Peltier Effect
Pass electric current through a junction of two dissimilar semiconductors and one side gets cold while the other gets hot. This is the Peltier effect — thermoelectric cooling without any moving parts. Watch electrons and holes carry heat energy across the junction as a thermal gradient develops in real time. Adjust the current to see how cooling power, temperature difference, and coefficient of performance change.
Q˙ = Π · I = S · T · I · COP = Qc / (Ptotal) · Π = S · T (Peltier coefficient)
The Peltier effect
Discovered by Jean Charles Athanase Peltier in 1834, the Peltier effect occurs when electric current flows through a junction of two different conductors or semiconductors. Depending on the direction of current, heat is either absorbed or released at the junction. This is the reverse of the Seebeck effect, where a temperature difference generates a voltage. Together, these phenomena form the basis of thermoelectric devices used for solid-state cooling and power generation.
How Peltier coolers work
A practical Peltier cooler consists of many pairs of N-type and P-type semiconductor elements (typically bismuth telluride, Bi2Te3) connected electrically in series and thermally in parallel. When current flows, electrons in the N-type material and holes in the P-type material both move away from the cold junction, carrying thermal energy with them. The cold side absorbs heat from its surroundings (cooling), while the hot side releases that heat plus the Joule heating from the electrical resistance. The net cooling power is Qc = S·Tc·I − ½I²R − K·ΔT.
Coefficient of performance
The COP of a Peltier cooler is the ratio of cooling power to electrical input power: COP = Qc / Pin. Unlike mechanical refrigeration (which can have COP > 1), thermoelectric coolers typically have COP < 1 at large temperature differences. Their advantage lies in having no moving parts, precise temperature control, compact size, and the ability to both heat and cool by reversing current direction. They are widely used in CPU coolers, portable refrigerators, laser diode temperature stabilization, and scientific instruments.
The Seebeck coefficient
The Seebeck coefficient S (measured in V/K) quantifies how much voltage a material generates per degree of temperature difference. For a good thermoelectric material, the figure of merit ZT = S²σT/κ should be as large as possible, where σ is electrical conductivity, κ is thermal conductivity, and T is absolute temperature. The Peltier coefficient Π = S·T relates to the heat carried per unit charge at the junction.