Peltier cooling effect explained at the molecular level. Peltier elements

I suggest watching two small videos.
Perhaps some of you have already met them online. Similar devices are used in computer technology.
However, let's talk a little more about the physical nature of this phenomenon below. Such small cooling devices are interesting in that their principle of operation is based on a specific physical effect.

Video 1

Movie 2

These devices are based on peltier effect.

This physical phenomenon was discovered in 1834 year Jean-Charles Peltier, a watchmaker from France. The resulting effect was named after the discoverer - the Peltier effect.Peltier found that when an electric current is passed through a circuit consisting of two different conductors, one of the junctions is cooled, and the other heats up.
The release of heat when exposed to electricity was already known and understandable by that time, but the release of cold was incomprehensible and not studied.

Then attempts to use the effect to obtain low temperatures were unsuccessful, since it was not possible to obtain a high EMF value. Therefore, the Peltier effect was forgotten for more than a hundred years.
The problem was solved by replacing the conductors with semiconductors, in which it is more noticeable. In the 30s of the 20th century, our compatriot academician A.F. Ioffe proposed and showed the ability of semiconductors to provide sufficient process efficiency.

The Peltier effect is reversed seebeck effect, better known as the thermoelectric effect.

The Peltier effect is reversible. We see this on video 2. If you change the polarity, then the contact that was hot before will become cold and vice versa.

As I already wrote above, if you use noble metals as conductors, then the maximum temperature difference that can be squeezed out between two points will not be higher than 3 K. Therefore, to obtain a greater temperature difference, they began to use combinations of materials - semiconductors, electrical conductivity, which between the conductivity of a pure metal such as copper. When direct current is passed, heat will be generated on one semiconductor, on the other heat will be absorbed. Such single-stage installations allow obtaining a maximum temperature drop of 70 ... 75 K.
Further lowering the temperature is possible only cascade connection thermoelements.
Thanks to this, it was possible to achieve: deeper cooling, increase the efficiency of the cooling process, reduce the dimensions of low-temperature units.
To obtain sufficient cooling capacity without increasing the electric current too much, connect Peltier elements in series into batteries.

Peltier battery

Advantages of chillers based on Peltier batteries:
- lack of moving parts, and therefore noise and vibration;
- lack of working substances (refrigerants and refrigerants);
- small size;
- the ability to continuously adjust performance within any limits.

But the disadvantages have extremely limited the use of such devices to niche products:
- low efficiency (COP), lower than vapor compression freon installations;
- low cold productivity;
- high price.

The main problem in the construction of high-efficiency Peltier elements is that free electrons in matter are simultaneously carriers of both electric current and heat. At the same time, the material for the Peltier element must simultaneously possess two mutually exclusive properties - it is good to conduct electric current, but poorly to conduct heat, which is difficult to achieve in practice.

Today, such coolers have found application in photographic equipment, night vision devices, and telescopes. Also used in computer cooling systems, car refrigerators.
Perhaps the use of new materials will open up new possibilities for the use of such systems and installations. The most promising application at the moment is in the cooling of computer systems.

If you watch the video carefully, you can see the designation TEC - This is an abbreviation for the English Thermoelectric Cooler, which means thermoelectric cooler, as Peltier elements are also called.

By the way, it was the USSR that was the leader in thermoelectric cooling technology, as in basic researchand in practical application... The first household thermoelectric refrigerators were created here in the 60s.

Peltier semiconductor refrigerators

The operation of modern high-performance electronic components that make up the basis of computers is accompanied by significant heat generation, especially when operating them in forced overclocking modes. The efficient operation of such components requires adequate cooling means to ensure the required temperature conditions for their operation. As a rule, such means of maintaining optimal temperature conditions are coolers, which are based on traditional radiators and fans.

The reliability and productivity of such tools are continuously improved by improving their design, use the latest technologies and the use in their composition of a variety of sensors and controls. This makes it possible to integrate such tools into the composition of computer systems, providing diagnostics and control of their work in order to achieve the highest efficiency while ensuring optimal temperature conditions for the operation of computer elements, which increases reliability and lengthens the time of their trouble-free operation.

The parameters of traditional coolers are constantly improving, however, recently such specific means of cooling electronic elements as Peltier semiconductor refrigerators have appeared on the computer market and soon became popular (although the word cooler is often used, but the correct term in the case of Peltier elements is the refrigerator).

Peltier refrigerators, containing special semiconductor thermoelectric modules, whose operation is based on the Peltier effect, discovered back in 1834, are extremely promising cooling devices. Such means have been successfully used for many years in various fields of science and technology.

In the sixties and seventies, the domestic industry made repeated attempts to produce small household refrigerators, the work of which was based on the Peltier effect. However, the imperfection of existing technologies, low values \u200b\u200bof the efficiency and high prices did not allow such devices to leave research laboratories and test benches at that time.

But the Peltier effect and thermoelectric modules did not remain the lot of scientists only. In the process of improving technologies, many negative phenomena were significantly weakened. These efforts have resulted in highly efficient and reliable semiconductor modules.

IN last years These modules, the work of which is based on the Peltier effect, began to be actively used to cool various electronic components of computers. They, in particular, began to be used to cool modern powerful processors, the work of which is accompanied by high level heat dissipation.

Due to their unique thermal and operational properties, devices based on thermoelectric modules - Peltier modules - allow achieving the required level of cooling of computer elements without any special technical difficulties and financial costs. As coolers of electronic components, these means of maintaining the required temperature conditions for their operation are extremely promising. They are compact, convenient, reliable and very efficient.

Semiconductor refrigerators are of particular interest as a means of providing intensive cooling in computer systems, the elements of which are installed and operated in severe forced modes. The use of such modes - overclocking (overclocking) often provides a significant increase in the performance of the used electronic components, and, therefore, as a rule, of the entire computer system. However, the operation of computer components in such modes is characterized by significant heat release and is often at the limit of the capabilities of computer architectures, as well as existing and used microelectronic technologies. Such computer components, the operation of which is accompanied by high heat release, are not only high-performance processors, but also elements of modern high-performance video adapters, and in some cases also microcircuits of memory modules. Such powerful elements require intensive cooling for their correct operation, even in standard modes, and even more so in overclocking modes.

Peltier modules

In Peltier refrigerators, a conventional, so-called thermoelectric refrigerator is used, the action of which is based on the Peltier effect. This effect is named after the French watchmaker Peltier (1785-1845), who made his discovery more than a century and a half ago - in 1834.

Peltier himself did not quite understand the essence of the phenomenon he discovered. The true meaning of the phenomenon was established a few years later in 1838 by Lenz (1804-1865).

