Thermoelectric cooling

Thermoelectric cooling uses the Peltier effect to create a heat flux between the junction of two different types of materials. A Peltier cooler, heater, or thermoelectric heat pump is a solid-state active heat pump which transfers heat from one side of the device to the other side against the temperature gradient (from cold to hot), with consumption of electrical energy. Such an instrument is also called a Peltier device, Peltier diode, Peltier heat pump, solid state refrigerator, or thermoelectric cooler (TEC). [http://www.redfishphotonics.com/thermoelectric_coolers.htm] Because heating can be achieved more easily and economically by many other methods, Peltier devices are mostly used for cooling. However, when a single device is to be used for both heating and cooling, a Peltier device may be desirable. Simply connecting it to a DC voltage will cause one side to cool, while the other side warms. The effectiveness of the pump at moving the heat away from the cold side is totally dependent upon the amount of current provided and how well the heat from the hot side can be removed.

Peltier devices can also be used to generate electricity (thermogenerator) if a temperature difference is maintained between the two sides.

Performance

Thermoelectric junctions are generally only around 5–10% as efficient as the ideal refrigerator (Carnot cycle), compared with 40–60% achieved by conventional compression cycle systems (reverse Rankine systems like a compressor). Due to the relatively low efficiency, thermoelectric cooling is generally only used in environments where the solid state nature (no moving parts, maintenance-free) outweighs pure efficiency.

Peltier (thermoelectric) cooler performance is a function of ambient temperature, hot and cold side heat exchanger (heat sink) performance, thermal load, Peltier module (thermopile) geometry, and Peltier electrical parameters.

Uses

Peltier devices are commonly used in camping and portable coolers and for cooling electronic components and small instruments. The cooling effect of Peltier heat pumps can also be used to extract water from the air in dehumidifiers.

The effect is used in satellites and spacecraft to counter the effect of direct sunlight on one side of a craft by dissipating the heat over the cold shaded side, whereupon the heat is dissipated by thermal radiation into space.

Photon detectors such as CCDs in astronomical telescopes or very high-end digital cameras are often cooled down with Peltier elements. This reduces dark counts due to thermal noise. (A dark count is the event that a pixel gives a signal although it has not received a photon but rather mistook a thermal fluctuation for one. On digital photos taken at low light these occur as speckles (or "pixel noise").

Thermoelectric coolers can be used to cool computer components to keep temperatures within design limits without the noise of a fan, or to maintain stable functioning when overclocking. A Peltier cooler with a heat sink or waterblock can cool a chip to well below ambient temperature.

Underlying principles

Thermoelectric coolers rely on the thermoelectric effect. When a current is run through an appropriately-configured thermoelectric device, heat is transported from one side of the device to the other.

See also

* Bismuth telluride, an efficient thermoelectric material
* Freezer, Refrigerator
* H₂Ceramic cooling - a hybrid combination of thermoelectric and liquid cooling
* Heat transfer
* Joule's law
* Pyroelectric effect - the creation of an electric field in a crystal after uniform heating
* Thermionic emission
* Thermoelectrics
* Thermoelectric effect
* Thermoelectricity
* Thermopower
* Thermotunnel cooling
* Thermoacoustics - competitor technology to thermoelectric cooling

External links

* [http://www.novelconceptsinc.com/ Online Peltier (thermoelectric) Calculators]
* [http://www.tellurex.com/cthermo.html Tellurex thermoelectric module]
* [http://www.customthermoelectric.com/TECmounting.html Custom Thermoelectric module mounting]
* [http://www.nextreme.com/pages/applications/ic_thermal.html Nextreme Thermoelectric Coolers]