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/sci/ - Science & Math

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2979060 No.2979060 [Reply] [Original]

Hey /sci/,
Does any of you happen to know how much psi a small butane explosion is? As in, a quick spray from one of them 'canned air' things, into a container that can hold roughly a quarter gallon (~1 liter).
I'm wondering if the potato gun I build is safe enough.

>> No.2979228

i'm not going to do the work for you, but I recently took a safety course on this

you can find the equations in a chemical engineering book. first you calculate an equivalent mass of TNT, based on the mass and energetic content of the propellant you are using. then you use empirical relations comparing two dimensionless groups to get an amount of overpressure caused by the explosion.

the book was Chemical Process Safety: Fundamentals and Applications by Crowl

it also has a lot of other helpful things like seeing how much of what chemicals will fuck you up real bad in what ways

>> No.2979408
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2979408

I can guarentee that it isn't safe, because you're retarded enough to use combustion instead of pneumatic power for a potato gun. The heat from the combustion will weaken the hull much faster, and it will eventually explode from the force of the explosion after enough use.

I'll just leave this here...

>> No.2979419

>>2979060
what is it made of?

>> No.2979437

>>2979408
not if its diamonds, the hardest metal

>> No.2979486

this would work, but it would be extremely dangerous.


you would need very strong container walls to prevent the explosion of the container, and instead force the potato out of the hole.

to be safe, I wouldnt use anything less than 1/4 inch thick, even though that may sound excessive.


even then you would want to be at least 100 feet away from it when you test it, because shrapnel from exploding metal containers can kill the fuck out of you.


but yeah... this is exactly the same premise as an ACTUAL cannon... they just use stable, easily stored solid combustibles, instead of relatively unstable, difficult storage gasses.


How much pressure? no idea. its a very difficult calculation.


its a chemical explosion, and the pressure depends on the internal geometry of the explosion vessel (eg: how much space inside the container that holds the back-end of the potato)...

it also depends on how much oxygen is present (how much combustion)


even a simple calculation, assuming 100% combustion, would be difficult because you cannot be sure how much of the gas has gone into the chamber.

>> No.2979489

>>2979437


troll or not, you can make diamond into a true semiconductor (eg: band gap accessible to kbT) by doping it.

>> No.2979492

>does science
>but is it safe?
YOU'LL NEVER DISCOVER FLUORINE THAT WAY.

>> No.2979523

>>2979489
>>2979489
troll, but did not know this. any reason you cant use any element though?

>> No.2979527
File: 71 KB, 1024x768, 2011-04-20 19.29.34.jpg [View same] [iqdb] [saucenao] [google]
2979527

Well, suddenly a lot of replies, I almost gave up.

>>2979408
I also have a pneumatic one that works like a charm, and I read a few guides that mentioned 'explosion powered' potato cannons made out of pvc, so decided to give it a try.

Thanks for the replies, everyone. Guess I'll stick to pneumatic.

>> No.2979543

Go to spudfiles.com. Best site for this sort of thing. You should build a pneumatic cannon. Much more powerful!

About your question, as long as you use pressure-rated pipes, you will be fine if you joined the pipes using primer and cement as is instructed.

>> No.2979563

This experiment doesn't sound like it has the potential to kill or maim people. Is this even science?

>> No.2979572
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2979572

>>2979527

Here is a pneumatic golf ball cannon I built a few yeas back. Powerful as hell.

>> No.2979588
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2979588

>>2979572

>> No.2979652
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2979652

>>2979572
That thing looks pretty badass, heh.

>>2979543
Interesting site, thanks!

>>2979563
My relatively weak pneumatic cannon shoots clean through 3 tin cans. I'd say that's at least a serious injury, and a headshot would be lethal.

>> No.2979677

>>2979527
PVC potatoe guns using combustion do work, but don't overdose on the combustion chemical, and do find a proven safe configuration:
AND FOR FUCKS SAKE, DON'T USE ABS IF YOU DON'T LIKE GETTING PLASTIC TO THE FACE.

>> No.2979681

Pressure would be low. No matter the size of the potato gun, the projectile will only fly at about 100 ft/sec. For real power, you need compressed butane and oxygen.

>> No.2979700

>Does any of you happen to know how much psi a small butane explosion is

It's enough pressure to do this:

http://www.youtube.com/watch?v=7hJFNuNoVfg

>> No.2979918

>>2979677

ABS will fail before PVC. But ABS has a much safer failure mode than PVC. PVC shatters while ABS rips. ABS is "safer" from a failure standpoint, but PVC is better from a yielding standpoint.

>>2979652

Spudfiles is the best for this kind of thing. Check out the wiki. I wrote some of it :)

>> No.2979926

>>2979681

If you want REAL power, check this out.

http://www.spudfiles.com/forums/lardas-first-hybrid-hygac20-t15524.html

>> No.2980048

>>2979926
>mfw

>>2979918
What's up with the crazy pressures? I was already impressed with the performance of my simple gun, shooting pebbles at 70 psi; and I read they recommend 200+ psi for a simple pen gun?!

>> No.2980054
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2980054

>>2980048
Forgot a pic, dur.

Also, I wrap my pvc cannons in ductape and/or electrical tape, to keep shrapnel to a minimum should they ever fail.

>> No.2980126

>>2980054

You can use math to show why you can use high pressures with low diameters. For a given wall thickness a smaller diameter can withstand more pressure. My golf ball cannon that I posted earlier runs on 100 psi, but the pipe is rated for 280. It's surprising how much pressure these things can handle.

That link I posted is pretty crazy huh?

>> No.2980192
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2980192

>>2980126
Yeah, an awesome piece of work.

With all the stuff my friend and I build so far (scorpion, trebuchet, various potato cannons, slingshots...) we just started out with a rough idea and used trial and error to get what we want, or just went at it by feel. Works fine most of the time, lol.
This little lego trebuchet for instance, just started building, and it worked amazingly well with the first shot, no modifications had to be made. Threw a marble well over 70 feet, and the onager next to it can throw one over 150 feet now (after a few changes).

I'm off to bed now, thanks for all the replies, everyone!