Evaporator Design Idea: "Open-End Flue Pan"

[CampHamp]

I can't believe how much more the front part of the flue pan pan boils than the back part. I wonder if this is due more to the cooling of the heat under the pan as it travels back or due the fact that the heat must drop down into the furnace to vent.

I have an idea to improve the heat flow pattern under a raised-flue pan. Instead of venting the flues under the pan base and back through the arch, why not open the flue ends through the back wall for a high-pattern flow?

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You would need to capture the smoke with a vent chamber. I was thinking something like this:

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I haven't shared the idea with any manufacturer yet and thought I'd solicit feedback from MapleTraders first.

Has this been tried already? Do you think it could work? Do drop-flue pans give a more even boil through the pan than raised-flue types?

I do have a patent pending (just in case it works!) to make it easy to discuss openly with operators and manufacturers...

Thanks, in advance, for any feedback!

[jrmaple]

It seems like it might work, only concern I can see is build up of soot and creosote in the pocket that you are showing, I would recommend tacking piece of metal or propping a piece of cement board on the back of your flue pan to personally try it first and see if it works; but also watch out for smoke build up if you don't have enough draft. Also if the back of your flue pan isn't boiling too good, have you checked your stack temps? Good luck and hope it works.

[CampHamp]

It seems like it might work, only concern I can see is build up of soot and creosote in the pocket that you are showing, I would recommend tacking piece of metal or propping a piece of cement board on the back of your flue pan to personally try it first and see if it works; but also watch out for smoke build up if you don't have enough draft. Also if the back of your flue pan isn't boiling too good, have you checked your stack temps? Good luck and hope it works.

Thanks jrmaple!

I am expecting that the chamber will need to be maintained just like the chimney. It should be removable from the pan for cleaning.

I don't think I'll be able to simulate this pan design until I build a prototype. If you're speaking of trying a vent chamber using fiber board, that might work but would want a pan with the special flues first...

[Waynehere]

I always thought that the reason for the harder boil in the front of the sap pan was because it is more exposed to the radiant heat from the fire? I lowered my ramp angle to my sap pan and now get a much more even boil over the whole pan. I heard that you get more heat from the direct line of sight radiant heat then from the flame/hot gases shooting by on their way up the chimney. Just like standing in front of a bon-fire. If someone is in the way, you can't feel the heat like you can when you have a direct line of sight. Might be worth a try and less expensive then trying to modify your pan? :)

[NTBugtraq]

I am on day 3 of my first evap. Its a drop flue design (CDL 18x60) and the front of my flue pan boils far more vigorously than the back, as you say. However, I reasoned it this way. You want to cold sap entering from the float to be heated as quickly as possible, and, you want the sap that's about to leave and enter the finisher to get a good blast also. This lets the gradient throughout the rest of the flue pan to be boiled less vigorously (which in my mind means it will stay there), and the entry and exit to be helped (by the more vigorous boil). IOWs, I thought that was on purpose...;-]

I'm not sure why you'd do a combo drop/raised flue pan, especially if you are forcing the air to flow down at the back of the pan. I guess you're thinking that blockage is going to accumulate heat? You could achieve this blockage on raised or drop flues alone. But only a wind tunnel is going to tell you for sure what that blockage is going to do to draft. The turbulence you create at the end of the flue pan may very well prevent proper draw. That could turn out to be a good thing, or not...

If the finishing pan was larger, extending over the entire firebox and then some, you'd be sure the flue pan was being exposed to a more even heat throughout...thereby causing a more even boil throughout the flue pan. If that's your goal, perhaps another approach will be more likely to achieve that?

But again, let me make sure you know, I'm on day 3 of my life using an evaporator...;-]

Cheers,
Russ

[sam1234]

Hi Camp Hamp,

Keep in mind the most important thing... Were working with maple sap...
Boiling is one thing... Niter and sand build-up is another one.... You need to get it out...
Flue pans have multi-partitions with sap flow... try this on your design.... it wil make the pan a lot more complicated.

Just my opinion...
Good luck! Every ideas deserve to be listened!

[CampHamp]

I always thought that the reason for the harder boil in the front of the sap pan was because it is more exposed to the radiant heat from the fire? I lowered my ramp angle to my sap pan and now get a much more even boil over the whole pan. I heard that you get more heat from the direct line of sight radiant heat then from the flame/hot gases shooting by on their way up the chimney. Just like standing in front of a bon-fire. If someone is in the way, you can't feel the heat like you can when you have a direct line of sight. Might be worth a try and less expensive then trying to modify your pan? :)

My ramp is pretty steep up to the front of the flue pan -- about 45 degrees. When you softened that angle on your's, your boil extended further back in the pan... interesting. It's hard to say if that is because there is "direct line of sight" or if your hot flames and gasses are now taking a different path under the pan. Either way, it sounds like it worked out well. What about in the last 25% of the flues? Are you getting the same boil there as the front or does it dwindle down?

