Thermoelectric Generator Device Research Articles

Economy, energy, exergy and mechanical study of co-axial ring shape configuration of legs as a novel structure for cylindrical thermoelectric generator

The n-type and p-type leg structure of any conventional thermoelectric module are in the form of filled rectangular shape which are placed next to the each other (see graphical abstract). In this paper, hollow cylindrical configuration is investigated as a novel leg structure for thermoelectric module in which the n-type and p-type legs are placed co-axial inside each other. A validated 3D numerical simulation was employed to investigate the proposed structure from thermal, economic, exergetic and mechanical viewpoints. The cylindrical ring-shape co-axial configuration can be made in different azimuthal angle, slant angle and width ratio all of which are probed in this research under different boundary conditions. The ring shape structure is able to reduce the thermal-stresses level without the reduction of thermal efficiency. Results indicate that the increment of hot side temperature can improve the output power and conversion efficiency of the cylindrical thermoelectric generator (CTEG) device but reduces the mechanical reliability of the system. It addition, with increment of slant angle of thermoelectric legs, the maximum Von Mises stress in the legs increases and power output of the CTEG is improved. The increase of the width ratio leads to the improvement of the output power and reduction of conversion and exergy efficiencies. Moreover, it is proved that the azimuthal angle of CTEG device has minor impact on the conversion and exergy efficiencies. It is found that the Von Mises stress attains the peak values in the contact regions between wielding layers and hot sides of the legs.

Investigation on waste heat recovery of a nearly kilowatt class thermoelectric generation system mainly based on radiation heat transfer

ABSTRACT Thermoelectric generation (TEG) is one of the most effective technologies converting heat directly into electric power. In this paper, a nearly kilowatt class TEG system mainly based on radiation heat transfer was designed and built. The open circuit voltage, the output power, the power density, and the conversion efficiency of the TEG system were investigated in detail at different temperature gradients. The maximum inverter power output of the TEG system assembled with 182 TEG devices can reach 684 W at a temperature difference around 125 K, and the corresponding power density can reach 845 W/m2. The inverter output power is almost proportional to the temperature difference between the hot and the cold side of TEG system. Our results confirmed that if the waste heat resource was sufficient to provide a greater temperature difference of 200 K in practical application, the output power and the power density of this TEG system would reach 1.23 kW and 1.51 kW/m2, respectively.

Experimental study of a thin water-film evaporative cooling system to enhance the energy conversion efficiency of a thermoelectric device

In the study, a new method to enhance the performance of a thermoelectric generator (TEG) device by utilizing the water-film evaporative cooling is proposed. An experimental device was constructed by incorporating a water-film cooling pond with a commercially available TEG. Experiments were performed to investigate the effects of the main operating conditions (ambient temperature Tamb was 25 °C), TEG hot-side temperature (TH = 50–100 °C), ambient relative humidity (RH = 15–90%), and water-film thickness (twater = 1–9 mm) on the TEG output performance. Additionally, the output performance of TEG under different cooling methods was compared. A TEG prototype device was constructed to generate electricity/steam using seawater evaporation cooling without external electrical energy. The results indicated that TEG hot-side temperature and water-film thickness significantly affected output performance. However, the ambient relative humidity did not considerably affect TEG output performance. Given TEG hot-side temperature TH = 100 °C, ambient relative humidity RH = 15%, the TEG prototype device-generated open-circuit voltage of Uopen = 1.55 V, maximum output power of Pmax = 290.32 mW, and a steam generation rate of 9.82 mg/s. The results showed that evaporative cooling is an innovative method to improve the performance of TEG.

