无量纲优值对热电制冷系统性能影响分析

建立了无量纲稳态系统热力学模型。并用该模型分析了优值系数对系统性能的影响,优值系数是热电制冷器性能的内在制约,散热和温度条件则是热电制冷性能的外在制约,无量纲优值体现了二者对系统的影响。热电制冷系统的特殊优势再度受到人们关注,但在热电材料优值系数受到限制的现实条件下,热电制冷系统在能效上是难以与压缩式制冷空调系统比较的。     

Optimal Electrical Conductivity for Maximum Thermoelectric Figure of Merit

A frequently employed approach for determination of the maximum thermoelectric figure of merit of a material involves a calculation of its maximum electrical power factor and the corresponding thermal conductivity. In this study, we show that the thermoelectric figure of merit determined using this approach is likely to be limited by the Lorenz factor. The maximum thermoelectric figure of merit is achieved at a different electrical conductivity. A simple way of estimating the optimal electrical conductivity for obtaining the maximum thermoelectric figure of merit is presented.     

不同模数对材料热电性能的影响

基于玻尔兹曼传输方程和Landauer方程,研究了一定能谱宽度内模数为常数和Guass型分布的热电优值、电导率和功率因子等热电参数的特性,并与模数为Delta型分布的情况进行对比。结果表明,引入能谱宽度后,热电优值有所下降,但是,电导率和功率因子将增加。这种模数会比Delta型更具有实际意义。     

一种测试半导体制冷器的瞬态方法

ZT值、最大制冷温差和响应时间是表征半导体制冷器性能的重要参数.文中介绍了一种能同时测量这三个参数的瞬态方法,并讨论了热沉对测试结果的影响.利用一个由恒流脉冲发生器和数据采集卡组成的简单测试系统测得制冷器在小电流下的电阻电压和塞贝克电压,通过这两个电压推导出ZT值、最大制冷温差.这种瞬态方法是非接触式测量,准确度高,可用于薄膜热电器件测试;另外瞬态方法耗时短,可大大缩短半导体制冷器可靠性测试的周期.采用这种方法对4mm×4mm×2.4mm的热电制冷器进行实验,环境温度300K时,测得ZT值为0.39,最大温差58.5K,响应时间20s.     

Thermoelectric Property Dependence and Geometry Optimization of Peltier Current Leads Using Highly Electrically Conductive Thermoelectric Materials

Thermoelectric materials are promising candidates for use in energy-saving devices in many fields. They are also useful in superconducting applications such as those using Peltier current leads (PCLs) to reduce system heat loss. In the case of PCLs, consideration must be given to Joule heating. Furthermore, the performance of PCLs is intricately dependent on their thermoelectric properties. In addition to the figure of merit Z, consideration of the electrical conductivity is also important for the design of high-performance PCLs. In this paper, we discuss the resistivity dependence of the performance of PCLs using model parameters obtained from real devices.     

一种测试半导体制冷器的瞬态方法

ZT值、最大制冷温差和响应时间是表征半导体制冷器性能的重要参数.文中介绍了一种能同时测量这三个参数的瞬态方法,并讨论了热沉对测试结果的影响.利用一个由恒流脉冲发生器和数据采集卡组成的简单测试系统测得制冷器在小电流下的电阻电压和塞贝克电压,通过这两个电压推导出ZT值、最大制冷温差.这种瞬态方法是非接触式测量,准确度高,可用于薄膜热电器件测试;另外瞬态方法耗时短,可大大缩短半导体制冷器可靠性测试的周期.采用这种方法对4mm×4mm×2.4mm的热电制冷器进行实验,环境温度300K时,测得ZT值为0.39,最大温差58.5K,响应时间20s.     

Thermoelectric figure of merit for bulk nanostructured composites with distributed parameters

The effective properties of composites whose structure includes nanocontacts between bulk-phase macrocrystallites are considered. A model for such a nanostructured composite is constructed. Effective values of the thermoelectric power, thermal and electrical conductivities, and thermoelectric figure of merit are calculated in the mean-field approximation.     

