Alkali Metal Thermoelectric Converter Research Articles

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.

An alkali metal thermoelectric converter/thermally regenerative electrochemical cycles/absorption refrigerator coupling system for power and cooling

The performance of an alkali metal thermoelectric converter (AMTEC) is restricted by the generation of surplus waste heat, so utilizing waste heat is a potential way to enhance the energy exchange efficiency of AMTEC. In this work, a novel coupling system comprised of an AMTEC, thermally regenerative electrochemical cycles (TRECs) and an absorption refrigerator (AR) is proposed, in which the waste heat is spilt into two parts to drive TRECs and AR to content with the actual demand for power and cooling. Taking into account the external heat leakage as well as the principal irreversible losses in the system, the equivalent power output and efficiency of the system are expressed mathematically. Furthermore, the generic performance features are demonstrated as well as optimum operation regions of the coupling system are obtained. After optimizing the proportional coefficient of heat flow distribution and the current density of the AMTEC, the maximum power output (MPO) and maximum efficiency (ME) could reach 29.49 W and 0.35, respectively. Meanwhile, the MPO and ME of the coupling system are 45 % and 28 % larger than the separate AMTEC system, and are also significantly higher than AMTEC/TRECs and AMTEC/AR. Finally, the impacts of the critical parameters on the systemic performance are evaluated, including the temperature-independent exchange current coefficient, the internal resistance, the regenerative efficiency and the heat-transfer coefficients. The present study may provide a new route for AMTEC to improve the conversion efficiency.

Performance optimization of a solar-driven alkali metal thermoelectric converter coupled to thermally regenerative electrochemical cycles

In order to improve the solar energy conversion efficiency, a novel coupling system comprised of a solar collector, an alkali metal thermoelectric converter (AMTEC), and thermally regenerative electrochemical cycles (TRECs) is constructed, in which the waste heat of AMTEC is used to drive TRECs to generate electricity. Taking into account the main irreversible losses, the analytical expressions for the efficiency and power output of the coupling system model are deduced. The optimum selection criteria of the system’s critical parameters are provided by introducing a multi-parameter combined objective function. Meanwhile, the efficiency and power output density are calculated under different given weight factors. Furthermore, the impacts of the surface temperature of the absorber, the current density in AMTEC, the electrolyte thickness, the regeneration efficiency of TRECs, and the incident spectral solar irradiance on the systemic performance at a given solar concentration ratio are evaluated in depth. Numerical calculation examples illustrate that with a solar concentration ratio of approximately 200, the maximum efficiency and maximum power output density of the coupling system are 28.57% and 49.51% higher than the solar-driven AMTEC system, respectively. Finally, the influences of the solar concentration ratio on the parametric optimum selection criteria are investigated. The present study may provide some new insights to enhance the efficiency of solar energy conversion.

Novel hybrid two-stage alkali metal thermoelectric converter and thermally regenerative electrochemical cycle to exploit waste heat of solid oxide fuel cell: Performance assessment and optimization

An innovative combination of a two-stage alkali metal thermoelectric converter (TAMTEC), and thermally regenerative electrical cycle (TREC) is employed to utilize the high-quality heat dissipated from solid oxide fuel cell (SOFC) for further electricity production. The superiority and effectiveness of the SOFC-TAMTEC-TREC system are verified compared to existing SOFC-based hybrid systems and sole SOFC. The performance of the system based on energy, exergy, and economic indicators is evaluated by varying the main design parameters. Parametric assessment demonstrates that the SOFC-TAMTEC-TREC system can reach the maximum power density of 12126 W m−2 with energy and exergy efficiencies of 47.13% and 50.46% as TAMTEC proportional constant increases to 107.5 m2 and rising SOFC pore and gain diameters to 3.77 × 10−6 m and 2.5 × 10−6 m, respectively reduce the cost rate density of system by 3.55 $ h−1 m−2. Furthermore, to achieve the maximum power density and exergy efficiency, and minimum cost rate density, NSGA-III multi-criteria optimization, and decision-making techniques are conducted. Outcomes indicate that Shannon entropy leads to the maximum power density of 8597.2 W m−2 with a 35.94% enhancement relative to a single SOFC and 1 $ h−1 m−2 increment in cost rate density of the hybrid system, while LINMAP and TOPSIS ascertain the minimum increase in the cost rate density by 0.6 $ h−1 m−2 with 31.04% improvement in power density relative to single SOFC.

