Peltier effect was discovered by a Frenchman Jean Charles Peltier (1785-1845) in 1834. During one of experiments he made the current to flow through a bismuth strip with copper conductors connected to it. During the experiment it was discovered that one connection bismuth-copper heats up, while another one cools down.
The scientist himself did not understand the essence of the phenomenon discovered by him to the full extent. The true meaning of the phenomenon was explained later (in 1838) by another scientist – a famous Russian physicist Emil Christianovich Lenz.
In his experience Lenz experimented with a water drop placed on the junction of two conductors — bismuth and antimony. When the current was made to flow in one direction, the water drop froze, and changing the current direction — melted. Thus, it was established that during the current flow through the junction of two conductors in one direction the heat is generated, in another — absorbed. This phenomenon was called Peltier effect.
In contrast to Joule-Lenz’s heat which is proportionate to the current intensity square (Q = R·I·I·t), Peltier heat is proportionate to the current intensity in the first degree and can be expressed by the formula:
Qп = П · q
where q &mdashis a charge flowing through the contact, П — is a so-called Peltier coefficient that depends on the nature of contacting materials and their temperature. Peltier coefficient can be expressed through Thomson coefficient:
П = a · T
where a — Thomson coefficient, T — the absolute temperature.
The classic theory explains Peltier phenomenon that with the transfer of electrons by current from one metal to another they accelerate or slow down by the internal contact difference of potentials between metals. In case of acceleration, the kinetic energy of electrons increases, and then discharged in the form of heat. Otherwise, the kinetic energy decreases, and the energy is replenished for the account of the energy of thermal vibrations of atoms of the second conductor, thus a cooling process begins. With the fuller consideration the change of not only potential but also complete energy is taken into consideration.
In the 20th century already, it was discovered that Peltier effect is expressed much stronger during the connection of different type semi-conductors. Depending on the direction of the electric current flow through p-n and n-p- transitions due to the interaction of charges represented by electrons (n) and openings (p), and their recombination, the energy is either absorbed or discharged, in this connection the heat is absorbed or generated. The combination of a large number of pairs of semiconductors of p- and n-type enable creation of cooling elements – Peltier thermoelectric modules of comparatively high power.
Peltier Effect Application
Studying the classic production technology of thermoelectric modules it was noted that special and sometimes diverse requirements were imposed to the heating line material that were hard to combine. Thus, the heating line should have good thermal permeability, serve as an insulator, and satisfy the needs of mechanical reliability. Today, most manufacturing companies use ceramics to produce heating lines.
Notwithstanding wide application, ceramics has a number of disadvantages being, in the first place, a brittle material, that is why to achieve the required strength it is required to form a heavy gage layer of ceramics that, in its turn, reduces the thermal conductivity of the heating line abruptly. At the same time, the application of ceramics preconditions additional complexities during the assembly of thermoelectric modules, such as the use of special instruments and lapping compounds.
The innovative technology developed by «THERMOINTECH» Company supposes the use of a principally another heating line. In thermoelectric systems the heating line is made of aluminum. Therefore, it is possible to avoid most drawbacks of ceramic heating lines, because aluminum heating line has higher thermal conductivity and reliability than ceramic one.