Thermoelectric Conversion Research Articles

Exploration and optimization on thermoelectric conversion of waste heat of blast furnace slag

The iron and steel industry involves processes that generate abundant waste heat resources. The energy utilization rate can be improved by using thermoelectric conversion technology to directly convert waste heat into electric energy through the Seebeck effect. In this study, a special waste heat recovery device, designed according to the production environment characteristics of blast furnace (BF) slag, is proposed. The heat transfer process between the BF slag and thermoelectric generator (TEG) is analyzed, and the heat source temperature field model is constructed. Based on the temperature distribution, the size of the TEG is determined. The heat transfer behavior of the thermoelectric module (TEM) is optimized using a non-contact heat collection mode and a water-cooling device, which improves the temperature gradient. A thermal conductive silicone grease is introduced as the thermal conductive layer to achieve uniform distribution of the hot end temperature and improve the heat transfer capacity of the collector plate. After design optimization, the temperature gradient of the TEM increased by 15.3 °C and 38 % on average. The experimental results show that a single TEM can generate about 3.084 J of electric energy. Using 70 kg of BF slag with an initial temperature of 600 °C, the TEG per unit installed area can generate about 1.23 kJ of electric energy in 1 h. This study provides an important foundation for research in thermoelectric conversion, utilization of BF slag waste heat and sustainable development of the iron and steel industry.

Enhancing thermoelectric performance of single-walled carbon nanotube films by poly(styrene sulfonate acid) dispersing and sequential base treatment

Despite single-walled carbon nanotubes (SWCNTs) have attracted great interest for thermoelectric (TE) conversion, the strong van der Waals forces between SWCNTs cause them to aggregate into bundles with poor dispersibility, which dramatically deteriorates the charge carrier transport, and thereby induces low electrical conductivity and TE power factor. Herein, we report a facile and efficient approach to enhance TE performance of SWCNTs via the addition of poly(styrene sulfonic acid) (PSSH) and sequential base treatment. PSSH is served as a dispersant and dopant to improve the dispersibility of SWCNTs and facilitate charge carrier conduction, contributing to high electrical conductivity of 3749 ± 122 S cm−1 and power factor of 117.7 ± 3.4 μW m−1 K−2 for 20 wt% PSSH/SWCNT composite film. Further base treatment induces partial removal of insulative PSSH and de-doping effect of SWCNTs, which decreases the barriers between adjacent nanotubes junctions and modulates charge carrier transport to synergistically optimize the electrical conductivity and Seebeck coefficient. With fine-tuning base treatment temperature, the PSSH/SWCNT composite film reaches highest power factor of 160.6 ± 7.9 μW m−1 K−2, higher than pristine SWCNTs of 70.2 ± 4.4 μW m−1 K−2. This work demonstrates the feasibility of this approach to boost the TE properties of SWCNTs, exhibiting potential application for high performance renewable energy harvesting.

Low-grade heat recycling of vertical thermoelectric cells based on thermal-induced electric double layer

Employing electric double-layer (EDL) capacitors to harvest low-grade heat (LGH) is a novel technique in the high-efficiency energy absorption field. This work reports the fabrication of a vertical thermoelectric cell, based on a nanoporous graphene electrode immersed in low-concentration saline solution, for use as thermo-charging supercapacitors to convert LGH to electricity via thermally induced voltage. Because of a large specific area and a large number of micropores of nanoporous graphene films, the effective thermoelectric coefficient of the thermoelectric cell containing 0.01 M KCl solution can reach as high as 4.73 mV/°C. However, many factors, such as electrode materials, electrolyte solutions, and energy conversion device components, determine the efficiency of a thermoelectric conversion device. In summary, the device has a lower internal resistance and higher output voltage when the concentration of KCl solution is 0.05 M, and demonstrates higher thermoelectric conversion efficiency. Moreover, improving the conductivity of the electrolyte solution without affecting the device output voltage is also a way to reduce the internal power consumption of the device. The specific power and thermoelectric conversion efficiency of the device are increased by several orders of magnitude when uniformly dispersed silver nanoparticles are added to the potassium chloride solution to enhance the conductivity of the solution. The specific power underwent an increase from 0.50 mW g−1 to 42.37 mW g−1, and the thermoelectric conversion efficiency also increased from 0.0022% to 0.1358%.

