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Flour Cannons

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Unread postAuthor: Hydra » Wed Jun 11, 2008 4:18 am

What is the thermal energy (J/mol) released by burning flour?

LOL ahaha this sentence made me fall of my chair. Infact this whole thread is pretty funny. Exploding Flour. Seriously...
:?
Flour is probably cheaper than propane though.
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Unread postAuthor: D_Hall » Wed Jun 11, 2008 9:56 am

Hydra wrote:Flour is probably cheaper than propane though.

And sand is cheaper than dirt.... But both are so ridiculously cheap that I submit that anybody who's making their decision based on cost is a moron.
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Unread postAuthor: THUNDERLORD » Wed Jun 11, 2008 10:30 am

I remember seeing something where in WW2 the Germans were developing/ experimenting on massive dust cannons for anti- aircraft use.

It looked like a huge bore pipe then they used mostly charcoal dust or wood inside it. (propelled/ignited with explosive)

They were going to aim them at aircraft thousands of feet up and try to generate a wind speed sufficient to snap the wings without use of a projectile! Interesting concept. :shock: 8)

BTW one time in a wood shop I worked at, an old alcoholic guy was smoking and the wood dust in front of him ignited.
Singed(sp.?) his hair a little, and scared the heck out of him.
LOL he said it looked like a demon appearing in front of him!
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Unread postAuthor: SNDM » Wed Jun 11, 2008 10:49 am

Flour is also a bit easier to get hold of than, say, propane (although to be honest that really isnt saying much).

This comment really caught my attention.....


Where do you live that flour is easier to get hold of than propane? In this small town I can think of three stores that carry flour (yes, grocery stores). Meanwhile, I can think of a dozen or more that carry propane (everything from yes, grocery stores, to sporting goods, to auto parts places).

@D_Hall: Note the bold, I knew this already. Im pretty sure they wont sell propane to me, although Im pretty sure they will sell flour.

Issues of how common they are are not what Im looking at here. Age restrictions, etc...
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Unread postAuthor: jimmy101 » Wed Jun 11, 2008 12:51 pm

psycix wrote:What is the thermal energy (J/mol) released by burning flour?

First approximation: basically the same as propane.

Second approx, from http://192.211.16.13/curricular/nbba/wrkshp1.htm
Code: Select all
TABLE 15.2. ENERGY CONTENT, IN KJOULES  PER  KILOGRAM, OF A VARIETY OF SUBSTANCES
Hydrogen                122,000
Natural gas          55,000 ++++++++
Heating oil                42,000 (gasoline the same)
Coal                         30,000 (lots of ashes)
Protein, pure dry      24,000
Wood, air dried       17,000
Starch, pure dry  17,000 (pure sugar the same)  ++++++++
Gunpowder              3,000 (contains own oxidant)
Salad oil                 37,000 (or any fat)
Walnuts                 27,000 (lots of oil)
Wheat flour       15,000 (mostly starch) ++++++++
Lima beans, raw      5,000 (67% water)
Potatoes, raw          3,000 (80% water)
Spinach, raw           1,000 (over 90% water)
Beef, T-bone steak 17,000 (37% fat)
Beef, flank steak     6,000 (6% fat)
Chicken, skinless     4,000 (2% fat)


Usual deal when comparing two fuels, the heat of combustion isn't the number you want. You want the heat released per mole oxygen.

Generic "starch" (i.e. flour) is roughly C<sub>n</sub>(H<sub>2</sub>O)<sub>(n-1)</sub> where n=100~200

Combustion equation:
C<sub>n</sub>(H<sub>2</sub>O)<sub>(n-1)</sub> + nO<sub>2</sub> = nCO<sub>2</sub> + (n-1)H<sub>2</sub>O

Now you would have to pick a value for n to calculate the oxygen per mole of fuel. (Turns out the result is independent of n as long as n is large.)

C<sub>150</sub>(H<sub>2</sub>O)<sub>149</sub> + 150O<sub>2</sub> = 150CO<sub>2</sub> + 149H<sub>2</sub>O

So, for each mole of O<sub>2</sub> we need (1mol flour/150mole O2)(4482g flour/mol flour) = 30g flour/mol O2.

For propane we need (1mol propane/5mole O2)(44g propane/mol propane) = 8.8g propane/mol O2

The table above says flour combustion produces 15,000 KJ/KG. For 1 mol of O2 we need 30g flour which is (30g)(KG/1000g)(15,000 KJ/KG) = 450 KJ.

For propane; (8.8g)(KG/1000g)(48,000 KJ/KG) = 422 KJ.

Now I'm intrigued by the idea of a chicken fueled combustion spudgun. :D

EDIT: Totaly hosed the balanced chemical equation and didn't take into account the molecular weights. Fixed. The result is basically the same.
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Unread postAuthor: DYI » Wed Jun 11, 2008 7:36 pm

Im pretty sure they wont sell propane to me, although Im pretty sure they will sell flour.


What do you do for fun, burn down houses or something? You must have a pretty terrible reputation if a store won't even sell you propane...

