I have been messing about with a fan that draws air through the top of the tube and out the cell end. 2 things I noticed, one was the air was drawn from further away from the ground (a tad less moisture) and that it really helped breakup any boundary layer of warmer air on the mirror surface.
I will probably end up with 2 fans, one axial fan blowing air across the face of the mirror (and will one day have the air drawn through a peilter cooled stainless steel tube filled with desiccant) ie: cooler than ambient and much drier.
The other fan will draw the used air out the back of the OTA.
The reason for the axial fan blowing across the mirror is because it is virtually closed to any light sources ,un like a typical blade fan.
The peilter cooler will of course be controlled by an ambient and mirror temp differentiator.
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