Chimney diameter

Discussion in 'UDS Builds' started by mosaicsmoker, Apr 28, 2013.

  1. mosaicsmoker

    mosaicsmoker Newbie

    My son and I just bought a couple 55 gal drums and are planning to build a couple UDS's loosely based on the "Nelly Bly" smoker described on the Make Magazine website, but welding the components instead of pop-riveting them. They're going to be vertical smokers, external firebox connected by flexible duct so we can experiment with different kinds of smoke-generators and vary the flexible duct length to cold smoke and hot smoke.  Our first question is about the chimney - the build plans use 3" diameter round duct to build an 18" tall chimney.  Our barrels have nice 2" threaded pour-holes in the top.  We were wondering if making a chimney out of electrical conduit (which we have in abundance since my son is an electrician) threaded into this opening would be workable.  The pour hole is offset to near the outer rim of the top.  Would the 2" diameter choke the air flow too much?  Would the chimney being near the outer rim instead of being in the middle of the top?

    At least one of these UDS's is going to be a testbed system - I'm going to mount a handful of temperature sensors/pyrometers to measure smoke box temp at several locations, firebox temp, ambient temp, probably 2 spots along the flexible duct between the firebox and smoke box.  All of this is going to be recorded by a Raspberry Pi microcomputer along with weight/type/time of wood additions.  I'm going to display these on a time-based graph and eventually use it to tune a PID algorithm to recommend when to add more wood to keep the temp in a desired range.   Anyone who has already done this have any advice on this?  One question I have related to the temp probes is sealing the holes where the leads go in - do you think Sugru would work for chinking the lead holes in the smoke chamber since the firebox is separated from it? If not, what type of gasket do you recommend?   I don't plan to store this where it'll be rained on so the chinking is more to control air flow than to make it waterproof.

    We'd like to use smaller drums for the different kinds of fireboxes we want to experiment with, but have been unable to find any.  Does anyone have ideas on how we could find some?  Everything seems to come in plastic drums these days.

    Our first firebox is going to be manual stick-fed but at some point I'd like to experiment with an augur-fed wood pellet/propane burner firebox (computer controlled, of course).  Anyone have an augur pellet feed in good condition from a defunct pellet-fed smoker they'd like to sell?

    Thanks in advance for the advice


    P.S. Since I've been cautioned that posts without pics are useless, here's are the barrels:

  2. I don't know about the chimney sizes but I would be concerned regarding conduit. Most rigid conduit is made of aluminum and it might not handle the heat well. Also, is there a risk of contaminating the food with aluminum? There has been a lot of concern regarding cooking with aluminum pots and pans....
  3. fwismoker

    fwismoker Master of the Pit

  4. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    What are you referring to ???
  5. fwismoker

    fwismoker Master of the Pit

    Micro computers, pid algorithms etc...are a bit out of my league.   It leaves me scratching my head.   
  6. mosaicsmoker

    mosaicsmoker Newbie

    I live on the edge of the floodplain of a lake that is fed by several creeks (commonly referred to as a swamp by everyone except real estate agents). Local laws prevent me from using a .45 to battle off the mega-bloodsuckers that sometimes come out of the swamp and the clouds of little 'squitos, ticks and horseflies seem to think that 100% deet is an excellent marinade for human flesh.  I'm very attracted to being able to sit in my nice air conditioned house watching my computer draw a graph of the temperature at several levels in the smokebox and the firebox plotted over the last hour or two so I can tell when it's time to rush out and throw more wood into the firebox.  At some point I'll try experimenting with a wood pellet feeder so I can let the smoker be self-running until time to rotate the meat or wet it down with sauce.
  7. mosaicsmoker

    mosaicsmoker Newbie

    Another question - we have the smoke box almost done - just need to weld on hinges for the door and  a couple minor things.  The firebox is the next major hurdle - we haven't had any luck finding something of the right size and sufficiently heavy metal to use for a firebox.  We don't have ready access to a scrap heap to search for plate that could be made into a firebox.  Anyone have suggestions on how to find something that could be cut/welded into an acceptable firebox?
  8. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Keith, afternoon....  Just thinking here....    How about propane for a heat source.....  get one of those DC stepper motors to control a needle valve on the propane supply line.... graph the temps and adjust....  You could probably have the puter control the temp by needle valve adjustments...  An AMNTS for 8+ hours of smoke.....    For a firebox, use one more 55 gal drum with an 8 / 10" pipe / duct connecting the 2 drums, wood stove black pipe is good...   FB air inlet 12 sq. in.   FB to CC opening 34 sq. in. (8" duct is a little big, flatten it to oval 9 x 6" and install like that..seal up with stove cement or high temp silicone)   I hate to see you battle the bugs every hour or so......   [​IMG]  ......

    Edit....  A 3" stack 30" tall above the top most of the CC is recommended..... exhaust pipe from a muffler shop is good....

   to enlarge..................

    Last edited: May 18, 2013
  9. dward51

    dward51 Master of the Pit OTBS Member

  10. He11 I can't even spell algorithm (copy and paste ). [​IMG]   I welded for several years and would normally be the 1st to raise the alarm about using galvanized and other such material.  In this case you want to use electrical conduit as a stack.  For this application I would say no problem as the smoke is exiting the smoke chamber.  The location of the threaded hole is not a problem but I would place the intake from the firebox 180 degrees from that opening.  In fact, in this application I'd angle the intake.  Place the intake at the bottom angled slightly upward and toward the side of the drum.  Create a tornado heat/smoke effect.  In other apps. this may not be desirable but I think it should work here with the smaller stack.  2" should work but go long with it,  say 30 -  36 inches.  That will be to long ( half that size should do it )  but do a test run and check the smoke draw.  Easier to cut it off than add to.  Just my 2 cents.  Maybe someone knows better than I do.  Keep Smokin!
  11. dward51

    dward51 Master of the Pit OTBS Member

    Al-Gore-ithm....  Isn't that how they came up with the theory of global warming?  And like a lot of theories before that one, neither one seems to be working very well (the global warming one and the Al Gore one).
  12. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    In order to do all that, you had to invent the internet first...  [​IMG]
  13. [​IMG]


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