Thermodynamic analysis of a spectrum splitting photovoltaic-thermoelectric system with a multi-physics coupling process

Quantifying the losses in the various energy transfer and conversion processes is essential for the study and application of the spectrum splitting photovoltaic-thermoelectric system because of the complex system structure. This paper develops a novel optical-electrical-thermal multi-physics coupling model for the spectrum splitting photovoltaic-thermoelectric system that correlates microstructure and macroscopic properties. Based on the multi-physics coupled model, a thermodynamic analysis method is employed to reveal the distributions of energy and exergy losses in the system, and the effect of the concentration ratio on the losses is investigated. The results show that the optical loss caused by the concentrating and splitting processes accounts for 33.3% of the total input energy. The losses in the energy conversion process are the largest of all the subsystem losses. The energy and exergy losses in the photovoltaic conversion process are 51.5% and 45.9%, while those for the thermoelectric conversion process are 87.8% and 74.5%, respectively. Raising the concentration ratio is an effective way to reduce the exergy loss in the energy conversion process, but it will also partially raise the exergy losses in the heat dissipation and cooling processes. The exergy efficiency of the SSPV-TE system can reach 21.75% at a concentration ratio of 500. The results are important for better understanding the operating principles, optimizing the performance, and advancing the application of the spectrum splitting photovoltaic-thermoelectric system.

An integrated alkali metal thermoelectric converter with sodium hydroxide thermoelectric water splitter and organic Rankine cycle for efficient power and hydrogen production

This study proposes the integration of the NaOH thermochemical water splitting cycle with both an alkali metal thermoelectric converter and an organic Rankine cycle. The objective of the proposed model is to enhance the overall efficiency by utilizing the waste heat generated by the NaOH thermochemical water splitting process and redirecting the heat from the alkali metal thermoelectric converter using bypass when hydrogen demand is low.Performance parameters such as system efficiency, system power, hydrogen production, AMTEC power production, and ORC power production were examined in the study. The results indicated an increase in power and hydrogen production with higher hot-end temperatures, along with an overall reduction in system efficiency for low values of load resistance. The system achieved a maximum efficiency of 53.37%.The system efficiency reached its peak at an AMTEC hot end temperature of 1173 °C, achieving 53.37 % efficiency at an RL value of 1.01 O. When the system operates at its maximum AMTEC power production, the AMTEC modules supply 12.81 kW, while the ORC generates 5.57 kW, and the hydrogen compressor consumes 0.13 kW. The total electrical power generation is 18.38 kW. The findings also indicate that the utilization of the bypass led to a reduction in hydrogen production while increasing the power output of the organic Rankine cycle.

Precision RMS-to-DC Converter

The developed model of a resistive-transistor thermoelectric converter, the technique for identifying its parameters and the results of circuit simulation using the proposed model of an RMS-DC converter are considered. The electrical circuit of the RMS-DC converter is given, the dependences of the conversion error on the input voltage level obtained by circuit modeling, on the basis of which the main requirements for reducing the error are formulated. The application of operational amplifiers of the OAmp11.2 type with input junction field-effect transistors, previously developed on the master slice array МН2ХА031, makes it possible to implement a precision RMS-DC converter in the form of a microassembly containing two crystals of the ПН001 thermoelectric converter, one МН2ХА031 crystal with a signal processing circuit and external filter capacitors. Circuit simulation showed that such a converter remains operational at an absorbed dose of gamma radiation equal to 1 Mrad and exposure to a neutron fluence of 1 ⋅ 1013 n/cm2 .

