Segmented thermoelectric generator: exponential area variation in leg

The innovative design of segmented thermoelectric generator with exponential area variation is introduced. Thermal efficiency and power output are assessed for various values of the design parameter (a = (L/x) ln[A_a/A(x)], where A_a is constant, and a is the dimensionless geometric parameter, L is the pin length, and A(x) is the pin cross‐sectional area), external load parameter (R_L/R₀, ratio of external electrical resistance to reference electrical resistance), and temperature parameter (θ = T_low/T_high, ratio of cold junction temperature to high junction temperature). The device efficiency obtained is validated through the previous experimental data for various hot and cold junction temperature differences. The findings reveal that thermal efficiency resulted from the current study agrees well with the experimental data. The innovative design of the segmented thermoelectric generator with exponentially decaying pin configuration enhances the thermal efficiency and output power as compared with the device having a single material pin configuration. Increasing temperature ratio results in the reduction in the thermal efficiency and the output power of thermoelectric generator. In addition, lowering the external load parameter improves the thermal efficiency and the output power of the thermoelectric device. The design parameter that maximizes the thermal efficiency of the thermoelectric generator does not maximize the device output power.     

High temperature solar thermoelectric generator

The performance of a sintered SiGe thermoelectric generator is assessed by computing power output per unit area and the efficiency of thermoelectric conversion. Previously developed high temperature solar energy absorbers were used. The power output and efficiency are considerably improved by using a water- or vapour-cooled heat sink in place of a radiative heat sink. The power density in the thermoelectric generator compares well with those in photovoltaic heterojunction cells using concentrated solar energy.     

Parametric study of asymmetric thermoelectric devices for power generation

Thermoelectric devices are considered a promising technique for recycling waste heat. In the present work, a three-dimensional numerical model is developed to study the output performance of thermoelectric devices. A comprehensive analysis is performed based on a conventional π-type thermoelectric couple. The results indicate that the maximum power of thermoelectric devices generally increases with a decrease in height and an increase in cross-sectional area; the maximum efficiency exhibits the opposite trends. The best way to reduce heat losses is by using ceramic plates with higher thermal conductivity. Moreover, the parasitic internal resistance exists in the thermoelements, and its influencing factors are studied. To minimize electric losses, an asymmetric structure is proposed for thermoelectric devices. The results exhibit that the optimal cross-sectional area ratio of the p-type and n-type legs (S_p/S_n) is mainly contingent upon the thermoelectric material parameters; the greater the differences in the parameters of p-type and n-type thermoelectric materials, the greater the gains provided by the asymmetric structure. Furthermore, the experimental data present great consistency with the numerical results. The research results may help guide the design of thermoelectric devices with relatively lower power losses.     

Modeling, experimental study on the heat transfer characteristics of thermoelectric generator

This paper investigates the heat transfer characteristics of a thermoelectric generator. The influence of heat dissipation intensity to the sub-thermal resistances distribution is experimentally studied. Based on the thermal network analysis and finite time thermodynamics, an analytical model including all thermal resistances (in both thermocouples and external heat exchangers) is developed to predict the performance of the generator. The results show that the computed values of output power agree well with the experimental values. The heat transfer enhancement on the generator cold side greatly reduces the cold side temperature and thermal resistance, and obviously improves the output power. Compare with air natural convection cooling, the main thermal resistance changes from the resistance between the fins and the ambient to the thermal contact resistances between the generator and the heat sink at the conditions of forced convection and water cooling. This study may be guide the optimization of generator structure.     

Inorganic thermoelectric materials: A review

Thermoelectric generator, which converts heat into electrical energy, has great potential to power portable devices. Nevertheless, the efficiency of a thermoelectric generator suffers due to inefficient thermoelectric material performance. In the last two decades, the performance of inorganic thermoelectric materials has been significantly advanced through rigorous efforts and novel techniques. In this review, major issues and recent advancements that are associated with the efficiency of inorganic thermoelectric materials are encapsulated. In addition, miscellaneous optimization strategies, such as band engineering, energy filtering, modulation doping, and low dimensional materials to improve the performance of inorganic thermoelectric materials are reported. The methodological reviews and analyses showed that all these techniques have significantly enhanced the Seebeck coefficient, electrical conductivity, and reduced the thermal conductivity, consequently, improved ZT value to 2.42, 2.6, and 1.85 for near-room, medium, and high temperature inorganic thermoelectric material, respectively. Moreover, this review also focuses on the performance of silicon nanowires and their common fabrication techniques, which have the potential for thermoelectric power generation. Finally, the key outcomes along with future directions from this review are discussed at the end of this article.     

