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.     

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.     

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.     

Energetic and exergetic analyses of a combined system consisting of a high-temperature polymer electrolyte membrane fuel cell and a thermoelectric generator with Thomson effect

A combined system model consisting of a high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC), a regenerator and a thermoelectric generator (TEG) is proposed, where the TEG is applied to harness the generated waste heat in the HT-PEMFC for extra electricity production. The TEG considers not only the Seebeck effect and Peltier effect but also the Thomson effect. The mathematical expressions of power output, energy efficiency, exergy destruction rate and exergy efficiency for the proposed system are derived. The energetic and exergetic performance characteristics for the whole system are revealed. The optimum operating ranges for some key performance parameters of the combined system are determined using the maximum power density as the objective function. The combined system maximum power density and its corresponding energy efficiency and exergy efficiency allow 19.1%, 12.4% and 12.6% higher than that of a stand-alone HT-PEMFC, while the exergy destruction rate density is only increased by 8.6%. The system performances are compared between the TEG with and without the Thomson effect. Moreover, the impacts of comprehensive parameters on the system performance characteristics are discussed. The obtained results are helpful in developing and designing such an actual combined system for efficient and clean power production.     

一种新型汽车尾气多通道热能发电系统

根据温差发电原理,设计了一种新型网格状通气管式的温差发电装置,实现对汽车尾气热能的再利用。通过优化温差发电装置的结构,改变了水箱结构,增加了废热通道数量,能够贴更多的温差发电片,从而提高转换效率。通过UG(计算机辅助设计软件)建立汽车尾气温差发电装置的理论模型,经过计算,当温差等于100℃时该装置的转换效率约等于5.67%。与其他温差发电装置进行比较,热油式温差发电器在260℃温差下最大热能转换效率可达4.389%,而汽车尾气温差发电器输出功率随着烟气温度的升高近似成线性递增,热能转换效率较低[1],通过比较得出,本装置不仅提高了转换效率,且达到相同转换效率时所对应的温差值也相应减少。     

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...     

Parametrical analysis of the design and performance of a solar heat pipe thermoelectric generator unit

This paper describes a solar heat pipe thermoelectric generator (SHP-TEG) unit comprising an evacuated double-skin glass tube, a finned heat pipe and a TEG module. The system takes the advantage of heat pipe to convert the absorbed solar irradiation to a high heat flux to meet the TEG operating requirement. An analytical model of the SHP-TEG unit is presented for the condition of constant solar irradiation, which may lead to different performance characteristics and optimal design parameters compared with the condition of constant temperature difference usually dealt with in other studies. The analytical model presents the complex influence of basic parameters such as solar irradiation, cooling water temperature, thermoelement length and cross-section area and number of thermoelements, etc. on the maximum power output and conversion efficiency of the SHP-TEG. Simulation based on the analytical model has been carried out to study the performance and design optimization of the SHP-TEG.     

Investigation into topping cycle: Thermal efficiency with and without presence of thermoelectric generator

Thermoelectric power generation due to solar heating is a current interest in green energy research. One of the applications of the thermoelectric power generator is involved with the topping cycle, in which the thermoelectric generators were placed on the heat collector elements of a conventional solar concentration power plant. Although the topping cycle is practical and easy to operate, the efficiency of the thermal system with and without thermoelectric generator needs to be examined. In the present study, thermal efficiency of the topping cycle is analyzed and compared with its counterpart without the presence of the thermoelectric elements. Thermodynamic analysis for the efficiency of both the systems with and without thermoelectric generator is presented. The fluid flow and heat transfer in a tube with presence of thermoelectric elements resembling the solar heating system incorporated in the topping cycle are simulated numerically. It is found that, for a certain combination of operating and thermoelectric device parameters, thermal efficiency of the topping cycle becomes slightly higher than that of the same system without the presence of the thermoelectric generators.     

