Annular Thermoelectric Generator Research Articles

Dynamic Energy Conversion Performance of Wearable Annular Thermoelectric Generators for Harvesting Human Body Heat

Dynamic Energy Conversion Performance of Wearable Annular Thermoelectric Generators for Harvesting Human Body Heat

Performance prediction and optimization of annular thermoelectric generators based on a comprehensive surrogate model

A traditional system-level thermoelectric model requires enormous computing power and time for simulation analysis, especially when multiple optimization algorithms are combined. This paper initially proposed a comprehensive surrogate mode for the accurate modeling, field analysis, and fast optimization of thermoelectric generators. The surrogate model is made up of an artificial neural network (ANN) and a conditional generative adversarial network (cGAN), which can achieve a prediction accuracy of 97 % and a structural similarity (SSIM) of 0.954. Using a twisted tape annular thermoelectric generator (TT-ATEG) as an example, the generalization capability of the comprehensive surrogate model is demonstrated by studying the change of the twisted tape geometry parameters on the output performance and field distribution of the annular thermoelectric generator. The combination of the surrogate model and NSGA-II achieves fast optimization of key parameters under different working conditions, and the computational efficiency is improved by 99.97 %. Meanwhile, the cGAN part can predict the pressure and heat flow fields within 5s to provide intuitive visual feedback. The trained surrogate model requires less computer arithmetic power compared to the traditional multi-physics field simulation software. The successful application of the comprehensive surrogate model in this work provides a new solution idea and an optimization method for system-level TEG.

A phase change material based annular thermoelectric energy harvester from ambient temperature fluctuations: Transient modeling and critical characteristics

Annular thermoelectric power generator has been increasingly considered in application of ambient energy harvesting owing to the advantages of simple structure and no pollution. To improve thermal stability and energy harvesting performance of this system, the latent heat of phase change materials to improve thermal management and the high thermal conductivity of the heat sink to enhance heat transfer with the ambient are harness to annular thermoelectric power generator. Motivated by this, a phase change material based annular thermoelectric energy harvester (PCM-ATEH) with fins is developed for ambient energy harvesting and its three-dimensional transient model is also built up through jointly with thermo-electric and phase change processes. This paper considers the influence of key parameters such as temperature fluctuation amplitude, temperature fluctuation period, height ratio of PCM and thermoelectric generator (TEG) and melting temperature on liquid fraction, temperature difference, voltage and power density. Moreover, the comparison of PCM-ATEH and PCM based thermoelectric energy harvester (PCM-TEH) with/without fins is further conducted in this study to explore thermal management and energy harvesting performance. The energy harvesting characteristics of PCM-ATEH with fins is developed concerning the combination of power generation of TEG and melting process of PCM. Based on the results, it is found that the temperature difference and power density of PCM-ATEH with fins vary periodically with the sinusoidal temperature boundary, and results show that increasing temperature fluctuation period is not always feasible. Additionally, the comparative results indicate that the peak power density and energy efficiency of PCM-ATEH with fins are increased by 0.126 W/m2 and 0.02 % compared with PCM-TEH with fins, and increased by 0.195 W/m2 and 0.041 % compared with PCM-ATEH without fins. The results of energy harvesting characteristics show that a maximum of 0.77$ per watt can be reached to power generation cost of PCM-ATEH with fins. This paper can provide theoretical guidance for thermal management and energy conversion of energy harvesting system.

Taguchi optimization and thermoelectrical analysis of a pin fin annular thermoelectric generator for automotive waste heat recovery

Enhancing thermoelectric performance while minimizing exhaust back pressure is a crucial step in advancing the commercial viability of automotive thermoelectric generators. To achieve high overall performance in a thermoelectric generator, an annular thermoelectric generator equipped with circular pin fins is proposed. A comprehensive three-dimensional numerical model is established to accurately predict thermoelectric performance and thermomechanical behavior. Detailed multi-physics field distribution characteristics are analyzed. Using an L25 orthogonal array, we examine five influencing factors and their five levels: exhaust temperature, exhaust mass flow rate, fin height, fin diameter, and the number of fins. The Taguchi analysis suggests that exhaust temperature is the most influential factor in determining thermoelectric performance, followed by mass flow rate, fin height, fin diameter, and fin number. The optimal values for these parameters are 673 K, 30 g/s, 20 mm, 3 mm, and 420, respectively. Under the optimal design parameters, the net power reaches 34.11 W, representing an 18.7% increase compared to the original design. Moreover, a comparative study is conducted between plate fins and pin fins, showing that the pin fin-based thermoelectric generator exhibits a 5.83% increase in output power and a 4.82% increase in maximum thermal stress compared to the plate fin-based thermoelectric generator.