Lenz placed a drop of water in a depression at the junction of two rods made of bismuth and antimony. When an electric current was passed in one direction, a drop of water froze. When the current was passed in the opposite direction, the formed ice melted. Thus, it was found that when two conductors of electric current pass through the contact, depending on the direction of the latter, in addition to the Joule heat, additional heat is released or absorbed, which is called Peltier heat. This phenomenon is called the Peltier phenomenon (Peltier effect). Thus, it is the opposite of the Seebeck phenomenon.

If in a closed circuit consisting of several metals or semiconductors, the temperatures at the places of contacts of metals or semiconductors are different, then an electric current appears in the circuit. This phenomenon of thermoelectric current was discovered in 1821 by the German physicist Seebeck (1770-1831).

Unlike the Joule-Lenz heat, which is proportional to the square of the current strength (Q \u003d R · I · I · t), the Peltier heat is proportional to the first power of the current and changes sign when the direction of the latter changes. The Peltier heat, as shown by experimental studies, can be expressed by the formula:

Qп \u003d П q

where q is the amount of electricity passed (q \u003d I t), P is the so-called Peltier coefficient, the value of which depends on the nature of the contacting materials and on their temperature.

Peltier heat Qp is considered positive if it is released, and negative if it is absorbed.

Figure: 1. Scheme of the experiment for measuring Peltier heat, Cu - copper, Bi - bismuth.

In the presented scheme of the experiment for measuring Peltier heat with the same resistance of wires R (Cu + Bi) lowered into the calorimeters, the same Joule heat will be released in each calorimeter, namely, Q \u003d R I I t. On the other hand, the Peltier heat will be positive in one calorimeter and negative in the other. In accordance with this scheme, you can measure the Peltier heat and calculate the values \u200b\u200bof the Peltier coefficients for different pairs of conductors.

It should be noted that the Peltier coefficient is significantly dependent on temperature. Some values \u200b\u200bof the Peltier coefficient for various pairs of metals are presented in the table.

Peltier coefficient values \u200b\u200bfor different metal pairs
Iron constantan		Copper-Nickel		Lead-constantan
T, K	P, mV	T, K	P, mV	T, K	P, mV
273	13,0	292	8,0	293	8,7
299	15,0	328	9,0	383	11,8
403	19,0	478	10,3	508	16,0
513	26,0	563	8,6	578	18,7
593	34,0	613	8,0	633	20,6
833	52,0	718	10,0	713	23,4

The Peltier coefficient, which is an important technical characteristic of materials, is usually not measured, but calculated through the Thomson coefficient:

P \u003d a T

where P is the Peltier coefficient, a is the Thomson coefficient, and T is the absolute temperature.

The discovery of the Peltier effect had a great influence on the subsequent development of physics, and later on various areas of technology.

So, the essence of the open effect is as follows: when an electric current passes through the contact of two conductors made of different materials, depending on its direction, in addition to Joule heat, additional heat is released or absorbed, which is called Peltier heat. The degree of manifestation of this effect largely depends on the materials of the selected conductors and the electrical modes used.

The classical theory explains the Peltier phenomenon by the fact that electrons carried by current from one metal to another are accelerated or decelerated under the action of an internal contact potential difference between the metals. In the first case kinetic energy electrons increases and then is released as heat. In the second case, the kinetic energy of electrons decreases, and this loss of energy is replenished due to thermal vibrations of the atoms of the second conductor. As a result, cooling occurs. A more complete theory takes into account the change not in the potential energy during the transfer of an electron from one metal to another, but the change in the total energy.

The Peltier effect is most strongly observed in the case of using p- and n-type semiconductors. Depending on the direction of the electric current through the semiconductor contact different types - p-n- and n-p-transitions due to the interaction of charges represented by electrons (n) and holes (p), and their recombination, energy is either absorbed or released. As a result of these interactions and generated energy processes, heat is either absorbed or released. The use of p- and n-type semiconductors in thermoelectric refrigerators is illustrated in Fig. 2.

Figure: 2. The use of p- and n-type semiconductors in thermoelectric refrigerators.

Combining a large number of pairs of p- and n-type semiconductors makes it possible to create cooling elements - Peltier modules of relatively high power. The structure of the semiconductor thermoelectric Peltier module is shown in Fig. 3.

Figure: 3. The structure of the Peltier module

The Peltier module is a thermoelectric refrigerator consisting of p- and n-type semiconductors connected in series, forming p-n- and n-p-junctions. Each of these transitions has thermal contact with one of the two radiators. As a result of the passage of an electric current of a certain polarity, a temperature difference is formed between the radiators of the Peltier module: one radiator works as a refrigerator, the other radiator heats up and serves to remove heat. In fig. 4 shows the appearance of a typical Peltier module.

Figure: 4. Appearance of the Peltier module

A typical module provides a significant temperature difference, which is several tens of degrees. With appropriate forced cooling of the heating radiator, the second radiator - the refrigerator, allows reaching negative temperatures. To increase the temperature difference, it is possible to cascade Peltier thermoelectric modules while ensuring their adequate cooling. This makes it possible, by relatively simple means, to obtain a significant temperature difference and to provide effective cooling of the protected elements. In fig. 5 shows an example of cascading typical Peltier modules.

Figure: 5. An example of cascading Peltier modules

Cooling devices based on Peltier modules are often called active Peltier coolers or simply Peltier coolers.

The use of Peltier modules in active coolers makes them much more efficient compared to standard types of coolers based on traditional radiators and fans. However, in the process of designing and using coolers with Peltier modules, it is necessary to take into account a number of specific features arising from the design of the modules, their principle of operation, the architecture of modern computer hardware and the functionality of the system and application software.

Great importance plays the power of the Peltier module, which, as a rule, depends on its size. A low-power module does not provide the required level of cooling, which can lead to malfunction of the protected electronic element, for example, a processor, due to its overheating. However, the use of modules of too large capacity can cause the temperature of the cooling radiator to drop to the level of moisture condensation from the air, which is dangerous for the electronic circuits. This is due to the fact that water, continuously obtained as a result of condensation, can lead to short circuits in the electronic circuits of the computer. It is pertinent to recall here that the distance between conductive conductors on modern printed circuit boards is often fractions of a millimeter. Nevertheless, in spite of everything, it was the powerful Peltier modules in high-performance coolers and the corresponding systems of additional cooling and ventilation that allowed KryoTech and AMD in their joint research to overclock AMD processors, created using traditional technology, to frequencies exceeding 1 GHz. , that is, to increase their frequency of operation by almost 2 times in comparison with the standard mode of their operation. And it should be emphasized that this level of performance has been achieved while ensuring the necessary stability and reliability of the processors in forced modes. Well, the result of such extreme overclocking was a performance record among processors of architecture and 80x86 instruction set. And the KryoTech company made good money, offering its cooling units on the market. Equipped with appropriate electronics, they have proven to be in demand as platforms for high-performance servers and workstations. And AMD has received confirmation of the high level of its products and rich experimental material to further improve the architecture of its processors. By the way, similar studies were carried out with Intel Celeron, Pentium II, Pentium III processors, as a result of which a significant increase in performance was also obtained.

