Nitrogen in Car tyres

[Dave Baker]

WHOOOOOOSH.

[Halmyre]

I always insist on hydrogen filled tyres. The reduction in weight does wonders for my fuel consumption, but it makes the handling a bit tricky.

-- Halmyre

[Adrian]

"Dave Baker" gurgled happily, sounding much like they were saying:

'ere, Dave. I think you've just picked a nail up in that tyre.

[Dinky Earnshaw]

Actually, it's not. It's largely extracted from fossil fuel natural gas.

[Fred]

I thought that once but I'm not so sure now. I found this on a balloon web site. Searching in google, the same text appears on a number of balloon web sites so they must all be copying from the same source. How correct that source is, I don't know. It says that helium is so light that once in the atmosphere it keeps rising and rising and escapes into space, and is lost from earth forever. It continues to say that most helium is obtained from the radioactive decay of uranium.

"If you put helium in a balloon and let go of the balloon, the balloon rises until it pops. When it pops, the helium that escapes has no reason to stop -- it just keeps going and leaks out into space. Therefore, in the atmosphere there is very little helium at any given time. The helium that is there comes from alpha particles emitted by radioactive decay..."

If helium is running out, I wonder how long before balloons are outlawed? It's surprising that the balloon companies are so open and honest about all this.

HTH

[Huge]

[Andy Dingley]

No, helium is stored in pork barrels.

It's an important story at present and yes, we're facing problems.

Helium is produced by radioactive decay in deep rocks. Then it mostly escapes into space (slowly). However some geological structures, the same salt domes that capture oil and gas, can trap it. So helium in industrial quantities comes from a few oil and gas wells. In the

1920s, the USA was expanding both oil drilling and airship use, so they saw a mutual benefit. Helium extracted in Texas was no longer vented as waste, but was stored back underground as a Federal reserve.

A few years ago, the US decided to sell this reserve off very cheaply (as a freebie to friends and family) meaning that helium is unrealistically cheap at present and we're starting to see the bottom of the barrel. At which point, superconductors will start becoming very expensive and non-hydrogen airships thoroughly impractical.

[Andrew Gabriel]

Helium released into the air is very quickly lost from the atmosphere out into space forever, so it can't be recovered from there. What's there is just in the process of leaking out through the earth's crust on its way into space. We were using some mixed helium and natural gas pockets which had got trapped in the crust (in Texas, I think), but they're just about empty. There is a tiny amount which comes up in some other oil and gas wells, which was passing through these reserves on its way up through the crust. It's a by-product of nuclear decay reactions deeper in the earth.

I did make enough hydroden to fill a balloon by electrolysis once, but look where that got the Hindenburg.

[Jules Richardson]

The balloon fetishists are just looking for an excuse to turn the planet into one giant balloon so we can go drifting off around the solar system. Feckin' nutters, they are.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Halmyre saying something like:

Oh, the humanity...

You should use some Helium before it all goes away.

[Dave Liquorice]

It's not as simple as just the pressure differential across the tyre. If you have a two containers with different concentrations seperated by something permiable the contents will even themselves out to equal concentrations each side. Have a dig about for osmosis.

[Reentrant]

It would have been the end of James Bond in "A View to a Kill".

[Dave]

What? And re inflate them every morning?

Dave

[Chris Hogg]

Apart from the point raised elsewhere in this thread as to how nitrogen, 'in a mixture with oxygen', differs from significantly from air, I am at a loss to understand how oxygen is supposed to _infuse_ into a car tyre from the atmosphere against the obvious pressure gradient, or why that should cause the tyre to slowly deflate, or why filling the tyre with air enriched with nitrogen should prevent it from happening, even assuming it does in the first place!

Graham's law of effusion is relevant here. See

's_law . (For the purposes of this situation, effusion can be approximately equated with diffusion).

Graham's law says that the ratio of the rates of diffusion for two gases of differing molecular weights is inversely proportional to the square root of the ratio of those molecular weights. For nitrogen and oxygen, with molecular weights of 28 and 32 respectively, the ratio of their diffusion rates is 1.069, which means that nitrogen diffuses

1.069 times faster than oxygen (say 7%). Lighter gases always diffuse faster than heavier gases, which is why party balloons filled with helium go flat faster than those filled with air.

OK, so the situation is made marginally more complicated by the fact that the partial pressure of nitrogen in air is four times that of oxygen, but that only serves to exaggerate the difference. A tyre filled with nitrogen should lose pressure by diffusion _out_ through the tyre wall faster than one filled with air, or one filled with oxygen, for that matter. Perhaps they're using the wrong gas!

On a purely practical point and irrespective of theory, if nitrogen and oxygen did, by some mechanism other than diffusion, pass through rubber at significantly different rates, it would provide a very convenient way of separating and thus concentrating them. Which, AFAIK, isn't the case.

The Kwikfit claim would seem to be complete and utter rubbish. It would be interesting to see what Trading Standards had to say on the matter.

[Dave]

I also wonder if he was ever told not to approach a wheel from the side, in case it exploded. In the event of a heavy landing, the brakes could be so hot as to cause the bolted together wheels to explode and kill you.

Dave

[Andy Champ]

Now I've fixed my computer (which is why I'm late to the party) let me add my vote in favour of the BS thesis.

If oxygen really did go through the tyre faster than nitrogen wouldn't it naturally concentrate inside anyway?

Andy

[Chris J Dixon]

I enquired where the evidence was for the information on their web site. They simply directed me to:

[Dave Baker]

people making the claims can't even spell or proof read their own site properly. From the "Nitrogen Tyre Infation" cockup in large print at the top right to various further errors in the text these people are clearly trying quite hard to brand themselves as idiots.

As to tyre inflation with gases other than air in F1, I looked into this in detail some years ago when it became apparent that Ferrari were doing something different to other teams. Some of the details have since emerged and there's a good article here.

gases are actually a mixture of HFCs (hydroflourocarbons) and CO2 rather than nitrogen and the aim is to conduct heat away from the tread faster and keep it cooler rather than anything to do with molecules leaking in or out which of course isn't going to be a remote issue over the course of a race.

[Dave Liquorice]

And to sum up the content:

By having your tyres at the correct pressures you will experience the

So points 1-4 are all covered by just checking that tyres have the correct pressure, which we all do don't we(*). Only point 5 can be considered directly related to N2 filling.

(*) But I bet the vast majority of people don't, they just add fuel when required and drive, servicing handed to garage as and when. Backed up by the the Sussex Police survey where 73% of all cars checked were 5 psi (+ or -) from the handbook pressure. If my tyres get that far out I *really* notice it in the handling, indeed even a couple of psi out is noticeable.

Trouble is the tyres checked in the survey would no doubt be hot as the survey was a roadside one, pehaps that is why they had the +/-5 psi tolerance?

[Halmyre]

You fool! Helium is four times heavier than hydrogen. I don't want to use four times as much petrol!

-- Halmyre