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• A transient fluid-thermal-electric multiphysics model for the TEG is established. • The effect of exhaust temperature on the dynamics is greater than that of flow rate. • Periodic exhaust heat can amplify the dynamic output, especially for conversion efficiency. • For a sin wave of exhaust mass flow rate, the efficiency experiences a 15.58 % improvement. The thermoelectric generator is a potential candidate to recover waste heat from exhaust gas. Regarding the fluctuations of exhaust heat in practical situations, this paper adopts a transient fluid-thermal-electric multiphysics model to investigate the dynamic performance of the thermoelectric generator. Results show that the fluctuation of exhaust temperature has a greater influence on the dynamic characteristics than the fluctuation of exhaust mass flow rate. The dynamic performance of the thermoelectric generator benefits from a decrease in exhaust heat, but suffers when the exhaust heat is in an upward trend. Compared with the constant power and efficiency values of 4.96 W and 2.49 %, the average power and efficiency of the thermoelectric generator show a notable increase of 5.50 % and 70.61 % respectively during a step decrease in exhaust mass flow rate. Similarly, under a linear decrease, the mean power and efficiency experience a rise of 6.04 % and 45.05 % respectively. Besides, periodic exhaust heat can effectively amplify the dynamic output performance, especially for conversion efficiency. When subjected to a sin wave of exhaust mass flow rate, the efficiency experiences a 15.58 % improvement. This work offers a comprehensive understanding of the dynamic characteristics exhibited by the thermoelectric generator employed for waste heat recovery. [ABSTRACT FROM AUTHOR]

In this work, a three-dimensional transient numerical model of a thermoelectric generator module considering the temperature-dependent properties and the topological connection of load resistance is proposed to study its dynamic response characteristics. The dynamic output power and conversion efficiency of the thermoelectric generator module under steady and different transient temperature excitations are compared and studied. A time delay exists in the output response of the thermoelectric generator module, and the time delay increases when the temperature rate increases. When the heat source temperature changes rapidly, the corresponding output power, conversion efficiency, and other thermal responses will show a more stable change trend. Moreover, the dynamic response characteristic of the output power is synchronous with that of the conversion efficiency. The periodic temperature excitation may amplify the output power, where the average output power of the sine and triangle waves are 4.93% and 2.82% respectively higher than the steady-state output power. However, the average conversion efficiency of both is almost identical to the steady-state conversion efficiency. The proposed model contributes to predicting the dynamic performance of thermoelectric generators, and can be further extended to the whole thermoelectric generator system. • A three-dimensional transient numerical model of a thermoelectric generator module is proposed. • Six typical temperature excitations are used to study the dynamic response characteristics. • The time delay increases with the increase in the rate of temperature change. • The dynamic response of the output power is synchronous with that of the conversion efficiency. • The periodic temperature excitation may amplify the output power. [ABSTRACT FROM AUTHOR]

The automobile thermoelectric generator is a promising energy conversion technology to enhance fuel economy and decrease the fuel consumption of vehicles. In order to boost the performance of the automobile thermoelectric generator, the fin distance and thickness of the heat exchanger are fully optimized according to a hydraulic-thermoelectric multiphysics model. The net power model of the automobile thermoelectric generator is established by factoring in weight loss, backpressure loss, and pumping power loss. It is found that the optimization of the fin thickness is primarily aimed at minimizing power loss, particularly backpressure loss, while the key parameter for determining the output performance is the fin distance. Based on optimization results, the optimal fin distance and thickness are 2 mm and 0.5 mm, respectively, resulting in a maximum net power of 45.02 W and a maximum net efficiency of 1.5%. By optimizing the fins of the automobile thermoelectric generator, significant improvements are observed in its performance, with output power, conversion efficiency, net power, and net efficiency increasing by 26.85%, 42.22%, 9.52%, and 22.95%, respectively, compared to the generator without fin optimizations. The results of this study are helpful to guide the design of the internal fins of the heat exchanger. • A hydraulic-thermoelectric multiphysics model for automobile thermoelectric generators is built. • The optimization of fin thickness is aimed at reducing power loss, particularly backpressure loss. • The key parameter for determining the output performance is the fin distance. • The optimal fin distance and thickness are 2 mm and 0.5 mm, respectively. • The net power and efficiency are respectively increased by 9.52% and 22.95% via optimizations. [ABSTRACT FROM AUTHOR]