Impact of Sintered Temperature on the Heat and Cation Transport in NaK-BASE Tube

Alkali metal thermoelectric converter (AMTEC) is a clean energy converter that can be coupled with biomass for power generation. In present research, the transport of heat and cation was investigated in NaK-BASE tubes prepared at different sintered temperatures. The heat conduction and the fractal model were employed to investigate the temperature distributions based on the microstructures of the NaK-BASE tubes sintered at different temperatures, and the transport of Na+ and K+ in NaK-BASE tube was simulated by Poisson-Nernst-Planck multi-ions transport model, and the cation concentrations and surface charge densities were obtained in the NaK-BASE tubes with different temperatures. The results showed that microstructure of the NaK-BASE was related to the sintered temperature, and the microstructure of the NaK-BASE impacted the temperature distribution, the cation concentration and the surface charge density of Na+ and K+ in the NaK-BASE tubes. At the same heat source temperature, the average temperature in the NaK-BASE prepared at high sintered temperature was higher than that prepared at low sintered temperature. In addition, the increase of the average temperature resulted in the increase of the cation concentration and the surface charge density of Na+ and K+ in the NaK-BASE, therefore, the performance of the NaK-AMTEC could be enhanced by increasing the sintered temperature and the average temperature of the NaK-BASE.

Dynamic simulation and performance evaluation of a novel solar heliostat-based alkali metal thermoelectric converter system

Solar tower plants (STPs) can foster reduce toxic emissions and a cleaner environment. Here, to step forward in this advance, this system is employed as a heat source for an alkali metal thermoelectric converter (AMTEC). Thermal energy storage (TES) is applied to stabilize the performance of the hybrid system along with solar irradiation fluctuations. The considered system is investigated on three different days for the humid subtropical climate of Bandar Abbas, Iran. This study's primary outcome and contribution is a novel simulation framework via TRNSYS to predict the performance of the system under fluctuations of solar irradiation at this site. Both TES and STP systems are defined in TRNSYS software as a new component type via utilizing the Fortran program. The effects of various parameters, including the total energy absorbed by the central receiver, the thermal capacity of TES, and the heliostats field area, are investigated on crucial output parameters of the AMTEC. The mass flow rate of the heat transfer fluid at several areas is then studied in different operating conditions. The optimum area for the heliostats (14,500 m2), leading to the highest AMTEC efficiency (18%) is determined, which requests a TES tank volume of 28.13 m3. This system is noticed to have its most remarkable performance in June and July.

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.

Parametric study and performance assessment of a biomass based alkali metal thermoelectric converter hybrid system

A novel system was developed by combining the alkali metal thermal to electric converter (AMTEC) and biomass gasification. The primary purpose of this study was to examine the feasibility of utilizing the emitted gas caused by biomass gasification as the heat source of the AMTEC device. Key features were studied at constant temperatures under the influence of changes in biomass. These studies were performed on the effects of the equivalence ratio and the fuel flow rate of the biomass system on the total output power, efficiency, and effective voltage of the intended AMTEC. Due to coupling circumstances, ER changes were limited between 0.3 and 0.4. The findings revealed that the equivalence ratio affected the output power, efficiency, and total current of the system reversibly while directly impacting the effective voltage. Increasing the fuel flow rate initially enhanced the efficiency and total output power, but they both were reduced above a specific fuel flow rate. A maximum efficiency of 18.5% was obtained at the optimum fuel flow rate of biomass. More tubes in the cell improved the overall performance of the developed system. However, design and construction cost limit the number of tubes. The results obtained reveal the advantages of the hybrid model.

Performance analysis of alkali metal thermoelectric converter and segmented thermoelectric generator hybrid system based on a comprehensive model

The conceptual hybrid system combined alkali metal thermoelectric converter (AMTEC) and segmented thermoelectric generator (STEG) is a promising static thermal to electric conversion system. A comprehensive model and an effective iterative numerical solution method for the AMTEC/STEG hybrid system have been developed in this paper. The comprehensive model includes the AMTEC unit model and the STEG unit model. The good agreement between the model calculation results and those provided in the published reference show the correctness and accuracy of the models. The effect of beta’’ alumina solid electrolyte (BASE) temperature and condenser temperature on the system performance, the load following characteristic and nominal operation conditions have been investigated using the comprehensive model in this paper. According to the performance analysis results, 1173 K and 653 K are selected as BASE and condenser temperatures. When system input power is 249 kW, the peak conversion efficiency can reach 34.2%. The nominal operation point has been selected according to the optimal performance parameters and load following characteristic of the hybrid system, at the nominal operation point, the system electric power, conversion efficiency, current and voltage of AMTEC and STEG can reach 84 kW, 34.2%, 165.5 A, 448.3 V, 51.7 A, 356.5 V, respectively.

