Thermoelectric Generation Applications Research Articles

Application of compact thermoelectric generator to hybrid electric vehicle engine operating under real vehicle operating conditions

A compact thermoelectric generator is developed for waste-heat recovery in a sedan-type hybrid electric vehicle. The shape and dimensions of the thermoelectric generator are precisely determined by performing a series of theoretical analyses to meet spatial and maximum allowable pressure drop restrictions. The waste-heat recovery performance of the thermoelectric generator is experimentally evaluated using a hybrid electric vehicle engine under the nine most commonly experienced driving conditions. One surface of the thermoelectric modules is heated by the exhaust gas flow, whereas the other surface is cooled by the engine coolant flowing at 10 L/min and 353 K. A maximum power output of ~118 W and an energy conversion efficiency of ~2.1% are obtained using 12 thermoelectric modules under the engine operating conditions that led to the highest exhaust gas flow rate and temperature. The waste-heat recovery characteristics of the present thermoelectric generator are systematically analyzed, and the results corresponding to thermal energy flow and heat recovery efficiency, as well as the voltage output–current output and power output–load resistance curves, are presented.

Experimental and Numerical Study on the Effect of Interfacial Heat Transfer on Performance of Thermoelectric Generators

The application of thermoelectric generator (TEG) systems in waste heat recovery has attracted more and more attention. In this work, the effect of interfacial heat transfer on the performance of TEG module was experimentally and numerically investigated. Three kinds of thermal greases with thermal conductivities of 2.0, 2.5, and 3.0 W/(m∙K) were used as thermal interface materials (TIMs) to improve interfacial heat transfer at different external pressures ranging from 0.1 to 0.4 MPa. The open-circuit voltage, output power, and thermal interfacial resistance were measured at different experimental conditions. It was found that the performance of the TEG module can be greatly improved by using thermal greases as TIMs. The open-circuit voltages increased from 1.73 to either 3.07, 3.4, or 3.57 V with k = 2.0, 2.5, and 3.0 W/(m∙K) thermal greases respectively used as TIMs when the temperature difference was 60 °C and external pressure was 0.1 MPa. However, the performance of the TEG was slightly affected by external pressure when thermal greases used as TIMs. The open-circuit voltages were 3.07, 3.13, 3.17, and 3.20 V at external pressures of 0.1, 0.2, 0.3, and 0.4 MPa when the temperature difference ΔT = 60 °C and k = 2.0 W/(m∙K) thermal greases were used as TIMs.

A short review on recent trends and applications of thermoelectric generators

The basic needs of the society were food, water and energy. The nexus between food, water and energy is unavoidable. Energy is the key element for the survival of all the living beings on the Earth. Energy crisis and environment deterioration are the two most faced glitches of the current scenario. Thermo electricity is one of the promising solutions for energy crisis that is experiencing in this 21st century. This particular article gives the brief description about the principle of thermoelectric devices and their necessity, classification and the applications of thermoelectric generators (TEG’s). Also, this paper gives a short description on materials, design and optimization of TEG’s. It concludes with the future research direction in the realm of thermo electricity generation.

Effect of the use of a thermoelectric generator on the pumping work of a diesel engine

Approximately a third part of the energy intake of a light-duty diesel engine is wasted through the exhaust system. Rising awareness of environmental issues together with fuel economy has encouraged research upon energy recovery in internal combustion engines. This article focuses on the application of thermoelectric generators in light-duty diesel vehicles. Most studies available in the literature tend to focus on maximizing the recovered electrical power, not always considering the increase in engine pumping work or testing conditions similar to those of a vehicle. The goal of this article is to evaluate the consequences of the modification of the cross-sectional area in the exhaust pipe that adding a thermoelectric generator implies and to compare them with the electrical power produced by the thermoelectric generator. The effect on the indicated and pumping parameters of the engine under common urban driving conditions is presented. From the results, it can be drawn that within the limits of engine speed and torque tested, the modification of the cross-sectional area does not have a significant negative effect on the engine pumping efficiency. This means that there is potential for the employment of this technique in energy recovery from light-duty vehicles.

