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You are correct, Mark, Minimizing or eliminating
laminar flow next to metal - in other words causing the laminar flow in the
boundary layer to become turbulence does promote heat transfer. It also
increase skin friction and drag. However, if the turbulence gets to the
point of causing air flow separation then that hurts both cooling and the drag
factor. So like most other things involving aircraft - compromise is
called for.
My cores are slanted - but, only because I could
not fit them in the space I had allocated for them any other way.
Otherwise they would be perpendicular to the air flow. Clearly slanted
cores do work and most of the time we install them in that orientation due to
space constraints or aesthetics as Pat Panzera indicated in his
response.
If you use the Streamline duct approach to the
duct design for a perpendicular core, it is easier to plot the coordinates and
fabricate the duct - in my opinion. My duct lengths are approx 3
1/2" on the short side and 6" on the long side making for a very short duct
indeed.
However, I keep the duct cross sectional
small until just before the core and then permit it to balloon into the bell or
trumpet shape of the streamline duct. This delays air flow separation and
the pressure recovery (according to the theory) that causes it - until
the last moment. Separation does occur but it occurs up in the corners
where it has minimal impact on air flow through most of the core. In fact,
the streamline duct equation even indicates at what angle of divergence of the
flare causes separation. It varies depending on the size of opening and
size of core/ratio - but, generally the separation occurs above 65 deg of
divergence and in some cases into 75 deg.
Some would disagree with this approach, but I
have flow with it for years now and my cooling system appears close to optimum
for my set up with minimum excessive cooling capacity and drag. Your
milage may vary of course (doesn't it always {:>))?
Ed
Ed Anderson
Rv-6A N494BW Rotary
Powered
Matthews,
NC
eanderson@carolina.rr.com
http://www.andersonee.com
http://members.cox.net/rogersda/rotary/configs.htm#N494BW
http://www.dmack.net/mazda/index.html
Sent: Thursday, May 01, 2008 7:45
PM
Subject: [FlyRotary] Re: radiator
orientation?
Ed,
But doesn't "creating turbulence" improve heat
exchanger efficiency? I thought that was why they put corrugated
fins on the cores.
Mark S.
On Thu, May 1, 2008 at 6:38 PM, Ed Anderson < eanderson@carolina.rr.com>
wrote:
Michael,
My
view is that slanting a radiator does nothing better for you than one
perpendicular to the air flow - except perhaps making it easier to fit a
space constraint, it which case then go with a slanted radiator.
A
slanted radiator (that has the same air flow and same frontal area) as a
perpendicular radiator is actually added going to have a bit more
drag. The air flow must now make at least one (and possibly two turns) going
into and out of the core channels creating turbulence and drag at those
points. NOT that it is going to make a real significant difference at the
airspeeds we fly. So for that reason, a slanted radiator is certainly
acceptable especially to meet installation constraints.
My
0.02
Ed
----- Original Message ----- From:
"Michael Silvius" <silvius@gwi.net>
To: "Rotary motors in aircraft"
<flyrotary@lancaironline.net>
Sent: Thursday, May 01,
2008 8:10 PM
Subject: [FlyRotary] Re: radiator orientation?
Geroge:
In
the end I will likely angle them a bit but my primary concern is if it
is
ok to install these radiators in the vertical orientation. I have
the space
up and down to use them this way. The nose bowl I have seems
to work well
with things set up that
way.
Michael
----- Original Message ----- From:
"George Lendich" <lendich@optusnet.com.au>
To: "Rotary motors in
aircraft" <flyrotary@lancaironline.net>
Sent: Thursday, May
01, 2008 5:50 PM
Subject: [FlyRotary] Re: radiator
orientation?
>
Anyonene see any issues of concern with instaling the radiators in
the
> vertical orientation as oposed to their normal orientation
with the
inlets
>
and outlet on the top. These are evaporator cores from a JMC
Jimmy-
Chevy
>
Blazer
>
> Michael in Maine
Michael,
The front
adds significantly to the flat plate drag and anything you
can
do
to
reduce that affects the total drag. Are you happy with the front
width,
could it be reduced with some angle on the rads?
George (
down under)
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