Reverse flow theory

[sqwib]

And I know a lot of guys would be against this but If I had to do it over again, I would run my pipe 5- 6" diameter and put a damper on it to help control the draft.

The one I have on Frank is a 4" diameter pipe but I always run it full open, on occasion I have closed it it for a minute to drop temps if they get too high.

I would use a configuration like this  4 or 5" closed 5 or 6" open, this takes the guess work out of proper sizing.The baffle would be like a washer.

baffle.png

• sqwib
• Jul 11, 2013

 

[sqwib]

The pic was thrown together in paint, there should be more clearance between the  top part and washer type piece, 4-5"

baffle.png

• sqwib
• Jul 11, 2013

 

[ribwizzard]

Thank you Sqwib,

We always preach about not choking the exhaust, but if the cooker has too small a pipe to begin with, there is nothing we can do about it.

On the other hand, if its too big and we need to hold in a little more heat, then how can it hurt to shut it down a little?  I looked around some on the web today and most cookers look to have way to small a pipe to begin with. Hearing you say that you wished you went with the bigger pipe helped me make up my mind. I went with the 4" id pipe, about 28" tall.

 

[ribwizzard]

I know it looks way to big for this cooker,....but I really wanted a free flowing cooking chamber...  I had to off set it a lil' for the door clearance.

I have not decided completely on my vent design either, so I'm holding back on that right now as well.

 

[ribwizzard]

And I still need to run a bead on the inside and trim and round it out some.....I also did not want to drop the exhaust down inside the chamber on this one either.   Hmm..look at all that grinding dust in there..all kinds of flavoring going on....

 

[sqwib]

Looking good!

 

[ribwizzard]

White...

 

[ribwizzard]

...to black!

 

[ribwizzard]

Anyway, yall have a good weekend,  I done wore myself out this morning.

 

[sqwib]

Anyway, yall have a good weekend,  I done wore myself out this morning.

You are a madman Rib.
Great job can't wait to see how this performs

 

[goinforbroke]

Coming in late here, and I'm not an engineer.. just an ol' HVAC guy.   

Thinking about the first mock up, wouldn't it be better to actually have A choked down to the fire boxe opening?   My rationale here is pressure differentials, and we know that air will flow through the A opening, provided the rest of the openings possess a lower static pressure drop.  In this sense, the flow, to me, seems more elegant when flowing toward a lower pressure, as opposed to having a 'choke point' midstream within the cook chamber, that "chimney effects" upon exit.   I don't own a RF, so grains of salt..   That said, I do like the circular reverse bend, as air flows better (less static pressure loss) across a round opening vs a square one.    Theoretical ideals would have the cook chamber cosisting of two flat ovals, joined at the other end by a flat oval of equal area.   Impossible to build in practical terms.  I love your experimentation and theory push.  stay busy!

edit to above:  I suppose my thinking for makign the most ideal RF design involves the combo of air flow through lowest pressure loss, while also having the ideal air change rate (to maximize the heated air).   In plain english, air flows in the chamber, stays as long as ideal for heat gain, then exits at a rate that just enough to fuel a fire.  I can't conceive of a way to even test this though.   So many variables, that, to the point of elimimating them would create a one-trick-pony smoker that was designed to burn at only 225 with the smallest amount of fuel.  Which is so variable in its own right.  ugh!  nevermind!  my head hurts.

 

[daveomak]

RW, evening.....   I keep lookin' at the "ducted tunnel", or what ever you have called it, at the end of the RF plate....  It intrigues me to the point I think that is one great idea..... I'm waiting for your test results, but, I think they will be 

 on the new design......   

 

[ribwizzard]

Well, I still have to make handles, grates, and decide on my firebox inlet vent design, and install gaskets on the doors, so I'm more than a week out from trial run, but I will keep you posted 

 

[ribwizzard]

Goinforbroke:

My theory is by choking it or bottle necking it at points "B" or "C", instead of "A" I will increase temperature in cook chamber under the reverse flow plate with out having to use a bigger fire, then by opening up the exhuast more, have cleaner smoke in the upper cooking chamber.

With that said all opening are bigger than required if it was a traditional reverse flow, so if it does not work, no fabricating will be required to swap it back, other than install some inserts that correct the openings.

I think the full length drip pan was worth it alone, I should be able to rinse out the entire cook area with out a drop of water hitting the firebox. This will let me clean it "hot" right before putting food on.

 

[ribwizzard]

Well, this ones getting close to cooking time,

got handles made and vent door about 75% done

 

[ribwizzard]

Got my 3/8" stainless rods turned into some nice heavy duty cooking grates

 

[ribwizzard]

I welded in some boss's on the back of the cooking chamber to hold the firebox grilling grate

It was also possition all the way to the left or the right as well.

 

[daveomak]

RW, Nice... very nice......    does the upper grate "slide" in ???? 

 

[ribwizzard]

I built the grates with the lateral bars extending the horizontal bars by 3/4 of an inch, so the boss's weld in are 3/4 of an inch deep, angle slightly to keep the grate level. So I'm just sticking two of the lateral bars into the bosses and it hold it in place. I didn't want any kind of racks mounted inside the cook chamber, so this was a simple way of adding the second rack and giving me a place to store the firebox cooking grate that also allows me to adjust it left or right in 13 different positions. Because all of the bars rest against the wall of the cooking chamber, its actually sturdier than I expected and even when installed in only one boss, holds itself level and feels like it will support more weight than Id ever expect to place on it.

Just one of those times that the simple solution was the best solution, for me at least. Im happy with it.

 

[ribwizzard]

Dave, did you say you thought it would be ok to use bioled linseed oil inside the cooker? I was thinking on using it on the reverse flow plate/drip pan. Wish I would have done it in stainless.