CC/FB hole opening ?

[staracin]

This will be my first RF build. I'm have 1/4 inch pipe 18 inch ID.

CC 18"x45" =11451 CI
FB 18"x18" round =254 CI
So I used Dave's (thanks Dave) calculations and came up with 45.8 CI opening FB/CC. This where I'm Confused is this considered a long and narrow smoker if so do I need to add 20-30% to the opening?
Thanks Rich

 

[daveomak]

You could add 10% to the FB/CC opening.. Under the RF plate... and at the end of the RF plate.... to insure good air flow...
The problem with my tutorial is.....
I don't know how to take into account the surface area of the metal vs. the volume... that ratio would eliminate the friction loss in a long narrow smoker.. Soooo, It's good you recognized a potential problem and asked the question... you will be rewarded for your attention to detail...

Dave

 

[staracin]

So using the Planetcalc using 52 has the the throat i come up with 13.125Wx5.682 . My ? is do I cut 1/2 of this measurement 2.841 out of each pipe.
Thanks Rich

 

[daveomak]

You will need 2 round plates 18" diameter.. One to cover the end of the CC and one to cover the end of the FB... Cut out the football shape on each end plate.... You can verify the shape by using the pipe as a template.... Tack weld one up to the end of the CC.... Slide the FB into place to match up with the "football" cut out, and Tack weld up the FB in place... Then slide the plate onto the end of the FB and Tack weld it in place.. The exposed football shape will now be the FB/CC opening... Weld the RF plate "just" above the football... about 1/2" or so.. Recheck all measurements before cutting and welding...

 

[staracin]

Thanks a ton Dave! Just wanted to verify measurement, just want to do it rite the first time.
Thanks again Rich

 

[Dutch_Erik]

I don't know how to take into account the surface area of the metal vs. the volume...

I tried solving this for my square stack, by calculating the total surface area on the inside of a round and a square tube...
Inner circumference x length = surface area... same could potentially be applied to a pipe, I guess?

What size tank/pipe is the calculator based on, as these calculations only work by comparing between 2 types?

 

[daveomak]

It' s based on an average of many operational smokers... The base is gallons... It's the length and diameter that important... a 24" D x 84" L =38,000 c.i. /231

 

[Dutch_Erik]

Hmm, are there any standard sizes of tank? We could work out the average friction surface per gallon from that.

 

[daveomak]

I can't post on this thread for some reason. Well , I guess it's numbers that won't post...

 

[daveomak]

It' s based on an average of many operational smokers... The base is gallons... It's the length and diameter that important... a
24" by 84" L is 38,000 c.i. is 165 gallons
36" by 37" L is 37,661 c.i. is 163 gallons

Now we can see where an 84" long skinny tank and a 37" wide fat tank are the same gallons...
The surface area discrepancy is where the friction comes into play.....
Since the original "calculator" works when you overcompensate for friction, I'm not smart enough to
factor in the friction when I don't know the optimum diameter/length smoker....
Then the sharp edges inside the smoker affect the flow also when you factor in the available areas for a
vena-contracta to have an effect...
I suppose with about 30 manometers hooked up to 30 different smoker designs one could achieve
an optimum calculator..

 

[daveomak]

There !