This idea isn't for a retrofit to my setup, it's just a thought about how a new design might help create a more rigorous boil towards the back for future pan construction. This concept assumes that there is a significant effect of hot flame/gas on the pan and not just radiant heat from the arch.

[CampHamp]

I am on day 3 of my first evap. Its a drop flue design (CDL 18x60) and the front of my flue pan boils far more vigorously than the back, as you say. However, I reasoned it this way. You want to cold sap entering from the float to be heated as quickly as possible, and, you want the sap that's about to leave and enter the finisher to get a good blast also. This lets the gradient throughout the rest of the flue pan to be boiled less vigorously (which in my mind means it will stay there), and the entry and exit to be helped (by the more vigorous boil). IOWs, I thought that was on purpose...;-]


Ahhhh day 3 of your fist evaporator boiling.... you're in a bit of heaven, I'm guessing. I thought that drop-flue rigs (flues that extend below the pan's base) often had good boils to the rear of the pan because the flames flow through the flues straight across to the chimney. Maybe I have that wrong, though. I've only seen a couple drops in action and you're saying that your pan is slow in the back (which you like, anyway).




I'm not sure why you'd do a combo drop/raised flue pan, especially if you are forcing the air to flow down at the back of the pan. I guess you're thinking that blockage is going to accumulate heat? You could achieve this blockage on raised or drop flues alone. But only a wind tunnel is going to tell you for sure what that blockage is going to do to draft. The turbulence you create at the end of the flue pan may very well prevent proper draw. That could turn out to be a good thing, or not...


Some manufacturers already build a "hybrid" style pan with both dropped and raised flues so they can have extra-tall flues and have very high evaporation rates. I included it in my drawing to show how my idea (opening the flues to the vent and chimney) could be accommodated with that existing type of pan.

Thanks for your comments. Much appreciated and enjoy your new toy!

[CampHamp]

Niter and sand build-up is another one.... You need to get it out...
Flue pans have multi-partitions with sap flow... try this on your design.... it wil make the pan a lot more complicated.


Good point. Thanks.

[Waynehere]

My flue pan is 2x3 and a drop tube. The top of the ramp hooks up about 2' back, so the back foot actually doesn't boil quite as hard as the front 2'. The only part that doesn't boil is the inlet, which is understandable. Either way, you always hate seeing all of that wonderful heat escaping up the chimney without making it as productive as possible.

[CampHamp]

My flue pan is 2x3 and a drop tube. The top of the ramp hooks up about 2' back, so the back foot actually doesn't boil quite as hard as the front 2'. The only part that doesn't boil is the inlet, which is understandable. Either way, you always hate seeing all of that wonderful heat escaping up the chimney without making it as productive as possible.

I just took a look at your pan at thesapshack.com -- wow. Do they spout sap up when boiling like the Bellagio? :)

[Michael Greer]

Very nice illustrations. I wish everyone could do that. I'm wondering if your idea might work too well, meaning that the flame path would be so smooth that more heat would go up the chimney before doing it's job. I think that little down ramp at the back is intended to impede the flow intentionally.

[Waynehere]

I just took a look at your pan at thesapshack.com -- wow. Do they spout sap up when boiling like the Bellagio? :)

Yeah, the tubes are like geysers most of the time. I had that deflector shield made after my first boil 2 years ago as I had sap all over the floor. :(

[Waynehere]

Very nice illustrations. I wish everyone could do that. I'm wondering if your idea might work too well, meaning that the flame path would be so smooth that more heat would go up the chimney before doing it's job. I think that little down ramp at the back is intended to impede the flow intentionally.

Actually I have a temp gauge under the syrup pan and in the stack. Usually with good dry wood, we average temps under the pan from 1500-1900 and the stack runs 700-900. So I would have to assume that the pans are grabbing an average of 1000 degrees from the fire. Of course I am always looking for better ideas on here. Love this website. The small ramp is for my preheater pan that also has drop tubes and does a pretty decent job. I got that idea from someone's design on here too. I felt that squeezing the flu space down at this point was beneficial.

[CampHamp]

Very nice illustrations. I wish everyone could do that. I'm wondering if your idea might work too well, meaning that the flame path would be so smooth that more heat would go up the chimney before doing it's job. I think that little down ramp at the back is intended to impede the flow intentionally.

I see what you mean. It might benefit from some baffles to confuse the flow somehow. As far as the illustrations, I've been using Google's "Sketch-Up" for a couple years now (free) to design my barn, sugar house, chicken coop, etc... It was pretty easy to learn (worth watching a few short training videos to get started). It has a huge library of objects that can be imported into your own drawings as well.