非均质温差发电器的性能分析

建立非均质温差发电器(TEG)理论模型,考虑热电材料的非均质导热系数以及温差发电器与热源间的传热热阻的影响,分析非均质温差发电器的一般性能.讨论热电元件对数、热导率、高温热源温度对非均质温差发电器性能特性的影响.结果表明,相较于均质温差发电器,导热系数不均匀强度越大,非均质温差发电器的最大输出功率和最大效率越高;热电元...     

Effect of non-uniform illumination on performance of solar thermoelectric generators

Solar thermoelectric generators (STEGs) are heat engines which can generate electricity from concentrated sunlight. The non-uniform illumination caused by the optical concentrator may affect the performance of solar thermoelectric generators. In this paper, a three-dimensional finite element model of solar thermoelectric generators is established. The two-dimensional Gaussian distribution is employed to modify the illumination profiles incident on the thermoelectric generator. Six non-uniformities of solar illumination are investigated while keeping the total energy constant. The influences of non-uniform illumination on the temperature distribution, the voltage distribution, and the maximum output power are respectively discussed. Three thermoelectric generators with 32, 18 and 8 pairs of thermocouples are compared to investigate their capability under non-uniform solar radiation. The result shows that the non-uniformity of the solar illumination has a great effect on the temperature distribution and the voltage distribution. Central thermoelectric legs can achieve a larger temperature difference and generate a larger voltage than peripheral ones. The non-uniform solar illumination will weaken the capability of the TE generator, and the maximum output power decrease by 1.4% among the range of non-uniformity studied in this paper. Reducing the number of the thermoelectric legs for non-uniform solar illumination can greatly increase the performance of the thermoelectric generator.     

Experimental study on low-temperature waste heat thermoelectric generator

In order to further studies on thermoelectric generation, an experimental thermoelectric generator unit incorporating the commercially available thermoelectric modules with the parallel-plate heat exchanger has been constructed. The experiments are carried out to examine the influences of the main operating conditions, the hot and cold fluid inlet temperatures, flow rates and the load resistance, on the power output and conversion efficiency. The two operation parameters such as the hot fluid inlet temperature and flow rate are found to significantly affect the maximum power output and conversion efficiency. A comparison of the experimental results with those from the previously published numerical model is also presented. The meaningful results obtained here may serve as a good guide for further improving the numerical model and conducting a system level optimization study in the next step. Also, the present study shows the promising potential of using this kind of thermoelectric generator for low-temperature waste heat recovery.     

Configuration of segmented leg for the enhanced performance of segmented thermoelectric generator

Thermal analysis of a segmented thermoelectric generator is performed, and the segmented leg configurations maximizing the efficiency and the output power are formulated. The effect of operating conditions such as external load resistance, the temperatures of hot and cold junctions, on the device performance is studied. The segmented thermoelectric generator has the leg configuration consisting of the combination of modified lead telluride and modified bismuth telluride. The segmented thermoelectric generator performance, such as device efficiency and output power, is compared with those corresponding to a single material leg configuration (modified lead telluride or modified bismuth telluride) for various operating conditions. It is found that a unique value of the segmented leg combination maximizes the efficiency and the output power for each operating condition. The variation in the operating conditions changed the locus points of the maximum efficiency and the maximum output power. The segmented thermoelectric generator gives rise to the higher device efficiency and the output power than those of the single material leg configuration, especially for the low external load resistance. Copyright © 2016 John Wiley & Sons, Ltd.     

两级热电热机的有限时间热力学分析

建立了考虑外部传热影响的两级半导体热电热机模型,用有限时间热力学对牛顿传热规律下两级半导体热电热机的性能进行分析,导出了功率、效率与工作电流的一般关系式,得到了两侧换热器的最优面积分配和热电单元数的最优分配,并分析了多种因素对其性能的影响。     

A numerical model for thermoelectric generator with the parallel-plate heat exchanger

This paper presents a numerical model to predict the performance of thermoelectric generator with the parallel-plate heat exchanger. The model is based on an elemental approach and exhibits its feature in analyzing the temperature change in a thermoelectric generator and concomitantly its performance under operation conditions. The numerical simulated examples are demonstrated for the thermoelectric generator of parallel flow type and counter flow type in this paper. Simulation results show that the variations in temperature of the fluids in the thermoelectric generator are linear. The numerical model developed in this paper may be also applied to further optimization study for thermoelectric generator.     

