TE Legs Research Articles

Flexible polyester-embedded thermoelectric device with Bi2Te3 and Te legs for wearable power generation

This study presents an approach for powering wearable sensors by integrating nanostructured bismuth telluride (Bi2Te3 and Te legs) into flexible polyester substrates. The choice of polyester as the substrate is because it is widely used in clothing, especially in items such as shirts, blouses, dresses, and sportswear. This enables seamless integration with wearable devices. By capturing wasted body heat, our small and flexible thermoelectric generators (TEGs) offer long-term operation without the need to plug the batteries. We demonstrate the feasibility of using commercially available polyester for reproducible electrochemical deposition of highly oriented Bi2Te3 and Te material. Through electrodeposition, we embed Bi2Te3 and Te legs within the flexible polyester, creating a cost-effective and easily scalable hybrid system for wearable energy harvesting.Our optimized TEG design, which can be worn on the arm or forehead, achieves impressive power density compared to existing state-of-the-art solutions. With a mere 3.5 °C temperature difference, only two pairs of p- and n-type legs, and a thickness of approximately 15 µm, our TEG generates a maximum open circuit voltage of ∼0.1 mV and a maximum power density of ∼0.04 mW·K-1·cm−2. With 250 pairs, 10 mV can be reached. This cost-effective design also integrates electrical contacts, surpassing previous flexible TEG performances. These advancements make our TEGs suitable for driving microwatt-level electronic sensors and open new avenues for efficient energy harvesting in wearable applications.

Design of metamaterial thermoelectric generators for efficient energy harvesting

Thermoelectric generators (TEGs) are widely recognized as clean energy solutions that can convert low-grade waste heat into electricity through a temperature gradient. Despite their significant potential, challenges such as low conversion efficiency and high costs have limited their practical applications. In this paper, we present an innovative metamaterial design concept for TEGs with significantly improved efficiency. A Finite Element Model is validated using Bi0.5Sb1.5Te3 bulk samples fabricated via the drop-cast method. This model can predict open-circuit voltage and output power as a function of an arbitrary metamaterial design using the commercial software ANSYS®. Four different metastructure designs, including 2D Triangular Honeycomb, Re-entrant, body-centered cubic (BCC), and triply periodic minimal surface (TPMS) structures, are systematically investigated. Through experiments and numerical analysis, the effects of annealing temperature, porosity, and unit cell numbers (UCNs) on the performance of TE legs are explored. It is found that 2D Triangular Honeycomb and BCC structures outperform other configurations due to their capacity to maintain a higher thermal gradient. Optimizing their porosity and UCNs can further enhance the output power. Compared to the traditional designs with bulk TE legs, implementing a 2D metastructure design with 30 % porosity and UCNs of 4 × 4 × 4 can lead to approximately a 100 % increase in power output.

Influence of Leg Geometry on the Performance of Bi2Te3 Thermoelectric Generators

This study utilized COMSOL Multiphysics to simulate the performance of a thermoelectric module (TEM) made by alumina (Al2O3), copper (Cu), and bismuth telluride (Bi2Te3) materials, specifically exploring different leg geometries. The TEM design had Al2O3 for insulation, Cu for conducting, and Bi2Te3 for TE legs between the Cu layers. Investigated the influence of square and rectangular TE legs with heights of 2.0 mm, 2.75 mm, and 3.5 mm on critical parameters, including temperature gradient, electric potential, normalized current density, and total internal energy within the TEM. Furthermore, the impact of varying thicknesses in the insulator and conductor layers of the TEM was explored. The results consistently demonstrated that the square leg geometry, particularly when configured with a height of 2.75 mm, outperformed other leg geometries. Consequently, it is recommend the adoption of square-shaped Bi2Te3 TEM, measuring 1 mm × 1 mm × 2.75 mm, with a 0.50 mm Al2O3 thickness and 0.125 mm Cu thickness during the manufacturing process. Study how factors like the Seebeck coefficient (S), thermal conductivity (k), and electrical conductivity (σ) affect temperature differences in the leg design of TE devices. At lower temperatures, modeling reveals lower electrical conductivity and enhanced thermal conductivity, highlighting the significance of S = ± 2.37×10⁻⁴ V/K. This illustrates the high potential of TEM for applications in thermoelectric generator (TEG) manufacturing.

