how to set power absorption for encapsulant?

[kosy]

hi erveryone..

i find difficulty to do my simulation by using Ansys Workbench. The problem is i know that the epoxy encapsulant for a high power LED will capture small amount(known amount) of heat. In my simulation, i dono how to apply this condition in.
What should i do?

thanks

 

[Transient1]

Kosy,

I am not sure what you mean "I know that the epoxy encapsulant for a high power LED will capture small amount(known amount) of heat. In my simulation, i dono how to apply this condition in."

You only have to apply heat sources where the heat is actually coming from in addition to your boundary conditions (such as a fixed temepratures).

 

[Stringmaker]

Would this be done automatically by specifying a thermal resistance for the encapsulant material? Afterall, the encapsulant will be an insulator.

 

[kosy]

hi everyone,

actually the condition is like this..

normally 20% of the power disspated from Die will transitted into light. however there is 5% of the light(heat)be captured in the encapsulation. this amount of heat might cause the LED become failure.
so by using ansys WB, how do i do the analysis for this 5% of heat?

thanks for replies. And i would like to appologize that i do not write my question clearly. thankz

 

[Transient1]

Well it sounds to me like you have your problem solved. If you know that the die is dissipating 100 Watts, but 20% escapes as light and 5% of that energy is captured in the die then you know all your dissipations at steady state:

80 Watts in the Die (Total Heat Flow on the dissipating face)
5 Watts in the Encapsulant (Total Volumetric Heating)


I am assuming this encapsulant is semi-transparent. Is it in 'perfect' contact with the die, or is there some sort of air (or vacuum) gap? Are you sure about your assumption on how much energy escapes as light and how much is captured in the encapsulant?

 

[kosy]

hi everyone,
fristly thanks for Transient1 replies. My assumption(in %)just a example but in fact the encapsulant will capture small portion of heat from light.

As transient 1 said, 5 Watts in the Encapsulant (Total Volumetric Heating), the problem is how do i apply this by using Ansys WB, because in WB there are only HEaT FLOW, HEAT FLUX, INSULATOR and HEAT GENERATION..

So, i don know which should i use..

thankz

 

[Transient1]

kosy,

Your welcome.

You can figure this out for yourself. Try inserting one of each heat condition and look at the units. You want the
heat source that represents a volume heating up. Then you want to assign your volumetric heating so that when it is multiplied by the volume of encapsulant you have the desired power. Good Luck and feel free to ask more questions.

(Personal Note: Thanks. It is spelled with an s.)