally Posted By: edhackett
XS650, you are thinking of R as the universal gas constant describing a perfect gas. In that case they all do change at the same rate. That's how the equation was used in basic classes. In that case the R in pv=nRt should be more properly denoted as Ru or R with a bar over it.
The values for the gasses I posted are the value of R for that individual gas. If R is larger, any change in T must result in a larger value for p.
I checked my somewhat fuzzy recollection here:
http://www.engineeringtoolbox.com/ideal-gas-law-d_157.html
Take a look and see if I'm looking at it correctly. Wouldn't be the first time I've gotten something bassackwards.
Ed
starting with pv=mRt
The way I am looking at it, once a tire is filled, neither v, m, or R change for any individual gas in the tire. Since they are constants for the condition being evaluated (a reasonable change in temperature), v, m,and R can all be replaced by a single constant Cx for any of the gases.
p=Cxt Where Cx = Co (C sub Oxygen), Cn (C sub Nitrogen) or Cw (C sub water vapor)
In all cases, if Cx is a constant for that gas, absolute tire pressure is directly proportional to absolute gas temperature, no matter what mix of gasses.
Of course, if there is enough water vapor that there is a phase change going on with temperature change all bets are off.
XS650, you are thinking of R as the universal gas constant describing a perfect gas. In that case they all do change at the same rate. That's how the equation was used in basic classes. In that case the R in pv=nRt should be more properly denoted as Ru or R with a bar over it.
The values for the gasses I posted are the value of R for that individual gas. If R is larger, any change in T must result in a larger value for p.
I checked my somewhat fuzzy recollection here:
http://www.engineeringtoolbox.com/ideal-gas-law-d_157.html
Take a look and see if I'm looking at it correctly. Wouldn't be the first time I've gotten something bassackwards.
Ed
starting with pv=mRt
The way I am looking at it, once a tire is filled, neither v, m, or R change for any individual gas in the tire. Since they are constants for the condition being evaluated (a reasonable change in temperature), v, m,and R can all be replaced by a single constant Cx for any of the gases.
p=Cxt Where Cx = Co (C sub Oxygen), Cn (C sub Nitrogen) or Cw (C sub water vapor)
In all cases, if Cx is a constant for that gas, absolute tire pressure is directly proportional to absolute gas temperature, no matter what mix of gasses.
Of course, if there is enough water vapor that there is a phase change going on with temperature change all bets are off.
I think we should add N (nitrogen) to our banned topics list ....
No R,S,P,N allowed.
No R,S,P,N allowed.
Wow. I'm amazed at all the Nitrogen hate here. I don't use the stuff, and I wouldn't recommend it (though I wouldn't decline to use it either) for passenger cars. Nevertheless, there's a reason why the stuff is the only fill permitted for jet aircraft tires.
Now, obviously, the stresses that high-flying aircraft impose upon their tires (that in virtually all cases ride in unpressurized wheel wells) are much more than seen in passenger cars, but OTOH, aircraft tires only have to serve their purpose for a very brief period compared to automobile tires.
Sure, most of us car drivers don't need pure N2 fills. I suppose the REAL question is where are the boundaries between UNNECESSARY, GOOD TO HAVE, and ESSENTIAL TO HAVE. I think I can reliably assure everyone here that profit-seeking airlines, who won't give you half of a 12 oz can of Coke for free, aren't pumping their 7x7s or Airbus's tires up with expensive N2 just to satisfy the egos of their maintenance chiefs...
Now, obviously, the stresses that high-flying aircraft impose upon their tires (that in virtually all cases ride in unpressurized wheel wells) are much more than seen in passenger cars, but OTOH, aircraft tires only have to serve their purpose for a very brief period compared to automobile tires.
Sure, most of us car drivers don't need pure N2 fills. I suppose the REAL question is where are the boundaries between UNNECESSARY, GOOD TO HAVE, and ESSENTIAL TO HAVE. I think I can reliably assure everyone here that profit-seeking airlines, who won't give you half of a 12 oz can of Coke for free, aren't pumping their 7x7s or Airbus's tires up with expensive N2 just to satisfy the egos of their maintenance chiefs...
Kestas
Staff member
I wonder if the air in a tire can have so much moisture that it condenses at certain operating pressures and temperatures... maybe more so for aircraft. Considering the water used to lube a tire, that can amount to a significant amount of moisture. This can create a big imbalance issue, especially at freezing temperatures. I'd like someone to throw some thermodynamics at that issue.
Again, N2 is used in aircraft tires because the FAA requires the use of an inert gas to mitigate fires from overheated brakes. N2 is the cheapest option. It bestows no magical performance properties other than not supporting combustion. They could use radon if they wanted. Well, OK that one might raise some eyebrows.
