The thermoconverter (Peltier module) works according to the principle opposite to the action of a thermocouple - the appearance of a temperature difference when an electric current flows.
How does the Peltier element work?
It is quite simple to use the Peltier module, the principle of which is the generation or absorption of heat at the moment of contact of different materials during the passage of current through it . The density of the energy flux of electrons before and after the contact is different. If the output is less, it means that heat is released there. When the electrons in the contact are inhibited by the electric field, they transfer kinetic energy to the crystal lattice, heating it. If they accelerate, heat is absorbed. This is due to the fact that part of the energy is taken from the crystal lattice and its cooling occurs.
To a large extent, this phenomenon is inherent in semiconductors, due to the large difference in charges.
The Peltier module, the use of which is the subject of our review, is used to create thermoelectric cooling devices (TEM). The simplest of them consists of two p-type and n-type semiconductors connected in series through copper contacts.
If electrons move from the semiconductor "p" to "n", at the first transition with a metal jumper, they recombine with the release of energy. The next transition from the semiconductor "p" to the copper conductor is accompanied by the "pulling" of electrons through the contact by an electric field. This process leads to energy absorption and cooling of the area around the contact. Similarly, processes occur at the following transitions.
When the heated and cooled contacts are located in different parallel planes, a practical implementation of the method is obtained. Semiconductors are made from selenium, bismuth, antimony or tellurium. The Peltier module accommodates a large number of thermocouples placed between ceramic plates made of nitride or aluminum oxide.
Factors Affecting TEM Efficiency
- Current strength.
- The number of thermocouples (up to several hundred).
- Types of semiconductors.
- Cooling rate.
It has not yet been possible to achieve large quantities due to low efficiency (5-8%) and high cost. For TEM to work successfully, it is necessary to ensure efficient heat removal from the heated side. This creates difficulties in the practical implementation of the method. If you change the polarity, the cold and hot sides change with each other.
Advantages and disadvantages of modules
The need for TEM appeared with the advent of electronic devices that needed miniature cooling systems. The advantages of the modules are as follows:
- compactness;
- lack of movable joints;
- Peltier module the principle of operation is reversible when changing polarity;
- simplicity of cascade connections to increase power.
The main disadvantage of the module is its low efficiency. This is manifested in high power consumption while achieving the desired cooling effect. In addition, it has a high cost.
TEM application
Peltier module is mainly used for cooling microcircuits and small parts. The beginning was laid for cooling elements of military equipment:
- microcircuits;
- infrared detectors;
- laser elements;
- crystal oscillators.
The Peltier thermoelectric module gradually began to be used in household appliances: to create refrigerators, air conditioners, generators, temperature regulators. Its main purpose is to cool small objects.
CPU cooling
The main components of computers are constantly being improved, which leads to an increase in heat dissipation. Together with them, cooling systems are developed using innovative technologies, with modern controls. The Peltier module found application in this area primarily in the cooling of microcircuits and other radio components. Traditional coolers can no longer cope with forced overclocking modes of microprocessors. And an increase in the frequency of the processors makes it possible to increase their speed.
Increasing the fan speed results in significant noise. It is eliminated through the use of a Peltier module in a combined cooling system. In this way, leading firms quickly mastered the production of efficient cooling systems, which became in great demand.
Heat is usually removed from processors by coolers. Airflow can be drawn in from the outside or from the inside of the system unit. The main problem is that the air temperature is sometimes insufficient for heat removal. Therefore, TEMs began to be used to cool the flow of air entering the system unit, thereby increasing the heat transfer efficiency. Thus, the built-in air conditioner is an assistant to the traditional computer cooling system.
Aluminum radiators are mounted on both sides of the module. On the cold plate side, cooling air is pumped to the processor. After he takes the heat, another fan blows it through the radiator of the module’s hot plate.
A modern TEM is controlled by an electronic device with a temperature sensor, where the degree of cooling is proportional to the heating of the processor.
Enhancing the cooling of processors also poses some problems.
- The simple Peltier cooling modules are designed for continuous operation. With reduced power consumption, heat dissipation is also reduced, which can cause crystal overcooling and subsequent processor freezing.
- If the operation of the cooler and the refrigerator is not properly coordinated, the latter can go into heating mode instead of cooling. A source of additional heat will cause the processor to overheat.
Thus, modern processors need advanced cooling technologies with control over the operation of the modules themselves. Such changes in operating modes do not occur with video cards, which also require intensive cooling. Therefore, TEM is ideal for them.
DIY refrigerator
In the middle of the last century, domestic industry tried to master the production of small-sized refrigerators based on the Peltier effect. Existing technologies of that time did not allow this. Now the constraining factor is mainly the high price, but attempts continue, and successes have already been achieved.
The widespread production of thermoelectric devices allows you to create your own small refrigerator, convenient for use in cars. Its basis is a "sandwich", which is done as follows.
