Bart,
I sure hope that you are correct about the browning
being from overheating and not from UV exposure.
It was in one of my previous stationary gap designs
from several years ago that I noticed this "browning"
of the PVC. I can't seem to remember a lot about the details of the
construction but I do remember the PVC
browning and even starting to flash over. I had assumed
that it was due to UV exposure but it could have been
just due to overheating of the electrodes that were in contact with
the PVC. I'm just guessing on the CFM of
my cooling fan on my current design. It's a Comair Rotron
"Tarzan" 59 watt, 120 volt, 6", electric fan, but I can't lo-
cate a CFM rating on it. It seems to move a good deal of airflow, though.
David