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myv65 · 08-06-2002, 06:22 PM

Hey Ben,

I'm going to backtrack for a sec a clear up a couple of things I said. First, my long post above was referring to your "island" design, not design #1 or design #2. Second, I had to take another look at Paul's block. Really the only difference between it and what I posted was his exit. I mistaken thought he had a center-inlet, aka direct impingement. (That WOULD be a nice upgrade

).

The big point I was getting at is that the delta-T between chip and the side of the block that meets the fluid depends on many things. If you constrain your cooling to an area equal to the die area then you are required to have a higher delta-T across the baseplate then if you allow spreading. When I read you idea for removing heat in the same way it enter, ie through a small rectangular area, I wanted to make clear that this is not an effective solution.

The absolute worst case scenario for the baseplate is having to pump heat through a small area. Per my example, pumping 75 watts through an 80mm^2 area 5mm thick requires a delta-T of nearly 12°C. Allowing 1/3 of the heat to spread outside that 80mm^2 region drops the peak delta-T by 4°C.

Now, you ask about having a hotter baseplate in contact with the fluid. Sure, this will raise the baseplate to fluid delta-T, but since the fluid temperature is practically fixed (say at ambient for ideal sake), then raising the fluid-baseplate delta-T requires a higher CPU temperature for a given baseplate thickness. This is obviously not good.

There's a whole lotta stuff to think about and this single thread is probably as good a discussion as I've seen.

08-06-2002, 06:22 PM	#94
myv65 Cooling Savant Join Date: May 2002 Location: home Posts: 365	Hey Ben, I'm going to backtrack for a sec a clear up a couple of things I said. First, my long post above was referring to your "island" design, not design #1 or design #2. Second, I had to take another look at Paul's block. Really the only difference between it and what I posted was his exit. I mistaken thought he had a center-inlet, aka direct impingement. (That WOULD be a nice upgrade ). The big point I was getting at is that the delta-T between chip and the side of the block that meets the fluid depends on many things. If you constrain your cooling to an area equal to the die area then you are required to have a higher delta-T across the baseplate then if you allow spreading. When I read you idea for removing heat in the same way it enter, ie through a small rectangular area, I wanted to make clear that this is not an effective solution. The absolute worst case scenario for the baseplate is having to pump heat through a small area. Per my example, pumping 75 watts through an 80mm^2 area 5mm thick requires a delta-T of nearly 12°C. Allowing 1/3 of the heat to spread outside that 80mm^2 region drops the peak delta-T by 4°C. Now, you ask about having a hotter baseplate in contact with the fluid. Sure, this will raise the baseplate to fluid delta-T, but since the fluid temperature is practically fixed (say at ambient for ideal sake), then raising the fluid-baseplate delta-T requires a higher CPU temperature for a given baseplate thickness. This is obviously not good. There's a whole lotta stuff to think about and this single thread is probably as good a discussion as I've seen.