Design Of Thermoelectric Devices Research Articles

Ultrathin Transparent Nickel Electrodes for Thermoelectric Applications

AbstractIn this work, ultrathin nickel films are developed for application as transparent electrodes in thermoelectric devices. The quality of the films is determined systematically by electrical, optical, and morphological characterization in a series of samples with different thickness. The thermal properties of the films show a dramatic dependence of the Seebeck coefficient on the film thickness. This dependence, with values ranging from −16 to +5 𝜇V K−1 for thicknesses from 10 to 2 nm, includes a change in the behavior of the thermoelectric response from n‐ to p‐type. It has also been demonstrated that the accurate estimation of the thermal conductivity in thin films is challenging due to substrate effects. In this situation, a differential measurement method based on scanning thermal microscopy is proposed, as in these conditions the measurements are less sensitive to the substrate effects. In further works, the dependence of the thermal properties of ultrathin nickel films can be exploited as a tuning parameter for the design of thermoelectric devices.

Enhanced phonon resonance by non-uniform surface nanopillars in Si nanowires

Based on the wave nature of phonons, the lattice thermal conductivity of nanowires can be regulated by phonon resonators such as surface nanopillars. In this study, the impact of the height and distance of the resonant nanopillars on the thermal conductivity of Si nanowires were investigated. The results calculated from the molecular dynamics simulations show that with increasing height of the nanopillars, the corresponding thermal conductivity decreases. We found that the nanopillars with non-uniform heights induce stronger phonon resonance effect and can further suppress the thermal conductivity, as compared to the models with nanopillars of uniform heights. On the other hand, changing the distance between two adjacent nanopillars does not obviously affect the phonon propagation. Phonon dispersion relations show the formation of flat bands, which confirms the occurrence of phonon resonances due to the nanopillars. When the heights of the nanopillars become non-uniform, more flat bands were generated, and the phonon group velocity further decreased. Analyses of phonon participation ratio indicate stronger phonon localization induced by the disorder stemming from the non-uniform nanopillar height. Our investigation yields new insights into the physical mechanisms governing heat transport in nanowires with phonon resonators, and thus opens potential new routes to the design of thermoelectric devices.

Fabrication of BN aerogels/Bi2Te3 composite thermoelectric generator (TEG) with high seebeck coefficient

Boron nitride (BN) aerogels materials have low density characteristics and stable three-dimensional network structure, which can be used as high thermal conductivity ultralight materials or thermal conductive polymer additives. The hexagonal boron nitride nanoribbons (BNNRs) aerogels material not only has a three-dimensional network structure with high specific surface area, but also has a two-dimensional band structure. It has ultra-low thermal conductivity along the in-plane direction, and has ultra-high aspect ratio and electrical insulation energy. However, the research on the thermoelectric properties of BN Aerogels and its composites is still blank. Therefore, it is of great significance to carry out the research on BN Aerogels, its thermoelectric composites, thermoelectric properties and the design of thermoelectric devices. In this paper, BN Aerogels were prepared by the combination of freeze-drying and high temperature thermal annealing, and the effects of 2-methyl-2-propanol (TBA) modification on the yield and quality of BN Aerogels were investigated. The experimental results show that TBA greatly reduces the width and thickness of BNNRs in BN Aerogels, and increases the aspect ratio of BNNRs. The composite thermoelectric particles were prepared by hot pressing to combine BN Aerogels and Bi2Te3 and the influence of the doping concentration of BN Aerogels on the thermoelectric parameters such as Seebeck coefficient and power factor of the thermoelectric battery was studied. The experimental results reveal that when the concentration of BN Aerogels is 1.48 wt%, the ZT value of BN Aerogels/p-Bi2Te3 composite thermoelectric particles is 0.719, while when the doping concentration of BN Aerogels is 1.96 wt%, the ZT value of BN Aerogels/n-Bi2Te3 composite thermoelectric particles is 0.577. And the TBA modified BN Aerogels/Bi2Te3 composite thermoelectric particles show that when the TBA doping concentration is 19.35 wt%, the ZT value of the TBA modified BN Aerogels/p-Bi2Te3 composite thermoelectric particles can reach 0.87, which is higher than that of BN aerogels/p-Bi2Te3 thermoelectric particles, and also much higher than that of the intrinsic p-Bi2Te3 thermoelectric particles. When the TBA doping concentration is 28.57 wt%, the ZT value of the BN Aerogels/n-Bi2Te3composite thermoelectric particles modified by TBA can reach 0.623, which is also higher than that of the BN aerogels/n-Bi2Te3 thermoelectric particles, and also much higher than that of the intrinsic n-Bi2Te3 thermoelectric particles. And based on the self-prepared TBA modified BN Aerogels/Bi2Te3 composite thermoelectric particles, the TEG thermoelectric battery was designed and manufactured. The Seebeck coefficient of the TEG thermoelectric battery can be reached 886.08 μV/K, the conductivity can be reached 9.74 × 104 S/m, and the thermoelectric power factor and power density are 7.65 × 104 μW/mK2 and 14.49 μW/cm3, respectively. This system reduces the need for physical space by using a common framework, which is conducive to the application of thermoelectric power generation technology in micro and small fields.

