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.     

Coupled thermal model of photovoltaic-thermoelectric hybrid panel for sample cities in Europe

In general, modeling of photovoltaic-thermoelectric (PV/TEG) hybrid panels have been mostly simplified and disconnected from the actual ambient conditions and thermal losses from the panel. In this study, a thermally coupled model of PV/TEG panel is established to precisely predict performance of the hybrid system under different weather conditions. The model takes into account solar irradiation, wind speed and ambient temperature as well as convective and radiated heat losses from the front and rear surfaces of the panel. The model is developed for three sample cities in Europe with different weather conditions. The results show that radiated heat loss from the front surface and the convective heat loss due to the wind speed are the most critical parameters on performance of the hybrid panel performance. The results also indicate that, with existing thermoelectric materials, the power generation by the TEG is insignificant compared to electrical output by the PV panel, and the TEG plays only a small role on power generation in the hybrid PV/TEG panel. However, contribution of the TEG in the power generation can be improved via higher ZT thermoelectric materials and geometry optimization of the TEG.     

A coupled 3D electrochemical and thermal numerical analysis of the hybrid fuel cell-thermoelectric device system

While the integration of the fuel cell (FC) and the semiconductor thermoelectric device (TED) to form a clean energy hybrid FC-TED system has been previously studied using 0-D mathematical equations, a 3-D finite element model that couples together the physics between the two devices is yet to be comprehensively studied. This paper introduces a 3-D finite element model developed in COMSOL Multiphysics that simulates both the FC and the TED subsystems where the FC electrochemical dynamics and the TED's thermoelectric effect and heat transfer physics take place between them. The studied FC stack is in direct contact with one side of the TED via the top of the gas channel structure and the other side is then convectively cooled by active air cooling. Results demonstrate that the proposed model can easily simulate the TED as both a thermoelectric generator (TEG) or as a Peltier device for cooling and heating. In the TEG mode, energy harvesting efficiency is observed at only 0.1% but expected to improve with better TED to FC relative sizing. The Peltier heating mode is also found to be advantageous in terms of quickly regulating the FC stack temperature, a valuable feature for startup processes.     

A Finite Volume Analysis of Thermoelectric Generators

ABSTRACT

The electric power produced by a thermoelectric generator (TEG) is strongly influenced by the applied heat sink. While a TEG is aimed at harvesting waste heat, the optimization of the efficiency of the heat sink is a key task for the design of waste heat recovery systems implementing TEG. A TEG model is proposed and implemented in an open source toolbox for field operation and manipulation (OpenFOAM) for the purpose of performing optimizations of the heat sink, using a commercially available TEG as basis. This model includes the multi-physics thermoelectric coupled effects. Conservation principles of energy and current are considered simultaneously. This includes the thermal and electric conduction, Seebeck effect, Peltier effect, Thomson effect, and Joule heating. Particular attention is given to a proper modeling of the boundary conditions. The thermoelectric model is implemented in such a way that it can readily be combined with other physical models in OpenFOAM. The model is validated by comparing the predictions to analytical results, measurements as well as the simulation data of other authors.     

Experiments and simulations on low-temperature waste heat harvesting system by thermoelectric power generators

In this case study, a system to recover waste heat comprised 24 thermoelectric generators (TEG) to convert heat from the exhaust pipe of an automobile to electrical energy has been constructed. Simulations and experiments for the thermoelectric module in this system are undertaken to assess the feasibility of these applications. A slopping block is designed on the basis of simulation results to uniform the interior thermal field that improves the performance of TEG modules. Besides simulations, the system is designed and assembled. Measurements followed the connection of the system to the middle of an exhaust pipe. Open circuit voltage and maximum power output of the system are characterized as a function of temperature difference. Through these simulations and experiments, the power generated with a commercial TEG module is presented. Overview this case study and our previous work, the results establish the fundamental development of low-temperature waste heat thermoelectric generator system that enhances the TEG efficiency for vehicles.     

