stoker
Junior Member
Posts: 61
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Post by stoker on Feb 16, 2016 14:21:32 GMT -8
Haven't experimented with a narrow version. I think I see where you're going with it though. Would probably be best to line the box with ceramic felt and then stack firebricks on their sides on both sides. That would leave just over a 4 inch wide box, 16 inches deep. Might give it a try sometime. That's the sort of experiment I had in mind. I'm wondering about a smaller version and thinking that shrinking just the width probably won't change its behaviour much, whereas shrinking other dimensions might mess up the near-circular rolling tumble that I imagine is happening: air flowing down the inside of the door, along the floor to the back, up the back, along the ceiling towards the throat. |
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Post by Vortex on Feb 16, 2016 15:37:37 GMT -8
I think another difference with these vortex fire chambers from a metal box stove is their ability to accumulate a lot of heat in the mass of the chamber. When this is combined with reduction of excess air the gassification process is more ideal. Kind of like a vaporizer… Also, this being a masonry heater, the combustion is intentionally decoupled from the heat distribution by the flywheel effect of the whole heater's body. Thus there is no danger of smouldering so long as we treat it right. Exactly. That's the difference. Scandinavian airtight box stoves were good at the 'long slow burn', but the trade off was huge tar production in the chimney because the temperature was to low. The vortex stove stores the heat from the initial hot fast burn in the masonry core of the firebox, and uses it later when the stove is shut down to gasify and burn the volatiles efficiently. That's the sort of experiment I had in mind. I'm wondering about a smaller version and thinking that shrinking just the width probably won't change its behaviour much, whereas shrinking other dimensions might mess up the near-circular rolling tumble that I imagine is happening: air flowing down the inside of the door, along the floor to the back, up the back, along the ceiling towards the throat. Thought that was were you were going with it. Your description of the flow sounds about right from what I see in the flame patterns. I think the deep firebox shape helps with the gasification, so I don't see why a narrower version shouldn't work. I'll have to try it and see I guess. |
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Post by stuartmc on Feb 26, 2016 14:15:45 GMT -8
I really like this design and the efficiency you've measured/posted. After looking at your pics/diagrams and plans I'm wondering about your choice of flow path. It apears that you skipped a longer option (pictured below). Did you play with the other option and abandon it for some reason?
Also, it appears that your cross sectional area seems to vary. Am I viewing this wrong or could you speak to that a little?
Thanks, Stuart
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Post by Vortex on Feb 26, 2016 15:12:43 GMT -8
Hi Stuart, Thanks for your comments. I can't see your picture, but all the Vortex stoves I've built have the same flow path as the original. I did change the position of the startup bypass, maybe that is what you are referring to? Also I was very careful to maintain the minimum Cross Sectional Area right through the system, some areas are larger though, so that might be what you are seeing.
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Post by stuartmc on Feb 26, 2016 15:55:43 GMT -8
Sorry, it took me a while to get my goofy photo uploaded. It was the only way I could figure out how to clearly convey my question. Thanks for the reply - "keep the minmial csa" makes sense.
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Post by Vortex on Feb 27, 2016 12:04:33 GMT -8
OK, I see what you mean now. I thought about that flow path when I was designing it on paper, but thought it would create to much resistance. The stove turned out to have much better gas flow than I ever expected it would, so that double contra-flow path would actually probably work OK.
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Post by patamos on Feb 27, 2016 17:10:28 GMT -8
Yes i think Trev is right. The one i built with two bells has very good gas flow. I managed to squeeze about 5.5 sq.m. ISA into the lay out, plus a smaller .5 sq.m. metal top deck. This is a little under what Peter recommends for the 6" batch box. But i think this fire box could handle larger - especially with open bells.
With contraflow lay out every change of direction is a friction increasing factor. Not necessarily a negative, just something to keep in mind.
