Peltier effect

The Peltier effect (also called thermoelectric effect ) is a physical phenomenon of displacement of Chaleur in the presence of a Electric current. The effect occurs in conducting materials different natures bound by junctions (contacts). One of the junctions cools then slightly, while the other is heated. This effect was discovered in 1834 by the Physicien Jean-Charles Peltier.

Definition

The figure opposite watch the basic thermoelectric circuit.

Two conducting materials of different nature has and B are connected by two junctions in X and W. In the case of the Peltier effect, a Electric current I is imposed on the circuit, while placing for example a source of Electric current between Y and Z, which involves a release of Chaleur Q with a junction and an absorption of Chaleur to the other junction. The Peltier coefficient relating to materials has and B Π_ab is then defined by:

\ Pi_ {ab} = \ frac {Q} {I} \,

If a current imposed in direction Y→W→X→Z involves a release of heat in X and an absorption out of W, then Π_ab is positive.

Theory

The Peltier effect is related to the transport of Entropie by the charge carriers (electron S or holes) within material. Thus when there are in the general diagram above a release of heat in X and an absorption out of W, that is due to the fact that the electrons or the holes gain entropy while passing from the material B to material has out of W (there is thus absorption of heat), while reciprocally they reperdent of the entropy while passing from material has with the material B in X (there is thus release of heat).

There are in fact two chemical reactions (chemical species being specific defects semiconductor):

an Endothermic reaction , which generates electric charges;
an Exothermic reaction , which cancels the loads.

The reactions are not possible that if there is a circulation of loads between the two seats places of the reactions.

One can make an analogy with a thermo plant and a heating:

the thermo plant is a machine being used to transform heat into electricity;
electricity is transported until to the private individual;
this electricity is used to produce heat with a heating.

In the Peltier effect, one is interested in the capacity of the thermo plant to absorb heat.

Applications

The Peltier effect is at the base of the cooling systems by thermoelectric effect:

cooling of the Microprocessor S on-given rhythm, in order to limit their temperature. Although not very powerful, it is appreciated insofar as it does not call upon any moving part, and is not thus source of any noise pollution. But a problem persists: that of condensation. Indeed, from its nature even, the Peltier effect creates an important differential of temperature between two metal plates, and a condensation occurs then on the coldest part;
Refrigerating S food of small size (for example of car);
cooling of the solutions in the biological and medical analysis laboratories. Process used in the cooling system of the Thermocycleurs;
containers used for the transport of bodies to transplant;
applications in which the vibrations constitute a considerable embarrassment, such as for example the guidance systems Laser;
applications for which the electronic background noise is awkward, for example for the dispersive Analyze in energy;
cooling system of the cameras of astronomy;
infra-red cooling system of homing heads of air-to-air missiles, for example on AIM-9 Sidewinder or the MICA IR.

Others

One can note that the opposite phenomenon exists: a difference in temperature between the two junctions W and X can induce a Potential difference electric, it is the Seebeck effect .

Lord Kelvin showed that the Peltier effects and Seebeck are dependant, and that the Peltier coefficient is related to the coefficient Seebeck S by the relation:

$\ Pi_ {ab} =S_ {ab} T \,$

See too

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