Thermoelectric conversion refers to thermal energy andelectric energyMutual conversion between.Thermoelectric effects include Seebeck effect, Peltier effect and Thompson effect.The discovery of thermoelectric conversion effect has aroused great interest in the scientific community, because from a macro perspective, thermoelectric conversion effect means the direct conversion between thermal energy and electric energy.How to make this effect into energy conversion and utilization in practical applications.
In our modern life, from industrial production, transportation to daily life, we are consuming a lot of energy every day, but these energies have not been fully utilized.In the process of energy utilization, there is always a part of energy that cannot be used, but is converted into heat energy and lost.applicationThermoelectric materialThis energy can be used for thermoelectric conversion.
Thermoelectric material
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Thermoelectric material is a kind of functional material that can transform electric energy and thermal energy through the movement and interaction of its internal carriers.Compared with the general power generation method, the advantage is that there are no external rotating parts, so there is no noise and wear between parts during operation.In addition, since it has no fluid medium, it can be said that there is basically no environmental pollution.The main characteristics of thermoelectric materials are that they can pack heat like compression software and transmit it to the carrier of electrical energy in the material - electron or hole carriers. When they transport heat from the high temperature end to the low temperature end, due to the directional movement of electrons or holes, voltage will be generated at both ends of this material.The generated voltage provides available energy for people.
Thermoelectric materialThe ideal characteristics of the general requirements, low internal resistance to reduce the loss of internal current (heating);Lower thermal conductivity (thermal conductivity) to reduce heat conduction from high temperature end to low temperature end;High thermoelectric EMF (open circuit).The thermoelectric EMF of most materials is only a few microvolts per degree temperature difference, which is not suitable for thermoelectric materials.The most suitable materials are semiconductor materials, such as lead telluride, silicon germanium alloy, germanium telluride, etc.[1]
Principle of thermoelectric effect
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Thermoelectric effects include the following three basic effects:
(1) The first thermoelectric effect is also called "Seebeck effect".Connect two different conductors into a closed loop. If the temperature of two contacts is different, an electric potential will be generated in the loop, called "thermal electric potential" (Figure 1a). The greater the temperature difference, the greater the thermoelectric potential.
(2) The second thermoelectric effect is also called "Peltier effect".When the current passes through the circuit composed of two different metals, in addition to producing Joule heat in the metal conductor, it also absorbs or emits a certain amount of heat at the contact - Peltier heat (Figure 1b).
(3) The third thermoelectric effect is also called "Thompson effect".If the temperature difference between two ends of a metal conductor is kept constantΔT. At timeτ If the current i is passed inside, a certain amount of heat Q will be released or absorbed between the two ends according to the different current directionsT(Thomson fever), and QT=σiτΔT
Whereσ——Thomson coefficient.Thomson effect is reversible (Fig. 1c).
The thermoelectric converter is also a heat engine, which absorbs heat from a high temperature heat source, releases heat to a low temperature heat source, and converts part of the heat into electrical work.Therefore, its highest theoretical efficiency is still the efficiency of Carnot cycle.Due to the existence of various losses, the efficiency of thermoelectric converters is far from the limit of Carnot cycle.Theoretical analysis shows that the efficiency of the thermoelectric converter can be more than 10%, but the efficiency of the actually built devices is much lower than this value. With the development of semiconductor materials, the efficiency of the thermoelectric converter is close to 20%, which is a reasonable goal.As for application, the residual heat of oil lamp can be used to power the radio in remote areas of Africa, and it can be driven by seawater temperature difference in the seaSonobuoy。[2]