It should be noted that Peltier modules generate a relatively large amount of heat in the course of their operation. For this reason, you should use not only a powerful fan as part of the cooler, but also measures to reduce the temperature inside the computer case to prevent overheating of the rest of the computer components. To do this, it is advisable to use additional fans in the design of the computer case to provide better heat transfer with the environment outside the case.

In fig. 6 shows the appearance of an active cooler, which includes a semiconductor Peltier module.

Figure: 6. Appearance of a cooler with a Peltier module

It should be noted that cooling systems based on Peltier modules are used not only in electronic systems such as computers. Such modules are used to cool various high-precision devices. Peltier modules are of great importance for science. First of all, this applies to experimental research carried out in physics, chemistry, and biology.

Information about Peltier modules and refrigerators, as well as the features and results of their use, can be found on sites on the Internet, for example, at the following addresses:

Features of operation

Peltier modules used as part of means for cooling electronic elements are distinguished by a relatively high reliability, and, unlike refrigerators created using traditional technology, have no moving parts. And, as noted above, to increase the efficiency of their work, they allow for cascade use, which makes it possible to bring the temperature of the cases of the protected electronic elements to negative values \u200b\u200beven with their significant dissipation power.

However, in addition to the obvious advantages, Peltier modules also have a number of specific properties and characteristics that must be taken into account when using them in the composition of coolants. Some of them have already been noted, but for the correct application of Peltier modules they require more detailed consideration. The most important characteristics include the following operating features:

Peltier modules, which emit a large amount of heat during their operation, require the presence of appropriate heatsinks and fans in the cooler, capable of effectively removing excess heat from the cooling modules. It should be noted that thermoelectric modules are distinguished by a relatively low efficiency (efficiency) and, performing the functions of a heat pump, they themselves are powerful sources of heat. The use of these modules as part of the means for cooling electronic components of a computer causes a significant increase in temperature inside the system unit, which often requires additional measures and means to reduce the temperature inside the computer case. Otherwise, the increased temperature inside the case creates difficulties for the operation not only for the protected elements and their cooling systems, but also for the rest of the computer components. It should also be emphasized that Peltier modules are a relatively powerful additional load for the power supply. Taking into account the value of the current consumption of the Peltier modules, the power value of the computer power supply must be at least 250 W. All this leads to the expediency of choosing motherboards and ATX cases with sufficient power supplies. The use of this construct makes it easier for the computer components to organize optimal thermal and electrical conditions. It should be noted that there are Peltier refrigerators with their own power supply.
The Peltier module, in case of failure, isolates the cooled element from the cooler radiator. This leads to a very rapid violation of the thermal regime of the protected element and its quick failure from subsequent overheating.
Low temperatures occurring during the operation of Peltier refrigerators with excess capacity contribute to the condensation of moisture from the air. This poses a danger to electronic components as condensation can cause short circuits between the components. To eliminate this danger, it is advisable to use Peltier refrigerators of optimal power. Whether or not condensation occurs depends on several parameters. The most important are: the ambient temperature (in this case, the air temperature inside the case), the temperature of the cooled object and air humidity. The warmer the air inside the case and the higher the humidity, the more likely moisture condensation will occur and the subsequent failure of the electronic components of the computer. Below is a table illustrating the dependence of the moisture condensation temperature on the cooled object depending on the humidity and ambient temperature. Using this table, you can easily determine whether there is a risk of moisture condensation or not. For example, if the outside temperature is 25 ° C, and the humidity is 65%, then moisture condensation on the cooled object occurs when its surface temperature is below 18 ° C.

Moisture condensation temperature

Humidity,%
Temperature environment, ° C	30	35	40	45	50	55	60	65	70
30	11	13	15	17	18	20	21	23	24
29	10	12	14	16	18	19	20	22	23
28	9	11	13	15	17	18	20	21	22
27	8	10	12	14	16	17	19	20	21
26	7	9	11	13	15	16	18	19	20
25	6	9	11	12	14	15	17	18	19
24	5	8	10	11	13	14	16	17	18
23	5	7	9	10	12	14	15	16	17
22	4	6	8	10	11	13	14	15	16
21	3	5	7	9	10	12	13	14	15
20	2	4	6	8	9	11	12	13	14

In addition to these features, it is necessary to take into account a number of specific circumstances associated with the use of Peltier thermoelectric modules as part of coolers used to cool high-performance central processors of powerful computers.

The architecture of modern processors and some system programs provide for a change in power consumption depending on the processor load. This allows them to optimize their energy consumption. By the way, this is also stipulated by the energy saving standards supported by some functions built into the hardware and software of modern computers. Under normal conditions, optimization of the processor's operation and its power consumption has a beneficial effect both on the thermal regime of the processor itself and on the general heat balance... However, it should be noted that modes with periodic changes in power consumption can be poorly combined with cooling means for processors using Peltier modules. This is due to the fact that existing Peltier refrigerators are usually designed for continuous operation. In this regard, the simplest Peltier refrigerators, which do not have control means, are not recommended to be used together with cooling programs such as, for example, CpuIdle, as well as with Windows NT / 2000 or Linux operating systems.

If the processor goes into a low power consumption mode and, accordingly, heat dissipation, a significant decrease in the temperature of the case and the processor crystal is possible. Overcooling of the processor core can in some cases cause a temporary cessation of its performance, and as a result, permanent freeze of the computer. It should be remembered that, according to the Intel documentation, the minimum temperature at which the correct operation of serial Pentium II and Pentium III processors is usually guaranteed is +5 ° C, although, as practice shows, they work perfectly well at lower temperatures.

Some problems can also arise as a result of the work of a number of built-in functions, for example, those that control the fans of coolers. Specifically, the processor power management modes in some computer systems involve changing the rotational speed of the cooling fans through the built-in motherboard hardware. Under normal conditions, this significantly improves the thermal performance of the computer processor. However, in the case of using the simplest Peltier refrigerators, a decrease in the rotation speed can lead to a deterioration in the thermal regime with a fatal result for the processor due to its overheating by the operating Peltier module, which, in addition to performing the functions of a heat pump, is a powerful source of additional heat.

