Alkali Metal Thermal Electric Converter Research Articles

Conceptual design and multi-objective optimization of a hybrid system based on direct ammonia protonic ceramic fuel cell and alkali metal thermal electric converter

As a power generation device, direct ammonia protonic ceramic fuel cells (NH3–PCFCs) also produce a significant amount waste heat, which not only results in energy wastage but also abnormal operation if the waste heat is not removed. To address these concerns and enhance generation electricity capacity, a novel waste heat recovery system based upon NH3-PCFC and alkali metal thermal electric converter (AMTEC) is first proposed, wherein the AMTEC converts the high-grade exhaust heat produced by the NH3-PCFC to extra electricity. Considering ammonia decomposition sluggish kinetics, various irreversible overpotential losses of NH3-PCFC as well as thermodynamic losses within the integrated system, the energetic/exergetic performance parameters evaluating the NH3-PCFC, AMTEC and the hybrid system are formulated. The general performance characteristics of the proposed system are revealed, along with a sensitive analysis conducted under specific operational conditions or structural parameters. Numerical calculation exhibited that the maximum attainable power density of the hybrid system has been promoted 20.5 % than that of stand-alone NH3-PCFC system. The multi-objective genetic algorithm is utilized to optimize the hybrid system performance for trade-off the power output and efficiency. Optimized results show the power density and corresponding efficiency of proposed system can respectively reach 6762.3 W m−2 and 49.8 % in the corresponding optimization conditions.

The feasibility study of cascade waste heat recovery in a molten carbonate fuel cell-driven system

The use of solid-state converters in power production, particularly in combination with molten carbonate fuel cells, holds promise for improving overall power generation efficiency. These systems are designed to capture and utilize the considerable waste heat generated during power production, leading to enhanced performance and energy recovery. The specific approach discussed in this investigation involves a solid-state system consisting of an alkali metal thermal electric converter and a thermally regenerative electrochemical cycle for waste heat recovery and additional power generation. The study conducts a comprehensive analysis of this combined system, focusing on various aspects, including energy, exergy, and economic considerations. One key variable investigated is the current density, which plays a significant role in determining system performance. The investigation considers sensitivity analysis by varying six design parameters, offering insights into how different factors affect the system's performance. One of the notable findings is the identification of the overall maximum power density, which reaches 2642 W/m2 at a specific current density of 4686 A/m2. Evaluating the overall performance of the system, the study reports energetic efficiency, exergetic efficiency, and exergy destruction rate density. The energetic efficiency stands at approximately 44.04 %, while the exergetic efficiency is notably higher at 47.09 %. Additionally, the exergy destruction rate density is reported at 2968 W/m2. The research highlights the significance of the operating temperature of the molten carbonate fuel cell, as it has a substantial impact on the overall performance of the system. Increasing the operating temperature of the fuel cell leads to improvements in system efficiency and performance. In summary, the investigation demonstrates the potential of a solid-state system with waste heat recovery components in combination with a molten carbonate fuel cell. This approach enhances power production efficiency, making it a promising solution for sustainable and efficient energy generation.

Three-stage integration system with solid oxide fuel cell, alkali metal thermal electric converter and organic Rankine cycle for synergistic power generation

Three-stage integration system with solid oxide fuel cell, alkali metal thermal electric converter and organic Rankine cycle for synergistic power generation

Evaluation and multi-objective salp swarm optimization of a new solid oxide fuel cell hybrid system integrated with an alkali metal thermal electric converter/absorption power cycle

