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Post by Karl L on Oct 19, 2022 11:05:45 GMT -8
At some point this summer or Autumn I'm going to convert my 125mm (5") DSR2 into a Vortex-style stove. Because I'm converting an existing stove, the new design has to fit in a narrower space than ideal. I hope that won't compromise the design too much. I think the available space can support a Vortex design with a system size of 115mm (4.5"). Part of the reason I'm doing this is to remove all of the ceramic fibre board from the stove and use vermiculite board only. Another reason is to get rid of the steel secondary air tube, which burns away and needs replacing too often. I am guessing it may be difficult to find/achieve the correct top chamber resistance. Also, it may be hard to figure out the size and positions for the various air inlets, given I want to use as much of the pre-existing metal work as possible. I finished converting my 125mm (5") DSR2 core into a 115mm (4.5") Vortex core a few weeks back. The weather has been too warm here to run it much, but it seems to work well. I wanted to see if the Vortex core would work with an unlined (~6m high) chimney, and it seems to be fine. I'll have to wait for the cold weather to really test it. Because I was worried about the lack of draw from the chimney I left the limiting primary air path restriction (the mesh) at 42%, as I could always reduce the inlet if necessary. Compared to the DSR2 I've found: - It's much easier to light
- Doesn't over fuel so easily (even with exactly the same 25mm Skamolex wall firebox)
- Burns for much longer
- Takes up only 75% of the volume
- Leaves firebox glass much cleaner
It's attached to a temporary bell -- a tall welded steel box with 2.0 msq internal surface area, surrounded by 250Kg of dry stacked firebricks.
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Post by Karl L on Sept 8, 2022 5:23:24 GMT -8
That's great, Martin. I've started rebuilding my DSR2 into a 115mm Vortex, and I'm thinking about whether I'll need a secondary air supply of some kind - does your stove work without it? (I'm currently working off Trev's specification of 30% primary air only - i.e. no secondary air).
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Post by Karl L on Aug 17, 2022 13:28:45 GMT -8
Primary air doesn't need to be hot, room temperature would be fine. Too hot and there's not enough oxygen in the volume of air. Resulting in similar problems I experienced with my DSR3 prototype. That's a real gem of info, Peter. It seems so obvious now, but it never crossed my mind before. Searching online I see that air raised from 22C to 49C increases in volume by 10%, I couldn't find info for higher temps, but if it carries on at that kind of expansion rate then that is a significant difference. Also room temperature air would expand more upon combustion in the stove creating more draft. The calculation is quite simple: The volume of any gas is almost exactly proportional to its absolute temperature -- i.e. it's temperature measured in degrees Kelvin (K). To calculate the temperature in K, just add 273 to the temperature in Celcius (C). So room temperature in K is 22 + 273 = 295K. So if the temperature of a gas rises from 20C to 320C, then it rises from 293K to 593K. So the proportional increase is 593/293 = 2.02. So the volume will double.
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Post by Karl L on Jun 19, 2022 8:49:42 GMT -8
Thanks - that's really useful!
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Post by Karl L on Jun 18, 2022 21:19:55 GMT -8
Trev, a while back I saw you were experimenting with increasing the surface area/volume ratio by placing pieces of vermiculite board in the top chamber, aligned with the gas flow. Did that work? Given the width restriction in my situation, I'll probably have to do something like that. The experiments with high surface area to volume ratio in the top chamber, showed that at the highest levels it creates a very stable low CO. burn, but the fire usually runs out of O2 at some point and then the CO. goes vertical. This happens because the high surface area drag leads to a much slower gas flow, which means less air over the fire. Thanks, and sorry, I realise I wasn't being very clear. I guess my question was: can the surface area/volume ratio be increased by adding an internal wall? I wasn't thinking of going for a very high surface area to volume ratio, just trying to get the same value as in your system (1.45), but in a situation where I have limited width. I have only 177mm internal width available for my top chamber. For a 115mm system, to get 1 CSA, the top chamber has to be 59mm high. The sa/v value for this is about 1.3. I was thinking that I could place some vermiculite board as a central divider, so the top chamber becomes two channels, with increased surface area/volume. Then, by making the divider less than full height, the surface area could adjusted to get the right sa/v value. Does that sound reasonable?
