DELICIOUSLY INEFFICIENT

Science  12 Jan 2007:
Vol. 315, Issue 5809, pp. 167
DOI: 10.1126/science.315.5809.167c

Coffee may be the fuel that keeps many of us going, but a coffeepot makes a lousy engine. As part of a project to explore the physics of kitchen devices, physicist Concetto Gianino of the Institute of Advanced Secondary Instruction “Q. Cataudella” in Scicli, Italy, and his students analyzed the classic moka coffeepot—a two-chambered device that sits atop a burner. When water in the lower chamber boils, the pressurized vapor drives the remaining liquid through a filter packed with coffee and into the upper chamber. Comparing the work done pushing the water into the upper chamber to the heat energy absorbed by the boiler, the group found that the pot turned heat into work with an efficiency of 0.02%—compared to about 20% for a typical steam engine. Gianino, who reports the work in the January American Journal of Physics, notes in the moka's defense that its job is not to move water efficiently but to flavor it.

CREDIT: ISTITUTO DI ISTRUZIONE SECONDARIA SUPERIORE

“This is the best way to show physics to young people,” says physicist Antonino Foti of the University of Catania. “You couple the image of a coffeepot to the physics of a heat engine, and students never forget it.”

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