Identification of pulsating flow effects with CNT nanoparticles on the performance enhancements of thermoelectric generator (TEG) module in renewable energy applications

In this study, performance assessment of a thermoelectric generator module located in between two channels where carbon-nanotube/water nanofluid streams flow is studied with combined effects of nanoparticle inclusion and flow pulsations. The finite element method is used to solve the 3D unsteady coupled fluid flow, heat transfer and electric field equations. Different pertinent parameters effects such as Reynolds number (between 250 and 1000), nanoparticle volume fraction (between 0 and 0.04), pulsating flow frequency (Strouhal number between 0.01 and 0.1) and amplitude (between 0.25 and 0.95) on the power generation are examined. It is observed that flow pulsation changes the dynamic features of thermoelectric power generated in the device. Higher power values are obtained when Reynolds number, flow pulsation amplitude and nanoparticle solid volume fraction rise. However, the effect is reverse for higher pulsation frequencies. Including nano sized particles further enhances the performance of the device with flow pulsation. It is also observed that 24.4 % enhancement in the power are achieved for nanofluid with flow pulsation when lowest and highest pulsation amplitudes are compared. At lowest pulsation frequency and highest amplitude 14.2 % enhancement in power is obtained for water as compared to steady flow case while this amount rises to 31 % for carbon nanotube nanofluid at the highest solid volume fraction. System identification method is used to obtain dynamic lower order model of the system for different pulsation amplitudes to predict the time dependent power generated in the thermoelectric generator device. • TEG module performance with flow pulsation and nanofluid is examined. • Higher amplitudes, ϕ, Re number and lower frequency resulted in higher powers. • When amplitudes are varied, 24.4% power enhancement is obtained with pulsation. • As compared to steady case, 31% enhancement is seen with nanofluid and pulsation. • System identification is used to construct dynamic model of the TEG module.

An expandable thermoelectric power generator and the experimental studies on power output

Technology using thermoelectric generators (TEG) has many advantages such as compactness, quietness, and reliability because there are no moving parts. One of the great challenges for TEG to be used for power generation is large-scale utilization. It is difficult to manufacture a TEGS system even at the scale of a few kilowatts (kW). To this end, we have designed and built a five-layer TEG apparatus with 90 individual power-producing TEG modules that can be installed with modularized units. Such a system with a layered structure could be expanded in power, something similar to solar Photovoltaics (PV). In this study, laboratory experiments were conducted using the built TEG apparatus to measure the power output and efficiency at different flow rates of water, different temperature, and different temperature differences between hot and cold sides. The effects of these parameters on voltage, power output, and efficiency were investigated and analyzed. The five-layer TEG device could generate about 45.7 W electricity with a temperature difference of 72.2°C between the cold and hot sides. The power of each module was about 0.51 W at this temperature difference. The experimental data can be applied to the design of commercial TEG systems. The expandable TEG system with layered structure provides a possible solution to scaling up TEG power generation to a commercial size.

Performance and profit analysis of thermoelectric power generators mounted on channels with different cross-sectional shapes

In order to generate electric power by thermoelectricity, thermoelectric modules are mounted on peripheral surface of a channel and hot fluid moves along the inside of the channel. Despite the importance of cross-section shape on the performance of power generator, no comprehensive study has been previously performed to clarify the thermal/hydraulic characteristics of different cross-sections on thermoelectric generators. Hence, in this paper, three-dimensional numerical simulations are carried out to investigate the performance of thermoelectric generators mounted on channels with five different cross-sectional shapes. The effect of Re number, hot air inlet temperature, thermoelectric cold side temperature, and load ratio on the maximum output power, pumping power, net power and thermal conversion efficiency are studied. Results revealed that the thermoelectric generator device with a rectangular-shape channel provides the highest output power and thermal conversion efficiency. With the increase of Re number, the amount of output power and pumping power increase. However, the net power and thermal conversion efficiency improves up to a specific Re number and then diminishes. Besides, increment of hot side inlet temperature intensifies the net power and thermal conversion efficiency of all channels while the increment of cold side temperature has a minor effect on the thermal conversion efficiency of thermoelectric.

Experimental investigation of a novel heat pipe thermoelectric generator for waste heat recovery and electricity generation

