ZT – figure of merit
The figure of merit, denoted as ZT, is a crucial parameter used to assess the efficiency of thermocouples and thermoelectric generators. It plays a central role in formulas related to these devices.
The phenomenon where a temperature difference along the ends of an electrical conductor induces an electrical voltage is known as the Seebeck effect, named after its discoverer, Thomas Johann Seebeck. The magnitude of this voltage is dependent on the material used, and the ratio of electrical voltage to temperature difference is referred to as the Seebeck coefficient.
The Seebeck effect is primarily employed in temperature measurement using thermocouples. Additionally, it is gaining significance in the conversion of waste heat into electrical energy through thermoelectric generators. These processes are reversible, and the Peltier effect, where voltage differences produce temperature differences, is its counterpart. The Peltier effect finds applications in cooling or heating, especially in microelectronics and nanotechnology.
The ZT value, a dimensionless index, increases with the square of the Seebeck coefficient, the average absolute operating temperature, and electrical conductivity. Conversely, it decreases with specific thermal conductivity. Since all these factors are temperature-dependent, calculating the ZT value becomes complex. The ZT value is defined by the equation:
ZT = Seebeck coefficient squared * absolute temperature * electrical conductivity / specific thermal conductivity the material values must be taken into account as a function of temperature and time.
Material values must be considered as functions of temperature and time in this equation.
To overcome the challenges in calculating the ZT value, precise measuring instruments are employed. Linseis provides such instruments for determining the figure of merit for electrical conductors and semiconductors, accurately measuring individual material values and delivering the ZT value.
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