Two-stage Thermoelectric Generator Research Articles

Graphene thermionic energy converter integrated with two-stage thermoelectric generator for energy cascade utilization

For the purpose of energy cascade utilization, a new coupling system consisting of a graphene-based thermionic energy converter and a two-stage thermoelectric generator is proposed, in which the waste heat of graphene-based thermionic energy converter is recovered by the two-stage thermoelectric generator for generating extra power. Based on thermionic emission, semiconductor physics, and non-equilibrium thermodynamics, mathematical equations for power, efficiency, and exergy efficiency of the coupling system are presented, and the general performance features of the hybrid system are revealed. Numerical analysis shows that the maximum efficiency, maximum power density, and maximum exergy efficiency of the coupling system are 54.99%, 7.93Wcm−2, and 68.75%, respectively. Moreover, the maximum efficiency and maximum power density of the coupling system are enhanced by 28.39% and 28.52%, respectively, and the maximum exergy efficiency is improved by 28.39% compared to the stand-alone graphene-based thermionic energy converter. Subsequently, comprehensive parametric analyses are carried out to derive the effects of the heat source temperature, Fermi level of graphene, cathode work function, semiconductor element area-length ratio, and the Thomson effect on the performance of the coupled system. The obtained results may be useful for the design and running of this kind of energy cascade utilization system.

Innovative design for thermoelectric power generation: Two-stage thermoelectric generator with variable twist ratio twisted tapes optimizing maximum output

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.

Dynamic performance optimization of two-stage thermoelectric generator: Impact of different geometric leg shapes in each stage

This study presents a single-stage and two-stage thermoelectric generator (TEG) with different geometric shapes of the legs (rectangular, trapezoidal, inverted trapezoidal, rhomboid, and hourglass shapes). The various geometric shapes of the legs are combined between the two stages using phase change material (PCM) to cool the generator. The study's objective is to determine the optimal dynamic behavior of the TEG through the geometric design of the legs. The results show the behavior of the efficiency, the generated voltage, and the time it takes for the PCM to melt. The legs of the optimal two-stage system, Rhomboid-Rhomboid (G) and Trapezoidal-Inverted Trapezoidal (B), with a relationship γT=4, reach the best efficiency of 3.88% and 3.9% for the first and second stages, respectively, applying a heat flow of Qh=0.1W. On the other hand, the single-stage rhomboid system achieves the same maximum efficiency as the two-stage rhomboid system (G system), which is 3.9%. The temperature difference of each module is almost the same as that of the single-stage system. However, the voltage generated by the two-stage TEG is higher, and the efficiency remains practically constant compared to the single-stage system, which decreases with time. The effect of PCM's phase change process on TEG performance is analyzed, considering the characteristic heat transfer of PCM.

Optimization and comparison of two-stage thermoelectric generators considering the influence of temperature variation on materials for waste heat utilization

Thermoelectricity technology, as a kind of cost-effective and pollution-free power generation solution, is often used for waste heat recovery and utilization. In this paper, the temperature distribution of a Two-stage Thermoelectric Generator (TTEG) under constant temperature conditions has been studied using a one-dimensional heat conduction model. Moreover, by combining the obtained temperature distribution with the three-dimensional size of TTEG, a calculation formula of resistance and voltage was developed based on the calculus method. When the sum of cross-sectional areas of all the PN-type thermoelectric arms respectively in high- and low-temperature layers is constant, the optimal ratio between cross-sectional areas of a single PN-thermoelectric arm respectively in high- and low-temperature layers can be calculated using the proposed formula in this study to achieve the maximum output power. Results also showed the relationship between the heights of PN-type thermoelectric arms and the temperature distributions in high- and low-temperature layers. Using PbTe as the medium temperature thermoelectric material and Bi2Te3 as the low temperature thermoelectric material, a case study was conducted on the PN-type thermoelectrics with the same total height and the same total cross-sectional area. The theoretical calculation results showed that the bigger of maximum output power between the two-stage thermoelectric generator and that of the Segmented Thermoelectric Generator (STEG) is related to the hot and cold end temperature.