Effect of reduction on the optical properties of Sr0.61Ba0.39Nb2O6 single crystals grown by optical floating zone technique

The effect of thermal reduction during growth of strontium barium niobate Sr0.61Ba0.39Nb2O6 (SBN61) crystal on its optical and electrical properties has been investigated. Single crystals of SBN61 were grown by the Optical Floating Zone technique in air ambience. Growth challenges such as formation of core and crystal cracking were eradicated by optimizing the synthesis and growth process parameters. The evidence of reduction was observed in the grown crystals that resulted in a characteristic gray colour. Further, the crystal became colourless on annealing in oxygen ambiance at ∼1200 °C for 20 h. The as-grown crystal is therefore identified as reduced SBN crystals due to formation of oxygen vacancies and the accompanied colour centers and charge compensated defects e.g. Nb4+ polaron in the as-grown crystals. X-ray powder diffraction analysis confirmed the formation of the desired phase and no structural change in the reduced crystal. Also, the absorption spectra revealed a broad absorption band centred around 500 nm in the as-grown reduced crystals confirming the thermal reduction of the crystal. Reduced crystals depicted a slight decrease in the optical band gap energy due to defect induced band tailing. An increase in the pyroelectric coefficient (p3) was observed for reduced SBN61 crystal in comparison to the crystal annealed in oxygen. The impedance measurement revealed higher electrical conductivity with smaller activation energy for the reduced crystal in comparison to the annealed SBN61 crystal. It shows that the thermal reduction induced defects influence the electrical conduction processes, causing the materials to be more conducting, which is desirable for a relaxor ferroelectric materials to be used as a thermoelectric generator application.

Numerical analysis on the segmented annular thermoelectric generator for waste heat recovery

In this paper, the thermoelectric performance and mechanical reliability of a segmented annular thermoelectric generator under steady state and transient conditions are investigated. The influence of structural parameter on the performance of segmented annular thermoelectric generators is discussed, the optimized design with high thermoelectric performance and reliability is obtained. These results present that with the increase of the structural parameter, the output power of segmented annular thermoelectric generators increases first and then decreases, and the max von Mises stresses in the hot-segment and cold-segment will always achieve an optimal value when the temperature in the hot end is larger than 300 °C. In addition, compared with the single-Skutterudite annular thermoelectric device, the output power of segmented annular thermoelectric generators can improve 18.3%, the max von Mises stress in the hot-segment is decreased by 12.5%. Finally, the thermoelectric performance and reliability of segmented annular thermoelectric generators operating in a sinusoidal heat source are investigated. The results show that the smaller the period and amplitude of the heat source, the better the overall performance of the segmented annular thermoelectric generator. These obtained results may provide some useful guidance for the application of segmented annular thermoelectric generators in the waste heat recovery.

High-performance terrestrial solar thermoelectric generators without optical concentration for residential and commercial rooftops

Solar thermoelectric generator (STEG) systems are attractive because they can convert solar heat directly into electricity via solid-state thermoelectric generators. Nevertheless, its low energy conversion efficiency has prevented it from wide-scale implementation and commercialization. To date, the best experimental efficiency for STEG without concentrated is 4.6%, and only testing single thermoelectric unicouple within a specific application deployment context. In this paper, a mathematical model containing various heat losses ignored by previous studies are developed and validated to confirm the possibility of improved STEG performance. We developed a high-performance solar thermoelectric hybrid device composed of heat pipe evacuated tubular collector, solar selective absorber, and TE modules by conducting a comprehensive optimization in terms of thermoelectric material, the optical and thermal efficiency of solar selective absorber, heat management and device integration. The experimental results show that the thermoelectric conversion efficiency of proposed device was enhanced significantly, it produced a peak electrical efficiency of 5.2%. And the residual solar energy is stored for either power generation or domestic used. The peak exergy efficiency of the system reached up to 7.17%. The efficiency is higher than the previously reported best value. We experimentally demonstrated the feasible of the scale application of solar thermoelectric generators. And the results indicated that STEG system is a promising alternative solar energy thermal utilization technology in the small scale co-generation applications.

