Thomas J. wrote:
Good idea!
Anyone ever tried one of those CPU-cooling units? They should come up
with
some voltage if "abused" as a windmeter.
They are way cheaper than a good handheld windmeter.
The objective is/was to confirm equal flow in all runners, the actual
quantity being of no concern (as long as they flow equal....)
I think you're referring to the tachometer-equipped cooling fans. The
CPU coolers might not work because of form factor (they don't usually
flow straight through), but a regular chassis fan might. I'd look into
removing the permanent magnets (assuming they didn't affect the
tachometer function) so that the fan free-wheels.
Or you could simply use a small fan (like from a tiny power supply) and
measure the output voltage with a voltmeter. Crude & coarse, but
perhaps sufficient.
Russell Kent
________________________________________________________________________
Subject: Air Flow sensors
Date: Mon, 25 Oct 1999 19:17:44 -0700
From: Paul <rotaryeng@earthlink.net>
To: zz <rotaryeng@earthlink.net>
So I came up with the idea of using those cheap little cooling fans
on Pentium processors as air flow sensors to gather
data under real world conditions while one is flying around.
One can get plug in cards for a PC that has counters on it.
You then need an LED and photo transistor to detect the blade RPM
which should (after calibration with the Omega air speed meter) be
proportional to air exit velocity from the back side of the rad.
Paul Lamar
Paul, some of those CPU cooling fans have a tachometer built in. I
used one and tied the output to a freqency counter to measure airflow
at only one point behind the radiator. The problem is that these
permanent magnet motors have to overcome the magnetism holding the
rotor inline with the stator to begin turning and requires air speed
of at least ~20 MPH. I took one of these apart and removed the coil
and iron stator so it would spin freely while keeping the tach
function intacked. Then it would start spinning at about 5 MPH. I
calibrated it by holding it out the window and driving at different
speeds noting the frequency on the counter.
I think this would have provided better information if I had used
four or more as you suggested. I was trying to optimize ducting but
with only one point of reference, results were inconclusive. I may try
it again when I get my radiator relocated.
Chuck Dunlap
chuck@zekes.com
Great work Chuck. Do you remember the brand name?
I will pop over to Fry's and buy half a dozen.
I could make a little switch box to use one counter and look
at each tach in turn like some EGT/CHT gauges work.
Wonderful news Chuck. Thanks.
Paul Lamar
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What works with much higher resolution and cheaper is a velocity rake (array of pito tubes)
and a water manometer.
Paul Lamar
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