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Post by Donkey on Jan 23, 2014 8:35:32 GMT -8
I had an email back from Ecolink reference the ABCAT I referred to above. The "filter element'' is a full metal Pd catalytic convertor. They go on to say "for cracking the most hazardous organic hydrocarbons (VOC) such as PAH's a temperature of approx. 350°C (660°F) will be required". As this fits on the outside of the stove it isn't suitable anyway for a rocket with much lower exit temperatures. I'm guessing the high temperatures needed are the same for all catalytic convertors? I don't think that a catalytic converter is the answer in this case.. We're pretty well burning off whatever CAN be burned (which is what catalytic converters deal with). The problem is light ash that can't be burned or converted.. My brain keeps sliding over to some kind of shape that will separate by centrifugal force. The problem is that I don't think that there's enough energy to provide the velocity needed to do that. And anyhow, velocity is what is picking up the ash in the first place. Also, building a centrifugal separating chamber with no moving parts, while an interesting problem, isn't a particularly practical solution for home DIY.. It seems to me that the static charge idea shows more promise. Didn't Peterberg say something about Swiffer?? A quick internet search for "electrostatic cleaning" found this interesting (but maybe slightly off topic) link: www.thunderbolts.info/tpod/2005/arch05/050531roverclean.htm |
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Post by pinhead on Jan 23, 2014 9:45:29 GMT -8
Seems to me, the beauty of these stoves is simplicity. Adding ion exchange, static charging, and centrifugal stratification, IMO, is over-complicating the entire process. One of the recent developments is the use of bells to extract heat from the exhaust gasses. A large square bell with a simple square filter which could be slid in and out, and washed (made of steel wool, etc to eliminate the possibility of creating a fire hazard) with enough area as to not reduce draft significantly should be pretty simple, though would obviously require more maintenance... I'm thinking filters like this: Aluminum, Galvanized & Stainless Mesh Filters Attachments:
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Post by 2tranceform on Jan 23, 2014 10:35:22 GMT -8
Interesting article Donkey. I am leaning toward an electrically charged filtration device, as well. I think because of the size of the particles, other filters may not be able to do it effectivley. I would not mind running an electrical filter during a burn to clean the exhaust, especially if the stove was my primary heat source. The interesting part is determining the polarity and voltage that best catches the particles.
Pinhead, what size of particles will a mesh filter be able to catch?
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Post by doggy1969bc on Jan 23, 2014 11:00:01 GMT -8
i know we used hy voltage low wattege to stabalise plastic film in the pakkaging industrie and they were dustcolectors (we needed to clean them once a month in a low dust inviroment)for them to work properly . so we could use an old microwave oven 's transformator put 12v to it (alternating ) and get hy voltage on the other side my 0.02 on it
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Post by pinhead on Jan 23, 2014 13:17:46 GMT -8
Pinhead, what size of particles will a mesh filter be able to catch? I suppose that depends on how much air resistance you can put up with; they can be made fine enough to use as an automotive air filter. I found some steel mesh filters that will filter down to 2 microns under a high pressure differential. Lower pressure differentials (lower mass flow) increases the filtering capability. |
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Post by patamos on Jan 24, 2014 21:59:53 GMT -8
Seems one of the keys is going back through the assumptions behind the statements that Matt was told: That 'once these particles enter the gas stream they aren't coming out'. Is that information based on an assumption that everyone is running their exhaust hot and straight up a vertical flue? If so, then velocity is a contributing factor and the low velocity of large horizontal bell ceilings are involving a whole different dynamic. In this case passive mechanical filtration ala pinhead's last post might hold some promise.
If the suspension of micro sized particles is more a matter of sub-atomic repulsion/attraction... then electro-magnetic solutions may be the ticket. In either case, i wonder what effect different kinds of filter material may have. Eg. is there a readily available material out there that particularly attracts and binds the suspended particles?
well being
pat
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Post by ronyon on Jan 25, 2014 8:53:57 GMT -8
Two words.Water Bong.
Ok, seriously, could draft be sustained if the gasses passed through a filtering fluid, water bong style?
