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Post by gadget on Jul 3, 2019 20:24:56 GMT -8
UPDATED: This heater is now running in an experimental configuration and has proven to be very powerful and therefore very dangerous. At this point I would just consider this thread entertainment and by no means a safe proven design. I have learned much and there has been some failures. I consider this design uncharted territory and pushing design limits. Its design is as complex as the goals with this heater. I will keep posting updates as I work through improvements but I don't know if it will ever be a viable/safe design. Its being testing in an outside environment and I would never consider it for indoor use.
I'm starting another experimental build to replace the test mini rocket build I did here in my greenhouse; donkey32.proboards.com/thread/3473/mini-rocket-forced-induction It worked well with the blower so this one will also be forced induction. After suffering through last winter with a tiny feed tube, I am going to over compensate buy using a 55 gallon barrel burn chamber that will accept fairly large pieces of wood. The burn chamber will have a sideways air inlets(across the glass) to promote a swirl or tornado affect in the burn chamber. I also decide to not use cob anywhere. It may have 3 blowers instead of just one. The main one for the exhaust and possibly 2 small ones for primary and secondary air. The other feature I'm looking forward to is a ceramic honeycomb for secondary air. This one is a 6" disk about 3/8 thick that the secondary air will pass through. I'm going to make it so it can be seen through the glass. 
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Post by gadget on Jul 3, 2019 20:36:06 GMT -8
Goals with this heater;
- Heat lots of water much faster than previous heater
- Handle large loads of wood / big pieces
- long run time between loading
- flue exit temp under 100F
- blower shut down fault circuit with loss of water flow
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Post by marcios on Jul 4, 2019 4:53:06 GMT -8
Creative design!
Could you show us the details of the port (primary to secondary throat)
and the main dimensions?
Don't you think the secondary air duct will suck a lot of heat from the riser, taking away the effectiveness of the second combustion?
(I think we should avoid anything that reduces the maximum temperature in the first part of the riser or second combustion chamber)
Another thing, wouldn't you need a lambda sensor EGO to control the secondary air blower in that counter-convective down flow ?
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Post by gadget on Jul 4, 2019 11:03:40 GMT -8
Creative design! Could you show us the details of the port (primary to secondary throat) and the main dimensions? Don't you think the secondary air duct will suck a lot of heat from the riser, taking away the effectiveness of the second combustion? (I think we should avoid anything that reduces the maximum temperature in the first part of the riser or second combustion chamber) Another thing, wouldn't you need a lambda sensor EGO to control the secondary air blower in that counter-convective down flow ? I can draw the general details but for now the only dimension I have is the ceramic honeycomb disk is 6" diameter Good point on the secondary air tube leading inside the riser. The idea was to preheat but I think you may be right on the heat loss. I may insulate that tube and make the top of the barrel the preheat. There is also some preheating via the ceramic disk but it should not draw to much heat from combustion. I would love to have a 02 feed back setup but that is much further down the road. I am collecting parts for it, I have electronic throttle bodies, O2 sensors saved from cars. I also am learning to use raspberry Pii. For now, its just manual adjustment for primary and secondary air. |
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Post by gadget on Jul 4, 2019 11:11:46 GMT -8
One of the 2 barrels and stainless steel hospital tub that will be the condensing bell. I was going to cover the tub in cob and make it a bench but its dimensions are just to large. I also need to have a lid that can be opened easily incase I need to clean the radiator. By not covering the tub with cob, it can radiator more heat to the air. I will build a table/counter over it and block the side from small hands touching it incase it gets to warm. I still need to figure out a lid setup. I may use the aluminum driveshaft as the flue pipe from the bell to the blower that will be mounted up high.  |
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Post by marcios on Jul 4, 2019 13:16:24 GMT -8
I can draw the general details but for now the only dimension I have is the ceramic honeycomb disk is 6" diameter Good point on the secondary air tube leading inside the riser. The idea was to preheat but I think you may be right on the heat loss. I may insulate that tube and make the top of the barrel the preheat. There is also some preheating via the ceramic disk but it should not draw to much heat from combustion. I would love to have a 02 feed back setup but that is much further down the road. I am collecting parts for it, I have electronic throttle bodies, O2 sensors saved from cars. I also am learning to use raspberry Pii. For now, its just manual adjustment for primary and secondary air. What about the air tube from side or bottom options? Wouldn't it be much easier and with similar effect? I think it would be simpler to make a analogic motor speed control. Anytime i will try with a car sensor that i have been saving for a long time. What kind of motor does your blower have? |
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Post by pigbuttons on Jul 5, 2019 8:29:39 GMT -8
I like it! That looks ambitious and very forward thinking. You don't mention what the secondary air input piping will be made of so I will guess that the 'cooling' of the secondary burn vs the preheating of the secondary air may have more to do with material selection than air flow; and that from two fronts. First, that area is going to be the hottest in the stove in my opinion what with the air flow from the firebox and the radiant heat from the fire itself. Second, the secondary air should be just that 'secondary', and I think the relatively small amount of air flow will not be that big a factor in cooling. The heat from the ceramic honeycomb should travel up that pipe via conduction. The key in my mind would be material, and steel will be short lived in that environment leaving ceramic as the way I would think best, with ceramic fiber blanket as a close second.
