Peltier Cells/Thermoelectric devices - Basics
| What does “Peltier” mean? | Named after Jean Peltier, who discovered the thermoelectric cooling effect in 1834. Thermoelectric cooler, or TEC, is a descriptive term even though they also heat. | ||||
| What does it do? | Used in many laboratory instruments for small heating and/or cooling applications. | ||||
| Theory | The principle behind thermoelectric devices was first discovered
in 1821 by Thomas Seebeck. He observed that if a closed circuit
was made from two dissimilar metals, an electric current flowed
when the junctions were maintained at different temperatures.
The reverse of this – application of a DC voltage to a
closed circuit comprising dissimilar metals gives rise to a
temperature change at the junction of the dissimilar metals.
Modern cells use semiconductors, usually Bismuth Telluride. As a DC current passes from N to P material, there is a decrease in temperature at the cold junction, resulting in absorption of heat from the environment. The heat is carried through the device by electron transport and released on the opposite (hot) side as the electrons move from a high to low energy state. The amount of heat is proportional to the current and the number of PN junctions. |
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| How it works |
Heat is emitted or absorbed at the junction depending on the
direction of current flow. The Peltier cell is made up of many junctions connected electrically in series. The junctions are laid out flat (thermally in parallel), and sandwiched between two ceramic plates. A typical application exposes the cold side ceramic plate to the object to be cooled and the hot side plate to a heat sink which dissipates the heat to the environment. Some equipment, such as Thermal Cyclers require to TEC to both heat and cool at different parts of the cycle. Very precise temperature control is possible using TEC’s connected to a temperature controller. The Peltier cells have the advantages of no moving parts, light weight, may be used in any orientation, in a vacuum and in zero gravity. They may be stacked to achieve greater temperature differential. |
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| Units of measurement | Degrees Celsius °C, Watts | ||||
| Typical values |
125 Watts per unit maximum 60°C differential between the sides. They are limited to small heating or cooling applications. |
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| Pictures of equipment | |||||
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