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Ed,
Do you keep your plane at the Munroe Airport?
Bill B
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Ed Anderson
Sent: Sunday, December 19, 2010
4:10 PM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: Fw: Water
temps
Looking at it from Q = MDt*cp. We know that the coolant mass
flow ( M ) through the system (both coolant and air) is going to be a
constant at some specific power setting and air speed. With an
oil/coolant heat exchange as part of the system - then the waste heat (Q) must
be exchanged with the air through the radiator. Therefore the efficiency
of the radiator in discharging heat to the air is an important
consideration. The more efficient - the smaller the radiator required and
lower cooling drag possible.
So since we want to get rid of the same total Heat Q and
since mass flow and Specific heat is constant that only leaves Dt as a factor to play with. So all else being
the same, the configuration that produces the greatest Dt between coolant and air will be the most efficient
and require the smaller radiator.
So if the coil cooler exchange is placed on the Hot side of
the radiator, that would increase the temperature of the coolant going into the
radiator and provided a larger Dt (more efficient) than if it were placed on
the Cool side of the radiator. If placed on the cool side
there is a greater transfer of oil heat to the coolant , since the coolant
has already passed through the radiator and is lower temp, but that results in
a higher temperature coolant going back into the engine. To keep the
coolant temperature at the same level prior to inserting the oil/coolant
exchanger into the circuit requires (as Tracy pointed out) you to
lower the coolant temp even more before it goes into the oil/coolant exchanger
by using a larger radiator.
Since the objective is to remove heat most efficiently from
the engine (and hopefully keep cooling drag down), it would appear that the
oil/coolant heat exchanger being placed on the hot side of the radiator offers
an overall advantage from that perspective. Clearly either way, it can be
made to work.
Edward L. Anderson
Anderson
Electronic Enterprises LLC
305 Reefton Road
Weddington, NC 28104
http://www.andersonee.com
http://www.eicommander.com
Sent: Sunday,
December 19, 2010 3:39 PM
Subject:
[FlyRotary] Re: Fw: Water temps
"no matter which leg of the coolant system you
pick up the heat from the oil cooler, you raise the temp of the coolant loop by
the amount of additional heat; so the rejection temp of the rad is higher
either way."
Not so fast! Here's my take
on it.
Yes, the total heat
rejection of the rad has to end up being the same. BUT with the cold side
oil cooler, to keep the engine coolant inlet temperature (and temperature of
the engine block) the same requires a 33% larger rad (compared to what we
needed a separate air to oil cooler). Actually, the rad has to be
even bigger than this because we have to have the rad outlet temp even lower to
compensate for the rise in coolant temp due to temp rise of oil
cooler. That means the median temp of the rad is lower and
therefore less efficient.
If you cool the oil on the hot side of the coolant circuit, the inlet
temp of the rad is now higher than in the cold side scheme and the required rad
size and/or the airflow through the rad size increase is smaller due to the
higher delta T between air and rad. This results in less cooling drag.
That's my story & I'm stick'n to it : )
Tracy
On Sun, Dec 19, 2010 at 12:13 PM, Al Gietzen
<ALVentures@cox.net> wrote:
For maximum cooling of the oil from an
oil/water HX (heat exchanger) you’ll want to plumb the oil from engine out to
the cooler; and plumb the cooler between the radiator and the engine
return. And I’m not quite sure about Tracy’s point because no matter which leg of
the coolant system you pick up the heat from the oil cooler, you raise the temp
of the coolant loop by the amount of additional heat; so the rejection temp of
the rad is higher either way. The assumption is, of course, that you have
sufficient capacity to keep the coolant exiting the engine below boiling for
extended high power.
On my Velocity 20B installation I have a
primary radiator in the cowl, and a secondary in the wing root; plumbed in
parallel. The wing root rad has an in-line 170F thermostat, and generally only
comes on line during extended climb. No thermostat in the engine that would
restrict flow and add a potential failure mode.
I have an oil/air cooler and an
oil/coolant HX, also plumbed in parallel. The oil/coolant HX is plumbed to the
exit of the primary rad. The oil temp runs about 20F higher than the
coolant (measured at oil return and coolant out). I could probably reduce that
difference by restricting flow to the oil/air cooler forcing more through the
oil/coolant HX; but I’m quite happy with the way things work.
Over 200 hours and lovin’ my rotary more
all the time.
Al G
----- Forwarded Message ----
From: "CozyGirrrl@aol.com"
<CozyGirrrl@aol.com>
To: keltro@att.net
Sent: Mon, December 13, 2010
4:05:31 PM
Subject: Re: Fw: [FlyRotary] Re:
Fw: Water temps
Thanks Tracy for the adjustment in my thinking. I
don't want to target temps unrealistically.
Where does that leave us with our pick up
and return points for the oil/water cooling system? If the oil were being
cooled with water only and we wanted the best possible chance at that, wouldn't
we want to feed it the cooler water from the high pressure side of the pump
prior to entering the block?
Whatever space we would use for an
oil/air cooler takes away from potential coolant radiator space. Putting the
two side by side becomes less efficient spacewise for both due to losses for
structure etc. If it is not possible to cool the oil adequately with water
alone then we'll need to back up a little and make other layout plans. I
remember Richter's Cozy III with three P-51 scoops, it got the job done but was
like dragging a parachute in drag.
Kelly, to your comment below, while I am
sure we'd have no problem putting adequate heat into the oil, I am very
concerned about keeping any more than just enough out of it. Much easier going
one way then the other =)
In a message dated 12/13/2010 2:49:02
P.M. Central Standard Time, keltro@att.net
writes:
My own opinion is that
after warm up and in flight the oil temp leaving the engine before the
coolers (air or water to oil) will
almost always be well above 160-180 F..............If it is not this
high then the oil to water cooler
will actually help warm it to a more efficient temp.........IMHO
Somebody correct me if this
is a fallacy !!.......................<:)
Kelly Troyer
"DYKE DELTA
JD2" (Eventually)
"13B ROTARY"_
Engine
"RWS"_RD1C/EC2/EM2
"MISTRAL"_Backplate/Oil Manifold
"TURBONETICS"_TO4E50
Turbo
From: "CozyGirrrl@aol.com"
<CozyGirrrl@aol.com>
To: keltro@att.net
Sent: Mon, December 13, 2010
12:52:06 PM
Subject: Re: Fw: [FlyRotary] Re:
Fw: Water temps
This is where I get confused:
-ideal water temp = 160*~180*F
If we are cooling oil with water that is
at best hotter than the ideal temp of the oil, then are we not adding heat to
it rather than removing it?
If we are trying to cool oil, why would
we feed the highest temp water to the oil/water cooler rather than the coolest
temp water by tapping into the pump housing where it enters the block?
Based on feedback, the water entering the
block may be as low as 150*~160*F, would this be cool enough to do an adequate
job of cooling the oil?
Also, which model of Mocal is being used?
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