reverse flow calculation

[HannibalFP]

hello everyone,
First of all I would like to apologize for my bad english.

I am planning the build of a reverse flow smoker that I could use for a whole pig.
I have a question about cooking chamber volume/ baffle plate(volume)
When I use the calculator they ask to use the volume of the cooking chamber, but I dont know if the volume below the baffle plate has to be included within the volume of the cooking chamber.

My example is the following.
Let say that I take a cooking chamber with the following dimension of 30x30x60.
The calculator tell me that the area of the air intake between the firebox and the cooking chamber is 27x8 ( I want to build an insulated firebox, this is why there is 1.5 inch on each side of the total wide), so I should have a "chimney like" space below the cooking chamber of 27x8x52.
My other question is also do i have to make this chminey like of 27 inch wide or can I make it of 30 inch wide?
If I can make it in 30 wide is this will change something on the calculation of the air intake between the FB and CC and betwteen the bafle plate and the wall?

Do I include this volume to the cooking chamber to make the calculation or not?

I hope that what I ask is understable.
Thank you for your help

 

[daveomak]

https://www.smokingmeatforums.com/t...eady-to-use-rev5-6-19-15.172425/#post_1264161

Use the above tutorial.... Calculate one (1) line at a time and write that number down...

 

[HannibalFP]

hello daveomak

I have been using this link.
What I am trying to say is the following
following this calculator for the reverse flow and taking some measurement I obtain this
area for the fb/cc chamber 216 square inch, so the opening will be 27x8=216
so my baffle plate will be 8 inch high from the base of the cooking chamber.
After that I let a lip of 1.5 inch for keep grease or what ever to go to the FB.
so in fact my cut will be 9.5 inch high.
between the baffle plate and the first rack I let a 4 inch space, and my rack is 1.5 inch high too.
My first line of "meat" will be at 15 inch from the base of the cooking chamber, and this is mean that the usable space to put a whole pig will be 15 inch high too.

this is why I ask, if I have to include the volume below the baffle plate within the cooking chamber or not.
If I have to include it that mean that a 30x30x60 is too small and I should use a 30 wide x 40 high x 60 long.

 

[daveomak]

If you don't understand how to follow this tutorial, in the next post, put down the length and diameter of your cook chamber and I will run the numbers...


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

Diameter X Diameter X 0.7854 X Length = Volume in cubic inches

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

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

Volume in cubic inches X 0.004 = Area required at the end of the RF plate in square inches
----------
For calculating the FB/CC opening.... You are calculating for the GREEN area... that will be the cut-out area in the FB that mates to the CC....

The green area is a segment. It is called a "Segment Area"... That area is the same as the FB/CC opening....

When you open the "Circle Calculator" link, Click on the "bullet" to the left of Radius & Segment Height ED....

Circle Calculator

Click on the 2 variables you know

......Radius and Central Angle...........................Radius & Chord AB
[X] Radius & Segment Height ED.....................Radius & Apothem OE
......................................................Radius & Arc AB
......Chord AB & Segment Height ED................Chord AB & Apothem OE
......Segment Height ED & Apothem OE...........Chord AB & Arc AB

You should have opened the circle calculator and a bunch of boxes will appear below..
and a box called [CALCULATE]..

Enter the radius in the box so marked.... If you tank is 24" OD, and has a 3/8" thick steel wall, the ID of the tank 23.25".... the radius is 11.625"..... these numbers need to be accurate if you want stuff to fit... ALSO, take into account the thickness of the FB steel when cutting out the tank...

Enter a guess for the Segment Height ED... I'd start with 6.0

Click on [CALCULATE]....

 

[HannibalFP]

I know how to use the the calculator but I dont understand how to manage the volume below the baffle plate.
the space below the baffle plate is like a chimney who conduct the smoke and the heat to the opposite of the smoker and then is felivered inside the cooking chamber and the food rack.
the volume who occupy this "chimney" is annoying me, do I have to consider this volume a part of the cooking chamber or not?
My smoker will be rectangular so the calcul of the radius or half cercle opening is not needed.
with all the plan I made I get to the conclusion that a 30x30x60 is too small because I dont have enought height to fit a whole pig.

inside my 30x30x60 I have to weld the baffle plate at 9,5 inch from the base, so it remains 20.5 inch of height, in wich I have to also let a 4 inch space between the baffle plate and the first rack, so my first will be at 9.5+4+1.5 wich is the height of the rack= 15 inch.
that is my problem

 

[daveomak]

The CC is everything between the exhaust stack and the FB... That is the volume that is important..

 

[pete mazz]

The grease dam in a RF is on the end of the BP, not at FB.

 

[daveomak]

I think "BP" refers to the RF plate... A dam on the end of the RF plate and a drain and ball valve to dump the grease through the CC to the outside is a very good addition...

 

[HannibalFP]

ok thank you very much, I will install, the grease retainer on the baffle plate.
I thought that a 4 inch space between the food rack and the baffle plate is enought.
What do you recommand?

 

[HannibalFP]

ok, so far so good, my final dimension will be 56 long x 30 wide x 40 tall
FB is 30 long x 27 wide x 30 tall (insulated)

cooking chamber is 67200 square inch
FB/CC opening =268.8 = 27"x10"
FB inlet = 67.2 divided in 80% and 20% =54 and=13.5
ESV=1478 plus 30%=1921.92
Exhaust calculation
7.2 X 7.5 x 36 =1944

Am I good?

 

[Bige619]

If you don't understand how to follow this tutorial, in the next post, put down the length and diameter of your cook chamber and I will run the numbers...


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

Diameter X Diameter X 0.7854 X Length = Volume in cubic inches

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

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

Volume in cubic inches X 0.004 = Area required at the end of the RF plate in square inches
----------
For calculating the FB/CC opening.... You are calculating for the GREEN area... that will be the cut-out area in the FB that mates to the CC....

The green area is a segment. It is called a "Segment Area"... That area is the same as the FB/CC opening....

When you open the "Circle Calculator" link, Click on the "bullet" to the left of Radius & Segment Height ED....

Circle Calculator

Click on the 2 variables you know

......Radius and Central Angle...........................Radius & Chord AB
[X] Radius & Segment Height ED.....................Radius & Apothem OE
......................................................Radius & Arc AB
......Chord AB & Segment Height ED................Chord AB & Apothem OE
......Segment Height ED & Apothem OE...........Chord AB & Arc AB

You should have opened the circle calculator and a bunch of boxes will appear below..
and a box called [CALCULATE]..

Enter the radius in the box so marked.... If you tank is 24" OD, and has a 3/8" thick steel wall, the ID of the tank 23.25".... the radius is 11.625"..... these numbers need to be accurate if you want stuff to fit... ALSO, take into account the thickness of the FB steel when cutting out the tank...

Enter a guess for the Segment Height ED... I'd start with 6.0

Click on [CALCULATE]....