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[peacmar]

Nozzle size is best determined by velocity of the gases through the orifice. To slow and you get bridging and burn out. Too fast and you get blow out and extinguish the bed of coals.

The calculation for velocity through a nozzle is:

Air Velocity, V=Q(air flow in cfm) divided by A(area of opening
              in square feet)

The ideal nozzle velocity for a gasifier using wood, based on calculations derived from Imbert dimensions, is About 8-15 feet per second.

     *I need to review some notes and may change that value  upon further calculations but it should stand as a good starting point*

[shane g]

once again  when i think i have enough info to build the gassaifier i get blown  away with more thing to figure and calculate LOL .
 which is typical i usualy get in over my head and work my butt off to get stuff like that done.
but i am not going to do that this time with the time line to get this thing done and how much the materials cost holy crap if i want to get a boiler in place i am going to have to build a simpler one
i took your guy's advice on the portage&maine boiler design and i think i canbuild one similar to the ML series except a octogon style boiler i can bend that at work and only have 2 seams to weld
hopefully it wont create too much smoke and tick off the neighbors
should i still by a 500 cfm blower or will a smaller one work better for this aplication
i am still going to build a quality stove so i am going to need alot of help from here so give me your thoughts

[peacmar]

How much water storage are you planning on having? You can calculate that by finding the volume of the water jacket minus the volume of the fire box in cubic inches then dividing by 231 as there are that many in one gallon of water. Also, what is the btu capacity of your current heating system? I only have a 75 cfm blower on mine and based on my water temp increase/time I am making about 150,000 btu per hour. Where my house only needs about 70,000 to keep the wife nice and warm under the coldest of Wisconsin weather. If you can get this info together we can work out a fan size based on a reasonable refueling schedule. Also, try to keep in mind that about %20 of the air should only hit the coal bed, there rest needs to feed the top of the fire. Look into high efficiency epa wood burners. It's a very simple concept once you see it. I use a pair of 2" diameter muffler pipes I bent to bring some of the air up to the top of the burn box for secondary air and have very minimal smoke a few minutes after in kicks up. I wish I built a gasser off the bat but was in the same position you are now and winter waits for nobody. The elm stove is another good source of ideas for clean burning. Once its up and running you'll find a few tricks to keep the smoke down also. And maybe end up like me building small gasifiers for fun just to tinker with till you are able to build a new owb that does what you learned and wished about the first

[shane g]

have not done the calculations yet been a long time since math classl  my waterjacket is going to be 5'x5' square design fire box is going to make the octogon firebox 32wide x42 long  with the water baffle  and do the heat exchanger on the top like the  portage and maine  6"x4" tubes
so thats the design i have settled on i will get my water storage figured (may need help from my kids with the math ) i know thats sad and then i get numbers out to you experts and help me get the cfm of my blower hoping to get the steel bent by next week and get started and get some pics on here thanks for the continued support  from everybody here

[shane g]

 if i have done my math right  my water jacket will hold 750 gallons but i am not a hundred percent sure i done it righti  its been fifteen years since i did this in school  my water jacket is 60x60x60
my fire box is 34x42 with two heat exchanger  pipes being 6x4 tube running the length of the water jacket 60" if any of you could double check my work i would appreciate it
thanks

[shane g]

i fat fingered the capacity i figured around 450 not 750 hahaha

[willieG]

if i have done my math right  my water jacket will hold 750 gallons but i am not a hundred percent sure i done it righti  its been fifteen years since i did this in school  my water jacket is 60x60x60
my fire box is 34x42 with two heat exchanger  pipes being 6x4 tube running the length of the water jacket 60" if any of you could double check my work i would appreciate it
thanks
[/quote

your water jacket of 60x69x60 inches would hold about 935 US gallons i think
i am unsure of your fire box size you say 34x42 (and i am guessing 60 incehs long?) if so this would take away about 370 US gallons
then you could add back on about 12 gallons for your tubes

i get rough figuring 577 US gallons?

you can do your own figuring 1 cubic foot is 1728 cubic inches and one cubic foot holds 7.48 US gallons

[shane g]

fire box was 34x34 octogonx42 long  and water jacket was 60x60x60 i dont know what i am doing wrong with my math

[peacmar]

It's the octogon shape that's throwing it off. If you could load a pic of a sketch with the dimensions of each face then I or someone else can run the numbers more accurately.


60^3=216,000 cubic inches

If its a true and perfect octogon, all 8 sides identical in length, then we can use the equation for surface area of an octogon:

A = s squared times 4.8284

Where s is the length of any one side, square it, then multiply by 4.8284 and you will have your surface area.

Multiply by 42" length and you have your volume.

Take 216,000 and subtract the volume of your octogon (Vo) and the volume of your heat exchangers [(6*4*60)2=2880] divide that result by 231 for your capacity in gallons.

216000-Vo-2880
__________________      = capacity in gallons
           231

Hope this leads you in the right direction.