Integrating high-temperature proton exchange membrane fuel cell with duplex thermoelectric cooler for electricity and cooling cogeneration

To harvest the waste heat from exothermic reaction processes, a novel hybrid system model mainly incorporating a high-temperature proton exchange membrane fuel cell (HT-PEMFC) and a duplex thermoelectric cooler is conceptualized to theoretically predict the potential performance limit. The duplex thermoelectric cooler is composed of a thermoelectric generator (TEG) and a thermoelectric cooler (TEC), where the TEG harvests the waste heat to generate electricity and the TEC utilizes the generated electricity for cooling production. A mathematical model is established to estimate the proposed system performance from both exergetic and energetic perspectives considering various irreversible effects, from which effectiveness and practicality of the proposed system can be examined. The hybrid system maximal output power density allows 14.1% greater than that of the basic HT-PEMFC, whereas the according destruction rate density of exergy is decreased by 7.7%. The feasibility and effectiveness of the proposed system configuration are verified. Moreover, substantial parametric analyses indicate that the proposed system performance can be improved by elevating the HT-PEMFC operating temperature, inlet relative humidity and doping level while worsened by enhancing the leak current density, electrolyte thickness and Thomson coefficient. The results acquired may be helpful in designing and optimizing such an actual hybrid system.     

Numerical model of a thermoelectric generator with compact plate-fin heat exchanger for high temperature PEM fuel cell exhaust heat recovery

This paper presents a numerical model of an exhaust heat recovery system for a high temperature polymer electrolyte membrane fuel cell (HTPEMFC) stack. The system is designed as thermoelectric generators (TEGs) sandwiched in the walls of a compact plate-fin heat exchanger. Its model is based on a finite-element approach. On each discretized segment, fluid properties, heat transfer process and TEG performance are locally calculated for higher model precision. To benefit both the system design and fabrication, the way to model TEG modules is herein reconsidered; a database of commercialized compact plate-fin heat exchangers is adopted. Then the model is validated against experimental data and the main variables are identified by means of a sensitivity analysis. Finally, the system configuration is optimized for recovering heat from the exhaust gas. The results exhibit the crucial importance of the model accuracy and the optimization on system configuration. Future studies will concentrate on heat exchanger structures.     

Experimental investigation of a novel heat pipe thermoelectric generator for waste heat recovery and electricity generation

Waste heat recovery helps reduce energy consumption, decreases carbon emissions, and enhances sustainable energy development. In China, energy-intensive industries dominate the industrial sector and have significant potential for waste heat recovery. We propose a novel waste heat recovery system assisted by a heat pipe and thermoelectric generator (TEG) namely, heat pipe TEG (HPTEG)，to simultaneously recover waste heat and achieve electricity generation. Moreover, the HPTEG provides a good approach to bridging the mismatch between energy supply and demand. Based on the technical reserve on high-temperature heat pipe manufacturing and TEG device integration, a laboratory-scale HPTEG prototype was established to investigate the coupling performances of the heat pipes and TEGs. Static energy conversion and passive thermal transport were achieved with the assistance of skutterudite TEGs and potassium heat pipes. Based on the HPTEG prototype, the heat transfer and the thermoelectric conversion performances were investigated. Potassium heat pipes exhibited excellent heat transfer performance with 95% thermal efficiency. The isothermality of such a heat pipe was excellent, and the heat pipe temperature gradient was within 15°C. The TEG's thermoelectric conversion efficiency of 7.5% and HPTEG's prototype system thermoelectric conversion efficiency of 6.2% were achieved. When the TEG hot surface temperature reached 625°C, the maximum electrical output power of the TEG peaked at 183.2 W, and the open-circuit voltage reached 42.2 V. The high performances of the HPTEG prototype demonstrated the potential of the HPTEG for use in engineering applications.     

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.     

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.     

