Peltier effect

When an electric current crosses a junction between two different conductors or semiconductors, heat is absorbed at one junction and released at another. Which junction warms and which cools depends on the materials and current direction; reversing the current reverses the heat-transfer direction. The process is distinct from ordinary resistive heating, although electrical resistance also produces Joule heat and affects a device’s net cooling performance.

Practical thermoelectric coolers generally use semiconductor elements arranged electrically in series and thermally in parallel between two ceramic plates. With direct current applied, one face absorbs heat and the opposite face releases it. Reversing current can switch the module from cooling to heating. Unlike compressor-based refrigeration, this solid-state approach has no moving parts within the module, which can make it useful for compact temperature control. The Peltier element does not make heat disappear: its hot side must reject both the heat pumped from the cooled object and the electrical power dissipated in the device.

A thermoelectric module’s performance depends on the heat load, current, temperature difference between its faces, and the surrounding heat-rejection system. More current is not always better: resistive heating increases with current, and beyond a suitable operating point it can reduce useful cooling. A heat sink—often assisted by a fan—must carry heat away from the hot face; inadequate heat rejection raises its temperature and undermines cooling. Engineers therefore select a module and operating point for the actual load and temperature range, rather than treating a published maximum temperature difference as a guaranteed operating condition.

The effect was reported by French physicist Jean-Charles-Athanase Peltier in 1834 while he investigated electrical circuits made from different materials. It is one of the thermoelectric effects. The Seebeck effect describes the production of an electrical voltage when dissimilar conductors experience a temperature difference; the Thomson effect concerns reversible heating or cooling along a current-carrying conductor with a temperature gradient. Together, these effects help describe thermoelectric energy conversion and temperature-control devices.