Waste heat recovery helps reduce energy consumption, decreases carbon emissions, and enhances sustainable energy development. In China, energy-intensive industries dominate the industrial sector and have significant potential for waste heat recovery. We propose a novel waste heat recovery system assisted by a heat pipe and thermoelectric generator (TEG) namely, heat pipe TEG (HPTEG)，to simultaneously recover waste heat and achieve electricity generation. Moreover, the HPTEG provides a good approach to bridging the mismatch between energy supply and demand. Based on the technical reserve on high-temperature heat pipe manufacturing and TEG device integration, a laboratory-scale HPTEG prototype was established to investigate the coupling performances of the heat pipes and TEGs. Static energy conversion and passive thermal transport were achieved with the assistance of skutterudite TEGs and potassium heat pipes. Based on the HPTEG prototype, the heat transfer and the thermoelectric conversion performances were investigated. Potassium heat pipes exhibited excellent heat transfer performance with 95% thermal efficiency. The isothermality of such a heat pipe was excellent, and the heat pipe temperature gradient was within 15°C. The TEG's thermoelectric conversion efficiency of 7.5% and HPTEG's prototype system thermoelectric conversion efficiency of 6.2% were achieved. When the TEG hot surface temperature reached 625°C, the maximum electrical output power of the TEG peaked at 183.2 W, and the open-circuit voltage reached 42.2 V. The high performances of the HPTEG prototype demonstrated the potential of the HPTEG for use in engineering applications.

Fabrication and Characterization of Ultra‐Lightweight, Compact, and Flexible Thermoelectric Device Based on Highly Refined Chip Mounting

AbstractThermoelectric generators (TEGs) are a promising power source for realizing a self‐powered sensor, which is a primary component of the rapidly developing Internet of Things. Here, the fabrication of a prototype for a compact and flexible TEG (CF‐TEG) using ultra‐fine chip mounting technique is reported. The CF‐TEG consisting of 84 p‐n pairs was fabricated on a 10 × 10 mm2 flexible substrate. A temperature difference (dT) of 150 K is successfully established for this TEG. Its maximum output voltage and power density are obtained as 2.4 V and 185 mW cm−2, respectively, which corresponds to a conversion efficiency of 1.12% at dT = 150 K. Further, the experimental results are validated through theoretical analysis in which the contact effects are taken into account. This analysis is also used to elucidate the effect of thermal and electrical contact resistance on the output power. It is observed that ≈40% output power of this device is lost by these resistances, which proves that the contact properties significantly affect the performance of the TEG device.

Spectral absorption control of femtosecond laser-treated metals and application in solar-thermal devices

Direct femtosecond (fs) laser processing is a maskless fabrication technique that can effectively modify the optical, electrical, mechanical, and tribological properties of materials for a wide range of potential applications. However, the eventual implementation of fs-laser-treated surfaces in actual devices remains challenging because it is difficult to precisely control the surface properties. Previous studies of the morphological control of fs-laser-processed surfaces mostly focused on enhancing the uniformity of periodic microstructures. Here, guided by the plasmon hybridisation model, we control the morphology of surface nanostructures to obtain more control over spectral light absorption. We experimentally demonstrate spectral control of a variety of metals [copper (Cu), aluminium (Al), steel and tungsten (W)], resulting in the creation of broadband light absorbers and selective solar absorbers (SSAs). For the first time, we demonstrate that fs-laser-produced surfaces can be used as high-temperature SSAs. We show that a tungsten selective solar absorber (W-SSA) exhibits excellent performance as a high-temperature solar receiver. When integrated into a solar thermoelectric generation (TEG) device, W-SSA provides a 130% increase in solar TEG efficiency compared to untreated W, which is commonly used as an intrinsic selective light absorber.

Experimental study of Thermoelectric Energy Harvesting

Waste heat energy harvesting aims to supply electricity to electric or electronic systems from different energy sources present in the environment without grid connection or utilization of batteries. These energy sources are solar (photovoltaic), movements (kinetic), radio-frequencies and thermal energy (thermoelectricity). The thermoelectric energy harvesting technology exploits the Seebeck effect. This effect describes the conversion of temperature gradient into electric power at the junctions of the thermoelectric elements of a thermoelectric generator (TEG) device. This device is a robust and highly reliable energy converter, which aims to generate electricity in applications in which the heat would be otherwise dissipated. The significant request for thermoelectric energy harvesting is justified by developing new thermoelectric materials and the design of new TEG devices. Potential TEG applications as energy harvesting modules are used in medical devices, sensors, buildings and consumer electronics. Present work is experimental study and analysis of thermoelectric energy harvesting and their low-power applications, and calculation of figure of merit which is dimensional less number for deciding harvesting efficiency.

