Early 19th century. The Golden Age of Physics and Electrical Engineering. In 1834, French watchmaker and naturalist Jean-Charles Peltier placed a drop of water between bismuth and antimony electrodes and then passed an electric current through the circuit. To his amazement, he saw that the drop suddenly froze.
ABOUT thermal effect electric current on conductors was known, but the opposite effect was akin to magic. One can understand Peltier’s feelings: this phenomenon at the junction of two different areas of physics - thermodynamics and electricity - still evokes a feeling of miracle today.
The problem of cooling then was not as acute as it is today. Therefore, the Peltier effect was turned to only almost two centuries later, when electronic devices appeared, the operation of which required miniature cooling systems. Dignity Peltier cooling elements are small dimensions, absence of moving parts, the possibility of cascade connection to obtain large temperature differences.
In addition, the Peltier effect is reversible: when the polarity of the current through the module is changed, cooling is replaced by heating, so systems for precise temperature maintenance - thermostats - can easily be implemented on it. The disadvantage of Peltier elements (modules) is their low efficiency, which requires the supply of large current values to obtain a noticeable temperature difference. It is also difficult to remove heat from the plate opposite the cooled plane.
But first things first. First, let's try to consider physical processes, responsible for the observed phenomenon. Without plunging into the abyss of mathematical calculations, we will simply try to understand the nature of this interesting physical phenomenon.
Because the we're talking about about temperature phenomena, physicists, for the convenience of mathematical description, replace vibrations of the atomic lattice of a material with a certain gas consisting of particles - phonons.
The temperature of the phonon gas depends on the temperature environment and properties of the metal. Then any metal is a mixture of electron and phonon gases that are in thermodynamic equilibrium. When two different metals come into contact in the absence of an external field, the “hotter” electron gas penetrates into the zone of the “colder” one, creating the well-known contact potential difference.
When applying a potential difference to the transition, i.e. When current flows through the boundary of two metals, electrons take energy from the phonons of one metal and transfer it to the phonon gas of the other. When the polarity changes, the transfer of energy, which means heating and cooling, change sign.
In semiconductors, electrons and “holes” are responsible for energy transfer, but the mechanism of heat transfer and the appearance of a temperature difference remains the same. The temperature difference increases until the high-energy electrons are depleted. Temperature equilibrium occurs. This is modern painting descriptions Peltier effect.
From it it is clear that efficiency of the Peltier element depends on the selection of a pair of materials, the current strength and the rate of heat removal from the hot zone. For modern materials (usually semiconductors), the efficiency is 5-8%.
And now about the practical application of the Peltier effect. To increase it, individual thermocouples (junctions of two different materials) are assembled into groups consisting of tens and hundreds of elements. The main purpose of such modules is cooling small objects or microcircuits.
Thermoelectric cooling module
Peltier effect modules are widely used in night vision devices with an array of infrared receivers. Charge-coupled device chips (CCDs), which are also used in digital cameras today, require deep cooling to record images in the infrared region. Peltier modules cool infrared detectors in telescopes, active elements of lasers to stabilize the radiation frequency, and in precision time systems. But these are all military and special purpose applications.
Recently, Peltier modules have found application in household products. Mainly in automotive technology: air conditioners, portable refrigerators, water coolers.
An example of the practical use of the Peltier effect
The most interesting and promising application of modules is computer technology. High-performance microprocessors, processors and video card chips highlight a large number of heat. To cool them, high-speed fans are used, which create significant acoustic noise. The use of Peltier modules as part of combined cooling systems eliminates noise with significant heat extraction.
Compact USB -refrigerator using Peltier modules
And finally, a logical question: will Peltier modules replace the usual cooling systems in compression household refrigerators? Today this is unprofitable in terms of efficiency (low efficiency) and price. The cost of powerful modules is still quite high.
But technology and materials science do not stand still. Eliminate the possibility of the emergence of new, cheaper materials with greater efficiency and high value Peltier coefficient is not possible. Already today there are reports from research laboratories about the amazing properties of nanocarbon materials that can radically change the situation with effective cooling systems.
