Configuration of segmented leg for the enhanced performance of segmented thermoelectric generator

Thermal analysis of a segmented thermoelectric generator is performed, and the segmented leg configurations maximizing the efficiency and the output power are formulated. The effect of operating conditions such as external load resistance, the temperatures of hot and cold junctions, on the device performance is studied. The segmented thermoelectric generator has the leg configuration consisting of the combination of modified lead telluride and modified bismuth telluride. The segmented thermoelectric generator performance, such as device efficiency and output power, is compared with those corresponding to a single material leg configuration (modified lead telluride or modified bismuth telluride) for various operating conditions. It is found that a unique value of the segmented leg combination maximizes the efficiency and the output power for each operating condition. The variation in the operating conditions changed the locus points of the maximum efficiency and the maximum output power. The segmented thermoelectric generator gives rise to the higher device efficiency and the output power than those of the single material leg configuration, especially for the low external load resistance. Copyright © 2016 John Wiley & Sons, Ltd.     

A model study for cyclic thermal loading and thermal performance of a thermoelectric generator

Thermal cyclic loading influences the life cycle of the thermoelectric device pins because of the thermal stress developed in the pins. Although thermal efficiency improves for different geometric configurations of the device pins, development of thermal stresses limit the selection of pin geometry in practical applications, particularly under cyclic thermal loading. Consequently, in the present study, thermal stress analysis of thermoelectric pins under cyclic thermal loading is carried out. The influence of thermoelectric pin geometry on the stress levels is examined when the device is subjected to the thermal cyclic loading. The predictions of thermal stress distribution are validated with the data presented in the open literature. It is found that pin geometric configuration has a significant effect on the stress levels developed in the pin when subjected to cyclic thermal loading. The pin configuration R_A = 1 (parallel pins) results in the minimum value of the maximum von Mises stress in the pins as compared to that corresponding to other configurations. Copyright © 2014 John Wiley & Sons, Ltd.     

Parametric study on the thermoelectric conversion performance of a concentrated solar‐driven thermionic‐thermoelectric hybrid generator

A concentrated solar‐driven thermionic‐thermoelectric hybrid generator composed of solar heat collector, thermionic generator (TIG), thermoelectric generator (TEG), and radiator is introduced in this paper. A theoretical model of thermoelectric conversion performance for the hybrid generator is built up based on the heat source of the concentrated solar radiation rather than isothermal heat source. Based on the model, the impacts of related parameters on the internal temperature distributions, output power, and efficiency have been discussed. Moreover, the optimal operating conditions of the TIG‐TEG hybrid device at its maximum output power and efficiency have been determined. Results show that when cascading the TEG with the TIG, there is very little change of the TIG cathode temperature in most conditions, namely, T_C ≈ T_C′. Meanwhile, the anode temperature becomes higher, and the TEG cold end temperature T₂ is close to the anode temperature T_A′ for the single TIG system, ie, T_A > T_A′ ≈ T₂. In theory, the optimal concentrated solar radiation I₀ for the maximum output power P_max and the maximum efficiency η_max differs, which are I_0,P = 2.5 × 10⁶ W/m² and I_0,η = 2 × 10⁶ W/m², respectively, whereas the output power and efficiency of the TIG‐TEG hybrid system simultaneously reach their maximum values when the optimal TIG anode temperature T_A,opt = 1025 K, the optimal TIG output voltage V_opt = 2 V, and the optimal ratio of load resistance to internal resistance (R₂/R)_opt = 2. However, in practice, the parameter values of I₀, Φ_A, and T_A should be strictly controlled under 1.8 × 10⁶ W/m², 1.4 eV, and 660 K, respectively. Generally, the maximum output power and efficiency of the hybrid TIG‐TEG system are, respectively, 35% and 4% higher than that of the single TIG.     

