Semiconducting coolers Pelte
(Continuation)

Пельтье units

In coolers Pelte the usual, so-called thermoelectric refrigerator which operation is grounded on effect Pelte uses. The given effect is named in honour of French watch-maker Pelte (1785-1845), made the opening more one and a half centuries ago - in 1834

Itself Pelte not absolutely understood essence of the phenomenon opened by it. The true sense of the phenomenon has been installed by several years later in 1838 Lentsem (1804-1865).

In deepening on the junction of two cores from bismuth and antimony the Lenz has placed a water drop. At current flow passage in one direction the water drop froze. At current passage in an opposite direction the derivated ice thawed. Thereby it has been installed, that at passing through the contact electrode of two explorers of a current flow, depending on a direction last, besides dzhouleva heat additional heat which has received the name of heat Pelte is selected or swallowed. This phenomenon has received the Peltier effect name (effect Pelte). Thus, it is the return in relation to phenomenon Zeebeka.

If in the shorted chain consisting of several metals or semiconductors, temperatures in places of contact electrodes of metals or semiconductors different in a chain there is a current flow. This phenomenon of a thermoelectric current also has been opened in 1821 German physicist Zeebekom (1770-1831).

Unlike heat of the Joule-Lenz which is proportional to a current intensity square (Q=R·I·I·t), warmly Pelte it is proportional to the first degree of current intensity and changes the sign at change of a direction last. Warm Pelte as have shown experimental researches, it is possible to express the formula:

Where q - quantity of the last electricity (q=I·t), P - the so-called Peltier coefficient, which value depends by nature contacting substances and on their temperature.

Heat Pelte Qп is considered positive if it is selected, and negative if it is swallowed.

Fig. 1. The circuit of experience for measurement of heat Pelte, Cu - copper, Bi - bismuth.

In the presented circuit of experience of measurement of heat Pelte at an identical resistance of wires R (Cu+Bi), omitted in calorimeters, it will be selected same dzhoulevo warmly in each calorimeter, namely on Q=R·I·I·t. Warm Pelte, on the contrary, in one calorimeter it will be positive, and in other it is negative. According to the given circuit it is possible to gauge heat Pelte and to calculate values of Peltier coefficient for different pairs of explorers.

It is necessary to mark, that the Peltier coefficient is in essential dependence on temperature. Some values of Peltier coefficient for various pairs of metals are presented in the table.

The Peltier coefficient which is the important technical characteristics of substances, as a rule, is not gauged, and calculated through Thomson coefficient:

Where P - Peltier coefficient, a - Thomson coefficient, T - Kelvin temperature.

Opening of effect Pelte has made the big impact on the subsequent development of physics, and in further and various areas of engineering.

So, the essence of open effect consists in the following: at current flow passing through the contact electrode of two explorers made of various substances, depending on its direction, besides dzhouleva heat additional heat which has received the name of heat Pelte is selected or swallowed. The degree of manifestation of the given effect appreciably depends on substances of the selected explorers and used electrical modes.

The classical theory explains Peltier effect to that elektrony, transferred by a current from one threw in another, are accelerated or decelerated under the influence of an internal contact potential difference between metals. In the first case kinetic energy elektronov increases, and then is selected in the form of heat. In the second case kinetic energy elektronov decreases, and this decrease of energy is enlarged at the expense of thermal oscillations of atoms of the second explorer. As a result there is a cooling. More complete theory considers change not a potential energy at carrying over elektrona from one metal in another, and change of complete energy.

Most strongly effect Pelte is observed in case of usage of semiconductors p - and conductance n-type. Depending on a current flow direction through the contact electrode of semiconductors of different type - p-p - and n-n-transitions owing to interaction of the charges presented elektronami (n) and holes (p), and their recombination energy either is swallowed, or selected. As a result of the given interactions and the generated energetic processes warmly either it is swallowed, or it is selected. Usage of semiconductors p - and conductance n-type in thermoelectric refrigerators illustrates fig. 2.

Fig. 2. Usage of semiconductors p - and n-type in thermoelectric refrigerators.

Multiplexing of a considerable quantity of pairs semiconductors p - and n-type allows to create cooling units - Пельтье units of rather big power. The structure of semiconducting thermoelectric Пельтье unit is presented on fig. 3.