Ed
Ed
Originally Posted By: ekpolk
Wow. I'm amazed at all the Nitrogen hate here. I don't use the stuff, and I wouldn't recommend it (though I wouldn't decline to use it either) for passenger cars. Nevertheless, there's a reason why the stuff is the only fill permitted for jet aircraft tires.
I hate the way "hate" is used to indicate "dislike".
I think I speak for several others here when I say my N2 stance here is aimed at the scams that sell it, not the N2 itself. I even fill my tires with 78% N2 mix, how much could I hate it? I like that stuff so much that I literally breath it every day.
No N2 hate here.
Wow. I'm amazed at all the Nitrogen hate here. I don't use the stuff, and I wouldn't recommend it (though I wouldn't decline to use it either) for passenger cars. Nevertheless, there's a reason why the stuff is the only fill permitted for jet aircraft tires.
I hate the way "hate" is used to indicate "dislike".
I think I speak for several others here when I say my N2 stance here is aimed at the scams that sell it, not the N2 itself. I even fill my tires with 78% N2 mix, how much could I hate it? I like that stuff so much that I literally breath it every day.
No N2 hate here.
Originally Posted By: Kestas
I wonder if the air in a tire can have so much moisture that it condenses at certain operating pressures and temperatures... maybe more so for aircraft. Considering the water used to lube a tire, that can amount to a significant amount of moisture. This can create a big imbalance issue, especially at freezing temperatures. I'd like someone to throw some thermodynamics at that issue.
If you fill your tires in a humid climate from a compressor without a tank, like a bicycle pump or a thankless compressor, you could get some condensation in your tires because it doesn't have place to go when it condenses like it does in a compressor with a tank.
Since you live in a place with humid summers and cold winters, out of balance tires in the winter due to ice in the tires would be a common problem if that were a real issue for cars.
That obviously doesn't answer your question about aircraft tires because they use higher pressures and see much more extreme temperature swings.
I wonder if the air in a tire can have so much moisture that it condenses at certain operating pressures and temperatures... maybe more so for aircraft. Considering the water used to lube a tire, that can amount to a significant amount of moisture. This can create a big imbalance issue, especially at freezing temperatures. I'd like someone to throw some thermodynamics at that issue.
If you fill your tires in a humid climate from a compressor without a tank, like a bicycle pump or a thankless compressor, you could get some condensation in your tires because it doesn't have place to go when it condenses like it does in a compressor with a tank.
Since you live in a place with humid summers and cold winters, out of balance tires in the winter due to ice in the tires would be a common problem if that were a real issue for cars.
That obviously doesn't answer your question about aircraft tires because they use higher pressures and see much more extreme temperature swings.
Originally Posted By: edhackett
Again, N2 is used in aircraft tires because the FAA requires the use of an inert gas to mitigate fires from overheated brakes. N2 is the cheapest option. It bestows no magical performance properties other than not supporting combustion. They could use radon if they wanted. Well, OK that one might raise some eyebrows.
Ed
Please notice that as I said in my last post, I'm not saying that any normal street driver needs N2 in his tires. If nothing else, the experience of about a bazillion drivers out there in the real world should put that question to rest. But that said, there are some advantages that, while largely theoretical/meaningless for grandma in her Buick, are nevertheless still there, and may, if one crosses certain performance thresholds, manifest themselves. For example, in addition to being purely inert (as in no O2 present), the N2, as supplied, should be nearly perfectly dry. That would mean no water to condense and freeze or to contribute to corrosion of metal parts.
Now, again, do any of us who drive street cars "need" pure N2 in our tires? Of course not. OTOH, reading this thread makes it sound as if using N2 (or even failing to vehemently object to its use) is the equivalent of drinking a beaker full of Ebola virus culture. It ain't that big of a deal...
Again, N2 is used in aircraft tires because the FAA requires the use of an inert gas to mitigate fires from overheated brakes. N2 is the cheapest option. It bestows no magical performance properties other than not supporting combustion. They could use radon if they wanted. Well, OK that one might raise some eyebrows.
Ed
Please notice that as I said in my last post, I'm not saying that any normal street driver needs N2 in his tires. If nothing else, the experience of about a bazillion drivers out there in the real world should put that question to rest. But that said, there are some advantages that, while largely theoretical/meaningless for grandma in her Buick, are nevertheless still there, and may, if one crosses certain performance thresholds, manifest themselves. For example, in addition to being purely inert (as in no O2 present), the N2, as supplied, should be nearly perfectly dry. That would mean no water to condense and freeze or to contribute to corrosion of metal parts.