Liquid metal based thermoelectric generation system for waste heat recovery

A new type of thermoelectric generator (TEG) system based on liquid metal which serves to harvest and transport waste heat, is proposed in this paper. To demonstrate the feasibility of the new TEG system, an experimental prototype which combined commercially available thermoelectric (TE) modules with the electromagnetic pump was set up. Output voltage from TE modules and temperature changes of the main parts (waste heat source, liquid metal heating plate, water-cooling plates I and II) of the liquid metal based TEG system were experimentally measured, as well as the flow rate of cooling water and the load resistance. It was shown that the maximum open-circuit voltage of 34.7 V was obtained when the temperature of the waste heat source was 195.9 °C and the temperature gap between liquid metal heating plate and cooling-water plates was nearly 100 °C. These experimental results obviously verify that using liquid metal based TEG system for waste heat recovery is highly feasible. In addition, the TEG system performance is discussed and a calculated efficiency of 2% in the whole TEG system is obtained. Possible suggestions to further improve this type of generator in the future are given.     

A novel choice for the photovoltaic–thermoelectric hybrid system: the perovskite solar cell

Most of the recent studies about the photovoltaic cell‐thermoelectric generator (PV‐TEG) hybrid system pay their attention to silicon PV cells. This paper is to estimate the feasibility and features of the integrated system consisting of the emerging perovskite solar cells and thermoelectric modules. The results in this paper show that the temperature coefficient of the perovskite solar cell is lower than 2‰. Because of such a lower temperature coefficient, the efficiency of the perovskite solar cell‐TEG hybrid system can amount to 18.6%, while the efficiency of the single perovskite solar cell is 17.8%. Therefore, the perovskite solar cell is a reasonable choice for the PV‐TEG hybrid system. By altering the thermal concentration, the volume of the TEG material can be decreased, and the cost of the hybrid system can be remarkably reduced. To study the influence of the thermal concentration on the performance of the hybrid system, a three‐dimensional numerical model of the hybrid system is developed in this paper. When the thermal concentration ration is lower than 100, the temperature drop is lower than 3 K, and the decline in the conversion efficiency caused by the thermal concentration can be neglected for the proposed PV‐TEG hybrid system. Copyright © 2016 John Wiley & Sons, Ltd.     

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.     

A mathematic model of thermoelectric module with applications on waste heat recovery from automobile engine

Over two-thirds energy of fuel consumed by an automobile is discharged to the surroundings as waste heat. The fuel usage can be more efficient if thermoelectric generators (TEG) are used to convert heat energy into electricity. In this study, a thermoelectric module composed of thermoelectric generators and a cooling system is developed to improve the efficiency of an IC engine. Two potential positions on an automobile are chosen to apply this module, e.g. exhaust pipe and radiator to examine the feasibility. To predict the behaviors of this module, a one dimensional thermal resistance model is also build, and the results are verified with experiments.     

高温温差发电装置集热器结构数值仿真研究

设计了一种针对高温烟气的圆筒式温差发电装置,在装置中设置分流桶增强烟气侧的换热效果。利用Ansys Fluent软件对装置的温度场、速度场及排气压降进行仿真模拟,分析了不同分流桶的桶直径、端盖孔直径和分流孔直径对热电模块冷热端温度分布的影响。仿真结果表明：温差发电系统集热器通道中设置分流桶可以实现高效温差发电,分流桶端盖未开孔时装置的换热效果优于端盖开孔结构;适当减小分流孔直径或增大分流桶直径会提升热电模块的冷热端温差,分流孔直径为2 mm时的换热效果最优,分流桶直径过大会使热电模块温度分布及温差的均匀性降低;系统烟气压降会随着分流孔直径的增大或分流桶直径的减小而降低。     

A three-dimensional numerical model of thermoelectric generators in fluid power systems

