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Post by pinhead on Oct 20, 2014 12:33:26 GMT -8
Okay, now I have learned again something: To increase the "pumping" effect, I have to work on the riser: -increasing the length, -increasing the temperature. -better insulation -increasing the distance between the end of the riser and the top of the bell. Yes, all of those factors will increase the positive pressure exerted by the heat riser into the rest of the system. But are there no other effects? What about -cooling down gasses at the surface of the drum - causing them to sink down (this was often remarked at permies and the youtube videos) This is, indeed, one of the reasons the exhaust gasses are able to allow hot(ter) air to move into the barrel - the barrel dissipates some of the heat from the gasses which, accordingly, become relatively cooler (and more dense) than the streaming hot gasses coming from the riser. The temperature differential between the outlet of the riser and the barrel is what allows the heat riser/barrel exchanger to work. -in a bell there are different hot gasses, some are sinking down - do the add to the acceleration of the exhaust gasses? The gas movement within the bell does very little to assist the overall mass movement of gasses between the inlet and outlet of the bell. In other words, the convection occurring within the bell has very little effect on the flow through the bell. -the shrinking of the gasses during cooling in a pipe with constant diameter do they add some kind of vacuum or not? and the condensing action, removing again volume? Condensation/cooling produces a vacuum in all directions - in other words, it is non-directional and doesn't greatly effect the mass flow through the system, though it does effect convection within the system. -the move downwards of the gasses constantly cooled down, does this affect nothing? (I am really asking - I don't know) It does a little. However, this effect is only a very small part of what drives the mass flow through the system. For instance, the reason the heat riser has to be much taller than the feed, is to force the flame downward in the presence of the cooler air of the feed. In other words, the "suction" of the riser has to overcome the "suction" of the feed which would want to naturally flare "up" and "back." Yes I have a strong radial fan, I just could add it, and there would be no problem - or possibly too much draft. But somehow this is not the way a rocket heater should be run... I've used various small fans in the exhaust when I was experimenting with too-small stoves with too warm outside air and mass that was too cold. They work, though defeat the purpose of having a rocket stove in the first place, IMO. And now I have another idea: Could there be something like a negative riser (or a "sinker") having the same pushing effect downwards as a riser? By means of using the cold sinking gasses? Which means there are somewhere two different hot gasses and the colder ones are accelerating downwards? The question is: Does everything depend on the temperature between the out-coming gasses and the ambient temperature? Or can there something reversal happen inside the system like the riser did? It has not only to do with the temperature or the weight of the gasses, but also with pressure. The rise is building up internal pressure, could there be something which reduces the pressure, thereby creating a "sucking" action or at least reducing the resistance? Yes, everything does depend on the temperature differential between the "source" and any vertical within the "medium." i.e. riser to barrel, barrel to plenum/mass and mass to chimney (if applicable). Here the idea of a negative riser: in a bell there is a pipe or barrel vertically attached to a cool wall. The gasses inside cool down, are sinking and runnnig towards a kind of funnel connected to the outlet of the bell, pushing the gasses out. Or: A vertical pipe leads the incoming warm gas towards the center of the bell, where the gasses are rising towards the ceiling, getting cooled down on the walls, and are pushing towards a funnel-shaped bottom with an exit in the center. And still I think this will happen automatically, even when only the outlet of the bell is a bit lower than the inlet. Conceptually that would work, though in order for the gasses to "fall" out of the exit of the bell, they must still be cooler than the air into which they are flowing - otherwise there will be no flow. I found already: a big plastic tank for the last (condensing) bell, a big metal hood with about 4,5 m² for one bell, and another 200 liter drum. As this project should run quickly, there will not so much mass be included. The heat storage will be left over for one bench and the already existing brick walls nearby. And I found out that the batch rocket is not so easy to handle, so I will start with a J-Style burner / riser.So far for today. Keep us apprised on how it works!
