discussing sap movement through the evaporator

[michiganfarmer2]

Ive thgouht a lot about what makes the sap move through the pans. I heard people say that saw sap pushes the rest through the pan. I dont think it works that way.

I think it has nothing to do with density differences. I think its all gravity. I think that because nothing is being drawn off at the draw off, but water is evaporating away, the level is lowering, and more sap comes in to replace it.

[Ausable]

OK - I buy that - evaporation is a big part - but the draw off also has an effect.... Here is the thing that puzzles me - as the lighter sap enters at the start of the pans -- why dosen"t it blend into the thicker almost syrup? Does the denser almost syrup resist the lighter sap? Every time I think I have it figured out - someone else asks me a new question on it -- and I am puzzled again. I guess all I have to know is that it works --------BUT WHY? --- Mike

[Big_Eddy]

You guys are both right. It's a combination of gravity, evaporation and draw offs. Gravity moves the sap forward, evaporation and draw offs both create "holes" which need to be filled with more sap. The only place to get more sap is the inlet valve.

Think about it this way. Forget the fire for a second, and fill the pans. Open the draw off valve. Gravity will make sap pour out and the float will open and more sap will flow in. Every individual "molecule of sap" in the pans is flowing downhill from the inlet to the outlet. Gravity makes them move forward and each one pushes the one it front of it until the first molecule comes out the spout. The last one in can not rush to the front of the line, each one needs to stay in line behind the one in front of it. There is some mixing going on as individual molecules jostle each other for their position in line, but essentially each molecule needs to travel the whole distance without taking any shortcuts. Close the valve, gravity levels the pan and each molecule holds its position in line (but still jostles back and forth with its neighbours).

Now imagine a fire under the final section of the pan only. (I know - theoretical) As the front of the pan boils, each "sap molecule" gives up some of its water and gets smaller, so the level drops, and new sap molecules move forward to maintain the level. Each molecule of sap in the queue moves forward, and the valve opens to replace what was lost. You can think of it as pushing or pulling, with evaporation creating a hole, and gravity filling it back in.

Extend the model so that you are heating the whole "queue" of molecules. As each molecule travels along the path, it gives off little bits of water at each stage in the journey, getting a little bit closer to syrup and leaving little "holes" that needs to be filled with more sap. The only place to get more sap is the inlet, so more sap enters to replace what evaporated and takes its place in the queue, the rest moving forward towards the "hole". There are millions of the little holes being formed, so all the way along, individual "molecules" of sap keep moving forward. By the time any individual molecule of sap gets to the "front of the line", all of the excess water has been evaporated, and only the syrup is left.

[northwoods_forestry]

Great description Big Eddy!

I'll just add one thing


Close the valve, gravity levels the pan and each molecule holds its position in line (but still jostles back and forth with its neighbours).

Big Eddy's molecule jostling has a name: Brownian Motion, which is basically the random movement of molecules through space. Brownian motion is what drives diffusion, the movement of molecules from areas of high concentration to low. That's what happens when you shut down the rig at night and close all the valves. Brownian motion and diffusion even out the sugar concentration in the syrup pan and the flue pan so that there is no longer a sugar gradient when you start it all up again the next day.

[Ausable]

Big Eddy and Northwoods --- Thankyou both --- best explanation I've ever heard ---- Now - I finally get it. -- Yep - Water - Sap seeks its own level. Also - at the end of the day --- Northwoods made it very clear - why I put my plugs in - Sweeten the pan - and keep -- the molecule from mixing it up till I start up again --- Gentlemen -- again - I Thank You both --- Mike

[MilesTeg]

As I am going through civil engineering school we use alot of principles in our designs and I've found that alot can be applied to the syrup world. What level happing in the evaporator is a change in potential head. What was previously said is true on a molecular level. Has a hole system though it is a change in the potential head of the liquid in the evaporator. In essence what is going on because of the evaporation and the draw offs the system doesn't have the same potential energy at the end of the system as it does on the inlet and this differential energy tries to right its self by adding sap and filling in the "holes" as discussed before. I don't know if that made sense but its a combination of the two principles.

[hardermaple]

Big Eddy, GREAT explanation!!!!!!! my peeps are going to think i'm smart now when i tell them how it works. Guys i have ruled that gravity has nothing to do with sap flow through the evap, and will work uphill. Don't laugh, but my sugarhouse is actually a sugarcube. A 8ft by 14ft box of a boxtruck from the family farm. It's my first year and it works great, except the steel floor. the heat from the arch buckled it on the first boil a bit, and knocked my 2 x 6 drop flue out of level by 1&1/4 inches down away from the front. And she still made syrup at the drawoff. i releveled after the second boil and it runs the same, no difference. sugarhouse coming soon, but i like the sugarcube.

[michiganfarmer2]

Don't laugh, but my sugarhouse is actually a sugarcube. A 8ft by 14ft box of a boxtruck from the family farm..

I used an 8 x 24 box truck for a few years when I had my 2x6. I even used it one year with my 3x12. There was so much steam in there you couldnt see your hand in front of your face,lol

[Haynes Forest Products]

Hardmaple Water seeks its own level and is stupid it doesnt know its in a level container or unlevel container. NOW try this. Mark a line on the walls of the evaporator following the SAP LEVEL ( when its crooked) now cut the walls off the evap untill till there level and tell me is the sap level LEVEL??? YUP your good to go............STFUC:)

[Clarkfield Farms]

I agree with all the above, and probably don't have much to contribute but here's another thought: Look at pipeline engineering -- different fluids are sent along the pipeline in sequence (they don't just send one volume of one specific material at a time, let it empty ((it won't)), then clean it and start another different material), and those fluids don't readily combine at all except for the miniscus and even at that point of contact, the mixing or cross-contamination is minimal. Yes, there's always planned consideration of which materials to send in tandem with regard to those that do not mix well, but the natural "barrier" between them keeps things flowing smoothly under pressure.

We all know that water is part of sap -- the larger portion of it, and that it's driven off by heat through the process of evaporation. BUT, try to dilute that same finished maple syrup with water (as for making wine, etc.) and they don't readily recombine. They WILL, but not as simply or as quickly as one might expect. Water isn't one part and sugar a completely separate part of sap, but as Big Eddy points out it's both a physical and a chemical process in separating them. So, to one degree or another, once it's "syrup" maybe it looks down its nose at its humble beginnings and cuts all ties with "saps." :) OK, that part's just silly. And maybe the rest of it is, too, but that's kind of how I see it. (except for the silly snobbishness stuff) :emb: