|
Post by invention1 on Oct 18, 2018 17:34:00 GMT -8
Yeah, I knew that turbo booster fan video would get people rioting. Ran another burn, today on pellets, with the fan. Using a dry-stacked brick firebox just a bit larger than the pellet pile, 100% of the primary air running through the pellets, then the flame runs through a tube of firebrick about 8" wide X 2" tall X 12" long (about 16 square inches. Primary air is about 5.6 square inches) this time with some secondary air inside this little burn tube. Getting quite intense flame coming out of the end of this tube and into the riser. The pellet burn was just light grey smoke as soon as it started drawing (needs a bypass to get started). After some fiddling it cleared up, Just a hint of grey, almost invisible. I ran it with the turbocharger fan, and it ran very well. Vigorous flame into the port and the riser (remember, the cordwood port isn't where the mixing is happening - there's a bitty secondary air inlet in the fire tube right after the pellet basket) Taking away the turbocharger fan, the flames became weaker, the smoke more visible, and the system just didn't work as well. Despite Peter's justified howling, I'm totally OK with having a fan on a pellet stove, 1 million commercial pellet stoves with fans can't be wrong! (yes, there are about a million pellet stoves in the US). The only commercial pellet stove without a fan is the Wiseway (and almost every hacker's DIY pellet stove). Almost all of those, commercial and DIY, use steel firetubes and stainless steel pellet baskets, and we know that metal is doomed. David S has made a dozen metal pellet baskets and says they burn up at least once a year and he has to de-tune his stoves to keep them from burning out. Bigelow Brook Farms says the same thing about his rocket stove pellet baskets. He cooked his stainless riser into a pile of slag. Her's the thing about the fan: I measured the airflow of the turbo fan I'm using (free air, not in the stove) at 14.5 CFM. I measured the airflow of the properly working stove without a bell, just a riser roaring like a dragon, at 13 CFM. The fan may just be simulating the operation of the whole system as if it had proper draw. Since I put the bell on there, I don't think the stove is drafting correctly and the fan is compensating for that lack. I'm pretty sure the primary airflow without the fan is reduced significantly - the stove always quits running right (from clear smoke to grey or even heavy white smoke) when I take the fan away. So the fan may be a good solution, or it may just be a symptom of marginal draw and blockage in the chimney path. In that case the turbo fan is a great diagnostic tool. Hopefully that will put a halt to people howling about it! It would be a major effort to fix the draft in the prototype stove. I'm not sure it is worth the effort. I've learnt a great deal with the prototype - proved that an over-and-under pellet/cordwood stove can achieve nearly perfect combustion in the same 6" riser, proved that the pellets need a smaller firebox, with its own secondary air and a smaller fire tube (I'd call it a riser if it wasn't horizontal). The fan could be a feature, especially with the pellet stove that may just have too many obstructions in the way of the airflow path to properly draw. A computer fan's worth of airflow would be all that is needed. I've shown that a pellet stove can be built with 100% refractory materials in the flame path, eliminating the doomed metal. I've made a pellet basket that self-cleans pretty well and can run for quite a while, letting ashes fall into an ash drawer instead of clogging up as many do. I know that my stove will need a bypass to start properly, and better workmanship on the masonry to seal up tight. I've come around to thinking that Matt Walker's pre-port tube is the way to go, after Matt pointed out that the pre-port also keeps crap from blocking up the port. I had one cordwood run that went poorly until I joggled a log out of the port. This pre-port tube has to be replaceable, as it inevitably burns up, and I think I have a way to make that work. At this point the prototype is getting pretty bad - it's got cracks all over it from me hammering and fiddling and removing bricks and whatnot, smoke pours out of every gap when it is starting up. Once it starts drawing there is a gap that sounds like a kazoo - I am not kidding. I've got a great kit of steel parts that would go into a real unit if I tore it apart. I may do a few more runs but I think I've learned enough to build a final version indoors. Besides, it's getting chilly outside.