A Rolled Organic Thermoelectric Generator with High Thermocouple Density

AbstractThe surge in the number of distributed microelectronics and sensors requires versatile, scalable, and affordable power sources. Heat‐harvesting organic thermoelectric generators (TEGs) are regarded as potential key components of the future energy landscape. Recent advances in the performance of organic thermoelectric materials have made practical applications of organic TEGs more feasible than ever before, yet the challenges of designing and fabricating organic TEGs suitable for real scenarios are scarcely addressed. Specifically, small sensors and wearables demand for micro‐thermoelectric generators (µTEGs) with high power density architectures and small form factors, while typical demonstrations of organic TEGs are characterized by < 10 thermocouples (TCs) per cm2. This work presents a rolled, organic µTEG architecture combining large‐area, solution‐based deposition techniques, such as inkjet and spray‐coating, and an ultrathin parylene substrate to achieve a thermocouple density of 1842 TCs cm−2. Such demonstrative µTEG reaches a thermoelectric conversion performance of 0.15 µW cm−2 at ΔT = 50 K. Such power output is well in line with finite element method simulations, which highlight the benefit of the architecture and show that remarkable power densities, in the mW cm−2 range at ΔT = 10 K, are realistically achievable with geometrical improvements and already ongoing advancements in organic thermoelectric inks.

Device level assessment of Ni and Ni45Cu55 as electrodes in Mg2(Si,Sn)-based thermoelectric generators

Owing to efficient thermoelectric conversion, non-toxicity, low density and cost, Mg2(Si,Sn)-based solid solutions hold potential for mid-to-high temperature waste heat recovery. Yet, challenges arise from n-Mg2(Si,Sn) degradation at ≥400 °C caused by Mg loss and charge carrier reduction, particularly in Sn-rich compositions. To build a thermoelectric generator (TEG) stable up to 400 °C, we propose binary Mg2Si as the n-type leg. Using Ni45Cu55and Ni yields low electrical contact resistance (<5 µΩ.cm2) without altering the thermoelectric properties of n-Mg2Si. We fabricated two 2×2 leg TE modules with the same electrode/TE combination for the p-type legs and with Ni or Ni45Cu55 for their n-type legs and tested up to 400 °C, allowing for a direct comparison between these twoelectrodes for n-Mg2Si at the device level. Ni45Cu55 outperformed Ni, resulting in a peak power density of 0.79 W/cm2 at ΔT ∼375 K and an efficiency competitive to Mg2(Si,Sn)-only TEG.Comparative simulations using a constant property model revealed a strong reduction of internal losses when using Ni45Cu55as the electrode for n-Mg2Si as the main reason for the high performance. The presented design overcame challenges such as Mg sublimation at targeted application temperature or electrode induced defect formation, resulting in a stable TEG.

Strain/deformation-insensitive wearable rubber composite for temperature monitoring based on the photothermal and thermoelectric conversion

Wearable sensor has been developed for the temperature monitoring. However, the motion of human muscles is a nonnegligible background interference which affects the stable and accurate transmission of output electrical signals for temperature sensor. Rubber, as an elastic and flexible material, has been widely applied all over the world due to the easy processing and low cost, which is potential to serve as a matrix of intelligent sensing material. But it is difficult to construct a conductive pathway in the solid rubber by the filling conductive media. Herein, we report a temperature-responsive rubber composite with strain-insensitive resistance based on a synergism structure constructed by Ag nanoflakes (AgNFs) and Ag nanoparticles (AgNPs) after the rubber latex film forming. The AgNFs are easier to overlap and form stable conductive paths to endow the material with a stable conductivity within a small strain (ε < 9 %) via the slide of AgNFs, showing a maximal value of (R-R0)/R0 at only 0.001. In this case, the AgNPs with slight agglomeration are filled into the space of AgNFs to construct conductive paths. Under the larger strain (9 % <ε < 143 %), the agglomerated AgNPs are pull-apart and migrated to form single AgNP, maintaining the conductive path with a high quality factor of 9.09. The resultant material owns a high photothermal conversion efficiency of 78.6 %. Based on the satisfactory conversion of “light-heat-electricity” and “heat-electricity”, material is used as a wearable temperature sensor, and it only takes 0.5 s to sensitively sense the changes in body temperature.

Efficiency Enhancement in Ocean Thermal Energy Conversion: A Comparative Study of Heat Exchanger Designs for Bi2Te3-Based Thermoelectric Generators.

