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Thermoelectricity is electricity produced directly from heat. The production of electricity from heat is called the Seebeck effect, named after the German physicist Thomas J. Seebeck, who discovered the phenomenon in the 1820's.
Thermoelectricity arises in an electric circuit in which two dissimilar conductors or semiconductors are joined at their ends. When one of the junctions is at a different temperature than the other, a direct electric current will flow in the circuit. For a given thermoelectric circuit operating in a given temperature range, the magnitude of the current depends mainly on the temperature difference between the two junctions; in general, the greater the temperature difference, the larger the current.
The Seebeck effect can be reversed; that is, when a direct current is sent through a circuit in which two dissimilar conductors or semiconductors are joined at their ends, heating will take place at one of the junctions and cooling at the other. This thermoelectric effect is called the Peltier effect, after the French physicist Jean C. A. Peltier, who discovered it in the 1830's. Small heaters and refrigerators whose operation is based on this effect have been developed.
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Peltier Effect (Left) Seebeck Effect (Right)[/caption]
Theory
An explanation of the Seebeck effect requires an understanding of the behavior of electrons inside a metal. Not all the electrons inside a metal are bound to specific atoms; some are free to move about. These free electrons behave like a gas. The density of the "free" electrons (the number per unit volume) differs from metal to metal. Consequently, when two different metals are placed in contact, their electron gases diffuse into one another. Because of the different densities of the electron gases and because electrons carry an electrical charge, the metals at the junction become oppositely charged. This difference in charge produces a potential difference across the junction. The extent of diffusion of the "electron gases" depends on the temperature. If the two junctions are at different temperatures, a potential difference will exist between the junctions and a current will flow.
The especially precise, environmentally-friendly, energy-saving heating and cooling system with Peltier technology is used in the Cooled Memmert Incubator IPP, the Constant Climate Chamber HPP and the Storage Chamber IPS. Heating and cooling in a single system: If a voltage is placed across a Peltier element, one side is cooled and the opposite side simultaneously heats up. Simply by reversing the polarity of the supply voltage, the hot and cold sides of the Peltier element can be swapped.
The Peltier technology works in a particularly economical and energy-saving manner at temperatures close to ambient temperature, since energy is only required if heating or cooling is needed, in contrast to compressor technology. Very fine adjustments can be made here to the heating or cooling functions.
In heating operation, in the same way as in a heat pump, thermal energy is removed from the ambient air and introduced into the inner chamber. Because of the closed Peltier cooling system, no outside air is exchanged. The advantages: No de-humidification of the inner chamber and a notably reduced risk of contamination.
 
      
Cooling with Peltier element in the cooled incubator IPP, constant climate chamber HPP and storage chamber IPS.
The heat pump principle in the heating mode of the cooled incubator IPP, the constant climate chamber HPP and storage chamber IPS.
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