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Post by mwalimu on Oct 21, 2014 2:11:28 GMT -8
My main, number one design criteria, the BIGGEST question that I always ask myself when designing something is this: Does this solution here, this solution that I'm now considering, solve more problems than it creates or does it create more problems than it solves? I always use the balance-beam of this question to answer the fundamental question: Is this worth it or not? On one hand, I REALLY like the direction your inquiry is going, I think that it is a worth-while line for experimentation. On the other hand, in my opinion, it is HIGHLY unlikely that solutions along these lines will be practical enough to satisfy my base criteria.. I fully agree with you, and I will not build a monster with a lot of first-aid-bandages. But I don't give up easily, and in most cases I came to good results of my projects. what I have learned already with the rocket mass heaters, that they are consisting out of several parts with different properties. Each part must be considered carefully separated and optimized in a simple way. What I have to work on is now: 1. Optimized riser for combustion and gas acceleration 2. Enough space above riser for diversion of hotter and cooler gasses to rise and to sink 3. Finding out, if shrinking gasses will accelerate the flu 4. Cooling gasses below thew point under any circumstances to get the extra heat out oft them. The last point is the most important one. The gasses of a wood fire contain up to 20% hydrogen, so a lot of vapor is there inside, additional to the humidity of the wood itself. and not every time you have really dry wood. A lot of energy is to be expected to be inside, so it is worth to try it (I think of 20-30% plus). In large scale wood burners this is already be done, so the question is how to downscale. And yes, they all are using fans to move the gasses trough the heat exchanger.... Why not me? One point not mentioned from me. Condensation will also remove micro particles from the air. Together with a clean burn such a stove will really be efficient and clean - much more than all these stinking stoves on winters days...
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Post by mwalimu on Oct 21, 2014 3:09:42 GMT -8
Pinhead wrote: The gas movement within the bell does very little to assist the overall mass movement of gasses between the inlet and outlet of the bell. In other words, the convection occurring within the bell has very little effect on the flow through the bell.
>>> What about designing a bell - Think about a vertical drum shape with a partition in the center 2/3 high from the bottom and vertical crevice in it. So - Colder gasses can pass directly through the crevice, no need to be lifted up - Hotter gasses are rising, being cooled and falling down at the other side and accelerating the mass flow For gasses in a closed system it is irrelevant if they move up or down in a tube. Only if gasses with different temperatures can communicate, the hotter will rise, the colder will sink. This communication will take place mostly in the upper part of the drum / bell and a bit in the crevice. The 2/3 lower riser / sinker part of the bell is to funnel and accelerate the gas masses. All right?
This is, indeed, one of the reasons the exhaust gasses are able to allow hot(ter) air to move into the barrel - the barrel dissipates some of the heat from the gasses which, accordingly, become relatively cooler (and more dense) than the streaming hot gasses coming from the riser. The temperature differential between the outlet of the riser and the barrel is what allows the heat riser/barrel exchanger to work.
>>> The downward effect in a normal rocket stove is quite poor. If you are putting a barrel over the riser, the gas flow will slow down. Even with insulation, the riser will give away heat after a while. The insulation is only slowing the heat flow, but after a time, the outside is also hot. Possibly to seperate the downward flow completely and cool it properly, e.g. with a water jacket? If you already plan to heat some water?
Condensation/cooling produces a vacuum in all directions - in other words, it is non-directional and doesn't greatly effect the mass flow through the system, though it does effect convection within the system.
>>> What if a gas mass is already moving and it's shrinking? A litte pull to the following gasses, accelerating them, and a little pull to the gasses in front, slowing them a bit down? So in general a draft towards the inlet of the system, but no increase in speed towards the end?
Still some theory to chew.
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Post by Donkey on Oct 21, 2014 7:10:16 GMT -8
Condensation will also remove micro particles from the air. Together with a clean burn such a stove will really be efficient and clean - much more than all these stinking stoves on winters days... This last point ties into something that I've been thinking about. A major obstacle to getting Rocket Stoves approved by EPA (in the US) and similar agencies abroad is the high particulate content of their exhaust. Although in EVERY OTHER WAY Rocket Stoves have ultra low emissions, because of high velocity movement of gasses through them, light ash is picked up and carried through to the exhaust. Every solution that has been discussed (that I know of) has been unsatisfactory. So, my thought is that perhaps light ash can be removed by cooling exhaust to the condensation point. Of course, the issue is that then temperatures would be too low to reliably run a chimney (which is the BEST draft inducer found so far). My thought is this: build the stove as a bell stove with double bells. The first bell would be small and so quite hot, the second bell would be large and drop exhaust temp. below condensation point. To re-induce draft, exhaust from the second bell would be routed through a vertical pipe (the chimney) that would set inside of the first, hot bell. In this way all of the needs are satisfied.