In thermoelectric generators, the heat sources are usually fluids or flames. To simplify the co-design and co-optimization of the fluid or combustion system and the thermoelectric device, which are crucial for maximizing the system performance, a three-dimensional thermoelectric generator model is proposed and implemented in a computational fluid dynamics (CFD) simulation environment (FLUENT). This model of the thermoelectric power source accounts for all temperature dependent characteristics of the materials, and includes nonlinear fluid-thermal-electric multi-physics coupled effects. In solid regions, the heat conduction equation is solved with ohmic heating and thermoelectric source terms, and user defined scalars are used to determine the electric field produced by the Seebeck potential and electric current throughout the thermoelements. The current is solved in terms of the load value using user defined functions but not a prescribed parameter, and thus the field-circuit coupled effect is included. The model is validated by simulation data from other models and experimental data from real thermoelectric devices. Within the common CFD simulator FLUENT, the thermoelectric model can be connected to various CFD models of heat sources as a continuum domain to predict and optimize the system performance.     

Numerical simulation of nanostructured thermoelectric generator considering surface to surrounding convection

Thermoelectric systems (TE) can directly convert heat to electricity and vice-versa by using semiconductor materials. Therefore, coupling between heat transfer and electric field potential is important to predict the performance of thermoelectric generator (TEG) systems. This paper develops a general two-dimensional numerical model of a TEG system using nanostructured thermoelectric semiconductor materials. A TEG with p-type nanostructured material of Bismuth Antimony Telluride (BiSbTe) and n-type Bismuth Telluride (Bi₂Te₃) with 0.1 vol.% Silicon Carbide (SiC) nanoparticles is considered for performance evaluations. Coupled TE equations with temperature dependant transport properties are used after incorporating Fourier heat conduction, Joule heating, Seebeck effect, Peltier effect, and Thomson effect. The effects of temperature difference between the hot and cold junctions and surface to surrounding convective on different output parameters (e.g., thermal and electric fields, power generation, thermal efficiency, and current) are studied. Selected results obtained from current numerical analysis are compared with the results obtained from analytical model available in the literature. There is a good agreement between the numerical and analytical results. The numerical results show that as temperature difference increases output power and amount of current generated increase. Moreover, it is quite apparent that convective boundary condition deteriorates the performance of TEG.     

Electricity generation using solar parabolic dish system with thermoelectric generator—An experimental investigation

The present electricity grid installation cost as well as the tariff is quite high in India, particularly remote rural areas, to electrify houses. These problems can be easily solved by installing standalone systems that operate on one of the clean energy sources such as solar energy. An experimental analysis of generating electricity from a thermoelectric generator (TEG) powered by a solar parabolic dish concentrator device with aperture area and focal length of 12.6 m² and 2.42 m, respectively, is presented in this article. A TEG is made up of a thermoelectric module connected to a flat receiver by an absorber layer. The studies were carried out in Indian climatic conditions at the National Institute of Technology, Puducherry. Over a spectrum of beam radiation, the system's maximum energy conversion efficiency, as well as efficient electrical output, are evaluated and presented. The proposed system's average effective electrical efficiency is 0.424%, corresponding to the TEG's average energy conversion efficiency of 2.76%.     

A cascaded thermoelectric generation system for low-grade heat harvesting

Thermoelectric generation (TEG) has its unique advantages in terms of distributed energy supply, low-grade heat recovery, and clean energy technology, but its low efficiency has constrained its application and promotion seriously. In order to obtain satisfactory efficiency and realize the adaptability to different heat sources, a novel cascaded TEG system (CTEG) is proposed. According to the temperature of heat source, three types of thermoelectric modules are used in the generator system. The module arrangement, cooling medium, and mode directly affect the performance of this whole system, since that the detailed model and CFD simulation were conducted to obtain the optimal collocation. Based on the optimization modeling, a CTEG prototype was constructed. From the experimental results, the efficiency of the CTEG achieved 5.92%, which significantly improved about 21.56% compared with the TEG which only contains one stage. Moreover, the key parameters of the system were identified. The stability and the improvement of the system were discussed comprehensively. For TEG system, CTEG increase the utilization of high-temperature heat sources, but also provides a structure for a TEG adapting to multiple temperature heat sources.     

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.