Conventional Thermoelectric Generators Research Articles

Numerical Study on Optimizing the Geometry of Segmented Asymmetrical Thermoelectric Generator

Quite large amount of heat generated in various industrial processes was wasted. Recovering the waste heat can save cost and benefit the environment protection. The device that convert heat energy to electricity is called thermoelectric generator (TEG), and therefore it can be used for waste heat recovery. Improving the efficiency is the main direction of present study. The configuration and geometry of the thermoelectric legs are proved can influence the thermoelectric performance of the thermoelectric generator. Compared with the conventional TEG which is assembled with symmetrical (rectangular) legs, asymmetrical thermoelectric generator (ATEG) has a greater temperature gradient in a leg due to the convergent geometry which can reduce overall thermal conduction of the device and Thomson effect is also harnessed. In this study, three-dimensional finite element analysis (COMSOL) is employed to investigate the numerical simulations of a segmented pyramidal thermoelectric generator (SPTEG) and a segmented cone thermoelectric generator (SCTEG) to optimize the leg length ratio of two materials, and it’s effect on the electrical and mechanical performances of SPTEG and SCTEG was also studied. Results obtained shows that the height ratio of SATEG can influence electrical and mechanical performances and the optimum height ratio provided a better electrical performance while thermal stress developed in leg was less. In addition, the open-circuit voltage of two types SATEG is similar because they have the same cross sectional area and the same volume, however, SCTEG has a dispersive thermal stress distribution while the thermal stress of SPTEG concentrates in four corners. Compared to the maximum von Mises stress in SPTEG, the maximum von Mises stress in SCTEG reduced about 10%. Results obtained from this study would provide references in producing and design of segmented asymmetrical thermoelectric generators.

Comprehensive Study and Realizing an Enhanced Efficiency of the Thermoelectric Generator Along with Its Thermomechanical Properties

This paper proposes a real-time simulation model to simplify the research and outcome of a portable thermoelectric generator (TEG) system in real conditions. Consequently, the model is divided into three parts: conventional, segmented, and hybrid TEG systems. The conventional TEG system consisted of Bi2Te3 as the p-type and the n-type materials, whereas the segmented and the hybrid TEG systems consisted of a different combination of materials, including PbTe and Sb2Te3. The optimization of the TEG system length was carried out to achieve the highest power output, which was found to be 2 mm. In addition, thermomechanical stress distribution analysis of the module was conducted to determine the maximum load the TEG system could withstand before undergoing fracture, depending upon the yield strength of the material. The stress was analyzed in all three TEG systems, and the results were evaluated. Results were observed from the optimized length at 2 mm. The conventional, segmented, and hybrid TEG systems showed maximum power output of 147.122 mW, 171.934 mW, and 550 mW, respectively, with a temperature difference at 50 K.

Geometry design for maximizing output power of segmented skutterudite thermoelectric generator by evolutionary computation

This study focuses on the design of a segmented thermoelectric generator system to maximize the system output power. Skutterudite, (Sr, Ba, Yb)yCo4Sb12 with 9.1% In0.4Co4Sb12, is used as the n-type element, while DD0.59Fe2.7Co1.3Sb11.8Sn0.2 is used as the p-type one. They both are employed as the hot side segments. Alternatively, hydrothermal synthesized nanostructure thermoelectric material (Bi0.4Sb1.6Te3) is chosen as the cold side segments. To achieve the optimum design, a numerical method is developed, while the multi-objective genetic algorithm is adopted. The evolutionary computation processes during seeking the optimum combination of the segments are visualized, and it is found that four generations are enough for reaching the target. With the leg length of 3 mm, the optimum n-type and p-type cold side segment lengths are 0.5 mm and 0.78 mm, respectively. Compared to the equal-segmented thermoelectric couple, the optimized couple at a temperature difference of 400 K can increase the output power by 21.94% and its efficiency is 14.05% which is much higher than conventional thermoelectric generators. The theory of impedance matching does not apply to the segmented thermoelectric generator. The heat flux distribution in the couple is dependent on the temperature difference. Overall, the segmented elements with evolutionary computation design is a promising tool for intensifying thermoelectric generator performance.