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joseph
Junior Member
Posts: 66
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Post by joseph on Oct 21, 2014 7:34:53 GMT -8
Condensation will also remove micro particles from the air. Together with a clean burn such a stove will really be efficient and clean - much more than all these stinking stoves on winters days... This last point ties into something that I've been thinking about. A major obstacle to getting Rocket Stoves approved by EPA (in the US) and similar agencies abroad is the high particulate content of their exhaust. Although in EVERY OTHER WAY Rocket Stoves have ultra low emissions, because of high velocity movement of gasses through them, light ash is picked up and carried through to the exhaust. Every solution that has been discussed (that I know of) has been unsatisfactory. So, my thought is that perhaps light ash can be removed by cooling exhaust to the condensation point. Of course, the issue is that then temperatures would be too low to reliably run a chimney (which is the BEST draft inducer found so far). My thought is this: build the stove as a bell stove with double bells. The first bell would be small and so quite hot, the second bell would be large and drop exhaust temp. below condensation point. To re-induce draft, exhaust from the second bell would be routed through a vertical pipe (the chimney) that would set inside of the first, hot bell. In this way all of the needs are satisfied. >> ... the high particulate content of their exhaust. Although in EVERY OTHER WAY Rocket Stoves have ultra low emissions, because of high velocity movement of gasses through them, light ash is picked up and carried through to the exhaust. Every solution that has been discussed (that I know of) has been unsatisfactory. << Perhaps a "Cyclonic separator" will work: "Cyclonic separation is a method of removing particulates from an air, gas or liquid stream, without the use of filters, through vortex separation. Rotational effects and gravity are used to separate mixtures of solids and fluids. The method can also be used to separate fine droplets of liquid from a gaseous stream." en.wikipedia.org/wiki/Cyclonic_separationOr has it already been tried? >> To re-induce draft, exhaust from the second bell would be routed through a vertical pipe (the chimney) that would set inside of the first, hot bell. << That idea may be useful in other ways. - joe
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Post by pinhead on Oct 21, 2014 7:34:56 GMT -8
This last point ties into something that I've been thinking about. A major obstacle to getting Rocket Stoves approved by EPA (in the US) and similar agencies abroad is the high particulate content of their exhaust. Although in EVERY OTHER WAY Rocket Stoves have ultra low emissions, because of high velocity movement of gasses through them, light ash is picked up and carried through to the exhaust. Every solution that has been discussed (that I know of) has been unsatisfactory. It seems that the Batch Box with an S-portal should greatly reduce particulate emissions since the air velocity over the fire is much lower. S-Portal TestsThe promised test session has been done, the results are very nice. We tried to provoke the stove into throwing the CO through the roof but it refused to do so. The usual tricks to let things go wrong did't work with this modification. I've got two diagrams to show, the first is a cold start, a refill halfway and some tuning of the primary air. Up to the point that the flames in the firebox became very lazy and the afterburner still roared at the same time.**EMPHASIS MINE**
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Post by mwalimu on Oct 21, 2014 14:22:21 GMT -8
Condensation will also remove micro particles from the air. Together with a clean burn such a stove will really be efficient and clean - much more than all these stinking stoves on winters days... This last point ties into something that I've been thinking about. A major obstacle to getting Rocket Stoves approved by EPA (in the US) and similar agencies abroad is the high particulate content of their exhaust. Although in EVERY OTHER WAY Rocket Stoves have ultra low emissions, because of high velocity movement of gasses through them, light ash is picked up and carried through to the exhaust. Every solution that has been discussed (that I know of) has been unsatisfactory. So, my thought is that perhaps light ash can be removed by cooling exhaust to the condensation point. Of course, the issue is that then temperatures would be too low to reliably run a chimney (which is the BEST draft inducer found so far). My thought is this: build the stove as a bell stove with double bells. The first bell would be small and so quite hot, the second bell would be large and drop exhaust temp. below condensation point. To re-induce draft, exhaust from the second bell would be routed through a vertical pipe (the chimney) that would set inside of the first, hot bell. In this way all of the needs are satisfied. This is one really good idea! Possibly one of the best ever created in the rocket stove business during the last years. - you add more than 20% heat efficiency - you remove the (somtimes acid) water - you remove ashes / micro particles - you're replacing a fan just by stealing some calories from a warmer place - you suck out a slightly warm, but dry air out, even in a hidden place (like a vertical pipe of a rain gutter) with no smell or smoke or vapor at all. One remark: According to my experience and the exhaust data I've seen in this forum, it is very likely that with two bells you will not reach the condensation point under any circumstances. So a third bells should be added for getting down to 30°C / 85°F for condensation. Or a plastic pipe (it will not melt as the water always will keep it at low temperatures) with a water jacket connected to a radiator somewhere in another place of the house... The challenge is to make this condensing unit simple and with a small footprint. So Donkey: You gave me a fan for my heater, you are a (pushing) fan for my project and I'm your fan!
