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Yep, as I see it we have at least three
factors:
1) Flow (speed) of coolant through engine optimized for maximum
heat removal.
2) Flow of coolant through radiator optimized for maximum heat
dissipation.
3) Flow of air (speed and mass) through radiator optimized for
maximum heat removal.
2 should be matched to 1 (hoses, radiator tubes, fins and size).
3 should be optimized for minimum needed air mass to remove heat,
and is achieved by optimized inlet duct or diffuser as well as
outlet ducting with flap to minimize to only needed airflow at
climb, cruise and max speeds at any OAT. Again, only the actually
needed air flow for each condition of flight.
Sounds simple, doesn't it? ;)
Finn
On 7/21/2021 1:39 PM, eanderson@carolina.rr.com wrote:
Just to add my 0.02. Like many other things, cooling is a
group of compromises. This sounds a bit like a shade tree myth
that has been around a long time.
The myth goes if you run hot water through a radiator and
measure input and output temperatures (of the water), the slower
the water flows through the radiator and more time the cooling
air has to remove heat. That is shown by the fact the slower
the flow the greater the water temperature difference between
intake and output of the radiator. And all of this is
absolutely factual.
The problem is - that is not the complete story. The
objective is to remove heat from the engine, the slower flow
will show greater delta T across the radiator - but, will not
remove as much heat from the engine (the objective) per unit
time - which is the true objective. However, if you increase
flow too greatly you are taking more HP to increase the flow
(watch out for cavitation) and therefore creating more heat -
although increased turbulence in the flow may help pick up heat
better and offset that to some degree.
Additionally, some folks early-on did try to increase their
flow and found increased engine temp rather than less. This
"proved" to them that fast flow was not as good as slower flow.
Only later was it realized that the attempt to increase flow was
by increasing water pump rotation speed which resulted in
caviatation and actually resulted in less coolant being pumped
by the faster rotating pump. But, it did add to the myth of
slow flow cools better. If that were the case, then taken to
the limit - stopped flow should cool best.😁
Again, like many things in the actual world, best cooling is
dependent on the circumstances and objectives.
Back to my hole
Ed
------ Original Message ------
Sent: 7/20/2021 11:48:32 PM
Subject: [FlyRotary] Re: Fwd: Inlet cooling article
Charlie,
No, no reference, just what I have read and also talking
to Rad manufacturers such as BWR in Brisbane. You can
check it out by passing your hand through a naked
flame. Quickly and there is no heat transfer. Pass
slowly and you will see what the argument is. As I
said the truth is there somewhere and as Lyn so aptly
puts it “I could well be wrong”..
Neil.
Hi Neil,
Do you have a reference for that? Slowing a medium down
so it has time to absorb the heat seems to conflict with
physics as I've been led to understand it
Charlie
On 7/20/2021 5:01 PM, 12348ung@gmail.com wrote:
Charlie,
Much wisdom out there, you just have to find the
truth! Max cooling is apparently 30 MPH, so Any
faster and it does not pick up heat before going
past. Look at big trucks, that grill is not only for
looks, they slow the air to get max cooling. If too
slow they have a quite large fan that kicks in to drag
air through at 30 MPH not 100!
As
you say, what do I know – I have seen too many that do
not work – without any degree.
Neil.
Subject:
Inlet cooling article
I remember the Laboda article about
enlarging their cooling inlets, but not many of the
details.
This:
The
plenum receives air through two circular air intake
ducts behind the propeller and squeezes it,
Bernoulli-style, so that the air accelerates across
the cylinders and between their fins, carrying the
heat back, down and out an outflow "gate" at the back
and bottom of the engine area, forward of the
firewall.
Is contrary to everything I've ever read about cooling
efficiently. Faster relative flow will always have
higher drag, all else being equal. Accelerating the air
even faster than freestream just sounds crazy. My
understanding is that there's a balancing act between
having the room in an a/c to 'recover' (increase)
differential pressure across the heat exchanger (engine
fins, in this case), and causing too much drag from the
air going through the fins too fast (there's aerodynamic
drag in the heat exchanger, just like over the a/c
itself). It's surprising to me that James made the
plenum the way he did. The rest sounds like putting
bandaids on stuff. The next-to-last image, of the final
inlet, shows what appears to be a *much* smaller plenum
inlet than the cowl ring in front of it, and a rather
sharp edged lip where the plenum starts. It looks like
the air would accelerate until it hits that sharp lip,
and immediately go turbulent, which will kill any
pressure recovery and actually slow flow into the
cylinder fins.
Most Lyc plenums I've seen (even the ones James made for
the 4 cyl engines) have significant volume above the
cylinders with smoothly expanding ducts feeding the
plenum. That allows the air to slow in an organized
fashion, which increases *pressure*, which is what
actually makes the air move through the fins.
But what do I know; I have an Economics degree....
Charlie
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