It should be noted that, as in the case of computer central processors, Peltier refrigerators can be a good alternative to traditional means of cooling video chipsets used in modern high-performance video adapters. The operation of such video chipsets is accompanied by significant heat release and is usually not subject to sharp changes in their operation modes.

In order to eliminate problems with variable power consumption modes that cause moisture condensation from the air and possible hypothermia, and in some cases even overheating of protected elements, such as computer processors, you should abandon the use of such modes and a number of built-in functions. Alternatively, however, refrigeration systems that include intelligent Peltier refrigerator controls can be used. Such means can control not only the operation of the fans, but also change the operating modes of the thermoelectric modules themselves used in active coolers.

There have been reports of experiments on embedding miniature Peltier modules directly into processor microcircuits to cool their most critical structures. This solution contributes to better cooling by reducing thermal resistance and can significantly increase the operating frequency and performance of processors.

Many research laboratories are working to improve systems for ensuring optimal temperature conditions for electronic elements. And cooling systems using Peltier thermoelectric modules are considered extremely promising.

Examples of Peltier refrigerators

More recently, domestically produced Peltier modules have appeared on the computer market. They are simple, reliable and relatively cheap ($ 7- $ 15) devices. Typically, a cooling fan is not included. Nevertheless, such modules allow not only to get acquainted with promising cooling means, but also to use them for their intended purpose in the protection systems of computer components. Here short parameters one of the samples.

Module size (Fig. 7) - 40 × 40 mm, maximum current - 6 A, maximum voltage - 15 V, power consumption - up to 85 W, temperature difference - more than 60 ° C. By providing a powerful fan, the module is able to protect the processor with up to 40W of power dissipation.

Figure: 7. Appearance of the PAP2X3B refrigerator

The market offers both less and more powerful versions of domestic Peltier modules.

The range of foreign devices is much wider. Below are examples of refrigerators in the design of which Peltier thermoelectric modules are used.

Active Peltier refrigerators from Computernerd

Name	Manufacturer / supplier	Fan parameters	CPU
PAX56B	Computernerd	ball-bearing	Pentium / MMX up to 200 MHz, 25 W
PA6EXB	Computernerd	dual ball-bearing, tachometer	Pentium MMX up to 40W
DT-P54A	DesTech Solutions	dual ball bearing	Pentium
AC-P2	AOC Cooler	ball bearing	Pentium II
PAP2X3B	Computernerd	3 ball bearing	Pentium II
STEP-UP-53X2	Step Thermodynamics	2 ball bearing	Pentium II, Celeron
PAP2CX3B-10 BCool PC-Peltier	Computernerd	3 ball-bearing, tachometer	Pentium II, Celeron
PAP2CX3B-25 BCool-ER PC-Peltier	Computernerd	3 ball-bearing, tachometer	Pentium II, Celeron
PAP2CX3B-10S BCool-EST PC-Peltier	Computernerd	3 ball-bearing, tachometer	Pentium II, Celeron

The PAX56B refrigerator is designed for cooling Pentium and Pentium-MMX processors from Intel, Cyrix and AMD operating at frequencies up to 200 MHz. The 30x30mm thermoelectric module allows the refrigerator to keep the processor temperature below 63 ° C with a power dissipation of 25 W and an external temperature of 25 ° C. Due to the fact that most processors dissipate less power, this refrigerator allows you to keep the processor temperature much lower than many alternative coolers based on radiators and fans. The PAX56B Peltier module is powered by a 5 V supply capable of supplying 1.5 A maximum. The fan of this refrigerator requires 12 V and 0.1 A maximum. Parameters of the fan of the PAX56B refrigerator: ball-bearing, 47.5 mm, 65000 hours, 26 dB. The overall size of this refrigerator is 25 x 25 x 28.7mm. The approximate price of the PAX56B refrigerator is $ 35. The indicated price is given in accordance with the price list of the company for the middle of 2000.

The PA6EXB refrigerator is designed to cool the more powerful Pentium-MMX processors that dissipate power up to 40W. This refrigerator is suitable for all Intel, Cyrix and AMD processors connected via Socket 5 or Socket 7. The Peltier thermoelectric module included in the PA6EXB refrigerator has a size of 40 × 40 mm and consumes a maximum current of 8 A (usually 3 A) at a voltage of 5 B with connection through a standard computer power connector. The total size of PA6EXB refrigerator is 60 × 60 × 52.5mm. When installing this refrigerator, for good heat exchange of the radiator with the environment, it is necessary to provide an open space around the refrigerator of at least 10 mm at the top and 2.5 mm at the sides. The PA6EXB refrigerator provides a CPU temperature of 62.7 ° C with a power dissipation of 40 W and an external temperature of 45 ° C. Taking into account the principle of operation of the thermoelectric module, which is part of this refrigerator, in order to avoid moisture condensation and short circuit, it is necessary to avoid using programs that put the processor into sleep mode for a long time. The approximate price of such a refrigerator is $ 65. The indicated price is given in accordance with the price list of the company for the middle of 2000.

The DT-P54A (also known as Computernerd PA5B) is designed for Pentium processors. However, some companies offering these refrigerators on the market recommend it to Cyrix / IBM 6x86 and AMD K6 users. The radiator included in the refrigerator is small enough. Its dimensions are 29 × 29 mm. The refrigerator has a built-in thermal sensor, which, if necessary, will notify about overheating. He also controls the Peltier element. The kit includes an external control device. It performs the functions of monitoring the voltage and the operation of the Peltier element itself, the operation of the fan, as well as the temperature of the processor. The unit will generate an alarm if the Peltier element or fan is out of order, if the fan is spinning less than 70% of the required speed (4500 RPM), or if the processor temperature rises above 145 ° F (63 ° C). If the processor temperature rises above 100 ° F (38 ° C), then the Peltier element is automatically turned on, otherwise it is in shutdown mode. The latter feature eliminates moisture condensation problems. Unfortunately, the element itself is glued to the radiator so tightly that it cannot be separated without destroying its structure. This makes it impossible to install it on another, more powerful radiator. As for the fan, its design is characterized by a high level of reliability and it has high parameters: supply voltage - 12 V, rotation speed - 4500 RPM, air flow rate - 6.0 CFM, power consumption - 1 W, noise characteristics - 30 dB. This refrigerator is powerful enough and useful for overclocking. However, in some cases of overclocking the processor, you should just use a large heatsink and a good cooler. The price of this refrigerator ranges from $ 39 to $ 49. The indicated price is given in accordance with the price list of several companies for the middle of 2000.

