Smoke Vault gas smoker makeover

[Nefarious]

Yea, it will draw from the path of least resistence, so if his box has a hole under the burner for it to draw air, and serve as a bottom vent, That's where the air is going to enter.

Thats correct, and that is the source of oxygen for the gas flame. So then, why did I think this would work at all?

There are two intake vents, one on each side at the wood chip level of the smoker. I reasoned these vents were there to supply fresh oxygen to allow the wood to burn. When I closed the vents the temperature in the smoker, without wood on the chip tray, lowered by somewhere around 8 degrees. i was only able to close them partially. It wasn't clear how much flow I would get from the vents, but it is some. i have closed off these vents, attempting to replace them with the mailbox.

i didn't know if I could change the thermodynamics of the box sufficiently to get enough pull to move the smoke from the mailbox to the smoker. As a last attempt, in the original plan I would add a convection oven fan to either push or pull the smoke into the smoker.

 

[Nefarious]

I have some 4" drain PVC laying around and I put an 18" piece over the exhaust port. I can see the heat rising from the top but very little smoke. None seems to be coming from the mailbox either, so maybe this is just what's being generated?

 

[Nefarious]

Well, I have a 34" stack, very unrealistic, just seeing it it changes the situation. One issue is there is just not much smoke. But it still comes out the bottom of the mailbox, clearly not enough draw to pull it all out.

My next step is to drill the holes in the bottom a size bigger, but I don't think that's the problem except the fire in the tube goes away down like not enough oxygen. We will see.

 

[Nefarious]

Need to think about this. Added wood chips to end of smoke tube to generate more smoke.

More smoke is pushed out the bottom holes in the mailbox. I think this means that this is the heat thermal route as well as the top stack.

If I open the door and no wind is blowing, the smoke flows out of the mailbox and none through the bottom mailbox vents.

I'm going to open one of the closed vents on the bottom and use a match or the smoke tube to see the direction of the air flow.

 

[Nefarious]

I did the test I should have started this project doing, testing the assumption that there was some draw from the side vents. No draw, the smoke would rather circulate under the smoker drawn by the gas fire. So, I go back to the original idea and use a fan to push/pull the smoke from the mailbox.

 

[Nefarious]

Ringer do you have a link to the fan you used or is it something you already had?

 

[Ringer]

Here you go sir:

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I mounted the motor side in a box attached to the smoker wall

 

[Nefarious]

I mounted the motor side in a box attached to the smoker wall

Thanks I appreciate it. I did the same for the thermometer on the back.

I'm also groping around with different ideas on how best to solve this problem and I thought of connecting an aquarium air pump to the outside of the mailbox and pressuring the the smoke from the mailbox to the smoker. I need to figure out a way to prototype without spending too much. I have already spent too much, there are many smoke generators I could just buy.

Something like this:

 

[mosparky]

I think the root problem is your exhaust vent is too small. Think about it, you are not only adding gas to the chamber, but igniting it. The resulting heat explands the air/fuel combo and has to go somewhere. Currently it's causing a back flow on the mailbox, thus the smoke coming out of the air intake holes on the mailbox.
Currently I only see 2 viable cures.
1. A smoke tube INSIDE the smoker may work out as they are meant for lower oxygen environments. Unfortunately that means abandoning the mailbox after so much effort has been put forth.
2. An exhaust fan to help pull the heated air out of the exhaust vent would likely be the best way to salvage the existing plan. Go cheap on the fan. Heat and smoke residue will make it a consumable item. I think Tallbm did an experiment with a cardboard stack with the fan mounted on a side tube, at an angle. This creates a venturi or syphon effect. It does keep the fan out of harms way but the assist may be nominal, (but possibly enough)

I wouldn't entertain the idea of a fan assisting incoming air on the mailbox. The extra air at that point will cause you to go thru pellets like mad and likely to cause them to flame up making even less useable smoke.

 

[Nefarious]

I think the root problem is your exhaust vent is too small. Think about it, you are not only adding gas to the chamber, but igniting it. The resulting heat explands the air/fuel combo and has to go somewhere. Currently it's causing a back flow on the mailbox, thus the smoke coming out of the air intake holes on the mailbox.
Currently I only see 2 viable cures.
1. A smoke tube INSIDE the smoker may work out as they are meant for lower oxygen environments. Unfortunately that means abandoning the mailbox after so much effort has been put forth.
2. An exhaust fan to help pull the heated air out of the exhaust vent would likely be the best way to salvage the existing plan. Go cheap on the fan. Heat and smoke residue will make it a consumable item. I think Tallbm did an experiment with a cardboard stack with the fan mounted on a side tube, at an angle. This creates a venturi or syphon effect. It does keep the fan out of harms way but the assist may be nominal, (but possibly enough)

I wouldn't entertain the idea of a fan assisting incoming air on the mailbox. The extra air at that point will cause you to go thru pellets like mad and likely to cause them to flame up making even less useable smoke.

