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Date: Tue, 18 Aug 2009 11:24:17 -0400
Message-ID: <1ab24f410908180824y21de8019j3aa9630756594bea@mail.gmail.com>
Subject: Swirl pots
From: Lynn Hanover <lehanover@gmail.com>
To: flyrotary@lancaironline.net
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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,
cheap.

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.

Lynn E. Hanover

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<div>Ed has all of the smarts on this. So pay attention when he writes anyt=
hing.</div>
<div>=A0</div>
<div>And now the Larch..................... </div>
<div>=A0</div>
<div>I hate to see a rotary engine go down the drain because the engine ove=
rheated on the first start. And a lot of them do die that way. The water pu=
mp is installed at the top of the engine, and will use any excuse to cavita=
te and stop pumping coolant. It has=A0no head on it. Pump talk for water pr=
essure caused by the weight of water above the pump. So a very small amount=
 of air behind the pump will stop it. </div>

<div>=A0</div>
<div>I have a Shrader valve on my make up tank, and charge the system to re=
lief pressure before starting the engine. </div>
<div>=A0</div>
<div>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 g=
ot 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,</div>

<div>cheap.=A0=A0</div>
<div>=A0</div>
<div>I should have removed the restrictor from the drawing before posting i=
t. It begs for comment. It is probably of no value in an aircraft applicati=
on. </div>
<div>=A0</div>
<div>Here is my thinking on that piece of the system, backed up=A0 by obser=
vation only and no technical understanding or evidence. </div>
<div>=A0</div>
<div>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 i=
mpinges on air flowing into the tube at any angle less than 180 into the tu=
be. So the CFM you would calculate for the tube diameter and pressure will =
be about half of the calculated flow when tested. </div>

<div>=A0</div>
<div>The smaller the tube diameter the more profound the effect. Now look i=
nto the tank on a radiator and notice the flattened tubes sticking up from =
the flat tank floor. Any vena contracta going on in there?</div>
<div>And it is in a liquid, way worse than flowing air.</div>
<div>=A0</div>
<div>While raising the pressure around the end of the tube,=A0flow does not=
 improve as an exact function of pressure. Or, doubling the pressure does n=
ot double the flow. And now more bad news. The same=A0construction at the o=
utlet end of the tubes creates another interesting condition, where high ve=
locity flow from the raw tube end, creates a high pressure differential bet=
ween the flow and coolant at rest in the tank, that caused the low speed co=
olant to constrict the flow exiting the tube. You can see this on a humid d=
ay 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 ven=
a contracta observable in broad daylight.=A0</div>

<div>=A0</div>
<div>I deduce from this that there is a considerable restriction involved i=
n forcing coolant through a radiator.=A0</div>
<div>=A0</div>
<div>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. =A0Notice also that the lower hoses are larger in diameter than th=
e upper hoses. </div>

<div>=A0</div>
<div>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 diffe=
rential. Unlike a Freon system that pressure differential is of no value in=
 our cooling systems. </div>

<div>=A0</div>
<div>So, the radiator(s) are the biggest restrictor in the loop, and the lo=
west system pressure is likely to be found between the radiator(s) and the =
pump inlet. When that pressure drops below local air pressure</div>
<div>the lower hose would collapse=A0if it were not for the wire inside, yo=
ur 22 pound pressure cap be damned.</div>
<div>=A0</div>
<div>So, the restrictor, limits the pressure differential across the radiat=
or, and helps prevent pump cavitation that shortens the vanes on the pump a=
nd 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 re=
strictor is=A0a help.=A0=A0</div>

<div>=A0</div>
<div>For airplanes, not so much.................Sorry for any confusion.</d=
iv>
<div>=A0</div>
<div>Lynn E. Hanover=A0=A0</div>
<div>=A0</div>

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