|
|
|
Post by drooster on Oct 19, 2018 9:18:16 GMT -8
Been there, done that, now it's gonna have to be something more aggressive, I'll ditch the 4" angle grinder and get out the 7". 80 grit sanding disk, the one I used to remove bark from trees. Ah OK. A bit off-topic but the absolute best flap-discs I use are Dronco Jet Ceramic 40-grit. Expensive but hellishly good at stock-removal on HARD metals (and long life). Also, since this is t'internet ; Supercharger, not Turbocharger. I'll get back to criticising improper use of apostrophes for plurals now ... *cough*
|
|
|
Post by invention1 on Nov 16, 2018 8:16:41 GMT -8
Well, the last round of the prototype ran. No pics (does that mean it didn't happen?) but I do have witnesses - a friend who's considered building a rocket stove, and has built masonry pizza ovens for a client. Used cordwood and used the super turbo booster fan or whatever it is called. We sat there for a half hour watching the burn, (not much entertainment out here in rural Missouri) every once in a while we had to open the door to make sure it was still burning, because the chimney was producing absolutely perfect clear smoke, just a bit of heat distortion at the top. He was like "No way that is a wood stove." Tearing the prototype down today to harvest metal parts for the real item. My existing, and working stove has been moved over 5 feet, after a half hour struggle with a car jack and some little wheels, so that the new stove can be built while the old stove is still operational (neat trick eh?) - it's freakin' winter out there! I'm expecting the better draw inside (good tall 8" chimney, better design with no constrictions at the rocket) to eliminate the need for the super-duper boostercharger fan, but we'll see. New stove is laid out on the floor with soapstone lines, I'll post some pics along the build. Here we go! Riser dia - 6" X 41"H (spec) Firebox 8" wide (8.68 per the spreadsheet spec) 12 high (13 is spec) 24 deep (spec) Port 9.5 H, 2.25 W 2" deep (as close to spec as I can build) Primary+secondary air combined in one tube (they go their separate ways inside the bricks) this allows one place to shut off the stove and any air leaks to the outside or backdrafting in the summer (this is a problem with my old stove, it stinks when you run the kitchen fan in the summer) Primary+secondary air inlet sized to 30% riser CSA to include 20% for primary air and 10% for Walker pre-port (Is this wrong?) making it a 2.9" X 2.9" inside square tube. I may weld this up out of steel plate if I can't find a square tube that suits. It's only a few inches long, but I want to fabricate a door for it to shut it down. Going to use a Walker pre-port with easily replaceable metal parts in the stove Dimensions in next post.
The Walker Pre-port will just slip fit into a socket int he floor of the stove that communicates with combustion air. The pellet firebox will be beneath the cordwood firebox. Pellet feeder on top of the whole shebang, separated from the fire by two layers of brick and one of ceramic insulation. Pellet gravity feeder tube runs down the side of the firebox and into the top of the pellet basket area. It will be metal behind firebrick. I'll have to draw the pellet firebox to communicate its dimension, but an earlier drawing I posted shows it pretty well. Using a jug of refractory cement bought locally, because I've never had any luck using clay, and don't fancy more experiments. Just use something that someone else spent a whole career developing and refining instead of reinventing it. I've got a message in to an ebay seller about a 2X2 pyroceram window or two, might put it in the door but it would be extra cool to look at the top of the riser. I'll order a few spares if I get glass. Found that Menard's had a cleanout door on clearance for $22, got another one from an old barrel stove, so two cleanout doors, one on the bench and one near enough to start a draft fire under the chimney inside the bell.
|
|
|
Post by invention1 on Nov 20, 2018 8:20:13 GMT -8
Pics, or it didn't happen!
Pellet basket under construction. Plain steel 7mm rods (not a stock item but still available cheap) are placed inside the ceramics. Ceramics cut to length with diamond blade. Welded into an angle iron frame. Edges will be covered with castable refractory eventually, no exposed steel.
