Need help calculating flow and fire box size for BBQ Bomb

[pitbull8151]

I am building a smoker out if a sphere type propane tank. It has a Dia. of 40.75 in. I have a piece of 12x24 tubing to build my fire box. How big do I need my fire box and what kind of flow would I need? I will post pics of my material to give you a idea.
Thanks.

[pitbull8151]

Here is what I have so far.

[Rick]

Frank or Smokertom are the guys with the calcs - they can tell you what size but it's prob going to be 30% firebox compared to the cook chamber or thereabouts. Looking at what you've got on that trailer I would suggest putting the firebox directly under the sphere and set a baffle (1/4"?) inside the bottom of the sphere and allow the heat to surround it as it comes up the ball and out the top - look inside a big green egg sometime that has the big hotplate accessory in it - that arrangement sure works well for them.

[pitbull8151]

I was thinking of putting firebox on back of trailer ( to be built) and running 2 pipes off top and into the middle of smoker. I also thought of adding a circular plate in middle to make it a sort of indirect cooker. The stack will come into middle down just off cooking grate.

What do you guys think? Will this work?

Also gonna build a spinning grate to access from one door.

Any thoughts?

[Frank_Cox]

I think i would do something like this if it was me...
http://smokerbuilder.com/forums/viewtopic.php?f=46&t=166
I would do a different counter weight system if it was going to be on a trailer.


If not that then i think what EK recommended would be best. however you build it, I think it would make one heck of a UDS! or a green egg clone.
If you do put a fire box under it and feed it from the center 30% would be a good number for that since you would not be able to go for a reverse flow very easy. I would not suggest using the pipe in between method really. that does not seem to work as well since there is so much restriction and heat loss in the pipes.
You could put the square tube you have at the bottom and feed it endways into the side of the sphere at the bottom and put the baffle above the opening a few inches above the top of the inlet. that would work well i think.

[Smoker Tom]

I have to agree that the calc isn't gonna work well since its not gonna be a reverse flow.

Myself, I would take the firebox and set it on edge 12 wide 24 tall then have the heat enter right in the center bottom of the sphere.

That will be more then enough firebox for the setup. I also really like the diffuser plate idea. Possibly even have the heat plate mounted on a threaded rod and be able to adjust it from the top of the sphere when the lid is closed. Depending in the lid design, the top of the threaded rod could have a sort of a bolt head on it. Then the lid would have a crank and a socket on the inside. WaLaa.

For the rack or racks I would have a pipe over the threaded rod for the racks to mount to. When cool you could open the lid and lift the racks out by sliding the pipe off the threaded rod.

Sorry about my typing but the comp crashed and all I have is my phone.

Sent from my MB860 using Tapatalk

[pitbull8151]

If I pipe in from the firebox into the lower middle of tank and put a diffuser plate to make heat go to outside, then bring stack down the middle. Will it work kinda like a reverse flow?

I want to have the grating work like a turnstile so I only have one door to open and can spin around to work it.

I will look into the Green Egg idea.
Should I cut the fire box down? The way I figured (probably wrong) is that the smoker area is about 34900 cu. in and if my fire box should be about 10500 cu in. I fugured 12x24x36 fire box....am I close or waaaaaaaaaay off?

[Smoker Tom]

If it was me. I would have the friends intake center bottom the size of your rectangle tube. Down about a foot. Then 90 it and have aprox 2 feet running horizontal on edge. Then a door at the end. Save the space on top of the firebox for warming pans of water or beans. This way you can change the location of the fire depending on ambient temps. Closer to the center the hotter it will run. Build the fire by the door and it will disapate heat before the smoker. This would give you plenty of room for adjustment.

Entering the fire center bottom really cut down on how big you need the fire box. And yes with the diffuser it will act somewhat like a rf. And yes to having the stack right in the center.

Nice idea on having a smaller door on one side with a carasol. I would still try and incorporate an adjustment on the damper/diffuser plate. Just like working with a drum. When you open it up your fire will build from the extra air. So if I was gonna have it open for a length of time, I would close the difusser to maintain my fire as well as slow the smoke in my face.

Just saying...

Sent from my MB860 using Tapatalk

[pitbull8151]

Ok yall. I need more info. How far apart do I need my divider away from cooking surface. After some discussion with my buddy I have scrapped the idea about the turn table grate and going with the double barn door opening. Just wondering how far I need to drop plate down and maybe still have some room to throw some charcoal incase may want to grill.

I have already cut my fire box and end caps. The cook chamber is 150gal and my fire box is 20X12x23 ( I thought it was 24) is there any other thoughts on my piping and stack size?

Thanks

[Rick]

I just put Edgar's grate 3 inches above the baffle plate and the baffle is 6 inches off the floor of the cook chamber/firebox roof - and that one is a center feed rf. HOWEVER, your cook chamber is a sphere so my numbers are not too helpful. You need to send Frank a PM and work out the calculations. Since this is a sphere - it's a little trickier to "rule of thumb" it.