No thermal results.

[JohnTomasik6493]

I've been trying to run a simple static thermal study.  Even with 25X the heat generation applied as boundary conditions, I'm getting no thermal change.  I've gone back through tutorials and previous studies, checked everything I can think of, but I can't identify where the issue is.   Attached is a screen capture showing as much as I could, as well as the flatline temp.

[JohnTomasik6493]

Jon,

If the electronics team doesn't provide their operating conditions in enough detail to generate relatively accurate heat output numbers, this is the only way I can come up with to figure it out.  I'm all ears if you know of other approaches.  Other than either getting accurate info from my electronics team that tells me real heat generation numbers, I'm not sure how else to do this.  Simply putting in chip spec input power isn't accurate, because that's like saying the chips are 100% inefficient.  What are other analysis approaches that you've seen effective?

Oh, besides that, your site provides guidelines for creating air space volume, based on the item's position (i.e., sitting on a table or suspended in air, etc.).  However, as we see in this thread, me using exactly those numbers doesn't always work (since the board is very thin).  In that case, we had to thicken the air space beyond the standard recommendation so that we can get more elements in the madel.  I want to ensure that I don't create an air space that substantially changes the analysis results.  Is there some other guideline, other than making sure there is more than one element, that I should be looking at?

I appreciate your feedback.  This software can turn into a huge tool for us to sell our business.

John Tomasik

[JohnTomasik6493]

Again,

I'll ask the question again in the hopes of a direct reply:  your site provides airspace sizing guidelines, but as we've witnessed in one of the analysis in this thread, that size had to be adjusted beyond suggested parameters to make the analysis perform.  My concern is that in a predictive mode, how do I know how to set this up properly to provide the most accurate results?  I'm at the point where I'm taking what I've learned based on emperical testing of development boards, and the next step is creating a CAD assembly of those three boards, putting them into an enclosure, sending that over to the software, and applying the conditions from the earlier studies to run the study.  We're going to make a lot of decisions based off of that study, so I want to make sure I'm introducing the least amount of error.

Also, how should I accurately model heat-sink via's?  Presently, I'm using a compact thermal model material property for my chips.  If thermal vias will be provided to help dissipate heat from the chip into the board, how do I set this up?  I believe I can't place two materials against the compact thermal model chip in the analysis, if I remember correctly.h

I must complete the first spin on this analysis by Monday of next week, so your feedback is needed as soon as possible.

[Jon.Wilde]

Hi John,

Apologies for not replying before -  you may actually wish to look into subscribing to support as then you will have direct access to our team. I thought it might help as you seem to be running some rather important analyses.

I think we need to re-visit the online documentation. You are not the only person to raise this issue. The main rule is that the box must be large enough to have no impact on the results. If the walls are too close we are introducing unrealistic flow, possibly accellerating the air through a smaller gap, or drawing out more heat than reality.

Regarding the heat loss from the chips, one could assume worst case and give them the full load. Check out the results and dial back from there.

I would have thought the external box should look something like this:

[JohnTomasik6493]

"Subscribe to support"?  Uh, we kinda got this Sim CFD thing thrown in our lap as a result of all of the Autodesk/Algor restructuring, so I'll expose my ignorance and ask how I subscribe to support.  

Oh, what you posted looks nothing like the ratios your site suggests...I'm talking way off.  And, if I remember correctly, when I made the air space excessively large, I believe I saw that my numbers seemed skewed on the light side of things.  I'll have to verify that.  But, from what you're saying, it sounds like my best bet is just to make a huge air space around this thing, and the heck with the ratios.  And, since it'll be a purely predictive analysis, I have nothing quantitative to "scale back" to, so then my guess would be as good as the next guy's.

[Jon.Wilde · Accepted solution]

Hi John,

Yes, my reason for suggesting it is so that you have a case for each issue, assigned to an engineer. It cannot get lost in the mire like forum posts.

Looking in our system, you do have this. Do you know a Stu Merritt in IT there? We need to find someone there who has access to the subscription centre, so they can add you, then you can log cases and get more direct assistance when needed.

Yeah, those ratios work well for many objects but when the length/width ratio is so large it clearly falls to pieces.

Aim for something like I sketched, that should get you pretty close.

Kind regards,

Jon