Thermal analysis of electronic system
Thermal analysis of electronic system
(OP)
Hi,
This is regarding the thermal analysis of electronic system.
Now a days,the application of electronic components in all industry is steadily increasing.But they should be robust enough to withstand the vibration and thermal loads.
We are trying to carryout the CFD analysis of electronic system. Earlier, we outsourced this project to an external agency. But the results were deviating considerably from the test results.They executed the project using Flowtherm. They represented all cylindrical components (Cylindrical capacitor, cylindrical transfomer) as rectangular, due to limitations in the software. I hope this resulted in different flow characteristics, then observed in reality.
Now, We are trying to carryout the analysis using industry standard CFD-Fluent software.But the software requires material properties for PCB board (FR4+ Copper), capacitor (Electrolytic), transformer, resistor and inductor needs to be specified. But these are not made of single material and the properties are not readily avialble. can we suggest anything rational about the consideration of material properties for the thermal analysis.
I look forward for your help.
Regards,
Logesh.E
This is regarding the thermal analysis of electronic system.
Now a days,the application of electronic components in all industry is steadily increasing.But they should be robust enough to withstand the vibration and thermal loads.
We are trying to carryout the CFD analysis of electronic system. Earlier, we outsourced this project to an external agency. But the results were deviating considerably from the test results.They executed the project using Flowtherm. They represented all cylindrical components (Cylindrical capacitor, cylindrical transfomer) as rectangular, due to limitations in the software. I hope this resulted in different flow characteristics, then observed in reality.
Now, We are trying to carryout the analysis using industry standard CFD-Fluent software.But the software requires material properties for PCB board (FR4+ Copper), capacitor (Electrolytic), transformer, resistor and inductor needs to be specified. But these are not made of single material and the properties are not readily avialble. can we suggest anything rational about the consideration of material properties for the thermal analysis.
I look forward for your help.
Regards,
Logesh.E





RE: Thermal analysis of electronic system
The properties for most components can be found at www.alldatasheet.com
RE: Thermal analysis of electronic system
Unfortunatly, modeling electronics in CFD is not an exact science -- it's still an engineering task. The right amount of detail to add to a particular component depends on the concern you have that it may overheat or cause ther parts to overheat.
1. Some components that do not generate heat, like capacitors, can be modeled with a bulk conductivity of about 5 W/mK. You are correct that the actual construction is much more complicated but the cap temperature will not be sensitive to those details. Cap temp will be primarily dictated by the local air temp and secondarily by the PCB temp.
2. You can also greatly simplify the material of most resistors. Yes, they generate heat but typically you want to know how that heat effects other components, the sensitive ones. You rarely need to know the temperature of the resistor element.
3. I agree that sometimes round components, like capacitors and resistors, should not be modeled as rectangular blocks. This is important if there is forced air and nearby heat-generating components. No CFD mesh perfectly fits a curved shape, but I know Flotherm is capable of modeling capacitors as near-round objects (about as round as any CFD program can handle) and I'm a little surprised your consultant didn't model them as Cylinder Objects.
4. For PCBs, use FR4 conductivity of 0.3 W/mK and Cu of 360 W/mK. There are short-cuts for simplifying the layers and vias so you're not bogging down your model with 0.04mm details. Let me know if you want some tips.
5. I have modeled transformers and inductors in great detail, but it's not a trivial task no matter what software you use. You have to get detailed construction info from the manufacturer and/or take the component apart.
ko (www.ecooling.biz)
RE: Thermal analysis of electronic system
TTFN
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RE: Thermal analysis of electronic system
RE: Thermal analysis of electronic system
The next largest error seems to occur when case-air convection is poor. Conduction from die to leads to pcb to air becomes very important, as well as radiation. So your model should reflect this (easier said than done...)
In models with good case-air, which usually means high power density, the interface losses can become more dominant and should be modeled more carefully. Don't just use bulk conductivity and an average TIM thickness. Contact force, surface finish, TIM wetting factor, etc, play a larger role in the accuracy of the model.
ko (www.ecooling.biz)
RE: Thermal analysis of electronic system
Thanks for your comments.
It has taken a quite bit of time to respond.
Regarding your first response
1) We observe similar kind of behaviour in the test.
2) Regarding the resistors, we observe slightly higher temperatures compared to other components in the forced convection conditions.
3) Yes.We understtod that Flowtherm can indeed include rounded objects.
4)There are short-cuts for simplifying the layers and vias so you're not bogging down your model with 0.04mm details. Let me know if you want some tips.
We will be definitely enriched with your tips. Advanced thanks for the tips.
Your tips based on the expertise and experience will be definite help practising young engineers like me...
5) Do you think that using fluent, even I can capture intricate details, which is already inbuilt in softwares like Flowtherm...?
I was under the impression that using Fluent may lead to greater insight into the details compared to the Flowtherm but at the cost of turnaround time. can We have your comments.
I am also equally thankful to tkordbyan, we are not quite sure with the power dissipation in most of the cases.
As we start acquiring data from simulation and test, hope I will be in better position to feed proper inputs.
Thanks once again transient1, K0,IR stuff,tkordbyan.
We have the similar uncertainities in the structural analysis of these electronic components.
Regards,
elogesh