Simulation and analysis of flexible TEG using polymer based and pyroelectric material for microdevice energy harvesting

Recently, an interest of thermoelectric generator (TEG) to manipulate and change heat waste into electrical energy has increased. The heat from electrical appliances, sun, human body, and natural environments can convert into electrical energy using TEG. However, typical conventional TEGs in the market have a hard and solid construction structure, hence difficult to bend according to curved surfaces of the heat sources. To overcome this problem, polymer-based material is proposing as the new packaging and substrate structure for the TEG. Besides, the thermoelectric conductor layer also changed using different types of pyroelectric for better heat absorption performance with low cost in mass-scale fabrication. Therefore, the simulation of eight pairs segmented conductive layer insulated with thin-film polymer due to standard modelling equation is present. The comparison of simulation with reference TEG to get the optimum output of temperature difference were also explaining. At the end of the simulation, polyimide as a packaging substrate with a conductive layer of Graphene (P-type legs) and Bismuth Telluride (N-type legs) has chosen for the best performance material for the flexible thermoelectric generator. The highest temperature difference produced by this design is 542˚C for 0.945V input voltage and 120˚C input temperature at the hot side.

Pulse mode of operation – A new booster of TEG, improving power up to X2.7 – to better fit IoT requirements

Internet of Things (IoT) is becoming the new driver for semiconductor industry and the largest electronic market ever seen. The number of IoT nodes is already many times larger than the human population and is continuously growing. It is thus mandatory that IoT nodes become self-supplying with energy harvested from environment since periodic exchange of batteries in such a huge number of units (often located in inaccessible places e.g. industrial environment or elements of constructions) is impractical and soon will be simply impossible. Photovoltaic generators may easily harvest energy where light is available, but the IoT nodes often work in dark, hidden locations where the only available energy sources are heat losses. There, ThermoElectric Generators (TEGs) could be the best candidate, if not that if we speak of exploiting heat losses it often means very low temperature differences. This means conditions where TEGs power production drops down dramatically. In this paper we put forward a new idea of TEG's pulse operation that boosts the power production up to X2.7. This extends the domain of applicability of TEGs to lower temperature differences, where conventional TEGs are out of the game. Next, we show that the improvement X2.7 maintains also at larger temperature differences that presents obvious advantages.

Large-area implementation and critical evaluation of the material and fabrication aspects of a thin-film thermoelectric generator based on aluminum-doped zinc oxide

A large-area thermoelectric generator (TEG) utilizing a folded thin-film concept is implemented and the performance evaluated for near room temperature applications having modest temperature gradients (<50 K). The TEGs with the area of ∼0.33 m2 are shown capable of powering a wireless sensor node of multiple sensors suitable e.g. for monitoring environmental variables in buildings. The TEGs are based on a transparent, non-toxic and abundant thermoelectric material, i.e. aluminium-doped zinc oxide (AZO), deposited on flexible substrates. After folding, both the electrical current and heat flux are in the plane of the thermoelectric thin-film. Heat leakage in the folded TEG is shown to be minimal (close to that of air), enabling sufficient temperature gradients without efficient heat sinks, contrary to the conventional TEGs having the thermal flux and electrical current perpendicular to the plane of the thermoelectric films. The long-term stability studies reveal that there are no significant changes in the electrical or thermoelectric properties of AZO over several months, while the contact resistance between AZO and silver ink is an issue exhibiting a continuous increase over time. The performance of the TEGs and technological implications in relation to a state-of-the-art thermoelectric material are further assessed via a computational study.

Textile‐Based Thermoelectric Generators and Their Applications

With the rapid development of Internet of Things and miniaturized electronics, the demand for wearable power sources with high reliability and long duty cycle promotes the exploration of wearable thermoelectric generators (TEGs). In particular, textile‐based TEGs that can perpetually convert the ubiquitous temperature gradient between human body and ambience into electrical energy have attracted intensive attention to date. These lightweight and three‐dimensional deformable TEGs comprised of fibers, filaments, yarns, or fabrics offer unique merits as wearable power source in comparison with conventional TEGs. In this review, we systematically summarize the state‐of‐the‐art strategies for textile‐based TEGs, including the structure design, fabrication, device performance, and application. Existing critical issues and future research emphasis are also discussed.

Thermoelectric properties enhancement of p-type composite films using wood-based binder and mechanical pressing

Thermoelectric generators (TEGs) fabricated using additive manufacturing methods are attractive because they offer the advantages of scalability, lower cost, and potentially higher power density than conventional TEGs. Additive manufacturing of TEGs requires active thermoelectric particles to be dispersed in a polymer binder to synthesize printable slurries, and printed films to be subsequently subjected to a long and high temperature curing to enhance their thermoelectic properties. A large amount of polymer binder present in composite films results in a sizable loss in the electrical conductivity. In addition, a long and high-temperature film curing results is a slow and energy intensive fabrication process. In this work, we demonstrate the feasibility of using a small amount (≤10−3 wt ratio) of novel nanofiber cellulose (NFC) as a binder to provide sufficient adhesion strength to hold the TE particles together in the composite films. We also demonstrate a pressure induced densification process to enhance the thermoelectic properties of printed composite films. This novel approach has the potential to fundamentally transform the manufacting method for printing TEGs by eliminating the need of long-duration and high-temperature curing. A higher applied pressure leads to a compact packing and densification of films resulting in an improvement in the electrical conductivity. The highest power factor achieved for best performing p-type thermoelectric-NFC composite film subjected to pressure induced densification is 611 μW/m-K2.