Pellet basket in place, in firebrick stove under construction.
Lennox and a few others make a carbide steel-cutting blade that fits a skilsaw. Really handy for cutting steel stock. wear your leather gloves and eye protection, it shoots sparks everywhere.
Sure are hella lotta metal parts in a stove where metal is DOOMED.
Stove door, two cleanouts for the bell and bench, primary air inlet, pellet feeder door, some support steel where my bricks don't quite span a gap, and the secondary air channel isn't even made yet.
|
|
|
Post by invention1 on Nov 20, 2018 10:53:57 GMT -8
Primary air: 20% system CSA (6" system size)
Secondary air: 9% CSA. I'm not sure what part of the Walker Pre-port system is actually this size unless it is the overall inlet.
Theoretical area Primary plus secondary: 8.19 sq inches (actual 8.25 sq in). I have one opening for both primary and secondary air.
Walker Pre-port tube 2.07" ID, 3.36" CSA, 11.9% system CSA, 9" exposed in firebox. Slot in the downstream side and open at the top.
Horizontal secondary air tube 1.6875" ID Square tubing, 2.84 Sq In, 10% system CSA
Currently I have a 3.25 X 2.75" pri+sec air opening, just a bit big, but adding a 0.25" plate to the bottom will give me 3"X2.75" = 8.25 CSA = 29.18% actual system CSA.
Horizontal part of secondary air will be built from nominal 2"X2" rectangular tubing, 1.6875" ID, 2.85 sq in, 10% system CSA (Matt is using 2.25" X 1.25, essentially same CSA) Horizontal part will have one surface exposed in the bottom of the firebox for extra preheating of secondary air.
The vertical tube will be a piece of Schedule 40 black iron pipe, 2.07" ID, 9" exposed in firebox. open at the top, with a 6" X 0.375" slot. Overall it will be maybe 11" long, 2" below decks will be in a tube that sleeves it, so it is easily replaceable. I'll work out the steel so that the bottom opening of the vertical tube is free for airflow. 2-1/2" Schedule 40 Steel pipe is 2.47" ID, 2" pipe is 2.375 OD, so that's a 0.10" slip fit, just right.
Position of the vertical tube will be 2" back from the port, and it just slip fits into a steel hole in the floor made of one-size bigger tubing.
I do not have any provision for separately shutting off primary air. I will only shut off secondary air in pellet mode, by some simple means. Matt apparently shuts off primary air on his stoves at some part of the burn. I hope I don't need to do this, because I probably won't remember to fiddle with it that much. On the pellet side, we are using the same primary+secondary air opening, 3"X2.75" Secondary air will be a slot between two firebricks just after the pellet basket as the fire enters the fire tube. There will be no secondary air preheating, which might be a negative, but many DIY pellet stoves are built with unheated secondary air right after the firebox, so I'm going with this idea. I was able to get clear smoke with this arrangement in the prototypes. I'm avoiding metal in the fire path when I can, which is why no preheat on secondary pellet air. Secondary air inlet for the pellet basket is a slot .3125" wide, 8" long, CSA 2.5" which is 8.84% system CSA. It's anybody's guess what this secondary air should be. I will use a wooden block to create a precise dimension in construction, however having no real specification I'm just guessing at it. Fire tube is a horizontal space made of firebrick, size is a guess, I'll say I'll shoot for just a little larger than the primary air inlet, maybe 4"X4". The pellet area is theoretically a J-Rocket, with the primary air the same as the system size. it has less fuel at a time than the firebox, but can burn continuously so eventually produce as much or more heat energy as the firebox. I'll try to make the fire tube take up 16" to 20" length or so. If I say my pellet system size is the same as my air inlet, then this would be an 8.25" system CSA, 2.87" system size, 2.07" base, or theoretically like a 20.77" riser. So if I can get a fire tube about 20" long, it will contain the pellet flames for a length that should facilitate good combustion. Once flames enter the riser they will cool in the larger space, and combustion will fall off. Air leaks will bring some cool air in the port, unless I am a better brickmason that I have been, also cooling the flames as they enter the riser. Combustion should be about complete, since it happened in the pellet firetube. The rest of the riser is just a chimney at this point. After the fire tube, the pellet fire enters the bottom of the firebox Riser . I will shut off the cordwood secondary air in pellet mode, at this point it is not needed and may actually reduce performance. Pull out the Walker Pre-port tube and pop in a steel plug. In pellet mode, all primary air goes through the pellet basket, in cordwood mode, a firebrick doorway is removed, and covers the pellet firetube outlet, so all all primary air enters the stove at the door end, passing through the firebox as a conventional batch rocket. I will draw a CAD drawing of this soon (I'm not Sketchup-enabled yet) so it is more clear. This sounds complicated but it is dead simple. matthewwalker or peterberg or one-a youse other smart guys please weigh in on my Walker Pre-port dimensions and tell me if I've got it right or am befuddled again. Thanks folks!