• A comprehensive hybrid transient CFD-thermal resistance model is proposed. • The ultra-high instantaneous efficiency of the ATEG system occurs due to thermal inertia. • The output power presents a more stable variation than the exhaust temperature. • The steady-state model overestimates the power and underestimates the efficiency. • The effect of the topological relationship of TEMs on the performance is investigated. This paper proposes a comprehensive hybrid transient CFD-thermal resistance model to predict the dynamic behaviour of an automobile thermoelectric generator (ATEG) system. The model takes into account the temperature dependences, the topological connection of thermoelectric modules, and the dynamic characteristics, which has the merits of high accuracy and short computational time. The dynamic behaviour of the ATEG system is determined and thoroughly examined using the transient exhaust heat as the heat source input. According to the transient model results, the dynamic output power of the ATEG system keeps the same variation trend with the exhaust temperature, but the variation of output power is more stable. Under the whole driving cycle, the mean power and efficiency of the 1/4 ATEG system are 8.91 W and 3.39% respectively, which are 3.39% lower and 47.52% higher than those expected by steady-state analysis. Beside, the model is validated experimentally, and the mean deviations of the output voltage and outlet air temperature are 7.70% and 1.12% respectively. This model is convenient to evaluate the behaviour of the ATEG system under different topological connections and gives a fresh tool for assessing the dynamic behaviour of ATEG systems. [ABSTRACT FROM AUTHOR]

To overcome the structural barriers of conventional annular thermoelectric generators (ATEGs), a new ATEG integrated with vapor chambers (VCs) is proposed in this paper, where the use of VCs enables a large hot-end contact area and a high temperature uniformity for traditional planar thermoelectric modules. Besides, a numerical model for the ATEG is built to conduct performance analysis and optimization under different parameters. Results suggest that the heat absorption of the ATEG increases with the increase of the number of VCs, thereby boosting the output power of the system. When the flow rate is lower than 35 g/s, the optimal number of VCs for the ATEG is 12, with the highest output power, conversion efficiency, net power, and net efficiency of 287.3 W, 5.36 %, 214.1 W, and 3.99 %, respectively, at the exhaust temperature of 800 K. Besides, the exhaust temperature does not affect the optimal result, while the ATEG should be designed with fewer VCs when applied to the waste heat recovery with a larger flow rate. The increase in the VC thermal conductivity is not related to heat absorption but can improve temperature uniformity, and the thermal conductivity of 4000 W m−1 K−1 already meets performance requirements. This study provides new perspectives on the structure design of ATEGs. • Annular thermoelectric generator integrated with vapor chambers is proposed to enhance its output performance. • The performance of the ATEG is investigated via a multiphysics numerical model and a net power model. • The system achieves a maximum net power of 214.1 W and a net conversion efficiency of 3.99 % at T ex = 800 K, m ex = 35 g/s. • The temperature uniformity coefficient of the system reaches 0.995 at λ vc = 10000 W m−1 K−1. [ABSTRACT FROM AUTHOR]

This work introduces a new heat pipe configuration into the automotive thermoelectric generator (ATEG) to boost its output performance, where heat pipes are arranged in a staggered up-and-down pattern and are in direct contact with the exhaust gas. Besides, a computational fluid dynamic (CFD) and thermal-electric hybrid numerical model is established to predict the performance of the ATEG. Meanwhile, the effect of staggering distance between heat pipes, fin thickness and spacing on the system performance is examined. The proposed heat pipe configuration allows heat pipes to absorb more thermal energy from the exhaust gas and then enhances the system's performance. The output power of the ATEG is in a parabolic relationship with the staggering distance, and the optimal staggered distance of L = 1.5 mm is determined. Both the thickness and spacing of the fins exert considerable influence on the heat absorption efficiency of the heat pipe, with the impact of fin spacing being considerably more pronounced than that of thickness. Besides, the ATEG reaches the maximum net power of 111.64 W at the fin thickness of δ = 0.5 mm and the spacing of d = 1.0 mm, experiencing an improvement of 15.07 % compared with the original structure. The research findings offer both a theoretical foundation and practical guidance for enhancing the output performance of ATEG systems incorporating heat pipes. • A novel heat pipe installation manner is proposed to improve ATEG output performance. • The effect of fin thickness and spacing on the heat pipe's heat absorption is studied. • The fin spacing has a greater effect on the ATEG performance than fin thickness. • The output power and net power are increased by 22.85 % and 15.07 % respectively. [ABSTRACT FROM AUTHOR]

