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Taguchi optimization and thermoelectrical analysis of a pin fin annular thermoelectric generator for automotive waste heat recovery
Abstract
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.
... Figure 25 represents a schematic diagram of the annular thermoelectric generator system. Yang et al. [164] optimized the system parameters and pin fin dimensions by utilizing the Taguchi method to maximize the output power. They demonstrated that the exhaust temperature is the most dominant factor for performance improvement, followed by the exhaust flow rate, fin length, fin diameter, and pin fin number, respectively. ...
... Schematic diagram of (a) annular thermoelectric generator and (b) single thermocouple[164]. ...
With the progress of modern times, automobile technology has become integral to human society. At the same time, the need for energy has also grown. In parallel, the total amount of waste energy that is liberated from different parts of the automobile has also increased. In this ever-increasing energy demand pool, future energy shortages and environmental pollution are the primary concerns. A thermoelectric generator (TEG) is a promising technology that utilizes waste heat and converts it into useful electrical power, which can reduce fuel consumption to a significant extent. This paper comprehensively reviews automobile thermoelectric generators and their technological advancements. The review begins by classifying different waste heat technologies and discussing the superiority of TEGs over the other existing technologies. Then, we demonstrate the basic concept of and advancements in new high-performance TEG materials. Following that, improvements and associated challenges with various aspects, such as the heat exchanger design, including metal foam, extended body, intermediate fluid and heat pipe, leg geometry design, segmentation, and multi-staging, are discussed extensively. Finally, the present study highlights research guidelines for TEG design, research gaps, and future directions for innovative works in automobile TEG technologies.
... Researchers are diligently enhancing the performance of TEGs from multiple perspectives, encompassing the development of novel thermoelectric materials [9], innovative thermoelectric module structures [10], optimization of circuit topologies [11], augmented heat transfer at the hot end [12], and optimization of heat dissipation [13]. Through these investigations, fundamental parameters governing the performance of exhaust waste heat recovery TEGs have gradually come to light. ...
In recent years, considerable effort has been dedicated to the development of highly efficient thermoelectric generators for waste heat recovery and thermoelectric power generation. In this study, we present employing twisted tapes with variable twist ratio to enhance thermal energy extraction efficiency, coupled with two-stage thermoelectric modules for heat-to-electricity conversion, resulting in a substantial increase in the power output of the thermoelectric generator. We established an experimental system that validated the superior power generation and heat recovery characteristics of the two-stage thermoelectric generator. Building upon these findings, we propose further optimizing the variable twist ratio twisted tapes to enhance the power output. We investigated the impact of tape pitch ratio, twist ratio, and twist ratio variation range on thermoelectric performance. Experimental results indicate that the influence of flow instability is more pronounced than that of swirl intensity, and twist tapes with the maximum twist ratio variation rate yield the highest net output power. Compared to an unmodified thermoelectric generator, the two-stage thermoelectric generator employing twist tapes with a twist ratio increase from π to 3π achieves a maximum net output power gain of up to 100%. These findings provide a practical framework for integrating innovative power generation modules and optimized heat exchanger designs into the application of waste heat recovery thermoelectric generators, marking a significant advancement in the field of thermoelectric generators.
... 1 Therefore, the energy recovery of exhaust waste heat is an important approach to improving the fuel efficiency of engines. Automotive thermoelectric generator (ATEG) systems can directly transfer heat energy into electrical energy, [2][3][4] which has the advantages of being small, stable operation, high reliability, and having no moving parts. [5][6][7] Therefore, thermoelectric technology is widely used to recover exhaust waste heat, which is also applied in battery thermal management. ...
To dynamically track the maximum power of an automotive thermoelectric generator (ATEG) system in real-time, this study introduces a novel maximum power point tracking (MPPT) algorithm that integrates Kalman filtering and fuzzy control. Employing a two-phase interleaved parallel DC–DC boost converter in the MPPT controller effectively reduces current ripple and switch loss. Results demonstrated a significant improvement in tracking time compared to the traditional incremental conductance algorithm, attributed to the elimination of high-frequency components in output power by the Kalman filter. The novel algorithm exhibits enhanced tracking stability through the application of fuzzy control. Ultimately, the tracking accuracy of the novel algorithm surpasses that of the incremental conductance algorithm by 5.2%, achieving an impressive 94.9%. This study, therefore, presents a valuable contribution to a novel MPPT algorithm for precisely and rapidly tracking the global maximum power points of the ATEG system throughout the entire vehicle driving cycle.
The performance optimization of thermoelectric generators (TEGs) is crucial for efficiently converting waste heat to green energy. This study analyzes the performance and thermal stress of a unileg thermoelectric module by combining the Taguchi method, analysis of variance (ANOVA), and artificial neural network. The results of the Taguchi method indicate that the leg geometry exerts a negligible effect on output power (OP) and conversion efficiency but significantly affects the thermal stress (TS). The analysis of the objective function (maximum OP-to-maximum TS ratio, denoted by P/S) reveals the optimal configuration results in a P/S value of 0.01255 W‧MPa−1, accompanied by a maximum output power (2.9 W) and thermal stress (232.32 MPa). The maximum thermal stress of the rectangle TE leg (182.29 MPa) is less than that of the triangle (279.85 MPa) by 34.86 %. The Taguchi method, analysis of variance, and artificial neural network have the same sensitivity order on P/S with leg height > leg geometry > copper thickness > ceramic thickness. Furthermore, an evolutionary neural network (ENN) method with five-step optimization from 4000 datasets has been developed to improve machine learning prediction. The average error of P/S value and conversion efficiency from ENN is 1.61 % and 0.35 %, respectively. However, for the ENN predictions, the relative errors of P/S value and efficiency between predictions and simulations are 1.28 % and 0.19 %, respectively. In conclusion, this work has demonstrated the numerical optimization of the performance of unileg TEM for the first time. The use of ENN can predict the performance of TEM precisely, saving running time and markedly reducing computational costs. Moreover, the results are conducive to designing high-performance TEGs with long lifespans.