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Post by mwalimu on Oct 21, 2014 14:43:54 GMT -8
This last point ties into something that I've been thinking about. A major obstacle to getting Rocket Stoves approved by EPA (in the US) and similar agencies abroad is the high particulate content of their exhaust. Although in EVERY OTHER WAY Rocket Stoves have ultra low emissions, because of high velocity movement of gasses through them, light ash is picked up and carried through to the exhaust. Every solution that has been discussed (that I know of) has been unsatisfactory. It seems that the Batch Box with an S-portal should greatly reduce particulate emissions since the air velocity over the fire is much lower. S-Portal TestsThe promised test session has been done, the results are very nice. We tried to provoke the stove into throwing the CO through the roof but it refused to do so. The usual tricks to let things go wrong did't work with this modification. I've got two diagrams to show, the first is a cold start, a refill halfway and some tuning of the primary air. Up to the point that the flames in the firebox became very lazy and the afterburner still roared at the same time.**EMPHASIS MINE** Congrats to the success! BTW, the S-Channel is behaving like a welding torch: The combustibles are in the middle of the flame and oxygen is surrounding the flame until all soot (= yellow flame) is burnt. Some interesting info and pictures about wood combustion can be seen here, if one understands German or likes to translate it with Google: www.farago.info/job/Kaminfeuer/ChemieVerbrennung.pdfI made some firing with my provisional J-Tube rocket and found it not always good working (backsmoking when the feeder is not totally full) even by adding sort of a P-Channel. So I'm thinking about adding a primary air inlet and a S-channel, extending the feeder and closing it with a lid. This would be a small batch rocket with automatic feed. I made also some trial with wood chips, the big pieces are working good, the smaller ones are choking the air entrance. With seperated primary air and s-channel I would be independent of the air inlet controlled by the space between the fuel.
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Post by mwalimu on Oct 21, 2014 14:49:36 GMT -8
"Cyclonic separation is a method of removing particulates from an air, gas or liquid stream, without the use of filters, through vortex separation. Rotational effects and gravity are used to separate mixtures of solids and fluids. The method can also be used to separate fine droplets of liquid from a gaseous stream." en.wikipedia.org/wiki/Cyclonic_separationOr has it already been tried? >>> cyclonic separators depend on high gas velocity, which is not available at the end of the exhaust. So a fan has to be added, wich adds costs to the seperator as well.
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Post by mwalimu on Oct 22, 2014 11:34:16 GMT -8
I made some practical experiments with my outdoor J-style heater. being not satisfied with the burn and getting sometimes backsmoke, I changed the feeder: - left and right of the feeder/firebox I put two flat roof tiles (earthenware), with some space behind, leading from the outside towards the riser. So I got something like a S-Channel for secondary air on both sides. - also the tiles heat up very quickly, and having few contact they will act like an insulation. - they also preheat the secondary air passing behind - I put also a hole for primary air in the bottom of the feeder - I enlarged the feeder in volume and height and closed it with a lid at the top
Very good results: Steady burn, flame in riser blue on the outside, poking in the feeder doesn't change anything, no backsmoking. Riser filled with small wood pieces burning mostly at the bottom, automatic feed.
Okay, all that was done dry stack, without adobe mortar. To make it tight will be the next step.
I seems, that the footprint of the feeder can be enlarged as well as the height, so it will be something between J-style burner and a batch stove with automatic feed. Not all of the fuel burns at once, only the lower layer.
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Post by mwalimu on Oct 22, 2014 11:48:52 GMT -8
In another house I have a kitchen stove with baking oven. There is also a valve which leads the exhaust gasses through a bench with brick mason flues, going up and down, heating the bun and the back.
I made some trials to make the stove rocketier:
-When warm, i closed the primary air under the grate completely -I placed the fuelwood towards one wall of the fire chamber (made out of firebrick / chamotte) to prevent too much air there and burning too quickly -I opened the upper door a bit, until the rocketing sound appeared -the flame were blueish and not so long as normal
I got a good draft and good heating, also in the bench, which was warm even hours later.
I try to put a plate of firebrick on top of the grate to keep the fire even hotter and to achieve a long, steady burn.
