Alkali Metal Thermal To Electric Converter Cell Research Articles

Concept design of solar thermal receiver using alkali metal thermal to electric converter (AMTEC)

A preliminary design of solar thermal generating system using alkali metal thermal to electric converter (AMTEC) is proposed and discussed in this paper. High conversion efficiency, compactness, lightweight, and maintenance free are its characteristics. A vapor-condense-type AMTEC cell incorporated in a solar receiver of about 10 kWe in size was designed. The thermal energy flow for the designed receiver has been calculated and examined. The analysis has been conducted under two operating conditions, maximum efficiency mode and maximum output power mode. On the maximum efficiency mode, the calculated conversion efficiency is 27% for the AMTEC system and 19% for the overall receiver system with the output power is 10.3 kWe at 1000 K. On the maximum output power mode, the conversion efficiency is 20% for the AMTEC system and 17% for the overall receiver system with the output power is 19.1 kW e at 1000 K. The preliminary calculated result has shown that the solar-AMTEC generating system has performance advantage in the solar power generating systems.

443 SOFC-AMTECの複合モジュール化に関する性能解析(燃料電池,電力貯蔵,環境保全型エネルギー技術)

The alkali metal thermal to electric converter (AMTEC) is a device for the direct conversion of heat to electrical power. Operating hot-side temperatures of AMTEC cells are well compatible with those of solid oxide fuel cells (SOFC), so that the stacks of the SOFC can be directly coupled to hot-side of the AMTEC cells. The AMTEC cells would produce electrical power from released heat of the SOFC, as well as control the SOFC operating temperatures by modulating current of the AMTEC cell. A new honeycomb type AMTEC cell is discussed in this paper. The cell uses advanced beta"-alumina solid electrolyte (BASE) configurations to improve the device performance over the conventional tube BASE systems. Expected power densities and efficiencies were calculated. The influence of temperature differences between heat source and anode side electrode is also discussed for vaper-fed type and vaper-vaper-fed type cells.

Review of Refractory Materials for Alkali Metal Thermal-to-Electric Conversion Cells

Refractory alloys are being considered as structural materials in multitube, vapor-anode alkali metal thermalto-electric conversion (AMTEC) cells for future use in radioisotope space electric power systems. In these power systems, the AMTEC cells would operate at a heat source temperature of » 1150 K and a radiator temperature of » 550 K, for a 7‐15 year mission lifetime. In addition to high strength, low density, and low brittle-to-ductile transition temperature, suitablematerialsmustbecompatiblewith thesodium working e uid and havelowthermal expansion and low vapor pressure ( 900 K). C-103 (niobium‐10% hafnium‐1% titanium‐0.5% zirconium ) is also suitable, particularly for thecell’ s colderstructurebecause of its higher strength andlowerthermalconductivity.However,thecompatibilityoftheseniobiumalloyswithsodiumattypicaloperating temperatures and in the presence of minute amounts of oxygen (>5‐10 ppm) for up to 15 years needs further evaluation. Despite the limited availability of rhenium, Mo ‐Re alloys, with a rhenium content of 14 ‐45%, are also good choices as structural materials in vapor anode AMTEC cells. However, their relatively higher density and thermal conductivity could lower the cell’ s performance and increase its specie c mass.

Performance analyses of an Nb–1Zr/C-103 vapor anode multi-tube alkali-metal thermal-to-electric conversion cell

The results of performance analyses of a refractory Nb–1Zr/C-103 vapor anode multi-tube alkali-metal thermal-to-electric conversion (AMTEC) cell are presented and discussed. This cell could be used with a radioisotope heater unit to provide electric power from tens to a few hundreds of watts. In the tens of kilowatts electric range, the AMTEC cells could be used with a parabolic solar concentrator or a nuclear reactor heat source. The present cell measures 41.27 mm in diameter and is 125.3 mm high and has eight sodium beta ′′-alumina solid electrolyte (BASE) tubes, which are connected electrically in series to provide a load voltage in excess of 3 V. The hot structure of the cell, including the hot plate, the BASE tube support plate, the hot plenum wall and conduction stud, the evaporator standoff and porous wick and the side wall facing the BASE tubes, is made of Nb–1Zr. The cell's colder structure, which includes the condenser structure, the interior thermal radiation shield, the casing and wick of the liquid sodium return artery and the side wall above the BASE tubes, is made of C-103. This niobium alloy is stronger and has a lower thermal conductivity than Nb–1Zr, reducing the parasitic heat conduction losses in the cell wall, hence enhancing the cell's performance. The base cell weighs 163.4 g and delivers 7 W e at 17% conversion efficiency and load voltage of 3.3 V (cell specific mass of 23.4 g/W e). These performance parameters were for TiN BASE electrodes characterized by B=75 A K 1/2/m 2 Pa and G=50, assuming a BASE/electrode contact resistance of 0.06 Ω cm 2 and a BASE braze structure leakage resistance of 3 Ω. Also, the inner surfaces of the thermal radiation shield and the cell wall above the BASE tubes were covered with low emissivity rhodium. The temperatures of the BASE brazes and the evaporator were below the recommended design limits (1123 and 1023 K, respectively), and the temperature margin was ⩾+20 K to avoid sodium condensation inside the BASE tube, shorting the cell. When high performance electrodes, characterized by B=120 A K 1/2/m 2 Pa and G=10, were used, the cell's electric power increased to 8.38 W e at 3.5 V, and the efficiency increased to 18.8%, decreasing the specific mass of the cell to 19.7 g/W e without exceeding any of the design temperature limits.

