An attemp for smaller bells on a 200mm (8") batch

[Deleted]

Hi everyone,

Here is an attemp to make much smaller bells ! It's a compromise — not as simple as empty, large hollow bells BUT :
- less materials,
- less inertia,
- not as massive-looking,
- a higher surface temperature,
- a higher discharge rate.

It's more adapted to houses that aren't well insulated and to users that are OK to make two or three fires a day.

The ideas behind that build are :
- to maximize the downdraft and horizontal parts because the exchange is better than on updraft ones
- to make multiple, small bells instead of a big one
- true double skin
- to make that most of the bricks inside the heater are heated on two faces
- each part of the heater must be accessible for cleaning
- the insulating bricks inside the "riser" must be accessible for replacement
- to keep the rules I use for bells "à la Peter" :
    - 5xCSA on the top of the first bell
    - 1.5xCSA opening or more at every turn
    - 1xCSA opening on a straigth path with transitions as smooth as possible
    - with the exception of the last updraft channel that can be smaller than the CSA.


So here it's a 200mm (8") batch based on these ideas. The mean power output based of two loads a day is 4400W.


The total weight with the metal parts is approx. 1250 kg, so the weight to power ratio is 285 kg/kW.
Material cost is approx. 1500 € with bricks delivered.

Heat emission is on a lower level than tall heaters. I tried to put a lot of surface area as low as possible so the radiation is closer to the ground level.

The drawing is not completely done yet, some little things missing but the general idea is there. As everything based on peterberg 's batchrocket, that work is released in Open-source CCBYSA4.0 (creativecommons.org/licenses/by-sa/4.0/deed.en) Please read it carefully..
Many thanks to Vortex and pyrophile for their help !


Gas path :

The gases go first in the little bell above the "riser". The top of the bell is 5 times the CSA of the system and the opening is 1.5 times the CSA (220x160mm). ISA equals 0.7 m2.

Then they go down on the right. The last part is a little bit cramped and it's 0.9 times the CSA. ISA equals 1.36 m2.

Then the gases go through a series of 5 little bells/channels. The channels are 1.7 times the CSA and the openings are 1.5 times the CSA. ISA equals 2.74 m2.

Then the gases go up through an opening of 0.8 times the CSA and then an updraft channel 1.4 times the CSA. ISA equals 0.7 m2.

Finally they go through a octagonal junction (0.65 times the CSA) that leads to the chimney flue that is 180 mm in diameter (0.8 times the CSA). ISA equals 0.57 m2 per linear meter of chimney flue.

So if we divide the ISA of the updraft parts by two because there the exchange is less good, and if we consider 2 meters of uninsulated chimney flue.. we have : an ISA of 5.7 m2.

On a single bell "à la Peter" it would have been 9.4 m2 (approx. 40% more). Now I need to test to see whether the exit temperature is higher or lower in order to make a comparison.

Sketchup plans (organised by layers) :
uzume-asso.org/assets/docs/experiences/P_4400W_V1/P_4400W_V1_010618.skp
uzume-asso.org/assets/docs/experiences/P_4400W_V1/P_4400W_V1_010618_sketchupV8.skp

Pictures :








The heater has not been tried yet but will be quite soon !

Ideas and comments are most welcomed and the bets are open !

Regards,

[matthewwalker]

Very nice Yasin. The gas path is almost identical to my Tiny Cook Stove. I can verify that it is an excellent layout for heating the bricks and allowing high surface temperatures on most of the outer surfaces. The side down channel to under firebox path is working very well for me in this heater. I believe you will be very pleased with the performance.

[Deleted]

Hi Matthew, thanks ! That's really great news !! It's funny that we came to the same flue path..!

Have you measured the total surface area of uninsulated material with this flue path ? What mean exit temperature do you have on a normal firing ? What is the mean O2% associated to this normal firing ? Your Tiny Cook Stove is a 6", no ?

That piece of information alone would spare me a lot of work ! Thanks !

[AlexHarpin]

Hi Yasin! What temp do you expect this heaters will reach?I mean what is your goal temp?

[Deleted]

Hi Alex, do you mean the exit temp or the bricks temperature ?

For the exit temp, 100-150°C measured one meter above the top level of the heater, on average on a single burn would be nice. If there is a reloading then 150-200°C on average.

For the max temperature on the bricks on the front I know they can reach 150°C (or more if the heater is overfired).

Regards,

[matthewwalker]

I have not measured internal surface area, but weight is roughly equal to yours. It is a 6" heater. Exit temps are typically right around 200°F after a few burns, 150°F after one load. My O2% is high-ish, I'm sure I have copious leaks so I don't trust it. Avg. is around 13%, low and stable is 9-10%.