The AC-P2 refrigerator is designed for Pentium II processors. The kit includes a 60 mm cooler, a radiator and a 40 mm Peltier element. Poorly suited to Pentium II 400 MHz and higher processors, since SRAM memory chips are practically not cooled. Estimated mid-2000 price - $ 59.

Refrigerator PAP2X3B (fig. 8) is similar to AOC AC-P2. Added two 60mm coolers. SRAM cooling issues remained unresolved. It should be noted that the refrigerator is not recommended for use with cooling programs such as, for example, CpuIdle, as well as under Windows NT or Linux operating systems, as moisture condensation on the processor is likely. Estimated mid-2000 price $ 79.

Figure: 8. Appearance of the refrigerator PAP2X3B

The STEP-UP-53X2 refrigerator is equipped with two fans that blow a large amount of air through the radiator. Estimated mid-2000 price - $ 79 (Pentium II), $ 69 (Celeron).

Computernerd Bcool series refrigerators (PAP2CX3B-10 BCool PC-Peltier, PAP2CX3B-25 BCool-ER PC-Peltier, PAP2CX3B-10S, BCool-EST PC-Peltier) are designed for Pentium II and Celeron processors and have similar characteristics, which are presented in following table.

Refrigerators BCool series

Item	PAP2CX3B-10 BCool PC-Peltier	PAP2CX3B-25 BCool-ER PC-Peltier	PAP2CX3B-10S BCool-EST PC-Peltier
Recommended processors	Pentium II and Celeron
Number of fans	3
Central fan type	Ball-Bearing, tachometer (12V, 120mA)
Central fan size	60x60x10 mm
External fan type	Ball-bearing	Ball-Bearing, tachometer	Ball-Bearing, thermistor
External fan size	60x60x10 mm	60x60x25 mm
Voltage, current	12V, 90mA	12V, 130mA	12V, 80-225mA
Total area covered by fans	84.9 cm 2
Total current for fans (power)	300 mA (3.6W)	380 mA (4.56 W)	280-570 mA (3.36-6.84W)
Number of pins on the heatsink (center)	63 long and 72 short
Number of pins on the heatsink (at each end)	45 long and 18 short
The total number of pins on the radiator	153 long and 108 short
Radiator dimensions (center)	57x59x27 mm (including thermoelectric module)
Radiator dimensions (at each end)	41x59x32 mm
Overall radiator dimensions	145x59x38 mm (including thermoelectric module)
Overall dimensions of the refrigerator	145x60x50 mm	145x60x65 mm
Refrigerator weight	357 gram	416 gram	422 gram
Guarantee	5 years
Estimated price (2000)	$74.95	$79.95	$84.95

It should be noted that the BCool group of refrigerators also includes devices that have similar characteristics, but which do not have Peltier elements. Such refrigerators are naturally cheaper, but also less effective as a means of cooling computer components.

In preparing the article, materials from the book "PC: tuning, optimization and overclocking" were used. 2nd ed., Rev. and additional, - SPb .: BHV - Petersburg. 2000 .-- 336 p.

PELT EFFECT

Release or heat during the passage of electric. current I through the contact of two diff. conductors. The release of heat is replaced by absorption when the direction of the current changes. Opened fr. physicist J. Peltier in 1834. The amount of heat Qp \u003d PI, where P is the Peltier coefficient, equal to: P \u003d TDa. Here T is abs. temp-pa, Da-difference thermoelectric. coeff. conductors.

P. e. is explained by the fact that cf. carriers of current depends on their energetic. spectrum, concentration and mechanisms of their scattering and therefore is different in different conductors. When passing from one conductor to another, the electrons either transfer excess energy to atoms, or replenish the lack of energy at their expense. In the first case, Peltier is released near the contact, and in the second it is absorbed. When electrons pass from a semiconductor to a metal, the energy of conduction electrons of the PP is much higher than the Fermi level of the metal, and the electrons give up their excess energy. With the opposite direction of the current, only those electrons can pass from the metal to the PP, the energy of which is above the bottom of the conduction band of the PP. In this case, thermal equilibrium in the metal is disturbed and restored due to thermal vibrations of the crystals. lattice. This absorbs Peltier heat. At the contact of two PPs or two metals, Peltier heat is also released (or absorbed) due to the fact that cf. the energy of charge carriers on both sides of the contact is different.

P. e. used for cooling in refrigeration plants and in some electronic devices.

Physical encyclopedic dictionary. - M .: Soviet encyclopedia. . 1983 .

PELT EFFECT

Allocation or absorption of heat at the contact of two dissimilar conductors, depending on the direction of the electric. current flowing through the contact. Discovered by J. Peltier in 1834. Heat dissipation power Q\u003d P 12 jwhere j - current density, P 12 \u003d P 1 - P 2 (P 1, P 2 - absolute Peltier coefficient of contacting materials, which are characteristics of these materials). The cause of P. e. is that cf. energy of charge carriers (for definiteness of electrons) involved in electrical conductivity, in decomp. conductors is different, because it depends on their energy. spectrum, concentration and scattering mechanism (see. Dissipation of charge carriers). When passing from one conductor to another, electrons either transfer excess energy to the lattice, or replenish the lack of energy from its account (depending on the direction of the current). In the first case, it is released near the contact, and in the second, the so-called. heat of Peltier. For example, at the semiconductor-metal contact (Fig.), The energy of electrons passing from semiconductor n -type in metal (left contact), significantly exceeds the Fermi energy, so they break in metal. Equilibrium is restored as a result of collisions, in which electrons are thermalized, giving off excess energy to the crystalline. lattice. Only the most energetic electrons can pass into a semiconductor made of metal (right contact), as a result of which the electron gas in the metal is cooled. The energy of the lattice vibrations is spent on restoring the equilibrium distribution.

Peltier effect on semiconductor contacts n - metal type; - Fermi level; - bottom of the semiconductor conduction band: - top of the valence band.