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Post by jojohannes on Apr 1, 2016 1:51:15 GMT -8
To anyone with a vortex stove. In particular to Vortex and patamos. I've read the entire thread twice now and thank you all for your work and sharing. I've dropped my original plan to build a rocket stove with bells and opted for the more compact vortex stove design recommended to me. I will call it "The Swirling Hermit's Hot Hog" now. Before I can get going I do have a few questions and appreciate any help and suggestions 1) dimensions My stove pipe running into the chimney is a 4.7" / 12 cm pipe. From what I understand I need to adjust the measurements (at least the inside measurements) of the firebox accordingly. If I get it right my factor is 0.783. Are the mini bells also affected in their scale or is all fine as long as the hot air channels through the thermal mass in one way or another? The latter is suggested by the bells used by patamos, but I wanted to ask just in case. Is the height of the firebox itself affected or is it not relevant to the "vortex action". What are the current recommendations for the firebox depth? Any new proportions? If my firebox is smaller than the thermal mass on the left side, should I put insulation on the outsides to keep the fire burning hotter - rocket stove style? 2) verdict on bells Since I do not need a large cooking area or too much instant heating and would rather have more thermal mass to store heat, I was thinking of putting a 5mm steel plate only on the right size. On the left (see drawing in red below) I would just add two rows of bricks on top making a hollow bell closed on top with chamotte plates instead of metal (I would keep the bypass option and stove pipe outlet - just make the walls taller). I know patamos has channeled the air into a bell after a downdraft. On the other hand I've read speculations here on how the stove get its efficiency that suggest that what is going on is a "horizional heat riser". In that case would it not be better to keep the top part level (with metal right and fire bricks/chamotte left)? I was also thinking of adding a small bench at the bottom and raise the stove a little (see illustration below). It might be a small area and get very hot close to door during parts of the burn cycle but Trev's cat just looks too comfortable to not to include something here for a very cold day when you come from the outside and want to warm up your bones for 5 minutes.  3) secondary air There was some discussion on secondary air. So I understood that in the original design a top gap at the door serves as a P channel. I also saw that there is a small back smoke issue in the case of patamos' version (your heater is an awesome "living room landscape" by the way). Vortex you saw that a delivery through the ash box bettered the result (would that be tertiary air?) Drawn in green I've included 2 Variants in the mockup above. Would you think any of these are feasible ideas? Var A: when moulding the bottom part include an air slit drawing room air from the right (above the ash tray) or Var B: a pipe with holes at the end coming in from the left delivering pre-heated air right above the door (which could be sealed at the top) or Var C (not depicted): a small opening like A coming from a mini bell on the left. Thus sending gases rather than air to be reburnt. This was one theory vortex explored if I got it right. Now about all that secondary air delivery. Could there be a problem (say with Var A) in terms of gases leaking at the end of the cycle with back draft or anything? I already got a CO alarm but would the chimney sweep maybe complain about safety if I have too many holes in the stove (well, only 2 really)? In that case of course secondary air could be drawn directly with piping from the outside. But I just wonder. 4) temperatures I've read about the hot inside temps of rocket stoves and found material recommendations of 1200+°C for the heat riser. What about the temp recommendations for different parts of a vortex? Looking at refractory cast material I found a variety of max temps (1050 - 1600) with differences in price obviously. They go from 30-90 € per 25 kg sack. What are the max heat recommendations for the following: a) refractory cast material ? b) glass for the door ? c) fire bricks ? d) pipe for secondary air (in case of Var B) ? 5) any innovations This thread was started over three years ago. After all the experimenting (trip wires, secondary air, bells) are the original designs still the way to go or is there something like a vortex 2.0? Thanks for any suggestions and help. I promise to video the whole building process and share it here (or a new thread if so desired) Cheers Johannes |
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Post by Vortex on Apr 2, 2016 5:24:57 GMT -8
To anyone with a vortex stove. In particular to Vortex and patamos . I've read the entire thread twice now and thank you all for your work and sharing. I've dropped my original plan to build a rocket stove with bells and opted for the more compact vortex stove design recommended to me. I will call it "The Swirling Hermit's Hot Hog" now. Before I can get going I do have a few questions and appreciate any help and suggestions 1) dimensions My stove pipe running into the chimney is a 4.7" / 12 cm pipe. From what I understand I need to adjust the measurements (at least the inside measurements) of the firebox accordingly. If I get it right my factor is 0.783. Are the mini bells also affected in their scale or is all fine as long as the hot air channels through the thermal mass in one way or another? The latter is suggested by the bells used by patamos, but I wanted to ask just in case. Is the height of the firebox itself affected or is it not relevant to the "vortex action". What are the current recommendations for the firebox depth? Any new proportions? If my firebox is smaller than the thermal mass on the left side, should I put insulation on the outsides to keep the fire burning hotter - rocket stove style? Hi Johannes, Is your whole chimney 4.7" / 12 cm or just the pipe running into it? Is it possible to put a 6" pipe into the chimney? If so this would be the way to go, otherwise you'll have to scale the stove down a lot. I've found the 16" deep firebox works best for me. When building a vortex stove with more mass I would definitely insulate the firebox. My original stove was designed to get as much mass within the small dimensions as possible. I wanted to get direct transfer of heat through the whole stove. I felt that if I insulated the firebox from the rest of the mass that I might not get enough heat transfer into the mass. The initial fast hot blast phase of the fire heats the firebox mass which then radiates back into the fire aiding the later combustion phases. 