need help burning wood underwater

[quarky]

Greetings. I'm cleaning out my notebook, and I can't quite throw this idea into the trash yet:

To get in the mood, float a tea candle in a bucket of water, and light it.
Quickly pull a sandwich baggie over the candle, and pull it completely underwater, so that an airspace remains, with candle still burning.

The flame goes out pretty soon. Yet, with an intake and exhaust tube running up under the bag, the candle will continue to burn.

Must go; will be back.

[Madalch]

It would have to be a large bag so that the temperature (and thus volume) of the air doesn't change suddenly with every sputter of the candle flame.

[Prometheus]

It's been done (http://snorkel.com/hot-tub-info/snorkel-and-scuba-stoves.php).

[GreyICE]

I suggest thermite.

[ponderingturtle]

It's been done (http://snorkel.com/hot-tub-info/snorkel-and-scuba-stoves.php).

Reminds me of a concept design I made a long time ago for a floating hot tub.

[CaveDave]

Grind the wood to smallish chips/sawdust.
Mix with ~50 % Magnesium turnings/shavings.
Pack into paper tube.
Tie to brick or long stick.
Light magnesium (Bright, white, quiet flame).
Plunge into water (wear goggles, stand back)

FIREWORKS!!



Cheers,

Dave

[quarky]

Sorry about that. I got called away suddenly.
I know about snorkle stove. This is a bit different.

The membrane is totally submerged. The 'breathing tube bends under the bag. A puff of air goes in. stops. allows a puff of exhaust to exit. A similar tube supplies a steady drip of fuel. Could be kerosene, actually floating on the isolated water.

To what advantage?
Well, this type of water heater could be accomplished with a sheet of plastic instead of fire brick or heavy metal construction. The flame could be visable.

The safety aspect would be potentialy good. In a catastrophic failure, the flame would die from lack of O2, or in worse scenario, would be extinguished by surrounding water.

The fancy part would be a system that regulates the fuel drip vs/ breathing tube flow.
Not insurmountable.

[quarky]

This might be easier to picture:

a flask with a 2 hole stopper is fitted with plastic tubing that extends into the flask, and a few feet outside, with valves that start out closed.

The flask is inverted, with an anchor tied to its neck, and forced underwater in a barrel.
Fuel is introduced by gravity drip from a fuel tank. It puddles on the top surface of the water under the flask, and is ignited by spark through wire in stopper.

Flame starts to deplete, the air hose valve opens, allowing some of the gas to escape; followed by a fresh puff of air from a pressure tank. A stasis is reached, allowing continual combustion. The heated combustion area gives up its heat to the surrounding water.

To shut down, turn off fuel drip and close air valve.
Depending on the use, the exhaust could be vented into the water for a little scub.
The fuel could also be introduced into the water in the neck of the flask, and float up to the combustion zone, for some sort of scrub.

The flask and the barrel in this scenario could be a plastic bag of water with a smaller upside down one inside. That's kind of cool. Major weight savings. Especially for something large scale.

[blutoski]

How about just using wood with a nugget of potassium wedged into it?

[JihadJane]

Hijack a nuclear submarine, dive, stick your wood in the reactor.

[Dilb]

I'm unclear on how this would be different than the scuba stove, and why this would make building it out of plastic any easier. Alternatively, how is this different than putting a fish tank on top of a wood burning stove?

In any case, I don't think you're appreciating the challenge of building a good stove. Burning wood is pretty close to an adiabatic process: the heat goes into the product gasses, not to the surroundings. This is why you can burn a floating layer of kerosene in the first place: there's relatively poor thermal contact between the flame and what it's sitting on. If it's pulsed the flame will die off well before the hot gasses transfer most of their heat.

[quarky]

It would be a stove made of water, with a thin barrier. Like a pellet stove, except plastic and water instead of iron and firebrick. Heat exchange would happen in the surrounding water. The hot gas in the containment wouldn't be much different than a stove with lots of thermal mass. The exhaust pipe could exit through the water, giving up some heat.

Loss of heat through exhaust gasses is a given in a conventional stove.
There's no way around that loss. It can be minimalized.
Assuming the flame was kept alive, the heat wouldn't go to the water below the flame, it would mostly heat the air in the bag, which would give it up to the surrounding mass of water. Further heat exchange from there. Not certain why its fundamentally different than a normal heater, as per how it would function.

I certainly could be mistaken.

[CaveDave]

I think that running the "bag" and the exhaust tube at or near the water temperature (as opposed to insulating enough with air or another material so it ran a few hundred degrees) would cause condensation of various nasty substances driven off uncombusted from the fuel as in destructive distillation.

IIRC, cold chimneys collect "creosote" faster than well-insulated, hot, ones do.

HTH

Dave

[OMGturt1es]

Why do I suddenly want a hot tub with a transparent, underwater, wood burning stove? Seriously, I'd buy it. If I had a hot tub. And a house. And some wood. And probably some cannabis. Oh wait. I have cannabis. That's why I want a hot tub with a transparent, underwater, wood burning stove.

Go back to posting. It all makes sense now.

[ponderingturtle]

Why do I suddenly want a hot tub with a transparent, underwater, wood burning stove? Seriously, I'd buy it. If I had a hot tub. And a house. And some wood. And probably some cannabis. Oh wait. I have cannabis. That's why I want a hot tub with a transparent, underwater, wood burning stove.

Go back to posting. It all makes sense now.

It wouldn't be clear for long anyway.

[quarky]

I think that running the "bag" and the exhaust tube at or near the water temperature (as opposed to insulating enough with air or another material so it ran a few hundred degrees) would cause condensation of various nasty substances driven off uncombusted from the fuel as in destructive distillation.

IIRC, cold chimneys collect "creosote" faster than well-insulated, hot, ones do.

HTH

Dave

good point. It would be difficult to keep a high combustion temp. The bag would blacken.

[Careyp74]

not to derail, but that hot tub must be a b*$%# to get started. I have to use enough kindling to get a normal stove itself hot before a fire will continually burn in it. If that stove were surrounded by cold water I would never get a good fire going.

[OMGturt1es]

It wouldn't be clear for long anyway.

We could make some sort of disposable underwater stove liner/condom.

[quarky]

not to derail, but that hot tub must be a b*$%# to get started. I have to use enough kindling to get a normal stove itself hot before a fire will continually burn in it. If that stove were surrounded by cold water I would never get a good fire going.

Not really diffferent than starting a fire in a cold stove, surrounded by cold air.
Its the gas that needs to get up to temp.