Thermoelectric coolers (TEC) operate by the Peltier effect (which also goes by the more general name thermoelectric effect). The device has two sides, and when DC current flows through the device, it brings heat from one side to the other, so that one side gets cooler while the other gets hotter.
The "hot" side is attached to a heat sink so that it remains at ambient temperature, while the cool side goes below room temperature. In some applications, multiple coolers can be cascaded together for lower temperature.
Two unique semi-conductors, one n-type and one p-type, are used because they need to have different electron densities. The semi-conductors are placed thermally in parallel to each other and electrically in series and then joined with a thermally conducting plate on each side.
When a voltage is applied to the free ends of the two semiconductors there is a flow of DC current across the junction of the semi-conductors causing a temperature difference. The side with the cooling plate absorbs heat which is then moved to the other side end of the device where the heat sink is. TECs are typically connected side by side and sandwiched between two ceramic plates. The cooling ability of the total unit is then proportional to the number of TECs in it.
Some benefits of using a TEC are:
- No moving parts so maintenance is required less frequently
- No chlorofluorocarbons
- Temperature control to within fractions of a degree can be maintained
- Flexible shape (form factor); in particular, they can have a very small size
- Can be used in environments that are smaller or more severe than conventional refrigeration
- Has a long life, with mean time between failures (MTBF) exceeding 100,000 hours
- Is controllable via changing the input voltage/current
Some disadvantages of using a TEC are:
- Only a limited amount of heat flux is able to be dissipated
- Relegated to applications with low heat flux
- Not as efficient, in terms of coefficient of performance, as vapor-compression systems
A single-stage TEC will typically produce a maximum temperature difference of 70°C (158°F) between its hot and cold sides. Thermoelectric coolers are typically used for applications that require heat removal ranging from milliwatts to several thousand watts. They can be made for applications as small as a beverage cooler or as large as a submarine or railroad car.
In video below you can see Peltier element in action. We put hot side of it at heat sink to ensure that this side stays at ambient temperature of about 23 °C. By applying 12V to its connector, Peltier element makes temperature difference of almost 70°C, making other side of it extremely cold. See what happened when we put some metal parts and few drops of watter on it :) Cool right?
After few minutes this is how it looked
Great thing about Peltier element is that when you change polarity it also work but hot and cold sides switch place. In this way you can regulate temperature in range of Troom temperature±70°C. Here is what happened when we reversed power supply polarity and now cold side is at room temperature while hot side, which is still frozen from experiment on first video, is at +70°C warmer than it.
This pocess is reverseble, menaning if you make temperature difference between Peltier element two sides, it will generate voltage on its connector. This characteristic is used in thermal energy harvesting applications. We measured geneated voltage on Peltier element when one side is kept on room temperature, while other side is heated using human body temperature by touching it with hand. You can see it on next video:
Peltier elements are commonly used in consumer products. For example, Peltier elements are used in camping, portable coolers, 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. A camping/car type electric cooler can typically reduce the temperature by up to 20°C (36°F) below the ambient temperature. With feedback circuitry, peltiers can be used to implement highly stable temperature controllers that keep desired temperature within +/-0.01 Celsius. Such stability may be used in precise laser applications to avoid laser wavelength drifting as environment temperature changes. Climate-controlled jackets are beginning to use Peltier elements. Thermoelectric coolers are used to replace standard heat sinks for microprocessors because they actively cool the module while heat sinks only provide passive cooling.
The vast majority of TECs have an ID printed on their heated side.
These universal IDs clearly indicate the size, number of stages, number of couples, and current rating in amps, as seen in the adjacent diagram.
Partial source: wikipedia