This work proposes a novel fluid-thermal-electric multiphysics numerical model to predict the performance of thermoelectric generator systems applied to fluid waste heat recovery, with the consideration of multiphysics coupling effects of fluid, thermal, and electric fields. The comprehensive numerical simulations of the thermoelectric generator system are performed via COMSOL coupled solver. Besides, the effect of the neglect of parasitic heat on the output performance is investigated through the comparison with numerical results predicted by ANSYS and COMSOL separate solver, wherein the fluid-thermal field is computed first, then the thermal-electric field. The results show that the output power predicted by COMSOL separate solver is 8.52% lower than that predicted by COMSOL coupled solver at the inlet air temperature of 550 K and inlet air velocity of 30 m/s due to the neglect of parasitic heat. The output performance of the TEG system predicted by ANSYS is less affected by inlet air boundary conditions than that predicted by COMSOL. Finally, the experimental results show that the fluid-thermal-electric multiphysics model solved by the COMSOL coupled solver shows the lowest output power deviation of 2.81%. The proposed model can guide the numerical modeling of the thermoelectric generator system applied to fluid waste heat recovery. Based on the proposed fluid-thermal-electric multiphysics numerical models, we investigated the performance of a thermoelectric generator (TEG) system using exhaust gas as the heat source and investigated the effect of the neglect of parasitic heat on the output performance. [Display omitted] [ABSTRACT FROM AUTHOR]

• Heat pipes are introduced to the heat exchanger to extend its hot side area. • Optimization for heat pipe distributions improves the output performance of the ATEG system. • Output power and heat recovery are improved at the cost of a tiny decrease in conversion efficiency. • The output power and heat absorption are increased by 42.95 % and 55.6 % respectively. In pursuit of enhancing the utilization of exhaust heat in the automotive thermoelectric generator (ATEG), this study introduces a novel heat exchanger with integrated heat pipes to extend the effective hot-side surface area. Meanwhile, a numerical model containing multiphysical fields is developed, and the quantity and arrangement of heat pipes are optimized based on this model. Results suggest that (i) The incorporation of heat pipes markedly enhances the recovery of heat energy from the ATEG, leading to a substantial increase in its output power; (ii) With an increasing heat pipe quantity, the ATEG's output power exhibits a continuous upward trend before eventually reaching stability; (iii) The arrangement of heat pipes also influences system performance, and through optimizations, the optimal quantity of heat pipes is determined to be N = 11 and toleration to be d = 1 mm. At an exhaust temperature of 550 K and a mass flow rate of 60 g/s, the ATEG achieves an output power of 213.19 W and a heat absorption of 4318.02 W, which increased by 42.95 % and 55.6 % respectively, compared with the traditional structure without heat pipes. This structural optimization concept for the heat exchanger provides a new approach to performance improvements of ATEGs. This study provides a design basis and guidance for optimizing the design of ATEG systems with integrated heat pipes. [ABSTRACT FROM AUTHOR]

