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Electrical power is generated by a Peltier element heated and cooled via aluminum profiles standing in two water bathes of different temperature (dT ~ 60 deg). The generated power drives a small electrical motor with a connected propeller.
Simple and easy demonstration of the peltier effect.
Update 07/2011 To be more precise: it is a demonstration of the Seebeck using a Peltier element.
The Seebeck effect:
The effect is that a voltage is created if you connect two
metals or semiconductors wires at one end: The
different electron densities of the two materials result in
a diffusion and charge separation. A voltage is
generated that is nearly proportional to the temperature
of the junction. A removal of energy in such a system is
only possible, when the other ends of the wires have a
different temperature then the junction. Otherwise a
voltage of the same amount is generated and the initial
voltage is annihilated when connecting an external load.
The heating of the junction yields to a net voltage that is
able to generate a current through a connected external
load. So a part of the heat input to the junction is
converted into electrical energy.
The created voltage is of the order of several microvolts
per kelvin difference between the junction and the other
end. Several of those junctions connected in series in
one housing form the thermogenerator, which is
constructed in order to increase the output voltage and
integrate all junctions in a compact module with two
surfaces for heat supply and cooling.