- A layer of heat-conducting paste of the type KPT-8 is applied to the upper radiator and the Peltier module is glued on one side of the ceramic surface.
- Similarly, another radiator is attached to it from the bottom side, designed to be placed in the refrigerator chamber.
- The whole device is tightly compressed and dried for 4-5 hours.
- Coolers are installed on both radiators: the top will remove heat, and the bottom will equalize the temperature in the refrigerator chamber.
The refrigerator case is made with a heat-insulating gasket inside. It is important that it closes tightly. To do this, you can use a regular plastic tool box.
12 V power is supplied from the vehicle system. It can also be made from 220 V AC, with a power supply. The AC to DC conversion circuit is the simplest. It contains a rectifier bridge and a ripple-smoothing capacitor. It is important that they do not exceed 5% of the nominal value at the output, otherwise the efficiency of the device decreases. The module has two outputs from colored wires. A plus is always connected to red, a minus to black.
TEM power should correspond to the volume of the box. The first 3 digits of the marking indicate the number of pairs of semiconductor trace elements inside the module (49-127 or more). The current strength is expressed by the last two digits of the marking (from 3 to 15 A). If there is not enough power, one more module must be glued to the radiators.
Note! If the current strength exceeds the power of the element, it will heat up on both sides and will quickly fail.
Peltier module: electric power generator
TEM can be used to generate electricity. To do this, create a temperature difference between the plates, and the thermocouples located between them will generate an electric current.
For practical use, a TEM of at least 5 V. is needed. Then it can be used to charge a mobile phone. Due to the low efficiency of the Peltier module, a step-up DC-DC converter is required. To build the generator you will need:
- 2 Peltier modules TEC1-12705 with a plate size of 40x40 mm;
- converter EK-1674;
- 3 mm thick aluminum plates;
- pan for water;
- heat resistant adhesive.
Between the plates, two modules are placed on the glue, and then the whole structure is fixed at the bottom of the pan. If you fill it with water and put it on fire, you will get the required temperature difference, which generates an EMF of the order of 1.5 V. By connecting the modules to the boost converter, you can increase the voltage to 5 V, which is necessary to charge the phone’s battery.
The greater the temperature difference between water and the bottom heated plate, the more efficient the generator is. Therefore, we must try to reduce the heating of water in different ways: make it flowing, often replace it with fresh, etc. An effective way to increase the temperature difference is to cascade the inclusion of modules when they are stacked on top of each other. The increase in the overall dimensions of the device allows you to place more elements between the plates and thereby increase the overall power.
Generator performance will be enough to charge small batteries, LED lamps or a radio. Note! To create thermal generators, modules are required that can operate at 300-400 0 C! The rest are suitable only for trial tests.
Unlike other means of alternative generation of electricity, they can work while driving, if you create something like a catalytic heater.
Domestic Peltier Modules
TEM of its production appeared on our market not so long ago. They are highly reliable and have good characteristics. The Peltier module, which is in high demand, has dimensions of 40x40 mm. It is designed for a maximum current of 6 A and a voltage of up to 15 V.
You can buy a domestic Peltier module for a small price. With a power consumption of 85 W, it creates a temperature difference of 60 0 C. Together with the cooler, it is able to protect a processor with a power dissipation of 40 W from overheating.
Characteristics of modules of leading companies
Foreign devices are on the market in a greater variety. To protect the processors of leading companies, a Peltier module is used as a refrigerator PAX56B, the price of which, complete with a fan, is $ 35.
With dimensions of 30x30 mm, it maintains the temperature of the processor no higher than 63 0 C with an allocated power of 25 watts. A voltage of 5 V is sufficient for power, and the current does not exceed 1.5 A.
The P6tier RA6EXH module, which provides normal temperature conditions with a dissipation power of 40 watts, is well suited for cooling the processor. The area of its module is 40x40 mm, and the current consumption is up to 8 A. In addition to its impressive size - 60x60x52.5 mm (together with a fan) - the device requires free space around it. Its price is $ 65.
When a Peltier module is used, its technical characteristics must correspond to the needs of the refrigerated devices. They should not have too low a temperature. This can lead to moisture condensation, which is detrimental to the electronics.
Modules for the manufacture of generators, such as TEC1-12706, TEC1-12709, are more powerful - 72 W and 108 W, respectively. They are distinguished by marking, always applied on the hot side. The maximum allowable temperature of the hot side is 150-160 0 C. The higher the temperature difference between the plates, the higher the output voltage. The device operates at a maximum temperature difference of 600 0 C.
You can buy a Peltier module inexpensively - about $ 10 or less apiece, if you search well. Quite often, sellers significantly raise prices, but can be found several times cheaper if purchased at a sale.
Conclusion
The Peltier effect is currently used in the creation of small refrigerators, which are necessary for modern technology. The reversibility of the process makes it possible to manufacture microelectric power plants that are in demand for charging batteries of electronic devices.
Unlike other means of alternative generation of electricity, they can work while driving, if you install a catalytic heater.