So it seems like flour might do slightly better than propane in optimum conditions. However, the flour would have to be in a gaseous state for such conditions to exist. So, I'd still say roughly equivalent to propane, in any practical setup at least.
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Unread postAuthor: xpitxbullx » Wed Jun 11, 2008 7:51 pm

Shoot a spud and bake a muffin at the same time. :lol:

Jeff
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Unread postAuthor: jimmy101 » Thu Jun 12, 2008 11:09 am

DYI wrote:So it seems like flour might do slightly better than propane in optimum conditions. However, the flour would have to be in a gaseous state for such conditions to exist. So, I'd still say roughly equivalent to propane, in any practical setup at least.

Actually, the energy released would be independent on the state of the flour, that's thermodynamics. Thermodynamics aren't the whole story though. Even if flour contained more energy that doesn't mean it will perform better. I would suspect that the flame propagation rate in a dust explosion is probably pretty slow, compared to propane+air.

There is some interesting info on dust explosions at http://books.nap.edu/openbook.php?recor ... 3&page=115
Some highlights;
1. In a closed chamber, without any obstructions, the burn rate looks to be pretty slow compared to propane+air.
2. In a chamber with obstructions the burn rate is faster. In the some situations a dust explosion will reach DDT.
3. It takes ~1000X more energy to ignite a typical dust explosion than it does to ignite propane+air.
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Unread postAuthor: SNDM » Thu Jun 12, 2008 2:40 pm

I admit that flour may not be as good as propane + air, but heck, its worth a try.
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Unread postAuthor: psycix » Fri Jun 13, 2008 4:19 am

Hydra wrote:
What is the thermal energy (J/mol) released by burning flour?

LOL ahaha this sentence made me fall of my chair. Infact this whole thread is pretty funny. Exploding Flour. Seriously...
:?


That scentence was not intended as a joke. Whats the fun of it?
Atleast Jimmy took it serious.
Nice calculation Jimmy! It cleared up some things.

I admit that flour may not be as good as propane + air, but heck, its worth a try.

Agree on that.
It is a nice experiment to try, but dont expect powerful results.
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Unread postAuthor: D_Hall » Fri Jun 13, 2008 1:36 pm

SNDM wrote:Issues of how common they are are not what Im looking at here. Age restrictions, etc...

So have your mom/dad buy it. :roll:
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Unread postAuthor: Ragnarok » Fri Jun 13, 2008 2:07 pm

jimmy101 wrote:IIRC, joannaardway did eventually get the "dust gun" to work.

If it was, it's news to me - there wasn't even a prototype, although there were a few tests done that suggested the possibilty of it working.
Thing was, the pneumatic bug struck the house around that time, and interest in combustions quickly dwindled.

Hydra wrote:LOL ahaha this sentence made me fall of my chair. Infact this whole thread is pretty funny. Exploding Flour. Seriously...

I'm sure it's hilarious to the families of people that have had relatives killed in flour mill explosions, which do happen.
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Unread postAuthor: daxspudder » Fri Jun 13, 2008 2:34 pm

I think its worth driving a few extra blocks to find somewhere that sells propane rather than spend weeks on the internet and an even further drive/more difficult search to get what you need to properly make flour explosive... just my 8g of copper
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Unread postAuthor: jimmy101 » Fri Jun 13, 2008 7:22 pm

I went back and read joannaardway old post (
http://www.spudfiles.com/forums/sugar-a ... rt,30.html)

One think joanna mentioned, that i didn't take into account, is the increase in the number of moles of gas as the fuel burns. More moles gas = higher chamber pressure. For a generic "carbohydrate";
C(H<sub>2</sub>O)</sub> + O<sub>2</sub> = CO<sub>2</sub> + H<sub>2</sub>O
Since the fuel is a solid it takes up essentially zero volume in the chamber. So, 1 volume of oxygen produces 2 volumes of products.
Compare with propane+air; 6 volumes propane+air produces 7 volumes of products. Take into account that 80% of what's in the chamber doesn't do anything at all (except absorb heat) and you get, as a rough estimate, carbohydrate producing almost 20% higher peak pressure than propane.

Folks had mentioned the possible difficulties in getting the thing to ignite. BBQ piezos are probably too wimpy, even a stun gun might be too wimpy. In the old thread folks discussed flame/jet ignition which might work but has some technical problems.

Perhaps an Estes rocket igniter? Does anybody know how many joules in one? Propane+air takes ~0.3mJ for igntion. Dust explosions perhaps 0.3J?
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Unread postAuthor: sandman » Fri Jun 13, 2008 7:54 pm

i dont know how many joules are in the rocket ignitors but it is obviously enough to ignite sugar and potassium nitrate, so i would venture a guess and say it would put out enough


and just an off the wall idea, if u filled the chamber with propane and flour would it work(if u added an extra atmosphere of air)? cause the combustion of propane should be enough to ignite the flour so it would be like a double bang, at least in my mind it seems that way
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