Semiconductor material production processes are evolving such that TE materials with controlled spatially dependent properties (Seebeck Coefficient, Electrical Conductivity and Thermal Conductivity) become more practical to fabricate on a commercial scale. Therefore, it is important to determine what performance advantages are achievable by fabricating such TE elements.
In this session, the governing equations for optimum performance of Distributed Transport Properties (DTP) TE systems are derived and solved in closed analytic form. The analyses assume TE material intrinsic properties are independent of temperature and are locally isotropic other than in the direction of intended change. A one-dimensional geometry is evaluated since added dimensions do not contribute to any further theoretical increase in performance. Other properties, ZT, current density, shape and boundary conditions are fixed, thereby expressing the effects of distributed intrinsic material properties in the absence of other confounding changes.
Results are presented as analytic solutions for optimum efficiency and DTP property variance with position. Performance gains are shown to increase with temperature differential. Gains are larger for cooling and heating and smaller for power generation modes of operation. Substantial variations in the Seebeck coefficient and electrical and thermal resistivities are required to achieve the theoretical maximum performance gains. This session will show that the performance of TE elements can increase maximum cooling temperature and COP at least 20% compared to TE elements with the same ZT but of uniform composition. Further gains are possible in production systems using DTP TE elements, since the performance decreases associated interfacial losses in cascades that degrade maximum cooling temperature differential and COP in current commercial systems are reduced or eliminated.