Evaporator geometry

[riley04]

Quick question on evaporators. Seems everytime I see once it's crankin...so I really haven't been able to see the bottom of the pan to understand what's happening in terms of the sugar density increasing. So each section is a little different? It allows the more dense or "closer to syrup" product to get to the end of the evaporator. The thermometer is there as well as the exit valve to open once it hits the correct temp. How does this actually work? Does it natuarally move as it gets more dense or is it gravity? Is the bottom of the pan angled maybe? If someone has a pic and a quick explanation that would be great!

[cpmaple]

Well the bottom of the pans are flat and level you also set the arch so its perfectly level then as the raw sap enters it will push the more dense product forward toward the draw off. Sap is less dense then syrup so that is how it moves the heavy product forward. hope this helps cpmaple

[Jim Schumacher]

This is definitely the most difficult aspect of maple production to explain to the onlooker that looks at the front pan of an evaporator. It is actually a very simple process. The sap at the end furthest from where the sap comes in has simply been there the longest. Yes, it is constantly being mixed, to a certain degree, with everything else. However, despite being constantly diluted, due to constant evaporation it will reach the correct density.

Picture a clear hose filled with a red liquid. If you started to purge the hose with a blue liquid the entire hose wouldn't immediately turn purple, it would stay pretty separate as the blue pushed out the red... That's one example that seems to work well...

[brookledge]

Gravity plays alot in it. As the water evaporates the level drops which causes more sap to move towards the lower levels. So while you necessarily can't see it happening the sap continues to concentrateand flow to the lower level by the fact that evaporation is lowering the level. Certainly the flow can be seen when you open the draw off valve. And of course the pans have dividers that create a maze effect that keeps the sap seperated
Keith

[Haynes Forest Products]

Thanks brookledge it was simple and precise. The sap ain't going to push crap until whats in front moves out of the way and that happens when it concentrates due to evaporation............Or draw off lowers the level............Now next time they warn about a tsunami run out to the beach and see what happens.................its kind of the same thing when liquid leaves other fills the void ........Now when liquid levels rise because of over filling it will move the syrup but will also raise the level in the entire evaporator............. BUT as the level lowers due to evap or draw off the floats open allowing liquid to enter to fill the void but only to maintain the level.......Thats my rant:)

[RileySugarbush]

Another way to help picture it is to imagine all the channels stretched out into a straight line. One really long and really skinny evaporator, with heat under the whole length. Forget about flues for now, they don't really matter for th explanation. Steam is rising all along the length, evenly lowering the level all along the evaporator. Occasionally take a bit out of the draw off end Since we only let new stuff in on the other end, there is net flow from inlet to outlet. Since the channel is really narrow and shallow, it can't easily mix, as in the hose example from Jim offered

A lot of confusion could be avoided if we just forgot about the density. The flow doesn't result from the density differences. It would be essentially the same even if the density didn't change. The density gradient develops because of the nature of fresh sap coming in only on one end and the continuous concentration along the whole length.

[Jim Schumacher]

Another way to help picture it is to imagine all the channels stretched out into a straight line. One really long and really skinny evaporator, with heat under the whole length. Forget about flues for now, they don't really matter for th explanation. Steam is rising all along the length, evenly lowering the level all along the evaporator. Occasionally take a bit out of the draw off end Since we only let new stuff in on the other end, there is net flow from inlet to outlet. Since the channel is really narrow and shallow, it can't easily mix, as in the hose example from Jim offered

A lot of confusion could be avoided if we just forgot about the density. The flow doesn't result from the density differences. It would be essentially the same even if the density didn't change. The density gradient develops because of the nature of fresh sap coming in only on one end and the continuous concentration along the whole length.

Bingo. Density has nothing to do with it. I'll have to remember the long narrow evaporator example. That's perfect.

[riley04]

Thanks guys. Every post got better....I like the one referencing an imaginary long/narrow evaporator. Def gets the point across1