Thermoelectric Property Dependence on Performance of Peltier Current Leads Under Overcurrent Conditions

Superconductivity can potentially provide a solution to the world??s energy needs because superconducting transmission and distribution (T&D) systems can decrease losses and are also capable of integrating renewables into the power grid. At Chubu University we have built a 200-m-class superconducting direct-current T&D system (CASER-2). To minimize heat leakage from the current leads, we investigated thermoelectric materials. The Peltier current lead (PCL) is one of the key technologies that will enhance the performance of superconducting systems: as direct current (DC) flows through the current lead, thermoelectric elements on opposite terminations of the superconducting line can be used to decrease the heat ingress to the cryogenic environment (n-type on one end, p-type on the opposite end). The heat leakage to the cryogenic environment depends on the properties of the thermoelectric materials. In this paper, we estimate the performance of PCLs in cryogenic operations, including the potential for overcurrent operation, through both modeling and experiments at CASER-2.     

Geometry Optimization of a Segmented Thermoelectric Generator Based on Multi-parameter and Nonlinear Optimization Method

As no single thermoelectric material has presented a high figure-of-merit (ZT) over a very wide temperature range, segmented thermoelectric generators (STEGs), where the p- and n-legs are formed of different thermoelectric material segments joined in series, have been developed to improve the performance of thermoelectric generators. A crucial but difficult problem in a STEG design is to determine the optimal values of the geometrical parameters, like the relative lengths of each segment and the cross-sectional area ratio of the n- and p-legs. Herein, a multi-parameter and nonlinear optimization method, based on the Improved Powell Algorithm in conjunction with the discrete numerical model, was implemented to solve the STEG’s geometrical optimization problem. The multi-parameter optimal results were validated by comparison with the optimal outcomes obtained from the single-parameter optimization method. Finally, the effect of the hot- and cold-junction temperatures on the geometry optimization was investigated. Results show that the optimal geometry parameters for maximizing the specific output power of a STEG are different from those for maximizing the conversion efficiency. Data also suggest that the optimal geometry parameters and the interfacial temperatures of the adjacent segments optimized for maximum specific output power or conversion efficiency vary with changing hot- and cold-junction temperatures. Through the geometry optimization, the CoSb₃/Bi₂Te₃-based STEG can obtain a maximum specific output power up to 1725.3 W/kg and a maximum efficiency of 13.4% when operating at a hot-junction temperature of 823 K and a cold-junction temperature of 298 K.     

Computational Optimization of a Thermoelectric Ice-Maker as a Function of the Geometric Parameters of a Peltier Module

The objective of this paper is to optimize a thermoelectric ice-maker installed in a no-frost refrigerator, by means of a computational model. This model provides the electric power consumption of the Peltier module and the ice production. The Peltier module is the most important part of the thermoelectric ice-maker; therefore, it must be optimized in order to obtain an efficient ice-maker. First of all, the length of the thermocouples of the Peltier module has been optimized in order to obtain the maximum ice production. It turned out that 3.5 kg per day could be achieved if 1.5-mm-long thermocouples were used. The coefficient of performance (COP) was 0.44. Second, the ice production was expressed as a function of the number of thermocouples of the Peltier module. Given a constant electric power consumption of the module, the results showed that the maximum ice production was achieved with a Peltier module with 254 thermocouples. However, if a module with 140 thermocouples was installed, the ice production would decrease by only 1%.     

Estimating Energy Conversion Efficiency of Thermoelectric Materials: Constant Property Versus Average Property Models

Maximum thermoelectric energy conversion efficiencies are calculated using the conventional “constant property” model and the recently proposed “cumulative/average property” model (Kim et al. in Proc Natl Acad Sci USA 112:8205, 2015) for 18 high-performance thermoelectric materials. We find that the constant property model generally predicts higher energy conversion efficiency for nearly all materials and temperature differences studied. Although significant deviations are observed in some cases, on average the constant property model predicts an efficiency that is a factor of 1.16 larger than that predicted by the average property model, with even lower deviations for temperature differences typical of energy harvesting applications. Based on our analysis, we conclude that the conventional dimensionless figure of merit ZT obtained from the constant property model, while not applicable for some materials with strongly temperature-dependent thermoelectric properties, remains a simple yet useful metric for initial evaluation and/or comparison of thermoelectric materials, provided the ZT at the average temperature of projected operation, not the peak ZT, is used.     

