Thermal simulation of Heat sinks using LED COB’s

[pkw6X2K4]

Hello,

Thermal simulation of Heat sinks using LED COB’s

This is a specific application of thermal analysis but one  that has a lot of interest especially to designers that, as they usually do, work independently without the resources of manufacturing industry. LED lighting design, from an early stage, requires thermal analysis to develop properly. I am not talking about standard heat sinks which already have the manufactures performance data. Rather, the unique designs that incorporate the function of heat sinks and all the other aspects of the design. Designers have had to adapt to the new challenges of LED technology, which some generations of designers have not been trained for.

In the world of Fusion 360 there is information to help. Some of it is accessible to the layman whilst some is science based and not accessible. Therefore, whatever the merits of thermal analysis in Fusion 360, is it reasonable to believe that a layman can get  useful results without a need to know all the science other than basic principles? The target in this analysis is to discover whether the design (with passive heat management)  is maintaining the Tc of the LED COB so that it is not over heating but working in a temperature range that insures the proper working life of the LEDs.

For all the information that is out there (from the Fusion team and independent sources) I have not found a sufficiently detailed and thorough step by step tutorial that allows the beginner success in this field. That is, starting with the requirements of the model that is the subject of analysis through each stage of the Fusion workflow.  If you need the answer to one question then I know that there are a host of helpful people only to willing to support you but if you have ten questions then perhaps there is a need for something more fundamental.  Is there a ‘Brad Tallis’ of  thermal simulation that can do this?

Even if I were able to scavenge enough information to get results, they would be iffy and insecurely based. It is clear from other tutorials that expert advice if vital to the proper functioning and use of any of the Fusion 360 tools. 

Thank you

p.k.w

[TrippyLighting]

@Anonymous might be able to help.

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@pkw6X2K4 wrote:

..., Therefore, whatever the merits of thermal analysis in Fusion 360, is it reasonable to believe that a layman can get  useful results without a need to know all the science other than basic principles?

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Marketing will tell you that the is easy to do and you only need the right tool and no skill or experience.

I beg to differ 😉

YMMV

[Anonymous]

When it comes to simulations, the user typically needs some form of education on the fundamentals behind the analysis. I agree with @TrippyLighting, regardless of what marketing tells you...a user not specifically trained in the simulation subject (heat transfer in this case) is going to have trouble getting good results and applying them. But everyone defines "good" and "expert" differently.

I will add that fusion 360 is far and wide the most user friendly and easy to pick up simulation program that I've used given how capable it is. It beats CREO simulate, Solidworks sim, ansys aim, workbench and many more from a usability standpoint. 

But when it comes to absolute thermal simulations, you really have to know the basics of conduction, convection and radiation to know how to improve your designs. It helps to understand the impact material has on your ability to conduct away from hot spots so you can better design heat spreaders. Understanding convection allows you to bounce around the trade between forced and free convection or added surface area. There isn't going to be a way around that and it's why those skills make a user more marketable in the workforce. I strongly recommend developing on this front as it will only make you a better designer.

We may have already messaged about this before, but I just made my thermal simulation course available on YouTube for free. There is a link to the first video below. It starts out slow and works through the simple math that a non engineer may be comfortable with. 

https://youtu.be/pWFtYFED19M

I do need to add a video that helps more on the selection and trade between materials, forced convection and heat sink shapes. I am on an incredibly tight timeline at work so itll be a few weeks before I can get to it...but if you have any specific questions to think of please let us know and i can address them in a video at that time.

[pkw6X2K4]

Hello,

Thank you.
I agree, your answer highlight's the problem.

I have been in touch with Sean Nathan and, like the kind hearted people that are out there,
he has just sent an email to me.

Plodding on in hope,

Best wishes,

pkw

[pkw6X2K4]

Hello,

Yes, we have been in touch before.

I have, therefore, watched some of your videos, but I must now check
what you have put on YouTube to see if am missing anything. I tried to get into
your original link to these videos but they were not available - is that because they are now on You Tube.

A problem is that an independent designer needs many skills without it being
possible to be an expert in them.

Just to repeat, I am not talking about pure heat sinks using the best design
solutions, rather where the heat sink aspect of a lighting design is part of a package that incorporates
other necessary functionalities, which ordinarily would be seen as a compromise to the
efficiency of a heat sink. One ’skill’ is learning to align more closely incompatible functionalities (the
problem of all design). The need, in any case, is to arrive at the operating temperature of the LED
or lower and to insure that the outer casing of the design is not a heat risk to users where the two
share a common path.

I need to check the videos before I know what the scope of my questions are but they concern,

1. Getting the modelling right.
In practice, I use a graphite foil TIM between the COB and the ‘heat sink’. I assume I should model this
and create a contact based on the the resistance of the foil given by the manufacturer. Or, do I also model
the COB from which the heat is emitted, which would mean a second contact and the resistance for this.
To which face do I apply the load?

2. Radiation/Emissivity.
Other than a ball park figure for anodised aluminium I have no idea where it would be between 0-1.
I have been using 0.77. The aluminium I use (EN AW-6082) is not covered in Fusion, then there are
matt, gloss and coloured or natural finishes apart from the depth of the anodising.

3. Convection loads (passive cooling/air).
Figures between 5-20W are mentioned. How can I be more specific when to calculate this seems horrific.

4. Meshing.
If the meshing is not adjusted then the mesh does not flow around curves in the model but steps around them in
straight lines. I can adjust this but it is not done with any specificity.

5. Heat source load
I have the LED manufacturers power dissipation data. But how much of this power (Wattage) is going through
the heat sink rather than out as light?

It would be a huge step forward if I were able to resolve these issues but I would still regard the results as approximations for various reasons.
Apart from the program itself, by simplifying the model in simulation mode I am removing determining aspects from the design such as diffusers that
would adversely effect the air flow or elements that might aid conductivity. My aim is to have a useful feedback from the analysis that
indicates where I am heading and that is sufficiently valid as to allow design changes in meaningful way. Then prototypes can be made and real world
heat tests carried out. And, I can see the differences between the simulation and fact. But it is clear, from what you have said, that unless the principles
of conduction, radiation and convection are understood it might not be possible to implement the design changes that are necessary or do it in the best way.

If I discover more question I will put them on the Forum and, hopefully, you will pick them up.

Thank you (again),

Best wishes,

p.k.w