This research introduces a new combination of an alkali metal thermal electric converter (AMTEC) and an absorption power cycle (APC) to boost the performance of the solid oxide fuel cell (SOFC) by recovering the high-quality heat released from the SOFC for further electricity production. The performance criteria of the proposed SOFC/AMTEC/APC hybrid system are mathematically derived using thermodynamic, exergoeconomic, and exergoenvironment-based carbon footprint analysis. Extensive parametric assessment is carried out to evaluate the effect of substantial design parameters on the system's performance criteria. Furthermore, the multi-objective salp swarm algorithm (MSSA) with decision-making techniques is performed to ascertain the hybrid system's maximum power density and minimum cost and environmental impact rates densities. Findings depict the effectiveness and merit of the proposed system with 81% power density improvement compared with the related SOFC-based system. Moreover, the system yields the maximum power density of 9589.37 W/m2, and the corresponding energy and exergy efficiencies are obtained by 55.2% and 57.74%, indicating 59.26% and 53.76% improvements relative to the single SOFC. Furthermore, the minimum cost and CO2 emission rate densities are achieved by 4.26 $/h m2 and 3.32 kgCO2/h m2, respectively, with 31.73% and 42.3% enhancements relative to the base point.

Study of employing a thermoelectric generator and an alkali metal thermal electric converter for waste heat recovery of a solid oxide fuel cell

Although solid oxide fuel cell is an appropriate candidate in the power generation sector, its high waste heat is a problem that should be managed to convert it into a positive feature. Accordingly, this study suggests a novel system for an efficient waste heat recovery of solid oxide fuel cell. Hence, the solid oxide fuel cell is coupled with a thermoelectric generator and an alkali metal thermal electric converter, where the alkali metal thermal electric converter recovers the waste heat of the solid oxide fuel cell, then the thermoelectric generator is used to recover the waste heat of alkali metal thermal electric converter. The plant's performance is evaluated against the current density to indicate the feasibility of the integrity, the optimum current density range, and the maximum current density corresponding to the best productivity of the scheme. Furthermore, eight different parameters are considered to assess the scheme's sensitivity. SOFC operating temperature, average pore diameter, proportional coefficient, TEG temperature, and temperature-independent exchange current coefficient positively influenced the evaluated variables. The highest power density is 10005 W/m2 at the maximum current density of 13066 A/m2 resulting in energetic and exergetic efficiencies of 43.30 % and 46.67 %, correspondingly.

Modeling and thermodynamic analysis of a novel combined cooling and power system composed of alkali metal thermal electric converter and looped multistage thermoacoustically-driven refrigerator

A large amount of high-quality heat from alkali metal thermal electric converter (AMTEC) is wasted, which greatly degrades its thermodynamic performance and causes serious thermal pollution. For solving this issue, a novel combined cooling and power (CCP) distributed system including two static energy conversion units, i.e., the AMTEC unit and looped multistage thermoacoustic-driven refrigerator (LMTADR) unit, is proposed. The general performance for the proposed system is analyzed via establishing the mathematical model, and the optimal region is obtained by considering both equivalent power density and exergy efficiency. Then, the parameter sensitive analysis is represented to provide some theoretical guidance for design of the proposed system. The results reveal that compared with a sole AMTEC system, the maximum equivalent power density and exergy efficiency of the combined system are improved by 42.4% and 22.5%, respectively. When the performance improvement rate reaches the maximum, the combined system achieves an equivalent power density of 9203.3 W m−2, a cooling rate density of 3190.2 W m−2 and an exergy efficiency of 25.8%. This study not only proves the superiority of AMTEC-LMTADR combined system, but also implies the extensive possibility of recovering medium and high-grade heat through LMTADR for refrigeration.

Energy, exergy and ecology performance prediction of a novel SOFC-AMTEC-TEG power system

• A novel triple-cycle power system is proposed. • Energy, exergy and ecology performance are analyzed. • Effectiveness and generic performance characteristics are demonstrated. • There is an optimum thermoelectric element number to optimize performance. In order to realize the cascade utilization of the waste heat for the solid oxide fuel cell, a novel triple-cycle system including a solid oxide fuel cell, an alkali metal thermal electric converter and a thermoelectric generator is proposed. In this system, the alkali metal thermal electric converter powered by the waste heat of the solid oxide fuel cell can drive the thermoelectric generator. The proposed system can efficiently generate electricity in a green and noiseless way, and Thomson effect is considered in the thermoelectric generator model. The results show that improving the number of the thermoelectric generator stages is not conducive to the improvement of the system performance. The maximum power density and ecology function density can result in 42.0% and 53.5% improvement over those of the sole solid oxide fuel cell system, respectively. Further sensitivity analysis confirms that there is an optimum element number of the thermoelectric generator to optimize the performance of the triple-cycle system. This work proves the feasibility of the triple-cycle system, and hints the broad prospect of high-grade heat recovery through an alkali metal thermal electric converter-thermoelectric generator unit.

