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Post by Johansson on Nov 9, 2016 5:50:03 GMT -5
I have been given a number of outdated scuba diving tanks and am thinking of building a steam rocket out of one, I just need to figure out how to effectively heat the water without stressing the tank material.
Heating the tank by external means is a big no-no, we almost blew up our old steam rocket that way, so I am thinking about mounting an electric heater at the bottom side of the tank.
Anyone with an idea where to find a small but powerful threaded metal heater that can withstand 20-30bar pressure? If I can find a compact 230V one it would be great, then I can just plug it in the wall socket and wait for the pressure to rise. I can even couple it through a pressure switch so the heater is deactivated once the set pressure is reached.
Cheers!
/Anders
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Post by Johansson on Nov 9, 2016 5:54:19 GMT -5
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Post by racket on Nov 9, 2016 15:48:18 GMT -5
Hi Anders You shouldn't have any problems safely heating a scuba tank to 30 bar using propane , the only requirement is that the water space is the only part heated , the steam space must be insulated from heating , steam boilers do the same job without problems, one of the boiler I operated had 100 mm dia water tubes that were only ~3-4 mm thick whilst running 200 psi and surrounded by 2,000 degree gases coming off a tonne of white hot coal burning in a 200 mm thick bed. Scuba tanks are very thick so heat transfer rates need to be considered , if heated too intensely you could end up with problems , this may have been your earlier difficulty. Do you have the "Steam Rocket" books from Aero Visions Inc , www.amazon.com/Steam-Rockets-B-J-Humphreys/dp/0912468084/ref=sr_1_12?s=books&ie=UTF8&qid=1478749034&sr=1-12&keywords=steam+rockets also the book by Truax, I have both books so if you need something explained , I'm your man ;-) Have you considered using the high pressure water/steam to discharge through a "turbine starter" for some high horsepower. Cheers John |
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jdw
Member
Joined: January 2012
Posts: 41
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Post by jdw on Nov 9, 2016 20:55:20 GMT -5
I would do internal heating, I inspect and give repair recommendations for pressure vessels in petrochemical facilities. I can run some calcs and get you a welding procedure to make it "safe". Electric would be optimal if you could source an element that could take the pressure and had the power available to run it. I'll brainstorm on it and see what I can come up with. I'm thinking a piggy back arraignment with the steam generator on the bottom and the reservoir on top would be ideal. I'll look into a forced heating arrangement using propane/fuel oil. Hopefully I can come up with something workable and has a reasonable level of risk, can't be burning up the boys.   |
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gidge348
Senior Member
Joined: September 2010
Posts: 426 
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Post by gidge348 on Nov 10, 2016 5:02:39 GMT -5
With the Eddie Baum/Scott Truax grand canyon steam rocket they use a High pressure pump (Karcher pressure cleaner type) pumping into a gas heater and then into the pressure vessel. The pressure vessel has a relief valve, so as the pressure washer pumps 1000-2000 psi into the heater, and then to the pressure vessel. As the pressure rises the vapour is vented via the relief valve set to what your vessel will take. The problem with heating the tank with a fixed amount of water in it is that you need to leave space for expansion of the water. Too little and you don't have enough thrust, too much and BOOM. This system allows you to safely fill the tank to maximum. This is a video of the unit www.youtube.com/watch?v=osrJTmImCNE as you probably guessed Scott's description is a joke...  |
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Post by Johansson on Nov 10, 2016 13:54:08 GMT -5
I am not sure I´d be comfortable heating the tank over a fire, and even if it is perfectly safe up to the 20-30bar I want it looks a bit too hazardous to do if there are other people nearby. Heating the water like the Truax rocket guys with an external pump is a very clever way of doing it but requires a bit too much auxiliary equipment for me, this is meant to be a quick project that can be filled with water, heated in a simple fashion and off it goes. I am not even sure I will have time to build it, but I´ve discussed it with friends and we don´t want to be anywhere near an externally heated steam rocket again after the near-death experience we had with the old one... |
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Post by Richard OConnell on Nov 15, 2016 2:25:00 GMT -5
You could always make some heating elements for the inside of the tank.
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Post by Johansson on Nov 15, 2016 5:53:15 GMT -5
You could always make some heating elements for the inside of the tank. The problem is how to get it in there without having to cut open the tank, and how the cables will be routed to the outside without any steam leaks around them. |
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Post by Richard OConnell on Nov 15, 2016 17:35:26 GMT -5
I was assuming your tank would be a flanged cylinder. The rear flange would go to the valve and nozzle. The forward flange would have a feedthrough for electrical. Theres some decent flanged feedthroughs floating around designed for high pressure application. I suppose its a matter of luck running across a good one at a reasonable price. I'm looking into flanged HV feedthroughs for ultra high vac now and they arent cheap, even in used condition. Just something to consider though.
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Post by Johansson on Nov 16, 2016 1:43:47 GMT -5
I was assuming your tank would be a flanged cylinder. The rear flange would go to the valve and nozzle. The forward flange would have a feedthrough for electrical. Theres some decent flanged feedthroughs floating around designed for high pressure application. I suppose its a matter of luck running across a good one at a reasonable price. I'm looking into flanged HV feedthroughs for ultra high vac now and they arent cheap, even in used condition. Just something to consider though. That is a good idea, a flanged water tank would make construction much easier. I will keep an eye out, I work with steam turbines among other things so I might run run across something useful some day. |
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