A New High Efficiency Segmented Thermoelectric Unicouple

Abstract

To achieve high thermal-to-electric energy conversion efficiency, it is desirable to operate thermoelectric generator devices over large temperature gradients and also to maximize the thermoelectric performance of the materials used to build the devices. However, no single thermoelectric material is suitable for use over a very wide range of temperatures (~300-1000K). It is therefore necessary to use different materials in each temperature range where they possess optimum performance. This can be achieved in two ways: 1) multistage thermoelectric generators where each stage operates over a fixed temperature difference and is electrically insulated but thermally in contact with the other stages 2) segmented generators where the p-and n-legs are formed of different segments joined in series. The concept of integrating new thermoelectric materials developed at the Jet Propulsion Laboratory into a segmented thermoelectric unicouple has been introduced in earlier publications. This new unicouple is expected to operate over a 300-973 K temperature difference and will use novel segmented legs based on a combination of state-of-the-art thermoelectric materials and novel p-type Zn 4 Sb 3 , p-type CeFe 4 Sb 12-based alloys and n-type CoSb 3-based alloys. A conversion efficiency of about 15% is predicted for this new unicouple. We present in this paper the latest experimental results from the fabrication of this unicouple, including bonding studies between the different segments of the p-legs, nlegs, and p-leg to n-leg interconnect.

Thermoelectric properties and efficiency measurements under large temperature differences

“…For Bi 2 Te 3 -based TE elements, the metallization material most commonly used is Ni, and its purpose is to allow soldering with low electrical and thermal contact resistances while acting as a diffusion barrier. 13 In the following analysis, no distinction is made between the intrinsic properties of the bulk and the properties of the contact. If significant contact resistances are present, they will be automatically lumped into the effective properties.…”

“…12 Furthermore, in real TE applications additional effects must also be considered such as electrical contact resistance at the junctions of the TE legs and radiation losses from the leg side walls. 13,14 In this work we develop methods to characterize a single TE leg operating under a large temperature difference. We aim to extract the three intrinsic properties of a single leg and verify the results by comparing the predicted power conversion efficiency from the property measurements to the actual measured efficiency.…”

Enhancement of automotive exhaust heat recovery by thermoelectric devices

“…The root cause for why the modelled energy recovery is higher than the experimental energy is not fully understood but probably involves assumptions about g HX and g TE . Basic studies on g TE not related to TE materials were conducted by Rowe and Min [20] and Caillat et al [21], among others. Rowe and Min [20] concluded that a higher g TE was obtained with TE devices having longer legs (thickness), but that such a design reduced the overall heat flux through the TE device and, hence, decreased the output power.…”

“…Different material combinations are being investigated to increase g TE without significantly reducing the TE power. For example, Caillat et al [21] proposed the use of a TE device formed of different segments joined in series, called a segmented unicouple, to optimize the performance over a wide temperature difference of 300-973 K, since a single TE device exhibits various efficiencies within that range.…”

Improved Thermoelectric Generator Performance Using High Temperature Thermoelectric Materials

“…So that developing high temperature thermoelectric materials is important for automotive applications. Meanwhile, segmenting the elements within the TEM using different thermoelectric materials can further improve the TEG performance [12]. Future thermoelectric modules are expected to have 10% to 20% efficiency and over 500°C hot side temperature limit.…”