Parametric study and design optimization of a thermoelectric generator system for waste heat recovery

This article proposes a transient simulation based on Comsol software to investigate the behavior of a segmented thermoelectric device (S-TEG) exposed to a pulsed heat flux. It is found that thermoelectric generators (TEG) incorporating segmented materials have offered greater thermal and electrical performance. An increase in the electrical output power and efficiency of 60% and 40% were reached respectively. Furthermore, the effect of segmentation is most noticeable for short TE leg lengths and large cross-sectional areas. For the S-TEG with a leg length of 2 mm, there is a 104% increase in output power compared to the TEG with a leg length of 3 mm. The effect of asymmetric TE legs on the improvement of the performance of the segmented TEG was carried out. It was found that when a pulsed heat source is applied, the performance of S-TEGs are maximum when the N-leg area is lower than the P-leg area (AN/AP <1). Therefore, to attain the highest TEG performance, an asymmetric shape of AN < AP is required.

Effect of Thermoelectric Legs on Electrical Performance of Single Leg Teg using Multiphyiscs Simulation

This paper was produced to examine the impact of the number of legs on TEGs while also demonstrating how to model and simulate a single-leg thermoelectric generator (TEG) using the COMSOL Multiphysics software platform. Using thermoelectric materials like SrTiO3 and Ca2FeMoO6, a simulation study of the performance of TEG was created. Therefore, by altering the hot side temperature from TH = 300K, 400K, and 500K and varying the load resistance from 0Ω to 20Ω, the influence of various performance metrics, such as output voltage and output power, has been demonstrated and investigated. It has been shown that the thermoelectric legs' material characteristics have a significant impact on how hot or cold the TE module is. Finally, it was discovered that single-leg TEG performs worse than TEG using a single thermocouple. By performing additional studies on the modeling of different numbers of TE legs, the performance of the TEG may therefore be further improved to help society deal with the energy issue.

Programmable and Surface-Conformable Origami Design for Thermoelectric Devices.

Thermoelectric devices (TEDs) show great potential for waste heat energy recycling and sensing. However, existing TEDs cannot be self-adapted to the complex quadratic surface, leading to significant heat loss and restricting their working scenario. Here, surface-conformable origami-TEDs (o-TEGs) are developed through programmable crease-designed origami substrates and the screen-printing TE legs. Compared with "π" structured TEDs, the origami design (with heat conductive materials) changed the heat-transferring direction of the laminated TE legs, resulting in an enhancement in enlarging ΔT/THot and Vout by 5.02 and 3.51 times. Four o-TEDs with different creases designs are fabricated to verify the heat recycling ability on plane and central quadratic surfaces. Demonstrating a high Vout density (up to 0.98-2 at ΔT of 50K) and good surface conformability, o-TEDs are further used in thermal touch panels attached to multiple surfaces, allowing information to be wirelessly transferred on a remote display via finger-writing.

Novel Thermoelectric Fabric Structure with Switched Thermal Gradient Direction toward Wearable In-Plane Thermoelectric Generators.

Wearable thermoelectric generators (TEGs) have exhibited great potential to convert the temperature gradient between the human body and the environment into electrical energy for maintenance-free wearable applications. A 2D planar device structure is widely employed for fabricating flexible TEGs due to its simple structure and facile fabrication properties. However, this device configuration is more appropriate for utilizing in-plane temperature differences than the out-of-plane direction, which limits their application in wearable cases since the temperature difference between the human body and the environment is in the out-of-plane direction. To solve this problem, a novel fabric-based TEG structure that can utilize the out-of-plane temperature gradient is proposed in this work. By introducing thermally conductive components in the generator, the out-of-plane temperature difference can be switched to the in-plane direction, which can be further utilized for 2D planar devices in wearable applications. The prepared thermoelectric fabric prototype with only 12 p-type TE legs exhibits a maximum open-circuit voltage of 4.69mV and an output power of 39.7 nW at a temperature difference of 30 K. This strategy exhibits a high degree of versatility and can be readily applied to other 2D planar TEGs, thus expanding their potential application in wearable technology.

