Thermoelectric power devices provide an attractive possibility for directly converting
heat energy to electricity. Their lack of moving parts results in a long
lifetime and practically no need of maintenance. Due to the relatively low
efficiency and power density of today's commercially available devices, they
are generally only used in environments where their solid-state nature outweighs
their poor efficiency. A prominent example is their use in satellites and
spacecraft. Further increase in efficiency and proper customization of given
thermal and geometrical conditions will open the wide range of
combustion engine applications. Predictive simulation is an essential tool for
thermoelectric device development and efficiency improvement.
An accurate model set for non-isothermal simulation incorporating large
temperature gradients has been assessed and implemented in Minimos-NT.
Therefore, the theoretical background has been elaborated between the two
approaches of phenomenological irreversible thermodynamics and systematic
derivation from Boltzmann's equation using the method of moments.
Every thermoelectrically relevant material defines its optimum figure of merit
in a certain temperature range. While silicon and Si/Ge are good performers
for relatively high temperatures, the lower temperature range can be covered by
lead chalcogenides and other selected compound semiconductors. Relevant data
of the important materials PbTe and PbSnTe has been collected from literature.
Mobility data has been extracted from Monte Carlo simulations in addition to
available measurement data. Proper models have been formulated and implemented
in Minimos-NT. In order to estimate the accuracy of the simulation results
carried out with Minimos-NT, a sensitivity analysis for several model
parameters has been carried out. The band gap model's accuracy has turned out
to be most important because of its big influence on carrier generation. A
simulation study of conventional and large-area pn-junction thermoelectric
generators has been carried out. The novel device structures benefit from
carrier generation in the heated zones, and thus higher electrical currents can
be obtained.
Several software tools working in conjunction with Minimos-NT have been
developed and extended. The structure generation tool, initially
limited to rectangular structures and Manhattan grids, was extended to
non-rectangular device structures and proper meshes. The optimization
framework SIESTA has been partially revised and extended by a user-friendly
graphical interface using state-of-the-art graphics libraries.
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