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This paper describes hundreds of pendulum tests examining the beamed energy conversion efficiency of different metal targets coated with multiple liquid enhancers. Preliminary testing used a local laser with photographic paper targets, with no liquid, water, canola oil, or methanol additives. Laboratory experimentation was completed at Wright‐Patterson AFB using a high‐powered laser, and ballistic pendulums of aluminum, titanium, or copper. Dry targets, and those coated with water, methanol and oil were repeatedly tested in laboratory conditions. Results were recorded on several high‐speed digital video cameras, and the conversion efficiency was calculated. Paper airplanes successfully launched using BEP were likewise recorded.

With serious concerns on global warming and energy crisis, there are plenty of motivations for developing and commercializing plug-in Electric Vehicles (EVs). It is believed that substitution of EVs for conventional fuel vehicles can help reduce the greenhouse gases emission, increase the energy efficiency, enhance the integration of renewable energy, and so forth. These advantages originate from the double role of the electrical vehicle’s battery. Thus, it may constitute firstly a controllable load that we are able to optimally control at convenient time frames and secondly, it may store and inject energy, acting as a storage device. Nowadays, a number of EVs use power grids around the world to charge and discharge their batteries. Smart Microgrids (SMs) seem to be the best solution for the management of modern Low Voltage (LV) grids with Distributed Energy Resources (DER) and EVs. Among these technologies, EVs pose both a risk by increasing the peak load as well as an opportunity for the existing energy management systems by charging and discharging electricity with the help of Vehicle-to-Grid (V2G) technology. The key to the implementation of V2G is how to effectively integrate information into energy conversion, transmission and distribution. V2G should be carried out within the framework of SM, so that the status information of power grid can be perceived. In this paper, a Low Voltage (LV) SM derived from an interconnection bus is considered which is characterized by the presence of DERs units and EVs. Firstly, an overview of plug in EV technologies is examined and then the main purpose of the paper is to investigate the effects of V2G charging and discharging strategies in a SM. With EVs and absence of DERs is considered as the base case. For each scenario, two different charging technologies are examined (Dump Charging and V2G) in terms of operational cost. All data are taken from Hellenic Distribution/Transmission System Operators and Hellenic Operator of Electricity Market. Matlab software is used for all cases of studies.

Guaranteeng the parameters in the output of the power electronics device is of great importance for achieving the desired quality of the process of energy conversion. The combined methods for realization of the electronic devices with guaranteed parameters requires the usage of systematic approach in the realization of the power electronics device – from the stage of the parameter formulation to the receiving of the end product. In the investigation the application of the modelling and software products for the research are growing more and more. In that relation it is necessary the creation of a common programming environment in which the diversity of application programs can operate. In the paper is present an automated synthesis and design of single-transistor dc-dc converters.Guaranteeng the parameters in the output of the power electronics device is of great importance for achieving the desired quality of the process of energy conversion. The combined methods for realization of the electronic devices with guaranteed parameters requires the usage of systematic approach in the realization of the power electronics device – from the stage of the parameter formulation to the receiving of the end product. In the investigation the application of the modelling and software products for the research are growing more and more. In that relation it is necessary the creation of a common programming environment in which the diversity of application programs can operate. In the paper is present an automated synthesis and design of single-transistor dc-dc converters.

This paper presents a numerical study of the savonius type direct drive turbine in typical chamber geometry of an oscillating water column chamber (OWC) for wave energy conversion. The paper deals with a numerical modeling devoted to predict the turbine efficiency in the components of an oscillating water column (OWC) system used for the wave energy capture. In the present paper, the flow behavior is modeled by using the commercial code ANSYS CFX. Three numerical flow models have been elaborated and tested independently in the geometries of a water chamber with a conventional three bladed savonius type wave turbine and a three bladed helical savonius type turbine. Conventional three bladed savonius rotors have high coefficient of static torque at certain rotor angles. In order to increase the efficiency of the system a helical savonius rotor with a twist of certain proposed degree is introduced. Constant periodic wave flow calculations were performed to investigate the flow distribution at the turbines inlet section, as well as the properties of the savonius type turbine. The flow is assumed to be two‐dimensional (2D), viscous, turbulent and unsteady. The commercial CFD code is used with a solver of the coupled conservation equations of mass, momentum and energy, with an implicit time scheme and with the adoption of the hexahedral mesh and the moving mesh techniques in areas of moving surfaces. Turbulence is modeled with the k‐e model. The obtained results indicate that the developed models are well suitable to analyze the water flows both in the chamber and in the turbine. For the turbine, the numerical results of pressure and torque were compared with each other.

