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F6 heatsink Calculations
F6 heatsink Calculations
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Old 14th November 2012, 12:18 AM   #1
dantwomey is offline dantwomey  Canada
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Default F6 heatsink Calculations

Revisiting the neverending discussion of heatsink calculations........

Refering to this webpage
ESP - Heatsink design and transistor mounting

I have,
You will use the following terms -

Tr - Temperature rise
Ta - Ambient temperature (example 22C)
Th - Heatsink temperature (example 54C)
Vh - Voltage to heater (example 12V)
Ih - Current to heater (example 3.5A)
Ph - Power applied to heatsink
Rth - Thermal resistance (in C/W) so ...

Tr = Th - Ta = 54 - 22 = 32C
Ph = Vh * Ih = 12 * 3.5 = 42W
Rth = Tr / Ph = 32 / 42 = 0.76C/W
I'd to like mount three or four of these heatsinks vertically on a piece of 1/4" plate aluminum. At there 100mm length they are rate at .85K/C.
Click the image to open in full size.

How do I calculate the effect of multiple heatsinks bolted to a base?

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Old 14th November 2012, 12:37 PM   #2
Eric is offline Eric  United States
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Location: Central PA, USA
F6 heatsink Calculations
If you orient this sink on its "edge" (closest surface in your image) with the fins running up and down and place multiple sinks side by side, you simply divide the c/w figure by the number of sinks you are using. For example, at 0.85k/w each, having 2 of them side by side will result in net dissipation of 0.42c/w. Having 4 of them will result in 0.21c/w dissipation.

However, is you take these sinks and stack them one on top of the other (effectively making a column of them), the impact of adding more is significantly decreased. One will dissipate 0.85c/w. Two (one of top of the other -effectively making it look like a single sink that is twice as tall) will increase your cooling by 0.85 / sqrt(2) or about 0.60c/w. Thus it is much less efficient to stack them than to place them side by side.

You might want to see the "heatsinking" section of my Aleph-X page for a more thorough description...
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