AUF/AOF for barrel stove evaporator

[crowellsr]

How many CFM should I be looking for in a AUF/AOF modification to my barrel stove evaporator?

[RileySugarbush]

Almost any additional air for AUF in a small evaporator like that will make a difference in evaporation rate. I would look for a cheap 200CFM (or more) squirrel cage blower and put a damper on the inlet to the blower to fine tune it. Too much air and the fire is really putting out the heat but it blows right past the pans with the high velocities and you end up with high stack temps and wasted wood.

I think it will be difficult to see any advantage of a high pressure AOF system on a short system like a barrel. Save the time, complications and money for when you have at least a 2x6.

[crowellsr]

Ok so anything is better than nothing in a AUF modification. I currently build the fire on the sand in the bottom of the barrel. Will I need to put in a grate to get the fire up off of the sand so the AUF can get under the fire better?

[Super Sapper]

Raising it up is a good idea even if you do not use AUF.

[crowellsr]

What is recommended for a grate so it is not effected by the heat?

[BRL]

A lot of people use 1/4" angle iron in this configuration VVVVV. Ashes build up in the V and keeps them cooler so they don't deform

[berkshires]

What is recommended for a grate so it is not effected by the heat?

Other people have fancier stuff, but I made one out of fencepost that works great. I drilled extra holes and left space between the beams. Looks like this:
http://mapletrader.com/maplegallery/data/649/mod4_with_trough.jpg

http://mapletrader.com/maplegallery/data/649/grate_brick_end.jpg

http://mapletrader.com/maplegallery/data/649/wings_cindrblock_grate.jpg

Because of the shape, they don't buckle in the heat.

[crowellsr]

Thanks everyone! I guess I better get to work

[RileySugarbush]

You definitely want a grate. Beneath that is the " under" of AUF, so that is where you introduce the blower air. I use the inverted steel angle mentioned here. It works well. Mine have gaps of about 1/4 to 3/8 inch between angles. The area under the grate needs to be closed off so all the air goes up through the wood. many, including me) block off the very front of the grate near the door so the airflow can't short cut past the wood in that area and to keep the door cooler.

Depending on your stack and the draft it creates, you may need to throttle the blower to keep ash from blowing out the gaps around your arch. Else you need to seal things up well.

[wobbletop]

I used a small bathroom vent fan for AUF. It uses a 3" vent pipe. I plan to add a variable speed fan control to it this year. Previously I had just blocked part of the inlet.

I used a BBQ grate for the grate. You can pick up replacement ones at home depot, etc. There is some drooping but I flip it over every batch so it's not an issue. They last a couple years.

[red/one]

Having trouble uploading these to the galleries, but anyway. This is my homemade AOF/AUF. 2x2 steel and 1/2" tubing feed the top and 2" pipe feeds the bottom via an old furnace fan. Haven't tested it yet.

170391704017041

[maple maniac65]

With a blower that size had better chain that arch down so it does not fly away:-)

[red/one]

Ha Ha! I thought so too. I actually had holes drilled in the back of the wood box and found out I had to completely close in the box. The air out is not too bad. Still have not yet put a fire in it yet.

[RileySugarbush]

red/one:

That blower will work ok for AUF and with the relatively small duct will not overpower the fire. In fact, you may not get as much air under the grate as you hope. Try it and see.

But it is the wrong kind of blower for AOF. For that you want a high pressure blower which has a totally different type of vanes, capable of generating at least 4" h20 pressure. That blower is a high volume/ low pressure blower, maybe 1" of h20. If that is what you have there, you will get slow jets of air that will only cool the bottom of your pans and will increase the overall velocity of the combustion gasses so that what heat you do have does not stay under your pans as long.

To confirm this, put a tube manometer on one of the AOF nozzles and see what kind of pressure you get.

[red/one]

Ok sounds like alot of work for nothing but the blower was FREE so I am trying it. I dont know what a mano whatever is. All I know is the top tubes do not really push alot of air and I would rather not cool the pans... I know I need HPLCFM for the top and LPHCFM for the bottom but this is what I've got besides a little 1/50hp 3340RPM blower that I used for AUF last year. I'm trying to get more than 9gph out of this evaporator. Thats what I got last year. Should I try the little blower I have for the AOF? Not much time left...
Thanks

[red/one]

Update: Small blower I have is crap. :lol: What is the best blower for AOF. That wont break the bank, very limited budget left.

[RileySugarbush]

Free is good! But AOF done wrong can actually reduce your performance. Don’t ask how I know. I think the best blowers for AOF are those made for kids bouncy houses. Nice and cheap. Made to run for long periods. And high output pressure. I replaced my Dayton industrial radial vane blower with one and it is much better.

You can make a manometer with a piece of clear tubing and some water to check your blower pressure.

[red/one]

Just pulled the trigger on a bounce house blower. Tuesday arrival. Stay tuned...

[RileySugarbush]

That's great. I think you will like it. What model did you order? My 1HP Koala puts out a pressure of 8" of h20, which results in jet velocities of about 80 mph. The size your nozzles to get the amount of air you want. The key is to only regulate the AOF flow at the nozzles and no where else. You can block the flow for firing, but otherwise you want big pipes from blower to nozzles. I have an Excel spreadsheet for calculating jet velocity and CFM for AOF if you are interested.

[BRL]

I am interested John!

[red/one]

Its a 1/2 hp "ZOOM" blower. I'm not sure of the CFM but looking through all the blowers it should provide 400-500cfm. My manifold is 2" pipe to 2" square to (28) 3/8" nozzles. Currently a ball valve to regulate. And an on/off switch. Cant wait!

[red/one]

Boiled twice. All my AOF/AUF and Zoom fan mods didn't seem to help much. Got a really good fire, load every 10min. Still only about 10gph. It doesn't seem like my AOF blows well. Maybe 3/8 opening is too big for my nozzles. When I open the door with the fan on you can see the fire pushing under the back pan. Just rambling...