Standard Reverse Flow Smoker Calculator... by DaveOmak and others... Ready to use.. rev5.. 6/19/15.

[Edward@SouthAfrica]

Yes.... If you are speaking of center feed fire/FB type thing.... You can make the adjustment of reducing the area under the RF plate by ~30%... Reason being, each side of the RF plate will be handling about 1/2 of the heat and air flow... The exhaust ect. will still need to be built based on FULL flow...

Thank you Dave. That made sense to me and I've adjusted drawings accordingly.

 

[daveomak]

.......

 

[daveomak]

One more thing.... it may be a problem having the heat/smoke travel 50/50.... one side may get hotter etc...

 

[Edward@SouthAfrica]

One more thing.... it may be a problem having the heat/smoke travel 50/50.... one side may get hotter etc...

Will get some pics and drawings up on my thread for this build. Thanks for the advise.

 

[Edward@SouthAfrica]

I keep on coming back here, recalculating things and adjusting design drawings...should be a pro soon
2 Questions.

1.

Recommended upper and lower air inlets... Upper air inlet directly across from the FB/CC opening to facilitate moving heat from the FB to the CC, and insuring good air flow through the CC.. The lower air inlet should be situated at or below the fuel grate.... The two air inlets can share the designated square inches of opening....

Assuming I have a center feed FB, with FB/CC opening center on top of FB (cylinder type), will it be okay if the lower air inlet and upper air inlet sit on different sides of the FB? Let say LAI located front side on door and UAI right side of FB. My donated FB is already setup this way, hence the question.

2.

Adjust the diameter of the stack, until the proper length is achieved... be sure to measure the actual internal diameter of the pipe used..
this is for round stacks only..

According to calculations my stack dia pipe must be 2.65in @ 36.5". Can I double the pipe dia and half the length to get the same result? I was looking to use a 5" dia pipe @ 18.25", or a 4" pipe @ 23.5".
/Or, is the recommended length of stack pipe set at 36"?

 

[daveomak]

I need a picture or something to understand this...

 

[gary s]

I would go with the larger Dia. stack As for as the upper and lower air inlets on the FB I would go with both in the door. And Lastly you will probably have one side that runs hotter than the other side How much ?? you want know till to fire it up and check.

Gary

 

[Edward@SouthAfrica]

I need a picture or something to understand this...

Some screenshots from my drawing design. You'll note I've included the 3 types of exhaust stacks as discussed previously. Note that CC size is slightly larger than noted on drawing. Gallon size is actually 39.6258 (150L) (I have to convert everything from metric to fit pit calculator...)

 

[JckDanls 07]

After looking at the drawings.. I don't see where upper vents (in the FB) would be needed as the heat from the fire will be going directly into the CC ... I would think two lower vents (1 each end) would be the better choice for this design...

If I remember correctly the calculator will tell you what size pipe for whatever length/height you want... Which is measured from the top of the tank and not the exit point ...

 

[Edward@SouthAfrica]

I think at this point I'll refer you to my build thread for further Q&A's. I don't want to hi-jack this thread with my build Q&A's

Link to my build thread: https://www.smokingmeatforums.com/threads/center-feed-reverse-flow-smoker.286000/

 

[AllTuckerdOut]

daveomak What's are you using Diameter X Diameter X 0.7854 X Length as a way to calculate the volume of what cook chamber shape? Seems like maybe a cylinder with no rounded sides?

 

[daveomak]

D x D x 0.7854= 3.14159 x r x r

3.14159 / 4 = 0.7854

It's just something math nerds do....

 

[AllTuckerdOut]

D x D x 0.7854= 3.14159 x r x r

3.14159 / 4 = 0.7854

It's just something math nerds do....

But isnt that the area? Not the volume?

 

[daveomak]

D x D x 0.7854 X LENGTH = VOLUME

 

[AllTuckerdOut]

Ok so this assumes it's the volume of a cylinder. So not necessarily a propane tank (cylinder with a some on each end - oil shape)

 

[daveomak]

From post #1 of this thread...

Volume of the Cook Chamber.... Use the Inside Diameter of the tank...
Diameter X Diameter X 0.7854 X Length = Volume in cubic inches ...

Yes, it's the volume of the Cook Chamber... If using a propane tank, I usually use ~50% volume of the end caps... Close enough for the meat we would be cooking... There's a science to this but it ain't rocket science... No moon landings...

 

[Edward@SouthAfrica]

One more thing.... it may be a problem having the heat/smoke travel 50/50.... one side may get hotter etc...

Question on that Center Feed Double Reverse Flow concept of mine. Will it work if I bend the 2 opposite ends of the RF plate down 90 degrees, lets say 2 inches in length? This will create a sort of heat pocket below the RF plate to even out the heat distribution and flow?

 

[Edward@SouthAfrica]

I would go with the larger Dia. stack As for as the upper and lower air inlets on the FB I would go with both in the door. And Lastly you will probably have one side that runs hotter than the other side How much ?? you want know till to fire it up and check.

Gary

Question on that Center Feed Double Reverse Flow concept of mine. Will it work if I bend the 2 opposite ends of the RF plate down 90 degrees, lets say 2 inches in length? This will create a sort of heat pocket below the RF plate to even out the heat distribution and flow?

 

[daveomak]

Bending the RF plate, or any obstruction in the laminar air flow, only adds resistance to air flow... Not good in a gravity feed system...
I have noticed, from members results, increasing the air flow gets the best results for uniform heat distribution... The upper air inlet, and it's proper use, verified that point..

 

[MikeFromTexas]

Finished my reverse flow build about 1 month ago. Not wanting to reveal my nerdy innards by performing a flow analysis through engineering software, I decided to follow the recommendations in this thread/tutorial. All I can say is that my pit is a great flowin machine. Great temperature control, temperature distribution and doesn’t seem to use that much fuel (about 12” log per hour).

specs:
45” cookin chamber
18” OD x 1/4 wall.

i’ll say this though, I spent a lot more money than I thought I would. Kinda like when I build ARs..