Math question, thermal dynamics
Le Mans Master
Joined: Mar 2004
Posts: 7,454
Likes: 1,479
From: Little Rock AR
P1 / T1 = P2 / T2
The pressure and temperature should be in absolute units.
The Volume will be assumed to be constant for convienience.
If you know P1, T1, and T2 then just do the math and get P2.
42.7 PSIA / 480 degrees Rankine = x PSIA / 530 degrees Rankine
SO... I get x=47.15 PSIA so we subtract 14.7 PSI to get to 32.5 PSIG
-Mark.
The pressure and temperature should be in absolute units.
The Volume will be assumed to be constant for convienience.
If you know P1, T1, and T2 then just do the math and get P2.
42.7 PSIA / 480 degrees Rankine = x PSIA / 530 degrees Rankine
SO... I get x=47.15 PSIA so we subtract 14.7 PSI to get to 32.5 PSIG
-Mark.
Le Mans Master
Joined: Oct 2000
Posts: 8,897
Likes: 1,353
From: Santa Ana CA
I think that tire places hype nitrogen and say it doesn't change pressure as much as air is due to the water vapor in the air they pump. When water flashes to steam, it expands 1,800 times. Thing is, there really shouldn't be any water vapor in their air.
Melting Slicks
Joined: May 2006
Posts: 3,438
Likes: 41
From: Raleigh NC
St. Jude Donor '13-'14
Except for the compressibility factor, which you happened to leave out. Unfortunately, I don't have DIPPR on this computer, so I can't look that up for you.
The amount of water that would be in any normal compressor is so minimal, I doubt you would notice.
And unless it is a record temperature day outside (ooh somewhere around 212°F) I wouldn't expect that flashing (except maybe at the outlet nozzle briefly before condensing again).
So don't fill your tires with water people!!! Global warming could lead to your tires exploding! (I hope I just opened a whole new can of worms
)
And unless it is a record temperature day outside (ooh somewhere around 212°F) I wouldn't expect that flashing (except maybe at the outlet nozzle briefly before condensing again).
So don't fill your tires with water people!!! Global warming could lead to your tires exploding! (I hope I just opened a whole new can of worms
)
Thread Starter
Safety Car
Joined: Feb 2006
Posts: 4,855
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From: Columbia South Carolina
Le Mans Master
Joined: Oct 2000
Posts: 8,897
Likes: 1,353
From: Santa Ana CA
Except for the compressibility factor, which you happened to leave out. Unfortunately, I don't have DIPPR on this computer, so I can't look that up for you.
The amount of water that would be in any normal compressor is so minimal, I doubt you would notice.
And unless it is a record temperature day outside (ooh somewhere around 212°F) I wouldn't expect that flashing (except maybe at the outlet nozzle briefly before condensing again).
So don't fill your tires with water people!!! Global warming could lead to your tires exploding! (I hope I just opened a whole new can of worms)
The amount of water that would be in any normal compressor is so minimal, I doubt you would notice.
And unless it is a record temperature day outside (ooh somewhere around 212°F) I wouldn't expect that flashing (except maybe at the outlet nozzle briefly before condensing again).
So don't fill your tires with water people!!! Global warming could lead to your tires exploding! (I hope I just opened a whole new can of worms
)No compressability factor in the ideal gas constant.
Recognize that as a tire, or anything heats up, it does not heat up perfectly evenly and the temperature represents an average fo the molecules. But some molecules are hotter while others are colder.
When a tire spins and builds up heat, it is certainly conceivable that some of the molecules could reach 212 degrees F and flash to steam if water vapor is present. And I've seen plenty of air compressors give a nice wet shot of air.
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Melting Slicks
Joined: May 2006
Posts: 3,438
Likes: 41
From: Raleigh NC
St. Jude Donor '13-'14
No compressability factor in the ideal gas constant.
Recognize that as a tire, or anything heats up, it does not heat up perfectly evenly and the temperature represents an average fo the molecules. But some molecules are hotter while others are colder.
When a tire spins and builds up heat, it is certainly conceivable that some of the molecules could reach 212 degrees F and flash to steam if water vapor is present. And I've seen plenty of air compressors give a nice wet shot of air.
Recognize that as a tire, or anything heats up, it does not heat up perfectly evenly and the temperature represents an average fo the molecules. But some molecules are hotter while others are colder.
