Mathematical modeling and numerical characterization of composite thermoelectric devices

A Composite Thermoelectric Device (CTED) is comprised of thermoelectric (TE) elements made of TE semiconductor materials bonded to highly electrically and thermally conductive material in a segmented fashion. Thermoelectric performance of such devices using numerical methods with temperature-dependent thermoelectrical properties has been investigated. The CTED performance in terms of produced electrical current, Ohmic and Seebeck potentials, power output P-0, heat input Q(h), and conversion efficiency eta is studied for various hot surface temperature T-h, load resistance, semiconductor thickness d, and convection heat transfer coefficient h values. The aforementioned CTED performance characteristics are compared to those of a conventional TED with geometrical equivalence. For a given T-h, a maximum P-0 is achieved at a load resistance value that is equal to the total internal resistance R-i of the device; an optimum eta, at an optimum load resistance R-optmL, which is typically higher than the R-i. A CTED with d = 1 mm, the optimum eta values are 24.8%, 26.2% and 29.9% higher than conventional TED values at T-h = 350 K, 450 K and 550 K, respectively. At R-optmL values, the difference in P-0 and Q(h) show significant and minor increases, respectively, in relation to differences in eta with an increase in T-h. The variation of the semiconductor thickness d has a substantial effect on the CTED characteristics and R-optmL values; as d decreases, a continuous increase in P-0 and Q(h) and an optimum value of eta are achieved. Intuitively, R-optmL increases with an increase in d and it reaches a maximum value at the conventional TED limit. With d = 0.5 mm, T-h = 450 K and h = 20 W m(-2) K-1 at a corresponding R-optmL. value, P-0 and Q(h) exhibit an eight- and six-fold increase, respectively, and eta is increased 22% compared to a conventional TED. The convective heat transfer coefficient has a pronounced effect on the CTED performance when it is greater than 100 W m-(2) K-1. From this study, the CTEDs show promise of extracting more heat in waste heat recovery applications when compared to conventional TEDs. (C) 2012 Elsevier Masson SAS. All rights reserved.