Today, households increasingly depend on water dispensers as necessary appliances. In this way, the demand for water dispensers with environmentally friendly systems is rising around the globe because there are no eco-friendly alternative water dispensers in the global market as alternatives to vapor compression refrigeration systems. In the present work, the improved Stirling water dispensers for cold and hot water are presented as an environmentally friendly alternative. A gamma-type Stirling water dispenser is improved by integrating twin wavy plate heat exchangers with varying dimensions. A thermodynamic model is developed to carry Schmitt's vision of overcoming the Stirling water dispenser to fruition. The suitable sizes of both heat exchangers are determined to achieve higher heat removal rates and a higher coefficient of performance (COP). Due to the heat exchanger's optimal size, the water cooler generates a cooling load of about 1.4 kW and a heating load of about 4 kW. A suitable and adequate tendency is identified by comparing the data from the past and the present. The performance of the gamma Stirling water dispenser was improved by about 22% as a result of using twin wavy plate heat exchangers.
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 5.062510 −6 m 3 , the total PN couple volume is 2.83510 −4 m 3 , and the net power and the efficiency can reach 20.85 W and 3.9%, 2 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.
The annular thermoelectric generator (ATEG) has received growing research interest due to its improved energy conversion efficiency compared to conventional flat-plate thermoelectric generators (FTEG). In this study, considering the influence of ceramic substrate and copper contact layer, a numerical model of the annular thermoelectric module (ATEM) was established for the studies of the influence of geometrical parameters on output performance under three typical application scenarios with different boundary conditions. It is found that when the heat flow on hot side is constant, the shape factors of the optimal performance are slightly different either if the convection coefficient or the temperature is considered constant on cold side. In both cases, the output power and the conversion efficiency decrease with the increase of the thickness of the thermocouple, and increase with the increase of the angle, length, and number of the thermocouples. When the temperatures are considered constant on both sides of the thermocouples, a conflicting relationship between the optimal output power and the efficiency exists. In this case, to obtain the best ATEG performance, multi-optimization problem is formulated and solved by the non-dominant sorting genetic algorithm with elite strategy method (NSGA-II).
In order to increase the energy conversion efficiency of thermoelectric generators for automobile systems where the heat sources are commonly cylindrical, a novel concentric annular thermoelectric generator (CATEG) consisting of annular thermocouples and a concentric annular heat exchanger is proposed. A numerical model of the CATEG is first established using a finite-element method, based on which the thermoelectric performances of the proposed CATEG and the conventional annular thermoelectric generator (ATEG) with a cylindrical heat exchanger are compared. The relationship between the size of the heat exchanger, heat transfer characteristics, and heat flow resistances are comprehensively studied. Furthermore, to balance the relationship between heat transmission and fluid flow resistances, and to extract the maximum net power, the optimal design of the concentric annular exchanger is obtained and analyzed. Simulation results show that the optimized ratio of the inner and outer diameters of the heat exchanger is 0.94, and the new ATEG with the proposed concentric annular heat exchanger can significantly increase the total heat transfer coefficient as well as the pressure drop, leading to a maximum net power of 65% higher than the conventional ATEG. 2
Utilizing the heat energy of exhaust gases is a promising application of thermoelectric generator (TEG), which can convert low grade thermal energy into electricity. The annular thermoelectric generator (ATEG) is thought to be much more feasible for cylindrical heat source compared to the flat-plate thermoelectric generator (FTEG) in reference to the compatibility. Nevertheless, the quantitative comparison is lacking to clarify the prevalent geometry of TEG for cylindrical heat source. In this work, the performances of ATEG and FTEG are compared in detail with varying inlet temperature, velocity and the convective heat transfer coefficient when cylindrical heat source is applied. The turbulent heat source is described by the standard κ-ε functions together with the two-equation heat transfer model, while the output power and conversion efficiency of the ATEG and FTEG are calculated by solving the coupled thermo-electric equations. Our results showed that the output powers and the conversion efficiencies of ATEG and FTEG both increase with the increase of the inlet velocity, temperature, and the convective heat transfer coefficient. The conversion efficiency of ATEG is always higher than that of FTEG. The conversion efficiency of ATEG becomes even larger than that of FTEG when inlet temperature and/or convective heat transfer coefficient are relatively larger. In contrast, the output power of ATEG has no obvious difference with that of FTEG. This study addressed the condition when the ATEG has obvious advantage compared to the FTEG with cylindrical heat source applied. Our results suggest the annular TEG is better choice for cylindrical hot source especially when the inlet temperature and/or convective heat transfer coefficient are relatively larger. It could be a helpful guide for choosing suitable geometry of TEGs for energy harvesting in complex condition.
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.
The humidification-dehumidification (HDH) technology is attractiving for limited desalination. The freshwater productivity using a centrifugal sprayer-based solar HDH system at different sprayer hole diameters and high speeds is discussed in the present work. The hole diameter and operating speeds range from 0.001 to 0.003 m and 1100–1800 rpm, respectively. Experimental data were analyzed using 120 experiments and optimized by the response surface methodology (RSM). The RSM was used to explain the effects of desalination system factors and their interaction to achieve optimum operating conditions for the highest freshwater productivity. The optimum conditions to reach the highest freshwater productivity are 0.00113 m hole diameter and 1149.48 rpm centrifugal sprayer speed at noon. Also, the optimum operating conditions obtained the highest accumulated productivity at a hole diameter of 0.001 m and a speed of 1219.76 rpm. The analysis of variance indicates that the models can predict freshwater productivity and accumulated productivity with a confidence level of over 98 %.
The existence of life on earth would be impossible without water. When it comes to the problem of water shortage, desalination is a viable option since it can purify salty water into drinkable supplies. The current work investigates a humidification-dehumidification (HDH)-based solar desalination unit utilizing a high-speed rotary humidifier. The water production is evaluated concerning the droplet slot bore and rotating speed. The total droplet surface contact area depends on droplet size and quantity. At the same water flow rate, tiny slots create frequent tiny droplets. Larger slots produce fewer big droplets. High spraying speed produces tiny, fast-moving water droplets, which evaporate more quickly. In contrast, the further increase in spraying speed leads to high flow resistance, which decreases the number of droplets produced from centrifugal spraying at high speeds. Also, the maximum production occurs at a slot bore of 0.001 m, with an 88% increase compared to 0.003 m. Furthermore, the maximum daily water production reaches about 17 kg of fresh water at a slot bore of 0.001 m, with a spraying speed of 1200 rpm.
