Modeling a Thermoelectric Generator Applied to Diesel Automotive Heat Recovery

Thermoelectric generators (TEGs) are outstanding devices for automotive waste heat recovery. Their packaging, lack of moving parts, and direct heat to electrical conversion are the main benefits. Usually, TEGs are modeled with a constant hot-source temperature. However, energy in exhaust gases is limited, thus leading to a temperature decrease as heat is recovered. Therefore thermoelectric properties change along the TEG, affecting performance. A thermoelectric generator composed of Mg₂Si/Zn₄Sb₃ for high temperatures followed by Bi₂Te₃ for low temperatures has been modeled using engineering equation solver (EES) software. The model uses the finite-difference method with a strip-fins convective heat transfer coefficient. It has been validated on a commercial module with well-known properties. The thermoelectric connection and the number of thermoelements have been addressed as well as the optimum proportion of high-temperature material for a given thermoelectric heat exchanger. TEG output power has been estimated for a typical commercial vehicle at 90°C coolant temperature.     

Modeling of a Thermoelectric Generator for Thermal Energy Regeneration in Automobiles

In the field of passenger transportation a reduction of the consumption of fossil fuels has to be achieved by any measures. Advanced designs of internal combustion engine have the potential to reduce CO₂ emissions, but still suffer from low efficiencies in the range from 33% to 44%. Recuperation of waste heat can be achieved with thermoelectric generators (TEGs) that convert heat directly into electric energy, thus offering a less complicated setup as compared with thermodynamic cycle processes. During a specific driving cycle of a car, the heat currents and temperature levels of the exhaust gas are dynamic quantities. To optimize a thermoelectric recuperation system fully, various parameters have to be tested, for example, the electric and thermal conductivities of the TEG and consequently the heat absorbed and rejected from the system, the generated electrical power, and the system efficiency. A Simulink model consisting of a package for dynamic calculation of energy management in a vehicle, coupled with a model of the thermoelectric generator system placed on the exhaust system, determines the drive-cycle-dependent efficiency of the heat recovery system, thus calculating the efficiency gain of the vehicle. The simulation also shows the temperature drop at the heat exchanger along the direction of the exhaust flow and hence the variation of the voltage drop of consecutively arranged TEG modules. The connection between the temperature distribution and the optimal electrical circuitry of the TEG modules constituting the entire thermoelectric recuperation system can then be examined. The simulation results are compared with data obtained from laboratory experiments. We discuss error bars and the accuracy of the simulation results for practical thermoelectric systems embedded in cars.     

System Modeling and Validation of a Thermoelectric Fluidic Power Source: Proton Exchange Membrane Fuel Cell and Thermoelectric Generator (PEMFC-TEG)

To facilitate the co-design and co-optimization of fluid or combustion systems and thermoelectric devices, a three-dimensional (3D) thermoelectric generator (TEG) model has been proposed and implemented in a computational fluid dynamics (CFD) simulation environment. The model includes all temperature-dependent characteristics of the materials and nonlinear fluid–thermal– electric multiphysics coupled effects. In this paper, the device-level model is first extended to the module level by taking a general geometry, identifying regions such as positive and negative thermoelements, and assigning properties to them. The system-level model is then demonstrated by coupling the module-level model with a fluidic–thermal system model in a single CFD simulator to predict the generation performance based on the thermal equilibrium that is achieved. The linked models are validated experimentally at the system level using data from three real thermoelectric modules installed on the surface of an exhaust pipe-like rig, where the temperature profile as well as the electricity generated can be measured and compared with the simulation results. The rig is intended not only to verify the proposed system model but also to mimic a practical exhaust recovery apparatus for a proton exchange membrane fuel cell (PEMFC). Based on the data obtained from the system-level test rig, a novel low-temperature low-cost application for auxiliary electric power appliances based on the waste heat of the PEMFC can be envisaged. Within the common simulator, it is shown that the thermoelectric model can be connected to various continuum-domain CFD models of the fuel cell itself, thus enabling further possibilities to optimize system efficiency and performance.     