2) verdict on bells Since I do not need a large cooking area or too much instant heating and would rather have more thermal mass to store heat, I was thinking of putting a 5mm steel plate only on the right size. On the left (see drawing in red below) I would just add two rows of bricks on top making a hollow bell closed on top with chamotte plates instead of metal (I would keep the bypass option and stove pipe outlet - just make the walls taller). I know patamos has channeled the air into a bell after a downdraft. On the other hand I've read speculations here on how the stove get its efficiency that suggest that what is going on is a "horizional heat riser". In that case would it not be better to keep the top part level (with metal right and fire bricks/chamotte left)? I was also thinking of adding a small bench at the bottom and raise the stove a little (see illustration below). It might be a small area and get very hot close to door during parts of the burn cycle but Trev's cat just looks too comfortable to not to include something here for a very cold day when you come from the outside and want to warm up your bones for 5 minutes. I found the 5mm steel was not thick enough, I had problems with it bowing up. I'd recommend you use 10mm. Having the steel hot plate only above the firebox side is OK, you'll get less instant heat that way. I dont think you need to keep the top part level, just the horizontal channels inside. The bench idea should work OK so long as you make the channel flow through it, otherwise it wont warm up much. 3) secondary air There was some discussion on secondary air. So I understood that in the original design a top gap at the door serves as a P channel. I also saw that there is a small back smoke issue in the case of patamos' version (your heater is an awesome "living room landscape" by the way). Vortex you saw that a delivery through the ash box bettered the result (would that be tertiary air?) Drawn in green I've included 2 Variants in the mockup above. Would you think any of these are feasible ideas? Var A: when moulding the bottom part include an air slit drawing room air from the right (above the ash tray) or Var B: a pipe with holes at the end coming in from the left delivering pre-heated air right above the door (which could be sealed at the top) or Var C (not depicted): a small opening like A coming from a mini bell on the left. Thus sending gases rather than air to be reburnt. This was one theory vortex explored if I got it right. Now about all that secondary air delivery. Could there be a problem (say with Var A) in terms of gases leaking at the end of the cycle with back draft or anything? I already got a CO alarm but would the chimney sweep maybe complain about safety if I have too many holes in the stove (well, only 2 really)? In that case of course secondary air could be drawn directly with piping from the outside. But I just wonder. The secondary air gap is between the top and sides of the door and metal door frame. Pat mistakenly thought it was between the metal frame and firebrick, which smoked back so he had to fill it up. I've never had any problem with smoke-back between the door and metal frame. The 2mm gap between the door and its frame delivers pre-heated air into the throat just as well as your idea 'A' of the pipe, so I think why complicate it when it can be incorporated in the door? Easiest way to make the bottom air is to make an air-tight ashbox door with an adjustable air vent on the front. That way you can experiment and see what works best for you. I did do some experiments to see if I could get recycled exhaust gases to be drawn back into the firebox and also up through the ashbox, but there wasn't enough of a difference in pressure. It didn't seem inclined to flow in either direction. Never had any problems with leaking gases or CO, even with the chimney damper almost completely closed. 4) temperatures I've read about the hot inside temps of rocket stoves and found material recommendations of 1200+°C for the heat riser. What about the temp recommendations for different parts of a vortex? Looking at refractory cast material I found a variety of max temps (1050 - 1600) with differences in price obviously. They go from 30-90 € per 25 kg sack. What are the max heat recommendations for the following: a) refractory cast material ? b) glass for the door ? c) fire bricks ? d) pipe for secondary air (in case of Var B) ? The castable and firebrick I used on my original stove was rated at 1400°C. I've had no problems with it. I've read several different ratings for stove glass, the lowest one was 1000°C. The Pyrex lids I used in the beginning were rated at 500°C, they lasted about a year on average. I've done 2 winters now with the same piece of proper stove glass with no problems. If you make your own door, make sure to allow room for the glass to expand and contract or it will break. The flat sticky backed fire-rope is ideal for cushioning the edges of the glass where it is held into the stove door. 5) any innovations This thread was started over three years ago. After all the experimenting (trip wires, secondary air, bells) are the original designs still the way to go or is there something like a vortex 2.0? All the improvements I've found have been discuses before in this thread: Insulation, Big glass door window. Thicker top plate with expansion plates. Bottom air. Chimney damper. Etc. Thanks for any suggestions and help. I promise to video the whole building process and share it here (or a new thread if so desired) Cheers Johannes You're welcome to post here, Johannes. I look forward to the video. Trev |
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Post by patamos on Apr 6, 2016 8:53:08 GMT -8
Hi Johannes, Just a quick note to say i have just had a read of your post and Trev's response. The simple version from me is i agree with all that Trev has mentioned. With the addition that my experiment with secondary air above the door frame was partly an attempt (along with a sloping lintel) to induce a 90 degree air injection for optimizing turbulence in the throat. But the smoke back on early warm up was reason enough to let go of it. Also, i have noticed on one of my classic j-feeds with barrel that combustion performance improves when i place a fan to push heat away from the barrel top deck. This tells me that the rapid radiation that one achieves from a thin metal/ceramic-glass surface just downstream of the throat is likely helping the fire to draw somewhat. At the same time, this core has inherently good combustion tendencies, so once you weigh in the other important factors (eg, channel length and friction, bell shapes and sizes, chimney height, and pressure planes within and around the building… ) you will have a good picture of what the heater can be made capable of. thoughts for now  pat |
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stoker
Junior Member
Posts: 61
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Post by stoker on Apr 14, 2016 14:42:04 GMT -8
Any chance of one or other of you trying that half-width-firebox experiment some time?
