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Aerogel Cannon

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LAN_403

Self Defenestrate

Wed Mar 08 2006, 02:19PM

Registered Member #87 Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191

I might go for an air actuated ball valve instead of a solenoid now, as ball valves are cheap, and I could probably build the air actuator for it. I don't understand what I'm being vague on, I'm using a sample cylinder, some sort of valve, and a length of tubing to build an air cannon to shoot a tiny peice of aerogel as fast as I can. I'm not trying to build a gun, but a device that will accelerate a projectile quickly to high speeds, and have extremely low energy as to not harm the "target". Aerogel was chosen because it will accelerate the quickest, and have the least static friction. The goal is to get the projectile to go as fast as possible, and because the projectile will near stop when it leaves the barrel from drag, the speed will be measured in the barrel itself.

Bored Chemist

Wed Mar 08 2006, 06:16PM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

If all you are trying to do is make it go fast so you can say you made it go fast (and that's a good enough reason for me) then you might wnat to try putting a mixture of hydrogen and oxygen behind it then lighting that mixture. Instant hot high pressure fairly light (better than air anyway) gas.
If you are only doing this on the about a cubic inch scale then it's no more of a hazard than the "pop" test for H2 in the school lab.

Bjørn

Wed Mar 08 2006, 06:54PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Bored Chemist put forward an excellent idea. It is both simple and efficient and should outperform any setups with compressed air on a lightweight projectile. You even get around the troublesome valve that would have been hardly open before the projectile had been halfway down the barrel.

Remember to have respect for even cubic inches of hydrogen and oxygen. A test tube that contains quite a bit less can hit the ceiling with enough speed that it shatters. I would not consider it dangerous but it is when you think it is completely safe you put your guard down and it puts out your eye.

Self Defenestrate

Thu Mar 09 2006, 04:12AM

Registered Member #87 Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191

Well, I'm looking at a 75cc ss cylinder IF I go hydrogen and oxygen. That would be 4.5 cubic inches, a respectable volume. Now, before I start to get too excited What sort of pressures could be reached? Lets assume .002mol of both O2 and H2 to start, ending in .004mol of gaseous H2O. I would geuss next we need to figure how hot the reaction will get, and by some gas law get the new volume? I'm a bit lost..

AndrewM

Thu Mar 09 2006, 01:08PM

Registered Member #49 Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362

O2 + 2H2 -> 4H2O

Thus, counting moles, you get a 1.5 time increase in moles after the reaction. This, coupled with the fact that its hot (use heats of formation for each species to find the adiabatic temp) you can use Boyle's law to guess the pressure.

You can also use a=(gamma*R*T)^.5 to find the speed of sound in your hot gas, which will be the speed the barrel chokes at, and thus the speed your projectile moves at.

Self Defenestrate

Fri Mar 10 2006, 02:29AM

Registered Member #87 Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191

Well, I got a cylinder, 300cc. I think I'll go for compressed air for the moment, and move towards a hydrogen system as I acquire parts. More later.

Maz

Fri Mar 10 2006, 03:16AM

Registered Member #111 Joined: Fri Feb 10 2006, 01:04AM
Location: Menasha,Wisconsin
Posts: 65

i can say something that will help out significantly.
put on some rock, and make a burst disk.
a burst disk acts by making a one time valve, and when it gets up to pressure it bursts all at once. shopping bags work decently for this if you use multiple layers. tinfoil also works.
the benefit.
imagine a clear tube with water in one end stopped by a clear valve from flowing to the other end. it dosent do it all at once because there is a choke piont in the valve before it opens all the way. now imagine the same water partitioned off resting vertically(again) then the partition is removed all at once. all the water falls at the same rate.

do you want to hit your gell all at once or do you want to use some force of the bat then the rest later escaping unused?

Self Defenestrate

Fri Mar 10 2006, 05:02AM

Registered Member #87 Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191

Good idea, but seems a bit uncontrollable. Its hard to get repeatable results, and not knowing when its going to fire sounds dangerous. If I calculate it out, I can find the exact length of barrel to match a pressure, so no air is wasted. This will equate to a very long barrel, but I can get massivly long lengths of seamless stainless, so no problem there.

I will however have Floyd playing for the build..

Self Defenestrate

Mon Mar 13 2006, 11:49PM

Registered Member #87 Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191

Just awaiting a proper fill valve assembly and I'm done.

Omicron

Wed Mar 15 2006, 12:40AM

Registered Member #131 Joined: Fri Feb 10 2006, 09:25PM
Location:
Posts: 185

Where in the world are you getting the aerogel? Do you know how expensive it is for shaped pieces? Or do you all ready have it?

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