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.
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.
Convection across circular concentric gaps between cylinders is crucial in industrial applications, including electronic cooling, heat exchangers, and solar collectors. The effect of longitudinal and annular grooves on the outside surface of the inside tube on natural convective heat transmission in enclosure concentric circular annulus is experimentally investigated in the present work. Twin pairs of circular aluminum cylinders with the same radius ratio, length, and surface area were examined. Each one consists of two concentric circular cylinders. To maintain a steady heat flux, the inside cylinder of each pair has an electrical heater connected. The results indicate that the increases in the Nusselt number of around 25%, 43%, 67%, 123%, 142%, 157%, and 172% are seen for groove depths of 0.05 cm, 0.10 cm, 0.15 cm, 0.20 cm, 0.25 cm, 0.3 cm, 0.35 cm, and 0.4 cm. In addition, increasing the depth of the longitudinal groove raises the Nusselt number by roughly 33%, 51%, 79%, 99%, 136%, 153%, 173%, and 184%. The longitudinal grooves with a depth of 4.0 mm enable a 38% increase in free convection over prior research. An annular groove of 4.0 mm depth increases free convection by 36%. Furthermore, a further advancement over earlier research is attributable to the extensive surface contact area of the inner cylinder made possible by longitudinal or annular grooves. ARTICLE HISTORY
Conventional methods of improving the heat dissipation performance of heat sinks require either modifying existing heat sink geometries or installing additional structures to induce chimney effect. These methods can be problematic to apply if there are limitations of space and cost. In this study, we address the aforementioned problems by developing a novel method of inducing the chimney effect by attaching aluminum tape to a pin fin heat sink. Geometric parameters for optimization were the width and attachment position of the aluminum tape, and changes in the thermal resistance of the pin fin heat sink with a rectangular base were observed according to its orientation angle. First, the widths and attachment positions of the outer and inner aluminum tape strips that minimized the thermal resistance of the heat sink were derived through simulation. The thermal resistance of the heat sink was estimated to be reduced by 10.8% or 7.7%, respectively, only by attaching the outer or the inner aluminum tape strip with optimal width to the top of the pin fin, and it was found to be further reduced by attaching both the outer and inner aluminum tape strips simultaneously. As the next step, the simulation results were verified by experimentally measuring the thermal resistance of actual pin fin heat sinks with and without aluminum tape. It was found that the thermal resistance of the pin fin heat sink was reduced by up to 17.1% by inducing the chimney effect simply through the attachment of both the outer and inner aluminum tape strips with optimal widths to the top of the pin fin. For all heat sink orientation angles tested in the range 0°−180°, the thermal resistance was found to be lower when the aluminum tape was attached than when it was not attached. As a result, the heat dissipation performance could be improved without changing heat sink geometry and by requiring no additional space to install a chimney structure. Our study results show that the safety of heat-generating devices that require heat dissipation can be significantly improved by enhancing the heat dissipation performance of heat sinks if the width and attachment position of the aluminum tape are optimized.
Organic Rankine cycle (ORC) and thermoelectric generator (TEG) have both been identified as reliable waste heat recovery (WHR) technologies, although they are different in energy conversion efficiency, volume size and operating temperatures. The combined thermoelectric generator and organic Rankine cycle (TEG-ORC) system enables TEG and ORC to be complementary. In this study, a novel TEG-ORC system is proposed in a light-duty vehicle application. Regarding the space limitations in vehicles, the proposed system effectively uses existing components in the car to reduce the overall size. In addition, the TEG-ORC is a bifunctional system, which not only works for exhaust energy recovery, but also acts as a heating device for fast engine oil warm-up. The fuel saving potential of the TEG-ORC system is assessed against that of the baseline, standalone TEG and standalone ORC systems. The results show that TEG-ORC system effectively reduces the engine oil warm-up time and system hysteresis time of WHR. A significant increase of fuel saving potential is obtained when TEG and ORC are combined, which is not achievable by a single TEG or a single ORC. This seems a breakthrough for waste heat recovery in vehicle applications since the proposed TEG-ORC system is compact and has an acceptable fuel saving performance.
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.
Phase change materials (PCMs) are useful means for energy storage and thermal management of thermoelectric generators (TEG) systems. Nevertheless, energy storage rate under transient heat loads is slow due to low thermal conductivity of PCMs. In this study, copper and nickel porous metal foams are applied in a PCM on hot side of a TEG to accelerate storage of fusion heat and power output of the TEG under transient boundary conditions. Therefore, continuous and fluctuating heat flows were imposed to the system initiating from ambient room temperature. Results of this study show that, adding the metal foams enhances heat flux through the PCM by reducing overall thermal resistance in the energy storage box. The PCM with copper foam makes higher percentage of increase of temperature in the box and higher power generation until the melting point, while the PCM with nickel provides higher storage temperature after the melting process. The metal foams improve the thermal conductance between the heat source and the TEG creating higher temperature difference across the module and making higher electrical power compared to the case with PCM-only. The corresponding power enhancement is 26.2% and 62.5% by the TEGs with the nickel and copper foams, respectively.
Developing new energy vehicles has been a worldwide consensus, and developing new energy vehicles characterized by pure electric drive has been China’s national strategy. After more than 20 years of high-quality development of China’s electric vehicles (EVs), a technological R & D layout of “Three Verticals and Three Horizontals” has been created, and technological advantages have been accumulated. As a result, China’s new energy vehicle market has ranked first in the world since 2015. To systematically solve the key problems of battery electric vehicles (BEVs) such as “driving range anxiety, long battery charging time, and driving safety hazards”, China took the lead in putting forward a “system engineering-based technology system architecture for BEVs” and clarifying its connotation. This paper analyzes the research status and progress of the three core components of this architecture, namely, “BEV platform, charging/swapping station, and real-time operation monitoring platform”, and their key technological points. The three major demonstration projects of the 2008 Beijing Olympic Games, the 2022 Beijing Winter Olympics, and the intelligent and connected autonomous battery electric bus project are discussed to specify the applications of BEVs in China. The key research directions for upgrading BEV technologies remain to be further improving the vehicle-level all-climate environmental adaptability and all-day safety of BEVs, systematically solving the charging problem of BEVs and improving their application convenience, and safeguarding safety with early warning and implementing active/passive safety protection for the whole life cycle of power batteries on the basis of BEVs’ operation big data. BEVs have acquired new technological features such as intelligent and networked technology empowerment, extensive integration of control-by-wire systems, a platform of chassis hardware, and modularization of functional software.
