Principles of Thermoelectricity
Two basic thermoelectric effects were discovered in the XIX century by European scientists. The first was Thomas Seebeck, who in 1821 discovered the phenomenon of direct conversion of heat into electric power; the second one was Jean Peltier, who discovered a solid state heat pump. In the period from 1940 through the 1950’s the Russian academic A.F. Ioffe and his colleagues synthesized semiconductor alloys, which put these effects into practice and that enabled full-scale production of thermoelectric cooling and power generating devices for wide use in various fields of human activity. A basic thermoelectric unit is a thermocouple, which consists of p-type and n-type semiconductor elements, or pellets. Copper commutation tabs are used to interconnect pellets that are traditionally made of Bismuth Telluride-based alloy.
Usually thermocouples are combined with a module where they are connected electrically in series and thermally in parallel between two ceramic plates. Peltier phenomenon consists of the following. A contact potential difference always appears at the point of junction of two different metals or semiconductors. If the electric current passes through them the potential difference at the junction assists or counteracts the flow. So as the current passes against the field of the potential difference the electrical source needs to expend additional energy to make the current pass through the junction and this additional energy consumption results in heat energy output at the junction. If the field of the potential difference has the same direction as the current the field supports it and enforces the movement of the charges. This energy is drawn from the substance and as a result the temperature at the junction is reduced. So, one side of the thermoelectric module is cooled and the other is heated. If the heat dissipation from the thermoelectric module’s hot side is provided efficiently, for example by a heatsink, the temperature of the cold side could get down to tens of degrees below the ambient temperature. In case the current changes its polarity the hot and cold sides would invert.