非金属基导热材料对HPLED散热性能影响

由于光电转换效率较低,产生的多余熬已成为提升单位体积下大功率LED (HPLED)灯光输出量的主要瓶颈,使有效减少HPLED灯热流回路上各界面接触热阻成为重要课题.研究了不同的非金属基导热界面材料在不同环境温度条件下,应用于HPLED灯具模型中的第二界面处时对灯具散热情况的影响.结果表明,具有相变特征的非金属基导热界面材料.在其相变转化点位置之上的某一特定临界点后的热传导性能优于导热系数相对更高的非金属石墨基的界面材料.第二界面材料之间的接触热阻对发挥其导热能力有重要影响.     

Rational Design of a Printable,Highly Conductive Silicone‐based Electrically Conductive Adhesive for Stretchable Radio‐Frequency Antennas

Stretchable radio‐frequency electronics are gaining popularity as a result of the increased functionality they gain through their flexible nature, impossible within the confines of rigid and planar substrates. One approach to fabricating stretchable antennas is to embed stretchable or flowable conductive materials, such as conductive polymers, conductive polymer composites, and liquid metal alloys as stretchable conduction lines. However, these conductive materials face many challenges, such as low electrical conductivity under mechanical deformation and delamination from substrates. In the present study, a silicone‐based electrically conductive adhesive (silo‐ECA) is developed that have a conductivity of 1.51 × 10⁴ S cm^?1 and can maintain conductivity above 1.11 × 10³ S cm^?1, even at a large stain of 240%. By using the stretchable silo‐ECAs as a conductor pattern and pure silicone elastomers as a base substrate, stretchable antennas can be fabricated by stencil printing or soft‐lithography. The resulting antenna's resonant frequency is tunable over a wide range by mechanical modulation. This fabrication method is low‐cost, can support large‐scale production, has high reliability over a wide temperature range, and eliminates the concerns of leaking or delamination between conductor and substrate experienced in previously reported micro‐fluidic antennas.     

Interfacial Reactions Between Diffusion Barriers and Thermoelectric Materials Under Current Stressing

This study investigates the stability of the interfaces between an n-type thermoelectric material, Bi₂Te₃, and pure tin solders in a thermoelectric module. The module was stressed by a current at elevated temperatures. A map of the failure criteria of the module was constructed. Ni was used as the diffusion barrier between the solder and the thermoelectric materials, but it reacted with these materials and formed intermetallic compound (IMC) layers. The phase transformation of the IMC layers formed voids at the interfaces and reduced the strength of the joints. Current stressing promoted the formation of IMC. The kinetics of the compound growth was studied. The results suggested that the formation of NiTe IMC was successfully inhibited, but the Bi₄Te₅ compound grew from an infinitely adaptive series of (Bi₂) _m (Bi₂Te₃) _n because of the depletion of Te.     

Aligned Silver Nanowires Enabled Highly Stretchable and Transparent Electrodes with Unusual Conductive Property

Transparent conductors for the next generation of soft electronic devices need to be highly stretchable, conductive, and transparent, while an inevitable challenge lies in enhancing them simultaneously. Cost‐effective silver nanowires (AgNWs) are widely used but the conventional random network yields a high junction resistance as well as degraded conductivity in the stretched state. Here, a novel, facile, and versatile agitation‐assisted assembly approach is reported to control the orientation direction and density of AgNWs and to layer‐by‐layer deposit the AgNWs monolayer or multilayers onto the prestrained soft substrate. This electrode demonstrates an unprecedented low sheet resistance of 2.8 Ω sq^?1 as well as high transparency of 85% and high stretchability of 40%. It is interesting to note that contrary to most other reports, such a device shows higher conductivity in the stretched state compared to the released state.     

