Thermoelectric properties and efficiency measurements under large temperature differences

Muto, Andrew; Kraemer, Daniel; Hao, Qing; Ren, Zhifeng; Chen, Gang

doi:10.1063/1.3212668

Cited by 72 publications

(55 citation statements)

References 10 publications

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“…This is because the (ZT) eng is ΔT-dependent whereas ZT lacks both effects of the temperature boundary condition and its cumulative effect. To overcome the inadequacy of ZT, the effective figure of merit ðZTÞ eff = ð R T h Tc SðTÞdTÞ 2 T avg =ðΔT R T h Tc ρðTÞκðTÞdTÞ has been reported (30,31), of which HH and SnSe is shown as solid lines in Fig. 3A, where (ZT) eff also has a tendency somewhat similar to the efficiency excursion rather than average ZTs.…”

Section: Resultsmentioning

confidence: 99%

Relationship between thermoelectric figure of merit and energy conversion efficiency

Kim

Liu

Chen

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

474

283

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The formula for maximum efficiency (η max ) of heat conversion into electricity by a thermoelectric device in terms of the dimensionless figure of merit (ZT) has been widely used to assess the desirability of thermoelectric materials for devices. Unfortunately, the η max values vary greatly depending on how the average ZT values are used, raising questions about the applicability of ZT in the case of a large temperature difference between the hot and cold sides due to the neglect of the temperature dependences of the material properties that affect ZT. To avoid the complex numerical simulation that gives accurate efficiency, we have defined an engineering dimensionless figure of merit (ZT) eng and an engineering power factor (PF) eng as functions of the temperature difference between the cold and hot sides to predict reliably and accurately the practical conversion efficiency and output power, respectively, overcoming the reporting of unrealistic efficiency using average ZT values.thermoelectrics | engineering figure of merit | engineering power factor | conversion efficiency | cumulative temperature dependence A thermoelectric (TE) generator produces electric power directly from a temperature gradient through TE material (1-4). The maximum efficiency of a TE generator was first derived based on a constant property model by Altenkirch (5) in 1909, and its optimized formula has been commonly used since Ioffe (6) reported the optimum condition for the maximum efficiency in 1957, which is (7)where T h and T c are the hot-and cold-side temperatures, respectively, and ΔT and T avg are their difference, T h − T c , and average (T h + T c )/2, respectively. The TE conversion efficiency by Eq. 1 is the product of the Carnot efficiency (ΔT/T h ) and a reduction factor as a function of the material's figure of merit Z = S 2 ρ −1 κ −1 , where S, ρ, and κ are the Seebeck coefficient, electrical resistivity, and thermal conductivity, respectively. Since the 1950s, the dimensionless figure of merit (ZT), such as the peak ZT (8-10) and the average ZT (2, 11, 12), has been used as the guide to achieve better materials for higher conversion efficiency.The maximum efficiency by Eq. 1 is inadequate when Z is temperature dependent. Due to the assumption of temperature independence, Eq. 1 only correctly predicts the maximum efficiency at a small temperature difference between the cold and hot sides, or in limited TE materials (13-15) that have Z almost constant over the whole temperature range. By ignoring the assumption and simply using Eq. 1, incorrect efficiency that is much higher than is practically achievable (16, 17) is often reported. In most cases for S, ρ, and κ that are temperature dependent, ZT values are not linearly temperature dependent (18)(19)(20)(21)(22) and they operate at a large temperature difference, so the prediction by Eq. 1 cannot be reliable. To overcome the inadequacy, complicated numerical simulations based on the finite difference method were carried out to calculate the efficiency while accounting for ...