An alkali metal thermoelectric converter hybridized with a Brayton heat engine: Parametric design strategies and energetic optimization

A model for a novel integrating system consisting of an alkali metal thermoelectric converter and a non-recuperative irreversible Brayton heat engine is presented. The efficiency and power output density of the overall system is analyzed at light of the main characteristic losses in each subsystem: the thickness of the electrolyte, the current density of the converter, and the internal losses of the Brayton cycle coming from the compressor and turbine. A detailed study on the behavior of the overall maximum power and maximum efficiency regimes is also presented. An analysis on compromise performance regimes from multi-objective and multi-parametric optimization techniques based on the Pareto front, for both the subsystems and the overall system, enhance the obtained results. The numerical results of the present model are compared with those of alkali metal thermoelectric converter working alone and with other different existing hybrid models. It is found that the exhaust heat discharged by the converter can be efficiently utilized by an irreversible Brayton heat engine. So, the maximum efficiency and maximum power output density of the present model attain 41.7% and 116×103 W/m2 which increase about 44.8% and 158% compared to the values of the alkali metal thermoelectric converter working alone and 20.5% and 80.4% when compared with a hybridized configuration including a thermoelectric energy converter.

Optimization of vapor anode multi-tube alkali metal thermoelectric converter based on an integrated model

The alkali metal thermal to electric converter (AMTEC) is a promising technology for direct conversion of heat to electricity. Design optimization and cell fabrication have been attracting wide interest to improve the cell performance. An integrated analysis model has been developed in this paper. The model includes three coupled parts of a thermal model, an electric model, and a pressure loss model, which are solved by numerical iteration method. All radiation view factors in the cell are calculated by the thermal radiation analysis software RadCAD based on Monte-Carlo ray-tracing technique to accurately and stably simulate the heat flux between the radiation surfaces to support design optimization. The integrated analysis model’s predictions are in good agreement with experimental results of PX-3A cell for a wide range of external loads, which confirms the accuracy of the integrated analysis model and the rationality of the solution processes. After model validation, the effects of various parameters on the cell performance are investigated, including the cold end temperature, geometry of the heat shield, number of BASE tubes, heat loss through the cell wall, and electrode material. The optimization suggestion and optimal parameter range are given in the analyses. At last, an integrative optimization is performed using achievable parameters under current technology. The peak power and conversion efficiency have been improved from 4 W to 6.7 W and 13.5% to 18.1%, respectively.

Performance assessment and parametric study of a hybrid system consisting of an alkali metal thermoelectric converter and an absorption refrigerator

A novel hybrid system model is established to boost the energy conversion efficiency of an alkali metal thermoelectric converter (AMTEC) by combining with an absorption refrigerator (AR). Based on the available models of the AMTEC and AR, the power output and the efficiency of the hybrid system are discussed. Power outputs and efficiencies of the subsystems and hybrid system are compared, and the advantages of the proposed device are demonstrated. Maximum efficiencies of the stand-alone AMTEC and hybrid system are 26.57% and 39.24%, respectively. The optimally working regions for the current density, power output, and efficiency of the hybrid system are determined. The effects of the cooled space temperature on the working region of the current density are revealed, and the influences of the condenser temperature of the AMTEC and the heat-transfer irreversibility on the established system performance are also discussed.