Derivation of generalized thermoelectric energy equations and the study of thermoelectric irreversible processes based on energy, exergy, and entransy analysis

AbstractThermoelectric (TE) generation is becoming a valuable and promising research direction. Many researchers have carried out system analysis and performance optimization of thermoelectric technologies based on the generalized thermoelectric energy balance equations. However, it is assumed that TE legs have no heat exchange with the ambient except at the junctions of the hot and cold ends where heat flows in and out. Based on basic thermoelectric effects and fundamental theories of heat transfer, a detailed derivation of the revised generalized thermoelectric energy equations considering convective heat transfer between TE legs and the ambient has been carried out. Irreversible heat transfer processes have been analyzed by employing energy analysis based on the first law of thermodynamics and exergy analysis based on the second law of thermodynamics. The results show that convective heat transfer leads to a decrease in both energy and exergy efficiencies: the rate and magnitude of the decrease in exergy efficiency are greater than those of the decrease in energy efficiency. The exergy efficiency is relatively high despite the low energy efficiency in operation, revealing the features and advantages of thermoelectric generators (TEGs) in low‐grade energy utilization. For TEG efficient operation, the load resistance value should match the system's internal resistance, or at least be greater than that, to avoid a sharp drop in power output and efficiencies. In an attempt at theoretical analysis, the concept of entransy was first introduced into thermoelectric analysis, yielding two concise relational equations which reflect the intrinsic link between Carnot cycle efficiency, energy efficiency, exergy efficiency, and entransy flow transfer efficiency. The entransy analysis based on the index of entransy flow transfer efficiency, together with energy analysis and exergy analysis, may be a novel and valuable guideline for the operation and optimization of TEGs, which needs to be further investigated.

A perspective on stretchable ionic thermoelectric supercapacitors for wearable applications: Present and challenges

The conversion of sustainable heat sources from the human body into electricity is a promising strategy for self-powered temperature monitoring and power supplies in wearable electronics. Recently, ionic thermoelectrics (i-TEs) have gained considerable attention because of their Seebeck coefficients (mV K−1), which are orders of magnitude larger than those of conventional electronic TEs (e-TEs). In particular, i-TE supercapacitors (ITESCs) based on thermodiffusion under a temperature gradient in redox-free electrolytes exhibit Seebeck coefficients larger than 10 mV K−1. This characteristic solves the requirement for numerous pairs of p/n type TE legs to achieve sufficient output voltage, thereby substantially minimizing device complexity. Therefore, the development of stretchable and wearable ITESCs capable of harvesting human-generated thermal energy is beneficial for future wearable platforms. From this perspective, recent studies have been summarized on stretchable i-TE electrolytes, which hold considerable potential for use in wearable ITESCs and sensors. Furthermore, the challenges of recent ITESCs have been presented, and the perspectives for the development of fully stretchable ITESCs have been provided for future wearable applications.

Performance enhancement of segmented annular thermoelectric generator based on multi-parameter and multi-objective optimization

The excellent performance of annular thermoelectric generator (ATEG) is crucial for its commercial application, and it has been validated that the segment configuration can effectively enhance the ATEG performance. Nevertheless, owing to the limitations in conventional optimization methods which fail to simultaneously consider the co-influence of multiple parameters, further exploration is required for achieving optimal design of segmented annular thermoelectric generator (SATEG). In this study, we present a novel approach combining multi-objective genetic algorithm (MOGA) with finite element method to implement the multi-parameter and multi-objective optimization of SATEG. This approach not only reduces the computational cost but also ensures precise control on SATEG temperature below its maximum acceptable operation temperature. Furthermore, the optimization results highlight the importance of emphasizing diversity between p- and n- type TE legs as well as recognizing the different optimal geometrical structures for two types of TE legs, which have been always overlooked in previous researches. By adopting the optimal geometrical structure at a hot end temperature of 600 K, significant improvements in output power of 32.839 % and efficiency of 61.915 % are achieved for SATEG.

