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Fixing the flue pan

With the continued cold weather this week we were able to tackle a project that has been on our to-do list for some time: fixing a small leak in the flue pan (sometimes called the back pan) on our evaporator.  Doing this required us to tip the pan on its side and gives us a chance to show you a view of the evaporator that you definitely won't see if you visit the shanty during the season: the underside of the flue pan.

Here you can see the flue pan tipped on its edge on the far side of the arch. The ridges you can see are the underside of the flues.  The purpose of the flues is to increase the evaporation rate by creating more surface area (an interesting fact is that liquid mostly boils on the surface of the pan.  You can see this if you watch water boil in a pot; most of the bubbles will form on the bottom and sides of the pan and then move up through the liquid).  By "folding" the bottom of the pan we can more than double the surface area and make the boiling much more efficient.  The smoke and other gasses created by the fire actually travel through the flues of the pan, allowing us to capture as much heat as possible from the wood.  

The movement of the smoke through the pan means that at least once a year we have to "punch" the flues, which simply means cleaning the soot off from them. (If we let this go too long, the soot would eventually fill the flues entirely, rendering them useless).  Usually this is a difficult process because we must work from the underside of the pan, accessing it through the firebox (there's an opening in the back of the arch as well, but its not convenient in our shanty).  With the pan on its side we were able to give the bottom of the pan a good brushing, which should increase our efficiency next season since the soot acts as an insulation.

 

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