There have been reports of the high thermoelectric efficiency of clastrates - solid solutions similar in structure to hydrates. When these materials leave the research laboratories, completely silent refrigerators with an unlimited service life will replace our usual home models.
P.S. One of the most interesting features thermoelectric technology is that it can not only use electrical energy to obtain heat and cold, but also thanks to it we can but start the reverse process, and, for example, obtain electrical energy from heat.
An example of how you can obtain electricity from heat using a thermoelectric module () look at this video:
What do you think about this? I look forward to your comments!
Andrey Povny
The Peltier effect is that when current is passed through a circuit, in the contacts of dissimilar conductors, in addition to Joule heat, Peltier heat is released or absorbed. Peltier heat quantity Q p proportional to charge It, passed through contact
Where P– Peltier coefficient.
If you change the direction of the current, the cold and hot contacts will switch places.
There is a direct connection between the Peltier and Seebeck effects: a temperature difference causes an electric current in a circuit consisting of dissimilar conductors, and the current passing through such a circuit creates a temperature difference between the contacts. This relationship is expressed by the Thomson equation
The mechanism of the Peltier effect can be most simply and clearly explained using a metal-n-semiconductor-metal circuit; where the pins are neutral. In this case, the work functions of the metal and semiconductor are equal, there are no band bends and depletion or enrichment layers. In an equilibrium state, the Fermi levels of the metal and the semiconductor are located at the same height, and the bottom of the conduction band is located above the Fermi level of the metal, therefore, for electrons moving from the metal to the semiconductor, there is a potential barrier of height - E fp(Fig. 7.12, A).
A) b)
Rice. 7.12. Energy circuit diagram metal-n-semiconductor – metal:
A– equilibrium states; b– passage of current.
Let us apply a potential difference to the circuit U(Fig. 7.12, b). This potential difference will fall mainly in the area with high resistance, i.e. in a semiconductor, where there will be a constant change in the height of the levels. A flow of electrons appears in the circuit, directed from right to left.
When passing through the right contact, an increase in the electron energy is necessary. This energy is transferred to electrons crystal lattice as a result of scattering processes, which leads to a decrease in thermal vibrations of the lattice in this region, i.e. to heat absorption. On the left contact the reverse process occurs - the transfer of excess energy by electrons E pf crystal lattice.
It should be noted that equilibrium charge carriers, after crossing the interface, turn out to be nonequilibrium and become equilibrium only after exchanging energy with the crystal lattice.
Based on these considerations, we will estimate the Peltier coefficient. The conductivity of a metal involves electrons located near the Fermi level, the average energy of which is almost equal to the Fermi energy. Average energy of conduction electrons in a non-degenerate semiconductor
Where r– exponent depending λ ~E r.
Thus, each electron passing through the contact gains or loses energy equal to
Dividing this energy by the electron charge, we obtain the Peltier coefficient
or taking into account (7.80) and (7.73)
A similar relationship can be obtained for a metal-p-semiconductor contact
Here N C And N V– effective densities of states in the conduction band and valence band (Section 5.3).
For metal-to-metal contact, the Peltier coefficient can be determined using (7.79)
P 12 =(α 1 -α 2)T, (7.85)
or taking into account the expression for α
Where E f 1 and E f 2 – Fermi levels in metals.
Analysis of the mechanism of occurrence of the effect shows that the Peltier coefficient for metal-metal contact is significantly smaller than in the case of metal-semiconductor contact (see paragraphs 7.1, 7.2).
In a contact between dissimilar semiconductors, on the contrary, the Peltier coefficient turns out to be significantly higher, which is due to a higher potential barrier at the boundary of the p-n junction. In addition, in such a circuit one of the transitions turns out to be connected in the forward direction, and the second in the reverse direction. In the first case, it prevails recombination electron-hole pairs and the release of additional heat, and in the second one occurs generation steam and, accordingly, absorption of the same amount of heat.
The cooling effect of the contact during the passage of current is of significant practical importance, since it allows the creation of thermoelectric refrigerators for cooling electronic equipment and thermal stabilizers for supporting elements equipment. Various cooling racks are also produced, used in biology and medicine.
In functional thermal electronics, this effect is used to create thermal pulses - information carriers.
