Baffle Installation?

Discussion in 'Reverse Flow' started by ultralow787, May 27, 2014.

  1. Ok, I finally got back to working on my little reverse flow smoker.

    My cook chamber is a 32" long and 12" diameter tank. I cut the lid out to open up a quarter of the chamber.

    My question is regarding placement of the heat baffle. My main cooking grill will be 12" deep by 24" long. This gives me 6" at the center from the bottom of my grill to the bottom of the tank.

    How far below my grill should the baffle be?

    Is the idea that the smoke will travel to the end furthest from the fire box and then pass over the food, or should some smoke also flow under the food grill?

    Should the baffle be level? Or, should I have a slope back to the offset fire box. I guess I could break a "V" in the plate to allow any drippings to flow to the center and have a drip drain there.

    I want to make up and get the baffle installed next before I add the fire box or grill supports.

    Thanks for your help folks!
     
  2. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    787, afternoon...... I don't know if you have found any calculators to base your numbers on.... I have put together one.... Try it.... If math is a problem, I will help you along, or there are many folks on here that can crank out numbers also....

    .click on pics to enlarge....

    Use for FB/CC opening, area under the RF plate, and RF plate width....

    http://www.1728.org/circsect.htm


    Remember all dimensions are "inside" dimensions..... example.... FB/CC opening.... take into account the metal thickness of the FB and the CC for the opening....
     
  3. Dave,

    That is awesome info you posted there in your drawing! Thanks so much. That answers a lot of questions  . Now, of course I have a couple more!

    I had not considered the heat shield. I think I saw it in another thread, but this clears it up well. The gap between the roof of the FB and heat shield is approx.. 1/2"? Should the heat shield fit fairly tight, or do you want a gap around the perimeter? What about the extension length into the CC?

    Tonight, I worked on the seals around the cook chamber door. I was real pleased with the fit! I am taking pictures along the build and will post

    them once I figure out how. lol!

    I will print out your drawing tomorrow for reference and see how I do with the calculations. Math is a definitely a weakness of mine!
     
  4. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    787, morning...... the heat shield needs a gap around the edge to allow for expansion,1/8" - 1/4" will work..... 1/4 - 1/2" gap is adequate to diminish the heat transfer and heat loss through the top, and reduce the heat to the RF plate, immediately out of the FB..... The heat shield is suspended by 2 bolts to allow for expansion....

    How far it extends into the FB is "per smoker"... I would guess about 1/4 of the RF plate length.... The heat shield can be installed at any time.... even after the build and test runs... The smoker may operate just fine for you.... A hot spot, near the FB, may be a good thing....

     
    Last edited: May 28, 2014
  5. Dave, I have a drawing that I would like to show you to get your opinion.

     I have a bit of trouble with the math part as well. i can calculate the area and volume of the CC and FB, but have trouble with the segment where they connect.

    My CC cylinder is roughly 12" diameter by 33 inches long. The firebox i plan to make will be oversized in relation to the CC because I want to be able to fit wood into it as well as charcoal. I have not cut the plate steel yet, so i am flexible. i would like to start on Monday with the actual fabrication. I picked up a bunch of .188 (3/16") thick plate on Friday.

    I'm assuming the FB to CC opening could be larger than calculated, but as you can see from the sketch, I am limited.

    Thanks
     
  6. lendecatural

    lendecatural Smoking Fanatic

    http://www.1728.org/circsect.htm

    This should help, you want a segment (green) area 1.5 times what is required by Feldons when you scale your firebox back down to 100%. Build the firebox however you want, but do use a value of 100% to obtain the required areas for the opening into the firebox, under the RF plate, and at the end of the RF plate where the smokes turns towards the grates.

    This is the tread about Feldon's calculator and the minor issues that may come into play when doing cooker calculations.

    http://www.smokingmeatforums.com/t/161795/is-feldons-calculator-really-flawed
     
    Last edited: Jun 7, 2014
  7. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    787, evening.....

    3732 c.i. CC calls for a 15 sq. in. opening for the FB/CC.... But that won't work because of the ratio of surface area to sq. in is way too high in small smokers....

    Soooooo, your numbers of a 4 1/2" segment height are over twice what is recommended, using my calculator, and perfect for this size smoker... for the RF plate width, 11.6" is what the calculator comes up with using a 4 1/2" seg. hgt. ... very close to your numbers......
    Use what you came up with ..... build the exhaust larger than what the calculator comes up with also.... same reasoning.... same with the opening at the end of the RF plate....

    FB, bigger is better....
    Exh. Stack ... maybe 3" x 24-30" above the CC.... think about using car exhaust tubing.... the calc. calls for about 10" of 3" but the alternate theory works here also...

    Any questions ??? I'm here somewhere.....

