Copper evaporation rate?

[spencer11]

I am looking into making a drop tube pan and was wondering how I could figure out the gph? I know stainless is about 1 gph per 1 sq. Ft. And copper is much better with heat transfer. So is there a way to figure out gph rate with copper drop tubes before I make the pan? Thanks.

Spencer

[Rossell's Sugar Camp]

i would calculate it for the 1 gph per square foot. that way you definently will not be dissopointed :D

[spencer11]

LOL. Maybe thats what I should do. I have been using 3 gph pre 1 sq. Ft. I don't know if it's right or not but Im hoping it's accurate?

Spencer

[Rossell's Sugar Camp]

i would doubt it is that big of a difference. if it were we would all be using copper. although it possibly could be. good luck. i found a thread on here mid summer with all the heat transfer ratings of different metals. stainless is actually lower on the list.

[Rossell's Sugar Camp]

here is what i found for you on that thread.






Other than the rust issue, steel is fine. In some ways better than stainless:

Thermal conductivity is a measure of how easily heat transfers through you pan. Stainless is actually pretty bad, which is one reason it's important to make stainless pans with very thin material.

Conductivity of 304 stainless is 17 Watts/(meter °C) at about the boiling point of water.

For comparison, carbon steel is 50 Watts/(meter °C), so 1/8" steel will conduct as well as .042" stainless! That's a bit thicker than 18 ga., so almost as good as stainless pans.

Copper is a great thermal conductor, over 20 times better than stainless at 400 Watts/(meter °C). Ever notice how some nice stainless kitchen pans are copper clad on the bottom?

[smokeyamber]

Based on those transfer rates, making steel pans with copper drop tubes is not a totally terrible idea.;) You could do either 16 or 18gauge on the carbon steel. If copper weren't so astronomically expensive :(I would make pans out it in a heartbeat. Soldering them up is way easier than tig welding stainless.:lol:

[spencer11]

i have seen that thread to. i dont know why maple companys dont make copper pans just for the heat transfer? i know it would be expensive but i think it would be worth the extra money. i think thats why people use copper tube for drop tube pans instead of stainless. im gonna build a pan with the drop tubes after this season and just see what i get. thanks

spencer

[RileySugarbush]

i have seen that thread to. i dont know why maple companys dont make copper pans just for the heat transfer? i know it would be expensive but i think it would be worth the extra money. i think thats why people use copper tube for drop tube pans instead of stainless. im gonna build a pan with the drop tubes after this season and just see what i get. thanks

spencer

Spencer,

Copper does have a tremendous conduction compared to stainless steel and better than many other metals. It is hard to say whether is is worth the extra cost, and indeed I don't know the extra cost.

Something to keep in mind is that the thermal conductivity is not the only thing that determines the evaporation rate. The heat has to get from the hot flue gasses into the metal, then through the metal, and lastly into the sap. In heat transfer terms, that is Convection, conduction, convection. The heat transfer (convection) from hot gases to the pan is the same regardless of material. Using copper helps the middle term, or conduction, but there is still some limitation on how fast the heat can transfer to the sap ( convection again). That means if we had a thermally superconducting pan, we would not get infinite evaporation rate.

Bottom line: If I was going to make a pan myself, I might use copper. It is easy to solder, you don't need a TIG welder,it conducts better and it looks cool. For home built drop tubes, and for preheaters, there is no question it is a better choice than stainless. One down side is it is not as strong as stainless and probably harder to keep clean.

[spencer11]

so i guess the only thing way to figure it out is to try it. well i guess i'll see.

spencer

[jd maple]

love the look of a set of new copper pans very cool. Easier for us home project kind of guys to built and I want to some day build a set, but a salesman from CDL told me that copper can discolor the syrup? any one know this to be true.

[spencer11]

i dont think it does. i have seen quite a few drop tube pans made with copper tubes and some old leader pans were made of copper. i havent heard that before. but still not sure?

spencer

[Teuchtar]

I would tend to agree with John/Rileysugarbush.
The overall conduction from the hot gas to sap comprises multiple layers: a)convection through the swirling gas b) conduction through a stagnant insulating surface air layer. c) conduction through a layer of loose soot, d) conduction through a layer of hard carbon creosote e)conduction through the metal, f)conduction through inner wall surface liquid layer g) boiling convection on the inside.
Changing to copper is only changing the resistance of one resistor in a series of seven. Even if you make the resistance (e) go away, you've still got six more resistors in the energy path.
All of us know that removing the soot by brushing before firing does restore the rate of boiling. If you can also remove the creosote layer using oven cleaner, it improves further. But if your copper tubes impede or discourage cleaning, then you've maybe given yourself a lot of expense, and your net result is worse off.
I believe stainless offers more opportunities to keep both the pan interior and combustion side more clean. In otherwords, you can use more powerful chemicals and more elbow grease on the stainless pans.
I might be wrong here, but I believe the use of copper for cooking pots is to spread the heat evenly across the entire bottom cooking surface. Not to speed the energy flow through the metal. This is to avoid concentrated hot spots that would burn the food.

