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Post by philippeelskens on Feb 9, 2016 16:45:42 GMT -8
I'm designing my rocket mass stove, and would like to get some feedback since I'm new to the whole thing... Please share all of your thoughts! General design/ dimensions/materials/combination of cooking plate and oven in the same unit...? 1: This picture shows the lining of the inner chambers (red), insulated with 2 inches of perlite around burn tunnel and combustion chamber. Everything is circular with a 6 inch diameter. The lengths of the feed tunnel; the burn tunnel; and the combustion chamber follow the 1:2:4 ratio rule: 176cm; 352.5cm; and 705cm. (= 69.5; 139; 277.5 inch)  2: Metal barrel over the whole inner system. -Situated 6cm (=2.36inch) higher, which should allow for over 150% gas expansion. -Barrel has a diameter of 43.18 cm (=17 inch). The corresponding area should allow for 279% gas expansion compared to the combustion chamber. Is this too much? Would it be better to allow for 150-200% expansion??  3: On top of the barrel I put a 2m (almost an inch) steel plate (as cooking plate), 75 to 55 cm (=30 to 20 inch). I'm assuming that the zone right above the barrel will be hotter than the zone more to the side, by which I could regulate my cooking temperature. The brown stuff is cob.  4: Outer dimensions are 97 to 60 cm, 90 high (= 38 x 23 x 35 inches)  5: What I would like to do is also include an oven. I am not sure though if this is possible. If I put an oven in the green area, insulate it al around (except for the barrel side), and have the exhaust run under it... will I get high enough temperatures in the oven???  |
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Post by peterberg on Feb 10, 2016 3:47:44 GMT -8
The first thing that jumped into view is the lack of insulation at the bottom of the feed, i.e. the start of the burn tunnel. The top end of the feed doesn't need insulation, better to keep that relatively cool, otherwise the chances are that the fire will creep out.
Second, you don't mention it, but the core of the thing shouldn't be made out of steel. This will be corroding like mad because of the high temperature / low carbon environment.
As for an oven, most practical would be a set-top type on the cooktop.
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Post by philippeelskens on Feb 10, 2016 19:58:13 GMT -8
Thank you very much for your feedback Peter! -Insulation at bottom feed: noted -I would make the core of the thing out of Perlite clay. Probably cast around something (a plastic pip that I extract before the first burn, or should I better use metal and just leave it in so the first burns can 'harden' the perlite until the metal is gone?) -With 'set-top type on the cooktop', do you mean a portable oven that I could put on the cooktop, but take it away if I would like to use cookplate instead of oven? Or did I misunderstand this. -A possible idea I just had: Why not create a horizontal space under the cooking plate that extends to the right. On top of that right side I place the oven. Hot air coming out of the riser is forced to travel across this horizontal space, before it can drop (in the hole you can see underneath the oven, colored green). Any thoughts? Would this heat both the cooking plate and the oven hot enough? Would having this horizontal space have detrimental effects on the burning process, when compared to the more tested barrel on top, where air that came out of the riser and has cooled down can drop immediately and all around the riser?  |
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lawry
Junior Member
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Post by lawry on Feb 14, 2016 11:27:06 GMT -8
I have built a similar stove prototype. It started as a J Tube then i later changed to the Batchbox. Mostly due to the smoking back and fires out of the feedtube. Batchbox directs the energy to the hot plates. Can't you put the riser exit on the furthest end of the cooktop (left side on your last pic)? Then the hot gasses travel in one direction towards the chimney. I directed the hot gasses downwards into the blackoven. It gets quite.... black. The oven never went above 140°C. It is a single skin and not insulated probably why it never got hot enough. Plus the source of the fire is too far from the cooktop/oven. No radiation... I changed to a white oven and after Peter's advice of making the turn openings larger than system size. I managed to get over 200°C I cant insulate the stove because I need it for heating. Here is an illustration of my stove:  |
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Post by philippeelskens on Feb 15, 2016 8:20:20 GMT -8
Thanks for your answer Lawry!
-Making sure the air flow is purely in one direction is a good tip.
-Insulating the oven is too
-How much larger do you think turns should be compared to straight parts?
-I will do some research on Batchboxes!
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lawry
Junior Member
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Post by lawry on Feb 15, 2016 8:36:16 GMT -8
Thanks for your answer Lawry! -How much larger do you think turns should be compared to straight parts? peter's response when i asked was that it should be AT LEAST 150% of THE SYSTEM SIZE |
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Post by philippeelskens on Feb 15, 2016 8:51:13 GMT -8
Ok, thanks Lawry!
What I forgot to ask: Could you share the dimensions of the RM oven you showed?
Thanks!
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lawry
Junior Member
Posts: 113
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Post by lawry on Feb 15, 2016 12:35:32 GMT -8
I tried uploading a picture but it says upload fail.
The size is 300x300x485 (oven box)
I've only baked potatoes in there.