Multi-criteria optimization of an integrated energy system with thermoelectric generator,parabolic trough solar collector and electrolysis for hydrogen production

In this research paper, a newly energy system consisting of parabolic trough solar collectors (PTSC) field, a thermoelectric generator (TEG), a Rankine cycle and a proton exchange membrane (PEM) is proposed. The integration is performed by establishing a TEG instead of the condenser as power generation and cooling unit thereafter surplus power output of the TEG is transferred to the PEM electrolyzer for hydrogen production. The integrated renewable energy system is comprehensively modeled and influence of the effective parameters is investigated on exergy and economic indicators through the parametric study to better understand the system performance. Engineering equation solver (EES) as a potential engineering tool is used to simulate the system and obtain the desired results. In order to optimize the system, a developed multi-objective genetic algorithm MATLAB code is applied to determine the optimum operating conditions of the system. Obtained results demonstrate that at optimum working condition from exergy viewpoint, exergy efficiency and total cost are 12.76% and 61.69 $/GJ, respectively. Multi-objective optimization results further show that the final optimal point which is well-balanced between exergy efficiency and total cost, has the maximum exergy efficiency of 13.29% and total cost of 63.96 $/GJ, respectively. The corresponding values for exergy efficiency and total cost are 10.01% and 60.21 $/GJ for optimum working condition from economic standpoint. Furthermore, hydrogen production at well-balanced operating condition would be 2.28 kg/h. Eventually, the results indicate that establishing the TEG unit instead of the condenser is a promising method to optimize the performance of the system and reduce total cost.     

Performance analysis of a hybrid solar thermoelectric generator

In this paper, a theoretical model is developed to investigate the performance of the hybrid solar thermoelectric generator (HSTEG) system, which is designed without (B-HSTEG) and with an evacuated glass tube (V-HSTEG). The heat loss, power output, thermal efficiency, and electrical efficiency of the B-HSTEG/V-HSTEG system are evaluated by analyzing the design parameters such as geometric solar concentration ratio, thermoelectric figure of merit, and cold-side inlet fluid temperature. The performance of the B-HSTEG is compared with the V-HSTEG system using two heat transfer fluids: water and Therminol VP-1. The maximum electrical efficiency of the B-HSTEG and V-HSTEG is estimated to be 12.2 and 15.6% (ZT = 3) with a corresponding thermal efficiency of about 61.9 and 60.3%, respectively. Overall, this paper provides a systematic performance analysis of HSTEG systems.     

Effect of irreversibilities on the performance of a thermoelectric generator

Using an externally and internally irreversible heat engine model, the maximum power and thermal efficiency at maximum power output have been determined for a thermoelectric generator. The irreversibilities can be characterized by a single parameter named the device-design parameter. The efficiency and power decrease with an increase of the device-design parameter which appears in the equations for maximum power and efficiency.     

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.     

The solar gas turbine for pump and electric generator drive

A turbine plant, using solar energy as a heat source, has been studied. The facility is used as a pump drive or electric-power generator. It is suitable for use in waterless areas, is easy to operate and maintain, and has high thermal efficiency. A computer-aided optimization was carried out for a regenerative solar gas turbine, including a parametric study of compressor, regenerator, concentrator, and turbine efficiencies. The effects of maximum cycle operating temperature and engine-pressure ratio on thermal efficiency and power output, as welll as corresponding optimum pressure ratios, were determined. The turbine and compressor efficiencies and the maximum cycle temperature exert the strongest influence on cycle thermal efficiency, power output, optimum pressure ratio for maximum work and efficiency: the regenerator has a greater effect than the receiver.     

The influence of the Thomson effect on the performance of a thermoelectric cooler

The temperature distribution of a thermoelectric cooler under the influence of the Thomson effect, the Joule heating, the Fourier’s heat conduction, and the radiation and convection heat transfer is derived. The influence of the Thomson effect on the temperature profiles, on the fraction of the Joule’s heat that flows back to the low-temperature side, and consequently on the maximum attainable temperature difference and the maximum allowable heat load are emphasized and explored. The results suggest that the cooling efficiency of a thermoelectric cooler can be improved not only by increasing the figure-of-merit of the thermoelectric materials but also by taking advantage of the Thomson effect. A possible development direction for the thermoelectric materials is thus given.     

