SpudFiles

I'm back with more of my dry icing.




After building a PVC dry ice cannon, http://www.spudfiles.com/forums/viewtop ... tml#243398, i decided that continuing with PVC was too dangerous, due to the temperature sensitive nature of PVC.

So i made one out of galvenised iron! Cost me a total of $80AU.
Its just a length of pipe with a cap on one end and a ball valve on the other. Dry ice goes in through the ball valve. I seal it, then dip the end in near boiling water. The ice sublimes.

The cannon alone weighs 5kg. I attempted to fire it horizontally like a gun. Shot back like a rocket about 10m. Left me with a nice bruise on my hip. Its like a damn rocket.

Vertically, i'm shooting small potatoes up in the air. From firing to hitting the ground is about 8-9 seconds. So i'm estimating about 50m up in the air.

In hindsight i probably should have used a smaller chamber. It would use less dry ice and there would be less recoil (and less rocketlike behaviour). I still love it. I think the ball valve might be beginning to fail though. Its becoming very loose to turn. It's only rated for 200PSI and I estimate im reaching a lot more than that.

Any suggestions would be great.

It must be pretty entertaining to shoot, but it could definitely be improved.

A longer, smaller bore copper barrel launching heavier rounds would improve efficiency over the current version (which is actually shooting about 100m in the air, equating to a muzzle speed of about 50m/s). A pressure gauge would be a really good idea as well, especially with that PVC barrel - it might not burst, but I wouldn't trust it. If you'd rather that it stay large-bore, a PP or ABS barrel would be safer. Either way, the barrel needs to be longer.

The recoil issue would certainly be solved by using less dry ice. As is, your propellant gas probably weighs more than your projectile

horizontal. bad move. you can see it pushing out of my hands

Clucking bell, did the neighbours let you have it back?



How about a burst disk between the valve and the barrel, to give you a bit of a delay to let you have full flow before your projectile starts moving.

Also, given the relatively slow opening valve, that tiny barrel isn't doing you any favours either. It should be at least 4 times as long, you'll get a significant increase in power and less muzzle noise to boot.

your ball valve should last

KineticAmbitions wrote:As is, your propellant gas probably weighs more than your projectile.

Hardly uncommon with smaller bore cannons. My current project will use 32 grams of air per shot. 95% of it's projectiles will weigh less than that.

With CO2 (half as dense again as air), it's not surprising.

Lets get some video!

Ragnarok wrote:

KineticAmbitions wrote:
With CO2 (half as dense again as air), it's not surprising.

CO2 is almost three times as dense as air. Molar mass 44g/mol. Air is mainly nitrogen and oxygen, which have molar masses of 14 and 16 g/mol respectively.

In terms of how much ice i'm using per shot, well its a fair bit. Im not measuring it, but i reckon at least 100g per shot. The chamber is 1.6L capacity (a mistake really, should be a lot smaller for a single shot cannon).

As for kinetic ambitions suggestion of a gauge, if someone can find me a place to get one for less than $100AU i will. Local plumbing place didnt have one in the right pressure range for less than $200, and it was massive. And ur right about the height. I did the physics calculations and got that. But it didnt seem right so i assumed wind resistance was playing a massive part.

The other issue I've got is that the joins are leaking. I've packed them with gas sealant tape, but still leaks. Any ideas?

And video:

Enjoy

evilducky wrote:CO2 is almost three times as dense as air. Molar mass 44g/mol. Air is mainly nitrogen and oxygen, which have molar masses of 14 and 16 g/mol respectively.

Nitrogen and oxygen are diatomic!
This means the molar mass is twice the elemental atomic mass, which means air's mean molar mass is 28.97 g/mol (considering percentage fractions), but it's easiest to remember as 29 g/mol.

I did actually do chemistry at high school, and I did pass the subject, but if you doubt me...

...Any suggestions would be great.

1) Loose the PVC.
2)-With that much volume, maybe it could use a "y" shape like some rigid electrical (metal) conduit pipes have...(haven't found link yet).
(think giant sandblaster nozzle).
It could have a magazine with a ball detent similar to Jackssmirkingrevenge's vortex design Here also similar to vogt pattern here. With a ball detent between the magazine exit and barrel (to help the shots fire one at a time rather than in a row).

