Using surface area to caculate evaporation rate

[Maple Man 85]

Is there a formula that calculates evaporation rate based on boiling surface area?

There are many variables to take into account such as varying BTU's, thickness of material as it relates to heat transfer and depth of sap in the pans but am wondering how projected evaporation rates are established. A good example of published evaporation rates are on the sunrise metal site http://sunriseevaporator.com.

If anyone could point me in the direction of the formula that would be great!

Maple Man 85

[mudr]

Stuff that I have gleaned from the various sites.

-1 gph per Sq ft of boiling surface. A flat 2x4= 8 gph. Your mileage may vary (wood quality, feeding interval, blower, etc).

-a flue pan rig still is at 1 gph per Sq ft of surface area, but you need to calculate the surface of all the flues in addition to the flat parts of the rig.

- in general, if you don't want to calculate flues, I think the old easy (less exact #) number is 2.5. So, a 2x6 flat/flue pan set is 12x2.5= 30 gph. Again, your mileage may vary, with the addition if different flue setups. For instance, a really deep flue will get you more.

I'm a rookie, but I read a lot. :)

[Maple Man 85]

Stuff that I have gleaned from the various sites.

-1 gph per Sq ft of boiling surface. A flat 2x4= 8 gph. Your mileage may vary (wood quality, feeding interval, blower, etc).

-a flue pan rig still is at 1 gph per Sq ft of surface area, but you need to calculate the surface of all the flues in addition to the flat parts of the rig.

- in general, if you don't want to calculate flues, I think the old easy (less exact #) number is 2.5. So, a 2x6 flat/flue pan set is 12x2.5= 30 gph. Again, your mileage may vary, with the addition if different flue setups. For instance, a really deep flue will get you more.

I'm a rookie, but I read a lot. :)

Thanks for the response mudr, that's what if figured as well however I am looking for the research to support it. I am in the process of evaluating manufacturers pans and attempting to establish something of a consumer review to have scientific evidence that supports why some pans perform better than others. Obviously thinner gauge stainless transfer heat better but another piece of the puzzle is surface area as you mentioned. Also BTU's is a variable in the study to eliminate this as a variable I would like to make this a fixed number so we can see purely how the pans perform. This is going to be hopefully the first of a series of studies that will assist in the purchasing of big ticket items like evaporators and RO's.

Here is my study parameters in an attempt to discover a superior pan manufacturer...

1. The pans will be for a 4x14 evaporator
2. The surface area (measured in square feet) will be a combination of the flue and syrup pans (please specify if flue pan is raised or drop flue)
3. The number of fins in the flue pan as well as height of the flues and number of dividers in the syrup pan(s) to achieve maximum evaporation rate.
4. The thickness of the material used to make the pans
5. Lastly the price of the pans (so we can establish a matrix that plots efficiency versus price)

[mudr]

You should have asked the evaporation rate of a 4x14. The answer is "really high". :)

[wiam]

I see no way to make comparisons like you want unless burning oil in a very closely tuned rig.

[Maple Man 85]

I see no way to make comparisons like you want unless burning oil in a very closely tuned rig.

There would have to be internal temp gauges within the arch to maintain a relative BTU for a consistent study. Evaporation rate varies as you mentioned based on applied heat, surface area and how conductive the pans are which consists of metal thickness. I do like your answer, but I would think there's an engineer somewhere that figured this out already I just have been unable to find the information.

[BreezyHill]

One must also include the mass that is being heated as an additional variable that will change from design to design.

If the sap enters both sides of the pan vs entering just one side. I like one side as this seems to be more efficient in our rig.

if the cool sap 180 on our rig entered more to the front I think we have a lower rate as well. If you watch the flue pan while drawing off syrup the add area drops in rate dramaticly on batch draws and less so on constant flow draw off.

One can get an average but as mudr said your mileage will vary greatly.

I had one sales man saw that the more flue area the poorer the boil rate...referencing the max flue pans; but any one science minded knows this is not correct as more area exposed to the heat of the flame the higher the boil rate will be as long as you can maintain heat all the way across the flue length.

"Figures don't lie...but liars sure can figure"

Ben

[Maple Man 85]

One must also include the mass that is being heated as an additional variable that will change from design to design.

If the sap enters both sides of the pan vs entering just one side. I like one side as this seems to be more efficient in our rig.

if the cool sap 180 on our rig entered more to the front I think we have a lower rate as well. If you watch the flue pan while drawing off syrup the add area drops in rate dramaticly on batch draws and less so on constant flow draw off.

Ben

Good point Ben, and it would make sense that depending on how the arch was designed along with the configuration of the pans there would be +-20% on the evaporation rate as well as the amount of mass in the pans playing a factor.

Interesting story... My grandparents ran a flat pan for years and cooked several hours daily because they over filled the pan so the sap couldn't reach max evaporation potential (because that's the way their parents taught them). After I stepped up and took the operation over it took years to convince them that less liquid = higher evaporation rate (just don't run so little it scorches the pan I run roughly an inch).

Anyway it still comes back to how can manufacturers advertise evaporation rates, how are they calculating it?

[Brian]

set up a rig and see how long it takes to go through a 150 gallons of water and there is your answer.

[BreezyHill]

Well lets look at how rigs are mad now.
There is an infinite adjustment to the float box...this is so you can get the depth adjust to your way of loading the firebox and to how warm your sap is coming in to the unit.
On our unit why have three points of adjustment market. 1-2-3. One is where we set the float when we shut down for the night. This is the lowest setting.
This way there is as little in the pan soyou can get up and running as fast as possible. This leaves about 3/8" over the flue tops.
At 2 you have about 1/2" and this works good if you don't open the hood and the rolling boil will keep everything covered and you are all good. But when I walk in to check the pan the bubbles recede and I see pan that is not covered with sap and FREAK OUT. So I set it to three.

