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Post by satamax on Dec 11, 2013 11:06:16 GMT -8
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Post by peterberg on Dec 11, 2013 13:28:45 GMT -8
Oh, that's easy. By using a fan.
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Post by satamax on Dec 11, 2013 14:01:58 GMT -8
Oh, that's easy. By using a fan. Well,i thought without a fan!  I know where the batch box originates from, i know the work you have done on it. My gut feeling is that with a properly tuned venturi, it could be better. To me what you have done is already a venturi. I wonder what it would take to make it work better with the full firebox, staggered sticks situation, you know when it belches black smoke. The batch box has let say speed 0.8 in the firebox, speed 3 or 4 going through the port, then speed 1 in the heat riser. Since it's smaller than the firebox. Plus there's the expansion of the gasses. You remember the drawing i had done with a 30x30 chimney flue element, a round hole on top, of about 70% heat riser size, and a round heat riser on top? Well, rechecked, it was a square hole. easycore.skp (84.71 KB) Well, i'm still thinking along this line. Let say, a box like this. 3 to 5 times the heat riser size. Which means speed in the heat riser should be about that 3 to 5 ratio, at least. But doing a real round venturi, like in a carburetor, well even better, with the right plane wing shape. Along 20/30cm. I don't know about the ratio. 60% heat riser size, may be less. You know, it's gut feeling, but, is there something behind this. I think, even J tubes could benefit from something like this. But, my opinion is that the turbulence, mixing of the gasses drags too much on the flow. In your batch rocket as well as in the J tubes. The idea would be to trade that change of direction induced turbulence, by "chocking" turbulence, in a venturi. And try to take advantage of the speed induced by the venturi, plus expansion of the gasses after the venturi, and their tendency to rise when heated, to have something which draws like mad. Forget altogether about horizontal of downdraft. But just concentrate the gasses together, trying to keep their velocity as high as possible. For the moment there's no snow, so i'm kind of jobless. I'll have to make the flat's batch rocket. But after. I wonder if i won't try that. Well, sorry for babling away. |
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Post by Rinchen on Dec 12, 2013 0:14:31 GMT -8
Hi,
Just my 2 cents on this...
First about the flame temperature, Wikipedia say this:
"The constant volume adiabatic flame temperature is the temperature that results from a complete combustion process that occurs without any work, heat transfer or changes in kinetic or potential energy. The constant pressure adiabatic flame temperature is the temperature that results from a complete combustion process that occurs without any heat transfer or changes in kinetic or potential energy. Its temperature is lower than the constant volume process because some of the energy is utilized to change the volume of the system (i.e., generate work)."
Which is a situation that is not achievable in a wood heater, you will always have volume change (work done), heat transfer and loss of kinetic energy due to drag.
Your "riser on top" core I think should really have the flue element in a vertical position and burn your wood top-down. The restrictor port can in this case be smaller, more like from 25% to 50%. Much like a TLUD.
Otherwiser the flame will want to stretch out too eagerly and this by itself will reduce the heat concentration. Take a look at center draft oil lamps, they are designed to keep the flame down, especially the ones with a flame spreader. If you lift the glass chimney a bit, the flame will stretch up into the chimney and it will generate black smoke. Going down this route you might get some more turbulence compared to a side drafter and the stove is less likely to smoke back, because the hot gasses can rise up immediately. Inducing secondary air at the restrictor area will still be very much needed. Nevertheless it is a new stove which would have to go through a whole lot of testing in order to get it to the same level as the batch box. Big plus with this design is that it can be made to run pellets or wood chips in a batch manner (TLUD).
It is not likely that you need to get the temperatures up more in order to burn more cleanly, this part has already been achieved. The temperature is already of such intensity that you need high quality refractory to make a durable heater.
Of course you might want to use it to melt metal, which is another matter alltogether for which charcoal is more suitable.
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Post by satamax on Dec 12, 2013 1:06:35 GMT -8
Thanks a lot Rinchen.
Well, i've noted this, using a vertical arangement for the wood.
And that it's not needed to burn hotter. If i want to play with metal, there's always the coal/charcoal options.
Yep, doing "ring injection" of air after the venturi seems realy clever.
And in the back of my head, there's that idea of regulating the draft mechanicaly. I mean, some gate would close a bit on the firebox, and aditional air port would be opened at the air ring of the venturi.
Well, plenty of things bubling into my head.
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Post by Robert on Dec 12, 2013 7:22:30 GMT -8
maybe there is good kind of a bubling... recently my friend ask me to do a rocket stove for him as kiln for his ceramic work... he said that the temperature of 1600C is needed for proper baking... as i was speaking with Peter he said me that 1200 was a maximum he calculated at the base of the riser, and 550 on the top of a riser...
in old kind of kilkns they were reaching those big temps, but with using a loooot of wood... that whay my friend asked me for a rocket... so he will not have to use so much wood... but is it possible to get more temps, thats the question.
if you find some solution please share... i am still thinking how to make that high temp. kilk for baking ceramics.
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Post by Rinchen on Dec 13, 2013 4:35:35 GMT -8
satamaxFun isn't it? If I had more time I would love to experiment with such a setup, but so far the construction of my new batchbox + brick shell is going quite slowly, little by little. So I don't think that is going to happen :-) robertThere is somebody in the Netherlands that is using rocket stoves for building glass melting ovens. He has gone through a lot of efforts to get high temperatures and is able to reach about 1200C in the dome above the heatriser. I suppose that is about as good as it gets. It still takes a good bit of stoking to reach that temperature. A fan would probably reduce the stoking time, but whether you will get higher temps.... that will have to be tested by someone :-)
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Post by Deleted on Dec 13, 2013 8:12:37 GMT -8
And try to take advantage of the speed induced by the venturi, plus expansion of the gasses after the venturi, Actually there is no expansion of the gases after the venturi, only a change of speed and distribution without real change of volume. Gas streams are incompressible below the speed of sound. |
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Post by satamax on Dec 13, 2013 8:48:59 GMT -8
And try to take advantage of the speed induced by the venturi, plus expansion of the gasses after the venturi, Actually there is no expansion of the gases after the venturi, only a change of speed and distribution without real change of volume. Gas streams are incompressible below the speed of sound. Karl, are you realy sure? There's no expansion of gases if the temp is equal But if we can manage to produce a good secondary burn just after the venturi, gases expand and become less dense as their temperature rise |
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Post by Deleted on Dec 13, 2013 10:41:01 GMT -8
Actually there is no expansion of the gases after the venturi, only a change of speed and distribution without real change of volume. Gas streams are incompressible below the speed of sound. Karl, are you realy sure? There's no expansion of gases if the temp is equal But if we can manage to produce a good secondary burn just after the venturi, gases expand and become less dense as their temperature rise It is not quite as simple. For example: One mol of CO has 28g, one mol of CO2 has 44g and both will occupy the same volume. The raise in temperature may not be enough to compensate for that. For a good secondary burn just after the venturi a high amount of excess air is needed. But in general you are right. |
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