Just my thoughts. I'm looking forward to your progress.
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Post by marcios on Jul 5, 2019 14:58:33 GMT -8
I think the first question would be precisely from where to extract the heat for air preheating, to obtain greater efficiency. Defining that, the air tube/duct material becomes a question of the path the air will have to travel and the way to warm it.
I guess the ideal would be to extract after the second combustion, so as not to reduce the temperature of the previous stages. If I can't preheat the primary air that way (not impossible), I'd try to do it in relation to the secondary air, at least partially.
But it's my limited cartesian thinking, there may be a merit to your idea that can be higher than that.
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Post by gadget on Jul 5, 2019 20:45:05 GMT -8
The secondary air tube was going to be made from very thick wall mild steel pipe. I have some trailer axles I was going to use. I could use stainless down the road but I am wanting to keep cost down. Part of the design is to make the tube lift out of the top of the barrel so it can be replaced easily.
The riser will be a basically a 5 minute riser.
Good input! This is why I love posting here, there are so many good ideas and to have other check your plans can save lots of head aches
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Post by gadget on Jul 13, 2019 19:27:52 GMT -8
This is the most interesting part of this build. I started getting this idea from another heater I am also building in my living room. It uses 9 rectangular ceramic honeycomb plates. This build will just use this single 6" round honeycomb. Current plan is to move the secondary air through the tiny ceramic holes above the fire. In theory, the small passages make small jets of air that helps with mixing. An alternative idea I have is to run the fire through the honeycomb and add secondary air just before the fire enters the honeycomb.  It looks off white but it is actually more pure white so I suspect it is just made from a high alumina ceramic. I was hoping for cordierite but this is what I got. Good news is it will conduct heat better if its high alumina. I'm hoping to learn allot with the honeycomb disk in this build that I can apply to the heater thats going into my living room. |
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Post by gadget on Jul 14, 2019 16:55:12 GMT -8
I was going through some designs on paper where the secondary air would enter just before the honeycomb vs above and I came up with this nested triple barrel design;  The honeycomb sits just below the riser. Secondary air enters below the honeycomb after being warmed from between barrel lids. The first small barrel covers the riser and extends the insulated burn path / adds mixing (per suggestion,no tube for secondary air inside the riser to preserve heat). Holes in the bottom of the first barrel route flue gases into the second barrel that has water coils. Flue gases exit the top of the second barrel into the third final barrel going down the sides and exiting at the bottom into the bell. Original plan was to line the inside of the burn chamber with ceramic fiber blanket that would be rigidized. A hard ceramic face coat would be added to areas where wood could cause abrasion. I have had some success with rigidizing and face coating CFB but I don't know if it will be strong enough to handle wood impacts and scrapes. Blanket is much weaker and less dense then board. I think board would work great but I don't know how it could be curved. I have been experimenting with perlite/clay matrix coated with ceramic coating and it looks promising. It will not insulate as good but it will be stronger and much cheaper. It would also work great with a much thinner face coat. I am curing the face coat with an acetylene torch and the perlite matrix could even work without the face coat if it the surface was turned into a ceramic with the torch. The face coat I am using is very white and would reflect more heat. |
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Post by jlmtech on Jul 26, 2019 14:59:48 GMT -8
Hi Gadget,I enjoy reading about your experiments. When I took chemistry many years ago, we were shown that a Bunsen burner flame will not pass through a fine screen. A fine screen is used in chemistry to support container of chemicals above the Bunsen burner. The gas will pass through but the combustion of the gas is stopped. Also the the gas can be lit above the screen and combustion of the gas will not pass down through to the nozzle of the Bursen burner. Your ceramic screen may be behave the same way. The ceramic screen can be tested with a small LP torch.