In previous papers I have shown that a revision is required to the basic approach for predicting net currents in thermionic energy conversion diodes. Revised equations were developed to properly account for electron reflection and temperature coefficient effects. Electron spectrum equations for averaging transmission coefficients were also developed. In this paper the spectrum equations are simplified and several new developments are presented that relate to the revised methodology. Recent developments include a demonstration of the general applicability of the new equations, equations for space charge that include the effects of reflection and an emitting collector, and electron cooling equations with electron reflection effects included. In addition, methods are developed to apply the new equations to non-uniform surfaces.

The paper presents an innovative concept of a cascaded solar bimodal power system with a high temperature Cs-Ba thermionic converter (TEC) and Alkali Metal Thermal to Electric Converter (AMTEC). Cs-Ba thermionic technology appears to be an ideal candidate for a TEC-AMTEC cascade due to high optimum collector temperature of such a TEC. Results show that the cascade conversion efficiency in excess of 45% is feasible. The efficiency of the high temperature a Cs-Ba TEC-AMTEC cascade is also compared with that of a Cs-Ba TEC-thermoelectric cascade. A cascaded solar concentration system which provides both high temperature (Cs-Ba TEC) and low temperature (AMTEC) energy conversion stages with their own concentrator, receiver and heat exchanger, and its advantages for solar bimodal systems are also discussed. The paper shows that the use of the high temperature Cs-Ba TEC-AMTEC cascade would allow the development of a highly efficient, compact and light power as well as bimodal systems to address future civilian and defense missions.

The paper presents conceptual design of the bimodal space nuclear power system (NPS) based on the high‐temperature reactor of ROMASHKA type with thermoninic energy conversion system. At the heart of the design is an employment of close‐spaced thermionic diodes, operating in a quasi‐vacuum mode. The paper gives preliminary estimates of the NPS neutron‐physical, electric, thermophysical and mass‐dimensional parameters for the reactor electric power of 25 kW and propulsive thrust of about 80 N. Discussed are peculiarities of the combined mode wherein electric power is generated along with propulsive thrust. The paper contains results of the design studies performed by the Small Business ‘‘NP Energotech’’ under the Agreement with Rockwell International/Rocketdyne Division and according to the Rocketdyne Division provided Design Requirements. Involved in the work was the team of specialists of RRC ‘‘Kurchatov Institute’’, ‘‘Red Star’’ State Enterprise and Research Institute of SPA ‘‘Luch’’

This paper presents an overview of the types of power systems available for providing power on the moon. Lunar missions of exploration, in situ resource utilization, and colonization will be constrained by availability of adequate power. The length of the lunar night places severe limitations on solar power system designs, because a large portion of the system mass is devoted to energy storage. The selection of the ideal power source hardware will require compatibility with not only the lunar base power requirements and environment, but also with the conversion, storage, and transmission equipment. In addition, further analysis to determine the optimum operating parameters for a given power system should be conducted so that critical technologies can be identified in the early stages of base development. This paper describes the various concepts proposed for providing power on the lunar surface and compares their ranges of applicability. The importance of a systems approach to the integration of these components will also be discussed.

At present, the world is in the historical transformation period of global cooperation, sharing and integration, and driving a new era of electrification level. The energy structure is accelerating to evolve toward low carbon and the level of cleanliness of energy supply and consumption has increased significantly. Energy efficiency continues to increase. As is known to all that energy transformation is a social system engineering, whose fundamental task is to build a clean, low-carbon new energy system. The fundamental way is re-electrification. As a new concept, re-electrification has not yet obtained a lot of research results, and has not received extensive attention from foreign scholars. In this paper, electrification-related technologies were identified and screened, a re-electrification technology selection model was built based on DEMATEL method, which has certain significance for the subsequent advancement of re-electrification.

With the increasing depletion of fossil fuels and the increasing prominence of climate and environmental issues, promoting energy transformation and making full use of clean energy has attracted the attention of all countries in the world. Based on the energy revolution direction of two alternatives and the Global Energy Internet Initiative proposed by Chairman Xi Jinping, this paper summarizes the law of energy development and proposes future changes in the world energy supply pattern.