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Post by Donkey on Oct 23, 2014 7:06:01 GMT -8
I made some practical experiments with my outdoor J-style heater. being not satisfied with the burn and getting sometimes backsmoke, I changed the feeder: - left and right of the feeder/firebox I put two flat roof tiles (earthenware), with some space behind, leading from the outside towards the riser. So I got something like a S-Channel for secondary air on both sides. - also the tiles heat up very quickly, and having few contact they will act like an insulation. - they also preheat the secondary air passing behind - I put also a hole for primary air in the bottom of the feeder - I enlarged the feeder in volume and height and closed it with a lid at the top Very good results: Steady burn, flame in riser blue on the outside, poking in the feeder doesn't change anything, no backsmoking. Riser filled with small wood pieces burning mostly at the bottom, automatic feed. Okay, all that was done dry stack, without adobe mortar. To make it tight will be the next step. I seems, that the footprint of the feeder can be enlarged as well as the height, so it will be something between J-style burner and a batch stove with automatic feed. Not all of the fuel burns at once, only the lower layer. Got images?
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Post by mwalimu on Oct 23, 2014 11:43:51 GMT -8
Images? Here you've got me! I am one of those handicapped persons who hav no working camera, no cellphone and no ability to open zip files. But I'm working on it. My plan is to have a smartphone with good camera and with the helb of my Kids I will learn that. But I'm also a big procrastinator and after some failed attempts with the junk phones of my kids I gave up. But as I see the pressing need, I will start now and buy one. Please pray for me - maybe this will help you to get pics.
Donkeys condenser fan: Having no pics, I try to describe a simplified version:
-Rectangular plastic tank 700 liter, about one meter high -about one ft over the ground a hole cut for the horizontal inlet of the exhaust / flu -one inch below a small hole for exit of excess water (w/hosepipe) -exhaust gasses (below 100"C / phase change) coming in, passing above the cold water, condense -the upper two thirds of the tank is also a bell, the warmer gasses are rising and getting cooled by giving away the heat to the room, -the water stores also some heat and releases it slowly* -Now the trick how to push out the de-condensed, dry, clean and cold gasses: --a hole is cut on the top of the tank and a 6" plastic or aluminium pipe is inserted until the lower end is 4" above the water level. --the pipe is also passing through the warmer gasses on the top of the bell and is heated on the outside, heating also the exhaust gasses a bit, and creating the needed flu for pushing them out. No need to go back to the first bell; the condenser bell has it's own hotter place. --the pipe goes up to the ceiling, and then outside the hose. - a tank like this could be put in a corner and covered like a wardrobe, footprint 2' by 3'
When it's ready and I have a camera, you will get images.
* 200 liters of water have the same heat storage ability as one ton of bricks (below boiling point).
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Post by mwalimu on Oct 24, 2014 0:11:14 GMT -8
It's getting cold now in my area. So I have to push my plans forward a bit.
No big time for making and curing an adobe bench. So I designed a Quick FiXX dry stack mass heater bench
-The feet/stands/spacers of the bench are wooden rectangular frames made out of 2" x 2" wood, inner clearance 10" x 14" (25 cm x 35cm +) -I need one after each half meter -I put them vertically on the floor -then a concrete slab 25 x 5 x 100 cm (ready and cheap - 1.50€ each - from the garden hardware store) lays inside -two more slab are put vertically 25 cm high left and right inside the fram -between a 15 cm (ca. 6") Aluminium coated flue pipe is laid and sealed with silicone -on top of the pipe bricks, smaller gaps are filled with gravel etc. -on top another concrete slab covers all of it, still inside the frame
What you have got is a flue pipe surrounded by concrete slabs, kept together from a wooden frame. The expected properties: -Circulating air around - and in the small spaces, overheating will not occur -Having no full contact, the pipe will heat up quickly -Through contact, radiation and convection inside the slabs, heat will transferred to the slabs. -Medium long storage time is expected -a wooden board could be mounted on top of the frame, wit some space to the wall. The seat will be heated a bit, warm air will also slowly rise to the wall, heat it, causing it to radiate some heat as well (warming the back).
Safety: This works, if the gasses are not too hot, cooled down through a big bell or drum. However, having everywhere spaces for air transporting excess heat slowly away, overheating is not likely to occur. Prudence would be to monitor the temperature under full heating load some times.
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Post by DCish on Oct 25, 2014 11:10:52 GMT -8
So if I'm getting this right, condensation removes micro-particles because the particles are the nuclei around which condensation drops form? So for final condensation there would need to be a radiator of sorts to shed heat fast from the already-mostly-cool gasses. Maybe the final bit of bench before the re-heater could be made of (or topped with) some sort of high surface area sheet metal bell or passage, under which could be a condensate collector and drain. Galvanized could could work well here for corrosion resistance while shedding heat faster than plastic.
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