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Post by gadget on Jul 27, 2019 15:29:02 GMT -8
Hi Gadget,I enjoy reading about your experiments. When I took chemistry many years ago, we were shown that a Bunsen burner flame will not pass through a fine screen. A fine screen is used in chemistry to support container of chemicals above the Bunsen burner. The gas will pass through but the combustion of the gas is stopped. Also the the gas can be lit above the screen and combustion of the gas will not pass down through to the nozzle of the Bursen burner. Your ceramic screen may be behave the same way. The ceramic screen can be tested with a small LP torch. That is very interesting, I'm going to give it a try this weekend and see. I have been actually feeling like running the fire through the honeycomb was not a good idea - I was concerned about ash buildup clogging it. You just gave me another reason to not go that route. I think I am getting close to having a final plan, this version would use the honeycomb above the rise as a third air inlet and there would be a second inlet just before the riser. I'm really liking the triple barrel setup and will most likely go this route. Percentage air inlet would be; Primary 50% Secondary 25% Tertiary 25%  |
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Post by eng on Aug 9, 2019 0:50:11 GMT -8
I liked the tertiary air tube coming down inside the riser design best, but it will burn out if made of metal, perhaps it is not necessary. The secondary from the top of the primary combustion chamber fed through the ceramic disc should be sufficient. The ceramic disc would reflect heat back into the primary combustion area if fitted at the entrance to the secondary combustion tube. A British Coal Board designed boiler for home heating using bituminous coal used this successfully. So out of favour now. The secondary air must be added to the entrance of the secondary chamber and to have time to mix with, and allow the unburnt gases to burn. The hotter it is the better. On the first wood burner I had forty six years ago the two 12mm ss secondary air tubes glowed red hot and were 500mm long supported only at the entrance to the fire box. It lasted at least ten years after I sold it.
I think your concept has a lot going for it.
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Post by gadget on Aug 9, 2019 21:52:51 GMT -8
I liked the tertiary air tube coming down inside the riser design best, but it will burn out if made of metal, perhaps it is not necessary. The secondary from the top of the primary combustion chamber fed through the ceramic disc should be sufficient. The ceramic disc would reflect heat back into the primary combustion area if fitted at the entrance to the secondary combustion tube. A British Coal Board designed boiler for home heating using bituminous coal used this successfully. So out of favour now. The secondary air must be added to the entrance of the secondary chamber and to have time to mix with, and allow the unburnt gases to burn. The hotter it is the better. On the first wood burner I had forty six years ago the two 12mm ss secondary air tubes glowed red hot and were 500mm long supported only at the entrance to the fire box. It lasted at least ten years after I sold it. I think your concept has a lot going for it. For sure I do want to go with the 3 barrel setup though you are right that the hanging tube does look promising. Perhaps a combination of both designs is best. I will see if I can come up with a design so that the ceramic disk can be used lower at the bottom of the riser. It is a very good idea to have the secondary air as early as possible. Just need to get the preheat done without exposing steel to high temperatures. I do like how the gases pass around the disk before entering the tube. It seems like allot of good mixing would happen I did do some testing with a torch on the ceramic honeycomb. I was impressed with how well it heated air I blew through it after I warmed it with the torch. Perhaps you are right and preheating is not as necessary since it will get so much heat from the fire below. As suggested earlier, it could be mounted from the sides. The drop down tube could still work, I would just insulated it from to much heat. Jethot ceramic coating is another option. One thing I like about it being suspended from above is there is nothing impeding air flow from the sides. |
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