At the contact of two semiconductors or two metals, Peltier heat is also released (or absorbed), due to the fact that cf. the energy of charge carriers involved in the current on both sides of the contact is different.
Expression for abs. coeff. Peltier P (charge carrier - electrons) has the form

where . - kinetic. energy and electrons, f 1 - non-equilibrium part of the electron distribution function, - density of states. As can be seen from (1), the coeff. P is a deviation cf. the energy of carriers in the flux from the Fermi energy per unit charge. To determine P, you need to know f-tion and find, that is, to solve the kinetic. ur-tion. In the case of parabolic. dispersion law of conduction electrons ( p) (p- quasimomentum) and the power-law dependence of the mean free path . on energy in the absence of degeneracy in the semiconductor coeff. P is determined by f-loy

Here is the scattering parameter, T - abs. temp-pa (see. Dissipation of charge carriers in a solid); measured from the bottom of the conduction band.
As seen from (2), eP but abs. value can reach tens kT. With an increase in the concentration of electrons in a degenerate conductor or a decrease T the value of P decreases and at

Coef. Peltier is related to coeff. thermoelectric power t. P \u003d T.

This allows the use of microscopic results for the evaluation. theory for Coef. Peltier, which is an important techn. characteristic of materials, as a rule, is not measured, but calculated by measuring which is more simple.
P. e. used in thermoelectric. refrigerators and thermostats, as well as to control the crystallization process due to the release or absorption of heat at the interface between the liquid and solid phases when passing electric. current.

Lit .: Anselm A.I., Introduction to the theory of semiconductors, 2nd ed., M., 1978; Askerov BM, Electronic transfer phenomena in semiconductors, M., 1985; Seeger K., Semiconductor Physics, 3. M. Dashevsky.

Physical encyclopedia. In 5 volumes. - M .: Soviet encyclopedia. Chief Editor A.M. Prokhorov. 1988 .

See what "PELTIER EFFECT" is in other dictionaries:

The release or absorption of heat when current passes through the contact (junction) of two different conductors. The amount of heat is proportional to the strength of the current. Used in refrigeration units. Discovered in 1834 by J. Peltier. * * * PELTIER EFFECT PELTIER EFFECT ... encyclopedic Dictionary

The Peltier effect is the process of generating or absorbing heat when an electric current passes through the contact of two dissimilar conductors. The amount of heat released and its sign depend on the type of contacting substances, current strength and transit time ... ... Wikipedia

The release or absorption of heat when current passes through the contact (junction) of two different conductors. The amount of heat is proportional to the strength of the current. Used in refrigeration units. Opened in 1834 by J. Peltier ... Big Encyclopedic Dictionary

The release or absorption of heat when an electric current passes through a contact (junction) of two different conductors. The release of heat is replaced by absorption when the direction of the current changes. Discovered by J. Peltier in 1834. The amount of allocated or ...

The Peltier effect is a thermoelectric phenomenon in which heat is released or absorbed when an electric current passes at the point of contact (junction) of two dissimilar conductors. The amount of heat generated and its sign depend on the species ... Wikipedia

Seebeck effect is the phenomenon of EMF in a closed electrical circuit consisting of series-connected dissimilar conductors, the contacts between which are at different temperatures. The Seebeck effect is also sometimes called ... ... Wikipedia

Peltier Jean Charles Athanaz (22.2.1785, Am, Somme, - 27.10.1845, Paris), French physicist and meteorologist. He worked as a watchmaker at A.L. Breguet. Having received the inheritance (1815), he devoted himself to science. Scientific works on thermoelectricity, ... ... Great Soviet Encyclopedia

The Thomson effect is one of the thermoelectric phenomena, which consists in the fact that in a homogeneous non-uniformly heated conductor with direct current, in addition to the heat released in accordance with Joule Lenz's law, in the volume ... ... Wikipedia

Jean Charles Peltier fr. Jean Charles Peltier Jean Peltier Date of birth ... Wikipedia

Thermoelectric phenomena ... Wikipedia

Federal Agency for Education of the Russian Federation

Bryansk State Technical University

Department "General Physics"

Course work

Peltier effect and its application

in the discipline "Physics"

Student gr. 07-EPM 2

Shapoval N.V.

Leader

ass. Krayushkina E.Yu.

Bryansk 2008

INTRODUCTION

1. PELTIER EFFECT

1.1 Opening the Peltier effect

1.2 Explanation of the Peltier effect

2. APPLICATION OF THE PELTIER EFFECT

2.1 Peltier modules

2.2 Features of operation of Peltier modules

2.3 Applying the Peltier effect

CONCLUSION

LIST OF USED LITERATURE

Scientific thought has the ability to stay ahead of its time. The discoveries made by scientists allow future generations, guided by them, to create devices and devices that improve human life; find new ways to protect his health and well-being. And the phenomenon, discovered in 1834 by the watchmaker Jean-Charles Peltier and later called the "Peltier Effect", was no exception. Therefore, the effect that took place in early XIX century, is relevant now.

The possibilities of its application are unlimited. Many laboratories and research centers are engaged in the development of ways to use it, because the discovery made by the French scientist makes human life comfortable, colorful, and the benefits of civilization available to a wide range of consumers.

In this course work we will consider the Peltier phenomenon and its application.

1.1 Opening the Peltier effect

Peltier effect was discovered by the Frenchman Jean-Charles Peltier in 1834. During one of the experiments, he passed an electric current through a strip of bismuth with copper conductors connected to it (Fig. 1.1.). During the experiment, he discovered that one bismuth-copper compound heats up, the other cools down.

Figure: 1.1 - Scheme of experiment for measuring Peltier heat

Peltier himself did not fully understand the essence of the phenomenon he discovered. The true meaning of the phenomenon was later explained in 1838. Lenz.

In his experiment, Lenz experimented with a drop of water placed at the junction of two conductors (bismuth and antimony). When the current was passed in one direction, the water drop froze, and when the direction of the current changed, it melted. Thus, it was found that when current passes through the contact of two conductors, heat is released in one direction and absorbed in the other. This phenomenon was called peltier effect .

Peltier heat is proportional to the amperage and can be expressed by the formula:

Q p \u003d P q

where q - the charge passed through the contact, P - the so-called Peltier coefficient, which depends on the nature of the contacting materials and their temperature. The Peltier coefficient can be expressed in terms of the Thompson coefficient:

П \u003d  T

where a - Thompson coefficient, T - absolute temperature.

It should be noted that the Peltier coefficient is significantly dependent on temperature. Some values \u200b\u200bof the Peltier coefficient for various pairs of metals are presented in Table 1.

Table 1

Peltier coefficient values \u200b\u200bfor different metal pairs
Iron constantan		Copper-Nickel		Lead-constantan
T, K	P, mV	T, K	P, mV	T, K	P, mV
273	13,0	292	8,0	293	8,7
299	15,0	328	9,0	383	11,8
403	19,0	478	10,3	508	16,0
513	26,0	563	8,6	578	18,7
593	34,0	613	8,0	633	20,6
833	52,0	718	10,0	713	23,4

The amount of heat released by Peltier and its sign depend on the type of contacting substances, the strength of the current and the time of its passage, therefore, Qp can be expressed by another formula:

dQ p \u003d П12ЧIЧdt.