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.

Efficient and geometry-matching two-stage annular thermoelectric generator for tubular solid oxide fuel cell waste heat recovery

Tubular solid oxide fuel cell (TSOFC) converts a great part of chemical energy within fuel into high-grade waste heat, leading to a decrease in overall fuel efficiency. In this paper, a steady-state hybrid system model based on TSOFC and two-stage annular thermoelectric generator (TATEG) is proposed. Considering various kinds of irreversible effects, mathematical model for the hybrid system is explicitly formulated and verified to guarantee the accuracy. Energetic and exergetic performance indexes of the hybrid system and subsystems are obtained, and the corresponding performance characteristics are revealed. Calculation results display that the power density, energetic and exergetic efficiencies of TSOFC-TATEG hybrid system can be 15.29 %, 11.25 % and 11.25 % higher than that of stand-alone TSOFC, respectively. The power density, energetic efficiency and exergetic efficiency of TSOFC-TATEG hybrid system are all increased by 5.65 % compared to that of TSOFC-ATEG hybrid system. Furthermore, this study reveals that enhancing the performance of the hybrid system is attainable through regulating variables, such as elevated operating temperatures, optimal quantities of thermoelectric elements, appropriate ratios between thermoelectric element numbers, well-considered thermocouple thickness, suitable thermocouple radial width, and the judicious selection of parameters like annular shape or height ratio.

Performance improvement and thermomechanical analysis of a novel asymmetrical annular thermoelectric generator

Enhancing thermoelectric performance hinges on optimizing the geometry of thermoelectric legs. In this study, we present a novel asymmetrical annular thermoelectric generator (ATEG) in which the proportions of P-type and N-type legs are meticulously balanced. We construct a one-dimensional analytical model tailored to this ATEG. Utilizing this model, we derive the relationship governing thermal-electrical impedance matching in an asymmetrical ATEG and formulate a general expression for optimizing the asymmetry coefficient. We explore the influence of various thermal boundary conditions on optimal impedance matching, ideal annular leg parameters, and the optimal asymmetry coefficient. Our findings reveal that thermal boundary conditions significantly affect the optimal load ratio. Furthermore, in comparison to traditional ATEGs, our proposed asymmetrical ATEG with the optimized structure exhibits a remarkable 16.2 % increase in output power while maintaining the same material volume. Additionally, we perform a three-dimensional numerical analysis of the asymmetrical ATEG using Comsol. Our research findings indicate that introducing the asymmetric structure leads to higher maximum thermal stress on the legs. Interestingly, the study of asymmetric thermal boundary conditions highlights that improving heat transfer between the ATEG and the cooler yields higher mechanical reliability compared to enhancing heat transfer between the ATEG and the heat source.

Energy Conversion Performance and Optimization of Wearable Annular Thermoelectric Generators

Energy Conversion Performance and Optimization of Wearable Annular Thermoelectric Generators

Proposing and thermo-economic optimization of an annular-thermoelectric gas heat recovery unit with a novel hybrid fin-pin vane and porous insert

Heat recovery from the cylindrical surface of the exhaust gas pipes is one of the promising applications of annular thermometric generators (ATEG). A pipe-shape based heat exchanger can be attached to the inner surface of the annular-thermoelectric generator to recover the hot exhaust gas in the form of electricity generation. In this paper, a novel grid annular fin-based heat exchanger with porous inserts is proposed which can boost the output power of the ATEG up to 1.45 and 2.12 times compared to the conventional common pipe-based heat exchangers. A comprehensive parametric analysis is carried out to investigate the impact of various geometric and operational parameters such as porous insert height, porous insert angle, porous inserts length, Re number, number of thermocouples, and so on thermal, exergetic, and economic factors. An optimized value of height, length, and angle of the porous insert can maximize the output power of the proposed system. Economic analysis is also provided to identify the corresponding costs of the grid annular fin-based heat exchanger with porous inserts for the heat recovery aim.

