Water pulsejet

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Mark
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Water pulsejet

Post by Mark » Wed Aug 09, 2006 3:50 pm

Could someone please find/dig up that article on that water pulsejet that uses bubbles? There was an article in Pop Science or Pop Mechanics about this engine, it was fairly technical, it had a colored diagram of how the water was aerated by making steam bubbles that collapsed and it was a fairly energetic engine that made impressive thrust from what I recall.
Thanks out there.
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vhautaka
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re: Water pulsejet

Post by vhautaka » Wed Aug 09, 2006 6:12 pm

http://www.artformfunction.com/projects ... /index.htm

Fourth Google hit on "water pulsejet" - maybe not this one?

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re: Water pulsejet

Post by vhautaka » Wed Aug 09, 2006 6:17 pm

During the last Kaljakellunta (www.kaljakellunta.com, see pics there) I thought, next year I'll just have to have a propane torch put-put engine for my rubberboat. Like a torch and a length of copper tube, some of which is coiled to make a flash boiler.

Those small toy boats all over the internet seem to move nicely with just a candle.

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re: Water pulsejet

Post by Mark » Thu Aug 10, 2006 2:12 am

Good stuff V.
Today I was talking to a submarine fellow who was at my house today with his son doing an appliance repair. We were talking about cavitation and I mentioned snapping shrimp that have been know to crack the glass in aquarium tanks with their snappy/collapsing bubble claws. He said you could hear them on the submarine quite some distance away, little shrimp snapping their claws, entertaining the US Navy. ha
Anyway, I was driving to work today and thought of the putt-putt boat and in some way it has/forms a little collapsing bubble of steam I suppose. The topic I was looking for uses milllions of bubbles of steam that collapse and draw water through the engine in this way.
I found this snippet just now that is kind of relavent. I will keep searching for the article myself, it just takes time, I just wanted to reread it.

"Cavitation in pumps is the presence of collapsing gas bubbles in a liquid stream. Under very low-pressure conditions the liquid vapourises and boils. The gas bubbles collapse when they enter a region of high pressure. It is often heard as a rumbling sound coming from the pump. The collapsing bubbles cause mini-implosions that tear metal out from impellers and volutes."
http://tinyurl.com/mxslm

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re: Water pulsejet

Post by Mark » Thu Aug 10, 2006 2:28 am

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In the science article I read in the past, I wanted to clarify somewhat how it worked. It was a water pumper pulsejet, the inventor injected steam into a duct so as to produce zillions of tiny steam bubbles which collapsed/cooled and created a vacuum of sorts.
In some vague way this reminds me of the little putt putt boats that vaporize water into steam in a tiny copper tubing, and then a backflow of water races in the tube and then re-vaporizes into steam. To me this is kind of the same effect, but also a variation on a theme with lots of surface area for the steam bubbles to cool and collapse quickly.
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re: Water pulsejet

Post by Mark » Thu Aug 10, 2006 2:32 am

Here's something about "it" I found from our archives.
Mark
http://tinyurl.com/943ch
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re: Water pulsejet

Post by El-Kablooey » Thu Aug 10, 2006 2:40 am

Wow, neat stuff. That's pretty amazing 30hp from a 20cm engine. Of course the boiler and air source aren't included in that. I'll bet it's very quiiet too.

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re: Water pulsejet

Post by Greg O'Bryant » Thu Aug 10, 2006 4:35 am

I have managed to scale up putt putt engines quite considerably. The problem is that they are extremely inefficient. I think that this is caused by the lower surface area to volume ratio so the heat transfer doesn't work efficiently during the heat up and cool down cycle. Also the surface tension that is present in smaller engines may add some resistance to the steam, creating additional pressure until the meniscus degrades causing the water to flash boil. Anyway Mark that post is interesting:)

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re: Water pulsejet

Post by Mark » Mon Aug 14, 2006 1:41 am

Some kind of water pulsejet snorkeler?
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http://uzaru.main.jp/02_design/snorkel/sk01-title.jpg
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Re: re: Water pulsejet

Post by Mike Everman » Mon Aug 14, 2006 3:48 am

Greg O'Bryant wrote:I have managed to scale up putt putt engines quite considerably. The problem is that they are extremely inefficient. I think that this is caused by the lower surface area to volume ratio so the heat transfer doesn't work efficiently during the heat up and cool down cycle. Also the surface tension that is present in smaller engines may add some resistance to the steam, creating additional pressure until the meniscus degrades causing the water to flash boil. Anyway Mark that post is interesting:)
Got any photos or video, Greg? I'm greatly interested in scale-ups of that.
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re: Water pulsejet

Post by Greg O'Bryant » Tue Aug 15, 2006 8:37 pm

Mike;

Sorry for the delay I have been very busy with my new job. I think putt putt boats could be scaled up if you made an engine that replaces the two functions that surface tension provides in the smaller engines. What I have observed is 1, surface tension allows for capillary action to reload the boiler with a new charge of water, and 2, it increase the pressure making so you have a more forceful flash into steam. This is just my opinion and it may be wrong. What is the effect that surface tension has on a boiling liquid? Does it super heat? Any way I have scaled up the engines by making them gravity fed instead of feed by capillary action. They work butt aren't at all forceful. I haven't thought of a way to deal with that function yet. I have attached a crude schematic of my idea. The largest engine I have made used a 3/4" water pipe. Also the water in the cooler part of the engine needs to reach a temp just below boiling so air cooling works. Last I have not actually tested the idea of using the air to transmit the force into the lake water, but I see no reason why it shouldn't work. Tell me what you think. At the moment I have shifted to a completely different idea that I'm not sure I should talk about. You know the extremely slight possibility it may be original:)
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img putt putt005.jpg
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re: Water pulsejet

Post by Mike Everman » Tue Aug 15, 2006 8:53 pm

Putt putts
My understanding is that the exhaust tube(s) run under water and are therefore cooled. Irrespective of start-up, the cycle goes:
1. Flash boil a bit of water, pushing out the water in the exhaust tube(s),
2. The steam condenses in the cooled, underwater section of tube, making a partial vacuum,
3. Water rushes in to fill the vacuum, and some reaches the flash boiler by virtue of its inertia.
4. Lather, rinse, repeat.

Thanks for the sketch!
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re: Water pulsejet

Post by Mark » Tue Aug 15, 2006 11:46 pm

If you get some of that thin copper tubing such as a putt putt uses and apply a propane torch flame full grease on the coils with the tips of the exhaust tubing under water you can really get it to sing and resonate. You can overdrive it into an interesting hum.
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re: Water pulsejet

Post by Mike Everman » Wed Aug 16, 2006 1:14 am

I'll try that after I stop playing with the simplest electric motor!
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re: Water pulsejet

Post by Greg O'Bryant » Wed Aug 16, 2006 1:15 am

Mike that is true with the smaller putt putt engines. The problem is when you try to upscale them the water just runs out when steam is produced. The vacuum phase doesn't happen. So I am under the impression that it actually is partly due to capillary action. That is why I inverted my engine. This solved the problem of getting the water back in but they still aren't that forceful. If you have any ideas on how to super heat the water before it flashes into steam I think you would solve the mistery of upscaling putt putt's :)

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