An available method exploiting the waste heat in a proton exchange membrane fuel cell system

Based on the models of a proton exchange membrane (PEM) fuel cell working at steady state and a semiconductor thermoelectric generator, a hybrid system consisting of a PEM fuel cell, a semiconductor thermoelectric generator, and a regenerator is originally put forward. Expressions for the efficiencies and power outputs of the fuel cell, thermoelectric generator, and hybrid system are derived. The relation between the operating electric currents in the fuel cell and thermoelectric generator is obtained. The maximum power output of the hybrid system is numerically given. The optimally operating electric currents in the fuel cell and thermoelectric generator are calculated, and consequently, the optimal region of the hybrid system is determined. The results obtained here will provide some guidance for further understanding the performance and operation of practical PEM fuel cell-thermoelectric generator hybrid systems.     

Design optimization of thermoelectric devices for solar power generation

We present an improved theoretical model of a thermoelectric device which has been developed for geometrical optimization of the thermoelectric element legs and prediction of the performance of an optimum device in power generation mode. In contrast to the currently available methods, this model takes into account the effect of all the parameters contributing to the heat transfer process associated with the thermoelectric device.The model is used for a comparative evaluation of four thermoelectric modules. One of these is commercially available and the others are assumed to have an optimum geometry but with different design parameters (thermal and electrical contact layer properties).Results from the model are compared with experimental data of the commercial thermoelectric module in power generation mode with temperature gradient consistent with those achievable from a solar concentrator system. These show that it is important to have devices optimized specifically for generation, and to improve the contact layer of the thermoelements accordingly.     

Thermal‐hydraulic design features of a micronuclear reactor power source applied for multipurpose

Microheat pipe cooled reactor power source (HRP) designed for space or underwater vehicles meets the future demands, such as safer structure, longer operating time, and fewer mechanical moving parts. In this paper, potassium heat pipe cooled reactor power source system which generates 50 kWe electricity is proposed. The reactor core using uranium nitride fuel is cooled by 37 potassium high‐temperature heat pipes. The shields are designed as tungsten and water, and reactor reactivity is controlled by control drums. The thermoelectric generator (TEG) consists of thermoelectric conversion units and seawater cooler. The thermoelectric conversion units convert thermal energy to electric energy through the high‐performance thermoelectric material. A code applied for designing and analyzing the reactor power system is developed. It consists of multichannel reactor core model, heat pipe model using thermal resistance network, thermoelectric conversion, and thermal conductivity model. Then, the sensitivity analysis is performed on two key parameters including the length of the heat pipe condensation section and the cold junction temperature of the TE cell. Meanwhile, the steady‐state calculations are conducted. Results show that the maximum fuel temperature is 938 K located in the center of reactor core and the outlet temperature of coolant reaches 316 K. Both of them are within the limitation. It is concluded that the preliminary design of HPR design is reasonable and reliable. The designed residual heat removal system has sufficient safety margin to release the decay heat of the reactor. This research provides valuable analysis for the application of micronuclear power source.     

The influence of operating and device parameters on the maximum efficiency and the maximum output power of thermoelectric generator

Thermoelectric power generators are one of the promising green energy sources. The operating and the generator parameters influence the generator output performance. In the present study, the influence of the operating and the generator parameters on the maximum output power and the efficiency of the thermoelectric power generator are examined. The output power corresponding to the maximum efficiency and the maximum attainable output power of the generator are compared. It is found that the maximum power of the thermoelectric generator corresponding to the high Figure of Merit is very sensitive to the operating temperature. The maximum power attainable is larger than that its counterpart corresponding to the maximum generator efficiency. Copyright © 2010 John Wiley & Sons, Ltd.     