My bottom chamber is a bell rather than a serpentine, but otherwise it's very similar.

[Deleted]

Thanks Matthew,

13% O2 on average is very good. I've not often seen burns that where lower in O2% on average. It seems that more O2 leads to more heat in the chimney.. that's why I asked.

Exit temperatures are very low, that's impressive ! But the weight is not a good indicator to compare things. I've measured a 7.5 kW contraflow ISA and it was 5.5 m2 only. As a comparison, a batch of the same power with a single hollow bell needs approx. 11-12 m2 to achieve the same extraction results, so twice as much.

The weight can vary so much depending on the number of skins, the size of the bricks, if the bricks are laid flat or not, and so on..

Regards,

[AlexHarpin]

Jan 6, 2018 9:48:14 GMT -8 @yasintoda said:

Hi Alex, do you mean the exit temp or the bricks temperature ?

For the exit temp, 100-150°C measured one meter above the top level of the heater, on average on a single burn would be nice. If there is a reloading then 150-200°C on average.

For the max temperature on the bricks on the front I know they can reach 150°C (or more if the heater is overfired).

Regards,

Yasin!

I was talking about the brick temperature. 150C is pretty hot! Thanks for the quick awnser!

A+
Alex

[josephcrawley]

Does 1300 euros include the doors and other metal work or just the bricks? If just bricks you should be able to drop the price a good bit by using common house brick for everything besides the firebox and heat riser. In the US 30 cents is a common price for house brick.

[Deleted]

Hi Joseph,

I my region of France, common bricks are quite expensive while very good firebricks brought directly at the brick maker costs roughly the same. I also think common bricks can be used for the outer skin, and if they are cheaper for you then it's a nice solution.

For the price, it was the total price of all the materials :
- 330 bricks (with a safety margin) of 220x110x60 mm, 2€ delivered so 660€
- 17 lintels (with a safety margin) of 600x110x60 mm, 12€ delivered so 204€
- 10 refractory insulating flame-contact bricks (with a safety margin) of 220x110x60 mm, 7€ delivered so 70€
- 2 buckets of 25kg of REFRACOL 240 mortar, 75€ delivered
- neoceram glass, 35€ delivered
- superwool + flat joints + round joints , 60€ delivered
- metal stuff, 250€ without the work !
- 20€ for two thermometers

So it's 1375€ plus a little safety margin (chimney flue, concrete, sand..) and we come to 1500€.

In france, industrial and artisanal mass heaters of this power go easily above the 5000€ mark.. so there is quite a big sum left to make cheaper heaters or a good salary, depending on the builder's goal.

regards,

[Orange]

if I understood Peter correctly, he doesn't count the uninsulated chimney into ISA if it is a vertical pipe that doesn't connect much with the heatear (like the brick chimney draws heat trough conduction).

and interesting, French are willing to pay more for the heater that doesn't have the bench

[pinhead]

There's only one thing I would change.

I would insulate the first internal "bell" (portion of the stove into which the riser feeds directly) with ceramic fiber or equivalent; such a short riser won't keep the gasses as hot for as long as the taller standard riser will. Insulating this portion will give the gasses more time to burn before the heat is extracted.

In the standard Batch Box, the Turbulence is provided by the transition from the throat into the riser, and the tall riser provides the Time. If you reduce either of these T's, the stove will take more time to clean up the smoke.

Insulating this portion should shorten your "warmup" time, making it quit smoking more quickly.

[Deleted]

pinhead , Have you seen my other thread about my cookstove with this same core ? Combustion results are excellent in my opinion. Far less than the french standard for mass heaters. It's not only the shortened riser, there is the half octagon not all the way up and the small bell above.

And what is your goal CO-wise ? At what level do you consider it burning clean enough ?

Regards,

[manU]

Hi. Really like this design, looking foward to see it burning.
I believe the first small bell will help prevent warping the cooktop and would also make a nice black oven after the fire is off. Closing it with a brick or something to keep the heat longer. Maybe would need a bigger door to it?
Another thought is that you could build the lower bells/base in a way it could be modified through the clean holes to try different bell setups. Moving bricks around for example.
Good job yasintoda! Thanks for sharing, and please keep that motivation going.
Cheers

[coastalrocketeer]

My observation of a hot water stratification tank system and the "kinetic energy input reducing" structure used to avoid disruption of stratification layers in the tank from hot water returning from the solar thermal panels at different temperatures throughout the day, and with existing temperature stratification layers at different heights, depending on the tank's current "heat charge," has me wondering how we can use structure within, or at entry into a bell similarly, to promote and preserve the desired stratification.

