Free Resource: Heat Sink Design Made Easy with One Equation

One of the biggest hurdles between me and my engineering degree was a required course on Heat Transfer. It’s been a few years now but what I remember the most vividly is my professor’s burly-ass-mustache and his undying love for this odd subject. I definitely did not share his enthusiasm. The semester long course culminated in a lesson on designing a proper heat sink, which required the use of almost every individual lesson we were taught in class. Unfortunately, I only understood a fraction of those lessons!

I learned enough to say that this is definitely a heat sink or a mustache comb.

As you may already be aware, the process of designing a perfect heat sink is extremely cumbersome and fraught with opportunities for typographical errors. The result of many tedious calculations and hours spend crying hysterically produces an exact number detailing the precise minimum functional size of the heat sink.

After completing all that work students were instructed to multiply the result by an arbitrary number between 2 and 4 that we engineers like to call a ‘safety factor’. Obviously the importance of this practice is unquestionable, but even so, a small part of me still feels absurd when I’m asked to take a precision calculation and multiply it by whatever number makes me comfortable. Why go to all that trouble when you are just going to over-design the finished product anyway?

Only a few months after the class ended did I discover an amazing trick for heat sink design. I stumbled on a random blog article in which the author discusses a shortcut he created to save himself some time (because the normal design process is so darn long). It only works if you assume that the heat sink is aluminum, has a ‘normal’ shape as seen above, and is used in air. Since a heat sink’s effectiveness is determined primarily by a single variable (surface area), he was able to create this beautiful little equation:

Just reading that equation made me jizz in my pants (probably NSFW)

With that single equation you can bypass all the extraneous work and just go straight to the result (albeit, an approximate one). There will be inevitable inaccuracies, but that doesn’t concern me if I’m just looking for a practical solution for everyday business purposes. If nothing else it can be used to provide a frame of reference to gut-check other calculations. (and who knows how far off my calculations were back in college)

Too often I find that I have arduously worked through the equivalent of proper heat sink design equations only to later realize that an alternative method would have been more practical.  As an engineer, I do the best I can with the limited information available to me, but logic and practicality can only take you so far (it took me as far as 3 credit hours of ‘C’ in Heat Transfer class). Sometimes you just need a bit more to get the job done. So I’ve created a heat sink quick reference guide to help if you happen to be working on that extremely specific topic.

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1. […] I did, I could have just used a single rule of thumb to estimate the performance instead. (That reminds me of something else). Electric motorcycles consume about 100 Watt-hr/Mile, and that’s most of what you need to know […]

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2. Paul Moore says:

Units? — For my business we do a lot of HS – basically a naturally cooled ( no fan) 200mm Sq HS has a limit of about 200W for fin type you have shown and rooted fin – up to about 300W – I wanted to check your concept out … so 50/200 = ,25 k/w , or 50 C rise for 200W – about right –

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3. John says:

If I calculate the required area using your equation what are the area units? Thanks

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