Mathematical modeling and numerical characterization of composite thermoelectric devices

Abstract

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 P0, heat input Qh, and conversion efficiency η is studied for various hot surface temperature Th, 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 Th, a maximum P0 is achieved at a load resistance value that is equal to the total internal resistance Ri of the device; an optimum η, at an optimum load resistance RoptmL which is typically higher than the Ri. A CTED with d = 1 mm, the optimum η values are 24.8%, 26.2% and 29.9% higher than conventional TED values at Th = 350 K, 450 K and 550 K, respectively. At RoptmL values, the difference in P0 and Qh show significant and minor increases, respectively, in relation to differences in η with an increase in Th. The variation of the semiconductor thickness d has a substantial effect on the CTED characteristics and RoptmL values; as d decreases, a continuous increase in P0 and Qh and an optimum value of η are achieved. Intuitively, RoptmL increases with an increase in d and it reaches a maximum value at the conventional TED limit. With d = 0.5 mm, Th = 450 K and h = 20 W m−2 K−1 at a corresponding RoptmL value, P0 and Qh exhibit an eight- and six-fold increase, respectively, and η 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.