SpudFiles

I have been toying with the idea of using an liquid oxygen bottle as a chamber for a hybrid cannon.The bottle is rated to 12,00psi and thus has a burst pressure of around 30,000psi the walls are 14mm thick alloy of some sort(aluminium but not sure what type)It has an internal volume of 3000cm3.I plan to make this a burst disk hybrid and use a metal union one with bolts and nuts just like 2 plates screwed together.I have pictures but mum took the camera to work.I plan to run this at a 6xmix and maybe oxygen enriched mixtures aswell.I plan to get suppersonic speeds and have proof of them from a chrony.One problem is the ignition were should i have the igniton and how many points of ignition should i have?I was thinking have a spark plug mounted in the bottom on the chamber.Any ideas on this cannon to improve it would be great.

DAMMIT!!! I had a link to some ASME codes but I lost it.

Anyway, it's basically the one-source guide for building pressure vessels.

You could take the tank and get the head cut off, bored out appropriately to 2-7/32", and tapped to 2" female NPT threads. Then, you can connect whatever kind of union you want with male threads.

But were the hell am i going to get a 2"NPT tap??I think i will just weld it onto it.At what pressure does propane liquify at?Anyone?I heard that you cannot have amix higher then 6x because of the propane turning to liquid is this true?

Propane usually liquifies at around 90 PSI.

But, that's partial pressure.

So, with a 4.2% mix, the propane would liquify at a much higher pressure.

Look under Dalton's Law of Partial Pressure.

EDIT: and whoever told you that was going the wrong way anyway because they forgot to subtract 14.7 from their figures.

Partial pressure does not mean that the propane won't liquify - that is a common misconception about the application of Dalton's law.

It's still at 90 psi, so it will still liquify.

Dalton's law of partial pressure is for entirely different situations, and partial pressure refers to what would the pressure would be if all other gasses were removed from the chamber - not if they're still in there.

Put the gasses back in, and you still have 90 psi - meaning liquified propane.

Seriously - go out, and try it. You will still end up with liquid propane. Partial pressure doesn't apply here.

The only way to get the liquification pressure of propane to rise is to heat it.

Trust me on this one, I've been studing pressure and flow laws flat out for months, both in school and in my own time.

Well, can we look at in on the molar level?

Propane liquifies at 90 PSI.

You mix 4.2% propane to air, and pressurize it to 90 PSI.

Here's a little view of what it would look like.

1= propane
0= molecules of air

111111111111111111111111
111111111111111111111111 = 90 PSI pure propane
111111111111111111111111

000000001000000000100000
100001010100000000010000 = 90 PSI stoichiometric propane/air mix
000001001000010000000010

I'm not saying you're wrong, as I couldn't find any conclusive data on this. I'm just saying that a mixture at that pressure doesn't have the propane molecules close enough togehter for them to clump together and liquify.

A second BLB on the way are we joannaardway??I no very little on the matter of Dalton's laws.But it will help.I saw in a thread a while ago that when u get acetylene to a certian pressure it spontaniusly(sp?) combusts.

Water condenses at <100*C (give or take) no matter what gasses you put in the chamber.
Goddamn good thing, or we wouldn't have rain...

Propane is going to behave the same way, although we're changing the pressure instead of the temperature.

No, I'm a physicist, with a to-be enginneer for a brother.

Until we actually prove it with an experiment, then it will remain a subject of contention.

However, consider it like this - those propane molecules are whizzing around in that mix. It is a simple fact that two of them will meet up at some point, forming a liquid "bond".

Then, more particles will meet as well, forming their own little bonds. The tiny clumps of propane will meet others, sinking to the bottom of the chamber, and pooling together.

Even if it took several propane molecules to form a liquid state between each other, that would still happen fairly often, and you'd still end up with a pool of propane.

Or, so I see it.

Perhaps I should gather some cheap parts and try testing the theory in a clear plastic bottle - then we'd know...

Heh... I though the same thing when I got home, but then, I realized....

I'm not going to be compressing a stoichiometric mix of propane and air to 90 PSI anytime soon, so it doesn't really matter to me.

Be safe if you do try!

I'll see what I can do. I have no propane available, but I'm sure I can improvise with some form of LPG, even if it's just one of those "cleaning" sprays filled with butane.

Depending on when it liquifies, we should have an answer.

I remember hearing about this on msn. I have an old thick metal helium bottle from a fair I might use for my new hybrid. Does anyone know what its rated too?

should hold around 200-400BAR around 2,900-5,800PSI

I beg to differ with Joanna (without having doen the experiments) about the condensation of propane.
I can prove it by an example however. At 20°C (~50F), water has a vapor pressure of 0.339 psi, but this does not mean all the water in the atmosphere condensates. In fact, liquid water will evaporate until the partial pressure of water vapor in the air is equal to that of its vapor pressure.
The same will happen with propane, if you had liquid propane at the bottom of the chamber and filled it with air at 200 psi, propan would still evaporate (though not boil) until the partial pressure is equal to the vapor pressure. If you have gaseous propane in the air already, it won't condensate until the partial pressure goes above the vapor pressure.
This can be easily tested by putting some propane (or butane, which has a lower vapor pressure and will make the experiment easier) in a syringe along with various amounts of air, and see what happens when the plunger is pressed to compress the mixture.

What you have to ask yourself is that within an ideal mixture (ie. Independent action of the molecules) does the pressure exerted by one gas on the walls of said chamber also directly affect the pressure of the other gas? I know for a fact that pressure exerted on what object gas can be used to seperate another (think of a petrol or gas pump at a filling station). So I would agree with Joanna...