Thermoelectric (TE) generation technology plays an increasingly significant role in a global environment. A desirable approach to improve the efficiency of thermoelectric generator (TEG) is to segment the n- and/or p-leg into several parts with different materials for increasing the average thermoelectric figure of merit of the legs, and to operate with a relatively larger temperature gradient. In this study, a three-dimensional model is developed for the performance analysis of a segmented TEG, and the geometric design optimization of the TEG is examined numerically with the use of the temperature-dependent thermoelectric materials. Specifically, the temperature, heat flow, electric potential, electric current and Joule heating in the thermoelectric modules are investigated in detail. Also, the efficiency and effectiveness of the TEG is analyzed with the design variables such as the ratio of cross-sectional area of p-leg and n-leg, the length ratio of different materials in the segmented leg, and the geometry configurations of p- and n-legs. Furthermore, the effect of the contact resistance on the TEG performance is considered. The results show that a proper design of the geometric parameters can lead to an optimal design of thermoelectric generation systems with higher efficiency.
Water dispensers are considered essential. So, water dispensers that use vapor-compression urgently need more energy-saving and environmentally friendly alternatives. Stirling water dispensers are a suitable option. However, the waste heat generated via friction between the pistons and their cylinders decreases the cooling load and power consumption. The present work uses the waste heat of both piston friction via water jackets to save energy and improve Stirling water dispenser performance. The result indicates that the heating and cooling loads of the present water dispenser are increased by about 2952 W and 834 W using the waste heat of both pistons at 1200 rpm. The increase of water flow rate within water jackets increases the heating and cooling loads due to the increased absorption of frictional heat. The comparison shows that the current water dispenser reveals an average increase in cooling load of up to 400 percent at low speeds and 61 percent at high speeds, and an increase in heating load of up to 390 percent at low speeds and 28 percent at high speeds.
Performance of a thermoelectric generator (TEG) mounted into a channel is analyzed by using double porous cylinders in channel flow with finite element method. COBYLA (Constrained Optimization BY Linear Approximations) algorithm is used to obtain the optimum size and permeability of the porous objects to achieve the highest power. As compared to a non-object channel configuration, the installation of the porous object results in higher power generation. A lower permeability of the double cylinders increases the TEG power while 10.5% increment is obtained when lowest and highest permeability configurations are compared. When sizes of the porous objects are varying up to 19% rise in the TEG power is attained as compared to no-object channel case. The optimum set of parameter to achieve the highest power is obtained as ap1=0.232hz,ap2=0.75hz and Da=10-6. At the optimum conditions, there is 22.5% rise of TEG power when hot side Reynolds number is increased from 200 to 600 while this value is 18% for the no-object case. At the highest nanoparticle loading, 20.5% higher power is obtained at the optimum case when compared to no-object channel case. The optimization assisted computational fluid dynamics (CFD) study of TEG installed channel flow with passive methods is very effective in achieving the best performance as compared to computationally expensive high fidelity multi-parametric CFD. As thermoelectric energy conversion and related devices are used in diverse energy systems technologies including solar-thermal applications, thermal management in different thermal systems, refrigeration and many others, the outcomes and computational methods will be useful for efficient design and optimization studies.
With the current emphasis on electrified vehicles, the use of internal combustion engines (ICEs) as the main propulsion source is challenged, especially for passenger cars. Even though this is not yet the case for freight transportation and the internal combustion engine is still considered the short to mid-term solution, significant improvements in its efficiency and pollutant emissions are required. An energy distribution analysis shows that the internal combustion engine already has two important heat rejection sources representing approximately 65–70% of the energy input: the exhaust gas system (∼35–40%) and the radiator (∼30%). Partially recovering some of this otherwise wasted heat can improve overall thermal efficiency. Compared to other thermal energy recovery methods (Organic Rankine Cycle, mechanical or electrical turbocompounding, etc.), thermoelectric generators have numerous advantages: environmentally friendly, no moving parts, little to no noise and vibration, no working fluids, high reliability (when working temperatures are not exceeded), low maintenance, scalable, modular, ability to operate over a wide range of transient temperature conditions, and the direct conversion of thermal energy into electrical energy. This effort seeks to bring together all aspects concerning the use of thermoelectric generators for internal combustion engine waste heat recovery in a comprehensive overview on the issue while aiding researchers and engineers in the development of efficient systems. This is accomplished by delivering two thorough summaries of both experimental and simulation results including, but not limited to the power output and parasitic losses, as well as the gain in efficiency and reduction in fuel consumption. Furthermore, this effort includes a recap of hot side heat exchanger design (e.g., external shape, internal structure, material, test temperature and gas flow velocity, etc.). As a result, the use of thermoelectric generators installed on the exhaust system and in other regions that can provide heat for power generation (i.e., radiator and exhaust gas recirculation) are fully described.
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.
Thermoelectric (TE) materials have attracted tremendous research interests over the past few decades, due to their application in power generation technology from waste heat, almost without producing any pollution in...
Despite the desirable perks offered by solar thermoelectric generators (TEGs), their efficiencies are nowhere close to those of solar photovoltaic systems. This has limited their large-scale reliance for power generation and competitive market advantage. It has been established that the use of variable area pins (VAPs), and nanomaterials, in place of traditional bulk semiconductor materials, have improved the performance of TEGs. However, more work is still needed to further improve the efficiency of TEGs. Therefore, we model a full nano-enhanced VAP TEG module with 127 thermoelectric pairs in three-dimensions using ANSYS 2020 R2. The shortcomings of the previous studies on VAP TEGs are also discussed and addressed. Results indicate that the power density and efficiency of the nano VAP TEG are 12x and 6x higher than that of the traditional bulk semiconductor VAP TEG, respectively.