Effect of geometrical variations on AMTEC cell heat losses

Alkali metal thermal to electric converter (AMTEC) cells are built with readily available materials. Improvement of the performance of an AMTEC cell requires improvement and development of components as well as cell geometry. The present paper shows parametric results obtained by changing cell geometry to determine the effects of these design changes on the cell performance. In order to improve the cell performance, heat losses, input thermal power, cell's output power and efficiency have been investigated in detail by varying the cell designs. Changing some geometrical dimensions of the cell has proved to be very effective in improving the cell performance. As a result of this overall effort we have been able to demonstrate the improvement in the efficiency of AMTEC cell by 17.5% over the one in operation called Ground Demonstration Converter System at Air Force Research Laboratory, Albuquerque, New Mexico.

Design optimization and integration of nickel/Haynes-25 AMTEC cells into radioisotope power systems

A number of nickel/Haynes-25, vapor anode, multi-tube Alkali Metal Thermal-to-Electric Conversion (AMTEC) cell designs, similar to the Pluto/Express series cells, were developed and optimized for improved performance. Optimization calculations investigated the effects of changing the number and length of the sodium Beta”-Alumina Solid Electrolyte (BASE) tubes, the cell length and the condenser temperature on the cell’s electric power output, conversion efficiency, temperature margin and the temperatures of the BASE brazes and the evaporator. Various options of integrating the high performance nickel/Haynes-25 cells with 238PuO 2 General Purpose Heat Source (GPHS) modules, into the electric power system’s configuration proposed by Advanced Modular Power Systems, were explored for satisfying an End of Mission (EOM) electric power requirement of 130 W e at 28 V dc for 10- to 15-year space missions. The power systems’ integration options explored included changing the number of GPHS modules and the number of AMTEC cells in the generator and using either fresh or aged 238PuO 2 fuel in the GPHS modules.

High-Performance Radial AMTEC Cell Design for Ultra-High-Power Solar AMTEC Systems

Solar thermal Alkali-Metal-Thermal-to-Electric-Conversion (AMTEC) power systems potentially have several important advantages over current solar photovoltaic power systems in ultra-high-power spacecraft applications for medium-earth orbit (MEO) and geosynchronous orbit (GEO) missions. This work presents key aspects of radial AMTEC cell design to achieve high cell performance in solar AMTEC systems delivering larger than 50 kW(e) with AMTEC cell conversion efficiency larger than 22 percent. A new design parameter methodology is demonstrated establishing optimum design parameters in radial cell design to satisfy high-power mission requirements. Specific temperature- and pressure-dependent relationships define critical dependencies between key cell design parameters, particularly the impact of parasitic thermal losses on Beta Alumina Solid Electrolyte (BASE) area requirements, voltage, BASE tube number, and system power production for maximum power-per-BASE-area and optimum efficiency conditions. High-level system tradeoffs are demonstrated using the design parameter methodology to establish high-power radial cell design requirements and determine optimum radial AMTEC designs. [S0199-6231(00)00102-7]

AMTEC cells challenge energy converters

Sodium-base alkali-metal-thermal-to-electric conversion (AMTEC) cells have been receiving attention. Recently they were selected for the next generation deep-space missions, which need a converter that makes electricity from radioisotope heat. The AMTEC cell, being an electrochemical converter of heat to electricity, has no moving parts and is not limited to Carnot-cycle efficiency. However, its heat source and sink have to be near each other, so the challenge in AMTEC design is to minimize thermal losses and maximize electricity production. This required clever thermal designs. By 1991, high-temperature materials and computer modeling became available. The important AMTEC application was generating power from radioisotope heat in deep space missions. These spacecraft power needs had previously been supplied by inefficient thermoelectric converters.