Maximum power density analyses of a novel hybrid system based upon solid oxide fuel cells,vacuum thermionic generators and thermoelectric generators

Apart from electricity, solid oxide fuel cell (SOFC) generates a great deal of high-grade exhaust heat, which must be immediately removed to guarantee SOFC's normal operation. To harvest the exhaust heat and improve the overall energy conversion efficiency, a new hybrid system model based upon a SOFC, a vacuum thermionic generator (VTIG) and a thermoelectric generator (TEG) is first proposed. Considering the main thermodynamic-electrochemical irreversible effects, the performance indicators assessing the whole system performance are mathematically derived. In comparison with the performance of sole SOFC, the effectiveness and feasibility of the presented system are verified. Numerical calculation examples illustrate that maximum achievable power density (MAPD) and its corresponding efficiency, exergetic efficiency and exergy destruction rate are, respectively, 26.8%, 9.8%, 9.8% and 8.8% larger than that of the stand-alone SOFC. Exhaustive sensitivity analyses are further conducted to investigate the impacts of various parameters on the tri-generation system performance. Results indicate that the grain size and average pore diameter of electrodes in SOFC and the thermoelectric element number in TEG can be optimized to maximize the hybrid system power density.     

Effects of the cross‐sectional area ratios and contact resistance on the performance of a cascaded thermoelectric generator

Thermoelectric generator offers many advantages such as high durability, environmental protection, and high reliability. Since the geometric optimization of a thermoelectric generator is a proper way to improve the performance, this study considers the multiparameter optimization of thermoelectric generators to investigate the effect of cross‐sectional area ratios and contact resistance on the performance of thermoelectric generator. Here, a ∏ ‐type cascaded thermoelectric system with two stages including two p‐legs and two n‐legs is examined numerically by ANSYS Workbench. The effectiveness and efficiency are obtained for different electric contact resistances. The results show that with a decreasing of the electric contact resistance, the efficiency and effectiveness are increased. Also, higher output power and efficiency of the TEG device are observed with a suitable ratio of cross‐sectional area.     

Rotor dynamics correlation for maximum power and transient control of wind turbines

In this paper, a new rotor dynamics model is developed for transient power output from a horizontal axis wind turbine. In addition to the standard maximum kinetic energy of the wind, the model incorporates rotor velocity and rotational acceleration to enhance the control techniques that convert mechanical to electrical energy via shaft rotation. With current methods, the wind kinetic energy is generally the primary parameter that establishes maximum power output. By relating this wind energy to the rotor dynamics, electrical systems can have a more useful upper bound for the rotor control strategy. The new model predicts the rotor velocity for various turbine configurations, operating over a range of wind conditions. The predicted results show that the same power output is obtained as the standard kinetic energy approach, but with significant additional opportunity to better control the rotor dynamics. Copyright © 2009 John Wiley & Sons, Ltd.     

Differentiation of multiple maximum power points of partially shaded photovoltaic power generators

Partial shading conditions have a major effect on the electrical characteristics of photovoltaic (PV) power generators. In this paper, the effects of partial shading on maximum power points (MPPs) of a PV power generator have been systematically studied by using Simulink simulation model of a PV power generator composed of 18 series-connected PV modules. It is shown that the local MPPs can be classified into MPPs at low and high voltages based on the MPP operating point of the PV generator. The results also show that based on the MPP current and voltage it is possible to directly know if the MPP at high voltages is a local or a global MPP. The differentiation between local and global MPPs at high voltages is based on the voltage difference between the actual MPP voltage at high voltages and the theoretical MPP voltage under corresponding uniform conditions. This differentiation method was also tested to work correctly by utilizing experimental measurements of the Tampere University of Technology Solar PV Power Station Research Plant. By using this method, it can be identified if the system is operating at a local or a global MPP. This method can further be utilized to develop global MPP tracking algorithms.     

太阳能驱动半导体温差发电器性能参数的优化设计

应用非平衡态热力学理论,研究太阳能驱动半导体温差发电器的性能特性,确定发电器在最大效率时的优化条件,对系统的主要参数作了详细的讨论,得到一些有意义的新结论。     

Matching of DC motors to photovoltaic generators for maximum dailygross mechanical energy

The matching to solar-cell generators of both separately excited and series DC motors driving pumping loads is addressed. It is shown that the maximum gross mechanical power can be obtained at slightly higher voltages and slightly lower currents compared to the maximum electrical-power points on the solar-cell generator characteristics at different insolation levels. Guidelines for constructing the loci of the motor voltage-current points for maximum mechanical power and for determining the optimal motor parameters to match the solar generator are derived in terms of the mechanical load characteristics and the solar array parameters. Results of applying these design criteria to practical case studies enabled the assessment and comparison of both kinds of motors, especially as far as the daily utilizable output mechanical energy is concerned. The superiority of the separately excited motors in such systems is quantitatively indicated. The results are also compared to corresponding information available in the literature