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Post by Donkey on Jan 25, 2014 22:17:58 GMT -8
Don't know.. Anyone up for that test?? Who wants to be the first to build a Rocket hookah? I'd just laugh too damn hard if the thing made that classic thip-thip, bubbling bong sound..  |
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Post by patamos on Jan 25, 2014 23:01:08 GMT -8
Oh this is something. As i was catching up on the last few posts here my mind was drifting over to the way ceramic filters take micron size impurities out of water. Then drifted into imagining some sort of... well... water bong. Morphic resonance or what. How about a giant bell-aquarium ?!?!? With mind bending bubble action nothing like water for heat absorption/distribution... get the fire cranking up a bypass flue then o'er she goes . thip thip for sure. we might have to reinvent the bell shape and ISA equations. but man that will be fun to figure out. A rocket core, a couple of elbows, a length of pipe and a bucket of water ought to tell us something. I'm busy tomorrow, but monday...? Maybe sink the flue well down into a deeper pool but with many small holes in the side walls of the submerged flue to expand its exit CSA(?) If straight down into the water filter seems too thick then maybe the flue can become wide and horizontal just below the water surface level to reduce the back pressure... in a wider shallower pool. And if not through the medium then what about tight across its surface in contained path... or through a looser fabric that sweats water ala pressurized irrigation tubing.... does anyone know how many kilojoules are used in the average human's bong inhalation? getting batty... just throwing things out there... |
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Post by patamos on Jan 27, 2014 22:18:03 GMT -8
Okay, built up a makeshift 6" L-feed with 4' of fairly well insulated 1/4" steel riser. 2 galvy swivel elbows and another 5' of 6" galvy pipe towards the ground at 60 degrees or so. Not the most powerful set up, but drafted well enough on its own with medium orange flamage in the core. When i placed the end of the downdraft tube in a tote full of water, it did fine til i tried to submerge the last 1.5" of pipe. Then it started back drafting out the feed tube. Tried it a few times, same result... Of particular interest was that the draft didn't depreciate noticeably between 0% and 80% submersion. Perhaps this is because the system CSA had volume to spare for the amount of fire it was running, and a little venturi acceleration at the end was not a problem. And/or, the water being very cold, could have amplified the cooling/contraction of the exhaust gasses. Not surprisingly, a great deal of steam was added to the exhaust upon final exit... Which gets me to thinking about phase change heat generation and yet another phase change if one were to add a condenser set up. All of which would make for considerable complexity  (As an aside, re phase change, check out Central Rocky Mtn Permaculture Institute's greenhouse heating if you haven't already) So a low powered system does not exert the PSI necessary to push through the density of near-surface water. Perhaps a batch box with a tall riser and much less of a downdraft run before contacting the water would. As i do not have that set up handy i'd best hand it off to the next curious explorer who does... And from there, how does one go about measuring micron sized emissions? well being pat |
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Post by ronyon on Jan 27, 2014 23:38:15 GMT -8
Very cool! I am confused though, where you able to submerge the open end of the exhaust 1.5 inches before draft was noticeably affected, or was the 5(inch or foot?) exhaust submerged much deeper?
Either way it seems like a properly constructed bell could have water in the bottom, a rocket exhausting below the surface of the water, steam condensing on the top and walls, an exit for at or below water level, and maybe a water heating coil under the surface of the water.
All in all, a lot of heat transferred to to a (hopefully) increasingly particle filled pool of water.
Or maybe I am totally misunderstanding your results, as you do say:
? Even if you only were able to submerge the open ended of the exhaust 1.5 inches without affecting draft, that still seems to do the trick.
I am not getting something...
Thanks by the way for do this experiment, great stuff!
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Post by pinhead on Jan 28, 2014 6:56:06 GMT -8
I had considered the "pool of water in the bottom of a bell" type filter. You would want a wide, thin "slit" at the entrance and exit of the bell, just above the surface of the water to both keep the entrance/exit low (enhancing the bell action) and to maximize the amount of exhaust gasses which come into contact with the water.
Submersion is absolutely impossible due to the extremely small pressure differentials a wood stove produces.
While this may make a good "filter" as well as a good thermal mass, it may be difficult to tune the system; this will virtually guarantee your exhaust temperatures to stay below 212°F/100°C since anything above that will simply boil your filter away, robbing a ton of energy from the exhaust gasses in the process (it takes a TON of energy to phase-change water).
An alternative could be a liquid with a higher boiling point - oil, perhaps - but you'd then have to worry about storing a highly energetic combustible liquid in the exhaust path of your stove. Not a good idea for safety, IMO.
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Post by matthewwalker on Jan 28, 2014 10:07:04 GMT -8
One possible addition to some of the solutions proposed here would be a TEG driven fan either pushing or pulling to provide the necessary force to get through either a dry particulate filter or the bong water. I've been playing with TEGs quite a bit lately and there are some very low voltage motors on Amazon that drive a fan surprisingly well just by setting a TEG between two heat sinks on the barrel top.
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Post by Deleted on Jan 29, 2014 6:31:21 GMT -8
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Post by patamos on Jan 29, 2014 9:08:35 GMT -8
Ho Y'all
To clarify for Ronyon, the 6" downdraft pipe was mostly submerged at about a 45 angle with only 1.5" open above water line. My sense was that the small amount of combustion i had going in that size of a system was not using up the available space in the riser and downdraft tube.
On further reflection, some or much of the steam i was noticing was probably coming from the slightly damp cedar i was burning.
I agree with Pinhead about full submersion not working. Next to earth, water is the densest material in our world, so pushing through it takes tremendous force. When inhaling through a water bong one is applying the powerful contraction of the body's diaphragm and/or intercostal (between rib) muscles to a very small aperture (bong tube). Inhalation via expansion of the ribcage expansion alone generates tremendous heat - as the yogis on frozen lakes in Kashmir demonstrate when they dry out blankets dipped in the icy water with their nasarga bhastrika breathing technique...
This much to say, the energy that goes into creating such air pressure differentials is considerable...
There could be ways to tweak the flue to water interface for slight sub-surface bubble action. I'll experiment with that soon for curiosity's sake.
I'm imagining a sort of corrosion resistant manifold with many perforated tubes that sit/floats on the water surface... with perforations facing down into the water and gasses bubbling out from there.
Curious also to see what Matt and others discover with TEG draft enhancements...
Sending gasses through air misting sounds interesting. The condensation from that would offer some phase change heat. Perhaps a TEG could power a small pump that returns the condensed water back up into the flue gasses for more misting. If this does catch the small particles it is intended to, then some soft of inline fluid filter pre or post pump might work...
If this kind of thing flies, then the whole interface between fire and water heating could take a quantum leap...
thoughts for now
well being
pat
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