This research focuses on enhancing the efficiency of Bi2Te3-based thermoelectric generators (TEGs) in ocean thermal energy conversion (OTEC) systems through innovative heat exchanger designs. Our comparative study uses computer simulations to evaluate three types of heat exchangers: cavity, plate-fins, and longitudinal vortex generators (LVGs). We analyze their impact on thermoelectric conversion performance, considering the thermal energy transfer from warm surface seawater to TEGs. The results demonstrate that heat exchangers with plate-fins and LVGs significantly outperform the cavity heat exchanger regarding thermal energy transfer efficiency. Specifically, plate-fins increase TEG output power by approximately 22.92% and enhance thermoelectric conversion efficiency by 38.20%. Similarly, LVGs lead to a 13.02% increase in output power and a 16.83% improvement in conversion efficiency. These advancements are contingent upon specific conditions such as seawater flow rates, fin heights, LVG tilt angles, and locations. The study underscores the importance of optimizing heat exchanger designs in OTEC systems, balancing enhanced heat transfer against the required pump power. Our findings contribute to a broader understanding of materials science in sustainable energy technologies.

Influence of the Anderson Transition on Thermoelectric Energy Conversion in Disordered Electronic Systems

So far, the efficiency of thermoelectric energy conversion remains low compared to traditional technologies, such as coal or nuclear. This low efficiency can be explained by connecting the thermoelastic properties of the electronic working fluid to its transport properties. Such connection also shows that operating close to electronic phase transitions can be an efficient way to boost the thermoelectric energy conversion. In this paper, we analyze themoelectric efficiency close to the metal-insulator Anderson transition. Our results reveal the direct link between the thermoelectric and thermoelastic properties of Anderson-type systems. Moreover, the role of the conductivity critical exponent in the thermoelectric energy conversion is analysed. Finally, we show that relatively large values of the thermolectric figure of merit may be obtained in the vicinity of the Anderson transition.

2D Materials for Photothermoelectric Detectors: Mechanisms, Materials, and Devices

Abstract2D materials, with outstanding optical, thermal, and electric properties, are emerging as promising candidates for fabricating high‐performance photodetectors. Recently, impressive progresses have been made in this area and some challenges are remaining to improve the properties of photodetectors. As one important part in the mainstream photodetection mechanisms, photothermoelectric (PTE) effect is showing unique priorities in fabricating advanced photodetectors, especially broadband detection operating in the mid‐infrared and terahertz spectral regime. Here, recent progress on PTE photodetectors based on layered 2D materials is reviewed. The physical mechanism of PTE effect is first discussed and then the optical and thermoelectric properties of various 2D materials are analyzed. Furthermore, strategies to improve the photodetection performance of PTE detectors are summarized in two major categories including enhanced photothermal conversion and thermoelectric conversion processes. Finally, the challenges and prospects for future research in 2D thermoelectric materials and PTE detectors are also provided.

Enhancing Ocean Thermal Energy Conversion Performance: Optimized Thermoelectric Generator-Integrated Heat Exchangers with Longitudinal Vortex Generators

The effective utilization of renewable energy has become critical to technological advancement for the energetic transition from fossil fuels to clean and sustainable sources. Ocean Thermal Energy Conversion (OTEC) technology, which generates electricity by leveraging the temperature differential between surface and deep ocean waters, enables stable power generation around the clock. In this domain, the combination of thermoelectric generators (TEGs) and heat exchangers has exhibited immense potential for ameliorating the deficiencies of conventional OTEC. This study uses finite element numerical simulation of the COMSOL5.5 software to investigate the fluid dynamics characteristics of heat exchangers with flat fins and different types of longitudinal vortex generators (LVGs) under the same number of fins. This research encompasses heat exchangers with rectangular, triangular, and trapezoidal LVGs. Concurrently, the analysis examines how the vortices generated by the LVGs influence the thermoelectric performance of the TEGs. The results demonstrate that heat exchangers integrating flat fins and LVGs can enhance the power generation efficiency of TEGs. However, the pumping power required by the LVGs constrains the thermoelectric conversion efficiency. Compared to rectangular and triangular LVGs, trapezoidal LVGs achieve a superior balance between output and pumping power. Heat exchangers utilizing trapezoidal LVGs can attain the highest TEG thermoelectric conversion efficiency with a specific seawater flow velocity. Overall, these findings provide valuable reference information for applying TEGs and heat exchangers in OTEC design.