A hybrid ceramic-based flexible thermoelectric nanogenerator with enhanced thermopower for human energy harvesting

The growing demand for power sources to run portable devices has led to the development of wearable energy-harvesting technology. The integration of wearable thermoelectric generators (WTEGs) into fabrics that can incessantly convert body heat into electricity has been researched extensively. Yet, commercial fabric-based wearable thermoelectric generators have not become conscious. In this study, a fabric-based flexible wearable thermoelectric device was designed using Cobalt doped ZnO nanorods via hydrothermal method as the n-type and Bi2Te3 nanostructures via dip coating method as the p-type and strips of each were connected to form TE legs. The structural and morphological analyses confirmed the formation of Co: ZnO and Bi2Te3 on the fabrics. The electrical conductivity and average Seebeck coefficient of Co:ZnO coated cellulose fabric were 4.80 S cm−1 and 390.5 µV/K. The device was fabricated and showed a device output voltage oscillating from ∼0.3 mV to ∼0.7 mV with a different human body temperature varying from 308 K to 309.4 K. The experimental data showed the output generated from the flexible device to be more suitable for energy harvesting from the human body and can be used in Biomedical sensing applications.

Flexible, Self‐powered Thermoelectric Module for Body‐heat Recovery

AbstractConversion of heat into electrical energy using a thermoelectric generator (TEG) will be beneficial for self‐powered wearable electronic systems. However, the output power of previously reported flexible TE generator (f‐TEG) is too low to meet the requirements of wearable electronic devices. Herein, we report an f‐TEG integrated with inorganic TE materials and exhibiting high output power. The proposed TE device has 60 pairs of p‐type Bi0.5Sb1.5Te3 and n‐type Bi2Te2.7Se0.3 TE legs, and has an extremely low internal resistance (1.09 Ω). This f‐TEG possesses good flexibility (with a bending radius of ∼1 cm) and high output‐power density (up to 4.49 mW/cm2 with a temperature difference of 30 K). To convenience use, a step‐up boost voltage converter is integrated with the TEG to convert the low voltage into a high voltage for micro‐device to work, it provides a new candidate scheme for self‐powered wearable electronic devices. Experiments showed that a LED can be lit up by the f‐TEG with a boost circuit. There results demonstrate that the proposed f‐TEG provides ultrahigh output power density and integrated self‐powered devices, can be used to powering low‐power electronics and sensors through heat harvesting.

Interfacial thermal stresses of segmented thermoelectric generators

The segmented structure can effectively improve the performance of a thermoelectric generator (TEG), but the interfacial thermal stress between adjacent segments seriously threatens the reliability of segmented TEGs. Noticing this, we investigate the mechanical performance of a segmented TEG via theoretical and numerical methods. Results show that the structural stress depends on the ratio of cross-sectional areas between p- and n-type TE legs rather than the absolute cross-sectional areas, while the height ratio of different segments has a significant influence on structural stress. Different from structural stress, the thermal stress induced by unmatched thermal expansion between different segments increases rapidly with the increase of cross-sectional area, and can easily exceed 20% of the total interfacial stress. Besides, both the conversion efficiency and interfacial stress can be optimized by adjusting the ratio of cross-sectional areas. Our results provide the theoretical basis and guidance in the design of segmented TEGs.

Enhanced thermoelectric properties of n-type CoSb3-based composites by incorporating In particles

Thermoelectric devices that consist of N-and P-type TE legs in series have been well known and applied owing to the ability that could convert waste heat into electric energy. Among them, skutterudite materials have been frequently studied as the main object because they are environmentally friendly and inexpensive. In this study, N-type CoSb3-based materials were synthesized using a low-temperature synthesis method and spark plasma sintering. Those thermoelectric matrix that incorporated Indium (In) particles were prepared via manual grinding method. The thermoelectric properties, microstructures, and morphologies of the pure and In-doped Co0.91Ni0.09Sb3 samples were systematically evaluated. A maximum power factor value of 3642.3 μW/mK2 was obtained at 723 K for a Co0.91Ni0.09Sb3/1 wt%In sample and the highest figure of merit value of 1.01 was attained for a Co0.91Ni0.09Sb3/2 wt%In sample. These results indicate that Indium particles as secondary phase can improve the thermoelectric performance of N-type CoSb3-based materials.

