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----- Original Message -----
From: "Ed Anderson" <eanderson@carolina.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Friday, November 29, 2002 10:11 PM
Subject: [FlyRotary] Re: Coolant loss : More cooling system test stuff.
>
> Here is my best guess. The molecules of any substance (in which they can
> freely move) will tend to increase their velocity if they are heated.
This
> increased velocity of individual molecules when integrated over their
total
> number exerts a force on any containment vessel (which we common refer to
as
> "pressure"). As the velocity (heat) of the molecules increases the
results
> is an increase in pressure inside the containment vessel. If this
pressure
> increases pass the capacity of the radiator cap then it will force some
> liquid into the overflow container. After the engine stops, the coolant
> cools down and the pressure drops (lower molecule velocity) which if it
> drops far enough now creates a negative differential pressure inside the
> coolant system sucking the coolant in the overflow bottle back into the
> coolant system.
>
> Another possible contributor to pressure increase is all liquid has air
> entrapped between the water molecules so that t when the liquid is heated
> the air molecules come out of solution (much as you see bubbles in boiling
> water) and occupy space. Perhaps the water when heated also tends to
expand
> (as its molecules increase their speed with temperature)This generates
> additional pressure which causes the water to push past the radiator cap
> pressure release.
>
> So there you have it, my 0.02 worth. Perhaps we have someone on the list
who
> really knows what is happening.
>
> Ed Anderson
Water does not expand much but ethelene glycol (an alcohol) expands a lot
with heat. Thats why they use alcohol in thermometers. 50 - 50 coolant mix
really does expand in the cooling system. The higher the ratio of glycol to
water, the more expansion you get. I'm still not sure why I needed more
overflow capacity than a typical car unless it is the higher load on the
engine. Cars virtually never get run at WOT for any length of time. When
climbing to cruise altitude, the engine can be at full throtle for 30
minutes at a stretch.
Tracy
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