Parametric design strategies of an updated alkali metal thermoelectric converter-thermoelectric generator system operating at optimum states

The aim of this study is to deeply search and understand the performance of the coupling system composed of an alkali metal thermoelectric converter and a thermoelectric generator. The main methods are to update the model of the coupling system, which includes the main irreversible losses existing in subsystems and coupling system, and obtain the analytical expressions of the power outputs and efficiencies of two subsystems and coupling system. The main novelties are to discuss the influences of the thickness of the β″-alumina solid electrolyte on the whole performance of the system and solve the matching problem between two subsystems. The main contents of this study include that the influences of the thickness of the electrolyte membrane, current density of the alkali metal thermoelectric converter, and electric current of the thermoelectric generator on the power output density and efficiency are discussed and the maximum power output density and efficiency of the system are calculated and compared with those of the single alkali metal thermoelectric converter and the existing coupling models. The results obtained reveal the advantages of the present model. The whole performance of the coupling system can be optimized and the parametric selection criteria of several key parameters of the coupling system operating at optimum states can be provided, When the thickness of the electrolyte membrane is optimally selected, the maximum efficiency of the present model attain 34.6% and increase about 10.4%, compared with those of the existing best coupling system. The waste heat released by the alkali metal thermoelectric converter can be efficiently utilized by the thermoelectric generator.

Analysis of the performance of an alkali metal thermoelectric converter (AMTEC) based on a lumped thermal-electrochemical model

The alkali metal thermoelectric converter (AMTEC) is a regenerative concentration cell for direct conversion of heat to electrical energy. Optimization of the components in AMTECs has been gained wide interest to improve power output and cell efficiency. A lumped thermal-electrochemical model has been developed in this work based on some previous efforts by Tournier et al. (1997). The main contribution of the present model is to simplify the calculation of radiation heat exchange by rendering the BASE, the condenser and the cell walls as a system of three closed-surfaces. The net radiative heat loss from the BASE is determined using a network method of radiation. For model validation purposes, the lumped model is applied to a PX-3A type cell. Good agreements have been obtained between numerical results and experimental data on variations of voltage, current, power output and cell efficiency within a wide range of external loads. Based on the numerical results, the role and separate influence of each component are quantitatively analyzed, including temperature levels for hot and cold ends, BASE properties, electrode materials, heat reduction methods and conductor leads. Optimum parameters are suggested in the analyses. With the recent advances in BASE and electrode materials, an integrated optimization is made to the AMTEC aiming for extra-terrestrial application. In the new module, the surface area of electrodes is increased, new electrodes materials are used and thermal radiation losses are minimized. With stable parameters, the peak power of the cell has been over 8.0 We. The stable voltage is over 3.0 V when RL > 1.2 Ω and the cell efficiency is over 20% when RL is within 1.2–4.0 Ω.

Direct energy conversion using liquid metals

Liquid metals have excellent properties to be used as heat transport fluids due to their high thermal conductivity and their wide applicable temperature range. The latter issue can be used to go beyond limitations of existing thermal solar energy systems. Furthermore, the direct energy converter Alkali Metal Thermo Electric Converter (AMTEC) can be used to make intangible areas of energy conversion suitable for a wide range of applications. One objective is to investigate AMTEC as a complementary cycle for the next generation of concentrating solar power (CSP) systems. The experimental research taking place in the Karlsruhe Institute of Technology (KIT) is focused on the construction of a flexible AMTEC test facility, development, test and improvement of liquid-anode and vapor-anode AMTEC devices as well as the coupling of the AMTEC cold side to the heat storage tank proposed for the CSP system. Within this project, the investigations foreseen will focus on the analyses of BASE-metal interface, electrode materials and deposition techniques, corrosion and erosion of materials brought in contact with high temperature sodium. This prototype demonstrator is planned to be integrated in the KArlsruhe SOdium LAboratory (KASOLA), a flexible closed mid-size sodium loop, completely in-house designed, presently under construction at the Institute for Neutron Physics and Reactor Technology (INR) within KIT.

Direct energy conversion using liquid metals

Liquid metals have excellent properties to be used as heat transport fluids due to their high thermal conductivity and their wide applicable temperature range. The latter issue can be used to go beyond limitations of existing thermal solar energy systems. Furthermore, the direct energy converter Alkali Metal Thermo Electric Converter (AMTEC) can be used to make intangible areas of energy conversion suitable for a wide range of applications. One objective is to investigate AMTEC as a complementary cycle for the next generation of concentrating solar power (CSP) systems. The experimental research taking place in the Karlsruhe Institute of Technology (KIT) is focused on the construction of a flexible AMTEC test facility, development, test and improvement of liquid-anode and vapor-anode AMTEC devices as well as the coupling of the AMTEC cold side to the heat storage tank proposed for the CSP system. Within this project, the investigations foreseen will focus on the analyses of BASE-metal interface, electrode materials and deposition techniques, corrosion and erosion of materials brought in contact with high temperature sodium. This prototype demonstrator is planned to be integrated in the KArlsruhe SOdium LAboratory (KASOLA), a flexible closed mid-size sodium loop, completely in-house designed, presently under construction at the Institute for Neutron Physics and Reactor Technology (INR) within KIT.

