doubling the power of an RMH by cooling the feed tube!!

On my experiment I confirm that the whole system works better if the draft is better.
The draft comes through the pumps:

A RMH has minimum 2 pumps: First the heat riser pumpes the hot air up. Second the barrel pumpes the air down on heat exchange over the surface.

If you do have a vertical chimney than you have a third pump.


At my RMH I got the problem that the feed tube got very hot in time. After some hours of use the temperature rises up to 900 °F. A new wooden stick starts to burn on all sides and on the total length immediately after putting it into the feed tube. Than smoke comes into the room...
The temperature of the barrel rises up to 300 °F at the upper part of the side of the barrel.

I expermineted with different materials for the feed tube: steel, refractory, vermiculite bord. Always the same problem.



Now I added a fourth pump at my RMH: On cooling the feed tube the wood is only burning sideways at the bottom. There is no draft upways in the feed tube any more. There is no more smoke coming into the room. There is no probem anymore on closing the door quickly and there we got hot water!

See what I have done:

I took the feed tube out of steel and added a thick plate out of steel to it:





Than I put a put with cold water on top. he feed tube getts now cooled by the water and the water gets hotter. And now I can regulate the size of the opening by cooking water.

Cooking waters seems to be hot. But 200 °F is much cooler than 900 °F!



At the end of the burn I move the pot more to the barrel to close the feed tube.



The heat at the side of the barrel (upper part) is now much more than 300°F. It usualy goes now up to 600 °F.
The draft is amazing!

If I would build a new RMH I would think about a feed tube with water cooling inside. With this hot water it could be possible to make much more nice things. (heat an radiator in an extra room; make a a heated floor)

Hot water is any way a thing I like. My RMH has included a 80 liter tank with drinking water. Usualy the temperature goes up to 140 °F on heating the RMH for some hours. I realy do like that. For safty I have installed all things which are importand on dealing with hot water. See a picture:



The RMH is quite small. It's just as small like the barrel. On the right side there is a 5 meter bench out of cob with stainless steel flueliner inside. Then the damp (nearly no smoke) leaves the room at about 80 to 90 °F.



How do you like the idea of cooling the feed tube?
I see at my place it's worth to try.

Konstantin

Konstantin Kirsch wrote:How do you like the idea of cooling the feed tube?
I see at my place it's worth to try.

Congratulations! Cooling the feed actively has been a nagging problem for me in 2011, at last I've used the secundairy air supply to cool the tube. See this link. The casted cores that are being sold by Dragon Heaters have these feature incorporated.

Using water to keep it cool is a nice idea, much more effective as compared to air. There has been another guy who's done something similar, dr. Richard Hill in 1977. See this pdf.

And yes, by keeping the temperature of the upper end of the feed tube below self-ignition of the fuel the stove will run hotter. The temperature difference between top and bottom of the feed will be greater thereby limiting the excess air more or less automatically, which in turn will result in less cooling of the fire.

That's a beautiful RMH. Thanks

Peter Berg wrote:... at last I've used the secundairy air supply to cool the tube. See this link.

I tested it with this kind of secundary air supply. (You can see the rest of it at the steel-feed-tube on the second picture.) But the draft was not enough. The secondary air supply made the draft between the wooden sticks even worse. This kind of constrution with secondary air supply might be very good working IF the draft ist strong. But on my situation it was not strong enough.

A active cooling could also be made in combination of pumped water powerd by thermoelectric generators.
For example this thing could work: http://thermalforce.de/de/product/thermogenerator/TG127-200-24h.pdf
5 Volt and 4 Watt at ΔT = 100K, max temp: 200 °C (price in germany: 30 Euro)

Than you could run the floor heating with RMH powerd in heat and electricity! If you like you could add some more thermoelectric generators to even fill your poor-winter-solar-battery.
For that funktion you probably would use this thing: http://thermalforce.de/de/product/thermogenerator/TG450-200-45S_.pdf
23 Volt and 6 Watt at ΔT = 100K, max temp: 200 °C

Would that be nice? Make fire and your batteries get filled AND the floor gets warm!!!

