Pro/Forums - View Single Post - Can someone with some real knowlege answer this question???

Cathar · 10-10-2002, 11:42 PM

I'll take a stab at this daunting question...

The point at which it gets no better (unless we start talking about the water evaporating and chilling as it moves through the air) is the CPU at the same temperature as the water.

The problem here is practical limitations to what you can achieve.

The theoretical best you could do is direct die cooling with a perfectly formed impingement jet of water covering the entire die surface. Now as the velocity of the water is increased, so is the convectional coefficient of the water striking the die surface. Is there is limit to how high it can go? No, not really. Practically? Yes. Can't inject the water at the die surface at 1000m/s and drill a hole into the die or wear it away in a few seconds, or crush it under the sheer force of the water striking it. Not mention what do we now do with all this water. How to we route it away, etc.

Okay, so let's not blast the die directly and have a water-block instead so we can route the water away and not damage the CPU. What works best here is an infinitessimally thin base-plate. Not practical again. 0.1mm thick? Also not practical. How thick then? That depends on the mounting pressure and the internal design of the block and how it braces the base-plate. Okay, so we build our block, now how fast can we blast the water at the block and not wear away the copper?

Basically what I'm saying is that there is no way to easily answer your question. It can be answered given a very particular set of parameters and substances, but also it's a case of how long do you want it to last? How robust is it? etc.

What I'm saying there's the theoretical best, which is easy to answer. CPU die = water-temp, and then there's the practical best, but this becomes suddenly subjective on your definition of practicality (10hp positive displacement pump? cost? etc).

What's the practical limit then? Well that depends on your budget...

10-10-2002, 11:42 PM	#2
Cathar Thermophile Join Date: Sep 2002 Location: Melbourne, Australia Posts: 2,538	I'll take a stab at this daunting question... The point at which it gets no better (unless we start talking about the water evaporating and chilling as it moves through the air) is the CPU at the same temperature as the water. The problem here is practical limitations to what you can achieve. The theoretical best you could do is direct die cooling with a perfectly formed impingement jet of water covering the entire die surface. Now as the velocity of the water is increased, so is the convectional coefficient of the water striking the die surface. Is there is limit to how high it can go? No, not really. Practically? Yes. Can't inject the water at the die surface at 1000m/s and drill a hole into the die or wear it away in a few seconds, or crush it under the sheer force of the water striking it. Not mention what do we now do with all this water. How to we route it away, etc. Okay, so let's not blast the die directly and have a water-block instead so we can route the water away and not damage the CPU. What works best here is an infinitessimally thin base-plate. Not practical again. 0.1mm thick? Also not practical. How thick then? That depends on the mounting pressure and the internal design of the block and how it braces the base-plate. Okay, so we build our block, now how fast can we blast the water at the block and not wear away the copper? Basically what I'm saying is that there is no way to easily answer your question. It can be answered given a very particular set of parameters and substances, but also it's a case of how long do you want it to last? How robust is it? etc. What I'm saying there's the theoretical best, which is easy to answer. CPU die = water-temp, and then there's the practical best, but this becomes suddenly subjective on your definition of practicality (10hp positive displacement pump? cost? etc). What's the practical limit then? Well that depends on your budget...