Thermoelectric properties of acene molecular junctions

By using non-equilibrium Green’s function method, we investigate the thermoelectric properties of molecular junctions based on acene-linked graphene nanoribbons. The effects of the length of the acene molecule, the contact position between the acene molecule and graphene nanoribbon electrode on the thermoelectric parameters are mainly considered in this work. It is found that the phonon contribution is dominant in the thermal conductance corresponding to the maximum of the thermoelectric figure of merit (<i>ZT</i><sub>max</sub>). As the length of the acene molecule increases, the phonon thermal conductance decreases monotonically, and eventually becomes almost independent of the acene molecule’ length. When the acene molecules contact the middle (upper) part of the left (right) electrode of graphene nanoribbon, the corresponding <i>ZT</i><sub>max</sub> is the highest. However, when the acene molecules contact the middle (middle) part of the left (right) electrode of graphene nanoribbons, the corresponding <i>ZT</i><sub>max</sub> is the lowest. As the temperature increases, <i>ZT</i><sub>max</sub> has a monotonically increasing tendency, regardless of the contact position. With the increase of the length of the acene molecule, the chemical potential corresponding to <i>ZT</i><sub>max</sub> becomes closer to the intrinsic Fermi level. The above findings may provide the valuable reference for the future design of thermoelectric devices based on the acene molecular junctions.

First-principles calculations to investigate third-order elastic constant, anharmonicity and temperature dependent second elastic constant of thermoelectric materials Cu3MSe4(M = V and Nb)

The research on material‘s mechanics is critical in thermoelectric. Herein, we study the second(Cij), third(Cijk) order elastic constants, anisotropic and pressure and temperature dependent elasticity of Cu3MSe4(M = V and Nb) utilizing density functional theory. The elasticity of Cu3MSe4(M = V and Nb) is anisotropic. In addition, the calculated Cij suggests that these materials show relatively weak mechanical properties as thermoelectric device, and the ratio of bulk modulus(B) versus shear modulus(G) suggest that they are brittle. Cijk and pressure induced Cij reveal that Cu3NbSe4 has stronger anharmonic strength than that of Cu3VSe4. Finally, the thermal expansions are evaluated via quasi-harmonic approximation, and the temperature dependent elastic constants Cij indicate that Cu3NbSe4 has weak temperature dependent than that of Cu3VSe4. This research is dedicated to the design of thermoelectric devices and discovering novel thermoelectric materials with high performance in view of mechanical properties.

