How does the thermoelectric Peltier effect work

The Peltier effect

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An electric current of amperage sets at the interface between two different conductors and with the Peltier coefficient and the amount of heat per time


free (Fig. 4). The sign of depends on the direction of the current. A negative sign of means that heat is withdrawn from the contact between the two conductors. In contrast to the generation of Joule heat, it is a reversible process.

The Peltier effect arises from the fact that in a homogeneous conductor of constant temperature a heat current flows at the same time as an electric current. Its greatness is through given. The Peltier heat (2) represents the excess or deficit between the heat flowing in and out at the contact point. This isothermal heat flow is caused by the fact that not all conduction electrons in an electric current have the same flow speed. Rather, the latter depends on the energy of the electrons. If, for example, the conduction electrons with an energy above their chemical potential (see below) receive a higher speed than those with lower energy, the electrical charge flow is associated with an oppositely directed heat flow due to the negative sign of the electron charge. The Peltier coefficient is then negative. It is the same with one -doped semiconductor in which the electric current is carried by electrons in conduction band states.

Between the absolute thermopower and the Peltier coefficient of a conductor there is the relation already found by Kelvin


which could only be validly justified within the framework of the kinetic theory for the conduction electrons or the theory of irreversible thermodynamics. The Kelvin relation (3) links the material constants for two very different physical effects, one of which (Peltier effect) has the simple explanation indicated above. Linking the two effects through the Kelvin relation does not relieve us of the task of finding an independent explanation for the Seebeck effect.

Next page:Thermoelectric cooling Upwards:About the cause of the Previous page:The Seebeck EffectKlaus Froboese