Thermodynamics and thermal stress analysis of thermoelectric power generator: Influence of pin geometry on device performance

Thermodynamics and thermal stress analysis of thermo-electric power generator is carried out. The influence of device geometry on thermal stress, thermal efficiency and output power is examined. The finite element method is incorporated to predict temperature and stress fields in the thermo electric device. It is found that thermal efficiency improves for certain geometric configuration of the device. In this case; the maximum thermal stress developed in the pin reduces slightly indicating improved life expectation of the device.     

Typical off-design analytical performances of internal combustion engine cogeneration

Based on experimental data, typical off-design characteristic curves with corresponding formulas of internal combustion engine (ICE) are summarized and investigated. In combination with analytical solution of single-pressure heat recovery steam generator (HRSG) and influence of ambient pressure on combined heat and power (CHP) system, off-design operation regularities of ICE cogeneration are analyzed. The approach temperature difference ΔT _a, relative steam production and superheated steam temperature decrease with the decrease in engine load. The total energy efficiency, equivalent exergy efficiency and economic exergy efficiency first increase and then decrease. Therefore, there exists an optimum value, corresponding to ICE best efficiency operating condition. It is worth emphasizing that ΔT _a is likely to be negative in low load condition with high design steam parameter and low ICE design exhaust gas temperature. Compared with single shaft gas turbine cogeneration, ΔT _a in ICE cogeneration is more likely to be negative. The main reason for this is that the gas turbine has an increased exhaust gas flow with the decrease in load; while ICE is on the contrary. Moreover, ICE power output and efficiency decrease with the decrease in ambient pressure. Hence, approach temperature difference, relative steam production and superheated steam temperature decrease rapidly while the cogeneration efficiencies decrease slightly. It is necessary to consider the influence of ambient conditions, especially the optimization of ICE performances at different places, on cogeneration performances.     

Performance optimization of a two-stage semiconductor thermoelectric-generator

A model of a two-stage semiconductor thermoelectric-generator with external heat-transfer is built. Performance of the generator, assuming Newton’s heat-transfer law applies, is analyzed using a combination of finite-time thermodynamics and non-equilibrium thermodynamics. The analytical equations about the power output versus the working electrical current, and the thermal efficiency versus working electrical-current are derived. For a fixed total heat-transfer surface-area for two heat-exchangers, the ratio of heat-transfer surface-area of the high-temperature side heat-exchanger to the total heat-transfer surface-area of the heat-exchangers is optimized for maximizing the power output and the thermal efficiency of the thermoelectric-generator. For a fixed total number of thermoelectric elements, the ratio of number of thermoelectric elements of the top stage to the total number of thermoelectric elements is also optimized for maximizing both the power output and the thermal efficiency of the thermoelectric-generator. The effects of design factors on the performance are analyzed.     

Flexible thermoelectric generator for ambient assisted living wearable biometric sensors

In this work we proposed design, fabrication and functional characterization of a very low cost energy autonomous, maintenance free, flexible and wearable micro thermoelectric generator (μTEG), finalized to power very low consumption electronics ambient assisted living (AAL) applications. The prototype, integrating an array of 100 thin films thermocouples of Sb₂Te₃ and Bi₂Te₃, generates, at 40 °C, an open circuit output voltage of 430 mV and an electrical output power up to 32 nW with matched load. In real operation conditions of prototype, which are believed to be very close to a thermal gradient of 15 °C, the device generates an open circuit output voltage of about 160 mV, with an electrical output power up to 4.18 nW.In the first part of work, deposition investigation Sb₂Te₃ and Bi₂Te₃ thin films alloys on Kapton HN polyimide foil by RF magnetron co-sputtering technique is discussed. Deposition parameters have been optimized to gain perfect stoichiometric ratio and high thermoelectric power factor; fabricated thermogenerator has been tested at low gradient conditioned to evaluate applications like human skin wearable power generator for ambient assisted living applications.     