Thermoelectric Properties of Li-Intercalated ZrSe2 Single Crystals

Zirconium diselenide (ZrSe₂) is one of many members of the layer-structured transition-metal dichalcogenide family. The structure of these materials features a weakly bonded van der Waals gap between covalently bonded CdI₂-type atomic layers that may host a wide range of intercalants. Intercalation can profoundly affect the structural, thermal, and electronic properties of such materials. While the thermoelectric potential of layer-structured transition-metal dichalcogenides has been formerly studied by several groups, to our best knowledge, neither the thermoelectric properties of ZrSe₂ nor the impact of intercalation on its thermoelectric properties have been reported (specifically, the full evaluation of the dimensionless figure of merit, ZT, which includes the thermal conductivity). In this proof-of-principle study, ZrSe₂ single crystals have been synthesized using an iodine-assisted vapor transport method, followed by a wet-chemistry lithium intercalation process. The results of resistivity, thermopower, and thermal conductivity measurements between 10 K and 300 K show that Li intercalation induced additional charge carriers and structural disorder that favorably affected the thermoelectric properties of the material. As a result, a dimensionless figure of merit ZT ≈ 0.26 has been attained at room temperature in a Li-intercalated sample, representing nearly a factor of three improvement compared with the pristine sample. These improvements, along with the abundance, relatively low toxicity, and low cost of such materials, merit further thermoelectric investigations of intercalated zirconium diselenide, especially in conjunction with a substitutional doping approach.     

Calculations of the charge-carrier mobility and the thermoelectric figure of merit for multiple-quantum-well structures

The thermoelectric figure of merit of structures with multiple quantum wells (MQWs) was calculated taking into account the variations in the relaxation time of charge carriers compared to that in a bulk sample. The mechanisms of scattering by acoustic phonons, at the short-range impurity potential, and the polar scattering in the approximation of the isotropic parabolic dispersion law of the charge carriers were taken into account. The model used is based on the assumption that the phonon spectrum in the MQW structures is no different from the spectrum of the bulk crystal. In addition, the scattering is assumed to be elastic and the relaxation-time approximation was used for all three mechanisms of scattering. A comparison with the results of calculations for a bulk sample shows that the expression for thermoelectric figure of merit is exactly the same for a MQW structure as for a bulk sample if the decrease in the charge-carrier relaxation time in MQW structures is taken into account. The magnitude of the figure of merit for a MQW structure is found to be equal to that for a bulk sample if the chemical potential in each of the cases is chosen from the condition for the highest figure of merit.     

Thermoelectric Properties of n-Mg2(SiGe)0.8Sn0.2 Solid Solution

Semiconductors - High values of the thermoelectric figure of merit (ZT = 1.5) in Mg2Si–Mg2Sn solid solutions are caused by a low thermal conductivity and a complex band structure, which is...     

Thermoelectric figure of merit of a p-n junction

The thermoelectric figure of merit of a semiconductor p-n junction is calculated in terms of the diode theory taking account of the bipolar thermal conductivity. The thermoelectric figure of merit of a Bi₂Te₃ diode is estimated and it is shown that the Ioffe criterion may be at the same level as the best modern thermoelectric materials but cannot exceed unity.     

Theory of materials for thermoelectric and thermomagnetic devices

The relation between the thermoelectric figure of merit Z and the basic properties of the material such as carrier mobilities, band structure, thermal conductivity and minority carrier lifetime is discussed. For isotropic materials with parabolic bands it is shown that the figure of merit based on the Seebeck coefficient will increase when a magnetic field is applied, if acoustic-mode scattering is predominant. If optical-mode scattering is predominant, the figure of merit will increase if ZT>0.77. Materials for devices based upon the Nernst or Ettingshausen effects will have large figures of merit only if 1) (m^*)^3/2µ/κL is large, 2) the energy gap is less than kT, and 3) the electron and hole mobilities are similar. Materials requirements for Nernst- and Seebeck-type devices are compared.     

基于Bi_2Te_3合金材料的热发电模块研究

为了提高Bi2Te3热电材料的性能,采用Bi2Te3纳米粉体前驱物快速熔炼烧结法,制备了在室温条件下具有温度敏感性的Bi2Te3合金材料,在425K时此材料的热电优值达到0.548。在此基础上,研制了热电模块,并对其性能进行了测试。结果表明,以该Bi2Te3合金材料制备的热发电模块具有良好的伏安特性和稳定的内阻,当热冷端温度分别为140和60℃时,模块的最大输出功率可达到0.39W,显现出潜在的应用前景。     

风冷热电空调器的研制

建立了风冷热电空调器数值模拟模型 ,对空调器进行了模拟计算 .在对风冷热电空调器研制的基础上 ,进行了最佳隔热层厚度、不同结构形式、变工况、变风量和复现性实验 ,验证了仿真程序的可靠性 ,并应用模拟程序对热电材料的优值系数和空调器冷、热端的传热系数进行了分析     

Nanostructured Thermoelectric Materials for Temperatures of 200–1200 K Obtained by Spark Plasma Sintering

Semiconductors - The broad application of thermoelectricity is constrained by the low efficiency of thermoelectric elements, which is mainly determined by the thermoelectric figure of merit of...     