Konstantin

Your whole rmh is insanely great!
What I love most about the feed tube cooling system is the ease of implementation.Any one who can build a rocket could do this.
Brilliant!

At this RMH I made another unusual thing to create better power:

The top of the barrel was very hot (500-600 °F) and heats up the ceiling. But I wanted to get more heat to side walls.
The other thing is that I rarely roast or bake something. If I cook, I like to have long time cooking in low temperature (160 °F / 70 °C).

bevore the change:



ad some clay, mixed with bricks-powder and water. (Sand would be not heat resistand enough)



At last I added a pizzastone on top:



The result is very good for me. Not for baking and roasting. The pizzastone reaches a temperature of 300 °F, holds the temperature for a while and the sides of the barrel gets now hotter than bevore and the room is very comfortable.
And, of course, the water in the added boiler getts hotter.

In practice I take a pot, ad some onion, cutted pumpkin, just a little water, close the lid and put it on the pizza stone.
Some hours later its ready to eat and not burned. I realy do like that.

Konstantin

- perhaps this should get filed under useless trivia, But- Konstantin's Pumpkin is a little closer to our squash, that to our pumpkin, and besides what do you really
think are in those cans? Big AL

Beautiful work Konstantin!

Any chance you could elaborate a bit more on how you implemented the hot water system? Perhaps you have some diagrams about you could share?

Hi Rob,

thanks for teh interest in the hot water system. I explain. But everybody is self responsible to build such things. Hot water is dangerous! If it changes to steam it can blow your home!

First I got a used boiler:



This is the lable with all infos about size etc.:



Than we dismantled the boiler and removed the electrical stuff and the insulation:





Here you can see the bottom of the stove with three bricks as pillars to hold the boiler in place and hight



In the middle of the boiler we closed the opening with bricks, using a small layer of fire resistant insulation between boiler and bricks.
So the down-half is under fire and the upper half is under insulation:





Starting the insulation (foam glass)



with small pieces of dried cob, I build the dome, always filling foam glass behind...



Than we cut a flower put in half for the upper end of insulation, to have access to the boiler.
We use the boiler "up side down" because we have fire unter it... Regarding the insulation it would be better to have the closed part on top. The best thing would be to have a boiler with access at the side. Than the insulation would be better and you could have fire under it.



On the left side of the picture you see the first try with a barrel out of bricks. This did not work as I want, so I changed it later to the steel barrel method.



I recognized a lot of condensate under the boiler. So I added a bowl for the condensate under it.



Here you see the bottom of the hot water system:



and here the top:



And now you get the explanation what you see:



I do not have the englisch word for "Thermische Ablaufsicherung"
You can find more about this here: http://de.wikipedia.org/wiki/Thermische_Ablaufsicherung
You can google to find more pictures.

This thing mesures the temperature in the boiler and opens the valve at the other end of the line if the temperature is more then 97° C (just bevore boiling)

The pressure controll is adjusted at 2 bar, so if the pressure is higher it opens the valve. I usualy use 0-1 bar because I live off grid. If you have higher pressure, you must use other pressure controll units.

So independent whats ealier: temperature or pressure too high, the hot water pipe is opend.

To have everything work right you must have a automatic valve for air at the top of the boiler. If not, the thermometers would probably not bee in water...

We never got it too hot, but I feel better to have these security things on board

Sorry for my englisch, its difficult to explain technical stuff, but I do my best.

Konstantin

Excellent craftsmanship!

I'm really impressed. Thanks for sharing these great pictures!

Ausgezeichnet!

Thanks for the praise. If you have any questions, just ask.