Power generation of annular thermoelectric generator with silicone polymer thermal conductive oil applied in automotive waste heat recovery

The annular thermoelectric generator (ATEG) matches the shape of the exhaust pipe. To improve the power generation efficiency of the ATEG in automobiles, a scheme is proposed to use a silicone polymer-based thermal conductive oil to transfer heat from the exhaust. Based on this concept, a new type of concentric tube heat exchanger is designed. A finite element model of the new system is established by considering temperature gradients, temperature dependence, and fluid resistance characteristics. Numerical simulations are performed to investigate the effects of exhaust parameters, thermal oil parameters, and heat exchanger structure on thermoelectric performance. The findings demonstrate a 15.2% increase in maximum output power of the new generator compared to a conventional ATEG, accompanied by a 19% decrease in the optimal thermoelectric module area. Furthermore, the net power first increases and then decreases with increasing thermal oil mass flow rate. The thermal oil mass flow rate can be adjusted in real-time based on fluctuations in exhaust parameters to achieve peak net output power. Finally, optimal fitting relationships between the heat exchanger dimensionless diameter and the total diameter, as well as between exhaust parameters and the optimal thermal oil mass flow rate, are obtained through parameter analysis and derivation.

Performance evaluation of a solar hybrid system integrating a two-stage annular thermoelectric generator

A novel cogeneration system made up of the dye-sensitized solar cell (DSSC), a solar selective absorber (SSA), and a two-stage annular thermoelectric generator (ATTEG) is developed in order to effectively use the solar energy captured by the DSSC. DSSC converts short-wavelength solar energy into electricity, while long-wave solar energy is converted into thermal energy by SSA to drive ATTEG for additional electricity. The mathematical equations for performance indicators of the hybrid system are derived in light of the numerous irreversible losses between DSSC and ATTEG, and the energy relationship between DSSC and ATTEG is investigated from the perspectives of energy and exergy, respectively. Moreover, a comprehensive comparison of the performance of the hybrid system with two-stage ATEG and single-stage ATEG is outlined under different solar irradiance and operating temperature. Furthermore, calculation result demonstrates that the energy and exergy efficiency of DSSC-ATTEG is 82.9% and 19.2% greater than a standalone DSSC when solar irradiation and thermoelectric components are given. Finally, detailed parameter analyses are performed. In addition to evaluating the conventional operating parameters, the effects of three important geometric parameters of ATTEG on the hybrid system are investigated, including annular shaped parameters, height ratio and angle ratio of thermoelectric elements. The outcomes can offer fresh ideals into the design and optimization of waste heat recovery from round shaped heat sources.

Proposing linear structure for annular thermoelectric generators; thermal, exergetic, mechanical, and economic analysis

Annular thermoelectric generators have been the subject of many studies in recent years due to their structure which improves the efficiency when recovering heat from round surfaces. A novel linear arrangement of legs is proposed in this paper which greatly increases the flexibility of design compared to the conventional π structure of annular thermoelectric generators. Every geometric feature of the legs in the linear annular thermoelectric generator can be changed and optimized independently. Numerical simulations are carried out to study the effect of various parameters such as height ratio (θh), total height (h), angle ratio (θφ), total angle (φ), thickness ratio (θt), total thickness (t), hot and cold side temperature on the output power, efficiency, mechanical and economic performance of the linear shape annular thermoelectric generator. Results indicated that the height ratio, angle ratio, and thickness ratio of 0.5 lead to the highest conversion and exergy efficiencies while producing the lowest thermal stress on the legs and having the least cost per watt of output power. Additionally, it is found that the increment of the total combined height, total angle, or total thickness of the thermoelectric legs increases the costs per watt of output power. For example, the dollar/watt value is grown by 7% when the total thickness is increased from 8 mm to 16 mm for an angle ratio of 0.5. The increase of the heat source temperature can boost the output power, and conversion efficiency, and lower the cost but also impose larger stress as well.

Economic and thermal performance analysis of two-stage thin-film solar thermoelectric power generator

One of the performance enhancement strategies in thermoelectric technology is application of two-stage leg instead of normal single stage leg structure. However, for a thin-film solar thermoelectric generator applying this strategy requires many in-depth considerations including economic -cost and reliability aspects. In this research, attempts are made to identify the economic and performance characteristics of a two-stage thin-film solar thermoelectric generator under various geometrical conditions and then compare with normal single stage configuration. Generally, in addition to being cost-effective compared to the single-stage design, the double-stage design can produce more power if the appropriate material is selected. The results of numerical simulations show that the use of bismuth tellurides in single stage thermoelectric generator (SATEG) legs improves the performance of the system in terms of power generation. But the use of skutterudites in the lower layer and bismuth tellurides in the upper layer of the two-stage case, in addition to increasing the output power, significantly reduces the dollar/watt value. Furthermore, the highest output power and exergy efficiency are obtained in the lower layer angle ratio of 0.8–1 and in the upper layer angle ratio of 2. Among the geometrical parameters, the radius of heated area (Rh) has the greatest effect on the performance of double-stage solar annular thermoelectric generator (DSATEG). The highest power output is obtained at Rh = 1.5, which is equal to 1.323W.

