Peltier Effect Discovery
Peltier effect was discovered by a French physicist Jean-Charles Peltier (1785-1845) in 1834, when during one of his experiments he ran the current through bismuth stripe with copper conductors attached. In the course of experiment he revealed that one bismuth-copper junction heats up while the other cools down.
The scientist himself didn’t realize in full the essence of the phenomenon discovered – its true gist was explained later (in 1838) by the other scientist – famous Russian physicist Emiliy Lenz.
In his tests Lenz was experimenting on the drop of water placed on the junction of two conductors – bismuth and stibium. Water drop froze when current passed in one direction and melted when the current ran in opposite direction. Thereby it was determined that whenever current passes two conductors junction in one direction the heat is released, and while passing the other direction it is absorbed. This phenomenon is referred to as Peltier effect.
In comparison to Joule-Lenz heat, which is in proportion to square current (Q = R·I·I·t), heat according to Peltier is in proportion to first degree current strength and can be expressed through formula:
Qп = P · q
where “q” is energy supply that runs through junction, “P” – so-called Peltier coefficient, which depends on the nature of contacting materials and their temperatures. Peltier coefficient can also be expressed with Thomson coefficient:
P = a · T
where “a” is Thomson coefficient and “T” – absolute temperature.
Classic theory explains Peltier effect in the following way – while electrons are transferred by current from one metal to another they are slow or accelerated by inner contact potential difference between the metals. During acceleration electron’s kinetic energy increases and then is released as a heat. In the opposite case kinetic energy decreases and is replenished at the expense of atom thermal vibrations energy of the second conductor and the cooling process begins.
On a more full examination full energy changes are taken into consideration alongside with the potential energy ones.
It was founded out only in the 20th century that Peltier effect shows more apparently when conductors of dissimilar types are connected.
Depending on the current direction through p-n and n-p junctions as a result of charge interactions represented by electrons (n) and opening (p) and their recombination energy is either absorbed or released. A multitude of p- and n- types conductors aggregated can create a cooling element – thermoelectric Peltier modules of relatively big power.
Peltier Effect Application
Taking classic thermoelectric modules manufacturing technology into consideration it can be noted that very special and at times diversified requirements which are not easy to meet are established. Conductor has to have good thermal conductivity, serve as an insulator and be mechanically solid. As of today the majority of manufacturers use ceramics when producing thermoelectric Peltier elements.
In spite of mass production and use, ceramics has number of disadvantages, being, in the first place, a brittle material. That is why in order to achieve necessary strength there is a need to form thicker ceramic layer which in turn substantially lessen thermal conductivity. Use of ceramics also creates additional complications during the mounting – use of lapping pastes and special instruments.
CERATOM® technology presupposes that an essentially different type of conductor is used. TERMIONA’s thermoelectric systems are made of aluminum, which lets solve all tasks of thermoelectric modules application due the fact that aluminum has much extended thermal conductivity level then the ceramics.