• Thermal and electrical contact resistances of 3.65 × 10−5 m2⋅K⋅W−1 and 1.18 × 10−10 Ω⋅m2⋅K are obtained. • Time average ZT value and effective efficiency are greatly improved by periodic heating. • Efficiency of 5.75% and ZT value of 1.12 are achieved under the optimal transient heat source. • Smaller leg height, larger leg area, more TE couples, and lower thermal conductivity are suggested. Thermoelectric power generation is regarded as a promising technology to convert waste heat into electricity. This study aims to address the low conversion efficiency of thermoelectric modules and introduces a novel periodic heating method to enhance their performance. Two new indicators, time average ZT ta value and effective conversion efficiency, are introduced to assess the dynamic behavior of thermoelectric modules. A Bi 2 Te 3 -based thermoelectric module with n-type Bi 2 Te 3-x Se x and p-type Bi x Sb 2-x Te 3 materials is adopted as the research objective and tested on a designed transient experimental setup. Besides, a transient numerical model is developed to explore the optimal transient heat source and study the effect of various parameters on dynamic behavior. Compared with the steady-state efficiency of 3.76% and ZT ta value of 0.78 at a heat supply of 60 W, the time average efficiency and ZT ta value are improved by 52.93% and 43.59% respectively using the periodic heating method. Also, a smaller leg height, a larger leg area, more TE couples, and lower thermal conductivity are suggested for improving the dynamic behavior. This work offers a new periodic heating method to improve the output performance of thermoelectric modules, which may promote the broader application of thermoelectric power generation technology. [ABSTRACT FROM AUTHOR]

Structural optimization is one of the effective means to improve thermoelectric generator (TEG) performance. Considering the inconsistent material parameters between P-type and N-type thermoelectrics, this paper proposes an L-type TEG configuration, where P-type and N-type semiconductors are designed with different heights and connected by L-shaped conductive strips. In addition, a thermal-electric-mechanical numerical model is established to evaluate and optimize the thermoelectric and mechanical performance of the L-type TEG. Results show that when the temperature difference is 400 K and the height ratio of the P-type to N-type semiconductor is 0.385, the L-type TEG achieves a maximum output power of 1.96 W and a maximum efficiency of 7.8 %. This is 2.39 % and 1.44 % higher, respectively, than the traditional π-type TEG. Although the temperature difference is not related to the optimal configuration of the L-type TEG, it will affect the extent of performance improvement, and the smaller the temperature difference, the greater the percentage gains of the L-type TEG compared to traditional design. In addition, the greater the difference in parameters (including Seebeck coefficient, thermal and electrical conductivity) between P-type and N-type is, the more significant the improvement of the L-type design will be. Specifically, the difference in electrical conductivity contributes to the increase of the output power, while the increase in the efficiency is affected by both the electrical conductivity and the thermal conductivity. This study provides a new perspective on the structural optimization of TEGs. • An innovative L-type configuration for thermoelectric generators is proposed. • A thermal-electric-mechanical numerical model is established to predict the TEG performance. • Power and efficiency are increased by 2.39 % and 1.44 % compared with traditional π-type design. • Greater disparities between P- and N-type lead to more gains when changing the π-to L-type design. [ABSTRACT FROM AUTHOR]

Thermoelectric power generation is a renewable energy conversion technology that can directly convert heat into electricity. In recent years, a great number of theoretical models have been established to predict and optimize the performance of both thermoelectric generators and thermoelectric generator systems. In this work, a comprehensive review of theoretical models is given with a specific focus on the different modeling approaches and different application scenarios. Firstly, the basic principles of theoretical models of the thermoelectric generator are presented, including the thermal resistance model, thermal-electric numerical model, and analogy model. Then, the theoretical models of the thermoelectric generator system are reviewed in detail, including the thermal resistance-based analytical model, computational fluid dynamics models, and fluid-thermal-electric multiphysics field coupled numerical model. The methods to improve the accuracy of theoretical models are also discussed. Furthermore, the transient thermal-electric numerical model of the thermoelectric generator and the transient fluid-thermal-electric multiphysics field coupled numerical model of the thermoelectric generator system are introduced, which can take into account the dynamic characteristics of the heat source, and may remain a hot research field in the upcoming years. Generally, thermal resistance models can quickly obtain the performance of the thermoelectric generator and thermoelectric generator system under different parameters, but suffer from relatively large errors; while it is the opposite for numerical models. To design a comprehensive thermoelectric generator system for practical application, it is suggested to combine the advantages of different models, to shorten the development time and ensure optimal performance at the same time. [ABSTRACT FROM AUTHOR]