Harvesting Low-Grade Heat via Thermal-Induced Electric Double Layer Redistribution of Nanoporous Graphene Films.

In this work, a closed thermoelectric cell based on a nanoporous graphene electrode is developed to convert low-grade thermal energy to electric energy. The thermoelectric cell consists of two nanoporous graphene electrodes in contact with the hot and cold ends, respectively, encapsulated in a KCl electrolyte, and the energy is harvested from the redistribution of the electric double layer (EDL) of the graphene electrodes under different temperatures. Because of the large specific surface and conductivity of nanoporous graphene electrodes, the electric voltage is 168.91 mV with the hot-end temperature of 61 °C and cold-end temperature of 26 °C, corresponding to the thermoelectric coefficient of 4.54 mV·°C-1, which is much larger than that of the conventional thermoelectric generator. The specific power output achieves 1.38 mW·g-1 and is also significantly larger than the previous EDL-based thermoelectric generator. System performance with the concentration of the KCl electrolyte is examined. The proposed thermoelectric cell can harvest low-grade waste heat from the ambient environment, which may have potential applications in energy supply, wireless powered devices, outdoor survival, and so forth.

Flexible heatsink based on a phase-change material for a wearable thermoelectric generator

Thermoelectric generators (TEGs) represent a promising technology for self-powered wearable systems. Since the conventional TEGs have limitation to be used on the human body due to its structural rigidity, flexible TEGs have been studied and developed so that TEGs can be attached to an arbitrarily shaped surface on the human body. However, flexible TEGs require a good heatsink with good flexibility to allow them to produce enough power for wearable devices. In this study, a high-performance flexible heatsink based on a phase-change material (PCM) was proposed. PCM blocks were arranged in an array and good flexibility was realized with an elastomer that filled the space between the PCM blocks. Given that PCM can absorb a large amount of heat at the phase-change temperature, the heatsink can hold the temperature difference across the TEG constant for a relatively long period of time. Thus, the generated power from the flexible TEG was maintained at around 20 μW/cm2 for 33 min. The flexible heatsink can be reused because the PCM solidifies at room temperature. Furthermore, the PCM-based flexible heatsink is smaller and lighter than the conventional metal heatsink. The proposed heatsink is expected to contribute to the commercialization of self-powered wearable devices.

Simulation study on regenerative thermoelectric generators for dynamic waste heat recovery

Abstract Regenerative thermoelectric generators (RTEGs) are used to recover waste heat from car engines. Compared to conventional thermoelectric generators (CTEGs), RTEGs can help significantly reduce the negative effects of engine transients on the performance of thermoelectric generators. In this study, a new type of RTEG, based on the CTEG, was designed. Numerical simulations of both the CTEG and the RTEG were performed using Fluent under dynamic temperature conditions based on the New European Driving Cycle (NEDC). The results show that the fluctuations in the hot-side temperature and output voltage decreased by 86.46-87.71% and 86.45-89.16%, respectively, with the use of different types of RTEGs compared to the CTEG. Moreover, the RTEG helped avoid the inversion problem of the electromotive force direction for a short time when the temperature of the heat source suddenly decreases.

Evaluation on High-Efficiency Thermoelectric Generation Systems Based on Differential Power Processing

Thermoelectric generators (TEGs) convert thermal energy directly into electrical energy using thermoelectric materials, with attractive advantages such as a lack of noise and pollution, considerable reliability, and a long lifetime. Because of the low output power and low output voltage of each TEG module, conventional thermoelectric generation systems are constituted by a centralized converter with series-connected multiple TEG modules. Power mismatch usually occurs in this system configuration due to the unbalanced temperature difference distribution, which results in lower conversion efficiency. In this paper, two solutions based on differential power processing (DPP) have been proposed to enhance the output power and conversion efficiency of the TEG system: the centralized-distributed hybrid structure and the cascaded power transfer structure, both of which realize the maximum power point tracking of each TEG module. The circuit designs and control strategies of the two proposed systems are here presented. Experimental results have demonstrated the feasibility and effectiveness of these two solutions; they have higher output power and better efficiency than the conventional TEG system. Each of these two solutions exhibits its own features and has suitable application situations. If the temperature difference distribution of all TEG modules has significant variations, the centralized-distributed hybrid structure outperforms the cascaded power transfer structure on the output power. While the temperature difference distribution is comparatively stable, the cascaded power transfer structure is superior to the centralized-distributed hybrid structure. With detailed evaluation and comparison between the two structures, the overall design for DPP-based TEG systems with different connection types has been proposed in this paper, which is the reference for the future implementation of practical TEG applications.