Thermoelectric Field Analysis of Trapezoidal Thermoelectric Generator Based on the Explicit Analytical Solution of Annular Thermoelectric Generator

The geometrical configuration is one of the main factors that affect the thermoelectric performance of a device. Research on the trapezoidal thermoelectric generator (TTEG) with varied cross section is mainly based on finite element simulation and experiment. In this paper, an explicit analytical solution of the maximum output power of annular thermoelectric generators (ATEG) is proposed, which has been proved to have high accuracy. Then, the maximum output power between ATEG and TTEG is compared. Results show that, for the appropriate geometric parameter δ, the relative error of maximum output power between explicit analytical ATEG and the simulated solution of TTEG can reach the order of 10−3. When the hot end is at the a side, the high temperature and θ is 510 K and 10°, respectively. For Bi2Te3 material and PbTe material, the relative error of maximum output power between the explicit analytical and simulated solution is 0.0261% and 0.074%, respectively. Under suitable working conditions, the explicit analytical results of ATEG can provide some reference for the performance optimization of TTEG.

A comprehensive investigation of PCM based annular thermoelectric generator for energy recovery: Energy conversion characteristics and performance evaluation

Annular thermoelectric generators (ATEG) are increasingly attracting attention and are pivotal in thermal energy recovery due to their unique characteristics, which can be perfectly adapted to cylindrical heat sources. Considering the efficient thermal management and power generation of thermoelectric generator (TEG), phase change material (PCM) can be integrated with the cold side of TEG as a favourable cooling medium to meet its functional requirements. However, previous studies have focused on the intrinsic connection between flat-plat TEG and PCM, while the impact of PCM on ATEG has not been systematically explored. In the present study, an annular thermoelectric generator with PCM (ATEG-PCM) under a pulsed heat source is proposed, and its dynamic characteristics and energy distribution are evaluated. The effects of PCM parameters such as height, latent heat and melting temperature are comprehensively explored from multi-index, including PCM temperature, liquid fraction, temperature difference, output power, energy and exergy efficiencies. Furthermore, a comparative investigation of ATEG-PCM, PCM-ATEG where PCM is applied on the hot side, and ATEG without PCM is further carried out to clarify the coupled mechanism of PCM on thermal management and power generation enhancement of ATEG. The results indicate that the energy efficiency of ATEG-PCM has saturated at PCM height of 10 mm to 12 mm, while the exergy efficiency merely slightly increases. Especially, the PCM melting temperature merely affects the time at which PCM initiates to change from solid state to liquid state, without affecting the total energy efficiency of ATEG-PCM. Furthermore, the comparison analysis determines that ATEG-PCM deserves more attention, judging by thermal management and power generation. This work not only contributes to the understanding of the coupling mechanisms between PCM and ATEG but also provides a research direction for energy recovery in PCM based ATEG hybrid system.

Modeling of annular thermoelectric generator considering temperature-dependent material properties and side surface heat convection

An annular thermoelectric generator (ATG) contributes to energy utilization in round structures. An accurate prediction of thermoelectric (TE) performance is key to the design of the ATG. By using the perturbation theory and the equivalent substitution of integrals method, an analytical model is proposed, which can easily deal with the nonlinear heat equation induced by temperature-dependent material properties. The TE performance of the ATG including the Thomson effect is studied by the proposed model, and the effect of structural parameters and operating conditions on the TE behavior is analyzed. The results indicate that if the Thomson effect is neglected, the predicted power output and efficiency will be much higher than the actual cases. Significantly, in both working conditions, the relative error of the predicted temperature field of the proposed model is less than 0.1%, far below the available theoretical models. In addition, the influence of side surface heat convection is also analyzed using a numerical method. Remarkably, the maximum power output may increase as the heat convection coefficient grows.

A novel economic-cost and thermal comparative case study between segmented and non-segmented thin-film solar annular thermoelectric generator

One of the key effective parameters on the efficiency of thermoelectric generator is the material of n-type and p-type semiconductors. Thermoelectric generator works based a huge temperature difference between two sides semiconductors. Unfortunately, the suitable efficient materials for high temperature range (hot side of thermoelectric) are not efficient for low temperature range (cold side of thermoelectric) and vice versa. That is why researchers have recently suggested segmented thermoelectric generator meaning the semiconductors are made of two different separate materials for each side of thermoelectric. This strategy has not been investigated for ultra-thin solar annular thermoelectric generator. Hence, in this research, a comparative case study is provided to clarify the efficiency of the segmented in-plane solar annular thermoelectric generator from economic, energetic and exergetic point of views. The results reveal that for a high range of heat flux, the segmented thermoelectric is more efficient even from economic cost aspect. For heat fluxes greater than 40 kW/m^2, Case 1 provides the lowest dollar/watt value, and for heat fluxes less than 40 kW/m^2, Case 4 shows the minimum dollar/watt value.

