Re: Why pressure in coolant system?

[Dave Head <dhead@sundial.sundial.net>]

At 03:40 PM 9/2/98 -0800, you wrote:
>mike sez:
>>Can someone tell me why coolant systems are made to develop & maintain
>>pressure in them?
>
>water boils at 212dF.
>add some coolant and the boiling temp rises.
>put the mixture under pressure and it rises further.
>it is cleaner and more efficient to operate the engine when coolant
>temps are in the 230dF range, so they use tricks to get the coolant mix
>to operate at the higher temps without boiling over.
>(also, the heat transfer is practically nonexistent wherever boiling
>occurs since the liquid phase isn't touching the hot metal.)
>

Actually, during the nucleate boiling phase the heat transfer capability is
at its highest. Them little steam bubbles carry away mucho thermal flux
into the cooler center of the channel. It's what happens afterwards that
ain't pretty...
When the boiling completely covers the surface (departure from nucleate
boiling) a 'rapid reduction in heat transfer capability' occurs (of course
we're talking 2000# pressure and 800 degree plate temps). Zirk hyriding is
next...

(creeping nukism here...)


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