What is Thermoelectricity and how is it related to Peltier, Seebeck and Thomson effects

What is Thermoelectric effect

The thermoelectric effect can be described as the direct conversion of temperature differences to electric voltage and vice versa. A thermoelectric device can create a voltage when there is a different temperature on each side and when a voltage is applied to it then it will create a temperature difference and this process is called as Peltier effect. At the atomic scale, an applied temperature gradient causes charged carriers to diffuse from the hot side to the cold side, hence current will be induced thermally. By using this effect we can generate electricity, measure temperature, objects can be cooled or heated. The direction of cooling and heating is determined by the polarity of the applied voltage. Thermoelectric devices can be used as a temperature controller.

What is Thermoelectricity

Thermoelectricity can be considered as the combination of two processes, it can either be the way a temperature difference between one side of the material and the other can produce electricity or to the reverse the way by which applying electric current through a material can create a temperature difference between its two sides, and this can be used to heat or cool things. The thermoelectric effect or thermoelectricity is depended on three separately identified effects they are the Seebeck effect, the Peltier effect and Thomson effect.

What is Peltier effect

When a voltage or DC current is applied to two dissimilar conductors then a circuit can be which allows the continuous heat transport between the conductor junctions. The current is transported through the charge carriers and the transfer of the heat occurs in the direction of charge carrier movement, by applying the current heat can be transported from the warmer side to the colder side.

Thermoelectricity is also known as a peltier-Seebeck effect. When the dissimilar metal devices were replaced by a semiconductor peltier the result was it produced larger thermal gradients. At the junction of two dissimilar metals, the energy level of conducting electrons is forced to increase or decrease, a decrease in energy level will emit thermal energy while in case of the increased energy level absorption of thermal energy also increases.

What is Seebeck effect

Seebeck effect is the conversion of temperature differences directly into electricity, and its efficiency is represented by the Seebeck coefficient. Which is defined as the ratio of generated electric voltage to the temperature difference, and it is determined by the scattering rate and the density of the conduction electrons. It can also be described as the temperature difference between two points in a conductor or a semiconductor results in difference in voltage between these two points. It could give rise to a built-in electric field and this is called the Seebeck effect or thermoelectric effect.

The spin Seebeck effect refers to the generation of spin voltage as a result of temperature gradient and this spin voltage generated from a temperature gradient can be measured by a metallic magnet, this thermally induced spin voltage persists even at distances far from the sample ends and spins can be extracted from every position on the magnet simply by attaching a metal. The spin Seebeck effect is applicable to the production of spin-voltage generators

What is Thomson effect

Thomson effect can be described as the absorption of the heat which occurs whenever an electric current traverses a temperature gradient along a single homogeneous conductor regardless of whether the current is supplied externally or is induced by the thermocouple itself. The Thomson effect occurs along the legs of the thermoelectric circuit and is associated with temperature gradients and Thomson effect is only concerned with the heat exchange, not the voltage.

Any current-carrying conductor with a temperature difference between two points either absorbs or emits heat. In certain metals like zinc or copper, whose temperature is directly proportional to their potential, when current moves from the hotter end to the colder end, there is a generation of heat and it is the positive Thomson effect. In metals such as cobalt and iron, whose temperature is inversely proportional to their potential, when current moves from the hotter end to the colder end, there will be the absorption of the heat and negative Thomson effect is occurred.

What are the laws of thermoelectric circuits

The Law of homogeneous metals

Thermoelectric current cannot be sustained in a circuit of single homogeneous material, however varying in cross-section, by the application of the heat alone

The Law of intermediate metals

The algebraic sum of the thermo-electromotive forces in a circuit composed of any number of dissimilar materials is zero if all of the circuit is at a uniform temperature.