Refrigeration equipment has become so firmly established in our lives that it is even difficult to imagine how we could live without it. But classic refrigerant designs are not suitable for mobile use, for example, as a traveling cooler bag.
For this purpose, installations are used in which the operating principle is based on the Peltier effect. Let's briefly talk about this phenomenon.
What it is?
This term refers to a thermoelectric phenomenon discovered in 1834 by the French naturalist Jean-Charles Peltier. The essence of the effect is the release or absorption of heat in the area where dissimilar conductors through which electric current passes are in contact.
In accordance with the classical theory, there is the following explanation of the phenomenon: electric current transfers electrons between metals, which can accelerate or slow down their movement, depending on the contact potential difference in conductors made of different materials. Accordingly, with an increase in kinetic energy, it is converted into thermal energy.
On the second conductor, a reverse process is observed, requiring replenishment of energy, in accordance with the fundamental law of physics. This occurs due to thermal vibration, which causes cooling of the metal from which the second conductor is made.
Modern technologies make it possible to produce semiconductor elements-modules with maximum thermoelectric effect. It makes sense to briefly talk about their design.
Design and principle of operation
Modern modules are a structure consisting of two insulating plates (usually ceramic), with serially connected thermocouples located between them. A simplified diagram of such an element can be found in the figure below.
Designations:
- A – contacts for connecting to a power source;
- B – hot surface of the element;
- C – cold side;
- D – copper conductors;
- E – semiconductor based on p-junction;
- F – n-type semiconductor.
The design is made in such a way that each side of the module is in contact either p-n or n-p transitions(depending on polarity). Contacts p-n heat up, n-p – cool down (see Fig. 3). Accordingly, a temperature difference (DT) occurs on the sides of the element. To an observer, this effect will look like a transfer of thermal energy between the sides of the module. It is noteworthy that changing the power polarity leads to a change in hot and cold surfaces.
Rice. 3. A – hot side of the thermoelement, B – cold side Specifications
The characteristics of thermoelectric modules are described by the following parameters:
- cooling capacity (Q max), this characteristic is determined based on the maximum permissible current and the temperature difference between the sides of the module, measured in Watts;
- maximum temperature difference between the sides of the element (DT max), the parameter is given for ideal conditions, the unit of measurement is degrees;
- permissible current required to ensure maximum temperature difference – I max;
- the maximum voltage U max required for the current I max to reach the peak difference DT max ;
- internal resistance of the module – Resistance, indicated in Ohms;
- efficiency coefficient - COP (abbreviation from English - coefficient of performance), essentially this is the efficiency of the device, showing the ratio of cooling to power consumption. For inexpensive elements this parameter is in the range of 0.3-0.35, for more expensive models it approaches 0.5.
Marking
Let's look at how typical module markings are deciphered using the example of Figure 4.
Figure 4. Peltier module marked TEC1-12706 The marking is divided into three meaningful groups:
- Element designation. The first two letters are always unchanged (TE), indicating that this is a thermoelement. The next one indicates the size, there may be the letters “C” (standard) and “S” (small). The last number indicates how many layers (cascades) there are in the element.
- The number of thermocouples in the module shown in the photo is 127.
- The rated current is in Amperes, for us it is 6 A.
The markings of other models of the TEC1 series are read in the same way, for example: 12703, 12705, 12710, etc.
Application
Despite the rather low efficiency, thermoelectric elements are widely used in measuring, computing, and household appliances. Modules are an important operating element of the following devices:
- mobile refrigeration units;
- small generators to generate electricity;
- cooling systems in personal computers;
- coolers for cooling and heating water;
- dehumidifiers, etc.
Let us give detailed examples of the use of thermoelectric modules.
Refrigerator using Peltier elements
Thermoelectric refrigeration units are significantly inferior in performance to compressor and absorption analogues. But they have significant advantages, which makes their use advisable under certain conditions. These advantages include:
- simplicity of design;
- vibration resistance;
- absence of moving elements (except for the fan blowing the radiator);
- low noise level;
- small dimensions;
- ability to work in any position;
- long service life;
- low energy consumption.
These characteristics are ideal for mobile installations.
