I think I made a major miscalculation, please help.

Discussion in 'Reverse Flow' started by turn4fun, Aug 3, 2010.

  1. turn4fun

    turn4fun Fire Starter

    So I finally got a little time to work on my smoker yesterday evening.  I was hoping to get my firebox put together and weld in the convection plate.  I had just picked up the plates to build my firebox and the first thing I did was cut out the firebox to cooking chamber opening on one of the side plates.  As luck would have it, just as I started to make the first weld I hit the end of the spool on my mig.  Dang-it!!!   Well what seemed like a minor inconvenience at the time may have been a blessing in disguise. 

    So I pick up some mig wire on the way home this afternoon and as I'm getting ready to start working something about that opening just keeps bugging me.  No matter how I look at it I just can't see it being anywhere near big enough.  Well it seems I have miscalculated the size of that opening.  I followed the RF calculator spreadsheet to a "T " except for one minor thing...... the calculator only gives you square, rectangular or round sizes and I needed a semi-circle.  I'm no math whiz so I calculated the size in rectangle format which was 3.25 x 4.00.  I then took the perimeter of that rectangle and reshaped it into a semi-circle and that's how I figured out how wide my convection plate needed to be (roughly 6.5").  It didn't occur to me at the time that just because the perimeter of a rectangle and a semi-circle are exactly the same doesn't make the interior areas the same.  

    So now I'm left scratching my head.  Obviously I'm gonna need a wider convection plate but I don't have a clue how to figure it out.  According to the calculator the opening needs to be 12.97 square inches. The interior diameter of my smoke chamber is 11.875".  Can someone help me figure out how wide my plate needs to be or point me to some sort of calculator to help me figure surface area of a partial circle.  
  2. duck killer 1

    duck killer 1 Smoking Fanatic SMF Premier Member

  3. duck killer 1

    duck killer 1 Smoking Fanatic SMF Premier Member

    if you want i can help you with your sizing. either post dimensions on this thread or shoot me a pm.
  4. turn4fun

    turn4fun Fire Starter

    Thanks, that is exactly what I needed.  I must have google searched semi-circle area calculators all afternoon and never found exactly what I needed.  I did find this one interesting since it helps calculate volume in tanks with sphearical ends.  http://www.arachnoid.com/TankCalc/   

    For my build I'm using a tank with interior diameter of 11.875" x 41.5".  Since it has sphearical  ends I rounded it off to 41"  (I didn't use TankCalc to figure out what it really is).  My firebox is 12" x 11.625" x 11.625" (interior dimensions).  Exhaust pipe is 3" x 12" and I'm going to use four 1.250" round air inlets. 

    I saw in one of your other posts that the calculator was designed to run a hot fire.  I don't particularly want this one to run much over 250 degrees.  What built-in variables should I think about tweaking to keep it on the cooler side without choking it off too much?
  5. tom37

    tom37 Master of the Pit OTBS Member SMF Premier Member

    I use this page. http://www.1728.com/circsect.htm

    All I did was enter my tank dia and the line ED. I am sure there is a more logical way to do it but I entered what I thought was going to be close. After you enter the number for the height ED, you can scroll and see what the area is.

    Such as tank dia is 24 and segment height ED is 4 will yield an area of 72.025

    This is a line straight across the end of the tank 4" up from the bottom. My opening is a teardrop shape so I did as I described above and then doubled the figure.

    Hope that makes sense. Here is a pic of my firebox opening, remember there is no dumb questions.

    And as far as tweaking the calc numbers, I would leave the numbers as is, that way if you want to cook when its cold out you can let the fire build a little hotter. When its warm out you can control the heat with the intake vents.

    BTW If you want to look at mine in person shoot me a PM. Some things are easier seen then told.

    Good luck
  6. duck killer 1

    duck killer 1 Smoking Fanatic SMF Premier Member

    hey tom, where's the pic? LOL!  [​IMG]
  7. duck killer 1

    duck killer 1 Smoking Fanatic SMF Premier Member

    I'll shoot ya a PM.

    and by the way... Tom is right.
    Last edited: Aug 4, 2010
  8. tom37

    tom37 Master of the Pit OTBS Member SMF Premier Member

    Oh Great, no dumb questions but it looks like I had a dumb answer by not loading my pic. LMAO

    Here it is I think LOL



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