Design question about flue size vs pan size?

[gadwayd]

I am designing a small 20" x 66 hobby evaporator. Is there an un-written rule of flue area vs front pan size? I calculate 40+ sq.ft of 8" flues and my worry is that it may be too much for a small front pan?
Also, has anyone tried using a foil between insulation blankets in the fire box (using oil) My goal is build a small and efficient, any words of wisdom on design appreciated.

Thanks,
Dale

[brookledge]

Dale
As you said 2/3 to 3/4 of the length of an evaporator is flue pan and the rest is syrup pan. You need to have this ratio to allow an area to make syrup. You wouldn't want to have syrup in the flue pan and it would boil to hard.
Also when you have drop flues and are fireing with wood if the flues are to long you might damage them tossing in wood
Keith

[gadwayd]

Thanks for the reply Keith. I guess I was not very clear so I edited my question. What I meant was, could I have too much flue area for a relatively small finishing front pan?

Dale

[brookledge]

Yes you can have to much flue pan. As I said you don't want syrup in a flue pan. Plus if you have a drop flue you don't want them getting hit when feeding the wood. So I'd say at a minimun figure 25% of the arch for a syrup pan.
I have seen set ups with all flue pans a long time ago before ROs but syrup wasn't made on it, it only fed another evaporator
Keith