Thermal Conductivity of Thermal Interface Materials Evaluated By a Transient Plane Source Method

The thermal conductivity of thermal interface materials (TIMs) has been studied using a transient plane source (TPS) method. In thermoelectric generators designed for vehicle waste heat recovery, high thermal conductivity materials are needed for the cold-side interface between a polyamide flexible circuit and an aluminum plate heat exchanger. The conventional heat flow method described by ASTM D5470 is often used to determine thermal contact resistance of an interface with a thin layer of interface material. The apparent thermal conductivity values provided by materials manufacturers are used to calculate heat transfer through the interface. However, estimated parameters based on the thermal conductivity of a TIM often do not agree with the actual heat transfer through the interface. Thermal conductivity of a series of 10 commercial TIMs were evaluated by applying a small quantity to an embedded TPS sensor. The 2-mm radius sensor was able to operate under standard bulk material measurement mode and produced consistent thermal conductivity measurements of the interface materials. The TPS method is shown to be effective in ranking the available interface materials by thermal conductivity and to ensure that the material with consistent performance can be selected for the thermoelectric generator applications.

Effect of real working environment/formation of oxide phase on thermoelectric properties of flexible Sb2Te3 films

Abstract Flexible Sb2Te3 thin films, for thermoelectric generator applications, were deposited by DC magnetron sputtering. As-deposited films were annealed in air to simulated a realistic operating environment. The oxidation behavior of the films was studied by monitoring their phase change on exposure to air at different temperatures between 50 and 300 °C for annealing times from 1 to 15 h. Oxidation of Sb and Te formed Sb2Te4 and TeO2 phases when annealing above 100 °C and Sb2Te3 decomposed into oxide phases at an annealing temperature of 250 °C for 15 h. The thermoelectric performance decreased as the content of Sb2O4 and TeO2 phases increased. These findings show the limitations of Sb2Te3 films operating in air without vacuum or a protective environment. We propose that the kinetic growth of oxide formation on the Sb2Te3 thin films depend on chemical activation energy and oxygen diffusion through the oxide barrier by the variation of annealing temperature and annealing time, respectively.

Impedance spectroscopy characterization of neutron irradiated thermoelectric modules for space nuclear power

The European Space Agency is currently supporting the research and development of advanced radioisotope power systems utilising thermoelectric modules. The performance of thermoelectric modules following exposure to neutron radiation is of significant interest due to the likely application of radioisotope thermoelectric generators in deep space exploration or planetary landers requiring prolonged periods of operation. This study utilises impedance spectroscopy to characterise the effects of neutron irradiation on the performance of complete thermoelectric modules, as opposed to standalone material. For a 50 We americium-241 radioisotope thermoelectric generator design, it is estimated that the TE modules could be exposed to a total integrated flux of approximately 5 × 1013 neutrons cm-2 (>1 MeV). In this study, an equivalent neutron dose was simulated experimentally via an acute 2-hour exposure in a research pool reactor. Bi2Te3-based thermoelectric modules with different leg aspect ratios and microstructures were investigated. Gamma-ray spectroscopy was initially used to identify activated radionuclides and hence quantify irradiation induced transmutation doping. To evaluate the thermoelectric properties pre- and post-irradiation, impedance spectroscopy characterization was employed. Isochronal thermal annealing of defects imparted by the irradiation process, revealed that polycrystalline based modules required significantly higher temperature than those with a monolithic microstructure. Whilst this may indicate a greater susceptibility to neutron irradiation, all tested modules demonstrated sufficient radiation hardness for use within an americium-241 radioisotope thermoelectric generator. Furthermore, the work reported demonstrates that impedance spectroscopy is a highly capably diagnostic tool for characterising the in-service degradation of complete thermoelectric devices.