非均质温差发电器的性能分析

建立非均质温差发电器(TEG)理论模型,考虑热电材料的非均质导热系数以及温差发电器与热源间的传热热阻的影响,分析非均质温差发电器的一般性能.讨论热电元件对数、热导率、高温热源温度对非均质温差发电器性能特性的影响.结果表明,相较于均质温差发电器,导热系数不均匀强度越大,非均质温差发电器的最大输出功率和最大效率越高;热电元...     

Numerical study of a solar thermoelectric generator with nanofluids based microcooling system

Abstract

Nanofluids have been recently gaining ever-increasing attention in solar thermoelectric applications due to their promising potentials as heat transfer fluids. This research investigates numerically the performance of a thermoelectric generator (TEG) that is cooled by Al₂O₃/water nanofluid flows in zigzag microchannel heat sinks (ZMCHS). The one-way fluid–structure interaction (FSI) tool was used to couple the thermal-electric and fluid flow tools in ANSYS 15.0. The present study focused on the effects of heat flux (2–50?kW/m²), laminar Reynolds number (5–1500), inlet flow temperature (293–303?K) and the nanoparticle concentration (1–6%) on the output electric power and the efficiency of the TEG module. The applied heat flux limitations and its relation to the thermal limitations of thermoelectric materials were considered. The results indicated that the increase of heat flux increased the output power and the efficiency of TEG. Higher Reynolds numbers (Re > 400), inlet temperature and nanofluid concentration had an insignificant impact on the TEG performance.     

Effect of irreversibilities on the performance of a thermoelectric generator

Using an externally and internally irreversible heat engine model, the maximum power and thermal efficiency at maximum power output have been determined for a thermoelectric generator. The irreversibilities can be characterized by a single parameter named the device-design parameter. The efficiency and power decrease with an increase of the device-design parameter which appears in the equations for maximum power and efficiency.     

Improving power density and efficiency of miniature radioisotopic thermoelectric generators

We have built and tested a prototype miniaturized thermoelectric power source that generates 450 μW of electrical power in a system volume of 4.3 cm³. The measured power density of 104 μW cm⁻³ exceeds that of any previously reported thermoelectric power system of equivalent size. This improvement was achieved by implementing a novel thermopile design in which wagon wheel-shaped thermoelectric elements contact the entire circumference of the heat source whereas traditional approaches utilize only one heat source surface. The thermopile consists of 22 wagon wheel-shaped elements (11 P–N thermocouples) fabricated from 215-μm thick bismuth–telluride wafers having ZT = 0.97 at 30 °C. The power source operates on a 150 mW thermal input provided by an electrical resistance heater that simulates a capsule containing 0.4 g of ²³⁸PuO₂ located at the center of the device. Our primary research objective was to develop and demonstrate a prototype thermopile and radioisotopic thermoelectric generator (RTG) architecture with improved power density at small scales. Output power from this device, while optimized for efficiency, was not optimized for output voltage, and the maximum power was delivered at 41 mV. We also discuss modifications to our prototype design that result in significantly improved voltage and power. Numerical predictions show that a power output of 1.4 mW, power density of 329 μW cm⁻³, and voltage of 362 mV, is possible in the same package size.     

一种新型汽车尾气多通道热能发电系统

根据温差发电原理,设计了一种新型网格状通气管式的温差发电装置,实现对汽车尾气热能的再利用。通过优化温差发电装置的结构,改变了水箱结构,增加了废热通道数量,能够贴更多的温差发电片,从而提高转换效率。通过UG(计算机辅助设计软件)建立汽车尾气温差发电装置的理论模型,经过计算,当温差等于100℃时该装置的转换效率约等于5.67%。与其他温差发电装置进行比较,热油式温差发电器在260℃温差下最大热能转换效率可达4.389%,而汽车尾气温差发电器输出功率随着烟气温度的升高近似成线性递增,热能转换效率较低[1],通过比较得出,本装置不仅提高了转换效率,且达到相同转换效率时所对应的温差值也相应减少。     

Experimental analysis and evaluation of a vacuum enclosed concentrated solar thermoelectric generator coupled with a spectrally selective absorber coating