|
|
|
Post by invention1 on Dec 31, 2018 7:55:36 GMT -8
Finally some progress! Here are a few photos:
This shows the details of the pellet-burning section - Pellet basket, secondary air inlet slot, and the firebox secondary air poking up through the middle. Firebox secondary air tube will be protected by masonry so it cannot erode, up till the exposed Walker Pre-Port tube. Walker Pre-port is a replaceable 9" piece of schedule 40 steel pipe, 2" size, just slipfit onto a smaller tube below it. I dunno how Matt works those bolts he's showing, just slipfitting a big thickwall pipe over a slightly smaller thin pipe seems easy.
Now we've added the cordwood firebox section. The pellet section is below a layer of firebrick splits. You can see the port to the right, then the Walker Pre-Port tube, off to the left is the beginnings of the pellet feeder tube, then a slot which allows access to the pellet basket. Pellet basket is removable for cleaning. In Cordwoord mode, this slot becomes the primary air inlet, in pellet mode it is covered by a fitted brick which blocks airflow directing it through the pellet section.
Here is a riser's eye view of the over-and-under cordwood and pellet stove looking in through the port:
Stove door view of the firebox. The pellet feeder tube will be covered by masonry before it's done. This commercial door unit has two openings, the lower opening will be the primary air opening in both pellet and cordwood modes, and this little door can be shut off to shut down the stove if need be. The cordwood firebox stretches a bit wider at the door end, just to accommodate the width of the door, but the port end of the firebox is very close to Peter's specs, to make the combustion physics work right. My understanding is that the volume of the firebox can vary a bit, but the area of the port, riser, secondary air, and the port end of the firebox need to be precise to create the turbulence that makes these stoves run right.
Pellet feeding test. Poured pellets into the feeder tube with a big funnel. It contained about four liters of pellets, and importantly, covered the pellet basket so that very little air can bypass the pellet pile. The feeder tube is about 2" above and about 1.5" behind the pellet basket, which allows it to fill the pellet basket to the top. Tube is surrounded by masonry so if the metal erodes, it will still function. A fitted brick will cover the pellet basket area int he photo, restricting primary air to the path of the pellet firebox. There is some exposed steel in the pellet basket, but this is easily replaceable and I might cover some of the steel with refractory cement or a bit of ceramic fiber insulation with refractory cement hardfacing.
|
|
|
Post by matthewwalker on Dec 31, 2018 9:34:27 GMT -8
Your pre port tube is restricted due to the smaller stub. It should be full CSA throughout.
|
|
|
Post by Dan (Upstate NY, USA) on Dec 31, 2018 12:24:40 GMT -8
Cool, how ya going to get the fly ash outta the pellet firing section?
