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Thermal Resistance Modeling of Active Heat Sinks

Question asked by Drew Castle on Jan 19, 2010
Hi everyone,

I've been working with this problem for a bit now, and haven't found a straightforward method of attacking it which actually works for me yet. Maybe you have? I am by no means an expert with this software, but I'm really trying to learn. We have the license at work, and nobody else even has a clue how to use it.

I've been running CFD thermal analyses on several differen electronic packages using Floworks/FloSim 2010, and one of the biggest problems I've been running into is the appropriate thermal resistance modeling of active heat sinks/CPU coolers when the specs are not given by the manufacturer. I can't work the whole model into the larger assembly, as the mesh necessary to model 0.0075in fins is entirely too large for my computer. I have the "real" values as determined by bench tests, but the simulation values don't line up.

I've attempted to model the finned heat sink, fan, and CPU similar to what is in the tutorial and then calculate deg-C/W based on the numbers generated from that simulation and plug them into an appropriately sized "Heat Sink Simulation" in the larger model. As I write this, the simulated point and surface temperatures are about 35C less than measured (and other times they come out as melting solids). I'm using psi=(Tsurface-Tambient)/Power dissipated. How close to the heat sink should I be calculating the local ambient temperature if I'm using that formula? Or should I be looking at it from a completely different angle?

I could go through an entire list of other things I've tried, but I'd love to know if anybody has an actual answer to tackling this than trying to come up with some nonsense workaround.

Thanks a ton in advance. An actual answer to this problem would be amazing.