Significant research in the past decade has been focused on quantitatively and qualitatively validating potential of solar thermoelectric modules to harness electricity. In the present study, we have experimentally analysed steady-state temperature variation of a spectrally selective solar absorber coating (α?=?0.954, ε?=?0.13) with variation in solar irradiation flux (concentration ratios?=?39, 50 and 65) using Fresnel lens and vacuum enclosure pressure (200?mbar to 900?mbar in steps of 100?mbar). It is observed that the experimental results so obtained go hand in hand with a COMSOL simulation model of the set-up. Further, we have carried out performance analysis of a solar thermoelectric generator (STEG) set-up enclosed in vacuum conditions equipped with Fresnel lens and absorber set-up coupled to Bi₂Te₃ thermoelectric module array electrically connected in series. The results depict a maximum power output of 0.91?W and a peak efficiency of 2.21% at a hot-side temperature of 642?K.     

Design and fabrication of thermoelectric waste heat reutilization system—possible industrial application

The current article discussed the detail design and development of an experimental test rig to derive usable energy by utilizing the waste heat energy through a heat exchanger made of Bi₂Te₃ material. The accuracy including the efficiency of the fabricated device is demonstrated further by verifying the associated parameter through a simulation model (commercial finite element package, ANSYS 15.0). To imitate the waste hot air from the industry is achieved via a heat gun and fed to the test rig for the generation of thermoelectric power. The simulation model accuracy has been demonstrated by juxtaposing the associated experimental data and computational readings. Subsequently, the feasibility and optimum range of design parameters are established by comparing the experimental and the simulation data (triggered temperature difference, voltage output, and heat flux) generated at the interface of the thermoelectric power generators. In addition, the coefficient of determination (R²) value has been evaluated statistically and verified with the current experimental results for the demonstration of the relevancy. The statistical study shows the existence of the correlation between the current experimental and the simulation model. Also, the experimental result indicates the possible implementation of the newly developed system for the recovery from the waste heat either the automobile exhaust or any other kind of dissipated heat from the industries.     

Geometric optimization of trapezoidal thermoelectric heat pump considering contact resistances through genetic algorithm

An alternate option for improving the performance of the thermoelectric heat pump (TEHP) is the variation in thermoelectric leg configuration. In this paper, the thermodynamic model based on first and second law of thermodynamics for an exoreversible TEHP including influence of Thomson effect as well as leg geometry on the coefficient of performance and heating load of the device has been developed and optimized. Modified expressions have been derived analytically for dimensionless heating load, irreversibilities, figure of merit, energy, and exergy efficiency. The effects of operating and geometry parameters such as shape parameter (A_c/A_h), temperature ratio (T_c/T_h), Thomson effect, thermal and electrical contact resistances on the coefficient of performance, and heating load of the TEHP have been analysed. The results indicate that the Thomson effect has adverse effect on heating load of the system. The optimal parameters obtained through GA optimization process have been compared with the optimal parameters obtained through analytical method which proved the validity of GA optimization method for optimization of TEHP. After the testing, the GA optimization has been performed to determine the optimum parameters corresponding to maximum energy efficiency and maximum heating load. It was found that the GA population converges quickly after 20 runs only which proved the GA as time and cost‐effective optimization tool. This study will be useful for designing of practical TEHP systems of different leg geometries.     

The influence of operating and device parameters on the maximum efficiency and the maximum output power of thermoelectric generator

Thermoelectric power generators are one of the promising green energy sources. The operating and the generator parameters influence the generator output performance. In the present study, the influence of the operating and the generator parameters on the maximum output power and the efficiency of the thermoelectric power generator are examined. The output power corresponding to the maximum efficiency and the maximum attainable output power of the generator are compared. It is found that the maximum power of the thermoelectric generator corresponding to the high Figure of Merit is very sensitive to the operating temperature. The maximum power attainable is larger than that its counterpart corresponding to the maximum generator efficiency. Copyright © 2010 John Wiley & Sons, Ltd.     