My future plan is to build outside a solar warmwater collector and to use the boiler in the RMH as the insulated storage for the solar-heated water. Than I will also have hot water in the summer when the RMH is not in job.
Because of the location I will have to use a pump to get the solar heated water down into the boiler. But when the sun in shining I have enough electricity. The water cicle to the collector will be a seperated cicle with antifreeze in it and a heat exchanger in the boiler.

Konstantin

This is the most technically advanced and well crafted system I've seen. The bar has been raised. How long has it been in use ? Do you have an estimate of the total weight of masonry materials, metal and water ? Did you consider using aluminum for the metal insert that cools the feed area ?

I see that the building is quite unique with curved walls. Could you take a few photos from further back, and from a few different locations, so that we can see the RMH in the context of the rest of the building ? Thank you in advance.

What is your regular job ? Your masonry skills are far superior to mine and to those of most people.

Thank you for showing us this and for taking high quality photos with descriptions.

I'm moving this to the top of the flagged topics list.

Konstantin Kirsch : A Very beautiful and well laid out design, with clear, 'clean' lines and lots of attention to detail! Great Job, Thanks for sharing!

Now that you have shown us how you are using Foam Glass Gravel in your Rocket Mass Heater/Boiler Build, perhaps you could give us a link to the other forum
where you commented on Foam Glass before.

Foam Glass Gravel seems to have more interest in Europe than here where it is usually placed on roofs of large Commercial type buildings, Does the gravel come in
sizes, or did you have to crush the Foam Glass to get the Uniform size pieces you seem to be using ?!! For the Good of The Crafts ! Big AL !

Hi Dale

Dale Hodgins wrote:How long has it been in use?

We started the build at september last year. The cooling system is just fresh made

Dale Hodgins wrote:Do you have an estimate of the total weight of masonry materials, metal and water?

I have not counted them. The water volume is 80 liter. The total weight might be somewhere between 1000 and 2000 kg

Dale Hodgins wrote:Did you consider using aluminum for the metal insert that cools the feed area?

I consider to use cupper because the heat is moving in cupper about 10 times faster than in steel. Aluminium would be also much better than steel, but cupper is better. The best materiel would be silver... would you sponser me to try this? ...

I realy think very often about doing it out of cupper or putting some cupper under the steel, to get the effekt stronger than now.

Dale Hodgins wrote:I see that the building is quite unique with curved walls. Could you take a few photos from further back, and from a few different locations, so that we can see the RMH in the context of the rest of the building?

You find pictures of the building in this thread:
https://permies.com/t/27725/green-building/Photos-growing-eco-buildings
The pictures are not more actuall, the stove is removed and the rmh is in, and so on... But you see the construction on this pictures.
(@allen: There I also write something about foam glass gravel.)

Dale Hodgins wrote:What is your regular job ? Your masonry skills are far superior to mine and to those of most people.

My job? I'm a permaculture designer and usualy only working in my garden. For a usual job is no time.
About 20 years ago I have studied architecture and city design, but I have not completed this. I have worked some weeks building houses with clay plaster. In a way I have done lots of things, I'm more a generalist than a specialist. This RMH is the first I made but I have rebuild and new build it about 10 times the last 4 months... on this way I have learned a lot t make it better, better, better.

Dale Hodgins wrote:I'm moving this to the top of the flagged topics list.

Thanks
Konstantin

Yes ! I will sponsor a tube made of silver. But diamonds give the very fastest thermal transfer if mixed with cob. I have a bag of those in Nigeria. Just send 200 Euros for shipping, to my bank in the Cayman Islands and everything will be shipped to you right away.

Thanks, Dale

Wow. Talk about fine German engineering.

Hi Dale,

nice to reed that you would like to sponser.
But I think I want to build only such things others can duplicate. So I stay at the basics:

The thermal conductibility coefficient λ in W/(m · K) of some metalls is:

silver 429
copper, pure 400
copper, usual 240 … 380
gold, pure 314
aluminium (99,5 %) 236
brass 120
iron 80
steel 40 ... 60

To compare steel and silver the thermal conductibility is about 10 times better, but the price for silver? Too much!
Copper is nearly as good as silver but its much cheaper.
The next interesting material is aluminium. Its not so good as copper, but extrem better than steel. And the good thing is: Its cheaper than copper.
So my thought is: Copper or aluminium is the material you should use if you want to build a feed-tube cooling system.

