Questions on air/smoke flow for a build...

Discussion in 'Smoker Builds' started by caustic, Jul 13, 2010.

  1. caustic

    caustic Newbie

    So I completed my first build of a smoker. Works great. I don't see any issues with its airflow so far. Now I'm working on plans for a bigger smoker. Something about the size of a Backwoods Competitor. Here are my questions:
    1. I would assume the CFM should slowly decrease throughout the smoker (from vent intake to hollow wall to cooking chamber to chimney) which would cause forced convection. Is this correct? And if so is there a rule of thumb as far as how much it reduces each step?
    2. As far as the air flow... would you want to make it flow as smooth as possible? I guess what I'm asking here is..does turbulence have an effect on proper air flow/smoke?
    3. Can turbulence cause smoke to "roll" inside the cooking compartment causing "stale" smoke?
    I don't know if these are stupid questions or not... or even if the answers have much effect on the cooking process itself. I'm just considering some variables I see and using my mechanical abilities to iron them out on my next build if it's lucrative to the build.

    Thanks ahead of time!
  2. caustic

    caustic Newbie

    Any ideas? Dumb questions? Wrong forum?

    /tap /tap

    This thing on? Haha.
  3. matts

    matts Smoking Fanatic

    The are not stupid questions.  Any change in direction will cause a drag in flow.  That much I know.  I am sure someone else can help on the rest of your questions.
  4. eman

    eman Smoking Guru Staff Member Moderator OTBS Member

    Tap Tap ,Test 1 2 3.

     yes it's on and some very interesting questions.

     As for reduction in cfm.

     As the smoke comes out the fire box (where temps are highest) and moves through the cooking chamber or through the reverse flow channel and across the grates it will slow down.

     So at any given point in the cooking chamber you would have a reduction in cfm from any given point closer to the heat / smoke source.

     As for the smoothness in flow ,i can't see where you could create enough tubulence to affect the flow of smoke.

     With the exhaust vent open you won't have smoke staying in one place long enough to worry about stale smoke.

     This is my opinion and i have no engineering background to back it up.
  5. caustic

    caustic Newbie

    Thanks for the replies. I believe one of my questions was misunderstood.

    As for the CFM question.... I was trying to find out if there was a set reduction in CFM required for proper smoke flow on a smoker.

    1. Firebox to Walls

    2. Walls to Cooking Chamber

    3. Cooking Chamber to Chimney

    4. Chimney to Atmosphere

    Those are basically the 4 direction changes and/or choke points for the smoke to go through in my design(something like a backwoods chubby). Also these are the four spots which can form turbulence. (which I don't know if this effects the smoking process or not). The CFM at each point is what I'm concerned with. At each point, should the CFM be reduced to keep the static pressure consistant through out the smoker?

    The same concept is applied to running ductwork. As a run gets longer.. the duct gets smaller... keeping static pressure up so that each "take off" from the main duct keeps enough pressure to push out the diffuser. Obviously the chimney's square inch area is smaller than the Firebox to Walls area.

    I'm sorry my question wasn't clear...sometimes it's hard to get down in text what you're trying to describe physically.

    Thanks again!

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