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 Heat distribution in a rocket stove

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PostSubject: Re: Heat distribution in a rocket stove   Thu Jan 23, 2014 5:13 pm

Mr. Heater wrote:
I think that a standard earth auger bit inserted inside the tube would be a good way to distribute the heat on a vertical or horizontal run.  It could be easily inserted into the pipe.  It would be interesting to see a model of the heat distribution using an internal spiral.


I have seen on a gas fired vertical water heater tank, the exhaust tube was vented up the center and it had a spiral type designed plate insert that run the full length. To me, it looked like the spiral plate was in the tube for heat retention purposes
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Mr. Heater

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PostSubject: Re: Heat distribution in a rocket stove   Thu Jan 23, 2014 9:23 pm

Ice augers are lighter weight, but the steel may be too thin to endure the extreme temperatures for very long. I agree that the center post is the heavy part, but complete augers are readily available. Maybe just a 6" piece at the combustion chamber, and a 8" piece at the exhaust would do the trick.
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jameshookway

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PostSubject: Re: Heat distribution in a rocket stove   Thu Jan 23, 2014 9:27 pm

If you could borrow an auger you could take a template off it and make it out of stainless.
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PostSubject: Re: Heat distribution in a rocket stove   Thu Jan 23, 2014 9:36 pm

That's a possibility. A template would make it much easier to form.

I tried twisting a rectangular piece of sheet metal into a spiral with disastrous results. You need to pull it with great force as it is twisted. The metal does not like to cooperate.
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PostSubject: Re: Heat distribution in a rocket stove   Thu Jan 23, 2014 9:39 pm

I have not tried it but constructing it in small sections maybe how to do it. I don't think it would matter if it was not a smooth spiral
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PostSubject: Re: Heat distribution in a rocket stove   Thu Jan 23, 2014 9:46 pm

Sheet copper as the material might be easier to work with, although I am not familiar with it's temperature melting point. You might end up with a puddle at the bottom of your tube.
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PostSubject: Re: Heat distribution in a rocket stove   Thu Jan 23, 2014 9:54 pm

This looks like a handy chart.

http://www.engineeringtoolbox.com/melting-temperature-metals-d_860.html
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PostSubject: Re: Heat distribution in a rocket stove   Thu Jan 23, 2014 10:00 pm

jameshookway wrote:
If you could borrow an auger you could take a template off it and make it out of stainless.

I would never tell anyone this wasn't a good idea or something that couldn't be done! I would be the very first one in line to say, watch me. :shock: 

That would be a lot of hard manual labor with out any special tooling and or tools, to make your own flighting out of stainless. I would personally look for some used stainless flighting of some kind, maybe obtainable in the food or dairy industry?

SS is a nice option to have available, if it can have a realistic use and purpose in a design build. If money was no object, everything in my world would be made of SS. Very Happy 

I feel that if a person was to understand and know more about the different types of steel materials. This in return would help with the build of their RS projects. Knowing first, what something can and can not do, will put more of a realistic  prospective on your design and build.

I have found this to be very helpful for me in the fabrication of other peoples projects, and repairs to damaged or worn out equipment. Very Happy Things are not made to last for a reason!  :evil:
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PostSubject: Re: Heat distribution in a rocket stove   Thu Jan 23, 2014 11:09 pm

Mr. Heater wrote:
This looks like a handy chart.

http://www.engineeringtoolbox.com/melting-temperature-metals-d_860.html

That is the very same one I have saved on my PC as a quick reference. cheers Good Stuff !  Very Happy
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Mr. Heater

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PostSubject: Re: Heat distribution in a rocket stove   Thu Jan 23, 2014 11:31 pm

Ok, don't laugh too hard on this idea.  Remember, this is brainstorming.