Ion-exchange membrane (IEM) may play an important role in the future of electrical energy generation which is considered as renewable and clean energy. Fell cell (FC) is one of the promising technologies for solving energy issues in the future owing to the interesting features such as high electrical efficiency, low emissions, low noise level, and modularity. IEM-based processes, such as microbial fuel cell (MFC) and reverse electrodialysis (RED) may be combined with water or wastewater treatment into an integrated system. By using the integrated system, water and energy could be produced simultaneously. The IEM-based processes can be used for direct electricity generation or long term energy storage such as by harnessing surplus electricity from an existing renewable energy system to be converted into hydrogen gas via electrolysis or stored into chemical energy via redox flow battery (RFB). In this paper, recent development and applications of IEM-based processes in energy conversion are reviewed. In add...

This paper has briefly described the concept of wave energy generation and six typical conversion devices. As for raft structure, detailed analysis is provided from its development process to typical devices. Taking the design process and working principle of Plamis as an example, the general principle of raft structure is briefly described. After that, a variety of raft structure models are introduced. Finally, the advantages and disadvantages, and development trend of raft structure are pointed out.

Solar energy is one of renewable energy resource where needs a photovoltaic module to convert it into electrical energy. One of the problems on solar energy conversion is the process of battery charging. To improve efficiency of energy conversion, PV system needs another control method on battery charging called maximum power point tracking (MPPT). This paper report the study on charging optimation using constant voltage (CV) method. This method has a function of determining output voltage of the PV system on maximal condition, so PV system will always produce a maximal energy. A model represented a PV system with and without MPPT was developed using Simulink. PV system simulation showed a different outcome energy when different solar radiation and numbers of solar module were applied in the model. On the simulation of solar radiation 1000 W/m2, PV system with MPPT produces 252.66 Watt energy and PV system without MPPT produces 252.66 Watt energy. The larger the solar radiation, the greater the energy of PV modules was produced.

The Virtual SCADA system is a software-based Human-Machine Interface that can visualize the process of a plant. This paper described the results of the virtual SCADA system design that aims to recognize the principle of the Nuclear Power Plant type Pressurized Water Reactor. This simulation uses technical data of the Nuclear Power Plant Unit Olkiluoto 3 in Finland. This device was developed using Wonderware Intouch, which is equipped with manual books for each component, animation links, alarm systems, real time and historical trending, and security system. The results showed that in general this device can demonstrate clearly the principles of energy flow and energy conversion processes in Pressurized Water Reactors. This virtual SCADA simulation system can be used as instructional media to recognize the principle of Pressurized Water Reactor.

Proton Exchange Membrane Fuel Cells (PEMFC), are energy efficient and environmentally friendly alternative to conventional energy conversion for various applications in stationary power plants, portable power device and transportation. PEM fuel cells provide low operating temperature and high-energy efficiency with near zero emission. A PEM fuel cell is a multiple distinct parts device and a series of mass, energy, transport through gas channels, electric current transport through membrane electrode assembly and electrochemical reactions at the triple-phase boundaries. These processes play a decisive role in determining the performance of the Fuel cell, so that studies on the phenomena of gas flows and the performance modelling are made deeply. This paper gives a comprehensive overview of the state of the art on the Study of the phenomena of gas flow and performance modelling of PEMFC.

The conventional RTD (Resistance Temperature Detective) thermocouples of types B, E, R, K and S are the efficient keys in the temperature sensing applications. These are the combinations of thermoelectric materials like Platinum, Rhodium, Constantan, Chromel, and Alumel which works on the Seebeck theory. The chief objective of this research work is only to explore their energy conversion efficiencies in the temperature range of 330°C by the generations of thermo emf. The present research work is carried out in the two parts; one is for the normal conditions and the other for the applied magnetic field of three different magnitudes i.e. 260Gauss, 360Gauss and 460Gauss. Hence this paper reports about the energy management aspects of RTD materials not only by the direct conversion of heat into electricity but also along with the magnetic field.

This paper aims to introduce the ability of thermo electric pallets to convert waste heat into electricity and also about the effect of electric or magnetic fields, which can exist already or applied in the conditions of their operation. Three thermo electric pallets (Bi2Pb3,Bi2Te3 and Pb2Te3) of cylindrical dimensions are prepared by 15mm mixture of different compositions. Thermo emf generations are carried out in the normal mode and then under the influence of applied electric and magnetic fields of different magnitudes in the temperature range of 460K.