Design of thermoelectric devices for extracting foreign objects from the human body by freezing

Objectives.The purpose of the article is to consider the designs of thermoelectric devices (TEC) for extracting foreign objects (IO) from the human body by freezing with various options for removing heat from the hot junctions of the thermoelectric module (TEM).Method. Modifications of thermoelectric devices are described for extracting the IO from the human body by freezing it to a special probe. Their technical design differs in the way of heat removal from the TEM hot junctions, for which air heat removal, melting working substances and preliminary cooling of the radiator are used. The basic relationships for calculating the technical means intended for the removal of heat from the hot junctions of the TEM are presented.Result. The graphs of the dependence of the temperature change of the TEM hot junctions in time are obtained for different values of its heat output when using an air heat removal system and the time of complete penetration of various working substances used in the device.Conclusion. The data obtained show that for the operating conditions of the TEC, the temperature of the hot junctions of the TEM with an air heat sink does not go beyond the permissible limits. With a module power of 8 W, 12 W and 16 W, the temperature of the hot junctions of thermoelements stabilizes rather quickly and takes the value of 308 K, 313 K and 318 K. maintaining their stable temperature is most preferred is nickel nitrate, less - elaidic acid and paraffin. Calculations of the design of a device with a pre-cooled radiator system also show the efficiency of heat removal from the hot junctions of the TEM for the duration of the entire procedure for removing the IO from the human body.

Decoupling of the Electrical and Thermal Transports in Strongly Coupled Interlayer Materials.

Thermoelectric materials which enable heat-to-electricity conversion are fundamentally important for heat management in semiconductor devices. Achieving high thermoelectric performance requires blocking the thermal transport and maintaining the high electronic transport, but it is a challenge to satisfy both criteria simultaneously. We propose that tuning the interlayer distance can effectively modulate the electrical and thermal conductivities. We find group IV-VI and V semiconductors with a moderate interlayer distance can exhibit high thermoelectric performance. Taking SnSe as an example, we reveal that in the out-of-plane direction the delocalized pz orbitals combined with the relatively small interlayer distance lead to overlapping of the antibonding state wave functions, which is beneficial for high electronic transport. However, because of the breakdown of the chemical bond, the out-of-plane thermal conductivity is small. This study provides a strategy to enhance electrical conductivity without increasing thermal conductivity and thus sheds light on the design of thermoelectric devices.

Near-room-temperature thermoelectric materials and their application prospects in geothermal power generation

In recent years, due to the shortage of fossil fuel energy and the deterioration of the environment, increasing attention has been paid to the utilization of geothermal power, especially medium–low-temperature geothermal energy, which occupies a large proportion of hot water resources. This paper summarizes the research status of Bi2Te3-, MgAgSb-, Mg3Sb2-, Mg2(Si,Sn,Ge)- Ag2Se-and AbSbTe2-based near-room-temperature thermoelectric (TE) materials and summarizes the research results of TE technology used in geothermal water power generation. TE power generation technology can directly transform heat into electricity by TE devices, with the advantages of environmental protection, low carbon emissions, no mechanical moving parts, high thermal and mechanical stability and no noise. The improving performance of the investigated TE materials suggests that TE power generation technology is the key technology for clean geothermal power generation. Future research directions include further improving the TE performance, reducing costs and enhancing the research and design of TE devices and power generators.

Thermal transport and energy dissipation in two-dimensional Bi2O2Se

Thermal transport and energy dissipation are important for a material in both thermoelectric and electronic devices. Here, we investigate the lateral and interfacial thermal transport of two-dimensional (2D) Bi2O2Se by Raman spectroscopy. It is found that thin Bi2O2Se flakes have a low in-plane thermal conductivity while maintaining an appropriate interfacial thermal conductance. The in-plane thermal conductivity of Bi2O2Se decreases with decreasing thickness, to as low as 0.92 ± 0.18 W⋅m−1⋅K−1 at a thickness of ∼8 nm. Such a low thermal conductivity is derived from the low phonon group velocity, strong anharmonicity, and large surface scattering of acoustic phonons of the Bi2O2Se thin layer. Simultaneously, thinner Bi2O2Se presents a higher thermal dissipation to the substrate than the thicker counterparts in the device. The interfacial thermal conductance increases with decreasing thickness, and reaches ∼21 MW⋅m−2⋅K−1 at ∼8 nm. These results provide critical information for the design of thermoelectric devices with high figures of merit and electronics with low-power consumption based on 2D materials.

