Airflow in my ECB


 
N

NateSebold

TVWBB Member
Wondering if any of you might take a look at some cooks and offer advice on my setup.

I have an El Cheapo Brinkmann heavily modded to be pretty air tight with an RD3 (thanks Ralph) hooked up to flexible copper tubing "airburner". I usually run it with a weber 4 hole top vent wide open and then the only other air is coming through the RD3. Everything else is pretty well sealed with silicon gasket.

For all these cooks I'm using 30/70 lump/charcoal with just a couple but hunks of apple.

For my water pan.. I used rocks and bricks for the first cook. And nothing for the second and third.

My main questions are do I need a more powerful blower? (I am currently running the standard blower)
Should I close up the top vent more? (How will that impact airflow? Will I keep more heat in?)
Do I need the top vent open to pull air through to the fire?
Is this just a result of no insulation in my smoker and losing heat as the temperature dropped across these three burns?
Would using something in the water pan help? (sand, rocks,,... i was thinking of making a heat resistant concrete mold specifically for my water pan)

You can see from this brisket burn that the thing holds temp pretty well. It stayed right at the set point for like 5 hours before I had to add more charcoal to finish it off in my brisket smoke here. It recovered well after I crutched it... The fan did pretty well except for when I ran low on charcoal. The airtemps were probably in the 70s

brisket.PNG


For the next one I did ribs, the air temp was a bit lower 60s but the thing did a good job with the set point but had to run the fan quite a bit more and I did have to add more charcoal so the same fuel load only lasted 3 hours here versus the 5 in the previous cook.

ribs.PNG


Last one I was doing a butterfly chicken and cranked my set point up to 300 and it took nearly an hour to get there and had a hard time staying up that high. The air temp probe I added here so it was in the 50s for the whole cook. It was a shorter cook but when I took it off I was probably about an hour away from needing to add more fuel.

chicken.PNG
 
It would be a good idea to maybe post a pic of your air burner setup. You may be getting some restrictions that are limiting the air flow to the fuel. The 6.7CFM fan should be plenty big enough to control temps in a Brinkman at much lower rates.
 
Sure thing here it is:

RD3 goes into 1/2" copper pie all the way to the center... then 90degree and reduction to 3/8" flexible copper tubing and you can see how I made a circular tube with some splits. You can see all the holes I drilled in the flexible copper tubing.

IMG_20161111_155045.jpg


IMG_20161111_155114.jpg
 
I've never run an airburner - I don't really like the idea of it, I try to duplicate a natural airflow as much as possible - but I think you're problem is you probably went to small on your tubing diameter.
 
If you have trouble maintaining / achieving heat you either don't have enough fuel, or enough air. My guess would be air. I believe that the RD3 is designed with a 1" outlet. You have dropped that down to 1/2" right away, and then down to 3/8". Assuming that they are 1/8" holes, you at least have enough area in holes for the 3/8" pipe. I'd try just undoing the compressions on the tee and see if that helps, but you may need a bigger "feed" pipe.
 
I'd agree that the small diameter of the tubing is the biggest bottleneck. I used 3/4" copper tubing on my air burner and air flows really well. I think the compression couplers are also very restrictive. I used regular elbows and T's for solid (not flexible) copper pipe, which are wide open and allow full flow. I am not on board with the compression fittings and small diameter pipe.
Someone else suggested you could disconnect the first T (remove the air burner) and see if that allows more flow to achieve higher temps, that'll give you your answer...
 
Thanks all for the feedback!

I think I will first try without any air burner and just blow air in and see how that works.
 
I definitely think it is an airflow issue. I just started my UDS and use a 7cfm blower and I get up to temp pretty quick:

 
I think the dynamic at play here is this...
The blower has a set amount of static pressure, when the full amount of static pressure is applied to small holes in a manifold it pushes out nice solid jets of air and stokes the fire well... as was my experience with the manifold I made using 3/4" copper pipe, which has an inner diameter similar to the size of the blower output. In your setup you've reduced down the inner diameter of your manifold to be less than half the size of the blower output (I would guess), so you are losing a good deal of the blowers static pressure due to that reduction in manifold diameter, and getting reduced flow from your air holes as a result.
Personally I would have built the manifold with the bigger 3/4" pipe so the air delivery is unhampered, but everything is a balance, so you may try larger holes or more holes in what you have to see if you can strike a balance that works....
 
So yeah I dumped the air burner and now its basically the dog-bowl set up.. I still have the RD3 reduction to the 1/2" but once it gets through to the other side it was all open.

A pretty good cook today. Air temp was a 50s and I was shooting for 225 and the fan ran a whole lot less. Pretty big fluctuations compared to my previous burn. The servo in my RD3 burned out so I'll have to get a new one and maybe with a little damper it would be a bit tighter. There was a weird moment in the middle where the lid open was tripped even though i didn't open the lid.. i think it was a big gust of wind or something. I also wonder if a heat sink would smooth out the temperature fluctuations.

Anyway here is my burn from today:

ribs11.13.PNG
 
You also need to keep in mind that flow is decreased exponentially as you decrease the diameter, not linearly. You've reduced the diameter by half of what Ralph has empirically found to work, which translates to 4X less flow. This is also neglecting the drag within the tube. Static pressure capabilities of your blower is where the drag coefficients start take effect, you increased your drag and decreased your flow. You can try drilling larger holes, but I highly doubt it'll work. You need to build a new one with an appropriately sized tubing to make it work, and make junctions restriction free.

Looking at your graph it seems to me your I is probably too high as well.
 
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