Developing a novel personal thermoelectric comfort system for improving indoor occupant’s thermal comfort

Personal comfort systems (PCSs), which target to condition only the occupied zones of indoor space, have received considerable interest due to their validity in thermal comfort improvement and building energy saving. Recently, the thermoelectric module (TEM) has been utilized in the design of PCS for its high reliability, small size and noise-free operation. However, the PCSs using the TEM generally lack the effective control strategy with occupant’s feedback, thus reducing their actual effectiveness on improving thermal comfort. In this paper, a novel personal thermoelectric comfort system (PTCS) is developed with a feedback control framework embedded into it. The PTCS is mainly composed of a thermoelectric conversion unit, a micro blower, control/drive modules and a tube network. A thermal comfort feedback control strategy is proposed for the PTCS. In this strategy, a thermal comfort feedback table is established based on offline experiments, and the tube outlet airflow velocity and temperature setpoints are obtained simultaneously through the table look-up method. Then, the neuron PID control algorithm and pulse width modulation (PWM) of voltage are adopted to adjust the tube outlet airflow velocity and temperature for tracking the obtained setpoints. Experimental results validate the effectiveness of the thermal comfort feedback control strategy. Thermal imaging results on human body demonstrate the availability of the developed PTCS. Performance comparison with other PCSs is also provided, which indicates the potential for practical applications.

Model predictive control for automatic operation of space nuclear reactors: Design, simulation, and performance evaluation

Space nuclear reactors possess the inherent benefits of independence from solar energy and the capability to withstand intricate external circumstances. Distinguishing themselves from terrestrial reactors, space nuclear reactors function within the realm of outer space, operating autonomously throughout their entire operational cycles. Consequently, the establishment of a dependable automatic control system assumes utmost significance. In this paper, a high-fidelity nonlinear space thermionic nuclear reactor model is established, encompassing neutron physics, thermal–hydraulic, and thermoelectric conversion system models. An automatic control system with a model predictive controller (MPC) is designed based on the system. A simplified state-space model is established based on system identification as the internal model for the MPC controller, demonstrating good agreement with the dynamic response of the nonlinear system model. The deployment of the MPC controller for system control simulations exhibits excellent control performance under various operating conditions. In the case of a nuclear power step response, the MPC controller achieves an overshoot of 0.07 % and a settling time of 0.65 s. For an electric power step response, the MPC controller yields an overshoot of 0.28 % and a settling time of 36.6 s. These control performances are significantly better than those achieved by the PID controller. In power tracking control, the MPC controller demonstrates virtually error-free tracking performance. When external reactivity disturbances are introduced, the MPC controller outperforms the PID controller in swiftly compensating for the disturbances, maintaining the system's operating state at the desired level.

Numerical research on performance of new structure centrifugal compressor for supercritical CO2 power systems

The supercritical carbon dioxide (sCO2) power cycle system is a potential thermoelectric conversion system with the advantages of high efficiency and compactness, which can be used in the fields of solar thermal power, nuclear power, and other thermal power systems. The compressor is one of the important machines in sCO2 power systems. To improve the performance and reduce the condensation risk of sCO2 centrifugal compressors, a new structure sCO2 centrifugal compressor is proposed in this paper, which has a partial-cover impeller and self-circulation-channel casing (PISC). The internal flow of the compressor with the new structure is analyzed by the CFD method. The flow and condensation in sCO2 centrifugal compressors with the PISC structure and that with the semi-open impeller and traditional casing (SITC) are compared. The results show that the PISC sCO2 compressor has an inhibiting effect on the condensation at the compressor inlet location, reducing the condensation volume to approximately 82% of that of the original structure under design conditions. The total pressure ratio and isentropic efficiency of compressors are simulated, and the result shows that the minimum stable mass flow rate is reduced by about 13% by introducing the new PISC structure into the sCO2 centrifugal compressor, and the maximum isentropic efficiency is increased from 83.5% to 84.4% compared to that of the SITC compressor. A new design idea for the impeller and sCO2 compressor structure is provided in this paper. The research results can be applied to sCO2 compressors and improve the performance and stability of sCO2 power cycle systems.

