[Brot]

Hello All, newbie here, I think I will be fairly active over the the upcoming period of time. I hope to quickly get a feel for how this place runs.

Is there a place where new members introduce themselves? I've used ANSYS Fluent quite a bit, and ANSYS Static and SW Simulation for structural stuff before.

My two questions are:

1- With Conjugate heat transfer in SW Flow Simulation 2015, is it necessary to define "wall" boundary conditions?
Because from what I saw in the electronics cooling tutorial, defining lid material as "insulator" and then as an "environmental pressure" boundary condition was enough, no need to define walls.
Correct?

2- How does grouping heat sources, boundary conditions, goals and fans work in SW flow simulation, and is grouping works the same for all what I previously mentioned? the safest way is to define each one individually, but you can imagine how time consuming that could be.

Thanks a lot.

[Boris_M]

Hi Brot,

1) No, this is the philosophy behind SWFS and FloEFD. If there is a solid geometry wall than this is what it is and there is no need to tell the software that there is a wall. Makes perfect sense, don't you think :-)

2) I would only group boundary conditions if they have the same amount or properties applied. So there is no problem for multiple part to be the same material or surfaces to have the same radiation properties. As for heat sources you have to be careful. If you apply a heat source as a power and select multiple components such as chips, the heat source is distributed per volume. Meaning that if you put 9 W on two chips and the one is double the volume than the other, the bigger one will get 6 W and the smaller one will get 3 W (so double the power for the two times bigger chip).
I wouldn't apply such a grouping to a fan or certain other boundary conditions that might have the same properties but are differently aligned or where the boundary condition is based on a flow rate etc. Since a flow rate of a fan is based on the pressure loss between inlet and outlet, if you select multiple fans at different locations the pressure at each of their inlets might be different and the fans would work on different points on their curve but if you've selected all inlet or outlet surfaces in one boundary condition of the fan, the pressure will be averaged form all of them to one value.

No, it can be a lot of work but doesn't necessarily have to be. If you have multiple components of the same part in your assembly for example like a part for a chip and that chip is built into the assembly 7 times and you want to specify a 2R-model then you can specify that on one chip and use the right click on that boundary condition and use "Copy to instances" and the software will automatically recognize the components in the assembly which are based on the same part and suggest them to you. So if you accept it, the software does the multiplication of the boundary condition automatically.

Boris

[doviatt]

Originally Posted by Boris_M

If you apply a heat source as a power and select multiple components such as chips, the heat source is distributed per volume. Meaning that if you put 9 W on two chips and the one is double the volume than the other, the bigger one will get 6 W and the smaller one will get 3 W (so double the power for the two times bigger chip).

Boris

Hi Boris, Can you explain this behavior better? Are you saying if you apply 9W to each chip that the larger surface area chip won't emit 9W? And total power won't equal 18W into the heatsink?

I am about to run a similar situation and remembered last time I tried this I got unexpected results (I had 8 MOSFET parts that I applied the same wattage on each and they didn't add up to total power when I turned them all on in the simulation).

Edit: I just re-read your words and I have mis-understood. You did say "distributed per volume".

[Boris_M]

Hi David,

No, if you apply 9W to several chips with one boundary condition and the sizes of the chips are not all the same, then the sum will be 9W but each single chip will not all have the same power as they are in different sizes and therefore the distribution is per size.
As an example: You have 2 chips, one is double the volume than the other. If you apply 9W to the two chips in one boundary condition, the smaller chip will have 3W and the chip with double the volume will have 6W (double the power). Together they are 9W as defined.
If you however have 2 chips with the same volume, then each chip will have the same power applied.

If you apply single boundary conditions then they have to add up to the sum as each one has his own boundary condition.

Boris