I have thoughts on why I agree with your explanation and why I am not positive about it.

When I open the door smoke flows from the mailbox out into the smoker. When the door is closed something is causing the the smoke flow to be blocked and it could be pressure from the expansion inside the smoker. This could then cause the smoke to be pressured out through the mailbox air intake holes.

Knowing this, I removed the plate over the side bottom vent on the smoker. If there is a buildup of pressure inside placing smoke source in front of this vent would indicate the direction of flow. If pressure is building on the inside it would push the smoke away from the smoker chamber. For the most part the air was stagnant, did not flow away from the smoker or into the chamber.

I did talk to Ringer about the experiment that tallbm did and will give that some thought. An alternative to the fan alternative is to add another exhaust vent.

The current exhaust vent is about 3.5" in diameter but only half of the area is open. One thing I might do tomorrow is to cut the rest of the vent hole open to give a small amount more area. If this doesn't work I can easily plug the hole and put the vent, with a bigger hole on the back near the top.

At this point I am just trying to find some evidence that points to what the issue/solution is.

1) Making the stack higher causes more smoke to go into the smoker but it does not stop the flow out of the mailbox intake holes.

2) Opening the door seems to cause smoke to flow into the smoker and stop the flow out of the mailbox bottom. I haven't spent enough time sorting through what this really means.

 

[DougE]

It may be that the exhaust is purposely restrictive in order to keep heat from dissipating so quickly that the box can't maintain temperature.

 

[Nefarious]

It may be that the exhaust is purposely restrictive in order to keep heat from dissipating so quickly that the box can't maintain temperature.

At this point anything is possible. Given that the side vents seem to have no real purpose, i could easily see that as a possibility. My longer range plan is to add thermal mass to the inside to help retain some of the heat. The box is just a tin can with a heat source at the bottom, it takes very little to drag it around.

Tomorrow I am going to cut the exhaust vent some to see if what mosparky proposed has validity. I will have no problem plugging the top vent and putting a couple of stacks on the back. All of the top stacks i've seen are too small.

 

[JckDanls 07]

I really wish you would have went with a 3'' duct instead of the 2 smaller ones on the mailbox... woulda made life easier...

The root of the problem is the big hole under the burner... It draws all it's air from that hole... in turn not drawing from your two ducts from the mailbox...

For another experiment... Find something to block the hole under the burner... heat the box up (to create a draw)... turn burner off... block big hole... see if it will draw from mailbox that way ...

 

[Nefarious]

There is one more piece of evidence I keep losing track of and thats that when I add a stack there is less smoke coming out of the mailbox intake. @ 18" less then no stack and at 38" even less and almost none.

Since a longer stack creates a greater pressure difference between the top and bottom of the stack smoke is pulled faster from the smoker.

 

[Nefarious]

Congratulations are in order to mosparky , the exhaust vent is too small. I cut the rest of the top vent out and put the small stack on and:

No smoke from the mailbox. Thank you for your inside, I appreciate it.

I can't use the exhaust duct on top because ai need a stack and all top stacks I have seen are only 2 inches in diameter. I will use first one, and if insufficient two stacks mounted on the back.

 

[Ringer]

Congratulations are in order to mosparky , the exhaust vent is too small. I cut the rest of the top vent out and put the small stack on and:
View attachment 526540

No smoke from the mailbox. Thank you for your inside, I appreciate it.

I can't use the exhaust duct on top because ai need a stack and all top stacks I have seen are only 2 inches in diameter. I will use first one, and if insufficient two stacks mounted on the back.

Glad you got it!

 

[Nefarious]

Glad you got it!

I certainly appreciate all of the advise you have given me. I still have to tune it the holes may be too big now.

 

[Ringer]

No problem man, this forum and its members have been invaluable to me, I'm just happy to be able to help from time to time.

Now, we need to see some smoked meat pics from this thing!!

 

[Nefarious]

I'm doing some big, 3 bones each, end of 3 racks I did last week for a soccer match party. We will see how they turn out. Thanks again.

 

[Nefarious]

No problem man, this forum and its members have been invaluable to me, I'm just happy to be able to help from time to time.

Now, we need to see some smoked meat pics from this thing!!

And the drain pipe stack has to go, wife will never adjust to that