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Post by jojohannes on Apr 14, 2016 23:30:00 GMT -8
I just returned from Italy (home of the hopeful "Hermit's Hot Hog" project) and was offline - hence the late response. But thanks Trev for your detailed response.
If I may, I have some quick follow-ups:
- chimney: I looked at it. It is built from stone and at the height of the pipe hole (which is 4.7") it would seem wide enough to accept a 6" pipe. But at the moment, I'm not certain the whole construction is straight enough not to create problems when trying to shove down a pipe. Where would you see the problem in scaling down the firebox to make it a 4.7" system (factor .78, I think)? I only have 25 m² compared to your 43 and they are really more like 12.5 on top of 12.5 (connected with a stairs through a hole). Or do you think the system will stop working as a system when scaled down that much?
-insulating the firebox: Would you insulate it all round (except for the metal top obviously) or just the wall between the micro bells and the firebox?
-10mm steel: I thought when reading previous comments that 10 mm would warp eventually? Or should it be fine in my case, because I only have half the area? I could maybe also get an old stove cook top that has the circle cut out and cut it to size.
Thanks Pat for your comment. Interesting observation about the heat up top. Maybe I should raid old PC parts and place a few heat sinks there :-)
Cheers,
Johannes
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stoker
Junior Member
Posts: 61
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Post by stoker on Apr 15, 2016 9:44:43 GMT -8
Also, i have noticed on one of my classic j-feeds with barrel that combustion performance improves when i place a fan to push heat away from the barrel top deck. This tells me that the rapid radiation that one achieves from a thin metal/ceramic-glass surface just downstream of the throat is likely helping the fire to draw somewhat. Right, that fits the standard theory of how gas-flow is achieved in J-and-barrel stoves with floor-height venting of the flue to the atmosphere. Reasoning about it: - Cooling the flue-gases when they're higher than the final exit to the atmosphere will help with draught, because the cooling makes them denser for their net-downward journey. The higher the cooling is done, the bigger the effect.
- Cooling the flue-gases when they're lower than the final exit will make draught worse, because the cooling makes the gases denser for their net-upward journey. The lower the cooling is done, the bigger the effect.
In a J-and-barrel stove, the barrel-top is often higher than the final flue-exit, so more effective cooling of the barrel-top makes for stronger flow. In these kitchen-stoves, if the choice is between cooling at the top plate or else somewhere lower down in the brickwork, then the top-surface cooling will mean better draught. But since the final exit is up a chimney, the draught will be better the hotter the gases are when they enter the chimney. So I think that having good cooling at the top plate just after the firefox will help draught when the internal brickwork of the stove is cold, but will make it worse when the internal brickwork is hot. |
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Post by Vortex on Apr 15, 2016 15:09:38 GMT -8
Any chance of one or other of you trying that half-width-firebox experiment some time? Sorry, Stoker. I've been looking for some insulating fire brick to stack against the insides of the firebox for the test, but still haven't been able find any available here except by the pallet load.. I just returned from Italy (home of the hopeful "Hermit's Hot Hog" project) and was offline - hence the late response. But thanks Trev for your detailed response. If I may, I have some quick follow-ups: - chimney: I looked at it. It is built from stone and at the height of the pipe hole (which is 4.7") it would seem wide enough to accept a 6" pipe. But at the moment, I'm not certain the whole construction is straight enough not to create problems when trying to shove down a pipe. Where would you see the problem in scaling down the firebox to make it a 4.7" system (factor .78, I think)? I only have 25 m² compared to your 43 and they are really more like 12.5 on top of 12.5 (connected with a stairs through a hole). Or do you think the system will stop working as a system when scaled down that much? -insulating the firebox: Would you insulate it all round (except for the metal top obviously) or just the wall between the micro bells and the firebox? -10mm steel: I thought when reading previous comments that 10 mm would warp eventually? Or should it be fine in my case, because I only have half the area? I could maybe also get an old stove cook top that has the circle cut out and cut it to size. Thanks Pat for your comment. Interesting observation about the heat up top. Maybe I should raid old PC parts