A translation from Wikipedia
A Peltier element is an electrothermal transducer that generates based on the Peltier effect (by Jean Peltier, 1785-1845) when current flows through a temperature difference or temperature difference in a current flow (Seebeck effect). Peltier elements can both cooling as well - are used for heating - with current reversal. A standard abbreviation of Peltier elements and the Peltier cooler TEC (eng. Thermoelectric Cooler).
Table of Contents
1 principle, basics
2 advantages and disadvantages
Schematic drawing of a Peltier element
Basis of the Peltier effect, the contact of two semiconductors that a different energy level (either p-type or n-type) having the conduction bands. On passing a current through two consecutive contact points of these materials, it must be taken on the one point of contact thermal energy so that the electron reaches the higher energy conduction band of the adjacent semiconductor material, hence it comes to cool. On the other contact point, the electron from a higher to a lower energy level drops, so that here energy is emitted in the form of heat.
Since n-type semiconductor having a lower energy level of the conduction band, the cooling takes place at the point where the electrons from the n-doped in the p-doped semiconductor transition (technical current flow that is, from p-doped to n-doped semiconductor).
The effect also occurs with metals, is here, however, very low and is almost completely overlapped by the Joule heat and the high thermal conductivity.
Detailed picture of a Peltier element with the cuboid semiconductors between top and bottom
A Peltier element consists of two or more small blocks each consisting of p- and n-doped semiconductor material (bismuth telluride, silicon germanium) which are connected alternately above and below each other by means of metal bridges. The metal bridges at the same time form the thermal contact surfaces and are insulated by an overlying film or a ceramic plate. Always two different cuboid are joined together so that they form a series circuit. The supplied electric current flows through all the rectangles in sequence. Depending on current speed and direction, the upper joints cool, while the lower heat up. The current thus pumps heat from one side to the other, and produces a temperature difference between the plates.
The most common form of Peltier elements usually consists of two square plates of aluminum oxide ceramic having an edge length of 20 mm to 90 mm and a distance of 3 mm to 5 mm, between which the semiconductor cuboid are soldered. The ceramic surfaces are for this purpose provided at their facing surfaces with solderable metal surfaces.
On cooling the warm side z. B. by means of an attached heatsink with a fan, the cooling side will be even colder. The temperature difference between the two sides, depending on the element and power, be in single-stage elements to about 70 Kelvin.
The reversal of the Peltier effect is the Seebeck effect. Thus, it is possible to generate by producing a temperature difference between the two sides of a Peltier element electricity (see also thermoelectric generator, energy harvesting).
Advantages and disadvantages
The biggest advantages of a Peltier element, the small size, low weight, avoiding any moving components, gases and liquids; a refrigerator on the other hand always requires a refrigerant and in most cases a compressor.
By reversing the direction of flow is possible with Peltier elements both cooling and heating. Thus, a thermostatic control of components can be achieved, when the ambient temperature is above or below the target temperature.
A disadvantage of the Peltier elements is the low efficiency of approximately 1/10 of the Carnot efficiency, which leads to high electric power consumption at relatively low cooling power and temperature difference. Further elements are larger than 60 mm × 60 mm rarely available. Nevertheless, Peltier elements are used for many applications.
Commercial Peltier element
disrupted Peltier element
Peltier element with screws and a coin in ice on the cold side
Peltier elements can be used anywhere where cooling is required with a low temperature difference, or no efficiency requirements. Peltier elements are used for example in chest, in which the use of a refrigeration machine for lack of space prohibits or would not be profitable because the required cooling power is low.
In addition, Peltier elements are used to cool the CCD chip in a digital still camera. (Z. B. in astrophotography) This image noise is significantly reduced at slow shutter speeds. Multi-stage Peltier elements are used to cool the radiation receivers in infrared sensors.
Increasingly Peltier elements also input in a variety of laboratory instruments, in which the temperature is an essential parameter, such as in density meters, viscometers, rheometers or refractometers.
In Taupunktspiegelhygrometern usually cool one or more cascaded Peltier elements from the mirror down to -100 ° C. Here made of the fact that you can control the cooling capacity of Peltier elements quickly electrically.
Also diode lasers are often cooled with Peltier elements and thermostatically controlled, ie kept at a constant temperature in order to keep their emission wavelength and / or efficiency constant. Also downstream optical elements of diode and other lasers are often thermostatically controlled with Peltier elements.
Peltier elements can here both for cooling as well - are used for heating - with current reversal.
Likewise, Peltier elements are sporadically used as a constituent of CPU coolers. The Peltier-element enables here, the CPU cool to temperatures below the housing interior temperature, either the over-clocking of the CPU without any loss of stability permits, or increases the life of the processor. The element is in this case built at the bottom of a heatsink with fan and supplied from the power supply with the necessary power. To date, such solutions have, however due to their additional energy consumption (the used electrical energy is dissipated as heat in the housing interior!) Not enforced, but could in the near future for highly bred processors with thermal power dissipation of 150 watts and more become interesting again.
Photodiodes, z. B. for reading scintillators can be due to their small surface with Peltier elements cool, making it possible to the noise and the dark current dramatically decrease.
In diffusion cloud chambers Peltier elements are used to maintain the temperature difference between bottom and lid.
The in molecular biology now part of the basic equipment thermocycler using Peltier elements, to heat and cool, which is for example in the polymerase chain reaction necessary samples quickly.
Satellite DXler can relatively inexpensive improve the signal-to-noise ratio by cooling their packed between two Peltier elements LNB. In this way, you can also receive a bit too small satellite dish television programs outside the actual illumination zone.
Peltier elements are used in dehumidifiers sometimes. Here flows to the humid air through the cooling element through the cooling of the contained water which is collected in a collecting vessel condensed.
Commons: Peltier elements - collection of images, videos and audio files
Descriptive statement of thermoelectric effects
Application example a Peltier element for CPU cooling
Peltier Element - Startseite
test series to voltage, short circuit current and power as a function of the temperature difference
The electrical component cooling technology