Analytical calculation of the effect of metal coating of thermoelectric legs on the efficiency of generator thermoelement
Keywords:
thermoelement reliability, thermoelectric leg, metal coating, shunt, thermoelectric figure of merit, effective thermoEMF, coating thickness, maximum thermoelement efficiencyAbstract
The effect of the protective metal coating of the lateral surface of thermoelectric legs on the efficiency of a generator thermoelement has been determined. At the same time, it is taken into account that the metal coating shunts the thermoelectric leg both in terms of electric current and heat flux. Theoretical calculations were made without taking into account eddy thermoelectric currents in the "thermoelectric material - protective coating" system and the temperature dependences of the characteristics of the metal and thermoelectric material for the "bismuth telluride - nickel" couple. The effects of the metal coating on the effective thermoEMF of the leg are taken into account. It is shown that when the influence of the metal coating on the thermoEMF of the leg is taken into account, the efficiency is a sharply monotonically decreasing function of the thickness of the metal coating, so that in order to achieve the efficiency of a thermoelement at a level of about 5%, the coating thickness should be no more than 0.5 µm at a leg height of 1 mm, about 0.9 µm for the leg height of 2 mm and about 1 µm with a leg height of 3 mm. In so doing, it is assumed that the electrical contact resistance is about 10-5 Ohm•cm2, and the thermal contact resistance is absent. However, in the presence of thermal contact resistance at a level of 0.8 K•cm2 /W, the efficiency of the thermoelement remains at a level of about 5.3% even with a coating thickness of 5 μm.
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