Peltier element as an electricity generator
Thermoelectric modules can work as electricity generators if one of their sides is subjected to forced heating. The greater the temperature difference between the sides, the higher the current generated by the source. Unfortunately, the maximum temperature for the thermal generator is limited; it cannot be higher than the melting point of the solder used in the module. Violation of this condition will lead to failure of the element.
For mass production of thermal generators, special modules with refractory solder are used; they can be heated to a temperature of 300°C. In ordinary elements, for example, TEC1 12715, the limit is 150 degrees.
Since the efficiency of such devices is low, they are used only in cases where it is not possible to use a more efficient source of electrical energy. However, 5-10 W thermal generators are in demand among tourists, geologists and residents of remote areas. Large and powerful stationary installations powered by high-temperature fuel are used to power gas distribution units, meteorological station equipment, etc.
To cool the processor
Relatively recently, these modules began to be used in CPU cooling systems of personal computers. Considering low efficiency thermoelements, the benefit of such structures is rather doubtful. For example, to cool a 100-170W heat source (fits most modern models CPU), you will need to spend 400-680 W, which requires the installation of a powerful power supply.
The second pitfall is that an unloaded processor will release less thermal energy, and the module can cool it below the dew point. As a result, condensation will begin to form, which is guaranteed to damage the electronics.
Those who decide to create such a system on their own will need to carry out a series of calculations to select the power of the module for a specific processor model.
Based on the above, using these modules as a CPU cooling system is not cost-effective; in addition, they can cause computer equipment to fail.
The situation is completely different with hybrid devices, where thermal modules are used in conjunction with water or air cooling.
Hybrid cooling systems have proven their effectiveness, but the high cost limits the circle of their admirers.
Air conditioner based on Peltier elements
Theoretically, such a device will be structurally much simpler than classic climate control systems, but it all comes down to low performance. It’s one thing to cool a small volume of a refrigerator, another thing to cool a room or the interior of a car. Air conditioners using thermoelectric modules will consume more electricity (3-4 times) than equipment running on refrigerant.
As for using it as a car climate control system, the power of a standard generator will not be enough to operate such a device. Replacing it with more efficient equipment will lead to significant fuel consumption, which is not cost-effective.
In thematic forums, discussions on this topic periodically arise and various home-made designs are considered, but a full-fledged working prototype has not yet been created (not counting the air conditioner for a hamster). It is quite possible that the situation will change when modules with more acceptable efficiency become widely available.
For cooling water
The thermoelectric element is often used as a coolant for water coolers. The design includes: a cooling module, a thermostat-controlled controller and a heater. This implementation is much simpler and cheaper than a compressor circuit; in addition, it is more reliable and easier to operate. But there are also certain disadvantages:
- water does not cool below 10-12°C;
- cooling takes longer than its compressor counterpart, therefore, such a cooler is not suitable for an office with big amount workers;
- the device is sensitive to external temperature, in a warm room the water will not cool to the minimum temperature;
- Installation in dusty rooms is not recommended, as the fan may become clogged and the cooling module may fail.
Tabletop water cooler using Peltier element Air dryer based on Peltier elements
Unlike an air conditioner, the implementation of a dehumidifier using thermoelectric elements is quite possible. The design is quite simple and inexpensive. The cooling module lowers the temperature of the radiator below the dew point, as a result, moisture contained in the air passing through the device settles on it. The settled water is discharged into a special storage tank.
Despite the low efficiency, in this case the efficiency of the device is quite satisfactory.
How to connect?
There will be no problems connecting the module; a constant voltage must be applied to the output wires; its value is indicated in the datasheet of the element. The red wire must be connected to the positive, the black wire to the negative. Attention! Reversing the polarity reverses the positions of the cooled and heated surfaces.
How to check the Peltier element for functionality?
The simplest and most reliable method is tactile. It is necessary to connect the module to the appropriate voltage source and touch its different sides. For a working element, one of them will be warmer, the other colder.
If you don’t have a suitable source at hand, you will need a multimeter and a lighter. The verification process is quite simple:
- connect the probes to the module terminals;
- bring the lit lighter to one of the sides;
- We observe the readings of the device.