Enhancing thermoelectric conversion efficiency of hydrogel-based supercapacitors by the three-dimensional ion channels hydration

Ionic thermoelectric (i-TE) supercapacitors are capable of converting low-grade heat directly into electricity, which has enormous potential for wearable power sources and the Internet of Things. However, the low thermoelectric conversion efficiency limits their applications. Here, we report a method for forming polar corona in a three-dimensional (3D) network based on chitosan-polyacrylamide‑silicon dioxide (PACS) hydrogel, significantly increasing the maximum thermogalvanic power density of 187.2 mW m−2 at a temperature difference (ΔT) of 5 K. The abundant functional groups on PACS confine free H2O molecules to the polymer network, forming polar corona, reducing the volume of thermally diffused ions, and enabling rapid conduction of lithium ions (Li+) in unsaturated coordination. In addition, demonstrating an impressive ionic conductivity of 50.2 mS cm−1 as well as a maximum thermal charging voltage of 200 mV (ΔT of 8 K), this work provides a new strategy for broadening applications of ionic thermally chargeable supercapacitors in harvesting low-grade heat and wearable devices.

Моделирование и идентификация элемента Пельтье TEC1-12706 для применения в малообъемных биореакторах искусственного ЖКТ рыб

The bioreactor of a static mini-model of the artificial gastrointestinal tract of fish will provide modeling of processes in the gastrointestinal tract of industrially grown fish (carp, trout, and sturgeon). The study aimed to determine the thermodynamic processes occurring in the bioreactor and the possibility of using the thermoelectric converter TEC1‑12706 in the temperature control system of the bioreactor. The temperature in a bioreactor with a volume of up to 200 ml should vary from 45 to 14℃, the accuracy of maintaining the temperature is 0.1℃. As a result, a mathematical model was obtained with an adjustment according to the identified system parameters, which makes it possible to evaluate thermodynamic processes in the bioreactor, select hardware and create its general mathematical model. The parameters of the Peltier element were identified using a prototype layout measuring the temperature of the cold side of the converter, the hot radiator, the environment, the temperature of the liquid in the reactor, and the current consumed. The operation of the real system took place at an external temperature of 28.31℃; all physical drives were in the temperature equilibrium and under the same initial conditions. A comparison of temperature changes in the real system and the mathematical model obtained as a result of identifying the parameters of the Peltier element showed a non-perfect match of values, but the nature of the temperature change is identical. The following conclusions have been drawn: in the mathematical model, it is necessary to take into account additional drives and flows describing non-ideal conditions of experimental data, for example, thermal reflection of the working surface of the table and partial reflection of air flows. One third of the maximum converter power is sufficient to reduce the temperature of the filled bioreactor by 2 to 3℃. Thus, the thermoelectric converter TEC1‑12706 can be used in an in vitro modeling system of the gastrointestinal tract of fish.

A biomass hydrogel solar evaporator based on low-grade tobacco leaves for water evaporation and thermoelectric conversion applications

A low-cost and eco-friendly solar steam generator was designed by combining polyvinyl alcohol hydrogels with low-grade tobacco leaves biomass photothermal materials, which apply for water evaporation and thermoelectric conversion.

Energy Density in Ionic Thermoelectric Generators by Prussian Blue Electrodes

Solid-state ionic thermoelectric generators have emerged as promising solutions for efficient harvesting of low-grade waste heat. However, the main challenge in achieving continuous power supply is the low efficiency of thermoelectric conversion. In this work, substantial achievements have been made in improving the thermoelectric conversion characteristics by introducing redox pairs on the electrode surfaces. This approach takes advantage of the synergistic effect of thermal diffusion and thermoelectric effects to maximize the conversion efficiency. To improve the thermoelectric storage and output power performance, Prussian blue was attached to a carbon woven fabric and used as an electrode. The incorporation of Prussian blue/carbon woven fabric electrodes results in an increase in current density output and an instantaneous power density of 3.7 mW/m 2 ·K 2 . Furthermore, under a temperature gradient of 10 K, the output energy density for 2 h is 194 J/m 2 , and the Carnot relative efficiency is as high as 0.12% at a hot side temperature ( T H ) of 30 °C and a cold side temperature ( T C ) of 20 °C. Our findings validate the efficacy of integrating thermal diffusion and redox reactions in ionic thermoelectric generators, paving the way for the progress of thermocharged devices and their potential commercial applications.