Now, again, do any of us who drive street cars "need" pure N2 in our tires? Of course not. OTOH, reading this thread makes it sound as if using N2 (or even failing to vehemently object to its use) is the equivalent of drinking a beaker full of Ebola virus culture. It ain't that big of a deal...
Originally Posted By: XS650
Originally Posted By: ekpolk
Wow. I'm amazed at all the Nitrogen hate here. I don't use the stuff, and I wouldn't recommend it (though I wouldn't decline to use it either) for passenger cars. Nevertheless, there's a reason why the stuff is the only fill permitted for jet aircraft tires.
I hate the way "hate" is used to indicate "dislike".
I think I speak for several others here when I say my N2 stance here is aimed at the scams that sell it, not the N2 itself. I even fill my tires with 78% N2 mix, how much could I hate it? I like that stuff so much that I literally breath it every day.
No N2 hate here.
Oh, you know what I mean. . .
Originally Posted By: ekpolk
Wow. I'm amazed at all the Nitrogen hate here. I don't use the stuff, and I wouldn't recommend it (though I wouldn't decline to use it either) for passenger cars. Nevertheless, there's a reason why the stuff is the only fill permitted for jet aircraft tires.
I hate the way "hate" is used to indicate "dislike".
I think I speak for several others here when I say my N2 stance here is aimed at the scams that sell it, not the N2 itself. I even fill my tires with 78% N2 mix, how much could I hate it? I like that stuff so much that I literally breath it every day.
No N2 hate here.
Oh, you know what I mean. . .
Originally Posted By: Kestas
I wonder if the air in a tire can have so much moisture that it condenses at certain operating pressures and temperatures... maybe more so for aircraft. Considering the water used to lube a tire, that can amount to a significant amount of moisture. This can create a big imbalance issue, especially at freezing temperatures. I'd like someone to throw some thermodynamics at that issue.
We had a crack at that here.
http://www.bobistheoilguy.com/forums/ubb...rue#Post1821475
I wonder if the air in a tire can have so much moisture that it condenses at certain operating pressures and temperatures... maybe more so for aircraft. Considering the water used to lube a tire, that can amount to a significant amount of moisture. This can create a big imbalance issue, especially at freezing temperatures. I'd like someone to throw some thermodynamics at that issue.
We had a crack at that here.
http://www.bobistheoilguy.com/forums/ubb...rue#Post1821475
Kestas
Staff member
Shannow, thanks for the link. Most of the discussion addresses what happens with water vapor and elevated temperatures. Living in a northern clime, my curiosity is with the effect of water vapor during ambient winter conditions. Let's say a tire is mounted during a hot humid day with water lube, then pumped to 35 psi. What happens to the air charge when the tire is chilled to 0°F (or less)?
More importantly, what would happen to aircraft tires under the same conditions, pumped to 300 psi, then chilled to -60°F? The answer may explain why dry nitrogen is a must for aircraft application, but not so critical for automotive use.
I'm too lazy to dig out my college thermodynamics books. I tried it once and couldn't find what I needed. I'm hoping a recent student can hash through this.
More importantly, what would happen to aircraft tires under the same conditions, pumped to 300 psi, then chilled to -60°F? The answer may explain why dry nitrogen is a must for aircraft application, but not so critical for automotive use.
I'm too lazy to dig out my college thermodynamics books. I tried it once and couldn't find what I needed. I'm hoping a recent student can hash through this.
Kestas, from what I've seen of recent students the last few years, you'll have to trust a 20 year out hack to find a few spare minutes.
That's one that hasn't crossed my mind, as even at -7C, my pipes freeze, but never considered my tyres.
That's one that hasn't crossed my mind, as even at -7C, my pipes freeze, but never considered my tyres.
This is an old racers trick. I do this with all my vehicles purely from a convenience perspective. In my experience, Nitrogen will not give you better mileage etc however I only lose around 1PSI per year when the tyres are filled with Nitrogen. This means that I can forego the weekly tyre pressure check. My tyre dealer will check and fill the tyres at my request so for around A$40, this is a no brainer as far as I'm concerned as I am cash rich and time poor.
This is one of the reasons why we 'Nitro-Haters' get excited!
There is no way that pure nitrogen will leak out any differently than 'plain' air!
And I am still laughing at XS650's saying: "I even fill my tires with 78% N2 mix, how much could I hate it? I like that stuff so much that I literally breath it every day."
Priceless thread.
There is no way that pure nitrogen will leak out any differently than 'plain' air!
And I am still laughing at XS650's saying: "I even fill my tires with 78% N2 mix, how much could I hate it? I like that stuff so much that I literally breath it every day."
Priceless thread.
- Status