The Design of a Thermoelectric Generator and Its Medical Applications

Growing energy demands are driving people to generate power in every possible way. New energy sources are needed to plug the energy gap. There is a growing interest in distributed energy generation due to its remarkable advantages such as flexibility, reliability, adaptability and minimal transmission losses. Thermoelectric generators (TEGs) are one such distributed power source that relies on thermal energy for electricity generation. The current review focusses on the design and optimization of TEGs to maximize the power output from the available thermal sources. The basic principle of thermoelectricity generation and suitable architecture for specific applications are explained with an overview of materials and manufacturing processes. Various cooling techniques to dissipate heat from the cold side and their influence on overall efficiency are reviewed in this work. Applications of TEGs for powering biomedical sensors have been discussed in detail. Recent advancements in TEGs for various implantable devices and their power requirements are evaluated. The exploitation of TEGs to generate power for wearable sensors has been presented, along with published experimental data. It is envisioned that this study will provide profound knowledge on TEG design for specific applications, which will be helpful for future endeavours.

Techno-economic analysis of thermoelectrics for waste heat recovery

ABSTRACTThis article analyses the technical and economic aspects relating to the application of thermoelectric generators in waste heat recovery. It is explained why material cost reductions are unlikely to result in significant reductions in overall device cost. The difficulties associated with manufacturing modules that can withstand high temperatures are shown to result in high cost to power ratios, despite the favorable thermodynamic conditions. This study also compares the performance of thermoelectric generators to Rankine and Stirling cycles and finds that Rankine cycles are able to achieve superior thermal efficiencies at power outputs above 100 kW. Between the ranges of 10 and 100 kW, the thermal efficiency of thermoelectric generators are comparable to that of Rankine cycles. Below 10 kW, thermoelectric generators have greater efficiency than Rankine cycles, but lower efficiency than Stirling cycles. Future expansion of their use in large-scale waste heat recovery will require commercialization of materials with significantly higher thermal efficiency than presently available.

Structural, optoelectronic and thermoelectric properties of antiperovskite compounds Ae3PbS (Ae = Ca, Sr and Ba): A first principles study

In the last years, alkaline-earth based antiperovskite compounds with small semiconductor band gap have been proven to be promising candidate for optoelectronic and thermoelectric applications. In this work, the structural, electronic, optical and thermoelectric properties of Ae3PbS (Ae = Ca, Sr and Ba) compounds have been predicted using first principles calculations based on the full-potential linearized augmented plane-wave (FP-LAPW) method and semiclassical Boltzmann transport theory. Exchange-correlation effect is treated with the generalized gradient approximation with Perdew–Burke–Ernzerhof scheme (GGA-PBE) and Tran–Blaha modified Becke–Johnson exchange potential. The lattice constant of considered materials increases as Ae goes in order from Ca to Ba and the hardness slightly decreases in this order. Ca3PbS and Sr3PbS are semiconductor with direct band gap of 0.199 eV and 0.116 eV, respectively, while Ba3PbS is nearly metallic. Important optical responses of studied antiperovskites are found in the visible and ultraviolet energy range. Finally, the thermoelectric properties including Seebeck coefficient, electrical conductivity, thermal conductivity, power factor and figure of merit are calculated. Obtained results show that Ca3PbS and Sr3PbS could be candidate for applications in thermoelectric generators at low and moderate temperatures due to their high figure of merit values.

Detailed Transient Multiphysics Model for Fast and Accurate Design, Simulation and Optimization of a Thermoelectric Generator (TEG) or Thermal Energy Harvesting Device

Described herein is a detailed and comprehensive multiphysics model of a thermoelectric generator (TEG). The one-dimensional model uses electrical–thermal analogies solved for transient response using SPICE. There are many advantages and applications of thermoelectric generators. Wider use and application advancements are generally limited by the tools available for engineering and scientific studies. Currently, available modeling tools are limited by some combination of speed, platform capabilities, or missing physics that are not used or assumed to be negligible. The TEG module model herein is made up of two sub-models, the thermoelement model and the non-thermoelement model. Rather than a lumped thermoelement model, the model herein makes use of distributed physics that include the following: Thomson effect, temperature dependence, mass, Joule heat, thermal resistance, Seebeck effect, and electrical resistance. The non-thermoelement model takes into account temperature dependence and simulates Joule heat generation, thermal resistances, thermal and electrical interface resistances, and mass for and between the ceramic, copper, and solder. The comprehensive model herein was correlated to experimental data that simultaneously varied electrical current and hot and cold side temperatures with time. Very minimal adjustments to reported thermoelectric properties were required to almost perfectly match the experimental transient power output. The effects of the non-thermoelement model, distributed Thomson effect model and distributed temperature dependent property model were quantified. The model ran very quickly, taking 2.5 real-time seconds to run a 4000 s transient simulation.