How about a blade on a pivot to distribute the air that actually spins ?  It might prove to be a maintenance nightmare, but it's an idea.  A simple pinwheel design.

http://www.ebay.com/itm/Viento-Stainless-Steel-Small-Pinwheel-ID-56221/130856496224?_trksid=p2050601.m2372&_trkparms=aid%3D111000%26algo%3DREC.CURRENT%26ao%3D1%
26asc%3D207%26meid%3D4319159638356055872%26pid%3D100085%26prg%3D1112%26rk
%3D2%26rkt%3D4%26sd%3D190517711617%26%26clkid%3D4319161659571092074&_qi=RT
M1562570

Ferrite rings could be used as bearings.
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PostSubject: Re: Heat distribution in a rocket stove   Thu Jan 23, 2014 11:55 pm

I think they have something similar to what your describing, I think they call them Turbos. Very Happy  They can turn into high dollars when it comes time to work on them. :( 

I prefer less moving parts and the simplicity of designs, all the whistles and bells are cool when they are new and working the way they are intended. cheers 

I been known to think outside the box on some of my crazy design ideas, it's really scary if they work ! :affraid:  :lol!:
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PostSubject: Re: Heat distribution in a rocket stove   Fri Jan 24, 2014 12:25 am

Agreed. I try to apply the KISS principle to my projects also. The less components in a system, the lower chance for failure down the road. A spinning turbine would have a high probability of failure given the environment it's in.
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PostSubject: Re: Heat distribution in a rocket stove   Tue Feb 25, 2014 5:02 am

James the two diagrams you have presented have given me reinforcement in the new direction I am taking in stove design.

If you take a look at the post hitchhiker posted, look at the video and pay attention to the steel grate with the upward fins, it looks like stainless steel a few mils thick.

Notice towards the end of the video at the down draft area, first they show the steel fins placed just under the downdraft area they are not really that hot, towards the end of the video they show a brief flash of the entire device cherry red hot, you have to be fast to stop the video to catch it.



What they are doing is using the cherry red hot area as a secondary ignition point for the gasses.

So the diagrams you show here prove their is a focal point where the heat is concentrated and this must be the main secondary ignition point.

I have designed a completely new down draft stove using some of these ideas along with secondary air to be injected.

The twinfire stove is reported to be up to 93 percent efficient.

What they are doing with the steel fins is creating a very super hot spot, as well if you check out their main website page they show a cast iron ball with open patterns in it, I suspect this is placed right over the downdraft opening to focus and concentrate the flame as well create turbulence before moving over the stainless steel super heated fins.

http://www.wittus.com/wpwoodtwinfiremain.htm

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PostSubject: Re: Heat distribution in a rocket stove   Tue Feb 25, 2014 5:31 am

Interesting :) 

These are large stoves which they claim to be giving off 41,000 BTU's (12KW)

I wonder at what point you can start the second burn and how fast it gets through wood
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PostSubject: Re: Heat distribution in a rocket stove   Tue Feb 25, 2014 8:42 am

try this one gives a much better view including a refill while lit

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PostSubject: Re: Heat distribution in a rocket stove   Tue Feb 25, 2014 11:12 am

Cant see how a stove putting 500f up the flue can be described as 93% efficient ?
They get the twinfire grate hot with the burn then turn the flue damper/diverter and force the gasses down through the grate. Notice the top burn slow down as the heat is sucked down. If you filled the top with new fuel you would probably have to re-heat the top section then switch over the damper once the wood is burning. Its not efficient to burn wood over a grate the hot ashes will fall to the bottom and be wasted. This stove will consume alot of fuel. But looks pretty.
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PostSubject: Re: Heat distribution in a rocket stove   Tue Feb 25, 2014 11:45 am

Hey gadily in that video you just posted must be another version or it was an early version.

They do not have the cast iron ball with the pattern cut outs in it, and as well do not have the finned stainless steel grate below.

Loz the stainless steel grate I am talking about the wood is not resting on it, it sits below in direct contact with the downward thrust of the flames super heating the stainless steel fins to a cherry red hot, I suspect it is achieving the same kind of idea of using an insulated steel tube to reach a focal point of high temps to further ignite the gasses.
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PostSubject: Re: Heat distribution in a rocket stove   Tue Feb 25, 2014 11:48 am

Gadily I am guessing that the secondary burn it taking place once the stainless steel grate just below the downdraft becomes super red hot.

It probably is in a range of temps that the insides of a rocket stove come near to.
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