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Fabrication Question


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  #1  
Old 10-06-2010, 10:00:01 PM
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Talking Fabrication Question

I have a "Question" for all the Fabricators of Stainless Steel, who might read this thread. If the Stock is 1/2" Stainless Tubing, what would be the tightest diameter Spiral Coil one could wind? I am hoping that it could be as tight as 1 1/2" ID, and maybe 12" long, but I do not know. Anyone, have an idea, or would like to try and make a prototype?
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Old 10-07-2010, 06:37:47 AM
Steve NW Ohio Steve NW Ohio is offline
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Default Re: Fabrication Question

The minimum bend radius is effected by the wall thickness and the series of stainless material. 3" ID might be possible, but 1 1/2" would be unlikely, in my experience.
Steve in Ohio
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Old 10-07-2010, 09:51:12 AM
rleonard rleonard is offline
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Default Re: Fabrication Question

I agree with Steve. In addition, the tubing would need to be filled with another material prior to bending to prevent it from flattening.

Sometimes lead is used, sand, shot, or other incompressible material. Even high pressure water is used in some cases

Bob
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Old 10-07-2010, 05:25:37 PM
rhkoch rhkoch is offline
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Default Re: Fabrication Question

Are you trying to wrap an exhaust pipe to recover heat? Would it be easier to get a surplus heat exchanger? Tell us more about the project.
Rich
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Old 10-07-2010, 10:58:59 PM
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Default Re: Fabrication Question

Hey, Bruce! How big is this still gonna be?
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  #6  
Old 10-08-2010, 01:49:33 AM
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Default Re: Fabrication Question

What I have in mind is a diesel genset Exhaust Heat Recovery System, for a 10Kw Genset. Can't make the Center Tube with Exhaust going thru it much more than 1 1/2" Pipe, and it would have to be Stainless to last at all. So, that dictates that the piping needs to be Stainless as well so that it can be welded to the Exhaust tubing, for good Heat transfer. I also plan to have two pieces of Stainless flat stock, welded in a cross, inserted in the tube and welded as much as can be gotten to, to facilitate the transfer of heat from the gases flowing up the tube to the coil wrapped around the tube. I use copper all the time, to do this in Wood Stoves, here in alaska, but the sulfur in the fuel would eat any copper based system in a few months, hence stainless. Up here we pay dearly for those BTUs, and to throw 2/3rd s them away, trying to heat the whole outdoors, just isn't a smart thing to do. Heat Exchangers for the Cooling system are no problem, but the Exhaust System is a bit more tricky. I really do not want to have to go to a Water Jacketed Exhaust Manifold, like in a Marinized engine, as I would need to have a different model for every different engine, where as, if I can design something that can be duplicated, easily, then it can be installed in just about ANY stationary engine exhaust system. The copper designs I use on stoves, are made from 1/2" copper pipe with a 6" OD on the coil, of about 5 turns, which is designed to go inside a 6" sheet metal stove pipe, just below the damper. These make very good ThermalSyphon heating coils and if your stove burns all day, you will have more Hot Water than you need, for any reasonable size cabin.

I have thought about using a Stainless Tube and Copper Coil, and then potting the whole thing in Thermal Conducting Epoxy, but I haven't found one that can deal with 1000F, yet.
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Old 10-08-2010, 02:26:28 AM
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Default Re: Fabrication Question

Bruce, why not have the engine's exhaust plumbed into an insulated stainless steel tank, then make a much larger coil inside? Not only will you get better heat transfer, there will be much more coil area you can use. I can see you recovering SOME heat from the system you describe, but I think a large insulated tank would work better.
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Old 10-08-2010, 07:55:48 AM
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Default Re: Fabrication Question

http://www.mandrelbends.com/tube-pip...-pipe-466.html

you could fabericate a spirial using smaller half bends and tig weld them, going to cost uless they can make a spirial? be good thing to sell once you get all the kinks out
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Old 10-08-2010, 08:31:34 AM
Tony Rye Tony Rye is offline
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Default Re: Fabrication Question

could you run them vertial and use 180 for turn back .
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Old 10-08-2010, 07:05:07 PM
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Default Re: Fabrication Question

It is VERY important to NOT cause any slight obstruction in the flow of water thru the coil, as it heats from the cold input at the bottom, to the hot output at the top, in a ThermalSyphon System. You can NOT have a place where the water does any tight turns, or goes in a downward direction, as it will vapor-lock the system.
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Old 10-08-2010, 08:26:21 PM
J.B. Castagnos J.B. Castagnos is offline
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Default Re: Fabrication Question

How about a tube inside a tube? You could get a piece of stainless to fit over your exhaust pipe like a shell heat exchanger. The water would have 100% contact with the pipe, outside would be insulated. You could twist a piece of flat stock and insert it into the exhaust pipe to swirl the exhaust to be sure you recover as much from the exhaust as possible.
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Old 10-08-2010, 08:49:54 PM
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Default Re: Fabrication Question

how many turns to the foot
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Old 10-08-2010, 09:28:25 PM
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Default Re: Fabrication Question

I would think 6-8 Turns/Ft would be good. I have been considering a unit like you suggest JB, only I think I would build a spiral into the water side as well, and spin it the opposite direction of the Exhaust Gases. That might be the only practical alternative, since the tubing idea seems to be a non-starter due to fabrication issues.
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Old 10-09-2010, 06:36:43 PM
K D Redd K D Redd is offline
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Default Re: Fabrication Question

I would try 1/2 Copper tubing. This would be easier to wrap and would last a relative long time. Yes, vibration of the engine would make the copper work but stainless will also work harder from the engine vibration.

Kent
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