Experiment 8.5: Drinking Duck
The felt of the duck´s head is wetted.
The duck begins to “drink” periodically.
Technically, the „drinking duck“ is a kind of „matter engine“ which uses the difference in the chemical potentials of liquid water and water vapor in the air.
Due to the phenomenon of mass action the chemical potential of water vapor strongly diluted in air is lowered below that of liquid water and the volatilisation process
can take place spontaneously.
The flow of vapor from the felt into the ambient air is coupled with an entropy flow. Therefore, the wet felt cools down and some of the vapor of the internal liquid (with a very low boiling point) condenses. The reduced pressure forces the liquid to rise up in the tube thereby gradually changing the centre of gravity of the duck.
By means of an appropriate equipment the movement of the duck can be utilized to do work, e.g. to lift a weight.
- Detailed description (pdf)