Soft Electronics: Progress and Perspective: Soft Thermoelectric Materials for Wearable and Internet‐of‐Things Applications (Adv. Electron. Mater. 11/2019)

Recent breakthroughs in soft thermoelectric materials have enabled the design of thermoelectric devices that exhibit commercially relevant efficiencies while simultaneously leveraging the unique processing and mechanical advantages of soft materials. In article number 1800823, Jeffrey J. Urban and co-workers discuss the current state-of-the-art in soft thermoelectrics materials and highlight outstanding challenges specific to organic and organic–inorganic hybrid systems, with an eye on potential applications in the Internet of Things and wearable technologies.

Poly(3,4‐ethylenedioxythiophene): Chemical Synthesis, Transport Properties, and Thermoelectric Devices

AbstractSince their discovery in the seventies, conducting polymers have been chemically designed to acquire specific optical and electrical properties for various applications. Poly(3,4‐ethylenedioxythiophene) (PEDOT) is among the most successful polymers as indicated by ≈12 000 articles mentioning it to date. PEDOT is found as transparent polymer electrodes in solar cells and light‐emitting diodes, as printed electrodes in transistors, and as the main component of electrochromic displays, supercapacitors, and electrochemical transistors. For around seven years, PEDOT has been classified as the first thermoelectric polymer that converts heat flow into electricity. This has triggered a renewed interest in the scientific community, with about 400 publications including the keyword “PEDOT” and “thermoelectric.” Among the topics covered by those scientific works are: i) the optimization of the thermoelectric properties, ii) understanding of the interplay between electrical properties and morphology, iii) the origin of the Seebeck coefficient, iv) the characterization of its thermal conductivity; and v) the design of thermoelectric devices. This work aims to be a pedagogical introduction to PEDOT but also to review the state‐of‐the art of its thermoelectric properties and thermoelectric devices. Hopefully, this work will inspire scientists to find chemical design rules to bring organic thermoelectrics beyond PEDOT.

Progress and Perspective: Soft Thermoelectric Materials for Wearable and Internet‐of‐Things Applications

AbstractSoft thermoelectric materials, including conjugated polymers and organic–inorganic hybrids, now demonstrate figures of merit approaching those of inorganic materials. These materials development breakthroughs enable the design of thermoelectric devices that exhibit appropriate efficiencies for commercial use, while simultaneously leveraging the unique processing and mechanical advantages of soft materials. Such a technology opens the door to a suite of new thermoelectric applications, including power generation for biomedical implants and the Internet of Things, or wearable heating and cooling devices. In order to realize deployment of such technologies, there is a fundamental need for deeper understanding of the complex transport physics underlying thermoelectric transport in soft materials. Here, the current state of the art in soft thermoelectrics materials is discussed, and outstanding challenges specific to organic and organic–inorganic hybrid systems are highlighted.

Monte Carlo simulation of single-crystalline PbSe nanowire thermal conductivity using first-principle phonon properties

Prior experimental studies showed that nanowires are promising structures for improving the thermoelectric performance of practical thermoelectric materials due to the strongly induced phonon-boundary scattering. However, few studies examined the impact of phonon-boundary scattering on the thermal conductivity of thermoelectric nanowires from a first-principle approach. In this work, we systematically study the role of phonon-boundary scattering with different boundary specularities on the thermal conductivity of PbSe nanowires by rigorously solving the full phonon Boltzmann transport equation without any adjustable parameters. We observe significant thermal conductivity reduction for rough PbSe nanowires with diameters less than a few hundred nanometers. The reduction reaches ∼40% for 10 nm thick, rough PbSe nanowires at room temperature. The diameter-dependent thermal conductivities are found to contain important information about the phonon mean free path distribution from a standard reconstruction algorithm. The simulation results are important for fundamental understanding of nanoscale thermal transport in thermoelectric materials and will guide the future design of thermoelectric devices to achieve better energy conversion efficiency.

