I want to reuse my old computer processor heatsinks for LED heatsinking. I think I can calculate their K/W value approximately by dividing the temperature difference vs TDP at their maximum load.
I ignore the CPU packaging thermal resistance and take it as an additional safety margin. This way I get about 60/100 = 0.6K/W for a beefy heatsink.
The problem is, that I want to get rid of the active component and derate the heatsink accordingly. Are there any approximations I can use for derating?
I know I'll have to add a healthy safety margin, but I still need a general figure as to decide what wattage can they sink.