Project:RMH,horizontal feed Batchbox model 6",

[Donkey]

As to plasters and their thermal properties:
It all depends on what is IN the plaster. Plasters that are high in fiber (chopped stray/horse manures/etc.) will be more insulative, sand rich plasters will be more conductive.

[dvawolk]

Thinking of complicated and simple bells. I have a hunch that better extraction is connected to larger ceiling ISA of a bell. Do you think that if having a bell with dimensions:
2 m x 0.5 m x 1 m (where 2 meters is height, 6.5m ISA)
compared to:
0.5 m x 1 m x 2.75 m (where 0.5 meters is height, 6.5m ISA)

would be different in heat extraction? They both have the same ISA the last one slightly larger volume.

It seems to me that the most friction(?) is present at the top of the surface... hot gasses are always pushing up. At the top there is probably higher pressure as at the bottom of the bell, i would say...


Klemen

[Deleted]

Apr 12, 2013 0:55:34 GMT -8 dvawolk said:

hot gasses are always pushing up

It's not like it seems obvious.
Hot gas does not want to rise,
but the colder gas follows the pull of gravity
forcing the hot gas out of its way.

At the top there is probably higher pressure as at the bottom of the bell, i would say...

Then the bell would not work.
The higher speed the lower pressure to the walls.
Heat transfer from gases causes always a pressure drop.
The pressure caused by the particle movement is the same in all directions,
but the pull of gravity adds pressure in only one direction.
Chimneys do not draw, gravity does.
The pressure at the bottom is the highest.

[dvawolk]

I have removed my test batchbox from under the balcony at my place. Now i am cleaning the chamotte bricks of clay and i have almost finished plan of my stove. Since last few posts i changed my plan from 2 bell to one bell system because i prefer more ISA and i want my bench to be as low as possible. The SketchUp plan is almost finished. I decided to go for 6.3 sq. meters of ISA and as i said, only one bell.
The upper part (above heat riser) will be firebrick, the lower part will be red clay brick (this is hand made brick that was used for older masonry stoves and the last part (bench) will be probably concrete (or maybe red brick with concrete for the top surface.
All will be hidden inside sand-clay-fiber mix plaster.

I do have one question though: what colors can be used to paint or to color the clay plaster. What is used for the top finish of this kind of plaster so that it wont get abraded so fast? I know that for earthen floor a cooked linseed oil is used but i doubt this will be a good idea for the stove... Any clue?

Klemen

[matthewwalker]

Klemen, I used regular concrete pigments to color my top plaster coat, and mixed in flour paste to help bond it and resist abrasion. It has worked very well for me.

[Donkey]

Often, you can find LOTS of different colored clays around. Here at home, we can find yellows, oranges, reds, gray-to-black. I've heard of some blue clays out and about, but have not found them myself.
You can burn the galvanization off of nails and leave them in a can of water for some time. This (iron oxide)will make for nice orangy-reds.
There are quite a few natural pigment companies online, you can order from them and as Matthew said, concrete pigments work well.

[satamax]

Donkey, there was white clay (kaolin) in my grandfather's garden long time ago, he now sold it. At 96 he can't grow stuff anymore! And in woodworking, to turn stuff grey or black ish for ageing, we put steel wool in hydrochloric acid. And brush that onto the wood. Might be worth a try with some clays!

[dvawolk]

Hum i checked the flour paste info and i'll try it.. I have a sample of clay-sand plaster and it looks ok. I will compare it with plaster when i add flour paste into it..

For the pigments, hum, around i can find light grey and light brown clay... I will see where does the external modding lead...

My older cassette fireplace is out, so there is no way back... I expect higher comfort for the next winter. A rocket comfort i should say :-)

At the beginning of this i talked about adding the oven inside the first part of the stove.. I changed my mind because i prefer longer bench even for the price of removing the oven - i had to do this because of ISA. Anyway this won't be my last project and i am staying in this house only for some years more, hopefully... This is a learning project and when me and my family are gone from here the stove will stay as some kind of "thank you" to my parents...

