The effect of temperature mismatch on thermoelectric generators electrically connected in series and parallel

The use of thermoelectric generators (TEGs) to recover useful energy from waste heat has increased rapidly in recent years with applications ranging from microwatts to kilowatts. Several thermoelectric modules can be connected in series and/or parallel (forming an array) to provide the required voltage and/or current. In most TEG systems the individual thermoelectric modules are subject to temperature mismatch due to operating conditions. Variability of the electro-thermal performance and mechanical clamping pressure of individual TEG modules are also sufficient to cause a significant mismatch. Consequently, when in operation each TEG in the array will have a different electrical operating point at which maximum energy can be extracted and problems of decreased power output arise.<p></p> This work analyses the impact of thermal imbalance on the power produced at module and system level in a TEG array. Experimental results clearly illustrate the issue and a theoretical model is presented to quantify the impact. The authors believe the experimental results presented in this paper are the first to validate a rigorous examination of the impact of mismatched operating temperatures on the power output of an array of thermoelectric generators

Feasibility of a photovoltaic-thermoelectric generator: performance analysis and simulation results

This paper describes a theoretical approach to evaluate the performance of a hybrid solar system made with photovoltaic cells and thermoelectric (TE) modules. After a brief treatment of the integrated system, energy conversion and performance parameters are evaluated through numerical simulations depending on the global radiation and temperature distribution obtained by the Joint Research Center of the European Commission and of the National Renewable Energy Laboratory. The contribution of TE module to total energy seems significant in southern European towns and less substantial when the locations considered are very distant from the equator and show the possibility of using TE devices for energy production

Contribution to the study of waste heat recovery systems on commercial truck diesel engines.

L'augmentation du prix du pétrole ainsi qu'une possible future réglementation des émissions de $CO_2$ encourage les fabriquants de véhicules industriels à trouver de nouvelles solutions pour améliorer encore la performance de la chaine cinématique. Dans ce cadre, deux solutions de récupérations d'énergie prometteuses sont très souvent rapportées dans la littérature: le système de récupération d'énergie par cycle de Rankine et le générateur thermoélectrique. Après un rappel des conditions limites du fonctionnement d'un camion long routier, cette thèse démontre tout d'abort des modèles 0-D réalisés sous le solveur de calcul Engineering Equation Solver destinés à la meilleur compréhension de ces deux technologies (notamment le choix du fluide de travail pour le système Rankine). Puis, pour ces deux systèmes, des logiciels commerciaux sont utilisés. Pour le générateur thermoélectrique, ce logiciel commercial développé sous Matlab dans le cadre d'un consortium de recherche, permet de modéliser une architecture inédite d'échangeur thermoélectrique (destinée à l'industrialisation). Des études paramétriques sont effectuées sur cette échangeur placé en amont de l'échangeur de recirculation des gaz d'échappement du moteur diesel. Ces études se basent principalement sur l'utilisation de deux matériaux prometteurs: le Mg2Si et le $MnSi$ mais d'autres matériaux thermoélectriques sont aussi considérés. Une conception du système Rankine est présentée et modélisée avec un solveur commercial 1-D très utilisé dans l'industrie automobile. Des validations partielles sont réalisées sur les composants se basant sur les données transmises par les fournisseurs mais également sur des résultats de test de composants (turbine). Ce modèle a ensuite permis d'étudier les transitoires du système pour mieux comprendre son fonctionnement. La charge en réfrigérant ainsi que le contrôle possible du système sont également abordés. A partir de ces études, il semble que le générateur thermoélectrique ne soit pas encore mature pour son utilisation dans un camion long routier. En effet, les matériaux thermoélectriques devront encore être améliorés. Le système Rankine doit quand à lui être testé sur un camion prototype pour pouvoir véritablement estimer son potentiel final.Fuel price increase as well as future fuel consumption regulations lead truck manufacturers to further enhance the current powertrain. In such a context, two waste heat recovery technologies appear as promising: the Rankine system as well as the thermoelectric generator. Both technologies are well studied within the past 30 years literature. After a reminding of truck boundary conditions, this thesis work defines a 0-D modeling done under the engineering equation solver for both systems (approaches enabling to define the working fluid for the Rankine system). Then, for both systems a commercial tool is used to further investigate the two technologies. For the thermoelectric generator this commercial tool, developed under Matlab, models a thermoelectric generator architecture (designed for mass production) developed in the frame of a research program. Parametric studies are done on the integration of a thermoelecric generator upstream the existing engine exhaust gas recirculation cooler. Main studies are done with $Mg_2Si$ and $MnSi$ as thermoelectric materials but other materials are also considered. A Rankine system design is presented and modeled under a well known commercial 1-D solver used within the automotive industry. Preliminary validations of the model based on supplier modeling data are presented as well as the modeling validation of the turbine component tested. Transient aspects are evaluated to better understand the behavior of the system and its bottlenecks. The amount of refrigerant in the circuit and the control schematic are also addressed. From these study, it appears that the thermoelectric generator technology is not yet mature for an integration into a long haul truck due too the low performance of thermoelectric materials. The Rankine system technology should handle a complete truck prototype testing to estimate its potential

