Wednesday, 16 June 2010

The heat engine which drives the device has been going through some considerable metamorphosis since I realised that what I originally had, ie ethanol bubbles working upwards on a submerged wheel; was not going to work.
I spent two months trying to get the system completely sealed (which, to my restrained pride, I eventually did), but the main problem was that in order for the bubbles to not immediately collapse the whole volume of ethanol would have to be heated to just below boiling. Doable, but an extreme hassle.

So I had the idea to instead pump liquid up and pour it into the wheel from the top. Tried a bubble pump, which worked but not well enough, improved this to a kind of geyser pump; better, ended up with some kind of weird steam-piston-by proxy hybrid thing which worked quite nicely, but still only about 30% of what I'm after.

The obvious solution was to insert some little mechanism which alternately switched on and off the flow of gas. That previous link has the reasoning why.

This has taken me the last six freaking weeks to solve. I've come up with at least half a dozen ways of doing it, but they all require some fairly precise and tricky components, which rules them all out.
This one little thing has, in all seriousness, been the hardest thing I've ever had to design. It's such a tiny thing, but I haven't been able to move on without it.

Finally, after burning through more brain kilojoules than the device is actually likely to produce, I think I've hopefully solved it: by completely redesigning the entire apparatus and kind of avoiding the problem altogether.

The trick was to use much less ethanol, so that it boils itself out after pumping enough for one correction, then refills. I probably should have thought of that earlier...

So this is the Connell Pump. Not very powerful, grossly inefficient, but absurdly easy to make and I'm actually quite proud of the design. It works good, and more importantly; it works at all.

  1. At the bottom right is the boiler, which holds about 2-3 ml ethanol.

  2. This boils and the vapour enters the 'chamber' (the half blue, half white (liquid and gas)), forcing out the liquid, which goes to the main reservoir.

  3. This continues until the eths in the boiler has boiled off to the extent that it can no longer overcome the rate of re-condensation in the chamber, which starts to suck, so to speak.

  4. This draws liquid from the reservoir, which passes through the boiler, shutting off the boil, the pressure drops quickly and the chamber and boiler refill with liquid.

  5. Two valves (the only moving parts) keep all this going in the right direction.

  6. Repeat.

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