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Post by Karl L on Jun 18, 2022 5:37:57 GMT -8
Increasing the depth of the top chamber would actually lower the surface area to volume ratio, ideally you want to increase it while still keeping it 1 csa, to get that you want it wide and shallow. The increase in surface area creates back pressure without a restriction, which makes the burn more stable. Trev, a while back I saw you were experimenting with increasing the surface area/volume ratio by placing pieces of vermiculite board in the top chamber, aligned with the gas flow. Did that work? Given the width restriction in my situation, I'll probably have to do something like that.
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Post by Karl L on Jun 11, 2022 12:08:57 GMT -8
At some point this summer or Autumn I'm going to convert my 125mm (5") DSR2 into a Vortex-style stove.
Because I'm converting an existing stove, the new design has to fit in a narrower space than ideal. I hope that won't compromise the design too much.
I think the available space can support a Vortex design with a system size of 115mm (4.5").
Part of the reason I'm doing this is to remove all of the ceramic fibre board from the stove and use vermiculite board only.
Another reason is to get rid of the steel secondary air tube, which burns away and needs replacing too often.
I am guessing it may be difficult to find/achieve the correct top chamber resistance.
Also, it may be hard to figure out the size and positions for the various air inlets, given I want to use as much of the pre-existing metal work as possible.
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Post by Karl L on Dec 2, 2021 13:04:51 GMT -8
I used to have secondary air around the sides of the door, but have recently found that it works better instead if you just increase the primary air at the bottom of the door to 50% and cover it with a mesh screen so it's about 30% when fully open. The position across the whole bottom of the door means that all the air has to travel up across the fire, and the screen diffuses and mixes the air into the gases. (ATM my air control is just held in place by 2 magnets until I get around to doing it properly) Thanks for that, Trev. Do you still have the 30mm high threshold, in the firebox, just inside door? I looks like the mesh you are using is around 7mm x 5mm aperture - is that right?
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Post by Karl L on Sept 21, 2021 22:26:36 GMT -8
Hi Trev, can you say more about why you need firebrick (thermal mass) in the firebox?
What happens if you use, say, vermiculte board for the firebox?
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Post by Karl L on Sept 20, 2021 22:11:38 GMT -8
Hello Trev, I think you have put the latest drawings of the Vortex Stove at the start of this thread, and also a Sketchup drawing.
The Sketchup file requires Sketchup 18.01, and I have 17.2.xxx - which I understand is the last version that is available to use for free.
Do you know how I can open your drawing without paying for Sketchup?
Thanks!
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Post by Karl L on Jun 18, 2021 3:08:44 GMT -8
Thanks for that information. It's good when companies are fully open about their products.
I found an industry response to this concern, with links to some research papers (https://www.ecfia.eu/facts-cs/). It's not easy for me to know how independent the researchers were, but the papers suggest that the bio reactivity of heated High Temperature Insulation Wools is not high.
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Post by Karl L on Jun 17, 2021 10:55:55 GMT -8
There's one catch with Superwool though: when it has been heated to a temperature above 800 ºC (1470 ºF) it will form crystals (Kristabolite) and those resulting fibers won't dissolve at all. Thanks for that, Peter. Where did you see this information about Kristabolite forming from Superwool?
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Post by Karl L on Mar 23, 2021 14:15:15 GMT -8
I think what Soloman is suggesting is that there is no physical mechanism by which more than a minute amount of heat can flow back from the barrels to the core.
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Post by Karl L on Mar 21, 2021 5:23:42 GMT -8
My reason for suspecting efficiency could be greater by using hot gas bypass is that the greater cooling of most of the flow will capture the heat of vaporization from more moisture in the gas. As I understand it, it may be possible to extract the latent heat of vaporisation by the codensation of the water vapour in the exhaust gases, but if that condensate is not removed, then it will eventually have to evaporate, and then absorb the same amount of heat it previously deposited. In which case, for this to work you'd need to have a condensate drain of some kind, just as in a condensing gas boiler.
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Post by Karl L on Mar 20, 2021 23:01:06 GMT -8
It seems to me that more cooling followed by hot gas injection can actually increase efficiency and result in dryer exhaust. Can you say why you think the efficiency might increase and that the overall exhaust will be dryer? Thanks!
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