|
|
|
Post by gadget on Jan 11, 2019 21:47:13 GMT -8
Hey Inventor1 I wished I lived near by you cause I would have a "pro fan" buddy. I don't know if I will ever have a heater that doesn't have a fan. I have a mini rocket in my greenhouse that has a blower on the exhaust. I burn all sorts of stuff in it, lots of cardboard and paper. I have not tried pellets yet but after reading through this thread I now want to try. I have dumped lots of wood chips in the burn tunnel and it did just fine. A blower and a pellet feeder work really well together since its a constant fuel supply and in theory, no over fueling. I don't think I would build a pellet stove that did not have forced induction or a "turbo". I know others have done it successfully going the "natural aspiration" route. Even with the blower, I noticed that the draw increases when I add in more fuel. The blower just kind of works as a buoyancy device in this particular heater, the riser still adds pumping affect when it warms up more. I couldn't get allot of your pictures to load but I wanted to suggest a few things; Get yourself a metal furnace blower that can suck the air through your heater vs pushing it in. That way you don't have to worry about gasses leaking out of the burn area and into the room. Or get one of those paddle style add on blower that fits the side of the flue pipe. If you can befriend and HVAC repair person, they often throw complete furnaces to the scrap heap and they have lots of good parts in them. Have you seen the cordierite honeycomb ceramic panels on eBay? Maybe they could be used for building a pellet burn box. Cordierite is a very good ceramic for high temp. It is insulative like mullite, not as conductive like 99.5 alumina and would keep the heat in the box. The holes are very small so I am not sure how well ash would get sucked through. They make em with larger holes. Search ceramic solder pad on eBay. Like this; They are cheap but you can also salvage them from large natural gas panel heaters. I got a dozen blocks from a heater my boss was tossing. Im going to use them for my secondary air on a project heater.
|
|
|
Post by invention1 on Mar 6, 2019 8:39:45 GMT -8
Cool, how ya going to get the fly ash outta the pellet firing section? I can reach most of the pellet combustion area with my hand, and plan to get myself an ash vacuum with a long custom snout to get back where I can't reach. Yeah, this is something I agonized over. So far no appreciable buildup.
|
|
|
Post by invention1 on Mar 6, 2019 8:43:22 GMT -8
Hey Inventor1 I wished I lived near by you cause I would have a "pro fan" buddy. I don't know if I will ever have a heater that doesn't have a fan. I have a mini rocket in my greenhouse that has a blower on the exhaust. I burn all sorts of stuff in it, lots of cardboard and paper. I have not tried pellets yet but after reading through this thread I now want to try. I have dumped lots of wood chips in the burn tunnel and it did just fine. A blower and a pellet feeder work really well together since its a constant fuel supply and in theory, no over fueling. I don't think I would build a pellet stove that did not have forced induction or a "turbo". I know others have done it successfully going the "natural aspiration" route. Even with the blower, I noticed that the draw increases when I add in more fuel. The blower just kind of works as a buoyancy device in this particular heater, the riser still adds pumping affect when it warms up more. I couldn't get allot of your pictures to load but I wanted to suggest a few things; Get yourself a metal furnace blower that can suck the air through your heater vs pushing it in. That way you don't have to worry about gasses leaking out of the burn area and into the room. Or get one of those paddle style add on blower that fits the side of the flue pipe. If you can befriend and HVAC repair person, they often throw complete furnaces to the scrap heap and they have lots of good parts in them. Have you seen the cordierite honeycomb ceramic panels on eBay? Maybe they could be used for building a pellet burn box. Cordierite is a very good ceramic for high temp. It is insulative like mullite, not as conductive like 99.5 alumina and would keep the heat in the box. The holes are very small so I am not sure how well ash would get sucked through. They make em with larger holes. Search ceramic solder pad on eBay. Like this; They are cheap but you can also salvage them from large natural gas panel heaters. I got a dozen blocks from a heater my boss was tossing. Im going to use them for my secondary air on a project heater. Are those panels tough and durable, or brittle and fragile like may ceramics? I thought about the idea of a metal fan sucking the pellets, but as we know metal is doomed. I've had little problem with leaks, except for some pinholes in my pellet feeder hopper which I fixed with silicone caulk. No high temperatures there. An 80mm computer fan keeps itself cool and has not been a problem with getting too hot. However see next post for other issues.