Periodic energy transmission and regulation of photovoltaic-phase change material-thermoelectric coupled system under space conditions

Phase change material (PCM) as highly efficient temperature control material has been used in photovoltaic-thermoelectric (PV-TE) coupling system to achieve higher power generation efficiency. The periodic energy balance and PCM regeneration are the key factors that affect the temperature control effect and system total performance. In present paper, a numerical model for space PV-PCM-TE system was established with the composite of paraffin and aluminum foam as PCM. Firstly, the impact of periodic energy imbalance on PCM regeneration characteristics and system overall performance was investigated under space conditions. Then, to regulate the periodic energy transmission of the coupling system, a global structural parameters optimization was performed, and the optimal parameter combination was derived and validated, where porosity of aluminum foam, thickness of PCM layer, thermal concentration factor, length of TE legs, and surface area ratio are 0.94, 4.08 mm, 25.83, 1.09 mm and 1.80, respectively. The validation results show that after optimization, the periodic energy balance and PCM full utilization and regeneration can be achieved. The average total efficiency of optimal case is 30.72%, which is a little lower than that with the surface area ratio of 7.0 (31.77%), but the average power density is 49.64% higher. The present work validates that periodic energy balance design is important for space PV-PCM-TE system and the global parameter optimization method is an effective optimization method, which is significant for the design and optimization of PCM based temperature control system.

A study of interfacial electrical contact resistances of thermoelectric generators for hypersonic vehicles by experimental measurements and two-scale numerical simulations

An enormous amount of aerodynamic heat is produced on the surface of hypersonic vehicles, and the thermoelectric generator (TEG) technique holds the potential to convert aerodynamic heat into electric energy. In a TEG, the micrometer-scale roughness on TE legs and electrodes surfaces leads to the constriction of interfacial electric current and brings about electrical contact resistance (ECR). The heat transfer and conversion processes of a TEG are greatly influenced by such type of ECR. In this work, a TEG includes two ceramic substrates and a middle TE layer is established, and the TE layer consists of insulation material, N- and P-type TE legs and electrodes to connect the TE legs. The ECR and its effects on the TEG performance are studied by two-scale numerical simulations and experimental measurements. First, the practical topography of rough surfaces for TE legs and electrodes is measured, and the micrometer-scale ECR prediction numerical models are established based on the reconstructed topography. An ECR measurement platform is developed and the platform consists of a pressure device, power supply and data acquisition system which are used to provide loading pressures, voltage, and acquisition of electric current and voltage signals, respectively. The ECRs under different temperatures, loading pressures and gap mediums are then predicted and the numerical models are validated by a series of measurements. Second, the TE conversion process of TEG is simulated by a millimeter-scale model including insulation materials, TE legs, electrodes, and equivalent interfacial layers of ECR. The influence of ECR on the TE performance of TEG for the hypersonic vehicle is thus clarified.

Optimal array alignment to deliver high performance in flexible conducting polymer‐based thermoelectric devices

• High charge mobility and optimal oxidation level leads to high power factor;. • Identification of the optimal distance between two adjacent TE arrays for devices;. • A flexible thermoelectric device shows a power density of 1.21 µW∙cm −2 . Flexible thermoelectric devices (F-TEDs) show great potentials to be applied in curved surface for power generation by harvesting low-grade energy from human body and other heat sources. However, their power generation efficiency is constrained by both unsatisfactory constituent materials performance and immature device design. Here, we used an optimal alignment of vertically-aligned poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) arrays to assemble a 2.7 × 3.2 cm 2 F-TEDs, exhibiting a maximum power output of 10.5 µW. Such a high performance can be ascribed to the outstanding power factor of 198 µW m −1 K −2 by the synergetic effect of both high charge mobility and optimal oxidation level and the optimized array alignment that maximizes the temperature difference utilization ratio across the TE legs. Particularly, optimized leg distance of 6 mm and leg length of 12 mm are determined to realize a high temperature difference utilization ratio of over 95% and a record-high output power density of 1.21 µW cm −2 under a temperature difference of 30 K. Further, reliable bending (1000 cycles) and stability (240 h) tests indicate the outstanding mechanical robustness and environmental stability of the developed F-TEDs. This study indicates our reasonable device design concept and facile material treatment techniques secure high-performance F-TEDs, serving as a reference for other flexible energy harvesting devices with wide practical applications.

