Small RF smoker - 30 gallon

Discussion in 'Reverse Flow' started by bator, May 4, 2016.

  1. bator

    bator Newbie

    Hi all - Just wanted to throw my numbers out there and see if I am on the right track. I am building my smoker out of a 30 gallon compressor tank. So far I have the wheels and top plate removed so I wanted to check with ya'll before I started cutting any thing else. Any assistance would be appreciated,  Thanx Bob

    Smoker Numbers

    Wednesday, May 04, 2016

    11:20 AM

    Calculations for a standard design, reverse flow smoker..

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

    Diameter X Diameter X 0.7854 X Length = Volume in cubic inches / 231 = Volume in gallons

    16 x 16 x 0.7854 x 36 = 7,238.2464 / 231 = 31.3344

    Volume in cubic inches X 0.004 = FB/CC opening in square inches

    7,238 x  0.004 = 28.952

    Volume in cubic inches X 0.004 = Area under the RF plate in square inches

    7,238 x  0.004 = 28.952

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

    7,238 x  0.004 = 28.952

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

    7,238 x  0.33 = 2,388.54

    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…

    7,238 x  0.001 = 7.238 

    Recommended upper and lower air inlets... Upper air inlet directly across from the FB/CC opening to facilitate moving heat from the FB to the CC, and insuring good air flow through the CC.. The lower air inlet should be situated at or below the fuel grate.... The two air inlets can share the designated square inches of opening.... approx. 20% upper and 80% lower...

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

    7,238 x  0.022 = 159.236

    Exhaust Calculation..

    ESV in cubic inches / 0.7854 X Stack Diameter X Stack Diameter  = Stack Length in inches (36" +/-)

    0.7854 X 4 X 4 = 12.5664

    159.236 / 12.5 = 12.7389

    0.7854 X 3 X 3 = 7.0686 

    159.236 / 7 = 22.748 

    0.7854 X 2.75 X 2.75 = 5.9396

    159.236 / 5.9 = 26.9892      

    0.7854 X 2.5 X 2.5 = 4.9088

    159.236 / 4.9 = 32.4971   

    0.7854 X 2 X 2 = 3.1416

    159.236 / 3.1 = 51.3665 

    [​IMG]

    The [Segment Area] box is what you area going to compare with the FB/CC opening in square inches...

    Volume in cubic inches X 0.004 = FB/CC opening in square inches

    7,238 x  0.004 = 28.952

    If the FB/CC opening number is smaller, change the number in the Segment Height ED box to 5.... continue changing that number until the [Segment Area] matches the FB/CC number.....

    Now look at the colored circles above.... Segment height ED is how tall the green area is and corresponds to the area to be cut out.....

    Segment height ED = 3.250

    Also, [Chord AB] corresponds to the width of the RF plate... NOTE... for ease in fitment, the FB should be at least as wide as the RF plate..

    Chord AB (RF Plate) = 12.87
     
  2. Numbers look good !! Will be a nice little patio smoker!!

    Mike
     
  3. Hi Bator,

    Your numbers seem very close to mine  http://www.smokingmeatforums.com/t/245332/new-patio-build-from-australia

    Mine is 34 gallons (longer but a bit skinnier) and the advice I have received is that for these smaller builds you need to exaggerate the numbers a bit. For example my segment height ED was 3.5" but I have pushed this up to 4.

    I have gone for a 3" ID pipe for my exhaust sitting around 35".

    Seems like you have a handle on the numbers though which to be honest is probably the trickiest part  [​IMG]

    Look forward to seeing your build.

    Bazza 
     
  4. bator

    bator Newbie

    Thanx for looking at the numbers Mike and Bazza, that helps great advice. Here are a few pics. Basically just cut off the running gear and mounting plate. I also cut out and patched the air inlets.





     
    martyinco likes this.
  5. bator

    bator Newbie

    Hi all  - 

    So the CC wall thickness is 1/8, should I make the firebox out of 1/4 or can I get by on 3/16? I have not bought materials but just wanted to check with you all.

    Thanx, Bob
     
  6. aussiq

    aussiq Smoke Blower

    I would go 1/4 on your fb as a minimum thickness
     
  7. bator

    bator Newbie

    Ya that is pretty much what I figured but thought I would ask anyway, thanx!
     
  8. bator

    bator Newbie

    Well got some work done this weekend. I got the tank cut for the firebox. I also cou the CC door an welded on the hingers. Of course after I cut the door I figured out it was a little out of square. I figure I can fudge a little on the CC border. Anywhy here are some pics.
     
  9. bator

    bator Newbie

    Ok not sure what is up with the pics, will try in the am from my pc.
     
  10. bator

    bator Newbie

    Ok so for whatever reason I can't seem to post pics from my phone. These were from this past week end.




     
  11. Coming along nicely!

    Bazza
     
  12. tykenn28

    tykenn28 Fire Starter

    How are you coming along on this project? I built a 250 gallon last year and now I've got a small compressor I want to use for a backyard smoker. My compressor appears to be a bit smaller than yours. I'd guess it to be around 20 gallon but this'll be a good thread for me to follow. 
     
  13. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Bator, morning....  If it's not too late, try increasing the FB/CC opening and raise the height of the RF plate and increase the width of the RF plate...  

    From the tutorial....

    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...edit 8-16-16... small volume patio type smokers will need some increases in measurements also.. FB/CC, under RF plate, end of RF plate... ~20-30%..
     

    I should have included that when it was written... 
     
  14. pcjack

    pcjack Smoke Blower

    Looking good! Keep posting!
     
  15. Lookin good !! Getting closer to a spot on the Patio !!

    Mike[​IMG]
     
  16. kdfiter

    kdfiter Newbie

    How is the build coming along .I'm in the procces of of getting all my material for a similar build
     
  17. bator

    bator Newbie

    Not to bad actually, I got the legs mounted and burned out the inside. I have since cleaned it all up. I just need to add the RF plate,cooking grate, temp gauge, handle and a little paint.

     

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