Multiphysics CFD Simulation for Design and Analysis of Thermoelectric Power Generation

The multiphysics simulation methodology presented in this paper permits extension of computational fluid dynamics (CFD) simulations to account for electric power generation and its effect on the energy transport, the Seebeck voltage, the electrical currents in thermoelectric systems. The energy transport through Fourier, Peltier, Thomson and Joule mechanisms as a function of temperature and electrical current, and the electrical connection between thermoelectric modules, is modeled using subgrid CFD models which make the approach computational efficient and generic. This also provides a solution to the scale separation problem that arise in CFD analysis of thermoelectric heat exchangers and allows the thermoelectric models to be fully coupled with the energy transport in the CFD analysis. Model validation includes measurement of the relevant fluid dynamic properties (pressure and temperature distribution) and electric properties (current and voltage) for a turbulent flow inside a thermoelectric heat exchanger designed for automotive applications. Predictions of pressure and temperature drop in the system are accurate and the error in predicted current and voltage is less than 1.5% at all exhaust gas flow rates and temperatures studied which is considered very good. Simulation results confirm high computational efficiency and stable simulations with low increase in computational time compared to standard CFD heat-transfer simulations. Analysis of the results also reveals that even at the lowest heat transfer rate studied it is required to use a full two way coupling in the energy transport to accurately predict the electric power generation

Summary and recommendations on nuclear electric propulsion technology for the space exploration initiative

A project in Nuclear Electric Propulsion (NEP) technology is being established to develop the NEP technologies needed for advanced propulsion systems. A paced approach has been suggested which calls for progressive development of NEP component and subsystem level technologies. This approach will lead to major facility testing to achieve TRL-5 for megawatt NEP for SEI mission applications. This approach is designed to validate NEP power and propulsion technologies from kilowatt class to megawatt class ratings. Such a paced approach would have the benefit of achieving the development, testing, and flight of NEP systems in an evolutionary manner. This approach may also have the additional benefit of synergistic application with SEI extraterrestrial surface nuclear power applications

Optimization of Thermoelectric Materials For Marine and Power Plant Application

Thermoelectric materials are an enabling technology that has the potential to increase overall plant efficiency and reduce greenhouse gas emissions for shoreside power plants and for the marine industry. These materials do this by directly converting waste heat energy into usable electricity that could be harnessed for use on any existing electrical grid. This dissertation describes work done to understand, model, and investigate improvements to bismuth telluride and bismuth telluride antimony thermoelectric materials to better match the materials to available heat flux from industrial plants. Presented within this work are models to investigate homogenous materials, functionally graded materials, and segmented materials; as well as work developing a testing apparatus to evaluate the performance of physical materials. The testing apparatus was used to evaluate bismuth telluride P and N type couples and measure their nano to micro scale voltage and current outputs

A comparison of four modelling techniques for thermoelectric generator

The application of state-of-art thermoelectric generator (TEG) in automotive engine has potential to reduce more than 2% fuel consumption and hence the CO2 emissions. This figure is expected to be increased to 5%~10% in the near future when new thermoelectric material with higher properties is fabricated. However, in order to maximize the TEG output power, there are a few issues need to be considered in the design stage such as the number of modules, the connection of modules, the geometry of the thermoelectric module, the DC-DC converter circuit, the geometry of the heat exchanger especially the hot side heat exchanger etc. These issues can only be investigated via a proper TEG model. The authors introduced four ways of TEG modelling which in the increasing complexity order are MATLB function based model, MATLAB Simscape based Simulink model, GT-power TEG model and CFD STAR-CCM+ model. Both Simscape model and GT-Power model have intrinsic dynamic model performance. MATLAB function based model and STAR-CCM+ model can be developed to have only steady state performance or to include dynamic performance. Steady state model can be used in quick assessment of TEG performance and for initial design optimization. However, only dynamic model can give the accurate prediction of TEG output during engine transient cycles. This paper also demonstrates finding the answers to three TEG related questions using STAR-CCM+, Simscape and MATLAB function based Simulink model respectively

