Radiator Cap

Clare Snyder clsnyde at ibm.net
Tue Oct 14 14:05:22 GMT 1997


Tom Cloud wrote:
> 
> >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
> 
>    Warning, dates in calendar are closer than they appear !
Think about your delta T again, only this time at the rad. Mabee then
you get your answer. Usually it is not getting the heat out of the
enginr to the rad that is the problem, it is getting the heat out of the
rad. This is all the Rad manufacturers are worried about at any rate -
they have no control over getting the heat from the block to the coolant
- they just get the heat from the coolant to the air. Here, your Delta T
arguement supports there spiel.
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