In the working module, when one of the sides is heated, an electric current is generated, which will be displayed on the device display.
How to make a Peltier element with your own hands?
It is almost impossible to make a homemade module at home, especially since there is no point in doing so, given their relatively low cost (about $4-$10). But you can assemble a device that will be useful on a hike, for example, a thermoelectric generator.
To stabilize the voltage, it is necessary to assemble a simple converter on the L6920 IC chip.
A voltage in the range of 0.8-5.5 V is supplied to the input of such a converter; at the output it will produce a stable 5 V, which is quite enough to recharge most mobile devices. If a conventional Peltier element is used, it is necessary to limit the operating temperature range of the heated side to 150 °C. To avoid the hassle of tracking, it is better to use a pot of boiling water as a heat source. In this case, the element is guaranteed not to heat above 100 °C.
Peltier effect Peltier effect
the release or absorption of heat when current passes through a 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.
PELTIER EFFECTPELTIER EFFECT, for thermoelectric phenomena (cm. THERMOELECTRIC PHENOMENA), consists in the release or absorption of heat when an electric current passes through a contact (junction) of two different conductors. The Peltier effect is the inverse of the Seebeck effect (cm. SEEBECK EFFECT).
Discovered in 1834 by J. Pelletier (cm. PELTIER Jean Charles Atanaz), who discovered that when current passes through a junction of two different conductors, the temperature of the junction changes. In 1838 E. H. Lenz (cm. LENZ Emiliy Khristianovich) showed that with a sufficiently high current it is possible to either freeze or bring to a boil a drop of water applied to a junction by changing the direction of the current.
The essence of the Peltier effect is that when an electric current passes through the contact of two metals or semiconductors in the area of their contact, in addition to the usual Joule heat, an additional amount of heat is released or absorbed, called Peltier heat Q p. In contrast to Joule heat, which is proportional to the square current strength, the value of Q p is proportional to the first power of the current.
Q p = P. I. t.
t - current passage time,
I - current strength.
P is the Peltier coefficient, a proportionality coefficient that depends on the nature of the materials forming the contact. Theoretical ideas make it possible to express the Peltier coefficient through the microscopic characteristics of conduction electrons.
Peltier coefficient P = T Da, where T - absolute temperature, and Da is the difference in thermoelectric coefficients of the conductors. The direction of the current determines whether Peltier heat is released or absorbed.
The reason for the effect is that in the case of contact between metals or semiconductors, an internal contact potential difference arises at the boundary. This leads to potential energy carriers on both sides of the contact becomes different, since the average energy of current carriers depends on their energy spectrum, concentration and mechanisms of their scattering and is different in different conductors. Since the average energy of the electrons involved in current transfer differs in different conductors, in the process of collisions with lattice ions, carriers give up excess kinetic energy to the lattice, and heat is released. If, when passing through a contact, the potential energy of carriers decreases, then their kinetic energy and electrons, colliding with lattice ions, increase their energy to an average value, while Peltier heat is absorbed. Thus, when electrons pass through a contact, the electrons either transfer excess energy to the atoms or replenish it at their expense.
During the transition of electrons from a semiconductor to a metal, the energy of the conduction electrons of the semiconductor is significantly higher than the Fermi level (see Fermi energy (cm. FERMI ENERGY)) metal, and the electrons give up their excess energy. The Peltier effect is especially strong in semiconductors, which is used to create cooling and heating semiconductor devices, including the creation of microrefrigerators in refrigeration units.
encyclopedic Dictionary. 2009 .
See what the “Peltier effect” is in other dictionaries:
The release or absorption of heat during the passage of electricity. current I through the contact of two different. conductors. The release of heat is replaced by absorption when the direction of the current changes. French opened physicist J. Peltier in 1834. The amount of heat... ... Physical encyclopedia
The Peltier effect is the process of releasing or absorbing heat when an electric current passes through the contact of two dissimilar conductors. The amount of heat generated 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 a 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. Pelletier... 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 allocated or ... Great Soviet Encyclopedia
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 type ... Wikipedia
Performed by a student from the AT-11 group
Mukharlyamov Ildar
Peltier effect
Input: electric current.