At three the boiling rate is reduced and I sit there scratching my head and wonder why boiling rate slows.

There is a simple mathematical equation that my be found in plumbers books but you an find on the web. It is for furnaces and is to calculate there efficiency. It takes the BTUs the furnace makes and the amount of water in the furnace and the capacity of the systems pump and gives how many square feet of house can be heated.

This can be used for your quire. You can calculate the capacity of your pan in cubic feet and then figure the BTUs you can supply and you can figure the boiling capacity from there.

One calorie is the energy to raise one gram of water 1 degree centigrade. How many BTUs to raise a gallon 1 degree centigrade. When you are at 99 degrees 1 degree will make her boil.

what is the temp of the incoming sap? This must be brought from say 5 degrees to 100 degrees. if you are bringing in 40 gallons of 5 degree sap how many BTUs to bring this sap to 100?

I am sure you can look at CDL or Bascoms catalogues where G/H rates are listed and get a calculation or at least a chart on productivity an compare the sizes.

[wiam]

Well lets look at how rigs are mad now.
There is an infinite adjustment to the float box...this is so you can get the depth adjust to your way of loading the firebox and to how warm your sap is coming in to the unit.
On our unit why have three points of adjustment market. 1-2-3. One is where we set the float when we shut down for the night. This is the lowest setting.
This way there is as little in the pan soyou can get up and running as fast as possible. This leaves about 3/8" over the flue tops.
At 2 you have about 1/2" and this works good if you don't open the hood and the rolling boil will keep everything covered and you are all good. But when I walk in to check the pan the bubbles recede and I see pan that is not covered with sap and FREAK OUT. So I set it to three.

At three the boiling rate is reduced and I sit there scratching my head and wonder why boiling rate slows.

There is a simple mathematical equation that my be found in plumbers books but you an find on the web. It is for furnaces and is to calculate there efficiency. It takes the BTUs the furnace makes and the amount of water in the furnace and the capacity of the systems pump and gives how many square feet of house can be heated.

This can be used for your quire. You can calculate the capacity of your pan in cubic feet and then figure the BTUs you can supply and you can figure the boiling capacity from there.

One calorie is the energy to raise one gram of water 1 degree centigrade. How many BTUs to raise a gallon 1 degree centigrade. When you are at 99 degrees 1 degree will make her boil.

what is the temp of the incoming sap? This must be brought from say 5 degrees to 100 degrees. if you are bringing in 40 gallons of 5 degree sap how many BTUs to bring this sap to 100?

I am sure you can look at CDL or Bascoms catalogues where G/H rates are listed and get a calculation or at least a chart on productivity an compare the sizes.

But the manufactures numbers are bogus. Because we all run them differently. Some run for fuel efficiency. Others run as fast as possible. When I had my 2x6 Mason I got way over rated evaporation. But I was running 1500 degree stack.

[Maple Man 85]

BreezyHill thanks for the information, I know a few plumbers that may be able to help with this calculation. As for manufacturers numbers I would agreed there is deviation because I do not believe there is industry standardized testing in regards to creating consistent and accurate numbers. If the industry continues to grow I would expect a study such as this would provide producers with valuable information from a business perspective to maximize profits in the sugarhouse. The ultimate goal of the research is to share it with the maple community so producers can keep more of our profits (lord knows we work hard enough for it).

[mudr]

It would be interesting to see an industry standard. The epa has a standard to test btus from wood stoves, I could envision something similar. For instance, to compare pans, boil on a fuel oil rig set to a certain degree stack, 1.5 inches of sap above flues. Boil for 2 hrs, calculate total evaporation rate across the 2 hours, and peak evaporation in the middle. It would be interesting to see.

[wiam]

It would have to be amount of oil burned per hour. Not stack temp. A more efficient pan would run a lower stack temp with the same btu's going in.

[BreezyHill]

I think that if you look a cdl catalogue you will find some data on square foor evap rates that they have worked hard to produce.

I am not vouching for the accuracy on these numbers or what variables were addressed as in sap temp into rig, or any others.

Yes we do work hard and as wiam states btus of oil into the unit would be more advantageous than stack temp...as we want everything out of the fuel we burn to heat the sap and as little as possible out the stack.

It would be nice to keep more profits agreed!

[Maple Man 85]

I think that if you look a cdl catalogue you will find some data on square foor evap rates that they have worked hard to produce.

I am not vouching for the accuracy on these numbers or what variables were addressed as in sap temp into rig, or any others.

Yes we do work hard and as wiam states btus of oil into the unit would be more advantageous than stack temp...as we want everything out of the fuel we burn to heat the sap and as little as possible out the stack.

It would be nice to keep more profits agreed!

I reached out to CDL to participate in the experiment but I have not heard back from them. I'll have to checkout the catalogue and see what I can find.

[WESTVIRGINIAMAPLER]

On a standard wood fired evaporator, we figure about 3gph for every square foot of pan. As the efficiency increases, these numbers go up to as high as 5gph on the very high efficiency arches.

I should point out the 3 gph is for a standard evaporator with standard size flue pan and 7" flues.

[Maple Man 85]

On a standard wood fired evaporator, we figure about 3gph for every square foot of pan. As the efficiency increases, these numbers go up to as high as 5gph on the very high efficiency arches.

I should point out the 3 gph is for a standard evaporator with standard size flue pan and 7" flues.

Thanks for the data Brandon, would you happen to know how these numbers were established or if there were studies published that support these numbers?