Fabrication of Bismuth Telluride Thermoelectric Films Containing Conductive Polymers Using a Printing Method

We prepared a mixture of thermoelectric bismuth telluride particles, a conductive polymer [poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)], poly(acrylic acid) (PAA), and several organic additives to fabricate thermoelectric films using printing or coating techniques. In the mixture, the organic components (PEDOT:PSS, PAA, and an additive) act as a binder to connect bismuth telluride particles mechanically and electrically. Among the organic additives used, glycerol significantly enhanced the electrical conductivity and bismuth telluride particle dispersibility in the mixture. Bi_0.4Te_3.0Sb_1.6 films fabricated by spin-coating the mixture showed a thermoelectric figure of merit (ZT) of 0.2 at 300 K when the Bi_0.4Te₃Sb_1.6 particle diameter was 2.8 μm and its concentration in the elastic films was 95 wt.%.     

Enhancement of Electrical Properties of Electrically Conductive Adhesives (ECAs) by Using Novel Aldehydes

To improve the electrical properties of electrically conductive adhesives (ECAs), different types of aldehydes, salicylaldehyde and transcinnamaldehyde, were introduced into ECA formulations. During the curing process, the aldehydes acted as a reducing agent and reduced metal oxide in ECAs. At the same time, aldehydes could consume ambient oxygen and prevent the oxidation of the metal fillers in the ECA. The oxidation product of aldehydes, carboxylic acids with shorter molecular chains, could partially replace or remove the long chain stearic acid (C ₁₈) surfactant on the lubricated Ag flakes and enhance the electrons tunneling between the Ag flakes in the ECAs. As such, the multiple effects of aldehydes in ECAs improved the conductivity significantly. Dynamic mechanical analysis and thermomechanical analysis studies indicated the improved performance for mechanical and physical properties of ECAs as well     

Thermoelectric Performance and High-Temperature Creep Behavior of GeTe-Based Thermoelectric Materials

New, efficient thermoelectric materials (GeTe) _x (Mn_0.6Sn_0.4Te)_1−x (0.8 ≤ x ≤  1.0) were prepared by hot pressing, and the effect of MnTe and SnTe contents on thermoelectric and mechanical properties of GeTe was investigated. The maximum dimensionless figure of merit ZT of the prepared materials is 1.57 in the temperature range from 720 K to 770 K for x = 0.15. Niobium was added to the quasiternary GeTe-based materials to suppress creep without degradation of thermoelectric properties. The distortion of the material with added Nb was less than 0.4% under experimental conditions of 100 N load at 873 K for 100 h. The favorable thermoelectric properties of these materials are accompanied by their stability in long-term use and the possibility of widening the service temperature range as a result of decreasing their phase-transition temperature T _c.     

Self‐Healable and Stretchable Organic Thermoelectric Materials: Electrically Percolated Polymer Nanowires Embedded in Thermoplastic Elastomer Matrix

Self‐healable and stretchable energy‐harvesting materials can provide a new avenue for the realization of self‐powered wearable electronics, including electronic skins, whose main materials are required to be robust to and stable under external damage and severe mechanical stresses. However, thermoelectric (TE) materials showing both self‐healing properties and stretchability have not yet been demonstrated despite their great potential to harvest thermal energy in the human body. As most existing TE materials are either mechanically brittle or unrecoverable after being subjected to damage, a novel approach is necessary for designing such materials. Herein, self‐healable and stretchable TE materials based on all‐organic composite system wherein polymer semiconductor nanowires are p‐doped with a molecular dopant and embedded in a thermoplastic elastomer matrix are reported. The polymer nanowires are electrically percolated in the matrix, and the resulting composite materials exhibit good TE performance. The composites also exhibit both excellent self‐healing properties under mild heat and pressure conditions and good stretchability. It is believed that this work can be a cornerstone for the design of self‐healable and stretchable energy‐harvesting materials as it provides useful guidelines for imparting electrical conductivity to insulating thermoplastic elastomers, which typically possess versatile and useful mechanical properties.     

