Need help on reverse flow smoker.

nickbbb · Jan 7, 2016

I have a smoker that I believe was supposed to be a reverse flow but I think the guy messed up (might be why I got it so cheap) so here it goes. The firebox is 36x20.5x26.5 inches. The chamber is 23 inch circumference amd 52 inches long. (Here's why I think reverse flow) it has a pipe (I think about 8 inch) it runs the length of the chamber and turns up at the end. BUT the smoke stack is on the same side as the opening of the pipe. So I want to move the smoke stack to the other side. But my question is - what size stack do I need? Everything I see as far as calculations is for round pipe and I want to use rectangle pipe. Thanks for the advice!

20150809_130032.jpg

nickbbb
Jan 7, 2016

mp4s · Jan 9, 2016

I used a square pipe for my build and had the same issue so you'll have to figure out the volume of the round pipe and use the same volume for your square tubing.

A 4" round pipe 48" long is 602.88 cubic inches (3.14 x radius squared x length). Volume of a square tube is Length x Width x Height so a 4" square pipe would need to be 37.68" long to be identical to the 48" round ( Length x Height = 16"...602.88 / 16 = 37.68"). Be sure to use the inside diameter for both measurements.

Good luck!

maple sticks · Jan 9, 2016

If your removing your current stack why would you not reinstall it at the other end.

Square stacks don't work quit as smoothly as round ones. If your smoker calls for an 8" round stack you should use a 8" square one the same length. Exhaust swirls as it travels through a smoke stack not utilizing the corners as much.

daveomak · Jan 9, 2016

mp4s said:
I used a square pipe for my build and had the same issue so you'll have to figure out the volume of the round pipe and use the same volume for your square tubing.

A 4" round pipe 48" long is 602.88 cubic inches (3.14 x radius squared x length). Volume of a square tube is Length x Width x Height so a 4" square pipe would need to be 37.68" long to be identical to the 48" round ( Length x Height = 16"...602.88 / 16 = 37.68"). Be sure to use the inside diameter for both measurements.

Good luck!

If you use a square that has the same volume as round, the surface area of a square has more surface friction and will not provide the same effective flow of exhaust gasses...

nickbbb · Jan 9, 2016

Thanks fellas. I don't want to reuse my existing stack for 2 reasons. 1) the clearance between the top of the smoker and the top of the fire box will not allow for it. 2) with the firebox measurements plugged into the "smoke stack calculator" it shows that the existing stack is severely under the requirement.

mp4s · Jan 10, 2016

Good luck!

If you use a square that has the same volume as round, the surface area of a square has more surface friction and will not provide the same effective flow of exhaust gasses...
[/quote]

I read this and thought, yup, that makes sense. When I checked though, the surface area of round and square with the same volume is equal.

maple sticks · Jan 11, 2016

In a circular tube air flow swirls and the speed of air through the tube is slowest near the sides due to drag. The speed increases as you move away from the edges with highest speeds in the center. In a square tube the regions near a corner are influenced by two sides so the speed will be even slower there. As you move away from the corners air starts to swirl like in a circular tube. What you end up with is the majority of the air will be flowing in a circular region inside the square. The corners do not add much to the flow. Its not a big deal. Round is better than square and square is better than rectangular.

daveomak · Jan 12, 2016

Maple Sticks said:
In a circular tube air flow swirls and the speed of air through the tube is slowest near the sides due to drag. The speed increases as you move away from the edges with highest speeds in the center. In a square tube the regions near a corner are influenced by two sides so the speed will be even slower there. As you move away from the corners air starts to swirl like in a circular tube. What you end up with is the majority of the air will be flowing in a circular region inside the square. The corners do not add much to the flow. Its not a big deal. Round is better than square and square is better than rectangular.

Very well said..... with patience and clarity..... It's obvious, when someone took the time to buy you books, you read and understood the printed matter... One more round for my friend...

sqwib · Jan 12, 2016

From my perspective, I would do one of two things;

1) remove the pipe and add tuning plates (leave exhaust stack in place)

2) Remove pipe, in place of the pipe add a reverse flow plate and move the exhaust stack to the other side.

In either case I would remove the pipe...although, I'm basing this on a description and not actual pictures.

nickbbb · Jan 12, 2016

I will have to Do some tinkering with the layout to get a round pipe I guess.

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Need help on reverse flow smoker.

nickbbb

Newbie

20150809_130032.jpg

mp4s

Fire Starter

maple sticks

Smoking Fanatic

daveomak

SMF Hall of Fame Pitmaster

nickbbb

Newbie

mp4s

Fire Starter

maple sticks

Smoking Fanatic

daveomak

SMF Hall of Fame Pitmaster

sqwib

Smoking Guru

nickbbb

Newbie

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