The annular thermoelectric generators design facilitates the integration into conventional tubular heat exchangers which could enable their large-scale implementation in waste heat recovery applications for power generation. An analytical model is developed to identify the critical design parameters of annular thermoelectric generators (A-TEGs) integrated in heat exchangers. These parameters are found to be the diameter ratio, the P-to-N thickness ratio, and the fill ratio. The diameter and fill ratios are found to have a significant impact on the performance of the A-TEG system while the power output nearly plateaued at thickness ratios higher than 1.1. A novel dimensionless design factor (β) is proposed to guide the design optimization of the A-TEG system for maximized power generation. This design factor combines the diameter and fill ratios of the A-TEG design to define the locus over which the power output from the A-TEG system is always maximized. A detailed analytical model is developed and validated to simulate an A-TEG integrated heat exchanger for the purpose of optimizing the A-TEG design using the design factor (β). A parametric case study shows that at the optimum design factor, the material volume of the A-TEGs can potentially be reduced by 75% by decreasing the diameter and fill ratios with a reduction in the maximum power of only 11%. The study findings provide a useful tool to guide the efficient and cost-effective design of A-TEGs for waste heat recovery applications.
Recently, several kinds of variable cross-section legs have been reported to improve the performance of thermoelectric generators (TEGs). This work further proposes an optimization study to maximize the output power of variable cross-section TEGs for solar energy utilization by coupling finite element method (FEM) and optimization algorithm. Six geometric variables along with the external load resistance are optimized by genetic algorithm (GA) and particle swarm optimization (PSO). Besides, Joule heating, Peltier effect, and Thomson effect are considered in the numerical model to improve the simulation accuracy. Optimization results show that distributions of the thermal resistance and the electrical resistance are significantly changed when the volumes of thermoelectric material remain constant. The optimized leg shape increases the temperature gradient in the high figure of merit (ZT) region by reducing the cross-section area. Although internal resistances of optimal TEGs are greater than those of rectangular TEGs, the improvement in electromotive force results in the enhancement of electrical performance. At heat flux of 35000 W m⁻², 40000 W m⁻², 45000 W m⁻², and 50000 W m⁻², temperature differences of optimal TEGs are increased by 12.77%, 18.36%, 41.93%, and 73.14%, while output powers are improved by 1.45%, 2.13%, 9.33%, and 20.13%, respectively.
A R T I C L E I N F O Keywords: Thermoelectric generator Plate and square pin fins Waste heat recovery Source term Computational fluid dynamic Compromise method A B S T R A C T How to improve the performance of thermoelectric generators is an important issue to recover waste heat and convert it into green power, which is conducive to practicing net-zero carbon dioxide emissions. The heat transfer and power generation of a thermoelectric module (TEM) under the influence of fin installation is investigated by three-dimensional fully numerical simulations where vehicle exhaust waste heat is harvested. This study considers a TEM in a hot channel without fins as well as with plate fins and square pin fins, while a cold channel is used to cool the TEM. The results show that installing plate fins or square pin fins can drastically intensify waste heat harvest, and the optimal number of square pin fins is 78 which increases the output power of the TEM by 24.14% compared to the plate fins. A compromise method in terms of heat flow rate ratio and heat flow rate ratio per unit area of square pin fins is conducted, which simultaneously considers the TEM's output power and material cost. As a result, it is found that the optimal number of square pin fins is 54. The influences of the temperature and mass flow rate of the hot fluid on TEM performance are also evaluated, and the results indicate that the former has a pronounced impact whereas the latter is relatively unimportant. Installing more square pin fins gives rise to a higher pressure drop. Nevertheless, the net output power of the TEM increases with increasing the number of square pin fins and the highest value occurs at 78.
Low-temperature waste heat has great potential for renewable power because it accounts for around 60% of total industrial waste heat. This study develops a model of integrating thermoelectric generation, computational fluid dynamics, and plate fins to figure out a low-temperature waste heat recovery system for power generation. The effect of the number of partitions of a thermoelectric module on its performance is examined, and the results show that a single module without a partition can provide accurate predictions. Four different combinations between wastewater and air in the hot and cold channels under three different Reynolds numbers (i.e., Re = 10, 100, and 1,000) on thermoelectric modules’ performance suggest that only combining hot wastewater and cooling water can contribute electricity to a certain extent. By installing fins with a number range of 0–27, it indicates that fin installation can dramatically intensify heat transfer and thermoelectric modules’ performance. The optimal number of fins at Re = 10 and 100 is 21, whereas it is 27 at Re = 1,000. The maximum total output power and mean conversion efficiency are 0.411 W and 0.95%, respectively, with 27 fins at Re = 1,000. These values account for 105.5% and 43.94% improvements when compared to the TEMs without fins. Even though installing fins increases the pressure drop in the channel, its value is much smaller than the generated power (less than1%). The developed method in this study can be used to efficiently and accurately predict the performance of thermoelectric modules, and obtained results have provided practical insights into the design of low-temperature waste heat recovery systems for green power generation.
Low heat transfer performance in the exhaust channel limits the thermoelectric conversion efficiency of the internal combustion engine exhaust thermoelectric generator. Enhanced heat transfer of exhaust channel improves the thermoelectric performance of the generator, though with an increase in exhaust back pressure. A new type of thermoelectric generator with heat transfer fluid circulation is proposed. A heat transfer fluid replaces the exhaust after heat exchange with the exhaust into the generator. It is possible to improve the thermoelectric performance of the system, counting on the high heat transfer coefficient of the heat transfer fluid in the generator without changing the exhaust channel. A mathematical model of the novel system is constructed, considering the system structure, resistance power consumption, temperature dependence of the physical properties of the module. The influence of structural parameters and heat transfer fluid parameters on thermoelectric performance are analyzed using this model. It is found that the peak net output power of the new generator can be increased by 77.5 % compared with the traditional generator, while the number of modules can be reduced by 83.2%. Therefore, an optimal exhaust heat exchanger configuration is obtained to maximize the net output of the system. In addition, as the heat transfer fluid flow rate increases, the net output power goes up and then down, an optimal heat transfer fluid flow rate can be obtained. The results also give technical guidance on the design and operation criteria of the thermoelectric generator.
