Thermal Resistance and Math...

[RadMan]

I remember reading an article about how to calculate the temp of a CPU by using the Thermal Resistance of the Cooler (ie .81c/w for the Chrome Orb), the heat released by the CPU in watts, as well as the ambient temperature.

Does anyone know the formula? As well, is a lower or higher Thermal Resistance factor preferable?

Thanks.

 

[BurntKooshie]

yes, the lower the thermal resistance, the better. What it means is that, for every watt of heat applied to it, the temperature of the heatsink will increase proportionally with the wattage with the thermal resistance, ie, that heatsink_temp = thermal_resistance * watts.

Therefore, the lower thermal_resistance is, the less its temperature changes due to heat output.

Ambient temperature plays a role because that is the starting temperature, the lowest limit at which anything can get to (that is within the ambient temperature) without the use of a peltier or ducting to bring in air that is cooler than ambient air, (or water )

 

[johncar]

RadMan,
BurntKooshie is correct, but in a general way, and no criticism of BurntKooshie intended, ok to generalize theory, be brief. But doesn't demo problems re "practice", so here's the detailed version for you to evaluate before you consider research/application.

Temp rise from air entering hs/fan to some "average temp" inside the cpu = (power dissipation of cpu in watts)*(thermal resistance of hs + therm res cpu to hs interface material "adjusted for chip surface area" + therm res of cpu materials from core to case top)....therm res in degC/watt. (Ignores minor heat flow thru chip bottom/sides, as even chip mfrs do).

Look at all the "hard/?impossible? to determine" information you need in order to estimate chip's internal temp. Be happy with knowledge of the process, and measure temp of thermal diode inside Intel chips, if you have one. Even with its possible error, (admitted by Intel), you'll be much closer.
John C.

 

[BurntKooshie]

thanks for the correction johncar - i've saved that 'bit of information

 

[RadMan]

Thanks guys!