The viability of a thermoelectric fuel conditioning system for a diesel engine utilizing biodiesel

Certain internal combustion engines, which run on hydrocarbon fuels, experience difficulty upon engine start-up in extreme cold weather. As ambient temperature decreases below the fuel cloud point and beyond, paraffin form in the fuel and eventually clog the fuel filter causing the engine to fail to start. This problem becomes more pronounced when the engine in question is a Diesel and the fuel utilized is biodiesel. As an alternative fuel source, biodiesel has many advantages; however, its cold weather performance is worse than even conventional diesel fuel. As biodiesel becomes more integrated into the world’s energy usage scenario, one of the systems within a Diesel engine that requires further investigation is its fuel conditioning system. This thesis describes research aimed at the development of a fuel conditioning system that utilizes several emerging technologies while decreasing the amount of electrical energy required for operation. The system utilizes a eutectic - thermoelectric (E-TE) combination which consists of a eutectic compound based latent heat storage device with adjacent thermoelectric elements to transfer waste heat stored in the eutectic reservoir into the fuel filter, thus diminishing the amount of electrical energy typically required for the fuel conditioning process. Simulations of the E-TE system are conducted while operating within three different modes (start-up, heat storage, and electrical energy generation) depending on fuel and ambient temperature conditions, while a supervisory controller distinguishes between desired operational status. The research activities and findings reported contained herein include development of E-TE system models which each consist of several components. The first of which is a set of control laws, implemented in Simulink, which control system performance using various temperature related variables. The second component is a supervisory control law, implemented in Matlab®, which controls the switching between various modes of operation. With system model developed, the viability of the system is examined

Analysis of Potential and Efficiency of Electric Generation Using Thermoelectric Effect

This research identifies the electrical potential associated with Thermoelectric Generators (TEG) under the incidence of solar rays and performs efficiency comparison using this type of devices and those photovoltaic. TEG characterization and modeling is presented to favor the estimation of the electrical potential, defined as power density (W/m2). The proper operation of thermal harvesting lays in maintaining a temperature difference of at least 26.31K between the TEG sides. With this requirement fulfilled, power conversion eficiencies of about 26.43% are obtained, higher than that of high-quality solar panels and without efficiency reductions associated with heating and soiling, while keeping the same superficial area of only 16cm 2. An estimate of at least 407.3mW corresponding to 2.44Wh of available energy is found considering specific operation hours determined statistically for a given geographic location. Thus, given such performance metric, a complete power unit is devised complementing the thermoelectric energy harvesting with a Li-Po battery to guarantee in that way a continuous operation. The total energy available from the prototype allows maintaining a battery discharge percentage of 38.05% considering the energy budget of a low-power remote sensor.MaestríaMagister en Ingeniería Electrónic

Prediction and analytics of operating parameters on thermoelectric generator energy generation

PhD ThesisThe efficient use of energy at all stages along the energy supply chain and the utilization of renewable energies are very important elements of a sustainable energy supply system, specially at the conversion from thermal to electrical energy. Converting the low-grade waste heat into electrical power would be useful and effective for several primary and secondary applications. One of the viable means to convert the low-grade waste heat into electrical energy is the use of thermoelectric power conversion. The performance of thermoelectric generators, subjected to thermal effects, can vary considerably depending on the operating conditions, therefore it is necessary to measure and have a better understanding of the characteristics and performance of the thermoelectric generator. It is important to understand the thermoelectric generator’s dynamic behavior and interaction with its operating environmental parameters. Based on this knowledge, it is then significant to develop an effective mathematical model that can provide the user with the most probable outcome of the output voltage. This will contribute to its reliability and calculation to increase the overall efficiency of the system. This thesis provides the transient solution to the three-dimensional heat transfer equation with internal heat generation. It goes on to describes the transfer and generation of heat across the thermoelectric generator with dynamic exchange of heat. This solution is then included in a model in which the thermal masses and the operating environmental parameters of the thermoelectric generator are factored in. The resulting model is created in MATLAB. The comparison with experimental results from a thermoelectric generator system confirms the accuracy of the artificial neural network model. This thesis also presents two practical applications, the prediction of the input parameters with a given output voltage, and sensitivity analysis designed for the model. This is to enable users to customize the thermoelectric generator for their requirements. This allows for better usage of resources eventually