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Originally Posted by Groth
Heatflow is directly proportional to the temperature gradient dT/dz. Your model gives a higher gradient as you move away from the die, implying greater heatflow in areas away from the die. Where is that heat coming from? You have either disequilibria or are generating heat inside the heatspreader and waterblock.
The curves may be right for the model, but neither the curves nor the model are right for reality.
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Yes, you're right, I've just rechecked the input and this play model is from just before the introduction of 'heat' in term of production: I've just checked the diffusion profile based on a huge initial load in the 'die' segment. I'll upload the 3-d mesh figure; you can see the slow concentration decrease in the first segment, explaining the curve at the die to TIM/IHS interface. Sorry for the confusion, it was a long time ago, the model had a very limited scope (checking of influence of TIM) and was way before the much more detailed waterchill modeling
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Originally Posted by Groth
Another question, did you ascribe the same properties to both TIM joints, or are they modeled on two different compounds?
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Yes, but the first TIM layer (die to IHS) was only for completeness. Later on, I've made a 2-D schematic to calculate the impact of a less perfect solid to solid interface. As you'll know this has more impact then the exact composition of the TIM.
Model assumptions:
Model for temperature diffusion simulation (from CPU die to cooler)
Assumptions:
thermal conductivity copper: 380 watt/(m.K)
thermal conductivity aluminum: 235 watt/(m.K) (0.62 x Cu)
thermal conductivity Artic Silver 3: 9 watt/(m.K) (0.02 x Cu)
thermal conductivity normal TIM: 4 watt/(m.K) (~ half of ArticSilver)
(0.01 x Cu)
Thickness of layer:
1) die: 0,005 (one layer in model)
2) TIM layer die -> ALU heat spreader: 0,025 mm (0,001 inch)
3) alu heat spreader: 1,0 mm
4) TIM ALU heat spreader -> cooler: 0,025 mm
5) Copper core: 2,0 mm
6) cooling fluid: 0,005 (one layer in model)
Layers of: 0,005 mm: 102 layers in total
-1) die = boundary -1
1) TIM = 5 layers
2) ALU = varial thickness of layers, total of 40
3) TIM = 5 layers
4) Vapo = varial thickness of layers, total of 50
-2) fluid = boundary -2