A thin film efficient pn-junction thermoelectric device fabricated by self-align shadow mask

Large area highly crystalline MoS2 and WS2 thin films were successfully grown on different substrates using radio-frequency magnetron sputtering technique. Structural, morphological and thermoelectric transport properties of MoS2, and WS2 thin films have been investigated systematically to fabricate high-efficient thermal energy harvesting devices. X-ray diffraction data revealed that crystallites of MoS2 and WS2 films are highly oriented in 002 plane with uniform grain size distribution confirmed through atomic force microscopy study. Surface roughness increases with substrate temperature and it plays a big role in electron and phonon scattering. Interestingly, MoS2 films also display low thermal conductivity at room temperature and strongly favors achievement of higher thermoelectric figure of merit value of up to 1.98. Raman spectroscopy data shows two distinct MoS2 vibrational modes at 380 cm−1 for E12g and 410 cm−1 for A1g. Thermoelectric transport studies further demonstrated that MoS2 films show p-type thermoelectric characteristics, while WS2 is an n-type material. We demonstrated high efficient pn-junction thermoelectric generator device for waste heat recovery and cooling applications.

A high-performance and flexible thermoelectric generator based on the solution-processed composites of reduced graphene oxide nanosheets and bismuth telluride nanoplates.

The fabrication of a flexible thermoelectric generator (TEG) with both high power output and good flexibility has drawn considerable attention. Solution-processed inorganic nanocrystals have good processibility in interface to retain excellent electrical properties of nanocrystals and can be processed into thin films on a flexible substrate by an easy scale-up printing or coating method. However, a high-performance TEG device based on inorganic solution-processed materials also poses challenges when it comes to flexibility of the whole device. Herein, flexible planar TEG devices are fabricated by printing an ink mixture comprising solution-processed bismuth telluride (Bi2Te3) nanoplates with reduced-graphene oxide (rGO) nanosheets onto flexible polyimide substrates. The interface treatment by hot ethylenediamine and the appropriate amount of rGO contribute to the high electrical properties of the material. Also, when rGO nanosheets of 1% mass ratio are added, the optimum power output of the corresponding rGO/Bi2Te3 TEG device with six elements reaches ∼1.72 μW at a temperature difference of 20 K. Moreover, owing to the contribution from flexible rGO nanosheets, the suitable thickness of each element, and the artful connection of elements with a soft copper wire in the devices, the 1% rGO/Bi2Te3 TEG device was found to be robust, and its electrical resistance merely changes by 2% after bending 1000 cycles on 5 mm in bending. These inorganic-based TEGs with both high performance and good flexibility will promote the development of new generation energy devices in the field of flexible electronics.

Effects of microstructure of Ni barrier on bonding interface diffusion behaviors of Bi–Te-based thermoelectric material

To enhance the conversion efficiency of thermoelectric generation (TEG) devices, they must withstand larger temperature differences. Previously, a large-scale flexible TEG device was fabricated for use in energy harvesting. However, its maximum operating temperature was limited to approximately 150 °C owing to the low melting point of the Sn–Ag-based solder (∼150 °C) that bonds TE materials and electrodes. Therefore, the present study attempted to develop a bonding interface resistant to heat up to 250 °C. Ag paste was chosen as the bonding material instead of the Sn–Ag-based solder because it has many advantages such as high-temperature stability (melting point ∼ 960 °C), printability, and low electrical resistivity. Ni/Au was used as a diffusion barrier layer. Ni/Au layers were prepared by sputtering and electroplating, respectively. Investigation of the element diffusion behaviors of these two bonding interfaces at 250 °C showed that electroplated Ni blocked electrode diffusion, but Ni itself significantly diffused into n-type Bi2Te3 and formed a NiTe phase. Conversely, sputtered Ni could not block electrode diffusion, but Ni hardly diffused into n-type Bi2Te3. This work provides a fundamental understanding of the grain-boundary diffusion and diffusion properties of crystals and amorphous materials.