Effect of electrolyte on the growth of thermoelectric Bi2Se3 thin films

Bismuth Selenide (Bi2Se3) is a thermoelectrical material showing high Seebeck coefficient and figure of merit. It can be obtained by electrodeposition which makes it highly suitable for application in sensor and thermoelectric generators. Here, electrodeposition of Bi2Se3 on silicon(100) substrate was studied using different deposition baths by changing the salts and acid concentrations. The thin films were characterized to obtain the morphology, structural and thermoelectric properties. An optimal bath was found that leads to crystalline thin films with compact and uniform morphology, showing high values of Seebeck coefficient. The total salt concentration directly changes the structural properties of the samples, while the relative salt concentration essentially modifies the stoichiometry of deposits. The acid concentration, otherwise, promotes changes in the grain size and morphology.

Protective Properties of Electrochemically Deposited Al-Based Coatings on Yb0.3Co4Sb12 Skutterudite

To protect CoSb3-based skutterudite thermoelectric materials from oxidation and to suppress the sublimation of antimony in long-time service, a series of surface coatings including Al, Al-Ni, Al-Ni-Al were deposited onto Yb0.3Co4Sb12 by using an electrochemical deposition method. The thermal aging behavior for the Yb0.3Co4Sb12 samples with and without different surface coatings were investigated by accelerated thermal aging tests at 873 K. Thermoelectric properties of Yb0.3Co4Sb12 with different coatings after aging are used as the evaluation criteria for coating effectiveness. After thermal aging at 873 K for 30 days, the thermoelectric properties of Yb0.3Co4Sb12 coated with Al-Ni double-layered coating were almost undecreased, indicating that the Al-Ni coating is suitable for protecting CoSb3-based skutterudite from oxidation and for suppressing the sublimation of antimony. It is expected that this coating could improve the reliability of CoSb3-based devices and could accelerate the application of skutterudite thermoelectric generators.

Facile synthesis of nanostructured n-type SiGe alloys with enhanced thermoelectric performance using rapid solidification employing melt spinning followed by spark plasma sintering

SiGe alloy is widely used thermoelectric materials for high temperature thermoelectric generator applications. However, its high thermoelectric performance has been thus far realized only in alloys synthesized employing mechanical alloying techniques, which are time-consuming and employ several materials processing steps. In the current study, for the first time, we report an enhanced thermoelectric figure-of-merit (ZT) ∼ 1.1 at 900 °C in n-type Si80Ge20 nano-alloys, synthesized using a facile and up-scalable methodology consisting of rapid solidification at high optimized cooling rate ∼ 3.4 × 107 K/s, employing melt spinning followed by spark plasma sintering of the resulting nano-crystalline melt-spun ribbons. This enhancement in ZT > 20% over its bulk counterpart, owes its origin to the nano-crystalline microstructure formed at high cooling rates, which results in crystallite size ∼7 nm leading to high density of grain boundaries, which scatter heat-carrying phonons. This abundant scattering resulted in a very low thermal conductivity ∼2.1 Wm−1K−1, which corresponds to ∼50% reduction over its bulk counterpart and is amongst the lowest reported thus far in n-type SiGe alloys. The synthesized samples were characterized using X-ray diffraction, scanning electron microscopy and transmission electron microscopy, based on which the enhancement in their thermoelectric performance has been discussed.

