|
|
Ed Anderson wrote:
Ok, Jim
I agree that the theory part gets
out of hand at times (my fault). Theory only counts if it works in
practice {:>). However, I think these question naturally arise when
we start talking about some of this stuff - the old "how it do that".
Exactly. But that is what I was referring to
loosely as qualitative analysis. IIRC, most of the books
measure the results in some "standard" radiator in a wind tunnel and
empirically create a "constant" that will get you in the ballpark for
non-standard stuff. Sadly, we are in a very empirical
environment.
<>The only part that really counted was
understanding what was necessary to keep air flow from separating from
the walls in a diffuser. If you eliminate that problem you have done
probably 90% of what you can do to achieve optimum diffuser performance
(my opinion of course). So you can have otherwise adequate core
surface and volume, but if you have a poor duct design with lots of
flow separation and eddies then your system may fail to adequately cool.
Exactly. And I'm suggesting that since the
downstream side of heat exchanger is pretty much a blunt instrument,
pressure drop across the exchanger tells you what you need to know
about the upstream side - how well it's working - and how much
you have to improve your diffuser.
Unless one is bent on reinventing the wheel ...
Jim S.
Ed A
-----
Original Message -----
Sent:
Monday, April 04, 2005 12:29 PM
Subject:
[FlyRotary] Re: A lot to learn
Is it possible we're dismissing some important factors getting a little
out of our depth here? Dynamic pressure in the cores and across the
cores would seem to be so highly dependent on surface friction and core
density and passage size as to be impossible to estimate, much less
quantify accurately.
If the purpose of the plenum is pressure recovery (converting dynamic
pressure into static pressure) and it's the static pressure drop that
drives the mass of air through the radiator core, why not just forget
about the molecular, boundary layer and core passage size
considerations for the moment since we can't quantify any of that
anyway. As Ed has stated so many times in so many ways, a good
inlet/plenum design does a better job of converting dynamic pressure to
static pressure than a bad one, and he's found out pretty much what he
has to do to make a bad one good.
If we measure static pressure at the forward and aft face of the
radiator and we've got the pressure drop across the core. Period. We
know how close we are to Ed's plenum. Then adapt the stuff that Ed has
pioneered for us to make it better An Airspeed indicator I find is
handier and more accurate than a water manometer. The Pitot connection
on the upwind side and the Static connection on the downwind side
should give me upwards of 100, maybe 120 kias drop across the radiator
at cruise. More is better. If I don't have sufficient pressure drop
across the radiator, I probably need to improve my intake and plenum to
get rid of the eddies Ed alludes to. That is what I've got the most
influence over. If I don't get enough pressure recovery, I study Ed's
findings and approach implement them better.
I think all this molecular stuff is more appropriate to the ACRE list
where nothing ever really has to fly. This list (to me) is the guys
who actually FLY. A sound qualitative analysis of the issues
involved (which we already have) will lead me to a workable solution.
That is very nice since an acceptably accurate quantitative
analysis is not possible. To that end (to coin a phrase) I don't have
to know how it works or why it works, I only have to know what I have
to do to MAKE it work. And I have been blessed that Ed has found out
most of this.
Are we PVORT. again? ... Jim S.
David Carter wrote:
----- Original Message -----
From: <jbker@juno.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Monday, April 04, 2005 7:07 AM
Subject: [FlyRotary] Re: A lot to learn ! Re: Cooling -Learned a lot
Charlie E wrote:
At the risk of embarrassing myself with a display of misunderstanding
the physics of it all, should your pressure sensors be measuring dynamic
pressure or static? Seems like I remember Tracy's measurement pics
having foam chunks over the pressure sensors to remove the dynamic
component of the pressure measurement. I couldn't remember if your setup
has that (& I really don't know if it should, either).
Charlie
---------------------------------------------
>> Homepage: http://www.flyrotary.com/
>> Archive: http://lancaironline.net/lists/flyrotary/List.html
|
|