Batch cookstove with a small riser

[esbjornaneer]

Dec 17, 2017 1:47:28 GMT -8 peterberg said:

 Making it wider in steps would create ridges at the inside which in turn could provide for additional small eddies along the walls, much like the trip wire effect.

This effect is similar to what I was offering you with regards to a 3rd shoebox on your DSR a while back and you said that further mixing would not be needed after going through the first port. I know the setup is totally different as we are still in a flame path here.

[Orange]

it's interesting how a classic steel barrel is just 0,5mm thick and can handle cooking and extreme temperatures.

why not use cast iron plate?

[Vortex]

Dec 17, 2017 23:02:53 GMT -8 @yasintoda said:

Hi everyone,

Vortex the plancha is 8 mm steel. I've made something similar than you to deal with the dilatation. I think I've just been too high during the "hard testing" and the outside temp of the plancha was 550°C at max which is very high.. For the next plancha we'll use steel angles welded under it to prevent wraping, but if you have another idea, that's welcomed !
I'll use that joint yes for under the plancha. It's the same we use for the glasses and the doors.

Regards,

550*C is a bit high for 8mm steel, especially on a plate of that size. Think of a cast iron plancha on a commercial cooking range, they're usually about half an inch or 12mm thick, and never in one piece as large as that without an expansion/dilation plate in the middle.

Dec 17, 2017 15:51:28 GMT -8 wiscojames said:

If you get a chance to post a picture, I'd love to see how it's welded, etc. Is it in your build thread? I have access to steel and welder, and it is more durable than a glass top.

Wisco, The best picture is here: www.vftshop.com/images/others/Stove/Explates.JPG

[Deleted]

Vortex thanks for the pictures that's very interesting. Here are the detailed pictures of the plancha and it's support. The round hole is the dilatation system. It is right above the riser because I wanted to see the vortex and because I thought it would be the hottest place. In fact the hottest place is approx. 10 cm on the left.

How do you manage to weld all this without wraping ? I had to use a heavy hammer to rectify everything in my setup.

Maybe the solution as you said is to make it smaller ? Something like two sheets of 600x300x8 mm each instead of a single one 600x600x8mm.





Orange bending a flat sheet of metal is very easy. In the barrel the metal that is orthogonal to the top sheet reinforces it a lot.
I don't use cast iron plates because they come from far away, they don't fit to the sizes and they are much more expensive. In the end, to make my own plate means that we're paid more while the cost of the heater is lower or similar.

regards,

[travis]

Haha thanks I am a little behind.

[Vortex]

I see you have 2 pieces on top of each other already, are they both 8mm each or 2 X 4mm to make 8mm total?

600mm is too large in one piece even with the very thick steel. I would divide the big one into 3. Works best if the hottest part is the middle of a small plate.

When I weld them I make small welds on each side, gradually moving around the sides, so each weld is in the middle of the welds I've already made, until it is all done. That way it doesn't warp the plates.

[travis]

Does that help dissipate the heat or just give extra strength?

[Orange]

maybe you can weld some "ribs" on the back for reinforcement, many cast iron plates are like that.

[Deleted]

Vortex thanks for your answer ! Both are 8 mm thick. I'll see then, maybe I'll make three different plates. Thanks.

Orange the ribs will be steel angles I referred to in a previous post, something like 50x50x5 parallel to the length of the bell. I haven't done it in the previous configuration because it would have bent the metal sheet. Now with two or three different sheets it's easy to implement.

travis it's for the strenght. The steel angles will do both because they add an exchange surface as well.

Regards,

[drooster]

The ribs on the underside of my 1960's cookplate Rayburn are absolutely huge (>5cm deep, and thick) and follow the hot gas path.
Even so, after presumably fifty years of running the whole plate is warped up at the ends.
I think the plate is cast steel but may be cast iron like the rest of the stove body.
I took a photo but it's ON, and four red stripes doesn't look very impressive.

[Dan (Upstate NY, USA)]

t's interesting how a classic steel barrel is just 0,5mm thick and can handle cooking and extreme temperatures.

Orange,

Steel barrel bottoms flex up to .5 inches when they get hot and expand. They move even more than those big plates.

They just spring back to their original shape after they cool off where the heavy plates can warp permanently.

[Deleted]

Hi everyone,

The plancha is now flattened but I'm still waiting for the joint to seal everything properly.

I've been observing the flames in the new configuration and there are still two distinct jets of flames. One being yellow pale and coming from the higher part of the port. This one goes quite directly up.
And there is also a darker flame going down at the bottom of the riser. This one is more turbulent.

Strangely enough, the octagonal shape in the riser is not producing a better double vortex..! As of now I've mostly seen a single big vortex.
In what I have seen it seems to me that the double vortex was better formed in the half octagonal configuration.

Some pictures :





Regards,

[Deleted]

Hi everyone,

I'd like to share some thoughts with you all. They come from a discussion I had with pyrophile where he said that he did'nt believe that testo measures where reflecting the true efficiency of a heater.

So I've been doing some analysis on the measurements I've done last week and on the cookstove the mean time between the beginning of the fire and the when I close everything (the primairy air inlet and the closing valve) is approximately 2h.

The mean time of a firing measured by a testo (between the beginning of the fire and 16.8% O2) is 50 minutes.

So on average, there is 70 minutes more to the firing that we don't analyse. The problem with those 70 minutes is that the efficiency gets quite low during this period because :

- the excess air is high because the fire is very small (red coals only) and because the draft that has been created during the firing is strong. On average the draft at the end of the testo firings is 14.5 Pa. At the beginning I've done less measurements but the draft is around 6-7 Pa when the heater is lukewarm.
- combustion efficiency is bad because the coals are exposed to too much cold air and so they get cooler and the combustion is impacted.

I haven't done testo measures on that period because it's long BUT I think I can safely extrapolate that in these 70 minutes, in my heater, the average global efficiency is around 60%.

From the testo analysis of the first 50 minutes of the combustion, the average global efficiency of this period is 86.7% for my cookstove.

From that I can say that the true global efficiency of my heater is : (50x86.7 + 70x60)/120 = 71.1 %

..Which is quite disappointing !



I have two conclusions about that :

- It seems that the threshold of the floor channel is making the red coal phase longer, so the threshold is lowering the global efficiency of the heater.

- Our way of measuring the efficiency of a heater is biaised and overestimates by approximately 15% the real global efficiency



So how can we shorten this red coals phase ?


Regards,

[rakettimuurari]

Dec 20, 2017 0:01:54 GMT -8 @yasintoda said:

I have two conclusions about that :

- It seems that the threshold of the floor channel is making the red coal phase longer, so the threshold is lowering the global efficiency of the heater.

- Our way of measuring the efficiency of a heater is biaised and overestimates by approximately 15% the real global efficiency



So how can we shorten this red coals phase ?

Hello Yasintoda,

It seems that optional under-air configuration with cast iron hearth-grid plate helps in that significantly. Cast iron grid will last remarkably long, even with the under-air being closed most of the burn. When flames die, you just close the door air inlet and open the under-air. Embers are done in 15 min. I have been using it for 1,5 months now and am really happy.

Marcus Flynn/ Pyromasse seem to have also similar implementation option in his commercial builds. 


My cast iron cents...

[peterberg]

The test runs are mainly done to compare different configurations and heaters with each other. As long as the tests are started and ended following the same parameters comparing is good.
When you want to know the real efficiency, keep measuring until the next burn.
How to shorten the red coal phase is easy: like the Austrians do, close the air inlet and keep the chimney damper open. The coals will die by themselves and there's a coal bed to start the next burn on. If I remember correctly, this will lower the CO production significantly.