Thermoelectric Coolers

About Peltier elements

What are Peltier elements?
How do Peltier elements work?
How are Peltier elements structured?
What are the advantages and disadvantages of Peltier elements?
What types of Peltier elements are there?
What can Peltier elements be used for?
What should be taken into account when using Peltier elements?

What are Peltier elements?

Peltier elements are electrical components that can transport heat from one side to the other without mechanically moving parts. They have now proven themselves in many areas of technology as a cooling element or for temperature stabilization. Peltier elements are also internationally referred to as "thermoelectric cooler", abbreviated to "TEC".

How do Peltier elements work?

In 1834, French scientist Jean Peltier published an article on his electrical experiments with contact points of different metals. When he connected the two ends of a bismuth wire to copper wires and connected them to a battery to allow current to flow, he found that one contact point is heating up and the other is cooling down . When the current flow is reversed, the heating and cooling effect of the two contacts also reverses. The cause of this effect was not known at first. Only after the legal principles of thermoelectrics had been discovered, there was an explanation. These are energetic equalizing processes of free charge carriers (electrons, holes) at the contact points, which are located on different energy levels depending on the material. For the jump to a higher energy level, the charge carrier of the environment extracts energy in the form of heat. When falling to a lower level, the charge carrier releases energy in the form of heat. A current-dependant temperature difference is created .

15 years earlier, the Prussian scientist Johann Seebeck had found out with a similar test setup that an electrical voltage arises between the two copper wires when one of the two contact points is heated. Both the Peltier effect and the Seebeck effect used in thermal elements have been known for a long time, but can only be used in practice with the development of modern technologies. Because Peltier elements and thermal elements are similar, a Peltier element can also generate an electrical voltage by heating one side and cooling the other .

1: Cold side

2: Ceramic plate

N semiconductor

4: P semiconductor

5: Hot side

6: Copper bridges

Basic construction of modern Peltier elements. The charge carriers are brought to a higher (lower) or lower (upper) energy level at the contact points and therefore absorb heat at the bottom and release it again at the top.

How are Peltier elements structured?

Modern Peltier elements (figures 1 and 2) consist of contacts between copper and the semi-conductor alloy bismuth tellurit (Bi2Te3) or silicon germanium (SiGe). This material has the shape of small cubes "Dices", which are connected together via copper bridges. The whole is attached to an aluminum oxide ceramic substrate. The top is also covered by a ceramic plate . The different N- or P-doping allows a large number of such elements to be connected in series, so that there are many contact points on both sides of the arrangement, which cool down or heat up at current flow. On the side, the wires for the power connection are led out. The N- and P-doped "Dices" are connected alternately with copper bridges .

1: Cold side

2: Ceramic plate

N semiconductor

4: P semiconductor

5: Hot side

6: Copper bridges

What are the advantages and disadvantages of Peltier elements?

Peltier elements have no mechanically moving parts and can cool or heat in the smallest space. The transported heat and thus the cooling power can be accurately metered with the current. The disadvantage is the low efficiency compared to the classic cooling system, which consumes much more space and works with compressors and requires a cooling medium. Peltier elements are therefore restricted to applications with low heat transfer power in the watt range .

What types of Peltier elements are there?

This Peltier element from TRUE COMPONENTS has a cooling capacity of 106 W and is only 2.8 mm high.

Standard Peltier elements are typically constructed in a square sandwich shape (see figure 3) and are produced in different dimensions of a few centimeters of edge length. The operating voltage depends on the amount of dices and is between a few and a few ten volts .

The cooling power that Peltier elements can produce is in the range from a few watts to about 100 watts .

The maximum temperature difference between the warm and cold side of the Peltier element is approximately 70 K.

What can Peltier elements be used for?

Peltier elements are now found in consumer goods such as thermoelectric cooling containers , mini-refrigerators or air dehumidifiers . Peltier elements are used in technology, for example, to cool lasers or optical sensors to reduce image noise. Peltier elements have also proven themselves as part of the cooler of computer chips, e.g. the CPU, due to their compact design.

The temperature-dependant oscillation frequency of quartz generators can be kept constant with the help of Peltier elements independant of the ambient temperature, because they can heat or cool depending on the current direction. In the laboratory, Peltier elements can be used to precisely and reproducibly adjust the temperatures of liquids, for example. In analytical technology, Peltier elements can be used to perform exact sample tempering.

A special controller module is available for optimum control of Peltier elements. The corresponding display unit shows, among other things Actual and set temperatures as well as heating and cooling mode. With these accessories, you can, for example Set up laboratory and measuring equipment with precise adjustment and control of the temperature.

What should be taken into account when using Peltier elements?

Peltier elements must be installed in such a way that they can absorb heat on one side and release it on the other side. If the heat accumulates on either side, the efficiency of the cooling process decreases. Surface-fit mounting with low thermal contact resistance is required.

Heat conductive paste should therefore be applied to the contact surfaces prior to assembly. On the warm side, heat dissipation must be possible without hindrance and should be supported with a large-area heat sink and, if necessary, with a fan for greater performance.

The electrical limit values Imax and Umax specified in the data sheets must not be exceeded.
Peltier elements that are frequently switched on and off in certain applications must have a high thermal cycle strength.
The commercially available Peltier elements are RoHS compliant.

About Peltier elements What are Peltier elements? How do Peltier elements work? How are Peltier elements structured? What are the advantages and disadvantages of Peltier elements? What types of Peltier elements are there? ...