|
|
|
Post by invention1 on Mar 6, 2019 9:03:11 GMT -8
Well we've hit a significant snag. All these guys on this forum seem to like mixing up their own clay and stuff for mortar. My early experiments with this had terrible results, so I gave up and decided to buy some refractory mortar instead. Except for here on this forum, virtually every other expert forum or blog on the Web recommends using commercial refractory mortar instead of mixing up mud and clay. Sounds like good advice. People here said that commercial refractory mortars are expensive - they cost about $40 a bucket, shipping cost is about that much again. I don't consider that expensive. I respectfully disagree with the idea that mixing up local clay is the "best" way to get refractory mortar. There are basically two kinds commercially - mortars that are a mix of sodium silicate and sand, and mortars that are a mix of sodium silicate and fireclays or silico-aluminates. I did my first experiments using Blakbond from Sheffield Pottery. Great stuff. Tough, resists high temperatures, etc. Later, Sheffield recommended Derby 3000 as a stronger mortar. Both are sodium silicate and fireclay formulations. I went to buy some firebrick at a local yard, and they have refractory mortar in stock right there. So I purchased a bucket of that to do the next project. This was, it turned out, a sand-sodium silicate mix from Alsey Refractories meant for residential fireplaces and the like. This product was a gigantic mistake. After three to four weeks I noticed some loose bricks in the roof of the stove. I shut the stove down, switched the chimney back to my old reliable Fisher, and started taking things apart to investigate. Virtually every joint that had been exposed to elevated temperatures had cracked and failed. Between bricks, I could pick the mortar off with my fingernails. Gentle prying with two fingers could separate mortared bricks. The floor of the firebox was fine, but the walls and roof were failed. So everybody here that likes mixing up local mud can say "I told you so" and they'd be right. At least about the crap I bought at the local brick company. I'm heading over there with a video of me picking apart the pricks with two fingers, and the reciept to demand my money back. Won't make up for 1/10th of the trouble I've had due to failure. Is all mortar in fact doomed?
|
|
|
Post by drooster on Mar 6, 2019 11:25:57 GMT -8
... I respectfully disagree with the idea that mixing up local clay is the "best" way to get refractory mortar. ... So everybody here that likes mixing up local mud can say "Nya Nya, I told you so" ... Not a single soul on this forum would have told you the first, and certainly not commented as the second. This is a very nice place, and the solid experts use mostly commercial mixes.