Nanoscale Organic Thermoelectric Materials: Measurement,Theoretical Models,and Optimization Strategies

The demands for waste heat energy recovery from industrial production, solar energy, and electronic devices have resulted in increasing attention being focused on thermoelectric materials. Over the past two decades, significant progress is achieved in inorganic thermoelectric materials. In addition, with the proliferation of wireless mobile devices, economical, efficient, lightweight, and bio‐friendly organic thermoelectric (OTE) materials have gradually become promising candidates for thermoelectric devices used in room‐temperature environments. With the development of experimental measurement techniques, the manufacturing for nanoscale thermoelectric devices has become possible. A large number of studies have demonstrated the excellent performance of nanoscale thermoelectric devices, and further improvement of their thermoelectric conversion efficiency is expected to have a significant impact on global energy consumption. Here, the development of experimental measurement methods, theoretical models, and performance modulation for nanoscale OTE materials are summarized. Suggestions and prospects for the future development of these devices are also provided.     

银粉形貌及表面处理对导电胶性能的影响

利用四点探针和电子万能试验机分别测定了同种树脂体系中不同银粉形貌及银粉表面处理下导电胶的体积电阻率和剪切强度,探索了银粉含量、形状尺寸及表面处理对导电胶性能的影响规律.     

导电胶研究现状及其在LED产业中的应用

伴随中国战略性新兴LED产业的迅猛发展,LED芯片与基板之间的连接材料—导电胶,也成为了当前学术界和产业界的研究热点之一。分别从导电胶主要成分方面阐述了导电胶近年来的研究成果,为导电胶研发过程中的成分选择及优化处理提供参考。并展望了今后导电胶的发展趋势和应用前景。     

导电PBO织物的制备及其吸波性能

以离子注入法制备了导电聚对苯撑苯并二噁唑(PBO)织物,并对其表面形貌、结构和导电性能进行了表征。以导电PBO织物制备了频率选择表面(FSS),研究了FSS对纳米碳纤维(CNF)复合材料吸波性能的影响。     

Development of Skutterudite Thermoelectric Materials and Modules

Multifilling with La, Ba, Ga, and Ti in p-type skutterudite and Yb, Ca, Al, Ga, and In in n-type skutterudite remarkably reduces their thermal conductivity, resulting in enhancement of their dimensionless figure of merit ZT to ZT?=?0.75 for p-type (La,Ba,Ga,Ti)₁(Fe,Co)₄Sb₁₂ and ZT?=?1.0 for n-type (Yb,Ca,Al,Ga,In)_0.7(Co,Fe)₄Sb₁₂. A thermoelectric module technology suitable for these skutterudites including diffusion barrier and electrode materials has been established. The diffusion barrier materials allow the electrode to coexist stably with the p/n skutterudites in the module??s working temperature range of room temperature to 600°C. Under conditions of hot/cold-side temperatures of 600°C/50°C, a skutterudite module with size of 50?mm?×?50?mm?×?7.6?mm exhibited generation performance of 32?W power output and 8% thermoelectric conversion efficiency.     

Shielding Efficiency of Electrically Conductive Protective Coatings for Magnesium and Aluminum Surfaces

Although several proprietory finishes have been available for aluminum and magnesium protection from corrosion, the electrical properties at radio frequencies have never been sufficiently defined. In order to evaluate the relative merits of such finishes for aluminum and magnesium, a test program was established. Fixtures were designed to measure bonding impedance from dc to RF, and to evaluate shielding efficiency and insertion loss from gaskets used in joint interfaces. Marked differences in performance were observed between the radio frequency shielding obtained at radio frequencies and the bonding impedance measurements, indicating that the commonly used criterion of dc or RF bonding impedance is not sufficiently sensitive to provide good control of conductive coatings. Corrosion tests indicated several finishes would be acceptable from both the corrosion and electrical viewpoint.