Numerical simulation of nanostructured thermoelectric generator considering surface to surrounding convection

Thermoelectric systems (TE) can directly convert heat to electricity and vice-versa by using semiconductor materials. Therefore, coupling between heat transfer and electric field potential is important to predict the performance of thermoelectric generator (TEG) systems. This paper develops a general two-dimensional numerical model of a TEG system using nanostructured thermoelectric semiconductor materials. A TEG with p-type nanostructured material of Bismuth Antimony Telluride (BiSbTe) and n-type Bismuth Telluride (Bi₂Te₃) with 0.1 vol.% Silicon Carbide (SiC) nanoparticles is considered for performance evaluations. Coupled TE equations with temperature dependant transport properties are used after incorporating Fourier heat conduction, Joule heating, Seebeck effect, Peltier effect, and Thomson effect. The effects of temperature difference between the hot and cold junctions and surface to surrounding convective on different output parameters (e.g., thermal and electric fields, power generation, thermal efficiency, and current) are studied. Selected results obtained from current numerical analysis are compared with the results obtained from analytical model available in the literature. There is a good agreement between the numerical and analytical results. The numerical results show that as temperature difference increases output power and amount of current generated increase. Moreover, it is quite apparent that convective boundary condition deteriorates the performance of TEG.     

Parametric study of asymmetric thermoelectric devices for power generation

Thermoelectric devices are considered a promising technique for recycling waste heat. In the present work, a three-dimensional numerical model is developed to study the output performance of thermoelectric devices. A comprehensive analysis is performed based on a conventional π-type thermoelectric couple. The results indicate that the maximum power of thermoelectric devices generally increases with a decrease in height and an increase in cross-sectional area; the maximum efficiency exhibits the opposite trends. The best way to reduce heat losses is by using ceramic plates with higher thermal conductivity. Moreover, the parasitic internal resistance exists in the thermoelements, and its influencing factors are studied. To minimize electric losses, an asymmetric structure is proposed for thermoelectric devices. The results exhibit that the optimal cross-sectional area ratio of the p-type and n-type legs (S_p/S_n) is mainly contingent upon the thermoelectric material parameters; the greater the differences in the parameters of p-type and n-type thermoelectric materials, the greater the gains provided by the asymmetric structure. Furthermore, the experimental data present great consistency with the numerical results. The research results may help guide the design of thermoelectric devices with relatively lower power losses.     

Multiresponse optimization of exhaust thermoelectric generator using Taguchi-based gray relation analysis

The best operating condition of the exhaust thermoelectric generator (ETEG) provides more power output and low-pressure drop (low-PD). So it is required to optimize the operating condition of the ETEG. In the present work, Taguchi's L₁₈(6¹ 3³) orthogonal array was chosen to find the optimal parameters. Analysis of variance was used to determine the percent contribution of the control factors such as engine loads (ELs), different types of heat exchangers (HEs) with and without inserts, water flow rate (WFR), and external load resistance (ELR) on the thermoelectric power output and PD in the HE. The confirmation test was carried out at optimum levels for the regression equations and Taguchi method. Gray relational analysis was performed to find the optimum value of the power output and PD. It is observed that the optimal operating condition is EL₆ HE₁ WFR₃ ELR₂ (EL₆ = 10 kg, HE₁ = G-type test section, WFR₃ = 0.08 kg/s, and ELR₂ = 40 Ω).     

S and Te inter-diffusion in CdTe/CdS hetero junction

Effects of post formation thermal annealing of the CdTe–CdS device on the inter-diffusion of S and Te at the junction in a substrate configuration device have been studied by Auger electron spectroscopy. While the migration of S and Te atoms increases with annealing temperature, the extent of S diffusion is always higher than the diffusion of Te atoms. Inter-diffusion of S and Te causes the formation of CdTe_1-xS_x ternary compound at the CdTe–CdS interface.