[martyinmi]

Shane-
   Don't be scared by numbers and figures that are coming at you. Just draw up a rough sketch and begin. I would imagine your firebox will start out as a 10' long sheet of metal that your supplier will bend in an octagon shape for you. 10x12=120. 120 divided by 3.1416= approximately 38.2" if it were round(just imagine 8-45* bends in it to get your octagon shape). 38.2"x38.2"x42"x.7854=48136 divided by 231= just over 208 gallons. 935-208=727 gallons. You'll lose another 9 gallons or so that your transfer tubes will displace for a grand total of around 718 gallons. Awesome! You are going boiler-size-king of this forum. jackel440 is king for now of the home-made OWB's, so you'll be dethroning him. Don't be afraid of a gasser either. Shoot for your nozzle area to displace 1.5-2.5 sq. in. jackel's 500 cfm fan is the same one I used on my gasser, but I put a 250(?) cfm draft inducer on my exhaust also.
   Good luck, and once again, we all like pics.

[shane g]

haha dont think i will dethrone him built a masterpeice i am going to hold off on the gassiafier and just build the boiler the boiler as efficient as i can maybe the next one is this too much water? making the stove smolder more than it should?
my boss is helping me with some drawings so i can give it to the operator at the plant to bend my firebox but he had an emergency this week and had to leavetown so hopefully next week i will be able to get the steel and get the drawing to the press operator  (the op is going to bend it on his break for a fifth of captain morgan LOL) then maybe i can start to put some of it together then i need to figure out how to get the right mix of air underneath and exactly what cfm fan i need to buy and how to route the tubes
just thought of another question when the water is up to temp i am going to have a spring return damper motor close the damper from the blower does the firebox get all air coming to it shut off as in air tight because i see some with a manual damper adjustment on the door and some in the flu
what is the best to have as far as eficiency and low maintenance because i want to be able to load this thing up before work and not worry with it until i get home 12 hrs later or longer
thanks for all the help

[rosewood]

im a big fan of mass storage,my furnace holds 1200 gallons .i believe this makes it more efficient because the fire cycles are longer burning cleaner ,putting more heat out . the off cycles are farther apart so less on the smoky startups, i also believe the larger mass holds temps longer. i have seen the benifits of more water capacity.in early fall i can shut off blower and control when i want it to burn without losing all its temp like a stove with smaller capacity of water. im adding a second air source ..to add to my forced draft.ill let you know now it works out when im done.

[peacmar]

The more mass storage the better. If you can get big hot all out burns and burn non stop from start to finish with no idle time you will have wasted no energy on smoldering and a roaring hot for is far more efficient than a smoldering one.718 gallons is a very respectable amount of storage. During mild weather you could probably get away without any smoldering idle time. And even during cold weather if you time it right.

You don't need any air adjustment in the door with a blower fan this would be bad. You would be blowing hit air right out of it. And no flue damper is necessary either. A damper on te inlet of the fan is best, there are a few ideas in the electronics section of the forum I believe for some retrofits on the shaver that work very well. You want your fan to be your only source of air so you have complete control if your burn. Airtight Fire box is the best way to go with proper air metering and control for best possible burn when not a gasser.

[jackel440]

haha dont think i will dethrone him built a masterpeice i am going to hold off on the gassiafier and just build the boiler the boiler as efficient as i can maybe the next one is this too much water? making the stove smolder more than it should?
my boss is helping me with some drawings so i can give it to the operator at the plant to bend my firebox but he had an emergency this week and had to leavetown so hopefully next week i will be able to get the steel and get the drawing to the press operator  (the op is going to bend it on his break for a fifth of captain morgan LOL) then maybe i can start to put some of it together then i need to figure out how to get the right mix of air underneath and exactly what cfm fan i need to buy and how to route the tubes
just thought of another question when the water is up to temp i am going to have a spring return damper motor close the damper from the blower does the firebox get all air coming to it shut off as in air tight because i see some with a manual damper adjustment on the door and some in the flu
what is the best to have as far as eficiency and low maintenance because i want to be able to load this thing up before work and not worry with it until i get home 12 hrs later or longer
thanks for all the help

Well I never tried to get on a throne.I just shared what I built to show others what was involved with the gasifier I built.I am just glad to see people taking my build and going out and doing something with it.
Heck alot of people seem to be impressed with my stove ,but I see too much that needs improved and things that I wish I had been able to do differently at the time.I'm just glad she performs as well as she does.
There wasn't very good documentation of furnace builds on the net so I wanted to share as much as I could.I am glad that there was this great site to document the build on.

You definatly want to have the fan to pressurize the air box,and be your only source for induction air.Just like you mentioned with the damper to seal the burn chamber use an damper actuater like I did.Mine is a Belimo unit.works like a charm!Go to my thread and look at the video I made of how mine works.You could build on like mine very easily,or your own design.Don't put any sort of damper in your door.
Some were concerned with my design not allowing any air to keep my fire going with long periods of idle.That was not a problem.Even when the furnace sat for 2 days without power.I had a 6" coal bed that as soon as I fired it up she relighted with no problem.

[peacmar]

Even when the furnace sat for 2 days without power.I had a 6" coal bed that as soon as I fired it up she relighted with no problem.

That's what happens when you wrap everything in ten billion square feet of kaowool


But it just goes to prove that insulating the burn chamber, at least the bottom half, helps with efficiency so much. Keep the heat where you need it for burning, then grab what you can after its all consumed. A hot bed makes for quick restart and less energy wasted getting the fire going again and piece of mind in those very cold deep winter nights when the furnace wants to keep running. You'll never choke it out if you can keep at least the coal bed hot enough.