Fastest way to cool down a cup of coffee?

  1. Stir the coffee around with a spoon
  2. Lift the coffee up and down with a spoon
  3. Blow on the coffee

The setup

  • An Arduino with a digital thermometer, that logs the temperature every 2 seconds.
  • A water heater.
  • A spoon.
  • Lastly, a mercury thermometer to check my readings are on point.
  • Upper left (purple ) is the control test, where nothing is done.
  • Upper right (orange) is blowing on the coffee
  • Down left (red) is lifting spoon up and down
  • Down right (blue) is stirring with the spoon
Doing nothing, blowing on the coffee, lifting spoon up, and stirring the coffee

Mechanics of heat transfer

Radiation

Sources: Coal: pixabay, Girl dancing: Route 94 — My Love, infrared coffee: FLIR infrared camera

Evaporative cooling

Image by Author

Convection

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Conduction

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Result and explanation

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  • They all help to distribute the heat around in the coffee. It’s called forced convection, since we are forcing the liquid around. Density is not at play here).
  • They all increase the surface area, for bigger conduction and evaporative cooling.

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