and place a few heat sinks there :-) Cheers, Johannes Hi Johannes, I wondered what had become of you. I presume you mean the entrance to the chimney is 4 feet 7 inches high? An old stone chimney will certainly not have a CSA of 4.7 inches. It would be better if the chimney was lined and insulated but not essential. If you can get a 6 inch pipe into the chimney then definitely build a 6 inch system. A 4.7 inch CSA system would be uncharted territory with this stove. Insulation seems to help but I haven't done enough experimenting yet to be able to say what the optimum is. I would still use normal firebrick but insulate between the firebox and micro bells, and all around the top above the firebox except of course the hotplate. The 10mm steel hotplate did eventually twist, the front r/h corner lifted up about 2 inches. It took 9 months and happened when the owner was burning whole cardboard boxes. After I cut out an expansion plate the twist disappeared and never happened again. My 5mm hotplate bows up quite dramatically which makes it difficult to cook on as it's not flat. A recycled hotplate from an old range would be ideal if you can find one the correct size. Also, i have noticed on one of my classic j-feeds with barrel that combustion performance improves when i place a fan to push heat away from the barrel top deck. This tells me that the rapid radiation that one achieves from a thin metal/ceramic-glass surface just downstream of the throat is likely helping the fire to draw somewhat. Right, that fits the standard theory of how gas-flow is achieved in J-and-barrel stoves with floor-height venting of the flue to the atmosphere. Reasoning about it: - Cooling the flue-gases when they're higher than the final exit to the atmosphere will help with draught, because the cooling makes them denser for their net-downward journey. The higher the cooling is done, the bigger the effect.
- Cooling the flue-gases when they're lower than the final exit will make draught worse, because the cooling makes the gases denser for their net-upward journey. The lower the cooling is done, the bigger the effect.
In a J-and-barrel stove, the barrel-top is often higher than the final flue-exit, so more effective cooling of the barrel-top makes for stronger flow. In these kitchen-stoves, if the choice is between cooling at the top plate or else somewhere lower down in the brickwork, then the top-surface cooling will mean better draught. But since the final exit is up a chimney, the draught will be better the hotter the gases are when they enter the chimney. So I think that having good cooling at the top plate just after the firefox will help draught when the internal brickwork of the stove is cold, but will make it worse when the internal brickwork is hot. Theoretically the rapid cooling caused by the barrel top or hotplate should help the gasses to descend in the sides of the barrel or contraflow channels, and an insulated chimney should then help them rise again. I've noticed the draw decreases as the firebox temperature rises. This actually works to our benefit though, because when the Vortex stove firebox is really hot it reflects the stored heat back into the fuel allowing it to gasify slowly but efficiently, so it doesn't need a fast draw, and the slower transit of hot gasses allows more time for heat transfer to the mass.
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Post by jojohannes on Apr 16, 2016 1:08:04 GMT -8
Hi Trev, thanks again for your help and time. Not taken for granted and much appreciated! 4.7" (12 cm) is the diameter of the exhaust pipe that goes from the (old) stove into the stone chimney. The chimney is square and I have only taken some measures at the opening (inside ca. 18 cm), where it appears wide enough (maybe not for a heavily insulated pipe but at least a regular one). If the chimney is somewhat straight from top to bottom with no rocks sticking out, I should be able to climb the roof, take off my "traditional stone chimney top hat" and put a 6" pipe down there.  Then I can make the opening wider in the room where the stove will so as to fit a new 6" (15 cm) exhaust pipe. If this is indeed doable, I can take your plans 1:1. If not, I guess I have to venture into uncharted waters and let you know how I fare. One last question about the "mini bells". Since I don't know yet what the fire bricks measure that I can acquire locally, do I have to watch out for the CSA when constructing the heat storage "labyrinth" (CSA = in English is "cross-sectional-area", right?). Or is the only thing that matters the dimension of the firebox in relation to the CSA of the exiting pipe and chimney to ensure that it is working. With all the bell constructions from RMH I looked at, I would imagine, the dimensions of the bells are on the fluid side (except maybe making sure that they are not narrower than the CSA the system is based on?) |
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