Elasto-thermoelectric beam formulation for modeling thermoelectric devices

The present paper provides a dynamic, non-linear and fully coupled Finite Element (FE) formulation based on the Timoshenko beam theory to study elasto-thermoelectric responses in thermoelectric devices. The two main motivations of this work are: i) to study mechanical responses in thermoelectric devices, which must be taken into account in the design of Peltier cells due to the fragility and relative low strength of the semiconductors, and ii) to provide a numerical tool that decreases the CPU time to allow the introduction of designs based on optimization processes and on sensitivity analyses that could require many evaluations. In order to undertake the objectives of this work, the general three-dimensional governing equations are reduced to one-dimensional ones by means of several assumptions. Then, a set of five multi-coupled partial differential equations is obtained. The resultant expressions are thermodynamically consistent and form a multi-coupled monolithic FE formulation, differently to stagger formulations that require two separated steps to reach the final result. Numerically, this set of multi-coupled equations is discretized using the FE method and implemented into FEAP Taylor, 2010 [1]. For a proper validation of the code, four benchmarks are performed using one-dimensional dynamic analytical solutions developed by the authors. Finally, this formulation is compared with a three-dimensional FE formulation also developed by the authors in Pe´rez-Aparicio et al., 2015 [2] to model a commercial Peltier cell. This comparison reveals that: i) relative errors are lower than 13% and ii) CPU times decrease significantly, more than one order of magnitude. In conclusion, the beam thermoelectric formulation is an accurate model that reduces CPU time and could be used in future design of thermoelectric devices.

Effects of Codoping with Ga and P on Thermoelectric Properties of Ba8Al16Si30 Clathrate System

We have investigated the effects of Codoping With Ga and P on the thermoelectric properties of the Ba8Al16Si30 clathrate system, attempting to optimize the carrier concentration. The elastic properties, which are important for design of thermoelectric devices, were investigated by ultrasonic testing. Ga/P-codoped specimens with nominal compositions Ba8Al16GaxSi30−2xPx (x = 1.0, 1.5, 2.0) were prepared by arc melting and spark plasma sintering and their Seebeck coefficient, electrical conductivity, and thermal conductivity were measured. Analytical studies revealed that the total content of Al and Ga, expressed as atoms per formula unit, increased to 15.65 at nominal x = 2.0, exceeding the maximum content (y = 15.16) of Al for the Ba8AlySi46−y clathrate system. Ultrasonic tests determined the Young’s modulus, shear modulus, bulk modulus, and Poisson’s ratio to be 102.55 GPa, 40.14 GPa, 76.85 GPa, and 0.2775, respectively, for Ba8Al16GaxSi30−2xPx (x = 2.0). The Hall carrier concentration decreased from ∼1.0 × 1021 cm−3 for Ba8AlySi46−y to ∼6.3 × 1020 cm−3 for Ba8Al16GaxSi30−2xPx (x = 2.0), suggesting that Ga/P codoping may be useful for tuning the carrier concentration. The value of the Seebeck coefficient at ∼320 K increased from −46 μV K−1 for Ba8AlySi46−y to −67 μV K−1 for Ba8Al16GaxSi30−2xPx (x = 2.0). The dimensionless thermoelectric figure␣of merit ZT at 900 K improved from ∼0.4 for Ba8AlySi46−y to ∼0.47 for Ba8Al16GaxSi30−2xPx (x = 2.0).

THERMOELECTRIC SEMICONDUCTOR DEVICE FOR CAUTERY OF BLEEDING

Objectives The aim of the work is to study the possibilities for using a semiconductor device to cauterise bleeding by means of cooling (cryocautery). Method The study is based on methods for approximate modeling of heat exchange processes. Results The construction of a device for cauterisation of bleeding, the actuating element of which consists of a thermoelectric battery operating in cooling mode at the time of blood flow cautery and in heating mode when removing the device from the damaged area, is considered. A model of a device, realised on the basis of the solution of the problem of solidification of a viscous liquid by the method of L.S. Leibenson, is proposed, taking into account the electro- and thermo-physical characteristics of the thermoelectric battery cold source. As a result of the numerical experiment, the dependence of the duration of the ice crust formation on tissues 1 mm thick (which corresponds to the cauterisation of bleeding) is obtained on the value of the supply current of the thermoelectric battery. With increasing current, the duration of the ice crust formation is reduced; this can be of the order of 160 s at 5 A. It was demonstrated that the selection of thermoelectric battery parameters and current should be guided by medical norms and standards in order to avoid frostbite in the tissues adjacent to the bleeding zone. Conclusion The special design of thermoelectric device provides an effective technical means for cauterising bleeding by freezing (cryocautery), providing high intensity of cooling, shortenened thrombus formation duration, and eliminating painful sensations when removing the device from a damaged area.