Thermal Cycling, Mechanical Degradation, and the Effective Figure of Merit of a Thermoelectric Module

Thermoelectric modules experience performance reduction and mechanical failure due to thermomechanical stresses induced by thermal cycling. The present study subjects a thermoelectric module to thermal cycling and evaluates the evolution of its thermoelectric performance through measurements of the thermoelectric figure of merit, ZT, and its individual components. The Seebeck coefficient and thermal conductivity are measured using steady-state infrared microscopy, and the electrical conductivity and ZT are evaluated using the Harman technique. These properties are tracked over many cycles until device failure after 45,000 thermal cycles. The mechanical failure of the TE module is analyzed using high-resolution infrared microscopy and scanning electron microscopy. A reduction in electrical conductivity is the primary mechanism of performance reduction and is likely associated with defects observed during cycling. The effective figure of merit is reduced by 20% through 40,000 cycles and drops by 97% at 45,000 cycles. These results quantify the effect of thermal cycling on a commercial TE module and provide insight into the packaging of a complete TE module for reliable operation.     

Calculation of the thermoelectric figure of merit for multilayer structures with quantum wells in the case of carrier scattering by polar optical phonons

The increase in the thermoelectric figure of merit in layered structures with quantum wells is calculated for the case of polar charge-carrier scattering by optical phonons. On the basis of previous and new calculations, it is concluded that the quantum confinement effect can give rise to the increase in the figure of merit only if the probability of carrier scattering decreases with increasing wave vector transfer.     

Thermoelectric studies of IV–VI semiconductors for renewable energy resources

In the present study we explore the structural, electronic and thermoelectric properties of IV-VI semiconductors using first principle calculations based on the density functional theory. Generalized gradient approximation (GGA-PBEsol) is used as an exchange-correlation functional for the structural properties of the different crystal phases of these semiconductors. The compounds SnS, SnSe, GeS and GeSe favor orthorhombic structure, lead chalcogenides (PbS, PbSe and PbTe) are stable in the cubic rocksalt structure, while SnS₂ and SnSe₂ exist in hexagonal structure. For band structures additional to GGA, modified Becke and Johnson (mBJ) exchange potential is used. These compounds are narrow band gap semiconductors in the energy range 0.2–2.8 eV. These binary IV-VI chalcogenides have direct band gap nature in cubic crystals while indirect in the orthorhombic phases. The post-DFT (BoltzTraP) calculations are performed to estimate Seebeck coefficient, electric and thermal conductivities, power factor and figure of merit of these compounds to check their applicability in thermoelectric devices. Spin orbit coupling effect influences the electronic and thermoelectric properties of these compounds due to the large size of the constituent elements. Further, the total thermal conductivity is computed using ad-hoc calculation with the experimental results. The calculated values of figure of merit for PbS, PbSe, PbTe and SnTe are in the range 0.68–0.77 at room temperature.     

电子器件热电制冷温度条件的优化

基于热电制冷热力学循环分析了热电制冷器正常工作的温度条件,以及两种极限工况性能受工作温度条件的制约关系。优值系数是热电制冷器性能的内在制约,散热和温度条件则是热电制冷性能的外在制约,热电制冷元件工作的温度特性与电子元件工作的理想温度条件是非常适应的。基于热电制冷的主动冷却技术对高热流密度电子集成部件的封装散热具有重大意义。     

A Novel zT Meter Based on the Porcupine Method and a Survey on the Size of the Snout Correction Needed for Various Thermoelectric Devices

Measurements of the dimensionless figure of merit of different thermoelectric devices are presented and discussed, as obtained with a prototype zT meter which is based on the porcupine method. The instrument’s architecture and operation are discussed to support claims made on the accuracy of results. Different types of thermoelectric devices were tested, focusing on the size of the porcupine’s snout for each. The latter is probably the major source of uncertainty in Harman methods, but is well measurable with the porcupine method, which therefore allows definition of the correction needed to obtain accurate evaluation of zT. Accuracies much better than 1% in the determination of the dimensionless figure of merit and series resistance are possible in this way. A survey of various devices is reported, and results are shown to indicate that corrections up to the 10% level and more are needed, depending on the configuration.