    Dave
     
    Last edited: Jun 7, 2014
  8. Dave,

    I have only had a day or so to work on this unit last week. I spent most of my time burning out the CC and cleaning all the paint off the CC. I did get the firebox built and it turned out pretty nice. I put the heat deflector in and it extends about half the length of the CC right now. I used your method of suspending by two 1/2" bolts in the center.

    I now have the CC cut out to connect up to the FB as well. Next step is to work on some air inlets, stack, and CC door hinges.

    I'm having fun and can't wait to get cooking on this thing, but it is a whole lot more work than I expected!

    How important is the drain line and shut-off valve for the CC? I plan to have two shallow pans under my food and they will probably be filled with water or juice.
     
  9. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    The collection of fat on the RF plate could catch fire.... when it comes to cleaning, a drain is always nice.... so in both those cases a drain would be handy... At least a drain on the CC itself will drain it and you won't have to wash stuff through the FB and out... That can be really messy with the ash and all....
     
  10. radioguy

    radioguy Smoking Fanatic

    Ultra,

    I installed 2 drains. I off a center drain on my RF plate for grease. And a 2nd on the CC floor for flushing it out. I recommend you do it now while you can.

    RG
     
  11. Guys, I'm confused by the calculator!

    My CC is only 12" dia x about 32" long. I made my FB larger than is required at 14" w x 14" H x 16" long. If I go by the calculator for air inlets and chimney, it wants to match these to the FB I'm assuming. I don't think I need to go that big on this little smoker.

    If I adjust the FB size to something smaller, say 10" w x 10" H x 12" long, the FB and CC are the same area and the number and size of air openings goes way down. I would like to use 4 x 1 1/4" holes for the air opening that should give me almost 5 SQ INCHES. Do you think this is more than adequate? I would do the same for the air inlet above the fire grate.

    I will use a 3" dia chimney, but again, how tall?

    Thanks in advance! I really don't want to screw this up at this stage!

    Brian
     
  12. lendecatural

    lendecatural Smoking Fanatic

    Here is a link that explains Feldon's calculator and it's strengths and weaknesses. You want to use a fake firebox that results in 100% of CC to get your openings and exhaust so your 10x10x12 is perfect to use for that purpose, then build it how ever big you want. The openings in the FB for draft can also be oversize since you have the ability to shut them down once you get up to temp.

    http://www.smokingmeatforums.com/t/161795/is-feldons-calculator-really-flawed

    If you go to Dave's post 7 above, he already did all the math required for the exhaust and RF plate location in the CC so you should be good to go.
     
  13. Thanks Len. I know what Dave posted, and that helped a lot.

    I was just concerned about the air inlets. Would the above fire inlets have to be the same size as the below grate inlets?

    Sorry, I don't mean to be so thick, but for some reason, I am paranoid about all this! lol

    I have 3" chimney pipe, and I will probably go about 24". I figure the same applies to this. If it is too much draw, just damper it down.
     
  14. lendecatural

    lendecatural Smoking Fanatic

    Sounds like you are right on track and don't worry about being cautious at this stage. It's like woodwork, once you cut one too short, it's too late....At least with steel you can patch and start again, it just cost you some time! The upper inlet can be smaller, most I see are half or less than the size of the lower inlets. Keep us posted and feel free to ask any questions along the way!
     
  15. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Above the fire inlets about 10-20% of the below the fire inlets....
     
  16. Thanks kindly Dave and Len!

    Seems like I have been at this forever. Getting anxious about actually trying it out. Hopefully by the end of next week I'll be ready to light er up!

    We spent two weeks traveling through the Ozarks, Memphis and Nashville areas as well. I sampled as much BBQ as we could find and amassed quite a collection of sauces to try as well.

    I'm going to try Jeff's recipes as well.
     
  17. lendecatural

    lendecatural Smoking Fanatic

    Glad to help, post up some pictures of your progress, interested in seeing how you are coming along!

    Len
     
    Last edited: Jul 30, 2014
  18. Len,

    Is there a link on here somewhere explaining how to post pictures?
     
  19. dandl93

    dandl93 Smoking Fanatic

    Yes there is go to the search and type in... How to post pics....I used it to learn how and if it can show me how any one can.hahahahaha

    Dan
     
  20. lendecatural

    lendecatural Smoking Fanatic

    The fifth icon from the right in the bar Below the "Reply" box is an icon that looks like a mountain scene, it is just to the left of the one that looks like a piece of film. That is the insert image link, click on it, then click on the upload image icon and it directs you to a folder on your computer where you select the picture. Go to the folder on your computer where the picture is stored, select the picture, and click the Open icon at the bottom of the screen. Type your text then you select Submit, it will be there with what ever text you included.
     

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