Received-SPF: none
 receiver=logan.com; client-ip=61.8.0.84; envelope-from=peon@pacific.net.au
Message-ID: <005001c4f54b$60e85e10$d125083d@ar1>
From: "Leon" <peon@pacific.net.au>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-595237@logan.com>
Subject: Coolant Flow was Re: [FlyRotary] Re: oi/water Exchanger
Date: Sat, 8 Jan 2005 17:29:15 +1100
MIME-Version: 1.0
Content-Type: text/plain;
	charset="iso-8859-1"
Content-Transfer-Encoding: 7bit

Hey Dave,

Just like the engine block,  the oil/water heat exchanger will ONLY cool
efficiently if you feed the sucker COLD water.  Now on the factory cars,
they take the HOT water from the back of the block.  The rear housing has a
T pipe for such prupose.

So basically,  the heat exchanger cops water that has already cooled both
rotor housings.  REALLY DUMB!!!.  The reason Mazda get away with this is
that the cars are very rarely driven flat strap for long periods on the
road.  It also assists in warming the oil rapidly in cold climates.  No
wonder nobody has had any success with them!!  Betcha everybody has used the
stock plumbing !!

Now for our case of aero engines,  we are going to be running these engines
anywhere between 65% and WOT most of the time.  So it needs COLD water with
which to exchange the heat from the oil..  It also needs to be under
pressure.  There obviously must be a differential pressure across the heat
exchanger to make the water flow.  So from whence does one get cold water
under pressure??  Answer as a P.S below.

Mazda,  in their infinite wisdom, dump the water back into the heater outlet
via a "T" piece on the firewall,  and this then is dumped into the water
pump INLET (low pressure "suck" side).  Which means that the hot water is
recycled through the engine again without ever saying "hello" to the rad
core!!  DUMB again!!!!

So, for aero apps,  you need to mount it in PARALLEL with the engine.  Take
a supply of cold water under pressure, (this will require a bit of
imagination!),  feed it to the heat exchanger,  and then dump it back into
the hot/ side of the rad,  which is AFTER the thermostat (if you use one - I
always do!!) ,  or into a fitting on the hot tank itself..  The idea is to
pass ALL the hot water through the rad core so it can cool! (this might
sound a bit facile/flippant,  but it's not meant to be).

Somebody mentioned that boat oil/water heat exchangers always work.  The
reason they work is that they cop cold water,  not HOT water.  The Mazda one
will work just as efficiently if you feed it with water from the COLD side
of the rad.  It's a really robust unit,  and I've never seen one leak.

Hope this clarifies the situation ...

Cheers,

Leon

P.S.
I get my cold water under pressure by drilling & tapping into the water pump
housing just before it goes into the block. Works a treat!!


----- Original Message ----- 
From: <daveleonard@cox.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Saturday, January 08, 2005 12:46 PM
Subject: [FlyRotary] Re: oi/water Exchanger [FlyRotary] Re: fluidyne oil
cooler


> I was considering the idea when I was planning my installation and one big
question kept popping into my mind: which side of the rad do you put the
interchanger?
>
> If you put the interchanger on the hot water coming out of the block, that
water is at least 180deg.  This hot water will have a very hard time cooling
that oil, and best case could only get it down to 190 or 200.  Likewise the
water is likely to boil before it get to the radiator since it is starting
at 180 (at least) and going up from there.
>
> If you put the interchanger after the radiator it will probably do a good
job of cooling the oil, but now you will be heating the water right before
it goes back into the engine.  In order to keep the water from overheating
in the engine it will have to come out of the heat exchanger relatively
cool, which mean it has to come out of the rad really cool.  To get it that
cold comming out of the rad that cold (assuming you had a big enough rad),
the temperature gradient really has to drop and the rad becomes very
inefficient as it is trying to cool the coolant that extra 20 deg.
>
> I decided the only efficient way to do it was to have two rads, one after
the interchanger and one before it.  I suppose that would work if you were
using 2 evap cores in series, but for me the obvious solution was to use an
oil/air cooler.
>
> Dave Leonard
>
> >
> > Good points of course, but I still can't help but be drawn to the
simplicity
> > of having only one scoop, one duct, and one radiator.  Even as I type,
I'm
> > trying to figure out where I can put a bigger radiator (within cosmetic
> > limits this time)  :-)    I'm even warming back up (so to speak) to the
idea
> > of using the stock 1st gen oil/water exchanger for the single rotor.  It
was
> > pointed out to me that the stock unit took hot water from the heater
outlet,
> > which doesn't really give the heat exchanger the best chance of success.
> >
> > If I get Ken's oil/water exchanger, I'll be mighty tempted to hook it up
to
> > the current two radiators to see how it does on the ground.  Since I'm
not
> > opposed to changing out the evap cores, there might be a way to enlarge
the
> > capacity some.  Barring all that, it'll make a nice paperweight.
> >
> > Cheers,
> > Rusty (now collecting oil coolers instead of manifolds)
> >
> >
> >
> >
>
>
> >>  Homepage:  http://www.flyrotary.com/
> >>  Archive:   http://lancaironline.net/lists/flyrotary/List.html
>