Fanning

[P3D Paul S. Boyer <boyer@xxxxxxxxxxxxx>]

George Themeis writes:
"This makes me wonder... Why did it take Kodak so many years to come
up
with this simple recommendation?  For years and years projectors were
supplied with a fan that can be operated separately and we were
advised
to use it to cool the system after the bulbs are turned off.  Has
something
changed in the projector or lamp design recently?  I would expect
that a
big company like Kodak making money from selling lots of projectors
would
have conducted a simple study on the effect of running the fan and
tell
us what the results are, long time ago.

I agree that what Great Yellow Father is saying now makes sense
regarding
the filament of the bulbs but what about the other components?  I am
specifically worried about the bakelite lamp holders of the TDC 116
projectors which are reported to crack under the heat of the 750W
bulbs.
Since these are air-cooled when the lamps are on, I believe that
their
temperature will rise when the bulbs and fan are turned off together.
I will continue to run the fan with the 750W bulbs to cool the lamp
holders, lenses, filters and other projector components.  As for the
reduction in filament life, I don't know if there is any and I don't 
care much."

Well, it is a good question what took them so long to experiment with
effect of blowing on hot bulbs once the current is off.  The same
sort
of principle would apply to the bakelite parts, though: a few more
minutes at a warm temperature would have to be balanced against the
probably greater risk of the stress caused by faster cooling.  If
anything,
I would expect the stress of temperature change to be worse for
plastics,
because they do not conduct heat as well as a filament, and therefore
it would
be easier to build up objectionable temperature gradients within
cooling
bakelite by blowing on it.
--Paul S. Boyer  <boyer@xxxxxxxxxxxxx>


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