Performance enhancement in hybrid static power generation by AMTEC–TEG systems: Energy, exergy, and interactions analyses and optimizations

Alkali metal thermal electric converter (AMTEC) and thermoelectric generator (TEG) are two static energy conversion devices with attractive attributes including high scalability and the ability to utilize renewable energy sources. The present study analytically simulates and optimizes the performance of a novel hybrid AMTEC–TEG system from energy and exergy perspectives. The study scrutinizes interactions between the two devices, exergy destruction sources, solutions toward enhancing exergy efficiency, and the impacts of the heat sink, not accomplished in the open literature. The results reveal that exergy loss within the AMTEC condenser is the main source of exergy destruction; nonetheless, there exists a number of optimal designs by which the TEG can effectively recover this lost exergy. Also, the results show that a simple fin-fan or a passive heat exchanger can be sufficient for cooling the hybrid system while protecting the hybrid system’s valuable features like static and maintenance-free operation. The maximum values of energy and exergy efficiencies and generated power, attained within an improved load-following range for the hybrid system, are respectively 35.6%, 47.8%, and 8136 W. Furthermore, comparisons with similar systems acknowledge the superiority of the proposed hybrid system. Overall, the hybrid system is seen to be of high potential as a flexible, modular, static power generation system whose advantages are thoroughly discussed alongside its weaknesses, providing beneficial information for future studies.

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

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

Thermodynamic analysis of the AMTEC ‐based nuclear power system under time‐varying characteristic of the lunar surface

The thermodynamic performance of the lunar surface nuclear power system based on alkali metal thermal electric converter (AMTEC) is analyzed based on the energy conservation of the system. A general mathematical model of the system has been proposed, and the time-varying characteristic of the lunar surface is evaluated. The effects of nuclear reactor parameters, electrode current density of AMTEC, heat rejection parameters and time in a rotational period are considered systematically. Results show that the performance of the lunar surface nuclear power system is unstable during a rotational period. Both of the conversion efficiency (ηs) and output power (P) are higher and steadier during the dark time than during the day time. ηs and P decrease first and then increases, and both of them achieve extreme values on the seventh day. Furthermore, higher nuclear reactor parameters (Tin, Qin) and electrode current density of AMTEC (J) can make positive effect on ηs. The peak conversion efficiency of the power system is about 29.6% when the reactor parameters and electrode current density of AMTEC are 500 kW, 1200 K and 10 000 A/m2, respectively. In short, the time-varying characteristic of the lunar surface makes the thermodynamic property of nuclear power system more complex than ground-based energy system.

A new combined system consisting of a molten hydroxide direct carbon fuel cell and an alkali metal thermal electric converter: Energy and exergy analyses

In addition to electricity, molten hydroxide direct carbon fuel cell also produces a number of high-quality waste heat, which may affect the cell normal operation if the waste heat is not removed immediately. Few efforts have been devoted to recovering the waste heat for additional electricity generation applications yet. In this study, a new combined system model that couples an alkali metal thermal electric converter to a molten hydroxide direct carbon fuel cell is first proposed. Based on the theories of electrochemistry and non-equilibrium thermodynamics, mathematical formulas for the power output, exergy destruction rate, energy efficiency and exergy efficiency of the combined system are deduced. The performance characteristics and optimum criteria of such a combined system are revealed. Numerical calculations show that the maximum output power density of the combined system is improved by 51.6% compared with that of a single molten hydroxide direct carbon fuel cell in the current literature, and its corresponding energy efficiency and exergy efficiency are also increased by 11.3% and 9.4%, respectively. A larger temperature, reactor compartment width, geometric factor for radiation losses or proportional coefficient positively is beneficial for the combined performance improvement, while the thickness of the β′′-alumina solid electrolyte can be tuned to optimize the combined system performance. The obtained results may offer some guidance for the design and optimization of such an actual combined system.