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.
The present study aims to achieve the highest cumulative yield of pyramid solar distillers. To achieve this, a new combination of several effective modifications was made to the design of the pyramid distillers. This novel combination of the effective modifications includes: coated the absorber surface with CuO nano black paint, reflective mirrors, and phase change material with pin fins. To illustrate the influences of this novel combination on a cumulative yield of pyramid distillers. Two pyramid distillers were designed and tested under the same weather conditions, namely; modified pyramid solar distiller (MPSD) with a novel combination of effective modifications and conventional pyramid solar distiller (CPSD) (reference case). The experimental, energy, and exergy analysis are also studied in this work. The experimental results presented that the utilization of this novel combination of effective modifications represents a very effective option to achieve the highest performance. The cumulative yield achieved by CPSD varying between 4085-4171 mL/m²/day, while the utilization of this novel combination of effective modifications was improving the cumulative yield to 9885–10015 mL/m²/day with 140.1–142% improvement compared to CPSD. Also, the daily thermal and exergy efficiencies of MPSD were improved by a rate varying between 138.1-140.1% and 243.6–252.9%, respectively compared to CPSD.
In this paper, a novel fluid-thermal-electric multiphysics numerical model is presented to predict the performance of a thermoelectric generator system applied in automobile waste heat recovery. The model considers the complete geometry, temperature-dependent material properties, topological connection among thermoelectric modules, and impedance matching, which can simulate the actual working conditions. Numerical simulations are carried out on the COMSOL platform combined with the exhaust temperature and exhaust mass flow rate under different vehicle speeds. In addition, the detailed physical field distribution characteristics of the automobile thermoelectric generator system, as well as the variations of output power, conversion efficiency, power losses, and net power with vehicle speed, are obtained. The position of thermoelectric modules on the hot side heat exchanger plays an important role in output uniformity, and the higher the vehicle speed is, the more uniform the output will be. At the vehicle speed of 120 km⋅h⁻¹, the output power and conversion efficiency of the automobile thermoelectric generator system are 38.07 W and 1.53% respectively. Considering the weight power loss and coolant pumping power loss, the net power is 23.66 W. This work fills the gap in evaluating the performance of automobile thermoelectric generator systems at different vehicle speeds comprehensively.
In this work, pin fin and plate heat sinks were investigated in terms of natural convection and radiation heat transfer by experimental means. One rectangular base plate and eight pin fin and plate heat sinks were manufactured particularly for this study. Eight different pin fin and plate heat sinks had four different pin fin numbers and hence pin fin spacings; and two different pin fin heights. Three different orientations of 0°, 90° and 180° were tested. Ten different constant heating rates were applied to heat sinks during tests, corresponding to Rayleigh number interval between 1 × 10⁶ and 7 × 10⁶. Heating powers were changed between 5 and 50 W by 5 W increments by means of DC electrical power source. All cases were compared with each other. Results were evaluated by calculating heat transfer indicators from experimental measurements, dependent Nusselt and Rayleigh numbers, and by drawing their corresponding graphics. It was detected that increasing pin fin number up to a threshold value increases thermal performance. After the threshold pin fin number, thermal convection coefficient decreases significantly. Up to the favourable highest pin fin number, the reason of thermal performance enhancement is due to increasing surface area without deteriorating thermal convection coefficient significantly. It is also seen that extended surface area by increasing number of pin fins partly compensates the reduction in thermal convection coefficient up to a level. However, increasing pin fin number further degrades heat transfer performance. Results show that the highest heat transfer is achieved by 121 × 40 pin fin and plate heat sink for all three orientation angles. The lowest heat transfer performance is realized by non-pinned plate. When plate orientation is considered, the highest heat transfer is achieved with upward facing orientation which has 0° orientation angle value, and the lowest heat transfer rate is realized with downward facing heat sink which has 180° orientation angle value. Therefore, it is concluded that inline pin fin and plate heat sinks are best used with upward orientation with optimum number of pins. Experimental dataset was analysed in terms of parametrical effects and accordingly empirical correlations expressions were composed and proposed.
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.
Exhaust gas recirculation (EGR) is one of the most measure to decrease NOX emissions in the cylinder. CO2 was introduced to intake charge as a simulated EGR (CO2), the combined effects of excess air ratio and EGR rate on combustion and emissions behaviors of a gasoline direct injection (GDI) engine with simulated EGR (CO2) at low load were analyzed and compared to assess the difference between actual EGR and simulated EGR (CO2). The results show that EGR slows combustion, and simulated EGR (CO2) deterioration combustion is weaker than actual EGR. The peak cylinder pressure, heat release rate and cylinder temperature of simulated EGR (CO2) all increase and their phases all advance compare to actual EGR under the same EGR rate and excess air ratio. Combustion center and combustion duration for simulated EGR (CO2) delay slowly with EGR rate at any excess air ratios. Simulated EGR (CO2) can significantly improve the COVimep of the engine. For actual EGR rate > 10% and excess air ratio of 1.2, the COVimep sharply increases. Simulated EGR (CO2) has a little effect on CO emission at lean-burn condition, and on HC emission at stoichiometric condition. The NOX and soot emissions decrease significantly with EGR rate under different forms of EGR and excess air ratios. At a fixed EGR rate, the soot emissions of simulated EGR (CO2) is higher than that of actual under any excess air ratios. Added 10–15% CO2 to intake charge, CO2 as simulated EGR (CO2) can be well applied in GDI engine.
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.
This study addresses the combined effects of the location and porosity of a flow straightener on the waste heat recovery performance of a thermoelectric generator (TEG). An exhaust gas channel was built for the flexible placement of a flow straightener with varying porosity in the range of 0.121–0.516 at five different locations. Customized thermoelectric modules were placed between the exhaust gas channel and two coolant channels for waste heat recovery. A diesel engine releases the exhaust gas flow into the exhaust gas channel of the TEG placed in the middle of the tail pipe. Experimental results showed that a TEG design in which a flow straightener is positioned near the inlet of the TEG needs to be avoided because of a low power output to pressure loss ratio. The net power output, energy conversion efficiency, and pressure drop characteristics were enhanced as the location of flow straightener moved rearward of the TEG. A friction factor correlation was also proposed for predicting pressure drop characteristics of TEGs equipped with a flow straightener to improve their practicality in industry and engineering fields.
