Baffles lengthwise or crosswise?

[torch]

We are taking the next step from our block rocket stove evaporator setup for next season. I've welded two barrels together, installed a barrel stove kit and will be fitting a ramp.

I plan on making a 304 stainless continuous feed flat bottom pan 18" x 48". It will have a draw-off valve at either end so the pan can be reversed each day, drawing off at the door end. The feed will be by drip from a warming coil around the chimney stack. The coil will be fed directly from the RO output.

I'm not sure if the baffles are better run cross-wise or length-wise, I've seen pictures of both but no information about the advantages or disadvantages. The pan size would lend itself nicely to two lengthwise baffles forming 6" wide channels or 5 crosswise baffles forming 8" wide channels.

[Pdiamond]

Most pans I have seen for what you are describing the dividers are running lengthwise. Your idea for the draw off and rotating is very good.

[maple flats]

For a single pan either will work good and drawing near the door OK.
Evaporators with a flue pan and a syrup pan, on most newer evaporators try to draw off at the back of the syrup pan, where the heat is more constant. Personally I prefer cross flow over lengthwise flow, especially if you draw at the back. Most of the issue is with lengthwise channels, the outside channel, where you have your draw off is not as hot because the sides overlap onto the edge iron of the arch.

[torch]

For a single pan either will work good and drawing near the door OK.
Evaporators with a flue pan and a syrup pan, on most newer evaporators try to draw off at the back of the syrup pan, where the heat is more constant. Personally I prefer cross flow over lengthwise flow, especially if you draw at the back. Most of the issue is with lengthwise channels, the outside channel, where you have your draw off is not as hot because the sides overlap onto the edge iron of the arch.

I guess it wouldn't be a problem to draw at the back. Just have to extend the line from the pre-warming coil.

Thanks all for the input.

[maple flats]

I really like drawing from the back better, but my pan is switchable draw, same side. I just close one valve and open another. I then need to move the float from one draw off to the other and because I use an auto draw I switch the wires on the control. I have 2 temp probes, one at each draw off, when I change it takes only a few seconds and I'm ready. I most often run on the back draw about twice as long as I do on the front draw.

[torch]

So I decided to try crosswise, with eight 6" wide channels. Same effective length as three lengthwise channels, the advantage of evening out the heat across each channel and potentially stiffer construction. I'm using 18 gauge 304 stainless (308 SS mig wire). Outer pan walls are 6" deep, baffles are 4" deep.



Then I realized that I need an odd number of channels, not baffles, so that the valves will be on opposite sides to make the pan reversible. Doh! Good thing it's just tacked up at the moment. I guess I have some grinding to do in the morning...

Once I correct that, the plan is to finish welding everything up, fill it with some sugar water and test fire. Whichever end runs hotter will be designated the sap end.

Still have to put in the ramp, but here's the progress thus far on the barrel stove this is intended to fit:

[maple flats]

Ouch, that hurts.

[darkmachine]

before i started making syrup i saw a pan constructed like this, two gentleman in their 80's boiled on it. The arch was made of parts from an old steam boiler, the cold sap went in on the end you fed the fire, and the draw off was on the end next to the stack. They controlled the sap flow in with a water faucet that look as old as the sugar makers, lol.

[torch]

Well I guess that means it worked. To some degree, anyway.

[torch]

Update:

Pan MkII has a wider section at either end to facilitate drawing off. This time I cut it all out of a single sheet and had a local HVAC contractor bend it up on their box brake. That way I only had to weld the 4 corners. Much faster and easier. I also had them fold a hem on the top of all 4 sides, stiffening them up better. And finally, I had them fold the edges of the baffles so I could make smoother spot welds for easier cleaning:



Overall, it works pretty well:



Having a little trouble getting enough heat to the back though. It just simmers gently, doesn't really boil. I'm going to have to tinker with the slope of the flue under the pan I think. So for now, we're drawing at the front: