Rigorous calculations related to functionally graded and segmented thermoelements

Abstract

Functionally grading thermoelements is an effective method of increasing the performance of a thermoelectric device. It is achieved either by a gradual change of the material composition along the length of the thermoelement, or by segmenting different materials, so that the figure-of-merit is close to maximum at every point of the thermoelement, under a given temperature difference. The overall performance of such a thermoelement strongly depends on the distribution of thermoelectric parameters and temperature, and on the operating conditions (large temperature gradient, high electrical current). In realistic calculations Thomson and distributed Peltier effects cannot be neglected. We use finite element analysis to obtain realistic results, which are compared with ones obtained using the formulae of Ioffe (1957). Influences of the Thomson and distributed Peltier effects are calculated for thermoelements operating in cooling and generating modes.