Performance optimization for a novel two-stage thermoelectric generator with different PCMs embedding modes

In this study, a novel two-stage TEG with different phase change materials (PCMs) embedding modes is proposed to improve the efficiency of TEG systems. The output power and electrical energy of single-stage and two-stage TEG combined with different PCMs is firstly compared at the limit of total length of the PCM containers. Furthermore, the effect of different PCMs embedding modes, including arranged at the heat source side, between two TEGs and heat sink side, on the performance of two-stage TEG system was discussed. Finally, the amount of different PCMs arranged at different locations was optimized. The results showed that although application of high temperature PCM on the heat source side can alleviate the effect of heat source fluctuations to provide more stabilized output power, the total electrical energy is seriously reduced in the two-stage TEG system. Compared with the single-stage TEG system, the two-stage TEG system provides a much higher output power and electrical energy, in which the harvested total electrical energy of the optimum two-stage TEG system is increased by 44.8% with a conversion efficiency of 6.9%. These results are of great significance to the design of advanced TEG system for waste heat recovery.

A two-stage sodium converter coupled to a two-stage TEG: Parametric optimization

The aim of this study is to deeply study and analysis of energetic performance of the novel coupled system composed of a two-stage sodium thermal electrochemical converter and a two-stage thermoelectric generator. The main methods are to establish the model of the coupling system by considering the main irreversibilities, and obtain the analytical expressions of the power outputs and efficiencies of two subsystems and coupling system. The main novelties are to obtain the optimum ranges of critical parameters of the coupled system and give the reasonably matching conditions between the subsystems. The main contents of this study include that the influences of the intermediate and condenser temperatures of the sodium thermal electrochemical converter and current density of the first stage sodium thermal electrochemical converter as well as the electric current of the two-stage thermoelectric generator on the efficiency and power output density are discussed and the maximum power output density and efficiency of the system are calculated and compared with those of the single two-stage sodium thermal electrochemical converter and the existing coupling models. Results show that the maximum efficiency and maximum power output density of the coupled system attain 0.413 and 68.7×103 W m−2 and exhibit an improvement of about 14.1% and 66.7% than those of the standalone two-stage sodium thermal electrochemical converter respectively, and the maximum efficiency of the whole system increase 37.7% compared with that of the existing coupling system. The results obtained indicate that the performance of the proposed system is greatly improved by efficient the exhaust heat utilization. In addition, the multi-objective and multi-parametric optimization analyses are adopted to search for the global optimization profile and validate the obtained findings.

Performance assessment of a molten hydroxide direct carbon fuel cell-based hybrid system coupled with a two-stage thermoelectric generator

A new hybrid system model is proposed to harvest the waste heat produced by a molten hydroxide direct carbon fuel cell (MHDCFC) for additional electricity production via a two-stage thermoelectric generator (TTEG), in which the TTEG considers Thomson effect combined with Peltier, Joule and Fourier heat conduction. Mathematical expressions for the energy efficiency, power output, exergy efficiency and exergy destruction rate of hybrid system, MHDCFC and TTEG are analytically obtained by considering the polarization losses in MHDCFC, regenerative losses, heat-conduction losses and Joule heat in TTEG, and heat leakage from MHDCFC to environment. The energetic and exergetic performance features and the optimum operating ranges for the MHDCFC/TTEG hybrid system are revealed. The attainable maximum power output density and the corresponding energy efficiency and exergy efficiency of the proposed hybrid system are, respectively, 55.4 %, 8.7 % and 8.8 % greater than that of a standalone MHDCFC, while the exergy destruction rate is decreased by 7.2 %. In addition, the effects of some decisive operation conditions and design parameters on the MHDCFC/TTEG hybrid system performance are studied.

Maximum Efficient Power Performance Analysis and Multi-Objective Optimization of Two-Stage Thermoelectric Generators.

Two-stage thermoelectric generators have been widely used in the aerospace, military, industrial and daily life fields. Based on the established two-stage thermoelectric generator model, this paper further studies its performance. Applying the theory of finite-time thermodynamics, the efficient power expression of the two-stage thermoelectric generator is deduced firstly. The maximum efficient power is obtained secondly by optimizing the distribution of the heat exchanger area, distribution of thermoelectric elements and working current. Using the NSGA-II algorithm, multi-objective optimizations of the two-stage thermoelectric generator are performed thirdly by taking the dimensionless output power, thermal efficiency and dimensionless efficient power as objective functions, and taking the distribution of the heat exchanger area, distribution of thermoelectric elements and output current as optimization variables. The Pareto frontiers with the optimal solution set are obtained. The results show that when the total number of thermoelectric elements is increased from 40 to 100, the maximum efficient power is decreased from to . When the total heat exchanger area is increased from to , the maximum efficient power is increased from to . The deviation indexes are 0.1866, 0.1866 and 0.1815 with LINMAP, TOPSIS and Shannon entropy decision-making approaches, respectively, when multi-objective optimization is performed on three-objective optimization. The deviation indexes are 0.2140, 0.9429 and 0.1815 for three single-objective optimizations of maximum dimensionless output power, thermal efficiency and dimensionless efficient power, respectively.