|
|
|
Post by gadget on Mar 6, 2019 18:22:13 GMT -8
Hey Inventor1 I wished I lived near by you cause I would have a "pro fan" buddy. I don't know if I will ever have a heater that doesn't have a fan. I have a mini rocket in my greenhouse that has a blower on the exhaust. I burn all sorts of stuff in it, lots of cardboard and paper. I have not tried pellets yet but after reading through this thread I now want to try. I have dumped lots of wood chips in the burn tunnel and it did just fine. A blower and a pellet feeder work really well together since its a constant fuel supply and in theory, no over fueling. I don't think I would build a pellet stove that did not have forced induction or a "turbo". I know others have done it successfully going the "natural aspiration" route. Even with the blower, I noticed that the draw increases when I add in more fuel. The blower just kind of works as a buoyancy device in this particular heater, the riser still adds pumping affect when it warms up more. I couldn't get allot of your pictures to load but I wanted to suggest a few things; Get yourself a metal furnace blower that can suck the air through your heater vs pushing it in. That way you don't have to worry about gasses leaking out of the burn area and into the room. Or get one of those paddle style add on blower that fits the side of the flue pipe. If you can befriend and HVAC repair person, they often throw complete furnaces to the scrap heap and they have lots of good parts in them. Have you seen the cordierite honeycomb ceramic panels on eBay? Maybe they could be used for building a pellet burn box. Cordierite is a very good ceramic for high temp. It is insulative like mullite, not as conductive like 99.5 alumina and would keep the heat in the box. The holes are very small so I am not sure how well ash would get sucked through. They make em with larger holes. Search ceramic solder pad on eBay. Like this; They are cheap but you can also salvage them from large natural gas panel heaters. I got a dozen blocks from a heater my boss was tossing. Im going to use them for my secondary air on a project heater. Are those panels tough and durable, or brittle and fragile like may ceramics? I thought about the idea of a metal fan sucking the pellets, but as we know metal is doomed. I've had little problem with leaks, except for some pinholes in my pellet feeder hopper which I fixed with silicone caulk. No high temperatures there. An 80mm computer fan keeps itself cool and has not been a problem with getting too hot. However see next post for other issues. The cordierite ones are strong as are the zirconia ones, that is as long as they aren't physically hit with something. Cordierite is very good with temperature swings. Its used as kiln shelves and pizza oven trays. You can use a plastic fan down stream if its cool enough. I am running a plastic one right now that sees temps from 50F to 80F. Its an induction blower off a gas furnace. It moves a ton of air. It was way more efficient then the metal one I was using. Check it out; donkey32.proboards.com/thread/3473/mini-rocket-forced-induction?page=2&scrollTo=32320It sucks through the system. Exhaust is 2" PVC Good luck with your mortar. Hopefully you can get it up and running again before things warm up.
|
|
|
Post by invention1 on Mar 7, 2019 7:27:05 GMT -8
Hey Inventor1 I wished I lived near by you cause I would have a "pro fan" buddy. I don't know if I will ever have a heater that doesn't have a fan. I have a mini rocket in my greenhouse that has a blower on the exhaust. I burn all sorts of stuff in it, lots of cardboard and paper. I have not tried pellets yet but after reading through this thread I now want to try. I have dumped lots of wood chips in the burn tunnel and it did just fine. A blower and a pellet feeder work really well together since its a constant fuel supply and in theory, no over fueling. I don't think I would build a pellet stove that did not have forced induction or a "turbo". I know others have done it successfully going the "natural aspiration" route. Even with the blower, I noticed that the draw increases when I add in more fuel. The blower just kind of works as a buoyancy device in this particular heater, the riser still adds pumping affect when it warms up more. Describe (or better, photograph if you can post pics somewhere) the feeder system you are using, please! What is the diameter of the tube that feeds material? Presumably large, over 4"? What are the rough dimensions of the burn area/firebox? Of course there are several ways to use fans around wood stoves - first to increase heat by blowing air through a heat xchanger at the chimney ( I have one of these "Magic Heat" things on my old stove"), blowing combustion air INTO the fire - as many commercial pellet stoves do, and pulling air out of the fire, as many condensing furnaces do. You seem to have been successful witht he latter. Although there are counterexamples, I am pretty convinced that it is far easier to burn pellets with a combustion air fan, and the easiest place to put a fan is blowing air into the unit. Computer fans are just about the ideal size, keep themselves cool as long as they are not too close to the flames, and just about the ideal airflow. I was seeing about 15 CFM on experiments earlier - if the airflow was down at 10 CFM the fire burned anemicaly. This depends a lot on the size of the fuel load obviously, and I was using a pellet fuel load of about 3700 mL. The same airflow - 15 CFM, was about right for the 6" prototype batch rocket. Many 80mm computer fans are in the range of 25-50 CFM free air, which will be half or less with obstructions. A 25 CFM 80MM fan will be quiet, a 50 CFM 80MM fan will make a bit of noise.
|
|