My experiments show that the water pot in the pictures is too small. Instead of 3 liters I recommend 5 to 10 liters to keep the cooling effect working well.
Or be prepared to use the hot water for something and replace it with fresh cold water.

Konstantin

Konstantin Kirsch wrote:Hi Dale,


To compare steel and silver the thermal conductibility is about 10 times better, but the price for silver? Too much!
Copper is nearly as good as silver but its much cheaper.
The next interesting material is aluminium. Its not so good as copper, but extrem better than steel. And the good thing is: Its cheaper than copper.
So my thought is: Copper or aluminium is the material you should use if you want to build a feed-tube cooling system.

My experiments show that the water pot in the pictures is too small. Instead of 3 liters I recommend 5 to 10 liters to keep the cooling effect working well.
Or be prepared to use the hot water for something and replace it with fresh cold water.

Konstantin

You could also use a smaller amount of the better more expensive stuff like Copper at the heat source to pull the heat faster from the source, then use a larger mass of cheaper stuff like aluminum to disperse the heat elsewhere like into the air water etc...

Many computer heat sinks are made that way for the processors actually. A copper core sits on the CPU to cool it quickly by pulling out the heat fast, then the copper transfers the heat into a much larger aluminum block. Also allot of cookware uses both metals on the bottom to work the same way. Copper to grab the heat fast then aluminum plate core to disperse the heat to the pot or pan evenly over the bottom.

I just found the info for the Rocket Mass Heaters and plan to build the first small one this weekend to experiment with myself. Thanks for posting the info on yours and the cooling of the intake as I had not yet seen anything about that yet till now.

Being such drastic temperature changes in our area I will probably not use much for a clay thermal mass, mostly need to build mine for instant heat and only hold heat a few hours. I may heat large barrels of water for the mass, hold the heat over night and if it suddenly warms up outside and house getting too warm just do laundry to use up the hot water fast and reduce the heat to house fast. LOL

The ultimate way to cool the feed tube would be to use heatpipes:
http://en.wikipedia.org/wiki/Heat_pipe

Quote:

Heat pipes are thermal superconductors, due to the very high heat transfer coefficients for boiling and condensation. The effective thermal conductivity varies with heat pipe length, and can approach 100,000 W/m K for long heat pipes, in comparison with approximately 400 W/m K for copper.

Do you have more and better ideas?

Konstantin

Why not use outside air? I'm using my stove as a space heater in a cold climate. I'm planning on ducting cold outside air to the feed tube to keep positive pressure in the house, better combustion w/ cold air, and finally, to cool feed tube. Seems like it would work.

What a gorgeous design and craftsmanship! Good work, man!

That is a very impressive system. You have put a lot of thought and care into that project. I have recognized the over heating feed tube problem and am very excited about your solution. You mentioned that your exhaust leaves at 80 - 90 degrees which is quite amazing. I am curious what your exhaust port / chimney looks like, and whether it leaves through the roof or the wall. Thank you so much!

thinking about the cooling idea. i also though about computer heatsinks. what may work well is to stack several thin sheets of copper together and rivet them together. if you used copper rivets they wont corrode. an old copper water tank contains a lots of copper. should be able to make a quite thick plate that way. love your work by the way. most of my things are technically fine but tend to not be beautiful. been intending to paint the walls of the coach for about 3 years after i insulated it. its nice and warm but not pretty.

These days I made the feedtube more cooling by using copper under the steel.

Great work!
How are the copper working for you?
still improving?

Hi Erik,

the copper workes well, but the waterpot has not enough water in it. I produce much more boiling water than needed. In the time the feed tube gets too hot even I cool it with this system. So I found that the cooling of the feed tube is very importand. I'm realy thinking of making an aktive water cooling system direct around the feed tube.