Performance analysis of Pluto/Express, multitube AMTEC cells

An AMTEC performance and evaluation analysis model (APEAM) was developed to predict the performance of next-generation Pluto/Express, multitube, vapor-anode alkali–metal thermal-to-electric conversion (AMTEC) cells. The model results compared well with the experimental data of PX-4C, PX-5A and PX-3A cells, tested at the Air Force Research Laboratory. The effects of various design changes on the performance of the cells were investigated. These changes were: (a) using a Creare condenser; (b) changing the number of BASE tubes and the electrode length; (c) using other electrode materials; (d) using molybdenum (Mo) structure on the hot side of the cell; and (e) using reflective rhodium coatings in the low vapor pressure cavity of the cell. The results showed that a stainless steel (SS) structure cell with improved electrodes (50% lower contact resistance than TiN, and an exchange current coefficient=200 A.K 1/2/Pa.m 2) could deliver 7.1 We at 3.5 V and an efficiency of 19.5%. When Mo was substituted for the SS on the hot side of the cell, the electrical power output increased to 8.8 We, and the cell efficiency increased to 20.2%. Using rhodium coatings in the Mo/SS cell increased the electrical power output to 9.7 We and the conversion efficiency to 22.5%.

Sodium Vapor Pressure Losses in a Multitube, Alkali-Metal Thermal-to-Electric Converter

A model was developed to calculate the vapor pressure losses and characterize the vapor flow regimes on the cathode side of a multitube, vapor-anode, alkali-metal thermal-to-electric converter (AMTEC) cell, with internal chevron's radiation shields. The dusty gas model was used to predict the vapor flow over a wide range of pressures, including the free-molecular, transition, and continuum flow regimes. Results showed that the vapor flow on the cathode side of a multitube AMTEC cell is typically in the transition regime, and that the pressure loss in the chevron's shield accounts for about 50% of the total pressure losses. An analysis is also performed to optimize the conical chevron's geometry for minimum pressure loss.

Design and integration of a solar AMTEC power system with an advanced global positioning satellite

A 1,200-W solar AMTEC (alkali metal thermal-to-electric conversion) power system concept was developed and integrated with an advanced global positioning system (GPS) satellite. The critical integration issues for the SAMTEC with the GPS subsystems included: (1) packaging within the Delta II launch vehicle envelope; (2) deployment and start-up operations for the SAMTEC; (3) SAMTEC operation during all mission phases; (4) satellite field of view restrictions with satellite operations; and (5) effect of the SAMTEC requirements on other satellite subsystems. The SAMTEC power system was compared with a conventional planar solar array/battery power system to assess the differences in system weight, size, and operations, Features of the design include the use of an advanced multitube, vapor anode AMTEC cell design with 24% conversion efficiency, and a direct solar insolation receiver design with integral LiF salt canisters for energy storage to generate power during the maximum solar eclipse cycle, The modular generator design consists of an array of multitube AMTEC cells arranged into a parallel/series electrical network with built-in cell redundancy. Our preliminary assessment indicates that the solar generator design is scaleable over a 500 to 2,500-W range. No battery power is required during the operational phase of the GPS mission. SAMTEC specific power levels greater than 5 We/kg and 160 We/m/sup 2/ are anticipated for a mission duration of 10 to 12 years in orbits with high natural radiation backgrounds.

Radioisotope powered AMTEC systems

Alkali Metal Thermal to Electric Converter (AMTEC) systems are being developed for high performance spacecraft power systems, including small, General Purpose Heat Source (GPHS) powered systems. Several design concepts have been evaluated for the power range from 75 W to 1 kW. The specific power for these concepts has been found to be as high as 18-20 W/kg and 22 kW/m/sup 3/. The projected area, including radiators, has been as low as 0.4 m/sup 2//kW. AMTEC power systems are extremely attractive, relative to other current and projected power systems, because AMTEC offers high power density, low projected area, and low volume. Two AMTEC cell design types have been identified. A single-tube cell is already under development and a multi-tube cell design, to provide additional power system gains, has undergone proof-of-principle testing. Solar powered AMTEC (SAMTEC) systems are also being developed, and numerous terrestrial applications have been identified for which the same basic AMTEC cells being developed for radioisotope systems are also suitable.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>