A Thermoelectric-Conversion Power Supply System Using a Strontium Heat Source of High-Level Radioactive Nuclear Waste

A thermoelectric-conversion power supply system with radioactive strontium in high-level radioactive waste has been proposed. A combination of Alkali Metal Thermo-Electric Conversion (AMTEC) and a strontium fluoride heat source can provide a compact and long-lived power supply system. A heat source design with strontium fluoride pin bundles with Hastelloy cladding and intermediate copper has been proposed. This design has taken heat transportation into consideration, and, in this regard, the feasibility has been confirmed by a three-dimensional thermal analysis using Star-CD code. This power supply system with an electric output of 1MW can be arranged in a space of 50m2 and approximately 1.1m height and can be operated for 15 years without refueling. This compact and long-lived power supply is suitable for powering sources for remote places and middle-sized ships. From the viewpoint of geological disposal of high-level waste, the proposed power supply system provides a financial base for strontiumcesium partitioning. That is, a combination of minor-actinide recycling and strontium-cesium partitioning can eliminate a large part of decay heat in high-level waste and thus can save much space for geological disposal.

Integrated synthesis of AMTEC electrode by using controlled thermal plasma processing

Thermoelectric materials (β″-alumina) for the alkali metal thermoelectric converter (AMTEC) have been synthesized with the use of a thermal plasma reactor based on the forced constricted type plasma jet generator. It is reconfirmed that the powder mixing ratio (i.e. the ratio between α-Al 2O 3, Na 2CO 3 and MgO), jet power and substrate position, strongly affect the synthesis of β″-alumina. Besides these, the synthesis of β″-alumina is also enhanced in the high-temperature region by oxygen injection. Those dependences are correlated with jet temperature and particle heating. The metal electrode of molybdenum is also prepared by spraying Mo powders. Porosity of the prepared films could be well controlled by varying the pressure.

Influence of SiO2 and Fe2O3 on Properties and Microstructure of .BETA."-Alumina.

In order to decrease the cost of β-alumina for solid electrolytes of AMTEC (alkali metal thermo-electric converter), it is desirable to use low purity starting materials. In this paper, we investigated the influence of impurities such as SiO2 and Fe2O3, which are usually contained in low purity alumina, for several hundreds ppm, on properties and microstructure of β″-alumina. The content of β″-alumina phase and the density decreased with the addition of SiO2, and the resistivity of β″-alumina increased even with the addition of amounts of SiO2 as small as 500ppm. Additional SiO2 formed as a glassy phase at multiple grain junctions, but no secondary phase was observed at boundaries between two adjacent grains. Si segregated along the grain boundaries. It was suggested that the segregated Si suppressed the sintering and increased the resistivity. The addition of Fe2O3 did not affect the properties such as content of β″-alumina phase, density and resistance, but the addition of Fe2O3 in ≥0.5 mass% resulted in grain growth. Because Fe ions were suggested dissolved in spinel block of β″-alumina, it was considered that Fe2O3 did not influence the properties of β″-alumina.

Synthesis of new ceramics from powder mixtures using thermal plasma processing

The synthesis of thermoelectric materials (β″-alumina) for the alkali metal thermoelectric converter (AMTEC) has been studied using a newly designed plasma jet reactor. Under not only atmospheric pressure but also low pressure, thin films of β″-alumina are successfully synthesized for the first time from powder mixtures of α-Al 2O 3, Na 2CO 3 and MgO. The powder-mixing ratio, jet power and substrate position strongly affect the synthesis of β″-alumina, which is found to be correlated with jet temperature. Synthesis of ferrite particles is also discussed. Under both atmospheric and lower pressures, ferrite particles are successfully synthesized from powder mixtures of Fe 2O 3, ZnO, NiO and CuO. In the high temperature region of the plasma jet, ferrite particles with high purity can be synthesized.