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# Mystery led heat transfer POWER LED

## Mystery led heat transfer POWER LED

(OP)
hi everyone
i made a test, i assembled two different type LED (citizen/cree) on the same heat sink, the power of the LED is same (36W) but in the first case i got a temperature (TC) of 70 °c in the second case i got 90 °c....so what the reason of this gap?
how can control this behaviour during the cfd analysis?

thanks

### RE: Mystery led heat transfer POWER LED

Change one model so that it becomes the other and see which change caused the difference.

Why do you want a reason for the temperature difference? Do you think one result is wrong or that they should be less different (how much less)? I guess temperature in an LED depends strongly on the thermal resistance of it's internal parts, which might be different for each one.

### RE: Mystery led heat transfer POWER LED

(OP)
during my analysis i assign the power (heat genereted) to the led, the material of the heat sink etc etc but i am wondering wich is the factor that i must assign to identify two different kind of led that have different thermal resistance?

### RE: Mystery led heat transfer POWER LED

(OP)
i tought in this field we could discuss about the cfd analisys for the led thermal behaviur

### RE: Mystery led heat transfer POWER LED

I don't clearly understand your question, but maybe this helps?

To model different thermal resistances, you could put an artificial resistive layer between the LED and the heatsink. Then tune that material's thermal conductivity to give the total thermal resistance you want. That's if you can't model the LED accurately with its actual material properties. Don't forget contact resistance of the interfaces between heatsink and LED, and any other contacting parts in the heat path. All these factors would affect the temperature of the part generating the heat.

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