The Best Part of Waking Up Just Got Better

If you ask us, one of life’s greatest pleasures is sitting down with a nice, hot cup of something of coffee, tea or hot chocolate. Of course, the best part of this ritual is when the beverage has cooled enough to reach that short window of optimal drinking temperature.

Often times the unthinkable happens—we sip too early and get burned, or else become distracted by watching cat videos reading our colleagues’ Hackaday posts and miss the window altogether. What’s to be done? Something we wish we’d thought of: using the beverage’s heat to cool itself by way of thermal dynamics. For [Scott Clandinin]’s entry into the 2018 Hackaday Prize, he hopes to harness enough heat energy from the beverage to power a fan that will blow across the top of the mug.

[Scott] enlisted a friend to smith a thick copper slab in a right angle formation. The gentle curve of the vertical side pulls heat from the ceramic mug and transfers it to the heat sink of a CPU cooler. Then it’s just a matter of stepping up the voltage produced by the thermoelectric generator with a boost converter. Once he’s got this dialed in, he’d like to power it with supercaps and add a temp sensor and a microcontroller to alert him that his moment of zen is imminent. We’ll drink to that!

23 thoughts on “The Best Part of Waking Up Just Got Better

  1. I like the simplicity and performance of the Kickstarter PCM cup project, that HaD poo-poo’d a few years back.

    It stored the excess heat in the PCM (phase change material) to not only cool down the coffee but also maintain that temperature for much much longer than even a well-insulated cup could.

      1. Heck, no. Think about it. What you are calling “steam” is actually fog: liquid droplets, condensed from supersaturated air. They are warm, and they are in (by definition) water-saturated air. They will do nothing but *warm* the heatsink, as they will never evaporate as long as that warm fog is being blown onto it.

  2. From the project page:

    >I need to charge the storage capacitor as quickly as possible, while being realistic about the maximum current draw available to me.

    There do exist specialized energy harvesting chips which can help with this; the BQ25504 includes programmable MPPT, so you can use a resistor divider to set the ~80% value used with most solar cells, or ~50% which the datasheet says is typical of a TEG.

    They’re a bit expensive ($5 in quantities of 1) and hard to solder by hand (small QFN-16 package), but it’s do-able and their reference design seems to work pretty well. They can also operate at very low voltages; the datasheet claims 330mV to cold-start, and operation down to 80mV.

  3. That unholy German-French alliance of Seebeck and Carnot will have something to say about this. This rig is only going to be able to convert a tiny fraction of the tiny heat flow through it to electricity.

    How much heat flow can you get through that ceramic (insulating!) mug and into that nicely reflective (in infrared) copper slug? (Maybe a watt if you can arrange nice intimate mechanical contact, and the ceramic is quite dense)

    How much of that heat is squandered just heating up that huge slug of copper, and how long will it take? (several minutes, at that one watt rate)

    How much of that heat can be converted to electricity? Here’s where Carnot bites and Seebeck laughs. You’ll be doing very well to get one percent of the heat power converted to electricity with that temperature differential. On a very good day with much higher temperature differences these devices can only approach 4%, before they melt.

    I would be amazed if the whole operation nets ten milliwatts or even one joule of energy out of the 50-100 kilojoules that’s in a cup of hot coffee.

    There would be a much higher output by putting the copper directly in the coffee — maybe a factor of ten.

    Looks like a fun exercise though, and kudos for even trying it. I’d have been put off by numbers on the back of the napkin.

  4. Several years ago I built a simple box with a muffin fan which came on when my mug of tea was placed on a coaster in front of the fan where it contacted a simple micro switch, which started a timer and turned off the fan at the exact right time when the tea was at perfect drinking temp. Knowing the tea temp at the start and the desired drink temp, adjusting the timer was easy. Would send photo but unit was lost during two moves. Probably build another when I have time.

  5. Probably 90+% energy loss, converting heat to electricity. If researchers can devise a micro-gravity coffee cup, seems to me using thermal convection to cool coffee (perhaps a nice nitinol thermal engine, or a nitinol-controlled lid that stays up or open until the coffee has reached the “right” temperature.)

    Would love to see analysis of the energy loss in the system proposed.

    And, lastly, “the best part of waking up is…knowing you haven’t died in your sleep.” Becomes more true the older we get!

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