Physics of ZnO/SiO2 electrolyte semi-conductive thermal electric generator

Thermoelectric generator generates electrical power from heat based on the temperature gradient. The total energy (fuel) supplied to the engine, approximately 30 to 40% is converted into useful mechanical work, whereas the remaining is expelled to the environment as heat through exhaust gases and cooling systems, resulting in serious greenhouse gas (GHG) emission. The technologies reported on waste heat recovery from exhaust gas of internal combustion engines (ICE) are thermo electric generators (TEG) with finned type, Rankine cycle (RC) and Turbocharger by the different researchers. The deficiency and acclimatization of existing TEG emphasis this study to develop a nanomaterial zinc oxide (ZnO)/Silicon di-oxide (SiO2) electrolyte based semi-conductive thermal electric generator (TEG) to generate electricity from the IC engine exhaust heat. This technology produces electricity from the exhaust heat due to the thermal motion, carrier drift and carrier diffusion. The ZnO/SiO2 simulated result based on the 60% of exhaust heat of IC engine shows that its electrical energy generation is about 80% more than conventional TEG for the exhaust temperature of 500C due to its higher thermal and electric conductivity and higher surface area both in radially and longitudinally. The ZnO/SiO2 electrolyte semi- conducive technology develops 524W to 1600W at engine speed 1000 to 5000 rpm, which could contribute to reduce the 10-12% of engine total fuel consumption and improve emission level by 20%.

Stretchable Thermoelectric Generators Metallized with Liquid Alloy.

Conventional thermoelectric generators (TEGs) are normally hard, rigid, and flat. However, most objects have curvy surfaces, which require soft and even stretchable TEGs for maximizing efficiency of thermal energy harvesting. Here, soft and stretchable TEGs using conventional rigid Bi2Te3 pellets metallized with a liquid alloy is reported. The fabrication is implemented by means of a tailored layer-by-layer fabrication process. The STEGs exhibit an output power density of 40.6 μW/cm2 at room temperature. The STEGs are operational after being mechanically stretched-and-released more than 1000 times, thanks to the compliant contact between the liquid alloy interconnects and the rigid pellets. The demonstrated interconnect scheme will provide a new route to the development of soft and stretchable energy-harvesting avenues for a variety of emerging electronic applications.

A Novel Electro Conductive Graphene/Silicon-Dioxide Thermo-Electric Generator

Thermoelectric generators are all solid-state devices that convert heat energy into electrical energy. The total energy (fuel) supplied to the engine, approximately 30 to 40% is converted into useful mechanical work; whereas the remaining is expelled to the environment as heat through exhaust gases and cooling systems, resulting in serious green house gas (GHG) emission. By converting waste energy into electrical energy is the aim of this manuscript. The technologies reported on waste heat recovery from exhaust gas of internal combustion engines (ICE) are thermo electric generators (TEG) with finned type, Rankine cycle (RC) and Turbocharger. This paper has presented an electro-conductive graphene oxide/silicon-dioxide (GO-SiO2) composite sandwiched by phosphorus (P) and boron (B) doped silicon (Si) TEG to generate electricity from the IC engine exhaust heat. Air-cooling and liquid cooling techniques adopted conventional TEG module has been tested individually for the electricity generation from IC engine exhausts heat at engine speed of 1000-3000rpm. For the engine speed of 7000 rpm, the maximum voltage was recorded as 1.12V and 4.00V for the air-cooling and liquid cooling respectively. The GO-SiO2 simulated result shows that it’s electrical energy generation is about 80% more than conventional TEG for the exhaust temperature of 500°C. The GO-SiO2 composite TEG develops 524W to 1600W at engine speed 1000 to 5000 rpm, which could contribute to reduce the 10-12% of engine total fuel consumption and improve emission level by 20%.

Wearable Thermocells Based on Gel Electrolytes for the Utilization of Body Heat.