Estimation of Thermoelectric Generator Performance by Finite Element Modeling

Prediction of thermoelectric performance parameters by numerical methods is an inherent part of thermoelectric generator (TEG) development and allows for time- and cost-saving assessment of material combinations and variations of crucial design parameters (e.g., shape, pellet length, and thermal coupling). Considering the complexity of a TEG system and its numerous affecting factors, the clarity and the flexibility of a mathematical treatment comes to the fore. Comfortable tools are provided by commercial finite element modeling (FEM) software offering powerful geometry interfaces, mesh generators, solvers, and postprocessing options. We describe the level of development and the simulation results of a three dimensional (3D) TEG FEM. Using ANSYS 11.0, we implemented and simulated a TEG module geometry under various conditions. Comparative analytical one dimensional (1D) results and a direct comparison with inhouse-developed TEG simulation software show the consistency of results. Several pellet aspect ratios and contact property configurations (thermal/electrical interface resistance) were evaluated for their impact on the TEG performance as well as parasitic effects such as convection, radiation, and conductive heat bypass. The scenarios considered revealed the highest efficiency decay for convectionally loaded setups (up to 4.8%pts), followed by the impacts of contact resistances (up to 4.8%pts), by radiation (up to 0.56%pts), and by thermal conduction of a solid filling material within the voids of the module construction (up to 0.14%pts).     

Modeling a Thermoelectric HVAC System for Automobiles

In automobiles thermal energy is used at various energy scales. With regard to reduction of CO₂ emissions, efficient generation of hot and cold temperatures and wise use of waste heat are of paramount importance for car manufacturers worldwide. Thermoelectrics could be a vital component in automobiles of the future. To evaluate the applicability of thermoelectric modules in automobiles, a Modelica model of a thermoelectric liquid–gas heat exchanger was developed for transient simulations. The model uses component models from the object-oriented Modelica library TIL. It was validated based on experimental data of a prototype heat exchanger and used to simulate transient and steady-state behavior. The use of the model within the energy management of an automobile is successfully shown for the air-conditioning system of a car.     

Modeling the Building Blocks of a 10% Efficient Segmented Thermoelectric Power Generator

This paper describes the development of a modeling tool used for design and analysis of the building blocks of thermoelectric generators (TEGs). The described model captures the performance of a thermoelectric couple at varying loads and temperatures. The model includes the effects of interfacial resistances and other thermal losses. Validation experiments have been conducted, and the results are discussed. Once validated, the model was then used to design a 10% efficient segmented TEG, which was then built and tested. With this effective design tool along with improving thermoelectric material performance, a 14% efficient TEG is within reach.     

Thin Thermoelectric Generator System for Body Energy Harvesting

Wearable thermoelectric generators (TEGs) harvest thermal energy generated by the body to generate useful electricity. The performance of these systems is limited by (1) the small working temperature differential between the body and ambient, (2) the desire to use natural air convection cooling on the cold side of the generator, and (3) the requirement for thin, lightweight systems that are comfortable for long-term use. Our work has focused on the design of the heat transfer system as part of the overall thermoelectric (TE) system. In particular, the small heat transfer coefficient for natural air convection results in a module thermal impedance that is smaller than that of the heat sink. In this heat-sink-limited regime, the thermal resistance of the generator should be optimized to match that of the heat sink to achieve the best performance. In addition, we have designed flat (1?mm thickness) copper heat spreaders to realize performance surpassing splayed pin heat sinks. Two-dimensional (2-D) heat spreading exploits the large surface area available in a wristband and allows patterned copper to efficiently cool the TE. A direct current (DC)/DC converter is integrated on the wristband. The system generates up to 28.5???W/cm² before the converter and 8.6???W/cm² after the converter, with 30% efficiency. It generates output of 4.15?V with overall thickness under 5?mm.     

Design of a Concentration Solar Thermoelectric Generator

Thermoelectric technology can be another direct way to convert solar radiation into electricity, using the Seebeck effect. Herein, a prototype concentration solar thermoelectric generator (CTG) and a discrete numerical model for the evaluation of the whole system are presented. The model takes into account the temperature dependence of the thermoelectric material properties by dividing the thermoelectric leg into finite elements and is proved to be more accurate for calculation of the conversion efficiency of the thermoelectric modules when large temperature gradients occur in the CTG system. Based on the best available properties of various bulk thermoelectric materials reported in the literature, the best possible performance of the CTG system is predicted, and the CTG system design, including the selection of the concentration ratio and the cooling method for different thermoelectric materials, are discussed in detail.     

温差发电器的设计

温差发电器是一种利用大自然中广泛存在的温差进行发电的装置。温差发电器主要由半导体温差发电模块和控制器两部分组成,半导体温差发电模块将热能转化为电能,并通过充电电路将电能储存在蓄电池中;控制器主要完成限流、欠压保护功能。同时,还设计了升压电路,从而使温差发电器输出较高的电压。     

Thermoelectric Generator for a Stationary Diesel Plant

This paper describes the development and testing of a thermoelectric generator (TEG) using the exhaust heat of a 50-kW stationary diesel power plant. The generator consists of six units that represent primary generators for each diesel engine cylinder. Each primary generator comprises five sections with gas heat exchangers, thermoelectric modules, and liquid heat exchangers. The sections were optimized for the exhaust gas operating temperatures. The generator electric power was 2.1 kW at rated power of 2.2 kW, corresponding to 4.4% of the diesel plant electric power.     