Columns throughout the bell, offset, such that gasses flowing between columns run into the face of the next column... could both store extra heat and slow and dissipate or spread evenly, the kinetic energy of gas flow entering and circulating within the bell. Thermal stratification would increase each time the lateral movement of the gasses was changed in direction, I would think. Some number of rows of columns, in the first part of the bell after the gas entrance, would increase stratification in the part of the bell after them.

A "perforated" wall from floor to ceiling with properly designed passages at various heights passing through it into the ''main bell" and designed to combine to an "effective CSA" that allows unrestricted flow, but dissipates kinetic energy before entry into the "main section" of the bell where we are trying to optimize thermal stratification, seems possible.

It is also possible for applications to use gas flow entry velocity to decrease stratification (increase turbulence and even mixing) in the top area of a bell to maintain even, high heat in the entire surface area of a tank suspended in the top half of a bell, for instance, or an evenly warm on top bench, while dissipating structures" in the bottom half of the bell reduce that kinetic energy, slow the gasses (into a larger CSA?) and allow stratification in the lower half of the bell, for allowing remaining heat to collect into the dissipating structure mass, before reaching the exhaust below that.

In a water tank hating bell, outside walls around sides of tank and supporting structure could be mass, with mineral wool or other heat resistant insulation outside, to provide that the the mass down low lose most of it's heat through the thin walls of the water tank, into the H2O portion of the total "heat storage battery" after the fire has gone out... (does this idea deserve it's own post for further development?!? ;-)

These things could conceivably help with things like "heating an open vat of water on top of and in the bell," even if they don't actually help much with the heat storage and extraction aspect for small bells beyond just having extra columns of mass inside the bell while maintaining enough CSA for the effective stratification of gasses...

Since all this is probably NOT JUST "potentially applicable to making bells smaller", I'll copy this comment to it's own thread and subject of "optimizing heat transfer in stove design through modification of stratification levels up or down in bells and other heat transfer chambers through the intentional induction or dissipation of kinetic energy within the gas flow, via the optimized design of gas passage and mass collection structures, and other means."

Another set of thoughtsI had just now, that may or may not be partially or wholly true, coalesced into the statement that:

"radiant heat (infrared through visible light range transferred heat, possibly other portions of the spectrum but almost assuredly those) generally does not heat transparent gasses or liquids well, but heats non insulative/conductive non-transparent MASSES well.

gasses and liquids transfer energy mostly through conductive heat and move it through convective heat and gas/fluid flow

When a gas/fluid stream is slowed/path altered by an obstacle in free space filled with that gas/fluid, molecules will preferentially change direction vertically based on bouyancy.

Structure and temperature can modify the distribution of kinetic energy, velocity, and direction, or lack therof, in gas/fluid flow through systems, and together with thoughtful system design, modify multiple factors locally in different areas of the system, such as time for conductive contact and heat transfer, and promoting uniformity of temperature or promoting stratification to optimize heat transfer.

We can use this knowledge to optimize gas flow in our systems, and transfer of heat or prevention therof to specific parts of our system.

(Disclaimer: None of the bouyancy/thermal stratification effects will work as well in lower gravity environments, or at all, in outer space/zero G, so don't design the same structures and expect the same results if using them on the moon, or the space station, or your next interplanetary mission!)

If anyone knows of real world examples of structure used to preform these types of functions comment to them here f applicable to making bells smaller, and in my primary thread topic inspired from this post... Anything from the masonry stove or kiln/furnace design world or other applicable research on these sorts of things as applicable to "gas flow in heat pools" it, let me know in my separate thread entitled "optimizing heat transfer in stove design through modification of stratification levels up or down in bells and other heat transfer chambers through the intentional induction or dissipation of kinetic energy within the gas flow, via the optimized design of gas passage and mass collection structures, and other means"

Though I expect stratification is not normally desirable in kilns and furnaces where even heating of the product being heated is desired, so may not be anything from that realm that is directly prescient, but maybe that is just an issue of holding the heat input to the bell higher than losses through it's insulation and exhaust gasses long enough to have the exhaust gasses rise to the temperatures needed for the process for the necessary period of time. Actually, I guess you want turbulence and uniformity of temperature in the area of things being heated in the furnace or kiln, and stratification below that but above/before the exit to retain that heat in the gasses of the "area of work"

I don't know if any of this is right, but it makes sense to me, in this moment.