The flow and heat transfer characteristics of different surface texture pin fins were experimentally investigated. The pin fin outer surface texture has been modified to different threaded surface texture (i.e., Metric, Worm, ACME, Buttress, Sharp V, Whitworth and square thread) without changing cross-sectional areas. The Reynolds number based on hydraulic diameter was varied from 2500 to 4500. This study reveals that threaded surface pin heat sink is 18.13% higher heat transfer than plain pin heat sink. In terms of specific performance consideration, threaded surface textures pin fins shows impending substitute design to plain circular pin fins. The threaded surface texture pin has decreased aerodynamic consequence compared to plain circular pin. The pressure drop across heat sink is 21.4% lesser in plain pin heat sink than screw surface pin heat sink. The thermal resistance difference between experimental and CFD analysis is 4.08%. The threaded texture increases surface area, flow turbidity and delays flow separation and these factors enhances the heat transfer.
The performance of the thermoelectric‐based waste heat recovery (WHR) system in an automobile greatly depends on the amount of heat extracted by the exhaust heat exchanger (EHE). In the present study, the thermohydraulic performance of the EHE having twisted ribs and the pressure drop across the entire heat exchanger have been experimentally investigated. The experiments were repeated for the various geometric parameters such as twist ratio (4‐8), angle of attack (30°‐90°), and pitch ratio (6‐10) on the Reynolds number within the range of 2300 to 25,000. The heat transport and fluid flow characteristics were compared with an internally smooth EHE using the thermohydraulic performance parameter. The maximum heat transfer rate was improved at 164.22%. However, the specification of the twisted rib for superior performance has been obtained at twist ratio of 4 and pitch ratio of 8 with 60° angle of attack. The highest thermohydraulic performance parameter value revealed as 1.93 at the same configuration. With the change in twist ratio, the pitch ratio, angle of attack, and the heat transfer rate increased by 39.52%, 60.85%, and 40.70%, respectively. Thus, the efficient heat transfer with the twisted rib would improve the extent of WHR in automobiles.
Structure-based optimization is an effective approach to improve the performance of thermoelectric generators. Aiming to increase the heat transfer and hot side temperature of the heat exchanger, a converging heat exchanger design is developed in this study. Furthermore, a multiphysics fluid-thermoelectric coupled field numerical model is proposed, which is used to perform comprehensive numerical simulations to evaluate the behaviour of the thermoelectric generator system. The results indicate that the converging thermoelectric generator system generates a higher output power, induces a lower backpressure power loss, and has a more uniform temperature distribution than the conventional structure. The output power of the converging thermoelectric generator system is approximately 5.9% higher than that of the conventional system at an air temperature of 550 K and an air mass flow rate of 60 g/s. Moreover, the power increment provided by the converging design increases with increasing air temperature and decreasing air mass flow rate. The maximum deviation in the output power between the numerical and experimental results is 2.4%, which validates the performance of the multiphysics fluid-thermoelectric coupled field numerical model. This work provides new insights for numerical investigations of thermoelectric generator systems and presents a novel concept for optimizing the exhaust gas channel of a heat exchanger.
Thermoelectric geometry and structure optimization are vital research areas which are being explored extensively in recent years due to significant performance enhancement achieved. However, the lack of a single review paper on this key area is a huge gap identified. Therefore, this review presents a first of its kind in-depth analysis of the start of art in thermoelectric geometry and structure optimization. The four main parameters including leg length or height, cross-sectional area, number of legs and leg shape which are paid attention to during optimization of thermoelectric geometry are discussed in detail. In addition, a review of the different thermoelectric structure available in literature such as flat plate, annular, segmented, cascaded, corrugated, concentric, linear, flexible and micro thermoelectric generators and coolers is presented. Furthermore, special attention is paid to both electrical and mechanical performance enhancement obtainable from thermoelectric geometry and structure optimization. A review of thermal stress optimization is presented alongside other optimization including contact resistance, heat pipe, pulsed heating and cooling. Geometry and structure optimization methods including three-dimensional finite optimization and multi-objective optimization are discussed in detailed and the most significant results obtained from the literature review are presented. This comprehensive review will be a valuable and essential reference literature on all issues relating to thermoelectric geometry and structure optimization.
Optimizing the geometry structures and operating conditions is an effective way to improve the performance of the segmented thermoelectric generator (STEG). A one-dimensional numerical model combined with genetic algorithm (GA) is presented for performance analysis and design optimization of the STEG. The model's predictions being in good agreement with experimental data in the published literature confirms the accuracy of the model. According to the compatibility factors, the Ba0.4ln0.4CoSb12, Bi2Te0.7Se0.3, Zn4Sb3 and Bi2Te3 are selected as materials for segments of N1, N2, P1, and P2, respectively. The p-segmented TEG is recommended through performance comparison between STEGs with four different structures. After that, the load following region and rated operating point are given, through load following characteristic analysis. At last, the effect of contact resistance on the performance of the STEG is analyzed. The analysis results show that, by reducing the contact resistance to 50 μΩ cm² per leg, the peak conversion efficiency of the p-segmented TEG proposed in this paper can reach 9.83% at a temperature difference of 350 K, which is 25.4% higher than that of traditional thermoelectric generator.
Based on the definition of numerical-type equivalent thermoelectric parameters through developing a 1D self-consistent numerical method, this paper established a novel coupled electrical-thermal impedance matching (CETIM) model for prediction of the maximum output power and the highest conversion efficiency of thermoelectric generator (TEG). CETIM model could highlight the impacts of thermal working conditions and temperature-dependent properties on the TEG performance. It also clarifies the unreasonable assumption of the impedance matching conditions in the literature, which would lead to underestimation by 10.9% for the maximum output power prediction under a large thermal resistance between TEG and heat reservoirs. The analytical expressions of the output power and conversion efficiency obtained through CETIM model were used to derive the single- and two-parameter geometry optimization models, which could be quickly and accurately solved without needing the complicated optimization methods. It is found that the two-parameter optimization model could lead to a higher output power compared with that based on the single-parameter model, such as the observed improvement by 27.8% for the maximum output power and 21.6% for the corresponding conversion efficiency, respectively. Impacts of the coupled thermal-electrical working conditions and geometric sizes on the TEG performance were also investigated in detail. The results indicated that decreasing the thermal resistance between TEG and heat sink could acquire a larger output power and conversion efficiency compared with that through reducing the thermal resistance between TEG and heat source, such as increase by 15% for the output power and by 4% for the conversion efficiency, respectively. The present study provides an accurate and time-efficient comprehensive modeling tool for geometric optimization of TEG, which was implemented by MATLAB open source codes presented in supplementary materials.
