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Rocket Mass Heater - problems

 
Posts: 4
Location: Croatia
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My English is not that good, but I hope you understand the text that follows.
A few months ago I started building a rocket mass heater.
I didn’t think much about the measures, the building materials, etc., well I built a rocket mass heater through one movie on Youtube that worked relatively well. ("Copy-Paste" method
After that I build the new version of the rocket mass heater with addition for water heating in the whole house. However, I got very poor combustion results. At the top of the oven I got only 220 degrees C.
I don’t know where the problem is, because the performance of this rocket mass heater is much worse than before.
I am sending pictures.
• The diameter of the heat riser is 16 cm.
• The depth of the firebox is about 30 cm.
• The distance between the top of the bell and the heat riser is 5 cm.
• The bell is 80 cm high and 57 cm wide.
• Without a bell, the rocket effect is very good, without smoke.
• The diameter of the flue is 13 cm and approximately 6 m long.
Rocket mass heater is made in an approximate ratio of 1: 2: 4 (30: 60: 120 cm).
• Now, combustion of rocket mass heater is with smoke. This is the reason of low temperature.
• The water heater is made of a 3/4 "iron tube located in the insulation space wound around a heat riser (10 coils). This is not an ideal solution but with the temperature that the rocket mass heater should develop, it should be enough. (In in this version I get a radiator temperature of only 40 degrees C)
I kindly  ask for advice or a recommendation for a book or other sources that deals with this type of rocket mass heater. (I thing this is J type).
IMG_20211002_091403.jpg
RMH - view 1
RMH - view 1
IMG_20211002_091450.jpg
RMH - view 2
RMH - view 2
IMG_20211002_091517.jpg
RMH - view 3
RMH - view 3
IMG_20211002_092325.jpg
Conection to watter heating
Conection to watter heating
IMG_20211002_100919.jpg
Bell of RMH is in position to test basic of RMH
Bell of RMH is in position to test basic of RMH
IMG_20211002_102853.jpg
Dimension of heat riser (outside measure)
Dimension of heat riser (outside measure)
IMG_20211002_102832.jpg
Dimension of heat riser (inside measure)
Dimension of heat riser (inside measure)
IMG_20211002_103020.jpg
Dimension of heaat riser with insulation
Dimension of heaat riser with insulation
 
Danijel Vrbanc
Posts: 4
Location: Croatia
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Here are attached 2 pictures of  water heater construction I did in RMH.

And one correction from a previous post: The main proportions of my RMH are 1: 2: 3.5 (maybe that's the main problem - increasing the heat reiser by about 15 cm might solve the problem)
IMG_20210508_181800.jpg
[Thumbnail for IMG_20210508_181800.jpg]
IMG_20210508_181820.jpg
[Thumbnail for IMG_20210508_181820.jpg]
 
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Location: +52° 1' 47.40", +4° 22' 57.80"
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Hi Danijel,

Reading through your messages and seeing the pictures, I can identify three major mistakes and one possible restriction.

The possible restriction is the top gap, in my opinion this should be at least 8 cm instead of 5 cm. This top gap is the distance between the riser's end and the top of the barrel. In your situation, the top gap could be even more cramped when the barrel heats up and the top buckles in, restricting the gap further. Make it 10 cm and this will be fine, no matter what.

Mistake one is the heat exchanger around the riser. This shouldn't be there, a better placement would be inside the barrel and against the wall. The riser need to be as hot as possible, you are cooling it now.

Mistake two is the chimney pipe: this should be the same size as the riser. The riser is now 1.5 times larger than the chimney, cross section area speaking. Combined with the unavoidable elbows this is a serious restriction point.

Mistake three: in a well-built RMH the riser need to be made out of refractory material. Steel won't melt though, but due to high temperatures and lots of free oxygen it will corrode like mad. Even stainless steel won't be stainless in those circumstances.

Edit:
In case the pipe in the bench is also the small size, this is hampering the rocket's workings even more.
 
Danijel Vrbanc
Posts: 4
Location: Croatia
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Hi Peter.
Thank you for your response to my post.
Well, obviosly, I have to do a lot of change to my reconstruction of RMH.
The reason I did this construction is the scrap material I had in my basement. (material costs was zero :))
Now I am very intersted in improvement of RMH so I have to invest to RHM. (I don't want to buy classic commercial heater with bad combustation).  
So first I want to prove that I will get the high temperatutre (good combustation) in my chamber.
Because diferences in cross section area of heat riser and flue (and pipes in the bench) I decide to reduce cross section area of heat riser to the same amount of both areas.
After that I will extend heat riser and bell for about 15 cm to get right proportional dimension 1:2:4
Do you think will it be a good idea?
The results will be published thru the pictures in the end of the next weekend.

P.S. I accepted your other remarks and I had idea for solving mistakes. First I want to get the right temperature. With no circulation in system, RHM operates like without heat exchanger.
InkedIMG_20211002_103020_LI.jpg
Inserting the new pipe smaller dimensions in heat riser to get the same dimension like pipes in bench and flue.
Inserting the new pipe smaller dimensions in heat riser to get the same dimension like pipes in bench and flue.
 
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Location: Southern alps, on the French side of the french /italian border 5000ft elevation
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Well, there is another problem that Peter might have not seen! In my opinion, your plenum or transition area is too small. The brick sides should slope down to the bottomof the pipe, from both sides of the barrel.  Check this thread

https://permies.com/t/61657/Flue-exhaust-transition-plenum-pictures

rocket-problem.png
[Thumbnail for rocket-problem.png]
 
Danijel Vrbanc
Posts: 4
Location: Croatia
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Thank you Satamax for your observation.
I read the thread your send me. It shows the one of problems I have with the combustion process because of big smoke flew  resistance in transition area.
I have to do more spaces in the transition area from bell to the pipe.
At the end of weekend I will do some changes in doing more space.
I hope, I will have a good news with pictures of success.
Thanks again.
 
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