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Section: Resultsmentioning

confidence: 99%

Relationship between thermoelectric figure of merit and energy conversion efficiency

Kim

Liu

Chen

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

474

283

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“…Due to these challenges, few reports exist on experimental demonstrations of efficiencies of thermoelectric module, couple and single leg devices [18][19][20][21][22][23][24][25][26][27] . In addition to the challenges in fabricating thermoelectric devices with low contact resistances, efficiency measurements are difficult due to various losses via radiative heat transfer between the device and surroundings and via heat conduction through leads attached to the device.…”

Section: Introductionmentioning

confidence: 99%

“…The sample is fabricated with silver contact pads in a three-step process which includes the ball milling of materials, a single hot-press process, and cutting the elements. In order to validate the developed methods we characterize a commercial p-type bismuth telluride leg which can be used as a standard sample due to its reliable and isotropic material properties and stable contacts 23 . We measure a record high efficiency of 8.5 % for the single leg device operating between 20 -245 °C.…”

Section: Introductionmentioning

confidence: 99%

High thermoelectric conversion efficiency of MgAgSb-based material with hot-pressed contacts

Kraemer

Sui

McEnaney

et al. 2015

Energy Environ. Sci.

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178

132

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The efficiency of heat-to-electricity conversion based on the thermoelectric effect depends on the materials' nondimensional figure of merit zT. While recent years saw an increasing number of reports of large peak zT in thermoelectric materials, efficiency data are scarce. High conversion efficiency requires not only a large average dimensionless figure of merit zT in the operational temperature range, but also good electrical and thermal contacts to the material. In this work, we experimentally demonstrate a record high thermoelectric conversion efficiency of 8.5 % with a single thermoelectric leg based on a recently reported p-type MgAgSb-based compound operating between 20 and 245 °C. The efficiency can exceed 10 % by increasing the hot side temperature to 295 °C. The sample is fabricated with silver contact pads using a one-step hot-press technique eliminating a typically required sample metallization process. This significantly simplifies the fabrication of thermoelectric elements with low electrical and thermal contact resistances.High conversion efficiency is demonstrated at a relatively small temperature difference for a MgAgSb-based single thermoelectric leg with hot-pressed contacts. 73x45mm (150 x 150 DPI)

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“…The numerical results were in good agreement with the experimental data obtained in both bulk and nano-SiGe materials. Muto et al [41] presented an experimental system to directly measure the thermoelectric conversion efficiency of a single thermoelectric element. This method achieved a more accurate ZT value than that obtained by measuring the electrical conductivity, the Seebeck coefficient, and the thermal conductivity.…”

Section: Poster Sessionmentioning

confidence: 99%

Report on 6th U.S.–Japan Joint Seminar on Nanoscale Transport Phenomena—Science and Engineering

Borca‐Tasciuc

Cahill

Chen

et al. 2008

Nanoscale and Microscale Thermophysical Engineering

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seminar. (The agenda of the seminar is attached at the end at this report [14].) The OPENING RECEPTION AND PRESENTATIONK. Okazaki gave a big picture talk on the evening of July 13, 2008, pointing to the urgency of global warming and the roles of nanoscale science and technology to address the challenges. Examples in CO 2 sequestration and catalysis were given. Okazaki's talk drew lots of discussion, including concerns about the long-term stability of proposed CO 2 sequestration methods. SESSION 1: KEYNOTE SESSIONThe first keynote session included talks by M.S. Dresselhaus [1] and S. Maruyama [2]. The speakers addressed very important directions to be noted by this continuing seminar series. Dresselhaus discussed the need for materials research to confront the challenge of the explosive energy demand increase. The world energy needs will reach 33 TW by 2050. Nanostructured materials are important for energybased applications due to (1) their unique physical phenomena, (2) their higher surface area, and (3) the independent control of each parameter that is not available in conventional bulk. Dresselhaus focused on solar energy, such as solar electricity (PV), solar fuel (biomass), and solar thermal, and thermoelectricity related issues. The importance of having a roadmap for the R&D, like Moore's law, which has served as the guiding role to the semiconductor electronics industry, was pointed out. The talk concluded with the challenges we face including the need for doubling and tripling the energy supply by 2050 and 2100, respectively, and of introducing

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Thermoelectric properties and efficiency measurements under large temperature differences

Cited by 72 publications

References 10 publications

Relationship between thermoelectric figure of merit and energy conversion efficiency

Relationship between thermoelectric figure of merit and energy conversion efficiency

High thermoelectric conversion efficiency of MgAgSb-based material with hot-pressed contacts

Report on 6th U.S.–Japan Joint Seminar on Nanoscale Transport Phenomena—Science and Engineering

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