Effect of materials

[Beweller]

There have been a number of posts questioning the effect of material and material gage on the performance of evaporators. The following table gives the temperature drop (degrees F) through the metal for a heat transfer rate of 16,000 Btu/hr sq ft (an evaporation rate of about 2 gallons/hr sq ft):

material 18 ga 20 ga 22 gag
Al 0.6 0.4 0.4
Steel 2.2 1.7 1.4
304L SS 7.1 5.3 4.4.

Compared to the total temperature drop, these are trivial. You could not detect a difference without elaborate laboratory instruments.

[WMF]

This is one of those situations where you need to keep playing with the formulas and calculations until you come up with an answer that agree's with what actually happens.

Going from an 18 gauge ss pan to a 22 gauge ss pan will increase your boiling rate significantly. There are a lot of factors going on when actually boiling sap that are hard to calculate like soot on the fire side of pan, sugarsand on syrup side of pan and the amount of bubbles insulating the liquid from the metal.