Methodological reviews and analyses on the emerging research trends and progresses of thermoelectric generators

Thermoelectric generator is among the earliest initiated electricity-harvesting methods. It is a very potential power harvester that can convert wasteful thermal energy into electricity. However, it often suffers from low energy conversion rate due to its inconsistent heat source, inefficient thermoelectric material (or thermoelement) performance, and incompetent structural issues. Progressively for the first time, detailed methodological surveys and analyses are made for bulk, thick, and thin films in this review. This is in order to accommodate better insights and comprehensions on the emerging trends and progresses of thermoelectric generators from 1989 to 2017. The research interests in thermoelectric generators have started back in 1989, and have continuously experienced emerging progresses in the number of studies over the last years. The methodological reviews and analyses of thermoelectric generator showed that almost 46.6% of bulk and 46.1% of thick and thin film research works, respectively, are actively progressed in 2014 to 2017. Nearly 86.2% of bulk and 44.1% of thick and thin film thermoelectric generators are realizing in between 0.001 and 4 μW cm−2 K−2, while 43.1% of thick and thin films are earning among 10−6 to 0.001 μW cm−2 K−2. The highest achievement made until now is 2.5 W cm−2 at a temperature difference of 140 K and thermoelectric efficiency factor of 127.55 μW cm−2 K−2. This achievement remarked positive elevation for the field and interest in thermoelectric power generation. Consecutively, the research trends of fundamental devices' structure, thermoelement, fabrication, substrate, and heat source characteristics are analyzed too, along with the desired improvement highlights for the applications of thermoelectric generators.

Impact of Thermal Interface Materials for Thermoelectric Generator Systems

A primary challenge still exists in the field of thermoelectric generators (TEG) for practical applications in which a thermal system of the TEG is a crucial factor in TEG power generation. The material development for TEG has contributed significantly towards advancement in TEG applications over a decade, the need for a thermal system configuration is inevitable considering the applications. The thermal efficiency of TEG depends upon the temperature difference across its modules (between the hot and cold surfaces). Thermal design of the thermoelectric system is important to ensure that there exists a maximum temperature difference across the hot and cold surfaces of the TEG. Thermal Interface Material (TIM) in thermoelectric systems plays a main role in improving the efficiency of thermoelectric systems by reducing the temperature difference between the heat source and the hot surface of the TEG and similarly, the temperature difference between the cold surface of TEG and the heat sink. This review paper predominantly focuses on the thermal interfaces between the TEG modules which reduces the performance of a thermoelectric system. The characteristics of TIM in a TEG system (contact pressure, surface roughness and thermal conductivity) were analyzed with a mathematical model to emphasize the importance of TIM in a TEG system. This paper also highlights the existing challenges for Thermal Interface Materials in TEG applications and concludes with a brief discussion on future directions of TIM in TEG thermal systems.

Enhanced Thermoelectric Performance in n-Type Bi2Te3-Based Alloys via Suppressing Intrinsic Excitation.

Currently, the application of thermoelectric power generators based on Bi2Te3-based alloys for the recovery of low-quality waste heat is still limited because of the aggravated intrinsic excitation of the material at elevated temperatures. In this study, excessive Te and dopant I are introduced to the n-type Bi2Te2.4Se0.6 material with the purpose of suppressing its intrinsic excitation and improving the thermoelectric performance at elevated temperatures. These Te and I atoms act as electron donors to effectively reduce the density of minority carriers (holes) and weaken their negative contribution to the Seebeck coefficient. Likewise, the initial band structure and the carrier scattering mechanism are scarcely altered. Similar to the p-type Bi2Te3-based alloys, we found the "conductivity-limiting" mechanism is also well obeyed in the present n-type Bi2Te2.4Se0.6-based materials. The reduced minority carrier partial electrical conductivity in these Te-excessive and I-doped Bi2Te2.4Se0.6 samples significantly decreases the bipolar thermal conductivity, leading to lowered total thermal conductivity at elevated temperatures. Finally, the peak zT is successfully shifted up to higher temperatures for these Te-excessive and I-doped Bi2Te2.4Se0.6 samples. A maximum zT of 1.0 at 400 K and an average zT of 0.8 at 300-600 K have been realized in Te-excessive Bi2Te2.41Se0.6.