Output: amount of heat, temperature.
Essence
When a direct electric current flows in a circuit consisting of dissimilar conductors, heat is absorbed or released at the contact points (junctions) of the conductors, depending on the direction of the current. The Peltier heat released or absorbed in the layer is proportional to the total charge passing through the junction, or the product of current and time. The Peltier coefficient depends on the type of contacting conductors and their temperatures.
R or n) (see picture). The explanation of the Peltier effect lies in the interaction of conduction electrons, slowed down or accelerated in the contact potential of the pn junction, with thermal vibrations of atoms in the semiconductor array. As a result, depending on the direction of movement of electrons and, accordingly, current, heating () or cooling occurs (T With ) section of the semiconductor immediately adjacent to the junction (R-n or n-p junction).
Mathematical description
,
Where 
- Peltier heat, J
P – Peltier coefficient;
q– charge passed through the contact, C;
I- Current in the conductor, A;
t– time, s.
The Peltier heat changes sign when the direction of the current changes. Parameter change limits:
up to 1 V – semiconductor;
I– up to several amperes;
Q– from 0 to 50 J (in 1 sec.)
The Peltier coefficient can be expressed in terms of the Thomson coefficient:
q T,
Where 
Thomson;
Application
The Peltier module is notable for the fact that when electric current passes through it, it acts as a thermal pump, i.e. pumps heat from one side to the other, due to which it is actively used in various systems cooling, from beverage refrigerators to cooling systems for high-power semiconductor lasers and various chips, especially where it is necessary to speed up the process of extracting heat from a heating element. The main areas of practical use of the Peltier effect in semiconductors: obtaining cold to create thermoelectric cooling devices, heating for heating purposes, thermostatting, controlling the crystallization process under constant temperature conditions.
To increase the signal-to-noise ratio of photomultiplier tubes (PMTs), a method is proposed for cooling photocathodes with thermoelectric elements located inside the vacuum shell of the PMT (US Pat. 3757151).
A gas sampling device in which the condensate drain is integral with the refrigerator. The cold junctions of the Peltier elements are fixed on the inside of the hollow cone, and a pipeline branches off from it for sampling the measuring gas. The refrigerator differs in that a battery of thermoelements is provided as a generator of current consumed by Peltier elements, the hot junctions of which are located in the flue gas channel, and the cold junctions are in the external space (Application 1297U02 Germany).
Device image
Pros and cons of using TEM
Often, the advantages of Peltier modules include:
relatively small dimensions;
the ability to work both for cooling and heating the system;
no moving parts or mechanical components subject to wear.
At the same time, TEMs have a number of disadvantages that significantly hinder their widespread practical use. Among them are the following:
low module efficiency;
the need for a current source for their operation;
large power consumption to achieve a noticeable temperature difference and, as a result, significant heat generation;
limited dimensions
Control questions:
What is the essence of the Peltier effect?
(When a direct electric current flows in a circuit consisting of dissimilar conductors, heat is absorbed or released at the contact points (junctions) of the conductors, depending on the direction of the current.)
What does the Peltier coefficient depend on?
(The Peltier coefficient depends on the type of contacting conductors and their temperatures.)
What conductors are used in the Peltier effect?
The Peltier effect is most pronounced at the contacts of semiconductors with different types of conductivity ( R or n)
How is the Peltier coefficient related to the Thomson coefficient?
q T,
Where 
Thomson;
T – temperature coefficient, K.
Main application of the effect?
(Used in various cooling systems)
Tasks:
Find the Peltier coefficient, knowing that a current of 10 A passed in 3 seconds and released 50 J of heat.
What will the Thomson coefficient be equal to if the charge is 70 C and the absolute temperature is 300 K. The Peltier coefficient is 1.7 V.
How much heat will be released at the points of contact of dissimilar conductors if the Peltier coefficient is 73 mV, and the charge passed through the thermal module is 40 C.
Solution: Qp=P*q=2.92 (J).
Find the time it takes for the current to pass in the conductor, knowing that the voltage is 120 V, the resistance is 10 Ohms. In this case, 1 J of heat is released, and the Peltier coefficient is 60 mV.
