Peltier Information
Thermoelectric phenomenon was discovered more than 180 years ago. However, it enjoyed its practical application in the middle of the XX century, 130 years later after its discovery thanks to the research work of Soviet academician Abram Ioffe.
Still, the pioneer in thermoelectrics was a German scientist Thomas Johann Seebeck (1770-1831), who was born in the Estonian town Revel. In 1822 he summarized the results of his experiments in the article called The Magnetic Polarization of Metals and Ores Produced by Temperature Difference (Magnetische Plarisation der Matalle und Erze durch Temperatur-Differenz. Abhandlungen der Preussischen Akad, Wissenschaften, pp 265-373) that was published in the Proceedings of the Prussian Academy of Sciences. Seebeck discovered that if the ends of the circuit consisting of two heterogeneous metals soldered under different temperature conditions were closed, a magnetic needle placed near it would rotate as if there were a magnet applied. The angle of rotation depended on the value of the temperature difference at the circuit junctions. This physical phenomenon is referred to as the Seebeck's effect.
However two years earlier, in 1820 Hans Christian Oersted (1777-1851) proved that electrical current affected the magnetic needle. Later on as Ampere, Biot, Savart, Laplace, and other scientists studied the interaction of electrical current and magnetic field, Seebeck disclaimed the electrical nature of the phenomenon. As the name of his article demonstrates, his scientific idea concerned magnetization of materials under temperature difference. According to this hypothesis, the Earth was like a gigantic circuit where temperature difference was kept with the two cold poles and with the hot equator. At least, this was Seebeck's point of view on the Earth magnetism.
Hans Oersted, who followed the thread of Seebeck's research work with much attention, was the first who named this phenomenon thermoelectric effect. Seebeck himself insisted on the name of thermomagnetism.
Seebeck gathered much research material that dealt with circuits consisting of various combinations of hard and liquid metals, alloys and compositions of metals and effect of temperature difference on them. Basing on this research work, he founded "thermoelectric row", which is still in use along with those, which were composed later.
The Peltier effect was discovered in 1834, 12 years later after Seebeck's breakthrough. Compared with the Seebeck's effect this is a counter phenomenon. The Peltier effect occurs whenever current passes through the circuit of two dissimilar conductors; depending on the current direction, the junction of the two conductors either absorbs or releases heat.
This phenomenon was discovered by French physicist and meteorologist Jean Charles Athanase Peltier (1785-1845). By the way, physics was just a hobby for him. Previously, he worked as a watchmaker at Brege. In 1815 after he inherited some property, he decided to devote himself to his hobby, in other words, he decided on conducting physical experiments and doing meteorological observations.
Like Seebeck, Peltier interpreted the results of his research work in a wrong way. For example, his discovery stated that the Joule - Lenz law, which determined that current passing through circuit releases heat, was not valid when low current passed through the circuit.
Only in 1838 Russian academician Emily Lenz (1804-1865) proved that the Peltier Effect was an autonomous physical phenomenon, which consisted in releasing and absorbing of additional heat on conductor's junctions when current passed through them. Moreover, the nature of the process (heat absorption or release) depended on current direction.
Twenty years later William Thomson (later Lord Kelvin) issued a comprehensive explanation of the Seebeck and Peltier Effects and described their interrelationship. This thermodynamic derivation made it possible for Thomson to predict the third thermoelectric effect, now known as the Thomson effect. In the Thomson effect, heat is absorbed or produced when current flows in material with a certain temperature gradient. The heat is proportional to both the electric current and the temperature gradient.
The discoveries triggered the development of a new engineering field - thermo power engineering, which studies processes of conversion of thermal energy into electrical power (the Seebeck Effect) and thermoelectric heating and cooling (the Peltier Effect) as well.
As mentioned before, the outstanding Russian scientist, great expert in physics, academician Abram Ioffe was one of the primary investigators of thermoelectric phenomenon (1880-1960). His research work run in the early 30th served as the basis for the future development of thermoelectric power engineering.
Kryotherm carries on traditions founded by Abram Ioffe and his research institute. Within the last ten years our engineers and researchers have done a great breakthrough in the development of high effective thermoelectric materials and manufacturing of cooling devices and power generating systems based on the Peltier effect. The range of thermoelectric applications grows constantly. Following this trend, Kryotherm constantly widens its product range.
We are sure that environmentally friendly cooling devices and power generating systems based on thermoelectric effect would be the core of the most prospective technologies of the future.
TEM Construction
Thermoelectric modules (TEMs) enjoy their primary application of diverse cooling. However, they can be equally used for power generation. Thermoelectric generating modules and coolers are constructed in the same way due to the similarity of the physical processes occurring in them. The major difference between them lies in the assembly techniques employed and the composition of semiconductor material. To give a general outline of how thermoelectric generating modules and coolers are made up, the construction of a most typical cooler is described below.
TEMs utilize the effect that was discovered by Jean Peltier, a French watchmaker. The basic idea behind the Peltier effect is that whenever DC passes through the circuit of heterogeneous conductors, heat is either released or absorbed at the conductors' junctions, which depends on the current polarity. The amount of heat is proportional to the current that passes through conductors.
The basic TEM unit is a thermocouple, which consists of a p-type and n-type semiconductor elements, or pellets. Copper commutation tabs are used to interconnect pellets that are traditionally made of Bismuth Telluride-based alloy.
Thus, a typical TEM consists of thermocouples connected electrically in series and sandwiched between two Alumina ceramic plates. The number of thermocouples may vary greatly - from several elements to hundred of units. This allows to construct a TEM of a desirable cooling capacity ranging from fractions of Watts to hundreds of Watts.
When DC moves across TEM, it causes temperature differential between TEM sides. As a result, one TEM face, which is called cold, will be cooled while its opposite face, which is called hot, simultaneously is heated. If the heat generated on the TEM hot side is effectively dissipated into heat sinks and further into the surrounding environment, then the temperature on the TEM cold side will be much lower than that of the ambient by dozens of degrees. The TEM's cooling capacity is proportional to the current passing through it. TEM's cold side will consequently be heated and its hot side will be cooled once the TEM's polarity has been reversed.