Konstantin

tight snazy build enjoy the pictures and forieghn scrap tech!

got a horizontal feed so when this problem occurs after hours of burn i slide a bridgde of bricks to lengthen my feed tube and choerce the smoke in the hole.

a thought on the problem ive noticed the first hour of burn where their is temp diffferential through the systems mass it rockets harder as the conduction through the mass slows as equalibrium is reached the rocketyness gets slighty more sluggish (on mine anyways)

i also have a hot water system when i break the thermocline in my boiler (by turning on the hot water) this jumpstarts the thermosiphon when it stalls on a insulative thermocline in the boiler(my boiler is not in the flu path though yours might behave differntly)

i bet you get hot water faster than mine i have two verticle 3/4" copper pipes outside the riser inside the barrel in the flu path in a thermo siphon loop to a hotwater heater under city pressure 1 hour take the chill out 2hours kinda hot 4 hours anyone for a steam sonna? havent thrown the preesure release valve yet

Though I am a newbie to this forum and have not yet built my own RMH (still researching things but building some brick style RMH toys in the back yard first LOL) I do have some thermal dynamic background and experience. I am not only impressed with your system and innovation but also your technical skills. Adding to the statements of others, "WELL DONE"

I had a thought about the insufficient water for your cooling that might allow for a passive continuous (for the most part) water supply cooling system vice an active (pump) style. This would be beneficial for those off the grid that have a technical mindset and enjoy tinkering on things.

If you extended the length of the cooling insert, possibly with a modification to the feed tube using fire brick or just making the length longer while maintaining the proper horizontal access port clearances, a copper pipe water coil could be wrapped around the extruding section of the insert and could be connected to an external tank of cooling fluid. A thermal siphon effect would drive the water and promote flow back to the tank. The extruding feed tube could also have cooling fins attached where the copper tube heat exchange pipe could go through these fins and the overall amount of heat transferred could be modified for optimal performance.

This could actually be designed to allow the water to boil off safely to an outside area through an additional heat exchanger to capture this heat for other purposes (perhaps a hot water tank preheater??) in a safe manner. This would allow the additional latent heat to be removed gaining additional cooling value while the steam condensation through the heat exchanger would provide additional heat input to the hot water pre heating system too. In a power plant this would be similar to creating a combined cycle design which captures the waste heat and gets useful work out of it.

A further enhancement would be in using this very low pressure steam to heat an additional radiator to capture this heat prior to exhausting outside for even more efficiency and comfort. The exhaust steam could even drive a small fan for those with the technical know how but would not be required for the system to work.

Of course proper safety precautions would need to be placed within the system(s) but the external water storage tank could be much larger and I believe that the system would even be safe if the water tank was not refilled and went dry. At the minimum, the impact of having a much longer time frame of your cooling water should allow for a sufficient amount of burn time for most of the RMH's I have seen discussed on this forum. In addition, the additional heat transfer area from the tube modifications along with the impact of additional air flow heat exchange everything above the feed tube will improve the cooling of the feed tube by itself even when the water system might boil dry.

Based on what I have read, copper tubes should be able to handle the temperatures you mentioned even when dry. Subsequent filling of a dry water tank and the copper tubing should be done after the system has cooled off of course.

Most items listed could be obtained at little to no additional cost for the frugal minded (like myself LOL).

I would be interested in your thoughts and those of others who are willing to evaluate and hopefully improve on this idea. I would like to eventually build a prototype with all of this, but for now time constraints make this just an idea to pass along. If anyone picks up on this idea and builds it please let us all know your results.

Hope to hear from others soon

Tom<>

Just a quick additional thought LOL.

The low pressure steam could possibly be utilized for a sauna environment as an additional option.

can i get the mix to make a stone like that ? and how is it holding up ? awesome work thanks mike

I know this is an old thread but how about some passive cooling with heat pipes? Has anyone tried this for feed tube cooling?