Geometry optimization for structural reliability and performance of a thermoelectric generator

The opposing requirements for the performance and reliability of a thermoelectric generator (TEG) are investigated with numerical finite element analysis simulations. The parameters that significantly influence the operational performance and structural reliability of a TEG are considered for simultaneous optimization. The design of experiments based response surface optimization methodology in conjunction with results from finite element analysis was employed to identify optimal parameters from the structural reliability and performance (power output and efficiency) perspectives. A high temperature bismuth telluride based TEG couple was used in the studies to demonstrate the general applicability of the methodology. The response surface methodology is found to be a robust technique that can expedite the process of geometry optimization of a TE device during the research and development phase of TEG devices fabricated from novel thermoelectric materials.

Power optimization and economic evaluation of thermoelectric waste heat recovery system around a rotary cement kiln

Cement rotary kiln is the main device utilized for industrial cement production in large scale. The shell temperature can reach several hundred Celsius degrees. Therefore, a thermoelectric waste heat recovery system can be utilized based on its advantages. In this study, an arc shaped absorber is designed and temperature distribution along the absorber circumference is obtained numerically. The calculated temperature is considered as the hot side temperature of thermoelectric generators (TEGs) that recover thermal energy on the absorber. In situations where the heat is free, the metric for designing a thermoelectric system is to reach the maximum power output. In order to reach regional optimal power from parametric design, the absorber length is divided into several sections. For efficient design of the TEG in each section, effect of significant parameters such as leg length and fill factor of the TEG and thermal resistance of the heat sink are studied. Effect of variation of the temperature and velocity magnitudes of the air next to the heat sinks is considered on thermal resistance and performance of the pin-fin heat sinks along the absorber. β-phase zinc antimonide (Zn4Sb3) and magnesium tin silicide (Mg2SiSn) are chosen as the p- and n-leg thermoelectric materials of the TEGs, respectively, because of their relatively high performance over the considered range of operating temperature. The results show that, staggered arrangement of the pin-fins is more effective for higher power generation and system performance compared to in-line arrangement of the fins. Moreover, by evaluation of the results, maximum matched power output in each section versus the fill factor and leg length can be determined in this study. The results show that, low fill factors between 0.05 and 0.2 can provide relatively a same maximum power as high fill factors. Furthermore, an economic evaluation is carried out to find optimal design of the TEG device for highest power generation and lowest investment cost. Various parameters of the cost function, such as cost of the bulk raw material (CB), manufacturing cost associated with processing bulk material (CM,B), areal manufacturing cost (CM,A), heat exchanger cost (CH-EX), balance of the system cost (CBoS) and the installation cost (CI) are taken into account in this study. The results show dominant parameter in the system cost is the heat sink.

Detailed Transient Multiphysics Model for Fast and Accurate Design, Simulation and Optimization of a Thermoelectric Generator (TEG) or Thermal Energy Harvesting Device

Described herein is a detailed and comprehensive multiphysics model of a thermoelectric generator (TEG). The one-dimensional model uses electrical–thermal analogies solved for transient response using SPICE. There are many advantages and applications of thermoelectric generators. Wider use and application advancements are generally limited by the tools available for engineering and scientific studies. Currently, available modeling tools are limited by some combination of speed, platform capabilities, or missing physics that are not used or assumed to be negligible. The TEG module model herein is made up of two sub-models, the thermoelement model and the non-thermoelement model. Rather than a lumped thermoelement model, the model herein makes use of distributed physics that include the following: Thomson effect, temperature dependence, mass, Joule heat, thermal resistance, Seebeck effect, and electrical resistance. The non-thermoelement model takes into account temperature dependence and simulates Joule heat generation, thermal resistances, thermal and electrical interface resistances, and mass for and between the ceramic, copper, and solder. The comprehensive model herein was correlated to experimental data that simultaneously varied electrical current and hot and cold side temperatures with time. Very minimal adjustments to reported thermoelectric properties were required to almost perfectly match the experimental transient power output. The effects of the non-thermoelement model, distributed Thomson effect model and distributed temperature dependent property model were quantified. The model ran very quickly, taking 2.5 real-time seconds to run a 4000 s transient simulation.

