Harman Measurements for Thermoelectric Materials and Modules under Non-Adiabatic Conditions

Roh, Im Jun; Lee, Yun Goo; Kang, Min Su; Lee, Jae Uk; Baek, Seung Hyub; Kim, Seong Keun; Ju, Byeong Kwon; Hyun, Dow-Bin; Kim, Jin Sang; Kwon, Beomjin

doi:10.1038/srep39131

Cited by 22 publications

(10 citation statements)

References 18 publications

(58 reference statements)

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“…To accurately optimize the aspect ratio, the electrical and thermal contact resistances at TE leg-electrode interface need to be considered. When electrical current or heat transfers from the TE leg to an electrode, the cross-sectional shape of the TE leg affects how the current or heat spreads into the electrode 51 . Furthermore, solder properties may be influenced by the TE leg thickness, if the TE leg is not sufficiently thick.…”

Section: Resultsmentioning

confidence: 99%

Cu2Se-based thermoelectric cellular architectures for efficient and durable power generation

Choo

Ejaz

et al. 2021

Nat Commun

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Thermoelectric power generation offers a promising way to recover waste heat. The geometrical design of thermoelectric legs in modules is important to ensure sustainable power generation but cannot be easily achieved by traditional fabrication processes. Herein, we propose the design of cellular thermoelectric architectures for efficient and durable power generation, realized by the extrusion-based 3D printing process of Cu2Se thermoelectric materials. We design the optimum aspect ratio of a cuboid thermoelectric leg to maximize the power output and extend this design to the mechanically stiff cellular architectures of hollow hexagonal column- and honeycomb-based thermoelectric legs. Moreover, we develop organic binder-free Cu2Se-based 3D-printing inks with desirable viscoelasticity, tailored with an additive of inorganic Se82− polyanion, fabricating the designed topologies. The computational simulation and experimental measurement demonstrate the superior power output and mechanical stiffness of the proposed cellular thermoelectric architectures to other designs, unveiling the importance of topological designs of thermoelectric legs toward higher power and longer durability.

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Section: Resultsmentioning

confidence: 99%

Cu2Se-based thermoelectric cellular architectures for efficient and durable power generation

Choo

Ejaz

et al. 2021

Nat Commun

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“…In addition, the frequency decreases to 1.37 mHz for the fixed condition ( f TE,fix = 44.3 mHz). Therefore, on the basis of the above analysis for the impedance at high and low frequencies, we propose a technique to estimate the dimensionless figure of merit quickly with repeatability considering the current frequency dependence beyond that in the Harman method, 10,11,15 which can estimate the dimensionless figure of merit zT Harman using the resistance R DC for a direct current and R AC for an alternating current at a certain frequency:…”

Section: Resultsmentioning

confidence: 99%

“…1 In addition, the Harman method sometimes applies an element and a module to estimate zT. 15 22 by impedance spectroscopy, where the element was suspended by attaching narrow lead wires in vacuum to satisfy the identical boundary condition; 4 however, controlling the temperature of the element and module based on impedance spectroscopy in the suspended condition is very important. Therefore, we have to determine the frequency dependence of the impedance under different boundary conditions to control the temperature and consider how to estimate the temperature-dependent zT of the module properly.…”

Section: Introductionmentioning

confidence: 99%

Temperature dependence of dimensionless figure of merit of a thermoelectric module estimated by impedance spectroscopy

Hasegawa

Otsuka

2018

AIP Advances

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Temperature dependence of dimensionless figure of merit zT of a Π-shaped thermoelectric module using bismuth-telluride materials was estimated on the basis of a theory of impedance spectroscopy, which is able to ascertain zT directly using only electrometric measurements from the frequency dependence of the impedance without any calorific measurement. The dependence of the module was measured from 5 mHz to 10 kHz with precise temperature control. From the analysis, the ohmic resistance, the impedance due to the Peltier effect, and the characteristic heat frequency at 300 K were determined under two different boundary conditions (the suspended and fixed conditions of a heat bath). A comparison between these boundary conditions revealed that their difference led to a slight change in the frequency dependence of the measured impedance due to the variation in the heat capacity of the module, and the estimated dimensionless figure of merit was identical for the two boundary conditions (zT ≈ 0.839 at 300 K). The temperature dependence of the dimensionless figure of merit of the module was successfully measured from 20 K to 300 K. The dependence of the thermal conductivity was also estimated with an assumed Seebeck coefficient from the definition of zT. In addition, a new method using only two impedances with repeatability was proposed and demonstrated to estimate the dimensionless figure of merit precisely (zT ≈ 0.845 at 300 K).

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“…In addition, adiabatic conditions are required, which are difficult to achieve due to heat losses by convection, radiation, or through the wires used to perform the measurements in the setup. 5,6 Moreover, a uniform current flow through the sample is required for a proper measurement of the ohmic resistance (ohmic voltage drop) of the sample. 7 Together these problems can lead to measurement errors of up to 35%.…”

Section: Introductionmentioning

confidence: 99%

“…7 Together these problems can lead to measurement errors of up to 35%. 6 Impedance spectroscopy has recently attracted attention as a suitable alternative method for the characterization of TE materials and devices. [8][9][10][11][12][13] This technique, in contrast to the Harman method, measures a wide range of frequencies and not only ac and dc conditions.…”

Section: Introductionmentioning

confidence: 99%

Experimental conditions required for accurate measurements of electrical resistivity, thermal conductivity, and dimensionless figure of merit (ZT) using Harman and impedance spectroscopy methods

Beltrán-Pitarch

Prado‐Gonjal

Powell

et al. 2019

Journal of Applied Physics

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The Harman method is used extensively for the characterization of the dimensionless figure of merit ZT of thermoelectric (TE) materials and devices. However, its accuracy has often been questioned, since in many cases there are relatively high errors associated with the method. The impedance spectroscopy technique, which has recently been shown as a suitable tool to also characterize TE materials and devices, has some similarities with the Harman method, and can also directly provide ZT. In order to obtain reliable measurements in both methods, there are some common critical points that must be taken into account, such as for example the requirement of fully adiabatic conditions, and a negligible Joule effect. In this study, we have evaluated the effect of different experimental conditions in the accuracy of both methods using a sample with known TE properties. Our analysis has led to the identification of different sources of errors and other issues that have not been clearly identified to date that can lead to inaccurate results. Namely, the need of a homogeneous Peltier effect at the junctions, problems arising from the use of Ag paint, and the selection of the right value for the current perturbation applied to the system. These problems and sources of error need to be identified and carefully considered if accurate results are to be obtained.

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Harman Measurements for Thermoelectric Materials and Modules under Non-Adiabatic Conditions

Cited by 22 publications

References 18 publications

Cu2Se-based thermoelectric cellular architectures for efficient and durable power generation

Cu2Se-based thermoelectric cellular architectures for efficient and durable power generation

Temperature dependence of dimensionless figure of merit of a thermoelectric module estimated by impedance spectroscopy

Experimental conditions required for accurate measurements of electrical resistivity, thermal conductivity, and dimensionless figure of merit (ZT) using Harman and impedance spectroscopy methods

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