The Clever Engineering Trick That Allows Simple Rice Cookers to Perfectly Cook Rice - kottke.org

The other day I posted a quick note of appreciation for my trusty rice cooker. I have what you might call a fancy rice cooker — it has all sorts of different settings and “advanced Neuro Fuzzy logic technology” — and it cooks my rice perfectly, every time. I am sure it is an engineering marvel.

But this $20 one-button rice cooker also cooks rice perfectly, every time. And it does so using some very simple and clever engineering involving magnets:

This button thing is made of an alloy that has a Curie temperature just a bit higher than the boiling point of water. This allows it to function as a temperature-dependent kill switch. Thanks to the outer spring, it’s always held firmly in contact with the bottom of the pot, which ensures it and the pot are at nearly equal temperatures. So long as there’s liquid water sitting in that pot, the pot itself cannot get hotter than water’s boiling point.

This means that the button remains magnetic, and the magnet is able to overcome the force of the inner spring, so the device stays in cook mode. But, once the rice has absorbed all of the water (and/or once all the remaining water has boiled away) the energy being added to the pot by the heating element is no longer being absorbed as latent heat.

Now, the pot can quickly start to exceed the boiling point of water. And once it gets past the Curie point of that little sensing button, the magnet is no longer attracted to it, so the spring overcomes the magnet and… *click* the rice cooker switches back to the warming mode.

Science is so cool. (via david)

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