Concentrated heat flux applied to faces


#1

Hi all,

I’m doing some research into the usability of Simscale for thermal analysis of some electronics but am finding it quite tedious to define boundary conditions due to volume / face / edge & node selection. Why isn’t it possible to apply concentrated heat flux to faces or sets of faces? I’ve created face sets that I was intending to use as heat inputs from the device to the PCB / heatsink. When selecting the concentrated heat flux as an input method it looks like the only option for topological mapping is nodes or node sets.

If you’re interested in looking at the study, here’s the link;

https://www.simscale.com/workbench?publiclink=cecc7c31-707a-4519-9f4e-2e13cbce1d6b

Many thanks,

Dale


#2

Hey Dale,

I see what you are pointing to here. But why do you want to apply concentrated heat flux to the face? The reason I am asking is that normally concentrated heat flux is applied to each node of the face and depending on the how your elements are distributed over this face, the heat distribution changes.

I think in this case you may need to apply a volume heat flux to your component. As you know the volume of your component from CAD, you can divide the heat flux with this value to get the exact volume heat flux that needs to be applied. Alternatively, if you are not interested in the heating of component itself, you can simply remove it and instead make a exact face cutout over PCB and apply surface heat flux instead on that cutout. Make sure to divide the total heat flux with the surface area of the cutout.

You can have a look at this example for more info.:

https://www.simscale.com/projects/ahmedhussain18/pcb_-_thermal_stress_analysis/

(Please note that this is a thermomechanical analysis but will give you the idea how volume heat flux is applied)

For surface heat flux, please see here:

https://www.simscale.com/projects/ahmedhussain18/thermal_analysis_of_heat_sink_led/

If you have any question/s, feel free to ask.

Best,
Ahmed


#3

Hi Ahmed,

Thanks for getting back to me!

I’m interested in applied a heat load per face to simulate the junction between the component and the PCB. I’m not interested in applying the heat load to the total volume as this will have an effect on the convective and radiative losses from the component. As my component geometry isn’t as simple as a box / cube in order to apply the heat load over a face using the “surface heat flux” option i’d need to know the surface area of the component in contact with the board (no way that I can measure surface area in Simscale) then apply a calculated W/m^2 for the surface area of the individual component. This is manageable when there are only a couple of components but the PCB i’m working on is part of a larger assembly with potentially 1000+'s of components making this a feat in itself. If I was to use the node option it doesn’t seem any easier as I would need to predefine node in to node sets or apply the “concentrated heat flux” to individual nodes then divide by the total number of nodes making the surface.

Overall it looks like Simscale is ok for small simple models but anything with added complexity requires a huge investment in set up time to get any meaningful results out. Are there any plans into improve the modelling and pre-processing sections of the application? Some of the problems i’ve faced include;

  • missed geometry and had to re-import STEP file with missing geometry meaning all face sets had to be redefined.

  • difficult and time consuming defining face sets but selection.

  • unable to highlight multiple face sets to check i’ve not missed the definition of faces.

  • no way to rename geometry / solids / faces to make identification and selection easier.

  • would be useful to have the option to specify all coincident faces / edges / nodes as bonded or free contact.

I’m sure I’ll have more thoughts as I try to solve more problems but without some improvements to the pre-processing can imagine i’ll revert back to other packages that offer the same capability with better user interface.

Any questions or should you want any additional detail about my concerns please do not hesitate to contact me at the earliest possible opportunity.

Best regards,

Dale


#4

I’m inclined to agree here, I commonly (on another package) define a heat source as a face in watts. I think instead of having all these Heat flux types it could be simplified to node/face/volume sources containing options on how the user can define the heat source i.e. I have a volume source, I want to be able to define it as a power, a power per unit volume or as a fixed temperature.

As for the bullets above, agree with all… the last one is very interesting. Can I suggest that you add these points individually to the vote for features section?

Kind regards,
Darren