> > Also, as my figures hopefully showed, you don't need much flow if
> > water mixes fully.
> >
> > 42 watts per (cc per second) at 10C rise.

> 10C rise seems rather high to me.

That deep-ends on what you think is rising relative to what.

And you CAN get very small water  temperature rise at the IC but still
get a terrible result overall.
Hopefully most people who design such systems will design all parts in
a balanced way. One can hope :-).

To get heat transfer you must get SOME rise.

The rise of 10 degrees I mentioned is in the water at the IC  - it's
saying that the water comes in 10 degrees cooler than the IC. This
doesn't say ANYTHING about how hot the IC is (except that it's
probably under 110C :-) ).

There are 4  temperatures iinvolved, assuming each is homogeneous
/uniform for substances involved.

Ta    Local ambient
Twc Water cold temp
Twh Water hot temp
Ths  Cooled heatsink temp

If water energy carrying capacity  at say a few degrees rise is large
compared with energy to be carried then Twh assymptotes to Ths BUT
what Twc does compared to Ta depends on how you get the heat out of
the water on the cold side.

eg if you had the very large flows I mentioned with the sample pumps
that could carry say 2 kW per degrees C rise then delta T at heat sink
will be small. ie Ths-Twh very low. As you suggest.

BUT if you do not do a good job of getting the heat OUT of the water
then Twc-Ta can be very high. You can end up with say 20 C ambient,
60C heatsink and 59C hot water and maybe 57 degrees cold water. Water
cooling is doing a good job of getting energy out of IC but you need a
large delta T to get it out of the water.


  Russell McMahon
--=20
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