Fig. 3. Пельтье unit structure

Пельтье unit, represents the thermoelectric refrigerator consisting of consistently jointed semiconductors p - and the n-type, derivating p-p - and n-n-transitions. Each of such transitions has the thermal contact electrode to one of two heat sinks. As a result of passing of a current flow of certain polarity difference of temperatures between Пельтье unit heat sinks is derivated: one heat sink works as a refrigerator, other heat sink heats up and is for heat extraction. On fig. 4 appearance of standard Пельтье unit is presented.

Fig. 4. Appearance of Пельтье unit

The typical unit provides considerable temperature difference which makes some tens degrees. At appropriate forced cooling of the heating up heat sink the second heat sink - the refrigerator, allows to reach negative values of temperatures. For temperature difference increase probably cascade inclusion of thermoelectric Пельтье units at support of their adequate cooling. It allows to receive rather simple resources considerable difference of temperatures and to provide effective cooling of protected units. On fig. 5 the example of cascade inclusion of standard Пельтье units is presented.

Fig. 5. An example of cascade inclusion of Пельтье units

Arrangements of cooling on the basis of Пельтье units often name as active coolers Pelte or is simple coolers Pelte.

Usage of Пельтье units in active coolers does them by essentially more effective on matching with standard types of coolers on the basis of traditional heat sinks and fans. However in the course of construction and usage of coolers with Пельтье units it is necessary to consider a number of the specific features following from a construction of units, their principle of operation, the architecture of modern hardware of computers and functionality of the system and applied software.

The great value plays power of Пельтье unit which, as a rule, depends on its size. The unit of low power does not provide necessary level of cooling that can lead to a malfunction of a protected electronic unit, for example, the processor owing to its overheat. However application of units of too big power can call a temperature drop of the cooling heat sink to level of condensation of a moisture from air that is dangerous to electronic chains. It is linked by that the water continuously received as a result of condensation, can lead to short circuits in electronic chains of the computer. Here pertinently to remind, that the distance between current-carrying explorers on modern printed circuit cards quite often makes shares of millimetres. Nevertheless, despite of everything, powerful Пельтье units as a part of high-powered coolers and appropriate systems of additional cooling and cooling have allowed in due time to KryoTech corporations and AMD in joint researches to disperse processors AMD created on traditional processing technique, to frequency, the exceeding 1 GHz that is to increase their frequency of operation almost in 2 times on matching with a regular mode of their functioning. Also it is necessary to underline, that the given performance level will reach in the conditions of support of necessary stability and dependability of operation of processors in the forced modes. Well, and a consequence of such extremal dispersal was the record of productivity among architecture and command system processors 80х86. And KryoTech corporation has not bad earned, offering in the market the installations of cooling. Supplied with an appropriate electronic stuffing, they have appeared claimed as platforms of high-powered servers and workstations. And AMD corporation has received confirmation of high level of the products and a rich experimental substance for further perfection of the architecture of the processors. By the way, similar researches have been led and with processors of Intel Celeron, Pentium II, Pentium III in which result considerable increase of productivity has been received too.

It is necessary to mark, that Пельтье units in the course of the operation select rather heat considerable quantity. For this reason it is necessary to apply not only the powerful fan as a part of a cooler, but also measures to lowering of temperature in tank of the computer for the warning of an overheat of other components of the computer. For this purpose it is expedient to use additional fans in konstruktive tanks of the computer for support of the best heat exchange with a surrounding medium out of tank.

On fig. 6 appearance of an active cooler in which structure semiconducting Пельтье unit is used is presented.

Fig. 6. Appearance of a cooler with Пельтье unit

It is necessary to mark, that systems of cooling on the basis of Пельтье units use not only in electronic systems, such as computers. Similar units are applied to cooling of various high-precision arrangements. Пельтье units have great value for a science. First of all it concerns the experimental researches executable in the physicist, chemistry, biology.

The information on units and coolers Pelte, and also features and results of their application can be found on sites in the Internet, for example, to following addresses:

• www.melcor.com
• www.kryotech.com
• www.computernerd.com
• www.tomshardware.com