A new molten carbonate fuel cell hybrid power generation system using two-stage sodium thermo-electrochemical converter/two-stage thermoelectric generator: Performance analysis and multi-objective grasshopper optimization

To enhance the poor power density of the molten carbonate fuel cell, a novel combination of two-stage sodium thermo-electrochemical converter and a two-stage thermoelectric generator is introduced to recover the heat waste of the molten carbonate fuel cell for further power generation. The performance criteria of the hybrid system in terms of power outputs, efficiencies, exergy destruction, and cost rate are mathematically derived and analyzed using energy, exergy, and exergoeconomic methods. Finally, the grasshopper multi-objective optimizer and decision-making procedures are applied to find the maximum power density and exergy efficiency for the hybrid system with the minimum power density cost rate. It is found that the preferable optimum operation of the system provides the highest power density of 2652.1 W/m2 with 53.96% and 57.58% energetic and exergetic efficiencies which are 42.28% and 38.89% larger than the individual molten carbonate fuel cell, respectively. Moreover, the minimum power density cost rate is calculated by 1.13 $/h m2, indicating a 26.14% improvement compared to the design condition and a 0.51 $/h m2 increase relative to the sole molten carbonate fuel cell. The results suggest that the present system is a favorable alternative to other hybrid systems.

Energy and exergy analysis of an integrated photovoltaic module and two-stage thermoelectric generator system

• The PVM-TTEG hybrid system is analyzed by energy and exergy. • The effectiveness and feasibility of the proposed hybrid system are proved. • The impact of Thomson effect on the hybrid system performance is investigated. • The effects of the key parameters on the performance of the hybrid system are revealed. To fully utilize the solar energy captured by the photovoltaic module (PVM) and improve its performance, a coupled system consisting of a PVM, the solar selective absorber (SSA) and the two-stage thermoelectric generator (TTEG) is investigated, where the TTEG considers the Peltier effect, Seebeck effect and Thomson effect. Taking account of the various irreversible losses within the coupled system, the mathematical expressions of energy conversion efficiency, power output, exergy efficiency and exergy destruction rate of the coupled system are established. The numerical results show that the maximum energy efficiency and maximum output power of the coupled system are, respectively, increased by 9.89% and 9.87% compared with a standalone PVM, and the maximum exergy efficiency is 10.4% higher than a standalone PVM. Finally, through sensitivity analysis, it can be seen that the coupled system is affected by several key parameters, including the diode ideality factor, thermoelectric elements, solar irradiance, and PVM operating temperature, so the coupled system can be improved by adjusting these parameters. The results of this paper may provide a new insight into the design and optimization of an actual coupled system.

Exergy analysis and optimisation of a two-stage solar thermoelectric generator with tapered legs

Numerous previous studies indicate that the performances of thermoelectric generators are enhanced by incorporating legs with variable area geometries. However, there is a dearth of comprehensive optimisation studies on these new thermoelectric generator designs. More so, the few optimisation studies that exist have rather employed unrealistic isothermal boundary conditions in their numerical models. Furthermore, these new leg geometries have not been applied to multi-stage systems. Accordingly, to address these gaps, a numerical optimisation, using ANSYS 2020 R2 software, is performed on a two-stage thermoelectric generator with variable area leg geometries; with optimisation parameters that include: leg geometry (height and area), intensified insolation with external load resistance, i.e., geometrical, thermal and electrical operation of the device. An exergy/irreversibility analysis is also carried out and techniques of minimising thermodynamic losses while allowing for the useful exergy output after solar energy conversion are proposed. Results indicate that, for an optimum leg height, area, concentrated solar radiation intensity and load resistance of 10 mm, 0.7 mm2, 20 suns and 1.3 Ω, respectively. Maximum energy and exergy efficiencies of 7.03% and 7.55% respectively, were obtained for the proposed system. This improves the energy and exergy efficiencies of the standard device by 23.44%.