When a tire spins and builds up heat, it is certainly conceivable that some of the molecules could reach 212 degrees F and flash to steam if water vapor is present. And I've seen plenty of air compressors give a nice wet shot of air.
First we were talking about water in a compressor flashing on discharge, now we're talking about spinning tires? So we've gone from a temperature change from morning to afternoon, to tempertaure change from somebody spinning their tires. So they have to spin the tires long enough that it heats up the inside (you got heat transfer through 1/2" of rubber) of the tire to ~275°F because your tire is under pressure to vaporize the small amount of water thats might be in there?
This is rediculous. This is blown out of proportion, and I know I'm not helping, but I can't.... seem.... to... stop...!!!
Last edited by LeMans Pete; Dec 3, 2008 at 11:00 PM.
Racer
Joined: Jan 2008
Posts: 338
Likes: 0
I think what he meant was the tire heats up as it flexes... like when you drive at very high speeds and pull over, reach down, and feel a hot tire... I just don't know if that would get up too over 212, which it would need to. At 30 psi (~ 2x ATM), phase change from liquid to steam happens at 250 deg F... (according to my trusty steam tables) Do tires get that hot?
Team Owner
Joined: Jul 2008
Posts: 23,419
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From: In limbo
St. Jude Donor '13-'15, '17 thru '22
If I am going to drink a relatively light domestic beer, like a regular budweiser, I like it best around 29-30 degrees farenheit, almost freezing. But, if I was going to go with something like a Sam Adams or Brooklyn Lager, I would be more interested in 42-45 degrees. I think this may have something to do with the compressability of the water vapor in my tires, but I am not sure.
Melting Slicks
Joined: May 2006
Posts: 3,438
Likes: 41
From: Raleigh NC
St. Jude Donor '13-'14
I think what he meant was the tire heats up as it flexes... like when you drive at very high speeds and pull over, reach down, and feel a hot tire... I just don't know if that would get up too over 212, which it would need to. At 30 psi (~ 2x ATM), phase change from liquid to steam happens at 250 deg F... (according to my trusty steam tables) Do tires get that hot?
Also, are we talking 30 psig or 30 psia? I would assume guage since that is what you'll be measuring, meaning you'll be closer to 275°F (http://www.spiraxsarco.com/esc/SS_Properties.aspx).
Le Mans Master
Joined: Mar 2004
Posts: 7,454
Likes: 1,479
From: Little Rock AR
So we're talking about normal driving, that tires are going to heat up to 200+°F? Unless you're doing burnouts, your tires should never reach that temperature.
Also, are we talking 30 psig or 30 psia? I would assume guage since that is what you'll be measuring, meaning you'll be closer to 275°F (http://www.spiraxsarco.com/esc/SS_Properties.aspx).
Also, are we talking 30 psig or 30 psia? I would assume guage since that is what you'll be measuring, meaning you'll be closer to 275°F (http://www.spiraxsarco.com/esc/SS_Properties.aspx).
That was confusing. The qualifier was the "2x ATM". Standard ATM is 14.7 PSIA. 2x ATM is about 30 PSIA but that is only 14.7 PSIG. 
Burn outs are much harder with only 15 PSIG in the tires. Not that I actualy DO burnouts. -Mark.
Team Owner
Joined: Jul 1999
Posts: 26,545
Likes: 46
From: Huntersville NC
I use a special patented blend of gases in my tires to achieve the ultimate in performance.
Start with 78.1% Nitrogen, blend in 20.9% oxygen, and top it off with .9% Argon for
stability and a smidge (.1%) carbon dioxide and some traces of other rare gases.
I can send you a tube if you like.
Start with 78.1% Nitrogen, blend in 20.9% oxygen, and top it off with .9% Argon for
stability and a smidge (.1%) carbon dioxide and some traces of other rare gases.
I can send you a tube if you like.
Melting Slicks
Joined: May 2006
Posts: 3,438
Likes: 41
From: Raleigh NC
St. Jude Donor '13-'14
I use a special patented blend of gases in my tires to achieve the ultimate in performance.
Start with 78.1% Nitrogen, blend in 20.9% oxygen, and top it off with .9% Argon for
stability and a smidge (.1%) carbon dioxide and some traces of other rare gases.
I can send you a tube if you like.
Start with 78.1% Nitrogen, blend in 20.9% oxygen, and top it off with .9% Argon for
stability and a smidge (.1%) carbon dioxide and some traces of other rare gases.
I can send you a tube if you like.
