The theories behind the operation of thermoelectric cooling first appeared in the early 1800s.
- Jean Peltier discovered a heating/cooling effect when passing electric current through the junction of two conductors.
- Alessandro Volta and Thomas Seebeck found that holding the junctions of two dissimilar conductors at different temperatures creates an electromotive force or voltage.
- William Thomson (Lord Kelvin) showed that over a temperature gradient, a single conductor with current flowing in it has reversible heating and cooling.
With these principles developed and the introduction of semiconductor materials in the late 1950s, thermoelectric cooling became a viable technology for small cooling applications.
A thermoelectric cooler (TEC), sometimes called a thermoelectric module or Peltier module, is a semiconductor-based electronic component that functions as a small heat pump.
By applying a low-voltage DC power source to a TEC, heat flows via the semiconductor elements from one face to the other. The electric current cools one face and simultaneously heats the opposite face.
Consequently, a given face of the device can be used for heating or cooling by reversing the polarity of the applied current. The characteristics of TECs make them highly suitable for precise temperature control applications and where space limitations and reliability are paramount or refrigerants are not desired.
A typical single-stage cooler consists of two ceramic plates with “elements” of p-type and n-type semiconductor materials (bismuth telluride alloys) between the plates. Figure 1 illustrates a single-couple; an array of these comprises a single-stage cooler. The elements of semiconductor materials are connected electrically in series and thermally in parallel.
When a positive DC voltage is applied as shown, electrons pass from the p-type to the n-type element, and the cold-side temperature decreases as the electron current absorbs heat, until equilibrium is reached. The heat absorption (cooling) is proportional to the current and the number of thermoelectric couples. This heat is transferred to the hot side of the cooler, where it is dissipated into the heat sink and surrounding environment.