As i have said i ended my testings with one bell system of total ISA about 6.3 sq. meters. Last few tests were showing good results repeatedly so i found what i was looking for (thanks for your help so far!).
I do must say that it helps *much* if i start a fire in a cold stove and add about 3/4 to 1kg of wood. The draw is here right away and then i wait for about 15 minutes. Only then i add wood to the top of batchbox. Because if the prime fire is not strong, then the fully loaded batchbox just cant start to progress with burning and drafting( it is a slow fire).

Here is the video:
You will see there the exhaust temerature (bit over 50°C) and the temperature measured after passing about 1.3 sq. meters of firebrick. On one ocasion i loaded my batchbox for another time (to the top) and this temperature showed almost 420°C. I one burning it usually stops rising at about 380°C.
This video shows about the part of burning at about 10 minutes from loading over the coals of prefire. Flashover usually starts when the temperature goes over 270°C to 290°C.

As you can see (or not see) the exhaust gasses are hardly seen... An it stays like that untill the end of burning.

[dvawolk]

And now to the changed plan of my inside RMH batchbox project.
The Sketchup plan is attached to the next post.

ISA: 6.3 sq. meters

red part = handmade fired clay brick
yellow part = firebrick
white part = concrete * (or maybe (fired)clay brick for walls and concrete for the tops)

* i would say that the incoming temperature of the gasses will never, ever be over 200°C. And usually never over 150°C.

All covered with clay plaster.
The gap between the batchbox and inner walls will be stuffed with insulation (with an exception of the right side so that gasses can freely move.
Behind the higher part of the stove there will be a void gap. This will be closed with clay but i will leave at least two holes (one at the top and the other a bit lower) so that i can get the heat from this part easily.

The arch will be holded together with iron U profiles like that:
fireworksmasonry.com/wp-content/uploads/2012/04/New-Jersey-Wood-Fired-Oven-Core-Exterior-3623-e1336767413669.jpg

Oh and as for clay plaster around the brickwork. I am thinking of being thicker at the higher part of the stove (about 5cm) and on the bench about 3 cm. I will probably also plaster the place above the arch so that it will be leveled and not curved.
I will not follow the exact lines with plaster, i will only use eyesight...

Please, suggestions and opinions..

Looking forward to replies,
Klemen

This is it, i think... Comments, please.

Attachments:

[dvawolk]

Attached .skp file for Sketchup plan...

Klemen

Attachments:

[satamax]

Klemen, i'm under the feeling that the batch box is too short.

Otherwise, it's nice. I hope you're good at brickwork, i'm not

[peterberg]

Klemen,

The firebox is made out of red bricks, these should be firebricks?

The bell could be slightly deeper, only 1/4 brick, making it possible to place the firebox in the middle. There would be enough space at the right side to allow the gases to flow into the bench from all around the firebox. No space enough for insulation, I'm afraid.

The sloped sides of the firebox are a bit too large, I'd prefer to have a flat floor the width of the port. Easier to clean the ashes out.

It would be nicer to have the exit hole right in the front base of the chimney, in that way there wouldn't be a bare pipe in the room. The clean out port should shift a bit to the right as well, of course.

Implementation of the bell and bench is spot on, this will work flawlessly. In spite of the bench being a dead end, it will be getting warm this way to the very end. Firebox is a bit short, as Max said already.

[morticcio]

I agree with Peter & Max, a longer firebox would be better.

If you shifted the firebox over to the centre as Peter suggested and raised it up 18" (45cm) (sitting it on a plinth on two/three brick piers)so it is level with the bench, the airflow on the left hand side would be able to go under the firebox, between the piers. It would also be easier loading the firebox.

[bernardbon]

HI

I think the firebox is that of a 177 but not the riser if I calculate well.

Bernard,

[peterberg]

May 15, 2013 12:34:39 GMT -8 bernardbon said:

I think the firebox is that of a 177 but not the riser if I calculate well.

The riser is wider, I've spotted that as well. But the system is suited for a round riser of 177 cm2 cross section area. This one is square, and the sides are just a little bit larger than the diameter of the round riser. In this system, the round riser is the better one. When using square, make it larger to compare for the loss of efficiency by the 90 degree corners. That's why I've used an octagon riser, it's a close approximation to a circle.

In fluid dynamics and in a vertical duct, the circle is on a par with a square c.s.a. when the circle diameter is the same dimension as the sides of the square.

Hmmmm... this do sound quite complicated, hope it's clear nevertheless.