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Date: Tue, 11 Nov 2008 21:06:37 -0700
From: Bob White <bob@bob-white.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Cooler orientation
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On Tue, 11 Nov 2008 18:06:45 -0800
"Lynn Hanover" <lehanover@gmail.com> wrote:

> The way I was visualizing it, if you have a bottom inlet then you
> would have a top outlet and vice versa.  I agree with what you are
> saying, but suspect you might get better distribution through the
> exchanger if the input were on the bottom.
> 
> I learned the ineffectiveness of plumbing a heat exchanger wrong with
> the heater core on my old '52 Ford.  Since radiators outlets were on
> the bottom and inlets on the top, I reasoned that the heater core
> should be the same.  As soon as the water level in the system got a
> little low (and it always did), the heater would only blow cold air.
> After switching the hoses around, water going in the bottom would
> always fill the core to the top outlet and the heater worked just fine
> even with low water in the cooling system.
> 
> Bob W.
> 
> On Tue, 11 Nov 2008 18:00:32 -0500
> "Thomas Jakits" <rotary.thjakits@gmail.com> wrote:
> 
> > Hi Bob,
> >
> > thanks for your reply!
> >
> > In both installations the oil-cooler is above the oil level by a good
> > margin.
> >
> > In my opinion the inlet position is not the critical issue, but the
> outlet.
> >
> > As the oil slows down considerable in the inlet tank, it may (or not)
> loose
> > the ability to push all the air out in front of it.
> > If at the initial filling of the cooler after start-up (or opening of the
> > thermostat) air gets trapped at the top of the cooler, this air never gets
> > pushed out, just compressed to oil pressure values.
> > With a top outlet, the air has no choice but leave the cooler through the
> > outlet....
> >
> > Am I way out there ?????
> >
> >
> > thjakits
> >
> > On Tue, Nov 11, 2008 at 2:46 PM, Bob White <bob@bob-white.com> wrote:
> >
> > > Hi Thomas,
> > >
> > > If the oil cooler is below the oil level in the bike, I don't think top
> > > or bottom inlet will matter too much.  If it's above the oil level in
> > > the pan, then bottom inlet will ensure the cooler is always full of oil.
> > >
> > > My 2 cents and that's probably more than it's worth. :)
> > >
> > > Bob W.
> > >
> > > On Tue, 11 Nov 2008 14:27:00 -0500
> > > "Thomas Jakits" <rotary.thjakits@gmail.com> wrote:
> > >
> > > > Hi all,
> > > >
> > > > I know this is a rotary and aviation list, but there is a lot of
> cooling
> > > > going on here, so I just dare to ask a OFF TOPIC - no pics, so it
> should
> > > > load quick too :)
> > > >
> > > > I would like to ask specifically* Lynn Hanover*, but if anyone else
> knows
> > > > something too, please let me know!
> 
> When the inlet and outlet must be on the bottom, the cooler needs to be long
> in tube length and short in tube count. Like a stock Mazda cooler or an MGA
> cooler. This keeps trapped air exposed to fast moving oil. Few tubes means
> higher velocity. And trapped air is minimized and not such a big problem.
> 
> Where the tube count is high, and the tube length is short large amounts of
> air may be trapped in the upper tubes, while hot oil uses the lower tubes.
> When oil pressure is very high and velocity improves through the cooler,
> much of the air is moved out of the cooler and appears in the pan or reserve
> tank.
> 
> Whenever oil coolers are mounted, no matter the location of the inlet, the
> outlet must be as high as possible. Oil in a piston engine foams and becomes
> an insulator. It becomes compressable. It begins to act unlike a lubricant.
> Engine parts run hotter. Air entrainment adds volume. So the sump may appear
> over filled. The one motorcycle seems to have it right with inlet and outlet
> on top. When the cooler has to be up and down, then inlet at the bottom is
> of course required, because the outlet *must* be on top.
> 
> The foaming problem in the rotary is worse, due to the two oil jets
> squirting oil into the spinning rotors. Multi grade oils add to the foaming
> problem because of long polymer chains that link up when heated. A straight
> weight oil foams less than multi-grades. Racing oils even less because they
> have more anti foaming agents than street oils.
> 
> I find water cooling far less difficult. The in at the bottom out at the top
> seems less important, as water gives up air bubbles readily.
> 
> Lynn E. Hanover
>
 
One additional thought that occurred to me was that if you needed the
outlet fitting on the bottom for simplifying hose routing, the output
could could have a tube extending to the top internally.

Bob W.


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