Jean Charles Athanase Peltier

The Peltier effect is the presence of heating or cooling at an electrified junction of two different conductors (1834).[6] His great experimental discovery was the heating or cooling of the junctions in a heterogeneous circuit of metals according to the direction in which an electric current is made to pass round the circuit. This reversible effect is proportional directly to the strength of the current, not to its square, as is the irreversible generation of heat due to resistance in all parts of the circuit. It is found that, if a current pass from an external source through a circuit of two metals, it cools one junction and heats the other. It cools the junction if it be in the same direction as the thermoelectric current which would be caused by directly heating that junction. In other words, the passage of a current from an external source produces in the junctions of the circuit a distribution of temperature which leads to the weakening of the current by the superposition of a thermo-electric current running in the opposite direction.[4]

When electromotive current is made to flow through an electronic junction between two conductors (A and B), heat is removed[7] at the junction. To make a typical pump, multiple junctions are created between two plates. One side heats and the other side cools. A dissipation device is attached to the hot side to maintain cooling effect on the cold side.[8] Typically, the use of the Peltier effect as a heat pump device involves multiple junctions in series, through which a current is driven. Some of the junctions lose heat due to the Peltier effect, while others gain heat. Thermoelectric pumps exploit this phenomenon, as do thermoelectric cooling Peltier modules found in refrigerators.[9]

The Peltier effect generated at the junction per unit time, ${\displaystyle {\dot {Q}}}$, is equal to

${\displaystyle {\dot {Q}}=\left(\Pi _{\mathrm {A} }-\Pi _{\mathrm {B} }\right)I,}$

where,

${\displaystyle \Pi _{A}}$ (${\displaystyle \Pi _{B}}$) is the Peltier coefficient[10][11] of conductor A (conductor B), and

${\displaystyle I}$ is the electric current (from A to B).

Note: Total heat generated at the junction is not determined by the Peltier effect alone, being influenced by Joule heating and thermal gradient effects.

The Peltier coefficients[10][11] represent how much heat is carried per unit charge. With charge current continuous across a junction, the associated heat flow will develop a discontinuity if ${\displaystyle \Pi _{A}}$ and ${\displaystyle \Pi _{B}}$ are different.

The Peltier effect can be considered as the back-action counterpart to the Seebeck effect (analogous to the back-emf in magnetic induction[12]): if a simple thermoelectric circuit is closed then the Seebeck effect will drive a current, which in turn (via the Peltier effect) will always transfer heat from the hot to the cold junction.

The true importance of this "Peltier effect" in the explanation of thermoelectric currents was first clearly pointed out by James Prescott Joule; and Sir William Thomson[13] further extended the subject by showing, both theoretically and experimentally, that there is something closely analogous to the Peltier effect when the heterogeneity is due, not to difference of quality of matter, but to difference of temperature in contiguous portions of the same material. Shortly after Peltier's discovery was published, Lenz used the effect to freeze small quantities of water by the cold developed in a bismuth-antimony junction when a voltaic current was passed through the metals in the order named.[4]