Radiator Cap

[Tom Cloud]

>Not only does it not absorb enough heat from the engine, it goes through
>the rad so fast it doesn't release the heat either. Getting the coolant
>up to a high enough temp  gets the temp difference at the rad higher,
>allowing the rad to shed more calories or BTUs. This effectively removes
>more heat, even if the operating temp is a bit higher. I know it does
>not make a lot of sense, but without a restrictor in an engine running
>without a stat, overheating of the valve area, for instance, with
>resulting head cracks and/or detonation can be a real problem.


my problem is not with the cfm rating of the thermostat but rather
with the claim of (aluminum) radiator manufacturers that slower flowing
water transfers more heat out of the engine.  Doesn't seem too
difficult to see that slower flowing coolant gets warmer, lessening
the delta-T and therefore the heat transfer.  Yes, that water may
carry more actual "heat", but it's not the amount of heat per unit
of water you're interested in but rather the amount of cooling -- or
heat removed -- for your engine .... and I cannot see how very rapidly
moving water that might absorb only 1/2 calorie of energy per gram
yet disposes of 2500 calories total per unit time would be preferred
over a system where the water absorbs 10 calories per gram, traveling
slower, yet only disposes of 2200 calories total per unit time.

This is a little off the diy-efi subject, but it keeps bouncing back
up on this and other lists ... and I've never seen anything to substantiate
the claim that -- in the same system -- slowing the water flow removes
more heat.  I can see that it might remove heat "more efficiently",
but I doubt the "efficiency" gain, if any, is of any consequence in
the total heat removed -- which is what we're after.  The implication
in the ads, as I understand them, is that the system would work better
if the flow were slowed -- and, I suppose this would be true -- if you
got a larger radiator!

Like I said in my original post -- I used to make water cooled heatsinks
for very large power supplies in research applications.  We never did any
scientific studies, but the temperature of the heatsink was directly
related to the flow rate of the water -- faster was definitely better.
AND ... the flow through those heatsinks was very likely as close to
"laminar" as you could ever get ..... water from a pump pushing through
round copper 1/4 or 3/8" copper tubing soldered to a brass heatsink.
 ... faster was definitely better !!

Tom Cloud

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