Innovative design of a thermoelectric generator with extended and segmented pin configurations

A thermoelectric generator is one of the key candidates for the renewable energy devices, which directly converts waste heat into electricity. The wide applications of the device are suppressed because of the device low efficiency. In this paper, a new innovative design of the thermoelectric generator incorporating the extended pin with segmented pin configuration is introduced. The new design allows the device operating at two different cold junction temperatures. The maximum efficiency and the output power for the innovative design of thermoelectric device are formulated. The performance of the thermoelectric device is evaluated using the operating parameters such as the hot and cold junction temperatures in terms of temperature ratio, and external load resistance ratio. The reveals that the innovative design improves the maximum efficiency and output power of the thermoelectric generator. Increasing the cold junction temperature difference increases the device maximum efficiency by 3.5–6.2%. The maximum device output power and maximum thermal efficiency occur at different values of external load parameter. However, the reduction in the efficiency is considerably small for the external load parameter maximizing the device output work.

Prediction of Optimal Load and Performance of Thermal Batteries

Nowadays, the possibility of applying alternative energy sources is increasingly discussed. In terms of application, a Seebeck thermoelectric generator seems promising for the direct conversion of heat (preferably waste heat) into electricity. In order to increase the performance and thereby the effectiveness of different thermoelectric modules, especially advantageous thermoelectric properties of materials and also innovative design of thermoelectric devices are now solved. However, the achievement of maximum possible performance and operating efficiency is not determined solely by material efficiency and geometric dimensions of thermocouples connected in a thermal battery. It is also necessary to predict an optimum load of the specific source of energy in order to use material design improvements optimally and ensure longer life of thermal batteries. Their manufacturers, except the power input as a “heat consumption” and the maximum power output of a thermal battery (at a certain temperature difference between cold and heated walls), should also declare such load by an appliance, which is optimal for the given type of thermogenerator. The present paper, therefore, proposes a method for determining the optimum load of a thermal battery.

Analysis of reliability improvement possibilities of thermoelectric cooling devices

The methods of reliability improvement of single- and multi-stage thermoelectric devices (TED) were considered.It is shown that in the range of modes from the maximum cooling capacity to the minimum failure rate, there are intermediate modes, in which the influence of the parameters of thermoelements (electric conductivity, thermoEMF, efficiency etc.) is different, which suggests that selecting the combinations of parameters allows to improve reliability indicators of the product.The methods of reliability improvement in the design of thermoelectric devices when changing the ratio of height to the cross-sectional area of the thermoelement, which reduces the required number of thermoelements and TED failure rate were analyzed. Within the constructive method, the possibility of choosing the optimal current operating modes of cooling thermoelements for various operating conditions using a criteria-based approach was shown.Possibilities of a parametric method due to: improving the quality of starting thermoelectric materials and enhancing their effectiveness; using various combinations of starting materials at the same efficiency were defined. According to the results of the comparative analysis of the basic reliability parameters and indicators for various combinations of parameters of starting materials, analytical relations for calculating the basic parameters for various operating modes and temperature fluctuations were obtained.It is shown that using the combined method allows to significantly increase the reliability of the device. The above methods of reliability improvement of cascaded TED are a tool in the design of highly reliable thermally loaded equipment using thermoelectric cooling.

Numerical Examination of the Performance of a Thermoelectric Cooler with Peltier Heating and Cooling

There has recently been much progress in the development of materials with higher thermoelectric performance, leading to the design of thermoelectric devices for generation of electricity and for heating or cooling. Local heating can be achieved by current flow through an electric resistance, and local heating and cooling can be performed by Peltier heating and cooling. In this study, we developed computer software that can be used to predict the Seebeck and Peltier effects for thermoelectric devices. The temperature, electric potential, heat flow, electric current, and coefficient of performance were determined, with the objective of investigating the Peltier effect in a thermoelectric device. In addition to Peltier heating and cooling, Joule and Thomson heating were quantitatively evaluated for the thermoelectric device.