I need to know what limits if any exist on how fast heat can be
transferred from aluminum to water and specifically are there
limitations or drawbacks to the speed at which water moves over the
aluminum surface. i.e is there a maximum speed for the water moving 
over the surface at which the benefit of fast moving water aiding in the
heat transfer process is lost?

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Request for Question Clarification by hedgie-ga on 14 Dec 2005 08:59 PST

re:
  is there a maximum speed for the water...

At certain speed the flow becomes turbulent -
at all changes - it  may actually help up to a point.

  The heat transfer depends on more parameters then just 
water - aluminium interface  and speed relative speed of coolant.

Lot of research was done (e.g. to cool electronics) -
but for such a low price it is hardly worth to sift 
through literature to obtain a specific answer,
You may want to look at:
http://answers.google.com/answers/pricing.html

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Request for Question Clarification by hedgie-ga on 14 Dec 2005 17:43 PST

Sorry about a typo:
at all changes - it  may actually help up to a point.

was supposed to be:

it (heat transfer) changes (on onset of turbulence), and 
rate of transfer may increase, ...

hey,
Im not totally sure,but maybe this can provide you some answers :
http://www.quantumlynx.com/water/vol7no1/story6.html

http://kywater.org/ww/ramp/rmal.htm

this is one of the best sites which provide you some answers in
genereal,there are many issues on chemisty and other stuff,there are
some regards to aluminum too,you really should consider read this to
see if it fits :

http://www.newton.dep.anl.gov/askasci/chem98.htm

Goodluck

thanks but this is not what I am looking for. my question is very
specific and I am looking for a specific answer - thanks anyway

In order to answer this question, we need to know the specifics of
your expected aluminum temperature, the expected flow speed, and the
expected water temperature.

Your question is somewhat open-ended.  Sure, if you could accelerate
water to the speed of sound (that would be the speed of sound through
water), then your water is gonna get mighty hot as it passes over the
aluminum, and it may end up heating your aluminum instead of cooling
it.

If your water is stagnant, then eventually, due to Newton's law of
Cooling, your Aluminum and water will be at the same temperature and
you will get no cooling effects.

Likewise, if your aluminum is roughly the same temperature as the
water, then you have a different set of criteria to consider than if
the aluminum is super-heated.  At some temperatures, the
aluminum/water will display the Lidenfrost Effect, which is what
happens when water "dances" on a hot pan.  If you are seeing the
Lidenfrost effect, very little water is actually making contact with
the aluminum, meaning cooling is not happening as effeciently as you'd
like.

So, as I said before -- it depends entirely on your expected temperatures/speeds.

Voiding in the water can be prevented by keeping the system under pressure.
Look up the design of water-cooled nuclear reactors.

Material properties are involved - including Conductivity, Specific
Heat Capacity, and Density.  Also the melting point or temperature at
which reaction between water and the metal takes place.

Heat transfer work is rather empirical - it involves matching various
dimensionless numbers in your situation to a similar one that's been
measured.