Al Gietzen wrote:
Attached are photos of my air flow test setup to measure flow
distributions
and pressure drops. It is shown here with the scoop and custom Ron
Davis
radiator. This is one of two radiators for my 20B, this one goes in
the
cowling of my Velocity pusher, and another of different
configuration is
in
the wing root. This is an "armpit" scoop (under the wing at the
fuselage),
and has a diffuser ratio a bit over 4 to 1.
I measured flow and flow distribution with a small handheld
anemometer
from
Radioshack; a very cool little instrument that gives digital readout
of
air
speed (see at their website); pressure measurements with water
manometer.
The output from the centrifugal blower unfortunately turned out to
be
about
half my design point for the rad, but it gave me some very useful
information on placing some vanes internal to the scoop/diffuser in
order to
get a good flow distribution through the rad.
The max flow rate from the blower through the rad was 1300 cfm. The
design
point for the installation is 2600 cfm. The radiator is a two row
1"
tubes
with 16 fins per inch and a core thickness of about 2 ½ ". The
core
is 16
x 11.5 for an area of 184 sq in. The measured pressure drop across
the
core
at this flow rate was only 0.4 in water. I think the pressure drop
goes
roughly as the cube of flow rate, so at design point flow, the drop
would
be about 3.2" water. This compares favorably with Ron Davis'
computed
value
of 3.7".
Note the length of duct from the blower to the scoop. The output
from
a
centrifugal blower is very turbulent, so if you want meaningful
measurement
of flow distribution, be sure to use a length of duct to help
straighten
things out.
Al,
You've basically got the experimental setup I was going to use to get
some
radiator data. The addition of some water flow through the radiator and
four
thermometers would finish the setup. To get a flow of hot water, at a
steady
temp, I was going to put a copper coil over my fish cooker (may require
some
finessing of the gas and water flows to get it right). To get a flow
rate
for the water, measure the flow into a bucket of known volume with a
stop
watch (take a series of five runs). I would use dial thermometers that
can
be sealed using a compression fitting or pipe fitting for the water
side.
The data needed is, water flow, air flow, air temp in/out, water temp
in/out. If you do this make sure to check the water flow to see that it
does
not vary, and to calibrate the thermometers with an ice bath and boiling
distilled water. Also measure the temp and barometric pressure, a basic
Idea
of relative humidity would also be nice (just get it off the weather
channel, no need to buy an fancy instrumentation) If you had that data
for a
series of flow rates of air and water you could optimize your system. I
can
crunch the numbers if you like, I just can't build anything right now.
All
my toys are in storage until the house is finished :-(
This info is sorely needed to be able to DESIGN a proper cooling system,
not
just guess.
Keep up the good work!!
Monty
The main limitation with the test setup is the limited flow from the blower.
I got the biggest one they had the heating and AC shop, but it puts out only
about half of what I need, and the flow drops off pretty rapidly with
pressure drop. About 3/4" of water is all the thing will generate.
I expect to generate the heat transfer data when the plane flies. From the
analysis I've done, and the limited confirming measurements, I'm confident
it will work. The big unknowns are in the actual installation; inlet
efficiencies, actual coolant and oil flow rates, etc.
Al
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