[spencer11]

im not saying that your wrong but i think it might get a better evaporation rate. in the drop tube pans i have seen people use copper tubes. i dont know if its cause copper is easier to get as tube than stainless or if it is the heat transfer. i will ask my science teacher next time i have class and see if he has any info.? but thanks for all the advice

spencer

[CBOYER]

cleaning the pans... Thats the reason why ss replace copper in everything cooked

[spencer11]

what was the cleaning problem? was it because the metal is very soft? is it cause it starts to turn green after a while? those would be my concerins.

spencer

[warners point]

I am looking into making a drop tube pan and was wondering how I could figure out the gph? I know stainless is about 1 gph per 1 sq. Ft. And copper is much better with heat transfer. So is there a way to figure out gph rate with copper drop tubes before I make the pan? Thanks.

This is how I figured my square footage on my 2x6 copper drop tube.

144 six inch tubes. .875 OD

one tube is .875x3.14x6=16.4 sq. in.

16.4x144 tubes=2374 sq. in.

2374/144 sq. in =16.4 sq. ft.

16.4+12=28.4 sq. ft

I can usually get around 40 gph. without trying to hard.

[spencer11]

thanks warners point. i planned on a a 2x4 or 2x3 drop tube. so if i will get around 40 gph that sounds good to me. thanks

spencer

[SDdave]

I know stainless is about 1 gph per 1 sq. Ft.

What thickness of stainless, or is it all? I have 304 stainless, just wondering if the 1 gph per 1 sq. ft still applies.

Thanks,

SDdave

[spencer11]

its just a general rule of thumb i use...so yes all thickness. if it is thick stainless it will just take longer to heat up and cool down. does anyone know where to get 201 stainless? i heard it was alot cheaper than 304 and it was also food grade?

spencer

[CBOYER]

what was the cleaning problem? was it because the metal is very soft? is it cause it starts to turn green after a while? those would be my concerins.

spencer

your two affirmations are good. Copper, like Stainless steel, make a protection against corrosion. On Stainless steels, it is chrome and nickel oxides, that are very hards to remove, and you dont see it. On copper, look on top of buildings, churchs, etc. the oxyde is green, and easily removable, so you cannot used chemicals.

also, as soon you get niter, on SS soldered pans, you could use dilute acid (vinegar) to remove it, but on copper, you will start attack of metal, and any mechanical way will dent it. Handle with care
in kitchen, now you get copper only on bottom exterior of pans, to reduce contact with acid foods

[spencer11]

so is copper safe to use? or would i have to get new drop tubes every year cause of corosion?is the green oxidation safe to have sap in contact with?

spencer

[RileySugarbush]

The copper drop tubes, made of copper water pipe or water hammer arrestors, is easy to clean and strong enough to survive rough handling. I used them for years with no corrosion problems, no off colors or tastes. The fellow I gave them too is still happy to be using them with similar good results. Don't panic. Fresh sap and sweet does not seem to be acidic enough to cause a problem of corrosion.

[spencer11]

well thats good to hear. drop tubes it is...for next year.

spencer

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[spencer11]

i clicked on the link and it did not work.

spencer

[Rossell's Sugar Camp]

i have seen that thread to. i dont know why maple companys dont make copper pans just for the heat transfer? i know it would be expensive but i think it would be worth the extra money. i think thats why people use copper tube for drop tube pans instead of stainless. im gonna build a pan with the drop tubes after this season and just see what i get. thanks

spencer



People want to make light syrup and a reverse osmosis will get rid of the extra water for the price of a brand new copper evaporator. they do have used ones. Stainless is definently the way to go.

[spencer11]

The thing is that I have the money for drop tubes but not enough for an RO. I think will just make a stainless flue pan. And then maybe get an RO eventually.

Spencer