There is no need for the entire cooling block to be made of copper ( you
could even do without copper, letting the cooling fluid pass directly over
the heat spreader); the cooling block could be plastic with a copper
bottom.
Koolance sells a cooling block with a plastic box and a copper bottom for
about $50 US; it has little pyramids cast in the top of the copper plate
(for better convection, I guess) and well designed mounting clips.
The simplest cooling block I have seen can be made using only a drill press
and pipe thread tap. Two holes are drilled most of the way from one edge of
the block to the opposite edge, then two more holes are dirlled most of the
way through from edge to edge, but at a right angle to the first two holes.
All four holes are tapped, with two on one edge closed with threaded plugs,
while the other two holes have barbed hose fixtures installed. That's the
whole thing, and it very likely works just as well as the Koolance block, it
just won't have the neat set of clips.
Peletiers have sorta come and gone already. Back when CPU's ran 25 to 35
Watts, a Peletier solution offered a lot of advantages for cooling below
room temperature (or even below 0 degrees C.) But now, with the fastest
CPU's approaching 100 Watts, Peletier arrays are not nearly so attractive.
The reason: Peletier arrays are not very efficient, and consume a lot more
power than they pump. A good rule of thumb for Peltier cooling is for the
Qmax rating to be two or three times the heat output of the CPU to get a
temperature differential between the hot side and the cold side (the cold
side is nearest the CPU). Qmax the MAXIMUM amount of heat that can be
pumped at ZERO temperature differential; no useful cooling. DeltaTmax is
the MAXIMUM temperature differential with ZERO heat being pumped; no useful
cooling. The "sweet spot" is about in the middle. For a CPU producing 80
Watts of heat, the Peltier array should have a Qmax rating of 240 Watts.
That Peltier array will consume about 200 Watts of power to give a
temperature differential of 40 degrees C when the CPU is producing 80 Watts
of heat. That means the heatsink (on the hot side of the Peltier array)
must handle 80 Watts + 200 Watts = 280 Watts. That is a LOT of heat, and
air cooling will not really be sufficient, especially as the CPU temperature
will depend directly on how cool the heatsink can keep the hot side of the
Peltier array. If the heatsink can only keep the Peltier hot side at 60
degrees C, then the Peltier cold side will be only 20 C ... not much cooling
for all the expense involved. That means water cooling is necessary for the
Peltier array hotside. If the water cooling can keep the hot side at 30
degrees C, the the cold side of the Peltier array can keep the CPU a bit
cooler than 0 degrees C. The 240 Watt Peltier array will need ~ 24 volts at
~ 8 Amperes or ~ 12 volts at 16 Amperes ( the voltages must be adjustable -
10%/+20%.
But then, just water cooling could keep the CPU near 30 C if the room
ambient temperature is ~ 25 degrees C. You can find more information on
Peltier arrays at
http://www.tellurex.com/ ,
and I have a small website at
http://www.mindspring.com/~pweldon/ with additional information on cooling.
--
Phil Weldon, pweldonatmindjumpdotcom
For communication,
replace "at" with the 'at sign'
replace "mindjump" with "mindspring."
replace "dot" with "."
