On Tue, 12 Jul 2005 18:04:49 -0800, floyd@apaflo.com (Floyd
L. Davidson) wrote:


>You can literally calculate the amount of heat that can be
>stored in any given sized reservoir of water, and from that you
>can calculate just exactly how long it will take to raise the
>temperature of your reservoir to any given point at which you
>estimate that the cpu will not get sufficient cooling. (And,
>once you get it installed you can measure that very easily.)

Not true because even if one tried to prevent it, heat would
be shed so long as ambient is less than water temp.

>
>If there is no air movement across the radiator, the reservoir
>is not going to shed any of the heat ...

One has nothing to do with the other.


>(or, at least very little
>of it). Hence it is not a matter of if it will rise to a
>temperature where your cpu is not getting sufficient cooling,
>but just a question of how long. (Note that it is just a bigger
>heat sink than is a regular air cooled heat sink. The air
>cooled device is so small that with no fan it only takes seconds
>to overheat the cpu.

Hardly, unless "seconds" means the better part of a minute
or the system was so poorly set up that it was barely under
the stable-temp margin while fan cooled.

>With a water reservoir, it takes minutes
>or even hours if it is large enough... but it still overheats.)

No, the reservior has little impact on it unless it's HUGE,
and even then, only to the extent that a huge reserviour has
high water-surface contact. It's not practical to plan for
a huge reservoir, if someone has THAT much free space they'd
be better off just adding a 2nd radiator.


>Because of the above, it would seem there is no point in trying
>to start off with no fans at all, unless you have some other
>arrangement to remove heat from the reservoir. It sounds as if
>you are talking about a relatively small reservoir and a system
>entirely enclosed in the computer case, which suggests that it
>will perhaps take many minutes to heat up, and many hours to
>cool off again. Which is probably not an acceptable recycle
>time.

A system should NEVER be planned based on "recycle time".



>The problem is that you need a way to *know* what is going on!


Actually, that's 100% completely wrong.
A properly engineered system has no need to inform the user
of anything, no need for the user to adjust anything, etc.
The only thing the user should ever need to know is that if
the system shuts down, it did so before it overheated enough
to cause damage.


>That means temperature probes in cooling system.

Ridiculous waste of time.


>The probe in
>the cpu is fine, but it doesn't tell you what the status of the
>reservoir is, and hence won't give you a clue about what the fan
>needs to be doing.

No, completely wrong. The fan control should be based on
the hottest part if it's based on anything. Multiple parts
with a relay control if it were to be more elaborate, but
NEVER based on water temp. Suppose pump breaks, or water
leaks, the water temp will not be as high because the
components being cooled are retaining more heat.



>Basically these devices allow you to have a fully metered
>cooling system. It is possible to measure coolant temperature
>in the reservoir, after the cpu waterblock, and after the
>radiator, and air temperatures in the case and on each side of
>the radiator, plus outside and room temperature too if you want!

Which is all trivia. In a water cooled system, the only
temps that should be weighed in determining fan control are
those of the water-cooled components. Doing anything
differently than this will only increase the margin of
error.


However, if the chassis exahust fan is cooling the radiator,
and that fan is also being controlled, then all passively
cooled components much also be weighed in the determination
of proper fan speed control, but still, NEVER the water
temp. Water is absolutely the very last thing anyone should
care about until it starts boiling- and if your water is
boiling you have far larger problems than which fans are
spinning.