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Post by philippeelskens on Feb 15, 2016 13:21:02 GMT -8
Ok, thanks! And the (inner) dimensions of the rest? It is L-tube right?
Area of burning chamber/riser; length burning chamber; height riser; dimensions cooking plate?
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Post by philippeelskens on Feb 15, 2016 15:46:54 GMT -8
Another question Lawry (or anybody),
Should the air that's inside the oven be the air that came from the combustion chamber, or is this unhealthy? Is it better to just use this hot air to surround the oven to heat it?
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Post by philippeelskens on Feb 16, 2016 15:33:48 GMT -8
I have built a similar stove prototype. It started as a J Tube then i later changed to the Batchbox. Mostly due to the smoking back and fires out of the feedtube. Batchbox directs the energy to the hot plates. Can't you put the riser exit on the furthest end of the cooktop (left side on your last pic)? Then the hot gasses travel in one direction towards the chimney. I directed the hot gasses downwards into the blackoven. It gets quite.... black. The oven never went above 140°C. It is a single skin and not insulated probably why it never got hot enough. Plus the source of the fire is too far from the cooktop/oven. No radiation... I changed to a white oven and after Peter's advice of making the turn openings larger than system size. I managed to get over 200°C I cant insulate the stove because I need it for heating. Here is an illustration of my stove: Ok, revised some things. I would love to your opinions about this concept! -Basically, this design is a P batch box, with the dimensions (of batch box, port and combustion chamber) Peter calculated. Inner diameter of the riser is 100mm (4 inches). I chose these dimensions because the whole thing is meant for cooking, so should be around 90 cm high. I am considering to change to a core similar to a Walker riser-less core, so I could have a larger core (so more output) for the same height. -Outer dimensions are 80 cm x 160 cm x 90 cm. -Bottom left shows the batch box. The metal component inside is based on Walker's secondary air inlet (I believe this one is called version 5). I placed the batch box on the side, since I have the feeling that if I put it at the front, it would be too hot to stand in that place to cook... is this a correct assumption? -Hot gases coming out of the riser are being forced along a path underneath a cooking plate. The cross-sectional area of this part is larger than of the riser, since it curves. The ratio between the two is 1.78, which is larger than the 1.5 I've read. Could this be too large? The area of the cooking plate that is in direct contact with these gases is 0.2 sq m. -After that, gases go into a white dome oven. I would build the interior of the oven out of cob to radiate, and the exterior of clay perlite to insulate, with some space in between them to let hot air circulate. Does anyone have recommendations for dimensions (thickness cob, thickness perlite and thickness in between space). The oven right now is pretty big (inner diameter 600 mm). -One of my main concerns is whether this setup will be hot enough (for both cooking plate and oven)...? The area the hot air has to cover in the oven is 0.375 sq m (floor) + 1.54 sq m (dome). I feel that adequate insulation (perlite clay) around the hot air path would make a big difference... -At the far right end of the oven, cooled down air drops in the exhaust. Area is the same as that of the riser in straight parts, 150 % in curved parts. At the bottom possibility of cleaning out ashes. Not shown in picture, but exhaust will go through a cob bench, and come back to go through chimney (located next to oven). Would love to hear your thoughts!!!   |
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docbb
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Back from ZA
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Post by docbb on Feb 17, 2016 7:53:40 GMT -8
Hello may be should you read this post (in dutch)about this little cook stove and the exhaust temp° he gets before using the gases in a conventional boiler    |
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Post by philippeelskens on Feb 17, 2016 10:18:34 GMT -8
Very interesting (and beautiful) build and discussion!
One of the major changes I have made so far is that the white oven will sit on top of the riser. After the oven, heat is guided under cooking plate. I would try to incorporate a mechanism by which I could bypass the oven and go directly to the cooking plate. This would allow higher max temperatures to cook; being able to regulate cooking temperatures better.
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lawry
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Post by lawry on Feb 18, 2016 1:33:53 GMT -8
Yes it is
The formula for that gap is
RISER CSA/CIRCUMFERENCE
if riser is round and if gasses are going out the riser in all directions. Yours seem to be leaving through half of the circumference so the gap is
RISER CSA/(CIRCUMFERENCE/2)
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Post by philippeelskens on Feb 18, 2016 10:12:12 GMT -8
Yes it is The formula for that gap is RISER CSA/CIRCUMFERENCE if riser is round and if gasses are going out the riser in all directions. Yours seem to be leaving through half of the circumference so the gap is RISER CSA/(CIRCUMFERENCE/2) Thanks for the reply Lawry! Could you explain the 'gap formula' a little better please, I don't quite understand it. -My round riser CSA is 65^2 x pi = 13 273 mm^2 -Gases coming out of the riser are basically pushed in 1 direction, but I made the initial space just above the riser slightly bigger. -What circumference should I use in the formula? -And what does the resulting number mean exactly? |
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