低温差下半导体温差发电器(火用)分析

半导体温差发电器的性能通常用输出功率和工作效率来进行评价，但在低温差对低品位能的利用上，只用工作效率来评价是不全面的。从[火用]的角度对低温差下半导体温差发电器的工作性能进行了分析，提出了[火用]效率，用炯效率来作为低温差下半导体温差发电器的评价参数。实验结果表明，随着温差的减小，半导体温差发电器的工作效率明显下降，但[火用]效率则基本稳定。     

Numerical modeling of the performance of thermoelectric module with polydimethylsiloxane encapsulation

This paper presents a 2‐dimensional finite volume model to investigate the performance of thermoelectric module (TEM) with polydimethylsiloxane (PDMS) encapsulation. The voltage and temperature distributions of the TEM under 2 kinds of boundary conditions (constant cold‐side temperature and fixed convection heat transfer coefficient) are studied. To validate the developed model, 2 TEMs with or without PDMS encapsulation are fabricated, and the experimental tests are carried out. Both model predicted and experimentally measured results showed that using flexible PDMS as the encapsulation material for the TEM can lead majority heat flowing through thermoelectric legs and is beneficial for heat harvesting. The geometrical parameters' effects of the PDMS encapsulation and thermoelectric legs are analyzed. Results demonstrated that the usage of larger thermoelectric legs and smaller width of the PDMS encapsulation can generate greater temperature difference and hence improve the voltage of the TEM. Thus, the developed model could be applied for optimal structural design of the flexible TEM with highest performance for heat harvesting.     

Analytical model of parallel thermoelectric generator

The paper studied the performances of parallel thermoelectric generator (TEG) by theoretical analysis and experimental test. An analytical model of parallel TEG was developed by theoretical analysis and calculation, based on thermodynamics theory, semiconductor thermoelectric theory and law of conservation of energy. Approximate expressions of output power and current of parallel TEG were deduced by the analytical model. An experimental system was built to verify the model. The results indicate that only when all of the thermoelectric modules (TE modules) in the parallel TEG have the same inherent parameters and working conditions, the parallel properties of the TEG are the same as that of common DC power. The existence of contact resistance is just like the increase of the TE module’s internal resistance, which leads to the deceases of output power. The thermal contact resistance reduces the output power by reducing the temperature difference between the two sides of the thermocouples. The results derived from the model are basically consistent with the experimental results, the model is suitable for the performance researching and designing of parallel TEG.     

Study of a TE (thermoelectric) generator incorporated in a multifunction wood stove

Replacing traditional open fire stoves, characterized by low efficiency, with improved ones is an important challenge for developing countries. Adding TE (thermoelectric) generators can provide electricity that permits not only the use of an electric fan increasing the ratio air to fuel to achieve a complete combustion in the stoves but also the satisfaction of basic needs: light, phones and other electronic devices. A review of existing TE generators for stoves is presented. To test the TE modules, an experimental device has been carried out in our laboratory where a gas heater simulates the stove. The generator set-up is described including the switching electric regulator that stabilizes the fluctuating voltage from the modules and stores the energy in a battery. The performance of the generator mostly depends on the heat transfer through the modules and especially on the thermal contact resistances. First experiments show the influence of the pressure on these resistances. Then a study of temperatures and electrical power measurements is compared to a theoretical analysis using TE and heat transfer equations. The very reasonable value of the obtained contact resistances shows that the mechanical design of the generator is almost optimized. The TE generator has produced up to 9.5 W.     

Performance effect on the TEG system for waste heat recovery in automobiles using ZnO and SiO2 nanofluid coolants

Enhancement in heat transfer of the cold side is vital to amplify the performance of a thermoelectric generator (TEG). With enriched thermophysical properties of nanofluids, significant improvement in heat transfer process can be obtained. The current study concerns the performance comparison of an automobile waste heat recovery system with EG‐water (EG‐W) mixture, ZnO, and SiO₂ nanofluid as coolants for the TEG system. The effects on performance parameters, that is, circuit voltage, conversion efficiency, and output power with exhaust inlet temperature, the total area of TEG, Reynolds number, and particle concentration of nanofluids for the TEG system have been investigated. A detailed performance analysis revealed an increase in voltage, power output, and conversion efficiency of the TEG system with SiO ₂ nanofluid, followed by ZnO and EG‐W coolants. The electric power and conversion efficiency for SiO ₂ nanofluid at an exhaust inlet temperature of 500K were enhanced by 11.80% and 11.39% respectively, in comparison with EG‐W coolants. Moreover, the model speculates that an optimal total area of TEGs exists for the maximum power output of the system. With SiO ₂ nanofluid as a coolant, the total area of TEGs can be diminished by up to 34% as compared with EG‐W, which brings significant convenience for the placement of TEGs and reduces the cost of the TEG system.