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Snip
That's exactly what I HAD thought, until I was told that
the air could pass through too fast and not pick up as much heat.
Mark... this is what I was trying to communicate. It could
be totally wrong so let's get more opinions. Ed??
With respect to exit area size only.
If the volume of air through the coolant radiator was
moving faster than optimum the air delta T would be lower than
it would be with slower air. Slower air at a higher delta T means less air needs
to exit the cowl. What is optimum? Every install is unique so it
needs to be viewed \ identified on each installation. Ed uses a 30%
duct air speed as a reference point. If I understand this correctly the diffuser
play a role in duct airspeed. If the air is not being diffused optimally the
airspeed could be much higher than 30% through the part of the core. Dennis H.
and I observed airspeeds through a test core at 50% + without a diffuser.
Your inlets are 72sqin with 306sqin core face for
water and 24.75 sqin with 102 sqin for oil. Both are
competing for the same exit area. IF this is
an exit area problem only then enlarging it should improve both water and oil
proportionally. Water should realize 2/3 of the improvement and
oil 1/3. 306 sqin vs 102 sqin. Your improvements after opening the
exit seem to track this very close. So increasing your exit area further
should show more improvements in both oil and water to a point. But you do not
need more water cooling improvements right?
Core 306 sqin at an airspeed of 115mph.
40% or 46 mph = 8602 cfm 8602 cfm at a 50 deg
air delta T = 7741 btu's \ min
30% or 34.5 = 6451
cfm 6451 cfm at a 80 deg air delta T =
7741 btu's \ min
In this example 2151 cfm less air needs to flow through the
water radiator to produce the same btu rejection. So what effect would 2151 cfm
less air through the water radiator and exit area have on the oil cooler's
ability to flow more air? Would it improve the oil cooler air flow by 1/3 or 717
cfm? Not sure.
Can your radiator produce a 80 deg air delta T? It may only
produce 60, 70 or??
Am I in left field here?
Bobby
(flow testing new radiator ducts prototype
today)
ED wrote:
<snip>
Mark, if you really had excess air flowing through your radiators the
coolant would drop more than 4 Deg F. In fact, the more air flow the more
coolant Delta T you would drop through the radiator.
<snip>
That's exactly what I HAD thought, until I was told that the air could pass
through too fast and not pick up as much heat. This didn't make sense to
me. Maybe I wasn't listening closely and missed the point altogether
(wouldn't be the first time).
What I DO know is that the air is flowing faster through the water radiator
than the oil radiator. (I'm not sure I have the ASI's hooked up correctly,
but they're both hooked up the same). I have a pitot behind each radiator
hooked up to two separate ASI's. In slow cruise, say 125-130 kts, the
water radiator ASI will read about 110knts and the oil ASI will read about 90
kts. The way it was behaving before I opened up the exit, it appeared that
the air from the water radiator was trying to exit backwards through
the oil inlet. I say this because of how high the oil temps were
reading. I enlarged the cowl exit, and both the water and oil
temps dropped significantly.
The ASI's are referencing the static port for these readings; should they
be referencing cowl or cabin pressure instead? Airspeeds readings seem
awfully high to me.
Mark
(Going to the airport today to recalibrate temp sensors)
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