Atomistic study of an ideal metal/thermoelectric contact: The full-Heusler/half-Heusler interface

Half-Heusler alloys such as the (Zr,Hf)NiSn intermetallic compounds are important thermoelectric materials for converting waste heat into electricity. Reduced electrical resistivity at the hot interface between the half-Heusler material and a metal contact is critical for device performance; however, this is yet to be achieved in practice. Recent experimental work suggests that a coherent interface between half-Heusler and full-Heusler compounds can form due to diffusion of transition metal atoms into the vacant sublattice of the half-Heusler lattice. We study theoretically the structural and electronic properties of such an interface using a first-principles based approach that combines ab initio calculations with macroscopic modeling. We find that the prototypical interface HfNi2Sn/HfNiSn provides very low contact resistivity and almost ohmic behavior over a wide range of temperatures and doping levels. Given the potential of these interfaces to remain stable over a wide range of temperatures, our study suggests that full-Heuslers might provide nearly ideal electrical contacts to half-Heuslers that can be harnessed for efficient thermoelectric generator devices.

Theoretical Analysis of the Thermoelectric Generator Considering Surface to Surrounding Heat Convection and Contact Resistance

A general theoretical model of thermoelectric generation (TEG) is proposed based on the one-dimensional steady heat transport in this paper. The effect of heat convection between the thermoelectric legs and the ambient environment, and contact resistance between the heat reservoirs and thermoelectric couple on the performance of the TEG is studied. Fundamental formulas and closed-form solutions for the output power and conversion efficiency are derived. Numerical results show that the maximum output power and maximum conversion efficiency of the TEG are lower than those of the ideal TEG when the influence of heat convection and contact resistance are taken into consideration. The heat convection has a very small effect on the maximum output power, but causes a large reduction of conversion efficiency for the TEG, and this reduction becomes more significant as the length of thermoelectric couple increases. In addition, there always exists an optimum length of thermoelectric couple for the actual TEG, so as to achieve the maximum conversion efficiency when the effects of heat convection together with contact resistance are considered. The results of this paper may help to improve the design and optimization of TEG devices.

A novel self-powering ultrathin TEG device based on micro/nano emitter for radiative cooling

This paper demonstrated a novel energy utilization that thermoelectric generation (TEG) device can achieve self-powering by radiative cooling (RC) continuously. An ultrathin TEG with a multilayer thermal emitter was fabricated to convert the heat from the environment into electricity directly by using radiative cooling. The TEG device was consisted of more than 46,000 P-N modules in series, and each two TE modules were connected by air bridge. Thermal emitter had 80.8% emissivity in the atmospheric window (8–13 µm). Besides, maximum temperature drop of 4 K was achieved. The output voltage of the TEG-RC reached up to 0.5 mV, and the TEG-RC exhibited a continuous average 0.18 mV output for 24 h. Extreme temperature gradients were surprisingly formed in cross section of 1.5 µm thick for micro/nano film materials.

Highly-efficient thermoelectric pn-junction device based on bismuth telluride (Bi2Te3) and molybdenum disulfide (MoS2) thin films fabricated by RF magnetron sputtering technique

Layered structure bismuth telluride and molybdenum disulfide thin films were successfully deposited on different substrates using radio-frequency magnetron sputtering technique. The structural, morphological, and thermoelectric transport properties of bismuth telluride and molybdenum disulfide thin films have been investigated systematically to fabricate high-efficient thermal energy harvesting thermoelectric device. The magnitude of the Seebeck coefficient of bismuth telluride thin films decreases with increase in film thickness. Bismuth telluride grown at 350 °C for 10 min, which is approximately 120 nm, displays a maximum Seebeck coefficient of −126 μV K−1 at 435 K. The performance shows strong temperature dependence when the films were deposited at 300 °C, 350 °C, and 400 °C. The power factor increases from 0.91 × 10−3 W/mK2 at 300 K to about 1.4 × 10−3 W/mK2 at 350 K. Molybdenum disulfide films show the positive Seebeck coefficient values and their Seebeck coefficient increases with film thickness. The AFM images of bismuth telluride thin films display a root-mean-square (rms) roughness of 32.3 nm and molybdenum disulfide thin films show an rms roughness of 6.99 nm when both films were deposited at 350 °C. The open-circuit voltage of the pn-junction thermoelectric generator (TEG) device increases with increase in ΔT to about 130 mV at ΔT = 120 °C. We have demonstrated a highly efficient pn-junction TEG device for waste heat recovery applications.