Optimization design by evolutionary computation for minimizing thermal stress of a thermoelectric generator with varied numbers of square pin fins

Thermal stress plays an important role in the lifetime of thermoelectric generators, and its minimization can prolong the usage of the generators. To figure out and efficiently lower the thermal stress, this study analyzes the thermoelectric performance and thermal stress of a thermoelectric module in a waste heat recovery system. The performance of the TEM with varied numbers of square pin fins in a flow channel is examined by computational fluid dynamics. The results indicate that for different numbers of square pin fins, the heat transfer rate of the module’s hot side increases as the number of fins increases. When the number of fins increases from 36 to 84, the heat transfer rate improves by 8.57%. In addition, the temperature distribution in the module in a waste heat recovery system is uneven due to differences in heat transfer. Therefore, the thermal stress of the module is uneven, and the maximum thermal stress occurs in the TE legs, which are located at the corners of the module. To reduce the maximum thermal stress, the thicknesses of the ceramic plate and the thermoelectric legs are optimized using the multi-objective genetic algorithm. The optimization results indicate that the maximum thermal stress of the module is proportional to its output power, meaning that as the maximum thermal stress in the module is minimized, its output power will approach the minimum value. Instead, the same method is employed to minimize the maximum thermal stress on the module while maintaining its output power. As a result, the maximum thermal stress is reduced by approximately 11.78%, and thermal stress is reduced under a ceramic plate thickness smaller than 0.8 mm and a TE leg thickness greater than 2 mm.

Design of cascade thermoelectric generation systems with improved thermal reliability

This paper presents a comprehensive analysis of novel, unileg cascade thermoelectric systems. Unileg systems offer the flexibility of selecting a single (p- or n-) thermoelectric material in a thermoelectric system compared to two (n- and p-) materials. Finite element analysis simulations were performed to design and analyze two and three stages of cascade systems. Simulation results show that unileg cascade systems perform significantly (∼75%) better than their unicouple counterparts in both two and three stage configurations due to the elimination of the poorly performing thermoelectric leg. In addition to the enhanced thermoelectric power generation, thermal stress is lowered in unileg systems since the mismatch of the thermal expansion coefficient originating between different TE legs material can be minimized. Overall, the presented unileg systems show their promise for the future thermoelectric energy generation or cooling applications for electronics.

Experimental and Theoretical Investigation of the Effect of Filler Material on the Performance of Flexible and Rigid Thermoelectric Generators.

Thermoelectric generators have found many applications where the heat source can be either flat or curved. For a curved heat source, flexible thermoelectric generators are generally used. A filler material with low thermal conductivity can provide additional mechanical support to the thermoelectric module and can reduce convection and radiation losses. Herein, the effect of three different filler materials on the output performance of rigid and flexible thermoelectric generators is investigated. At first, theoretical models are derived and the experimental study validated the models. The experimental study revealed that the flexible thermoelectric modules outperformed the rigid modules; this is due to the reduction of the number of thermal junctions in the flexible modules and due to the differences in the thermal conductivities of the flexible and rigid substrates. Likewise, among TE modules without filler/with air between the TE legs, with polyurethane foam filler material, and with polydimethylsiloxane filler material, air has the lowest thermal conductivity, and therefore, the thermoelectric generator without filler generates higher output power and higher power density than when the other two filler materials are used. For the fixed temperature gradient, the highest power densities for the flexible and rigid thermoelectric generators without filler are 155 and 137.7 μW/cm2 for temperature gradients of 10.8 and 10.3 °C, respectively.