Converting body heat into electricity is a promising strategy for supplying power to wearable electronics. To avoid the limitations of traditional solid-state thermoelectric materials, such as frangibility and complex fabrication processes, we fabricated two types of thermogalvanic gel electrolytes with positive and negative thermo-electrochemical Seebeck coefficients, respectively, which correspond to the n-type and p-type elements of a conventional thermoelectric generator. Such gel electrolytes exhibit not only moderate thermoelectric performance but also good mechanical properties. Based on these electrolytes, a flexible and wearable thermocell was designed with an output voltage approaching 1 V by utilizing body heat. This work may offer a new train of thought for the development of self-powered wearable systems by harvesting low-grade body heat.

Wearable Thermocells Based on Gel Electrolytes for the Utilization of Body Heat

AbstractConverting body heat into electricity is a promising strategy for supplying power to wearable electronics. To avoid the limitations of traditional solid‐state thermoelectric materials, such as frangibility and complex fabrication processes, we fabricated two types of thermogalvanic gel electrolytes with positive and negative thermo‐electrochemical Seebeck coefficients, respectively, which correspond to the n‐type and p‐type elements of a conventional thermoelectric generator. Such gel electrolytes exhibit not only moderate thermoelectric performance but also good mechanical properties. Based on these electrolytes, a flexible and wearable thermocell was designed with an output voltage approaching 1 V by utilizing body heat. This work may offer a new train of thought for the development of self‐powered wearable systems by harvesting low‐grade body heat.

Analysis of the Effect of Module Thickness Reduction on Thermoelectric Generator Output

Conventional thermoelectric generators (TEGs) used in applications such as exhaust heat recovery are typically limited in terms of power density due to their low efficiency. Additionally, they are generally costly due to the bulk use of rare-earth elements such as tellurium. If less material could be used for the same output, then the power density and the overall cost per kilowatt (kW) of electricity produced could drop significantly, making TEGs a more attractive solution for energy harvesting of waste heat. The present work assesses the effect of reducing the amount of thermoelectric (TE) material used (namely by reducing the module thickness) on the electrical output of conventional bismuth telluride TEGs. Commercial simulation packages (ANSYS CFX and thermal–electric) and bespoke models were used to simulate the TEGs at various degrees of detail. Effects such as variation of the thermal and electrical contact resistance and the component thickness and the effect of using an element supporting matrix (e.g., eggcrate) instead of having air conduction in void areas have been assessed. It was found that indeed it is possible to reduce the use of bulk TE material while retaining power output levels equivalent to thicker modules. However, effects such as thermal contact resistance were found to become increasingly important as the active TE material thickness was decreased.

Low-cost flexible thin film thermoelectric generator on zinc based thermoelectric materials

The high cost and complex production technique restrict the use of the conventional thermoelectric generators. In this work, we demonstrate a promising flexible thin film thermoelectric generator using the N-type Al-doped ZnO and P-type Zn-Sb based thin film. By using the cost-effective zinc based thermoelectric materials and flexible substrate, we greatly reduce the cost production of thin film thermoelectric generator. The maximum output power of our device with 10 couples is 246.3 μW when the temperature difference is 180 K. The maximum output power of the flexible thin film thermoelectric generator produced per couple and per unit temperature difference was 0.14 μW per K-couple, which is about several times that of other thin film reported. The thin film thermoelectric generator with low cost and excellent output power was fabricated on flexible substrate, which is can be made into various shapes for micro- and nano-energy application.

Thermodynamic studies and maximum power point tracking in thermoelectric generator–thermoelectric cooler combined system

Thermoelectric generator (TEG) operated thermoelectric cooler (TEC) is a highly compatible combination for low-cooling power application. The conventional TEG–TEC combined systems have low operating efficiency and low cooling power because maximum power output from the TEG is not fully utilized. This paper proposes and analyses the combined system with maximum power point tracking technique (MPPT) to maximize the cooling power and overall efficiency. This paper also presents the effect of TEG, TEC source temperature and the effect of heat transfer area in the performance of the combined system. The thermodynamic models of the combined system are developed in MATLAB simulink environment with temperature dependent material properties and analysed for variable operating temperatures. It has been found that, in the irreversible thermodynamic model of the combined system with MPPT, when the hot and cold side of TEG and TEC are kept at a temperature difference of 150K and 10K respectively, the power output of TEG increases from 20.49W to 43.92W, cooling power of TEC increases from 32.66W to 46.51W and the overall combined system efficiency increases from 2.606% to 4.375% respectively when compared with the irreversible combined system without MPPT. The characteristics improvements obtained by this practice in the combined system for the above mentioned operating conditions is also true for other range of operating temperatures. It is also been observed that the external irreversibilities decreases the cooling power and the overall system efficiency of the combined system by 36.49% and by 16.9% respectively.