The total power output of a thermoelectric generator system can be increased by enhancing the heat transfer performance of its hot-side heat exchanger. However, heat transfer enhancement is usually accompanied by the consumption of additional pump power. Therefore, it is unclear whether the net power output, that is, the difference between the total power output and the pump power, increases. Developing a comprehensive evaluation method based on the net power output is necessary to determine the heat transfer enhancement effect on performance improvement of the system. In this paper, the concept of net power ratio which integrates the total power output and the pump power consumption was proposed to evaluate the heat transfer enhancement effect on the performance improvement of a thermoelectric generator system. Based on a ring-shaped thermoelectric generator, the analytical solution of the net power ratio was theoretically derived. Compared with the numerical and experimental methods, the proposed net power ratio in a thermoelectric generator system is convenient and time-saving with adequate accuracy for engineering applications. Moreover, the application of net power ratio in a real thermoelectric generator system was investigated by case studies. Results show that both the inlet fluid temperature and the mass flow rate affect the net power ratio. When using net power ratio to evaluate the performance improvement of a thermoelectric generator system, net power should also be considered to obtain optimal working conditions for a thermoelectric generator system.
Thermoelectric module can be used as a generator to convert thermal energy into electricity, or as a cooler to convert electricity into heat. In this work, a comprehensive model is proposed to predict the performance of thermoelectric generator and cooler by setting different boundary conditions. Based on the proposed model, the influences of height, cross-sectional area, number of couples, ceramic plate, and heat loss on the generator and cooler are investigated. To balance the output performance and cooling performance of thermoelectric modules simultaneously, a comprehensive study on the thermoelectric module is conducted. The results indicate that (i) A relatively lower leg height enables the enhancement of output power, cooling power, and COP, despite a slight reduction in conversion efficiency; (ii) When increasing the total cross-sectional area of legs, thermoelectric generator should aim at adopting more thermoelectric couples, whereas the cooler should apply a larger area for every single leg; (iii) For the optimization of ceramic plates, more attention should be paid in improving the thermal conductivity. Also, fillers are not recommended for thermoelectric module in general environment. The findings of this work may guide the design and parametric optimization of thermoelectric module used for both power generation and cooling.
In this study, numerical analysis of forced convection in a thee dimensional pipe with elliptic cross-section is considered by using CNT-water nanofluid as working fluid. Three dimensional steady flow and heat transfer equations with k- ϵ turbulence model is solved by using finite element method. Effects of aspect ratio of elliptic cross-section and solid nanoparticle volume fraction on the heat transfer performance were analyzed. An experimental validation of the numerical study was performed and comparisons were made with other existing correlations for turbulent flow in a pipe. It was observed that significant enhancements in the heat transfer rate are achieved with the use of CNT nanoparticles which are in the range of 59% to 84% depending on the mass flow rate. The average Nusselt number deteriorates for higher values of aspect ratio in turbulent three dimensional configuration while the trends are similar for fluid and nanofluid. When the aspect ratio enhances from 0.5 to 1.67, approximately 53% reduction of average Nusselt number is obtained both for water and for nanofluid. Finally, a practical modeling strategy for estimating the average Nusselt number is proposed which uses linear interpolation among polynomial model coefficients for water and for nanofluid at the highest solid particle volume fraction.
In this study, thirty of customized bismuth-telluride (Bi2Te3) thermoelectric modules (TEMs) were fabricated for waste heat recovery of a diesel engine using a thermoelectric generator (TEG). By installing a plate-type porous medium whose porosity ranges from 0.121 to 0.516 in the TEG, the effects of the porosity on energy harvesting performance were investigated. Experimental results show that at the highest engine rotation speed of 1400 rpm, a maximum power output of 98.3 W was obtained using the lowest porosity (0.121), and a maximum energy conversion efficiency of 2.83% was obtained using the optimal porosity (0.416). The most significant improvements in the power output and conversion efficiency compared with the base case without porous media were 44.5% and 10.1% with porosities of 0.121 and 0.416, respectively, at the lowest engine speed of 1000 rpm. We concluded that the conversion efficiency and power output of the present TEG can be maximized via application of porous media with porosities of 0.461 and 0.32, respectively. The use of a porous medium with a porosity of <0.32 in the present TEG configuration should be avoided, as the backpressure would exceed the allowable limit of ~3 kPa for a passenger vehicle.
Thermoelectric module (TEM) has been widely used to recover the waste heat contained in the fluid. However, its performance will be limited since all the thermoelements are connected in serial and the generated current each of them is not the same. To work out this deficiency, a novel TEM structure is disclosed, where the cross-sectional area of thermoelements is increasing gradually along with the hot fluid downward flow. Besides, this work develops a steady-state, three-dimensional and fluid-thermal-electric multi-physical model to evaluate the TEM performance. Based on the numerical results, the influences of different TEM structures, hot air temperature and mass flow rate on the TEM output performance are investigated. The results show that (i) Compared to conventional TEM, the novel TEM structure with the same quantity of thermoelectric material can reach a better performance when ΔW=0.01mm or 0.02mm, and the higher temperature and mass flow rate, the more gains of the novel TEM; (ii) Compared with temperature, mass flow rate has a much higher effect on the output performance of the novel TEM structure; (iii) The maximum output power occurs when the load resistance is slightly greater than internal resistance. Apart from that, the verification experiments are conducted and the results indicate a good agreement of the proposed numerical model. The findings of this work may provide a new idea to optimize the TEM structure and improve its performance.