Written By: Aleksey Moshkov, Lead Engineer for EnvisionSTEM
The thermoelectric effect involves the interaction of electricity and temperature, made up of three different effects: the Seebeck effect, the Peltier effect, and the Thomson effect. Together, these effects describe the conversion between heat energy and electrical energy.
Seebeck effect
The Seebeck effect is a phenomenon that occurs when a voltage is generated due to a temperature difference between two wires made of different materials. To produce this effect, three key requirements must be met: the use of two wires composed of different conductors, a closed loop circuit, and a temperature gradient across the wires. However, the voltage generated by the Seebeck effect is typically very small, usually on the scale of microvolts. In order to enhance the effectiveness of this effect, multiple junctions can be connected in parallel to generate a usable voltage. Additionally, the Seebeck effect is used to convert waste heat produced from resistive conductors into useful electrical power.
The Seebeck coefficient is a parameter of conductors used to determine the voltage produced by the Seebeck effect in response to a temperature difference. It can have positive and negative values, depending on the type of charge carriers involved. A positive Seebeck coefficient is observed when the charge carriers are positive, such as electron holes, while a negative Seebeck coefficient is observed when the charge carriers are negative, such as electrons.
Peltier Effect
The Peltier effect occurs when a current is passed through a junction between two dissimilar conductors, resulting in the production or absorption of heat at a junction. The Peltier coefficient represents the amount of heat energy carried per unit charge during the Peltier effect. This coefficient is specific to the metals involved in the junction and is proportional to the Seebeck coefficient. The Peltier effect is used in Peltier coolers for thermoelectric cooling and heating systems. These devices transfer heat from one side of the device to the other, cooling one side, while heating up the other.
Thomson Effect
The Thomson effect refers to a phenomenon observed in conductors when an electric current carries a temperature difference along its length. When a conductor with an electric current experiences a temperature gradient, heat is either absorbed or expelled on both sides of the gradient. This occurs because the heat gradient in the wire causes the electrons to become more mobile. As a result, the current forces the free electrons to accumulate on one side, making it more electron-dense and reducing their mobility, which leads to a cooling effect. Consequently, the other side of the conductor, which has fewer electrons, provides more space for electron movement, resulting in increased electron mobility and consequent heating of the conductor.
Positive Thomson Effect
If a copper, silver, zinc, or cadmium wire is heated in the middle while the ends remain at a normal temperature, the temperature gradient is established along the wire. When an electric current passes through the wire in the direction of the current flow, heat is absorbed until the temperature gradient and heat is released past the point of the temperature gradient.
Negative Thomson Effect
If an iron, platinum, nickel, cobalt, or mercury wire is heated in the middle while the ends are at a normal temperature, the temperature gradient is again established. However, in this case, when an electric current flows through the wire in the direction opposite to the current flow, heat is transferred from the cold region to the hot region. This behavior is referred to as the negative Thomson effect.
Comments