Performance evaluations and parametric selection strategies of a three-stage solid oxide fuel cell-based integrated system providing power and cooling

A model of the three-stage integrated system consisting of a solid oxide fuel cell, an alkali metal thermal electric converter, and an absorption refrigerator is proposed, where the main irreversible losses are considered. Based on the respective parameter relations of three subsystems, the power output and efficiency of the integrated system are analytically derived. The influences of the current densities of the fuel cell and the converter, electrolyte thickness and temperature in the low-temperature side of the converter, and area ratio of the converter to the fuel cell on the systemic performance are discussed. The maximum power output density and optimally working regions of the integrated system are determined. The main novelties are to provide the optimum selective criteria of some vital parameters. It is expounded that the results obtained from the present model may be directly used to derive the optimum performances of the coupled system only comprised of both the fuel cell and the converter. It is found that the maximum power output density of the integrated system increase about 15.8% and 79.8%, compared with that of the coupled system and the solid oxide fuel cell, respectively.

Comparative performance analyses of molten carbonate fuel cell-alkali metal thermal to electric converter and molten carbonate fuel cell-thermo-electric generator hybrid systems

Purpose of this paper is to compare the performance of an alkali metal thermal electric converter (AMTEC) and thermoelectric generator (TEG) as a subsystem for utilizing rejected heat from the molten carbonate fuel cell (MCFC). AMTEC and TEG have various advantages such as; higher power density, no maintenance needed, silent and generally lower cost. Therefore, they have good potential to utilize waste heat. Performance parameters of systems are defined as power output density, exergy destruction rate density, energy and exergy efficiencies. Results show that the system MCFC-AMTEC hybrid system is more advantageous than the MCFC-TEG hybrid system. Some important results are listed follows; maximum power output densities for the MCFC-AMTEC and MCFC-TEG are 2425.833 (W/m2), and 1964.389 (W/m2), respectively, while efficiencies are %, 76.6% and 76.4 %.

The optimal operation states and parametric choice strategies of a DCFC-AMTEC coupling system with high efficiency

The aim of this study is to deeply search the performance of the coupling system comprised of a direct carbon fuel cell and an alkali metal thermal electric converter. The main contents of this study are to propose the model of the novel coupling system by considering the main irreversible losses, derive the efficiency and power output of the whole system, discuss the influences of the electric current of the fuel cell, the electrolyte thickness, and the ratio of the electrode areas of two subsystems on the systemic performances, and, evaluate and compare the performances of the whole system and the fuel cell. The main novelties are to provide parametric optimum choice criteria and give the reasonably matching schemes of two subsystems. The results obtained reveal the advantages of the present coupling system.

Optimum operation states and parametric selection criteria of an updated solar-driven AMTEC

A novel model of the coupling system consisting of a solar collector and an alkali metal thermal electric converter (AMTEC) is proposed, in which various irreversible losses are considered. Analytical expressions for the efficiencies of the solar collector, AMTEC, and coupling system are derived. The operative temperatures of the solar collector and AMETC are determined by energy balance equations rather than some specified parameters. The influences of the thickness of the electrolyte membrane, current density, and area ratio of the absorber to the AMTEC on the performance of the system are discussed. The maximum efficiency and power output density for a given value of the solar concentration ratio are calculated and revealed to be two different operation states of the coupling system. The effects of the solar concentration ratio on the optimal regions of some key parameters are discussed in detail. The optimum selection criteria of these parameters are provided.