Here P12 \u003d P1-P2 is the Peltier coefficient for this contact, associated with the absolute Peltier coefficients P1 and P2 of the contacting materials. In this case, it is considered that the current flows from the first sample to the second. When Peltier heat is released, we have: Qp\u003e 0, P12\u003e 0, P1\u003e P2.

When Peltier heat is absorbed, it is considered negative and, accordingly: Qп<0, П12<0, П1<П2. Очевидно, что П12=-П21.

Dimension of the Peltier coefficient [P] SI \u003d J / Kl \u003d V.

The classical theory explains the Peltier phenomenon by the fact that when electrons are transferred by current from one metal to another, they are accelerated or slowed down by the internal contact potential difference between the metals. In the case of acceleration, the kinetic energy of electrons increases and then is released in the form of heat. In the opposite case, the kinetic energy decreases, and the energy is replenished due to the energy of the thermal vibrations of the atoms of the second conductor, thus it begins to cool. A more complete examination takes into account the change not only in potential, but also in total energy.

In fig. 1.2. and fig. 1.3. depicts a closed circuit composed of two different semiconductors PP1 and PP2 with contacts A and B.

Figure: 1.2 - Peltier heat generation (contact A)

Figure: 1.3 - Peltier heat absorption (contact A)

Such a circuit is usually called a thermoelement, and its branches are called thermoelectrodes. A current I, created by an external source e, flows through the circuit. Figure: 1.2. illustrates the situation when Peltier heat Qp (A)\u003e 0 is released at contact A (current flows from PP1 to PP2), and at contact B (the current is directed from PP2 to PP1) its absorption is Qp (V)<0. В результате происходит изменение температур спаев: ТА>TV.

In fig. 1.3. a change in the sign of the source changes the direction of the current to the opposite: from PP2 to PP1 at contact A and from PP1 to PP2 at contact B. Accordingly, the sign of Peltier heat and the ratio between the contact temperatures change: Qp (A)<0, ТА<ТВ.

The reason for the appearance of the Peltier effect on the contact of semiconductors with the same type of current carriers (two n-type semiconductors or two p-type semiconductors) is the same as in the case of a contact between two metal conductors. Carriers of current (electrons or holes) on different sides of the junction have different average energy, which depends on many reasons: energy spectrum, concentration, scattering mechanism of charge carriers. If the carriers, having passed through the junction, enter a region with a lower energy, they transfer excess energy to the crystal lattice, as a result of which Peltier heat is released near the contact (Qp\u003e 0) and the contact temperature rises. In this case, at the other junction, the carriers, passing into the region with higher energy, borrow the missing energy from the lattice, and the Peltier heat is absorbed (Qp<0) и понижение температуры.

The Peltier effect, like all thermoelectric phenomena, is especially pronounced in circuits composed of electronic (n - type) and hole (p - type) semiconductors. In this case, the Peltier effect has a different explanation. Let us consider the situation when the current in the contact goes from a hole semiconductor to an electronic one (p®n). In this case, electrons and holes move towards each other and, having met, recombine. As a result of recombination, energy is released, which is released in the form of heat. This situation is illustrated in Fig. 1.4., Which shows the energy bands (ec-conduction band, ev-valence band) for impurity semiconductors with hole and electronic conductivity.

Figure: 1.4 - Peltier heat generation at the contact of p and n-type semiconductors

In fig. 1.5. (ec is the conduction band, ev is the valence band) illustrates the absorption of heat by Peltier for the case when the current flows from n to p-semiconductor (n ® p).

Figure: 1.5 - Peltier heat absorption at the contact of p and n-type semiconductors

Here, electrons in the electron and holes in hole semiconductors move in opposite directions, moving away from the interface. The loss of current carriers in the boundary region is compensated by the pairwise production of electrons and holes. The formation of such pairs requires energy, which is supplied by the thermal vibrations of the lattice atoms. The resulting electrons and holes are dragged in opposite directions by the electric field. Therefore, as long as the current flows through the contact, new pairs are born continuously. As a result, heat will be absorbed in contact.

The use of semiconductors of different types in thermoelectric modules is shown in Fig. 1.6.

Figure: 1.6 - Use of semiconductor structures in thermoelectric modules

Such a chain allows the creation of efficient cooling elements.

2.1 Peltier modules

Figure: 2.1 - Structure of the Peltier module

The Peltier module is a thermoelectric refrigerator consisting of p- and n-type semiconductors connected in series, forming p-n- and n-p-junctions. Each of these transitions has thermal contact with one of the two radiators. As a result of the passage of an electric current of a certain polarity, a temperature difference is formed between the radiators of the Peltier module: one radiator works as a refrigerator, the other radiator heats up and serves to remove heat. In fig. 2.2. the appearance of a typical Peltier module is presented.

The Peltier effect is a process involving the appearance of a temperature difference on two different materials when an electric current is passed through them. First explained by academician and inventor Lenz.

Acknowledgments

We cannot ignore the gratitude of the USSR Academy of Sciences and Academician A.F. Ioffe for his grandiose work on the development of thermoelectricity in the USSR and for bringing the research results to the attention of the public.

Applicability

The Peltier effect is used for cooling; heating is possible with any conductor according to the Joule-Lenz law. Therefore, the phenomenon is useful:

For creating low voltage and direct current refrigerators. With the possibility of heating when changing the polarity of the supply. In the west, this is how road sandwich makers are designed. The cold keeps the food from spoiling, the reverse polarity allows the food to be served hot.
CPU coolers make a significant contribution to the overall noise characteristics of the system unit. If you replace them with Peltier elements, sometimes a common fan is enough. It does not make as much noise, the case is devoid of a powerful radiator, and the mount is reliable (unlike the material of the motherboard).

Development of cooling theory

The Peltier effect did not attract close attention of scientists, it seemed useless. Opened in 1834, it was gathering dust on the shelves of scientific libraries for more than a century before the first significant technical solutions in this area began to appear. For example, Altenkirch (1911) declared the impossibility of using the Peltier effect in refrigeration units, in his calculations he relied on the use of pure metals, instead of alloys and semiconductors.

