Reverse flow mini for camping and tailgating

Discussion in 'Reverse Flow' started by jbssmokedmeats, Jul 20, 2015.

  1. Hello
    I am starting my 3rd build right now. I put my 2nd build on hold as I won't need it till this winter.
    My cook chamber is a old propane tank off of a forklift I have the top cut and the valves out and rinsed once so far need to rinse once more and cut into it!

    The tank measures 12"x20" roughly should be within a half inch. Here is a screen shot of Feldons calculator I'm going with a 15"x3" stack and 4x1.5" round vents in fire box and I'll have one at top of door. My only ? Is.. How big of a Fb to cc opening do I need in inches from bottom of tank to rf plate? Like I said earlier I will soak the tank over night and get started tomorrow nite on cutting cc opening and the fb to cc opening. This is going to be a fast paced build as it will need to be finished enough to cook on in 3 weeks for a hometown rib comp. at the bar here is the tank before I cut the top off and pulled out the valves.


    And some q view of hot smoked chicken I did on my weber
     
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  3. jcbigler

    jcbigler Smoking Fanatic SMF Premier Member

    I'll be watching this one closely as I have a small propane tank about that same size as well. 
     
  4. locovet

    locovet Fire Starter

    Subscribed!
     
  5. Can anybody help me with the fb to cc opening not sure how tall in inches it needs to be??

    Side note: cc door is cut and I burned it out last night pics coming tonight
     
  6. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

  7. jcbigler

    jcbigler Smoking Fanatic SMF Premier Member

  8. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    The smaller the smoker, the more some numbers need to be made larger... it's a friction loss thing....
     
  9. I got the cook chamber cut open and burned out firebox is tacked together got my hinges today and my stack today
     
  10. Here is the firebox all tacked up with hinge material. I'm going to go with a 2" opening for cc to fb opening and a 3" stack 20" long
     
  11. jcbigler

    jcbigler Smoking Fanatic SMF Premier Member

    Check with Dave. Just because the calculator comes out to a 2" opening, my gut tells me that you will be better with a larger opening...maybe 4"-ish? 
     
  12. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Volume of the Cook Chamber.... Use the Inside Diameter of the tank...

    Diameter X Diameter X 0.7854 X Length = Volume in cubic inches 12x12x.7854x20=2263

    Volume in cubic inches X 0.004 = FB/CC opening in square inches 2263x.004=9 (27)

    Volume in cubic inches X 0.004 = Area under the RF plate in square inches= 9 (27)

    Volume in cubic inches X 0.004 = Area required at the end of the RF plate in square inches= 9 (27)

    Volume in cubic inches X 0.33 = minimum volume of the Fire Box= 746

    The above areas are necessary for great air/heat/smoke flow.... using less may cause an overheated FB.... Narrow / Long CC may require an increase in those numbers due to increased surface area friction to volume... Wide/Fat Short CC may use smaller numbers due to reduced surface area friction to volume...

    Volume in cubic inches X 0.001 = FB air inlets in square inches... 2263x.001 = 2.26 (use 5") (4" below the fire grate and 1" across from the FB/CC opening)


    Volume in cubic inches X 0.022 0.017 = Exhaust Stack Volume in cubic inches, above the CC.... (ESV) 50 CI (~150 CI)
    (The increase in volume ~30% shows a dramatic improvement in equalized temperatures across the cooking surface... edit 6/19/15 )

    Exhaust Calculation..

    ESV in cubic inches_____________________________ ... = Stack Length in inches (36" +/-) 50/.7854/2/2 = 15"... (150/.7854/3/3=7" 3" stack 21" tall)
    0.7854 X Stack Diameter X Stack Diameter

    Adjust the diameter of the stack, until the proper length is achieved... be sure to measure the actual internal diameter of the pipe used..
    this is for round stacks only..


    I would go with a 3.5" segment height (that is the size of the opening. add material thickness to insure proper dimensions... )
    11" wide RF plate
    27 sq. in. segment area

    Smokers that small need a few numbers exaggerated to get the heat to flow...
    I arbitrarily tripled the numbers hoping the smoker would flow heat well.....

    Just one more SWAG to add to the collection... (scientific wild a$$ guess)
     
    Last edited: Jul 23, 2015
  13. So if im following you... A 3.5" opening is what I'm looking for... Add 3/16 for thickness of plate? And I need the same on other end of rf plate correct??
     
  14. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    The segment height is 3.5" + thickness of the top of the FB... so you have 27 sq. in. opening...... the GREEN ZONE.....


    This is all spelled out in the circle calculator in the smoker build tutorial....

    Just so we are on the same page...
     
  15. Going to cut the opening and test fit fb and if I get fb welded solid I'll tack it on the cc put door seal on cc door and put hinges on if my back let's me I have a severe herniated disk at L4-L5 seeing a surgeon in morning but my back hasn't been letting me get a lot done usually after working all day it is so inflamed that I take a couple pain pills and relax in the house
     
  16. Yes but its a little more difficult on a cell phone I got it now what is the in parentheses pink 27 for??
     
  17. Ok so 4 1.5" intake vents is enough then plus one 1.5" at cc opening
     
  18. My stack is 24" by 2.5 Id will that be enough??
     
  19. This is my shop where it all happens!

     
  20. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    It might be.... no way to know for sure..... I thought you had a 3" stack you were putting in...
     

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