Performance evaluation and parametric analysis of AMTEC/TEG hybrid system

A general mathematical model of the AMTEC/TEG hybrid system consisting of alkali metal thermal electric converter (AMTEC) and thermoelectric generator (TEG) has been developed, in which the load parameters and main geometric parameters were considered. Instead of specifying some parameters, the evaporating temperature and condensing temperature of the AMTEC as well as the operating temperature of the TEG subsystem were determined by solving energy balance equations. Results show that electrode current density has a quite noticeable influence on both AMTEC subsystem and TEG subsystem. The maximum conversion efficiencies for AMTEC and AMTEC/TEG are 27.42% and 31.33%, respectively. Besides, it is interesting to note that the optimal value of the ratio of thermoelectric module area to electrode area is always near 0.2 regardless of the ratio of evaporator heat transfer area to electrode area. The length of thermoelectric arms l and the ratio of the thermoelectric couple area to the total area of the thermoelectric module b are critical factors, b ≥ 0.55 and l ≤ 11 mm should be satisfied to obtain a compact and low-cost system.

Evaluation of CaO–Al2O3 adhesive bonding properties for β″-Al2O3 solid electrolyte sealing for alkali metal thermal electric converter

The β″-Al 2 O 3 solid electrolyte (BASE) tube is an essential component of the alkali metal thermal electric converter (AMTEC) system for inducing the conduction of Na ions and generating electricity. Maintaining gas-tightness to produce Na vapor pressure deference and providing insulation to prevent the loss of generated current from BASE are important factors for the AMTEC system. The Na–sulfur (NAS) battery has a similar driving system and uses glass adhesives, which are not adequate for operation temperatures higher than 800 °C or in a Na atmosphere. In this study, CaO–Al 2 O 3 was used as the adhesive to resolve such bonding issues. The bonding strength changes were evaluated as the adhesive bonding process temperature varied and also the results showed that CaO–Al 2 O 3 maintained bonding shear strength of 400 MPa for more than 1000 h in a molten Na environment. This study also proposes an experimental technique based on tube-type impedance measurement to assess the bonding between the BASE and the α-Al 2 O 3 insulator and to detect Na leakage. After conducting the experiment for 500 h, CaO–Al 2 O 3 adhesive can offer higher reliability than glass adhesives.

AMTEC의 소디움액체 순환윅에서 압력손실 및 열손실해석

AMTEC기술은 열을 직접 전기로 변환시키는 기술로서 소디움을 작동유체로 사용하고 있으며, 작동유체의 순환은 모세관윅을 사용한다. 순환계통에는 증발부윅, 순환윅 및 응축부윅으로 구성되고, 각각의 윅은 소디움의 액체 또는 증기가 순환하면서 압력손실이 발생하므로 소디움의 순환을 위해서는 증발부윅의 모세관압력이 윅내의 총압력손실보다 커야만 한다. 본 연구에서는 100 watt급의 AMTEC시제품설계을 위해 소디움의 순환계통으로 구성되는 증발부윅, 순환윅 및 응축부윅에서의 압력손실과 증발부에서 응축부로의 열손실을 순환윅의 직경과 길이에 대해 분석하여 증발부윅의 소결입자 직경과 순환윅의 설계에 활용하코저 하였으며, 분석결과에서 순환계통의 총압력손실보다 큰 모세관압력을 위해서는 증발부윅의 소결입자크기는 10 μm이 적합한 결과를 얻었다.<BR>

An overview of advanced space/terrestrial power generation device: AMTEC

Alkali metal thermal electric converter (AMTEC) technology offers several advantages over conventional forms of electric generation. Some of these advantages are high efficiency, high density, reliability, absence of moving parts, and competitive manufacturing costs. These and other advantages make AMTECs ideally suited for several space, aerospace, military and domestic applications. Current AMTEC designs suffer from some drawbacks that need to be rectified if the full potential of the technology is to be realized. These are current cell efficiencies that are still at values below the theoretically possible, and the adverse power–time characteristic of the cell. The PX-3A AMTEC cell, for instance, shows decreasing values of the maximum power output with time. Maximum power decreases from 2.54 W at the end of 172 h to 1.27 W at 18,000 h of cell operation. This latter problem, called power degradation, in particular, will preclude the use of the cell for applications that require operation of the cell for long periods of time. This paper discusses in detail the advantages of AMTEC technology and the problems with current designs. In particular, the problem of power degradation is dealt with in some detail and some measures are suggested that will help arrest this loss of power with time.