Good question, Jeff, I tried some commercial
water “wetter” in my cooling system early on when I was having
cooling problems as I had heard it could reduce temps by 10F or more.
Well, it may work for some, but in my case, I could not tell any difference at
all. Now, it may be at the time I was only using water and no antifreeze
which may have some bearing on the lack of any detectible results.
So I too would like to know if anyone has
used it with measurable benefits.
Ed
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Jeff Whaley
Sent: Tuesday, August 18, 2009
12:01 PM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: Swirl
pots ... coolant and dish soap.
I believe adding
dish soap or water wetter is supposed to reduce surface tension between coolant
and block.
What is the measured
net benefit of either additive? 1%-5% improved cooling?
Jeff
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Lynn Hanover
Sent: Tuesday, August 18, 2009
11:24 AM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Swirl pots
Ed has all of the smarts on this. So pay attention when he writes
anything.
And now the Larch.....................
I hate to see a rotary engine go down the drain because the engine
overheated on the first start. And a lot of them do die that way. The water
pump is installed at the top of the engine, and will use any excuse to cavitate
and stop pumping coolant. It has no head on it. Pump talk for water
pressure caused by the weight of water above the pump. So a very small amount
of air behind the pump will stop it.
I have a Shrader valve on my make up tank, and charge the system to
relief pressure before starting the engine.
In the olden days, that center iron had a flat spot with some kind of
fat sensor stuck in it with two nice threaded holes along side. That hole got a
flat plate with a Shrader valve sans core installed. A nice metal cap on the
valve body kept the coolant inside. On a new fill up, you take that cap off and
pour in coolant until it came out of the Shrader valve with no bubbles. Then
put the cap back on. Fast, simple,
I should have removed the restrictor from the drawing before posting
it. It begs for comment. It is probably of no value in an aircraft application.
Here is my thinking on that piece of the system, backed up by
observation only and no technical understanding or evidence.
On my flow bench I see a vena contracta around all exposed tube ends,
(like the raw end of the shop vac hose) that reduces the effective diameter of
the hose. The air making a 180 degree turn around the end of the tube impinges
on air flowing into the tube at any angle less than 180 into the tube. So the
CFM you would calculate for the tube diameter and pressure will be about half
of the calculated flow when tested.
The smaller the tube diameter the more profound the effect. Now look
into the tank on a radiator and notice the flattened tubes sticking up from the
flat tank floor. Any vena contracta going on in there?
And it is in a liquid, way worse than flowing air.
While raising the pressure around the end of the tube, flow does
not improve as an exact function of pressure. Or, doubling the pressure does
not double the flow. And now more bad news. The same construction at the
outlet end of the tubes creates another interesting condition, where high
velocity flow from the raw tube end, creates a high pressure differential
between the flow and coolant at rest in the tank, that caused the low speed
coolant to constrict the flow exiting the tube. You can see this on a humid day
when a war bird revs up for take off. The vapor rings from the prop tips are
compressed inward and stay closely attached to the fuselage. Or, a vena
contracta observable in broad daylight.
I deduce from this that there is a considerable restriction involved in
forcing coolant through a radiator.
I am not alone in this thinking. Notice that the lower radiator hoses
on cars have a spiral of wire installed to prevent the collapse of the hose at
high engine speed. Even with the use of modern higher pressure caps now common.
Notice also that the lower hoses are larger in diameter than the upper
hoses.
So, the radiator, like the power valve or restrictor in a Freon system,
where a restriction of some sort is required to generate a pressure
differential. Unlike a Freon system that pressure differential is of no value
in our cooling systems.
So, the radiator(s) are the biggest restrictor in the loop, and the
lowest system pressure is likely to be found between the radiator(s) and the
pump inlet. When that pressure drops below local air pressure
the lower hose would collapse if it were not for the wire inside,
your 22 pound pressure cap be damned.
So, the restrictor, limits the pressure differential across the
radiator, and helps prevent pump cavitation that shortens the vanes on the pump
and renders it ineffective. When you are shifting at 9,600 RPM and miss the
shift, (the rev chips are 9,600s) or the driver selects 1st instead of 3rd
successfully (easy with dog rings) and the revs go to the moon, then the
restrictor is a help.
For airplanes, not so much.................Sorry for any confusion.
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