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Published byGavin Heyward Modified over 2 years ago

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Physics of a Good Coffee Andrei Varlamov COHERENTIA INFM-CNR, Roma Giuseppe Balestrino Universita’ “Tor Vergata”, Roma Wroclaw, September,15 2006

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Italian Moca

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Filtration: the Darcy Law atm + P P(T)=P atm + P } P = Q L/(S κ) ( °C) = 10 -3 Pa s P 4· 10 4 Pa → T* ~ 110 °C Q = m/t~200 g/min L~ 1 cm atm P=P atm → Q = κS Pρ/ ( L) S~ 10 cm 2 κ ~ 10 -12

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The limitation of the Darcy Law at small pressures: opening of the cappillars

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Moka explosion. κ ~ 10 -12 κ ~ 10 -13 ~ 10 -14 M=150 g, V=200 cm 3 T max ~ 300 0 C→P max ~ 10 3 atm E ~ PV ~ 40 KJ → v=200 m/s PV=m/μRT

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Espresso machine

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