Global structural optimization of annular thermoelectric generators based on a dual-finite-element multiphysical model

The conventional methods to improve the performance of annular thermoelectric generators (ATEGs) heavily rely on optimizing the thermal design of individual annular thermoelectric couples (ATECs). However, since a practical ATEG consists of many ATECs, the optimal structure of the ATEG can differ from the ATEC-based design. On the other hand, optimization by simply considering all ATECs can lead to a heavy computation burden. This work first proposes a high-fidelity, fluid-thermal-electric multiphysical ATEG model, solved by a computationally-efficient dual-finite-element method to cope with the challenge. This model explores the effects of ATEC microstructure and heat exchanger structure on ATEG performance under various operating conditions. Comparative multi-objective optimization studies were performed at three levels, i.e., for a single ATEC, a single ring of ATEG, and the entire ATEG. The results reveal that the optimized structural parameters of ATECs have some new features when considering the entire ATEG as the optimization objective. The optimal height, angle, and thickness of ATECs are 12 mm, 2.35°, and 10 mm, respectively. The corresponding net power, efficiency, and power density of ATEG are 321.6 W, 6.58 %, and 634.15 W/m3, respectively. Compared to the traditional design method based on a single ATEC and a single ring, the net power of the ATEG designed with the proposed method can be enhanced by 168 % and 197 %, respectively, at the expense of only a 20 % reduction in the power density.

Optimal design of annular thermoelectric generator with twisted tape for performance enhancement

The adaptation of annular thermoelectric generator (ATEG) to cylindrical heat sources exhibits a better performance compared to widely studied flat plate type thermoelectric generator (FTEG). To enhance heat transfer and improve the overall performance, a novel structure of the heat exchanger of the twisted-tape annular thermoelectric generator (TT-ATEG) is proposed in this paper. A three-dimensional finite element model of TT-ATEG is established for the first time. The net power gain coefficient and the efficiency gain coefficient are defined to quantify the performance of TT-ATEG, and the gain effects of the length, twist ratio and radius of the twisted tape are analyzed respectively. To maximize the comprehensive performance of TT-ATEG, the optimal weighting factor of net power and efficiency are determined, and the full-parameter optimization of the twisted tape is completed. The results reveal that the optimal performance of TT-ATEG is obtained if the weight ratio of net power and conversion efficiency is 1:4. In our case study, dimensionless factors radius ratio Rr, length ratio Lr and twist ratio of the twisted tape are 0.714, 0.479 and 136.84 respectively. Compared with the ATEG without twisted tape, the net power and efficiency are improved by 10.41% and 22.51%, respectively. The results demonstrate that the novel design of TT-ATEG could accelerate the heat transfer effectively and enhance the overall performance.

Economic configuration optimization of onboard annual thermoelectric generators under multiple operating conditions

Highly variable automobile operating conditions and the ever-fluctuating exhaust parameters pose fundamental challenges to optimizing the design of automobile annular thermoelectric generators (ATEGs). This paper establishes an advanced non-isothermal mathematical model of ATEGs using the finite element method for solving this problem. First, the effects of different vehicle operating conditions on the optimal thermoelectric semiconductor volume are investigated. Based on the results, the optimal range for selecting the thermocouple volume is determined. Aiming to maintain a high net power of ATEG under variable operating conditions, two new schemes are proposed to optimize the system configuration, including 1) a weighted power deviation method and 2) a multi-objective intelligent optimization algorithm. Then, a new method for assessing the power generation cost is proposed for the ATEG. Combined with the characteristics of vehicle exhaust fluctuation in the New European Driving Cycle, the economics of the above two schemes are calculated and compared, and the optimal design is obtained. The results show that the optimal ATEG system configuration is: the PN couple volume in a single ring is 5.0625 × 10−6 m3, the total PN couple volume is 2.835 × 10−4 m3, and the net power and the efficiency can reach 20.85 W and 3.9%, respectively. The proposed model and method contribute to optimize the structural configuration of the on-board ATEGs, and can be further extended for other application scenarios of the thermoelectric generator system.