3) Besides a burst-disc, spring load the ball-valve with a long spring OR extend the handle and use a coil spring like a rat-trap or car hood spring?

4)Abstract, but if you had a large enough CO2 tank something similar to This ???
Maybe when the gas ran out it could spin fast enough for low speed descent unpowered ?

BTW, YMBASI: you fire that more than once!!!
Firing Looks cool. 8)

Also, I knew I might have a use for that water heater tank element I ripped from a hot/cold spring water dispenser yesterday...I was after the compressor, but spent over 1hr. hacksawing the element with water tank intact!!! ...Sometimes things work out like "God's will" or something...

EDIT: forgot, suggestion 5) make a double barrel version.
EDIT:2 Dang, also forgot, i was thinking the "Volcano mkII" might be a cool name for it(?)

Ragnarok wrote:

evilducky wrote:CO2 is almost three times as dense as air. Molar mass 44g/mol. Air is mainly nitrogen and oxygen, which have molar masses of 14 and 16 g/mol respectively.

Nitrogen and oxygen are diatomic!
This means the molar mass is twice the elemental atomic mass, which means air's mean molar mass is 28.97 g/mol (considering percentage fractions), but it's easiest to remember as 29 g/mol.

I did actually do chemistry at high school, and I did pass the subject, but if you doubt me...

touche, sir. ur right.... gee i hope i dont do that on my chem exam this year

thanks for the suggestions thunderlord.
1. Fair enough. I have the gas rated PVC that i used for the last one. Im going to use that as the barrell because its here and ready to go. im pretty sure im not going to explode it (its got a pretty big opening and the barrell thread isnt sealed with gas tape).
2. Difficult to hook up and seal something like that. As for a magazine, there's really no point. for every shot, i have to remove the barrell to put more dry ice in. im really more designing this for long distance single firing.
3. burst disk is probably the next step. i really have no idea how ill do it though.
4. I'm not sure what ur getting at?
5. A double barrell one that fires both barrells simulatenously is a possibility.

Thanks

One thing to think about, depending on the amount of"ice" you're using, It will cease to sublimate once it reachs roughly 850psi(depending on temp), even with heat, once the critical pressure is attained it will just melt as opposed to sublimating, and become supercritical co2, and when you open the valve the pressure drops enough to allow flash boiling the remaining liquid which turns your launcher into a liquid co2 rocket/volcano.... I'm sure Rag or somebody can prolly second this opinion... I'm sure you could calculate the amount of "ice" by weight to reach a given pressure in a given chamber and gain much performance over you're current method(not to mention conserving "ice")...

evilducky wrote:4. I'm not sure what ur getting at?

This is Thunderlord. He sometimes goes off on tangents.

At least he's not talking about poop today.

jeepkahn wrote:One thing to think about, depending on the amount of"ice" you're using, It will cease to sublimate once it reachs roughly 850psi(depending on temp), even with heat, once the critical pressure is attained it will just melt as opposed to sublimating, and become supercritical co2, and when you open the valve the pressure drops enough to allow flash boiling the remaining liquid which turns your launcher into a liquid co2 rocket/volcano.... I'm sure Rag or somebody can prolly second this opinion... I'm sure you could calculate the amount of "ice" by weight to reach a given pressure in a given chamber and gain much performance over you're current method(not to mention conserving "ice")...

I knew that it stopped around 800PSI. Thing is, i didn't think i was getting close to 800PSI yet. And yeah a bit of ideal gas law would do the calculation for me, but unfortunately i don't have something to weigh the ice with. But god i could turn this thing into a rocket... if i packed it with dry ice....how much 'burn time' could i get?

...2. Difficult to hook up and seal something like that. As for a magazine, there's really no point. for every shot, i have to remove the barrell to put more dry ice in. im really more designing this for long distance single firing....

Well it's like this,"for every shot" you get more shots.
IDK if this design is "safe" for you anymore.

...3. burst disk is probably the next step. i really have no idea how ill do it though....

Union, Burst- disc inside???
Worth a try.

...4. I'm not sure what ur getting at?...

...But god i could turn this thing into a rocket... if i packed it with dry ice....how much 'burn time' could i get?

Answered your own question with that one.
Stick around maybe... 8)