CF RF Build questions

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Pale Horse
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CF RF Build questions

Post by Pale Horse » September 29th, 2018, 9:13 am

Good Morning,

Its been a while since I was last on but I finally got moving on my build. I have a 270 gallon oval tank which I finished a big burn in and pressure washed all the old paint off it so I have bare steel to work with. I am going to put cabinet doors on the oval tank and have a big rectangular tank for my fire box which I am going to mount directly behind at the bottom of the oval tank. I was looking at some of the CF, RF designs and they all have 2 chimneys in the middle of the CC. I have my calculations for how big I need the throat and chimney to be for the size of the CC and FB, but I was thinking about going with long thin rectangle dimensions for both the throat and the chimney to achieve the necessary hole sizes...my thought being that the smoke would pull more evenly and I would have more uniform heat and smoke distribution throughout the CC. I plan on installing a digi-Q with a couple pitbull fans, so maybe I wouldn't gain very much by doing this. Any thoughts or feedback?

By the way the Mack build/pics are AWESOME...I plan on buying those drawings to help with my build. Thank you!

Dan



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Re: CF RF Build questions

Post by inkslinger » September 29th, 2018, 9:19 am

Im not sure if there is any real advantage to dual exhausts as opposed to a single one. If it has the correct/suggested internal dimensions, the smoke and heat will flow efficiently.

Ultimately the goal is for even and consistent heat. So no matter how you get there... get there, and the Q will be divine.


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Re: CF RF Build questions

Post by Pale Horse » September 29th, 2018, 9:44 am

Thanks for the feedback, I figure if it doesn't work its metal so I can always redo it. Another question if I am using the Pitbull fans I don't need a damper on the firebox right...the fans are supplying the air so I just need ports for the fans and doors to load the wood, and ash drawer...want to make sure I am not missing something. I have been thinking about/planning this build for years...now that I started it I am anxious to keep working on it...need to sell a trailer and buy a plasma cutter. I am a brewer too Inkslinger and grow my own hops...speaking of which I need to brew a batch...



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Re: CF RF Build questions

Post by towtruck » September 29th, 2018, 9:47 am

Read this link about pipe shape......it's about fluid but it's relevant.
https://physics.aps.org/articles/v8/94

There is less surface area in a round pipe, less friction loss. I believe two round pipes would flow better than one long rectangle of the same internal volume.



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Re: CF RF Build questions

Post by inkslinger » September 29th, 2018, 10:03 am


Per towtrucks info...
towtruck wrote:There is less surface area in a round pipe, less friction loss. I believe two round pipes would flow better than one long rectangle of the same internal volume.
... Maybe one larger round pipe would do. It is what I did for my Center-feed Reverse-flow (almost finished building mine by the way!).

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Re: CF RF Build questions

Post by Pale Horse » September 29th, 2018, 11:02 am

Yeah I read somewhere that if you go with a rectangle shape you need to increase the square inches by 10-15%



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Re: CF RF Build questions

Post by Pale Horse » September 29th, 2018, 11:06 am

"Skinny ducts had negative skewness, whereas fat, nearly square ducts had positive skewness. Strangely, the duct with zero skewness—the one most like a circular pipe—was not square but rectangular, with a width-to-height ratio of approximately 1.87. The team plans to run experiments to check this result, but their finding that particles in a rectangular duct spread more symmetrically than those in a square one has left them "baffled," Camassa says. Another puzzle was that very skinny elliptical ducts had zero skewness, but similarly-elongated rectangular ducts had negative skewness."

Interesting....maybe I do a super skinny and long oval shape;)



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Re: CF RF Build questions

Post by Big T » September 29th, 2018, 3:20 pm

The pit calculator will figure square or round exhaust stacks and give you the needed dimensions. There's probably a set of plans that are designed for your style tank, the Mack plans are awesome but will be of little benefit with a tank of different dimensions.


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Re: CF RF Build questions

Post by Pale Horse » September 29th, 2018, 8:06 pm

Thanks Big T, I was thinking about getting the plans because I have never built a smoker before and I would like a guide/reference to all the pieces and parts I will need, that I am not thinking of or aware of. I did look for an oval tank CF RF flow smoker plans but I didn't see one on Smokerplans.net. It looked like the Mack design doors were pretty simple to build and looked really good, figured I could use the same process and modify the dimensions as needed, but maybe that is not the best way to go...I will do some more digging for plans.



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Re: CF RF Build questions

Post by Big T » September 29th, 2018, 9:12 pm

Here's a 275 oil tank that was built as an offset but he framed out the doors with square tubing and has some good pictures of how he done it. http://www.smokerbuilder.com/forums/vie ... allan+tank I believe that the plans on smokerplans.net for the 275 have the doors framed out with angle iron if I'm not mistaken. I'll try to see if I can find an older thread that has some pictures of how it's done. Are you wanting the FB directly under the CC or behind the CC ? If you want it behind the CC then the plans for the 275 would really help you out because the FB would be the same size as an offset RF but if you want it mounted underneath the CC the the FB doesn't have to be as large because you don't have the heat loss through the top of the FB. A set of plans will really help you out seeing as you've never built a smoker because you'll get detailed drawings plus customer service for anything that you have any questions about or don't quite understand.


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Re: CF RF Build questions

Post by Pete Mazz » September 30th, 2018, 4:26 am

Here is a stack calc that does what you're looking for.

https://planetcalc.com/6097/


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Re: CF RF Build questions

Post by Rodcrafter » September 30th, 2018, 8:32 am

That Pete knows his stuff


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Re: CF RF Build questions

Post by Pale Horse » September 30th, 2018, 5:15 pm

Big T, thank you for that thread it is very helpful. I am planning to put the FB centered behind the CC so I can build a WC on top of the FB. So then I could just get the 275 gallon plans and the mods would just be moving the FB back. I don't think I can wait to buy a plasma cutter...going to see if I can rent or borrow one...my dad is master machinist and has a killer shop with a monster lathe, bridgeport, 50lb hammer, couple forges, nice welder and a boat load of other tools...but no plasma cutter...which is the next tool on his list. Hope to get back down to the farm mid-October and get more knocked out! All I seem to be able to think about is different ways I could do things and am anxious to keep the project moving forward...I already have the BBQ bug...I may have acquired another bug with this building thing!!



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Re: CF RF Build questions

Post by Big T » September 30th, 2018, 5:34 pm

The plans would give you the dimensions of the FB, throat, stack length and show you how to layout the doors but the layout of the BP would be totally different. I would be sure that you have some sort of a plan before you start cutting on your tank because it's not fun to have to start welding parts back on to the tank because you've got ahead of yourself.


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Re: CF RF Build questions

Post by Pale Horse » September 30th, 2018, 9:54 pm

Yeah I assume as long as I have the same/similar square inches on the clearance for the baffle plate I should be good to go.



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Re: CF RF Build questions

Post by Pale Horse » October 4th, 2018, 10:03 pm

Do you include the ash drawer dimensions in your FB size calculations or leave that separate?



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Re: CF RF Build questions

Post by Rodcrafter » October 20th, 2018, 7:03 pm

The ash pan sits flat on the floor of the FB so it doesn’t change the calculations


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