This is an interesting thread to come across now that I have partly rebuilt my rocket, because of feed geting hot and causing smoke back.
I never realized this was an issue for others...
I'd never hed this problem until two weeks ago I painted barrel (inside too, so I had to replace it) and changed one bridge brick, as weather had warmed up a little.
It's a fact that temperatures were higher than in January, but I couldn't believe smoke back issues started because of that... Wouldn't it be too much of a coincidance?
So I stripped again my rocket and rerendered manifold. inside and out, as Erica and Ernie point air leaks down there can cause this.
It's so warm that I fear there will bo no more chance for me to really run my rocket in cold weather.
But having read that this isn't such an uncommon thing, I may rest assured (or illusioned ) until October.

In any case, are there ways to cool refractory bricks? Running a fan only helped little and not for long...

Thanks for cheering me up, Konstantin

What I did was to make a metal insert sleeve similar to the OP's, but arrange the core so that secondary combustion air (to feed the P-channel) enters below the sleeve top, encircles the feed tube sleeve, and then goes to the P-channel. This heats the incoming air and cools the feed tube at the same time.

Thanks, Glenn.

Since this was not an issue before attempted changes, I really hope I won't need any modifications now, that i've amended manifold.

All in all, if next year I am to rebuild the rocket, I will surely do it differently.

I'm sorry if this question has appeared or even been answered.
A thought just crossed my mind what causes condition of feed warming up. Would that be  bell's heat radiating onto bricks? Or rather coals inside feed? Or just heat rising? It puzzles me because, until I did changes mentioned in my previous post, I had never experienced those feed's top bricks too hot to touch...
One thing I mentioned in my thread was that there was quite some ash build-up on the feed side of bell. It might have acted as insulator. Though I am not fully convinced, as, firstly, from the beginning (thus without this ash), I never had any smoke back. Secondly, bell was way hotter compared to before changes. And since bench responce was way slower, i figured draft was the issue. Well, not long to go now. I will be firing the beast tomorrow.

I would guess that you had stronger draft originally, which pulled so much fresh air through that it cooled the feed area, and moved the exhaust through the system quickly enough that it didn't have time to give up most of its heat to the barrel and early duct run.

I really don´t know any more, Glenn...
After rebuilding, it worked as a charm. Though wind helped spin cowl and so helped with draft...
It won´t be cold enough to do any full scale tests now. and with over 35C where the rocket would be running, it won´t help with cooling coth feed and bell.
All I have is to hope in October it will again be my sweet cozy heater, hahaha

Glenn Herbert wrote:I would guess that you had stronger draft originally, which pulled so much fresh air through that it cooled the feed area, and moved the exhaust through the system quickly enough that it didn't have time to give up most of its heat to the barrel and early duct run.

Glenn,

I've just come across this post of yours.
It is all spring here with temps of 20-25C, but I decided to fire my heater one chilly morning.
As described in my thread, heater started behaving strange after small (mostly esthetic) changes.
One other thing that I notice now (apart from reduced draw, which, in my wishfull thinking, I atribute to warm temps outside and cold firing, since the system cools off completely before fired again) is unseen before amount of charcoal in the burn tunnel and feed tube. I can't remember seeing any significant amounts prior to the changes made (and my J-tube has not been altered other than to replace cracked bridge brick).
Sealing front door has already been discussed and I still doubt it causes problems, because, at times, I open it and no change seems to take place. Besides, there is still a 1/4'' gap over its threshold.
Do you have any thought what might be the cause? Of course, the draw itself may be an explanation. And I won't be surprised if there was one common culprit.
Another thing worth mentioning is that, at times, the draw is breaking up. Almost as if you'd hear a steam train... And this only appeared after the changes.

I see some problems with (at least mine) masonry manifolds and I think I will try to rebuild with all metal or cast iron, but I do hope to, at least pinpoint, cause of problems I am experiencing.