Thermoelectric generator (TEG) can utilize solar heating to generate electricity without any fossil fuel consumption. However, conventional solar driven TEG fails to achieve high efficiency power generation for 24-h, due to the losing of solar concentration at the hot end and additional cooling capability at the cold end. Therefore, a novel TEG system with the combination of solar concentration, greenhouse and radiative cooling is proposed. With the aim to significantly increase the temperature of hot end, a dish-type concentrator is introduced to concentrate solar radiation and a greenhouse seals up heat. Radiative cooling panel is used to decrease the temperature of cold end, which can realize temperature differences of TEG at night. The eight-day outdoor experimental test indicates that the thermoelectric system achieves a maximum temperature difference of 47.5 °C and a voltage output of 1293.8 mV. The system attains the average power outputs of 3.6 W/m2 on sunny and 0.16 W/m2 on cloudy. Moreover, even at the nights of high humidity and low temperature, the system also achieves a maximum power output of 0.08 W/m2, which can enable continuous power generation throughout the day. This innovative TEG system presents a viable strategy for powering small-scale devices in remote areas. [ABSTRACT FROM AUTHOR]

• A novel annular thermoelectric generator structure is proposed for harvesting waste heat. • The optimal length difference of thermoelectric elements in different columns is 0.06 mm. • The optimal structure is not sensitive to the exhaust gas temperature and velocity. • The power and efficiency experienced an improvement of 8.97% and 8.93% respectively. The annular thermoelectric generator (ATEG) gains significant attention in the automotive waste heat recovery field due to its compatibility with the exhaust pipe's shape. To address the performance deterioration issue due to the temperature drop, a novel annular thermoelectric module (ATEM) structure is proposed, in which the cross-sectional area of the thermoelectric elements continuously increases along the direction of heat flow. To assess the performance and perform parameter optimizations, this work develops a three-dimensional, steady-state, and fluid-thermal-electric multiphysics numerical model of the entire ATEG. The length difference of thermoelectric elements in different columns (Δ L) is comprehensively optimized through numerical simulations, and the effects of exhaust temperature and velocity on the optimal Δ L value are studied. The results indicate that a great temperature drop exists inside the ATEM, suggesting the advantages and effectiveness of the proposed novel structure configuration for modules. The optimal Δ L value is not sensitive to the exhaust gas temperature and velocity, and when Δ L = 0.06 mm, the novel ATEG achieves the highest output performance, with an output power of 76.66 W and an output efficiency of 1.45 % at the exhaust gas temperature of 550 K and the exhaust gas velocity of 30 m/s. The power and efficiency experience an improvement of 8.97 % and 8.93 %, respectively, compared to the traditional structure. Additionally, the lower exhaust gas temperature and velocity contribute to a greater performance improvement for the novel ATEG. This ATEM structural design provides a new approach to enhance performance when encountering temperature drop issues. [ABSTRACT FROM AUTHOR]

• A transient fluid-thermal-electric multiphysics numerical model is proposed. • The dynamic responses of the automotive thermoelectric generator are studied. • There is a time delay in output response with the change of exhaust temperature. • Steady-state model overestimates the power of automotive thermoelectric generators. • The tiny fluctuation of exhaust gases has a slight influence on output performance. The automotive thermoelectric generator system is a promising technology of exhaust waste heat recovery, but reasonable theoretical models to predict its dynamic performance are lacking. In this work, a transient fluid-thermal-electric multiphysics coupling field numerical model is proposed for the first time, and the model is used to evaluate the dynamic performance of a simplified automotive thermoelectric generator system under vehicle driving cycles. The transient numerical model, which takes into account the dynamic characteristics, fluid-thermal-electric multiphysics field coupling effects, and material temperature dependence, is thus far the most complete model ever. Numerical results reveal that there is a delay in output response with the change of exhaust temperature, and the change of output voltage and output power is often accompanied by the change of exhaust mass flow rate. The small and short-term fluctuation of exhaust gases has a slight influence on output performance. With the transient variation of exhaust characteristics, the output voltage and output power show more stable changes and slower responses, but the situation is the opposite for conversion efficiency. The output power predicted by steady-state numerical simulation is 12.6% higher than that of transient numerical simulation. Moreover, the proposed transient numerical model is recommended to investigate the dynamic performance of automotive thermoelectric generator systems. [ABSTRACT FROM AUTHOR]