Exergy analysis and optimisation of a two-stage thermoelectric generator with tapered legs

Exergy analysis and optimisation of a two-stage thermoelectric generator with tapered legs

Experimental investigation of factors affecting two-stage thermoelectric generator integrated with phase change materials

In light of limitations in the performance of thermoelectric materials, this study proposes a two-stage thermoelectric generator (TEG) system integrated with phase change materials (PCMs). Three sets of experiments were designed to investigate the factors influencing the proposed TEG-PCM system. Two of them examined the effects of different heat sink configurations on the heat generated with and without paraffin wax as the PCM. The third experiment investigated the thermoelectric performance of the proposed system using a single-cavity heat sink with different PCMs. The results show that the heat source had a greater influence on the performance of the system than the thermal resistance of the heat sink. The PCM reduced the second-stage voltage, but it lasted for a long time. The configuration of the heat sink had a greater influence on the second-stage voltage (U2) than the first-stage voltage (U1). Although the mean value of U1 for the four-cavity configuration without PCM was slightly larger than that of the single-cavity configuration by 10 mV, the maximum value of U2 for the latter was larger than that of the former by 60 mV. The single-cavity configuration is thus more suitable for the two-stage TEG system. Under a 10 W power supply, the properties of different PCMs significantly influenced the duration of voltage in each stage while U1 was maintained at 600 mV. The results show that the factors considered here influenced the performance of the two-stage TEG-PCM system in the order of heat source > thermal resistance of the heat sink > type of PCM.

Effects of different electrical arrangements and Thomson effect on the system performance as well as the optimum allocation of thermocouples in a self-driven two-stage TEC & TEG

In this study, four different electrical arrangements of a two-stage thermoelectric cooler (TEC) driven by a two-stage thermoelectric generator (TEG) are analyzed, and the best combination is identified in terms of maximum cooling capacity and coefficient of performance (COP). The results demonstrate that the inclusion of the Thomson effect increases the maximum COP and cooling capacity and shifts the optimum thermocouple ratio towards a lower value. Simple regression equations are developed for quick and accurate prediction of optimum thermocouples ratio for maximum cooling capacity and maximum COP conditions. As observed, the optimum thermocouple ratio is a strong function of total thermal conductance, source and sink temperatures, thermocouple ratio in stages of TEG and TEC and the type of electrical arrangement. The best combination is further confirmed by analyzing the variation of exergetic efficiency with the total thermocouple ratio. Although both the arrangement, i.e. TEG in parallel and TEC in series and TEG in series and TEC in series, yield comparable COP, TEG in parallel and TEC in series is quite advantageous from the cooling capacity point of view. In the absence of the Thomson effect, TEG in parallel TEC in series yields the best COP and cooling capacity.

Performance investigation of an updated alkali metal thermoelectric converter-thermally regenerative electrochemical cycles-thermoelectric generator hybrid system

For further recovery of waste heat, alkali metal thermoelectric converter (AMTEC), thermally regenerative electrochemical cycles (TRECS), and two-stage thermoelectric generator (TTEG) are incorporated into a novel thermoelectric coupling system. The waste heat from AMTEC is split into TRECS and TTEG simultaneously. A general mathematical model including the main irreversible losses inside the system and the external heat leakage is built. With the optimization of the current density of AMTEC, the electrolyte thickness, and the fraction of heat dumped into each subsystem, the maximum modeling efficiency and power output are about twice as much as the single AMTEC system. They are 11% and 14% higher than the efficiency and power output obtained if the heat provided to the TRECS and TTEG are equal. Proper distribution of waste heat is necessary. The parametric selection criteria for the optimum states of the hybrid system operation are achieved. Furthermore, the effects of a set of critical factors relevant to TRECS and TTEG are also evaluated. The optimal dimensionless current of TTEG can maximize the power output of the hybrid system, while the internal resistance of TRECS decreases the power output. The conclusions obtained here are general and involve several special cases.

The Combined Impacts of Leg Geometry Configuration and Multi-Staging on the Exergetic Performance of Thermoelectric Modules in a Solar Thermoelectric Generator