Power-Generation Performance and Durability of a Skutterudite Thermoelectric Generator

By using a p-type (La, Ba, Ga, Ti)₁(Fe, Co)₄Sb₁₂ skutterudite with a dimensionless figure of merit, ZT, = 0.75 at 500°C and an n-type (Yb, Ca, Al, Ga, In)_0.7(Co, Fe)₄Sb₁₂ skutterudite with ZT = 1.0 at 500°C, we fabricated a thermoelectric power-generation module capable of working at high temperatures (up to 600°C). When its hot and cold sides were at 600°C and 30°C, respectively, the power output of a 50 mm × 50 mm × 7.6 mm skutterudite module was 34 W and its thermoelectric conversion efficiency was 8%. In a durability test with the module’s hot and cold sides continuously maintained at 600°C and 80°C, respectively, for 8000 h, power generation first decreased by approximately 6% in the initial 300 h then remained constant.     

An Introduction to System-Level,Steady-State and Transient Modeling and Optimization of High-Power-Density Thermoelectric Generator Devices Made of Segmented Thermoelectric Elements

High-power-density, segmented, thermoelectric (TE) elements have been intimately integrated into heat exchangers, eliminating many of the loss mechanisms of conventional TE assemblies, including the ceramic electrical isolation layer. Numerical models comprising simultaneously solved, nonlinear, energy balance equations have been created to simulate these novel architectures. Both steady-state and transient models have been created in a MATLAB/Simulink environment. The models predict data from experiments in various configurations and applications over a broad range of temperature, flow, and current conditions for power produced, efficiency, and a variety of other important outputs. Using the validated models, devices and systems are optimized using advanced multiparameter optimization techniques. Devices optimized for particular steady-state operating conditions can then be dynamically simulated in a transient operating model. The transient model can simulate a variety of operating conditions including automotive and truck drive cycles.     

A Seamless Mode Transfer Maximum Power Point Tracking Controller For Thermoelectric Generator Applications

A boost-cascaded-with-buck converter-based power conditioning system employing a seamless mode transfer maximum power point tracking controller is proposed to maximize energy production of a thermoelectric generator while balancing a vehicle battery, alternator output power, and vehicle load. When a vehicle battery is fully charged, the proposed controller switches to a power matching mode seamlessly by a dual loop control system, which detects the input and output voltages and currents of the boost-cascaded-with-buck converter, and adjusts the commands accordingly. Both voltage and current loops are designed in a frequency domain using small signal models to ensure stable operation. A mode selection and voltage and current commands are determined by a digital signal processor-based controller. The experimental results with a dynamic source and load steps are presented to show the effectiveness of the proposed approach.      

Analysis of Thermoelectric Generator Performance by Use of Simulations and Experiments

A method that enables accurate determination of contact resistances in thermoelectric generators and which gives detailed insight into how these reduce module performance is presented in this paper. To understand the importance taking thermal and electrical contact resistances into account in analysis of thermoelectric generators, full-scale modules were studied. Contact resistances were determined by means of non-linear regression analysis on the basis of results from 3D finite element simulations and experiments in a setup in which heat flow, voltage, and current were measured. Statistical evaluation showed that the model and the identified contact resistances enabled excellent prediction of performance over the entire range of operating conditions. It was shown that if contact resistances were not included in the analysis the simulations significantly over-predicted both heat flow and electric power output, and it was concluded that contact resistance should always be included in module simulations. The method presented in this paper gives detailed insight into how thermoelectric modules perform in general, and also enables prediction of potential improvement in module performance by reduction of contact resistances.     

柴油发电机组建模及其带脉冲负载系统运行分析

脉冲负载逐渐成为电力负载的发展趋势,与传统负载不同,这类持续加卸载的突变型负载对于柴油发电机组等容量和惯性较小的冲击较大,易造成系统运行不稳定。分析柴油发电机组带雷达脉冲负载的系统结构,结合脉冲负载的工作特点对柴油发电机组结构进行细化考虑,建立柴油发电机组的数学模型。并在Matlab/ Simulink中搭建系统仿真模型,分析了脉冲负载工作时系统的运行情况,研究了系统的运行与脉冲负载功率PL、输出占空比D、和开关周期TS的关系。搭建了柴油发电机组带脉冲负载系统的试验平台,通过试验验证了所建模型能够较真实地反映系统的运行行为。