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September 10th, 2009

Phase change material in coffee (and beer!) mugs

Published on September 10th, 2009 | By: pwray@ceramics.org

I remember losing my fifth grade science competition to John Immel, a young boy who designed a coffee mug with a battery to keep his mom’s coffee warm in the mornings. I don’t know if it actually worked (I’m pretty sure it was just a battery duct-taped to a coffee mug), but the British Telegraph reported that a pair of German scientists came up with a high-tech mug they claim keeps coffee at the perfect temperature.

Fed up with spiced wine that was either too hot or too cold, Klaus Sedlbauer and Herbert Sinnesbichler, both directors of the Fraunhofer Institute for Building Physics, found the solution in phase change material.

The high-tech mug is made using a porcelain shell whose hollow interior is filled with a honeycomb structure made of ribbons of highly conductive material, such as aluminum. This honeycomb structure is then filled with PCM. “So now, if you are drinking hot coffee in one of these cups,” Sinnesbichler explains, “the drink’s heat is directed straight into the still solid PCM. This heat, in term, melts the PCM – kind of like wax – and turns it into a liquid.”

Once the material has become liquid, it retains thermal energy, but without absorbing any more heat. The temperature at which it becomes liquid depends on the specific type of PCM, each of which has slightly different chemical properties and melting temperature. “Warm drinks – like coffee or tea – are best enjoyed at 58°C (136.4°F),” Sedlbauer explains. “In order to reach and maintain this temperature, we fill the mug with a type of PCM that becomes a liquid at exactly 58°C.”

The material absorbs the warmth of the mug’s content like a sponge, stores it and brings it down to the optimal temperature. And then the PCM helps maintain the content’s temperature at this optimal level by slowly releasing the stored heat back into the mug’s contents. “Under ideal circumstances,” Sedlbauer says, “the optimal temperature can be maintained for 20 to30 minutes.”

In order to even further insulate the mug and permit less heat to be lost, the outside part of the mug’s hollowed-out cavity – that is, the part farthest from the material whose temperature needs to be maintained – is lined with a razor-thin layer of either plastic or ceramic. This helps further ensure that the contents of the mug only start cooling down once the PCM has released all of its stored thermal energy and returned to a solid state.

But PCMs aren’t just about keeping things warm. “Cold drinks or ice can also be well regulated in PCM cups or mugs,” Sinnesbichler says. As he explains, beer tastes best at 7°C, and ice is best at -12°C. “So you want to make cups or mugs that have a PCM type that melts at exactly these temperatures,” he says. For the consumer, this means that you need different types of high-tech mugs for different beverages, depending on whether you want them hot, cold or ice-cold.

Hot coffee to get your through your day at work and then cool brew to relax into the evening with!  I’ll take two of each, please.

There’s no information on how much these new mugs will cost, but the Fraunhofer Institute hopes to have them available to buy before the end of 2009.


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