More noise from your Z06 and Nitrogen Tires

[Peter L.]

Re: Is it Physics or Chemistry or some of both?

Fun discussion, but I think Clem's comment is most appropriate.

The other problem is we get to work with equations and theories that are called "Ideal Gas Laws" that apply to "Ideal Gases" and the major components of air, i.e. nitrogen, oxygen, plus lesser amounts of water vapor or more lesser amounts of water vapor depending on where you live and even lesser amounts of "inert" gases are NOT "Ideal Gases."

So, like most other things we just have to deal with the reality of the situation(s) as presented in the real world we live in.

Pete

[Duke W.]

Re: Questions about physics

Yes, if the temperature drops below the dew point, then Boyle's law won't yield an accurate pressure prediction because some of the gas has turned into liquid increasing the specific volume (which is the same as reducing density) of the gas. Actual pressure will be lower than predicted by Boyles law, but not by much.

Water will condense to liquid once the vapor pressure drops below the saturation partial pressure for water vapor at the particular temperature, which is the 100 percent relative humidity point. If the tire is at 70F and the dew point of its contained air is 45F and the car sits out overnight with the temperature dropping to 35F, then there will likely be condensation, and the cold tire pressure will be slightly less than predicted by Boyle's Law though it's arguable if the difference could be measured with a typical pencil type tire gage.

Then if the car is driven in the morning, the tire will heat up from use, and once the air in the tire goes above 45F for any length of time the water will evaporate and Boyle's law will again apply, because the water vapor acts as an ideal gas just as the other components of the air.

Liquid water will evaporate as long as its vapor pressure is greater than the water vapor saturation pressure of the surrounding air. An example is wet streets following a rain shower. If the air mass that follows the rain shower is relatively dry, the water on the streets will quickly evaporate. If the rain is followed by fog (near 100 percent relative humidity) the streets will remain wet until the relative humidity decreases.

Water evaporates at any temperature above freezing. Boiling just means that the vapor pressure of the liquid is equal to the surrounding ambient pressure, so gas bubbles form in the liquid and vaporization is much quicker. If water didn't evaporate until the boiling temperature, then the streets would be forever wet. The key is to understand the vapor pressure-temperature function and the concept of water vapor saturation of air.

Using dry nitrogen will prevent any water condensation since dry nitrogen contains virtually no water vapor, but you can achieve the same result by watching the weather and having a decent water trap on your air compessor.

Duke

[Joseph T.]

That deserves a WOW! *NM*

[Duke W.]

Re: That deserves a WOW!

Well, not really. It's 200 year old science that I learned in high school chemistry class over 40 years ago. My freshman chemistry classes as an engineering undergrad were essentially the same course, so I got "A" grades, and the knowledge was reinforced. I still have Linus Pauling's "College Chemistry" textbook in my library and probably refer to it a few times a year for either data or explanations, but I didn't need it for this discussion.

Understanding basic science helps one understand "how stuff works" and allows one to blow holes in all the marketing hype and junk science that saturates our culture.

Duke

[Clem Z.]

with the tire pressure indicators on the C-5s and

C-6s you can see the pressure difference in the tires on the sun side of the corvette vs the shade side while driving down the road. sometimes as much a 3 PSI

[Patrick H.]

Re: That deserves a WOW!

The real kicker is that you didn't have to look it up.
I haven't looked at it in 18 years, and I'd guarantee you I'd have to look it up even though I was a chemistry major.

Patrick

[Duke W.]

Re: That deserves a WOW!

That reminds me that since physicians and dentists take a lot more chemistry than I did (I managed to avoid organic chemistry), I always ask them how "carboxylate technology" (organic acid) can provide corrosion protection for engine cooling systems. Dexcool uses this organic technology to provide corrosion protection, and about all I know is that aspirin is a carboxylate.

So far no physicians or dentists that I have talked to have even the remotest clue how it works.

Corrosion control remains a very esoteric subject.

Duke

[Duke W.]

Re: with the tire pressure indicators on the C-5s

Back in 1989 when the Silver State Classic Challenge was delayed due to a fatal crash I observed a 911 driver bleeding air out of the sunny side tires as we approached a restart after a couple of hour delay. Their pressure increased relative to the shady side from the mid-morning sun.

I recommended that he not bleed air because it was due to solar heating and after he got on course and sun was higher, the side to side pressure would tend to equalize. He didn't listen.

After the race he complained that his car handled "squirrely". I reminded him of our brief prerace discussion, and I think he finally got it.

Duke

[Duke W.]

Re: Is it Physics or Chemistry or some of both?

It's always been my understanding that within the limits of the temperatures and pressures that we are working with in this example (and most terrestrial or man made fluid systems) that Boyle's Law is a very good approximation - within a fraction of a percent.

It's not until we get into plasmas (very high temperature gases that shed their electons for those not familiar with the term, but plasmas don't typically exist in the terrestrial environment except the laboratory) that Boyle's Law breaks down as a good approximation.

Did I miss something in chemistry class forty years ago?

Duke

[Jack H.]

Does Avagadro turn in his grave...

when Boyle's Law is stated neglecting the mole factor?

PV=RT is the common expression, but

PV=nRT is correct comprehending the number of moles of ideal gas at work

For closed systems, 'n' can be ignored. But, without it Mr. Avagadro would never have been able to calculate his well known constant that 'excited' so many of us back in the days when one hand ran the slide rule while the other hand tracked orders of magnitude for the correct position of the decimal point in the resulting solution...

[Patrick H.]

Re: That deserves a WOW!

I'd bet that I could give it a reasonably close guess. I do know someone, though, who could tell me. He was on the DexCool team.

I didn't mind organic at all once I figured out a few of its secrets. I absolutely hated Physical Chemistry, though. The fact that there was only one particular prof and I didn't ever understand him didn't help.

Patrick

[Duke W.]

Re: Does Avagadro turn in his grave...

That's why I expressed Boyle's law as Pv = RT, where the lower case "v" represents specific volume. I actually prefer working with Boyle's Law in the form P =(rho)RT, rho being the lower case Greek letter used to represent density.

I'm not sure what Avagandro would think of this "new math", but he might damn it 6.023E23 times.

Duke

[Duke W.]

Re: That deserves a WOW!

As an engineering undergrad, not only did I avoid organic, but P-chem, too, and I recall guys whinning about both!

If you can get to it, I'd like to hear what the Dexcool team guy has to say about how it works.

Duke

[Patrick H.]

Re: That deserves a WOW!

I'll e-mail you his name, address and phone number. He's retired from GM, now runs his own shop. We discussed DexCool very briefly at the 2004 Windsor convention.

Patrick

[Mark K.]

Re: Is it Physics or Chemistry or some of both?

quote: It's not until we get into plasmas (very high temperature gases that shed their electons for those not familiar with the term, but plasmas don't typically exist in the terrestrial environment except the laboratory) that Boyle's Law breaks down as a good approximation.

Depends on your definition of a "good approximation. Boyle's Law actually breaks down for much significant measure far earlier that at temperatures that cause events that quantum theory is necessary to explain. Because Boyle’s law assumes the gasses are ideal gasses and thus point masses, the interaction between molecules is assumed at (or near) zero. But molecules do have volume and at higher pressures act as “real” gasses. To calculate the deviation from ideal, physical chemists use the van der Waals equation which includes empirically derived constants for compressability.

But I guess for the purposes of this discussion, Boyle’s law can work and thus could be considered a “good approximation”.