# COMMUNITY : FORUMS : GREEN

## Boiling a fluid to make a inverse water wheel?

Ok, how about this; Submerge a waterwheel type structure with cups facing downwards on one side. Under the cups you have some kind of heating element. The fluid is methanol or some other low boiling fluid. A very small amount of heat from the element will produce bubbles, which rise and are caught in the cups, the wheel turns and can generate electricity or whatever. I'm using this principle in another application, but thought it could be quite an efficient means of generating electricity from heat. If the meths is sitting at forty something degrees and boils around 50, it shouldn't take hardly any energy to tip it over. And since you're effectively generating force from gravity (the weight of the fluid on the other side of the wheel) you're kind of getting ten times your force back. ie producing one litre of bubbles will give you 9.8 Newtons of force (for water, 8ish for meths). So (excuse my dodgy maths) 125 litres of bubbles in an hour would give you 1 kiloWatt hour? One cola bottle per minute, doesn't sound very much and that much energy could easily be produced through concentrated solar. Slight risk of explosion... How efficient do you think it would be, overall?

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petzlglyph8 years ago
? A different application ? There is a way to pump water up out of a well by pumping air into a pipe that is submerged into the water by 40 to 50 % of the overall height. The water comes up with the air. Your air wheel could harvest this air to do additional work instead of letting the air go to waste. These are called air pumps or bubble pumps. The air wheel could be housed inside a box that is located below where the water / air comes out. Or find another source of waste air bubbles? Check out the "no moving parts water pump" Instructable.
SolarFlower_org (author) 8 years ago
That wonder wheel thing is pretty cool. 85% efficient? Really? Wow. Turbines and steam type engines would no doubt be far more powerful and efficient, but this inverse wheel thing would be almost effortless to construct and maintain...
8 years ago
I suspect your design is possible but would be ridiculously inefficient. If you are going to boil a liquid there is probably far more energy to be had from its expansion than from using the lifting power of bubbles. I agree with Kiteman, the Minto wheel is a more practical application of the principle and one of those cool things I would love to see work. The major problem it has is that using small temperature differences are inefficient (hence low-temp stirling engines being toys, not practical generators), but I think combined with some sensible concentrating solar power they could be useful devices.
SolarFlower_org (author)  PKM8 years ago
Yeah. I'm now inclined to agree. Oh well, it was worth thinking about. It's still fine for the other thing I'm using it for since that requires very little force.
Goodhart8 years ago
Another wrinkle to this would be the need to recondense and cycle back fluids that could be lost as steam / fumes. If water is used, this is not overly difficult, but it would take more energy to condense say, evaporated alcohol.
NachoMahma8 years ago
. My gut instinct is that your method won't work very well, but there may be something to it. . Seems to me that the difference in density between liquid and gas is what gives you your driving force, but it may have more to do with vapor pressure and/or expansion factor. See if you can find a material with a large difference. You also want something that will boil at the appropriate temp and power input. . As lemonie says, there will be considerable drag from the fluid that you will have to take into consideration. Cups shaped like those on anemometers (just half of a hollow sphere) may not be the most efficient, but should be a good place to start. . Keep in mind that your bubbles will be getting smaller and smaller as they rise and cool, so they will provide less and less lift until they finally cool to below boiling. This will probably limit you a LOT. . Which would work better: a lot of small bubbles or a few large bubbles?
Kiteman8 years ago
You want to take a look at Wally Minto's Wonder Wheel (I kid you not).

Another treatment of the same proposal.
lemonie8 years ago
Remember that the fluid will exert drag on the whole wheel. When converting energy from boiling liquids (e.g. water) people have found that gas turbines or triple expansion piston engines tend to be pretty good at the job. L