The erroneousness of the conclusions of the German scientist was confirmed later, in which a significant role was assigned to the semiconductor laboratory of the USSR Academy of Sciences. By 1950, a harmonious theory was created, which made it possible to create the first electrothermal refrigerator over the next several years. With a relatively low efficiency of 20%, the device lowered the temperature by 24 degrees, which in most cases was enough for domestic purposes. Years later, the temperature difference was already 60 degrees.

In the physics of the 50s, the Peltier element was considered as a refrigeration machine with electronic gas instead of freon. The system was reviewed accordingly. The main parameter is the refrigerating coefficient, the ratio of the amount of heat taken per unit of time to the power that is spent on it. For modern freon air conditioners and refrigerators, the figure exceeds one. In the 50s, the Peltier element barely reached 20%.

Effect from the standpoint of thermodynamics

The Peltier effect is described by a formula showing how much energy is transferred at a given amount of electric current. Expressing it in time units, the power of the device is found, based on which the needs of the refrigerator are determined. Quiet Peltier elements for processor coolers are popular today. A small plate cools the crystal and is cooled by the cooler heatsink. The Peltier element serves as a heat pump that is guaranteed to remove heat from the central processor, preventing overheating.

In the formula in the figure through alpha, the thermo-EMF coefficients of the halves (component parts) of the element are indicated. T is the operating temperature in degrees Kelvin. In each element, as a rule, there is a side effect of Thomson: if a current flows through the conductor, and there is a gradient (directional difference) of temperatures along the line, in addition to the Joule heat, other heat will also be released. The latter is named after Thomson. In some parts of the chain, energy will be absorbed. This means that the Thomson effect has a strong influence on the operation of heaters and refrigerators. But, as already mentioned, it is a side, unaccounted for factor.

It follows from the formulations that thermal insulation between the junctions will be an effective solution to achieve maximum efficiency. The pair uses semiconductors capable of generating thermo-EMF, the electric current has to overcome its resistance. The consumed energy is proportional to the temperature difference and the difference in the thermo-EMF coefficients of substances and depends on the flowing current. The graphs represent curves, and by differentiating them in order to find extremes, it is possible to obtain the conditions for achieving the maximum temperature difference (between the room and the refrigerator).

The figures show the results of the derivative operation, where the optimal currents for the resistance R of the thermocouple and the limiting increase in the refrigeration effect are calculated. It follows from these formulas that an ideal car will turn out if:

The conductivity of the thermocouple materials is the same.
The thermal conductivity of the thermocouple materials is the same.
Thermo-EMF coefficients are the same, but opposite in sign.
The cross sections and lengths of the thermocouple legs are the same.

It is difficult to implement these conditions in practice. In this case, the limiting coefficient of performance is equal to the ratio of the cold junction temperature to the temperature difference. Let us recall that this is a characteristic of an ideal machine, which in reality is still unattainable.

How to optimize the operation of a Peltier chiller

The figures show graphs of quantities affecting the efficiency of Peltier elements. The first thing that catches your eye is that the thermo-EMF coefficient tends to zero as the concentration of charge carriers increases. This is a reminder that metals are not considered the best material for creating thermocouples. On the other hand, thermal conductivity increases. In thermodynamics, it is believed that it consists of two components:

Thermal conductivity of the crystal lattice.
Electronic thermal conductivity. The indicated component, for obvious reasons, depends on the concentration of free charge carriers and causes the growth of the curve in the presented graph. The thermal conductivity of the crystal lattice remains practically constant.

Researchers are interested in the product of the square of the thermo-EMF coefficient and electrical conductivity. The mentioned value is in the numerator of the expression for the coefficient of performance. According to the data, the extremum is observed at a concentration of free carriers in the region of 10 to 19 power units per cubic centimeter. This is three orders of magnitude less than that observed in pure metals, from which the conclusion directly follows that semiconductors will become the ideal material for Peltier elements.

The share of the second component is already relatively small to the smaller side along the abscissa; it is also allowed to take materials from this interval. The electrical conductivity of dielectrics is too low, which explains the impossibility of their use in this context. All this makes it possible to establish the reason why Altenkirch's conclusions are not taken seriously.

Quantum theory applied to Peltier elements

Thermodynamics does not allow an accurate calculation, but it qualitatively describes the process of selecting materials for Peltier elements. To remedy the situation, physicists are calling for help from quantum theory. It operates with the previous values, expressed through the concentration of free charge carriers, chemical potential, Boltzmann's constant. Such theories are also called kinetic (or microscopic), because the illusory and unknown world of the smallest particles is considered. Among the designations there are:

l is the mean free path of charge carriers. Depends on temperature. The result is determined by the exponent of the electron scattering mechanism r (for atomic lattices it is 0; for ionic and below Debye temperatures - 0.5; above Debye - 1; for scattering by impurity ions - 2).
f is the Fermi distribution function (over energy levels).
x is the reduced kinetic energy of charge carriers.

The integrals of the Fermi functions are listed in tables, their calculation is not difficult. The equations of the microscopic theory are solved with respect to the coefficients of thermo-EMF and electrical conductivity, which makes it possible to find the coefficient of performance. These complex operations were performed by B.I. Bock, who established that the optimal value of the Seebeck coefficient is in the range between 150 and 400 μV / K, but depends on the degree of the scattering mechanism. At first glance, it is clear that the values \u200b\u200bfor metals are not observed. As a result, a group of physicists led by Ioffe showed that the best material for thermocouples must satisfy a number of conditions:

Maximum ratio of carrier mobility to the thermal conductivity of the crystal lattice.
Carrier concentration according to the formula shown in the figure.

V.P. Juse shows which substances have the required mobility. Their crystal structure is in the middle between atomic and metallic. The introduction of impurities into the material always lowers the mobility. This explains the fact that the thermo-emf coefficient for alloys is higher than for pure materials. But impurities increase r. For an ideal substance that does not exist in nature, the thermo-EMF coefficient should remain constant, equal to 172 μV / K. It is required that the concentration changed according to the law indicated in the figure (see item 2).

Semiconductors are distinguished by the ability to select materials where the concentration of charge carriers depends on temperature, and to find those where the difference is practically zero. By combining these qualities, it is possible to try to find the material closest to the ideal.

Refrigerator designs

To enhance the effect, Peltier elements are combined in parallel. In this case, their capacities add up. To design your own refrigerators, you need to be aware of the calculation of heat loss through plane structures. Special calculators have been created, many are available online.

Designing at random is not profitable for obvious reasons. And the good news is that Peltier elements have dropped significantly in recent years. On Ali-express, buy 60 W products from China for 300 rubles. It is not difficult to make sure that for 3000 you can assemble a refrigerator. And what temperature it will maintain depends on the design that requires calculation.