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Dufour Effect

The Dufour effect is the energy flux due to a mass concentration gradientoccurring as a coupled effect of irreversible processes. It is the reciprocalphenomenen to the Soret effect.

The inverse phenomenon of thermal diffusion. If two chemically different nonreacting gases orliquids, which were initially at the same temperature, are allowed to diffuse into each other, thenthere arises a difference of temperatures in the system. In gases this difference can reach severaldegrees (for example, for nitrogen with hydrogen), while in liquids it measures approximately103C. The difference in temperatures is retained if a concentration gradient is maintained. Theeffect was first observed by the Swiss physicist L. Dufour in 1873

Thermophoresis, thermodiffusion, orSoret effect (orLudwig-Soret effect)

Soret effect is a phenomenon observed when a mixture of two or more types of motile particles(particles able to move) are subjected to the force of a temperature gradient and the differenttypes of particles respond to it differently. The term "Soret effect" normally meansthermophoresis in liquids only. The term "thermophoresis" is most often intended to mean thebehavior in aerosols, not liquids, but the broader meaning is also common. The mechanisms ofthermophoresis in liquid mixtures differ from those in gas mixtures, and are generally not as wellunderstood.

The phenomenon is observed at the scale of one millimeter or less. An example that may beobserved by the naked eye with good lighting is when the hot rod of an electric heater issurrounded by tobacco smoke: the smoke goes away from the immediate vicinity of the hot rod.As the small particles of air nearest the hot rod are heated, they create a fast flow away from therod, down the temperature gradient. They have acquired higher kinetic energy with their highertemperature. When they collide with the large, slower-moving particles of the tobacco smoke

they push the latter away from the rod. The force that has pushed the smoke particles away fromthe rod is an example of a thermophoretic force. Seebeck effect.

Diagram of the circuit on which Seebeck discovered theSeebeck effect. A and B are two different metals.

The Seebeck effect is the conversion of temperaturedifferences directly into electricity and is named for

German physicist Thomas Johann Seebeck, who, in 1821discovered that a compass needle would be deflected by aclosed loop formed by two metals joined in two places,with a temperature difference between the junctions. Thiswas because the metals responded differently to thetemperature difference, creating a current loop and amagnetic field. Seebeck did not recognize there was anelectric current involved, so he called the phenomenon the

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thermomagnetic effect. Danish physicist Hans Christian rsted rectified the mistake and coinedthe term "thermoelectricity". The voltage created by this effect is on the order of severalmicrovolts per kelvin difference. One such combination, copper-constantan, has a Seebeckcoefficient of 41 microvolts per kelvin at room temperature.[2]

The voltage Vdeveloped can be derived from:

where SA and SB are the thermopowers (Seebeck coefficient) of metals A and B as a function oftemperature and T1 and T2 are the temperatures of the two junctions. The Seebeck coefficients arenon-linear as a function of temperature, and depend on the conductors' absolute temperature,material, and molecular structure. If the Seebeck coefficients are effectively constant for themeasured temperature range, the above formula can be approximated as:

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