Abstract The performance of thermoelectric generators (TEGs) can be improved either by the adoption of multi-stage or tapered leg configuration. So far, a hybrid device that simultaneously uses both multi-staging and tapered leg geometry to improve its performance has not been conceived. Thus, we present a thermodynamic modeling and optimization of a two-stage thermoelectric generator (TTEG) with tapered leg geometries using ansys 2020 r2 software. The optimized parameters include the leg height, area, concentrated solar radiation, and external load resistance. First, the X-leg TEG only improves the performance of the trapezoidal leg TEG below a leg height of 3 mm. Beyond 3 mm, the performance of both TEGs become very similar. Long thermoelectric legs provide higher efficiencies, while short legs generate maximum power densities. To obtain maximum efficiencies, the initial leg height of the thermoelectric legs, 1.62 mm, is increased by 517.28%, while the initial leg area, 1.96 mm2, is decreased by 64.29%. Also, the proposed TTEG with tapered legs (trapezoidal and X-legs) improves the exergetic efficiency of the base case, single-stage rectangular leg TEG, by 16.7%. Furthermore, the use of tapered leg TEGs, in single and multi-stage arrangements, reduces the exergy conversion index of conventional rectangular leg TEGs by 1.89% and 0.98%, respectively. Finally, the use of tapered legs and multi-stage configurations increases the thermodynamic irreversibilities of conventional rectangular leg TEGs, thus reducing their thermodynamic stability.

RETRACTION NOTICE: A novel configuration and performance for a two-stage thermoelectric heat pump system driven by a two-stage thermoelectric generator

RETRACTION NOTICE: A novel configuration and performance for a two-stage thermoelectric heat pump system driven by a two-stage thermoelectric generator

Performance analysis of a new hybrid system composed of a concentrated photovoltaic cell and a two-stage thermoelectric generator

A new cogeneration system model that integrates a concentrated photovoltaic cell (CPV) and a two-stage thermoelectric generator (TTEG) considering the Peltier, Seebeck and Thomson effects is proposed, where the CPV converts the inlet solar energy into electricity and heat, and the TTEG further harvests the heat for additional electricity production. Mathematical relation of the operating electric currents between TTEG and CPV is determined. Mathematical formulas for the power output and efficiency of the proposed system are specified under different operation conditions. The maximum power density (MPD) and maximum energy efficiency (MEE) of the proposed hybrid system are about 8% greater than that of the stand-alone CPV, respectively. Furthermore, the impacts of the operating temperature of CPV, solar irradiance, concentration ratio, thermocouple number ratio between top-stage and bottom-stage, total number of thermocouple and different thermoelectric materials on the hybrid system performance are revealed. The results may provide some new insights into designing such an efficient solar-to-electricity hybrid system.

Performance evaluation of a hybrid alkali metal thermal electric converter-two stage thermoelectric generator system

• A two-stage thermoelectric generator is proposed to recover waste heat from AMTEC. • Feasibility and effectiveness of TTEG as bottoming cycle are justified. • Power density, energetic and exergetic efficiency gain obvious improvements. • Effects of some key parameters on the system performance are revealed. A great part of high-quality heat is wasted, which significantly lowers the performance of alkali metal thermal electric converters. To achieve gradual and efficient utilization of the waste heat, a new cogeneration system model composed of an alkali metal thermal electric converter and a two-stage thermoelectric generator is established, in which the high-quality waste heat of alkali metal thermal electric converter is further reused by two-stage thermoelectric generator for additional power generation. Based on the theories of electrochemistry and non-equilibrium thermodynamics, mathematical expressions of power outputs and efficiencies of alkali metal thermal electric converter, two-stage thermoelectric generator and hybrid system are derived by taking the main irreversible losses into account. Calculations show that the maximum attainable power output density and its efficiency of hybrid system are, respectively, 5152.7 W/m 2 and 30.0%, which are approximately 54.1% and 27.7% greater than that of the sole alkali metal thermal electric converter system in previous studies. Two-stage thermoelectric generators are efficient to utilize the waste heat from alkali metal thermal electric converters. Comprehensive parametric studies show that operating conditions and designing parameters can be tuned to optimize the hybrid system performance. The results may offer some theoretical guidance for designing and running such a hybrid system.

Performance optimization of a class of combined thermoelectric heating devices

A detailed model of thermally-driven combined thermoelectric (TE) heating device is established. The device consists of two-stage TE heat pump (TTEH) and two-stage TE generator (TTEG) with four external heat exchangers (HEXs). Both internal losses and external heat transfer irreversibilities are considered in the model. The heating capacity and the coefficient of performance (COP) of the device are improved through numerical optimization, which is of great significance to the application of the device. The distribution of the total TE element number among four TE devices and the distribution of the total external heat conductance among the four external HEXs are optimized. The results show that both the reservoir temperatures of TTEG and TTEH have significant influences on the performance and the corresponding optimum parameters of the device. The COP can reach 0.14 after optimization when the temperature difference of heat source is 150 K and the temperature difference of heating is 10 K.