The force that acts on a thin vane immersed in rarefied gas when a temperature gradient is imposed along or across the vane has historically been known as the Radiometric force. First observed by Fresnel in 1825, the radiometric force has regained its former popularity in recent decades due to the advent of micro-machines, where a transitional flow regime can occur at atmospheric pressures. Whether used for its force potential or simply viewed as a nuisance, this force cannot be ignored in micro-devices where thermal gradients exist. Potential applications of radiometric force now span from atomic force microscopy to astrophysics to high altitude flight. This paper describes an application of these forces to a conceptual micro-scale energy harvester, where two possible geometries of operation are described. It is shown that one configuration is significantly simpler to fabricate while the other geometry is more efficient at producing larger forces. The effect of pressure, feature separation, and feature-to-ring gap are analyzed. For consistency and the accurate treatment of the relevant flow conditions, an implementation of the SMOKE code that solves the ES BGK equation was used in all computations.

Maximum power point tracking (MPPT) is a very important necessity in a system of energy conversion from a renewable energy source. In this paper, is made an attempt to provide a brief review of 12 very recent publications, not analyzed in the last surveys appeared in 2010 and 2011, and to make a comparative analyze and a classification of all available MPPT algorithms, highlighting their strength and drawbacks. After addressing the reasons for use of MPPT techniques, various power optimization schemes are surveyed. The comparative analysis and a classification of the MPPT algorithms are useful for the designers of wind energy power systems.

Energy source was considered as a key essential in this paper to describe energy conversion process in air‐breathing laser propulsion. Some secondary factors were ignored when three independent modules, ray transmission module, energy source term module and fluid dynamic module, were established by simultaneous laser radiation transportation equation and fluid mechanics equation. The incidence laser beam was simulated based on ray tracing method. The calculated results were in good agreement with those of theoretical analysis and experiments.

In this paper we present design considerations and experimental results of a thermosyphonic hybrid PV/T solar system that is investigated at the University of Patras. Hybrid PV/T systems can provide electrical and thermal energy, thus achieving a higher energy conversion rate of the absorbed solar radiation. We tested outdoors PV/T prototypes consisted of pc‐Si PV modules and heat exchanger of copper sheet with copper pipes, for two system types (PVT/UNGL and PVT/GL). We used commercial PV modules, which give about 12%–15% efficiency, depending on the operating temperature and the use or not of additional glazing. During the experiments the generated electricity was transmitted to a load, simulating real system operation. Steady state tests of the system were performed outdoors to determine collector thermal efficiency. The glazed PV/T collector presents remarkably higher thermal output than the unglazed PV/T collector, but the electrical output of it is reduced due to additional optical losses. The experimental study of the tested thermosyphonic hybrid PV/T solar device showed that it can perform effectively during all year long, achieving at least 40° C of hot water and producing electricity at a satisfactory level.

Cross flow turbine also known as Banki turbine, is a hydraulic turbine that may be classified as an impulse turbine. At present it has gained interest in small and low head establishments because of its simple structure, cost effectiveness and low maintenance. Therefore, the present paper expands on this idea and aims at implementing the Direct Drive Turbine (DDT) for wave power generation. Wave power has enormous amount of energy which is environmentally friendly, renewable and can be exploited to satisfy the energy needs. A Numerical Wave Tank (NWT) was used to simulate the sea conditions and after obtaining desired wave properties; the augmentation channel plus the front guide nozzle and rear chamber were integrated to the NWT. The augmentation channel consisted of a front nozzle, rear nozzle and an internal fluid region which represented the turbine housing. The front and rear nozzle were geometrically identical. Two different nozzle configurations were studied; spiral rear wall type and a straight rear wall type. In addition to this, the effect of front guide nozzle divergent angle was also studied. The general idea is to investigate how different augmentation channel geometry and front guide nozzle divergent angle affects the flow, the water horse power and the first stage (primary stage) energy conversion. The analysis was performed using a commercial CFD code of the ANSYS‐CFX. The results of the flow in an augmentation channel of the Direct Drive Turbine in oscillating flow for all the cases are presented by means of pressure and velocity vectors. The water horse power (WHP) and first stage energy conversion for the models are also presented.

In Microwave Rocket, a high power microwave beam ionizes atmospheric air inside of the thruster and the ionization front drives a shock wave. In this paper, CFD simulation was conducted using measured propagation velocity of the ionization front to evaluate the engine performance. As a result, maximum cycle efficiency was obtained at the power density of about 200 kW/m2 which is the transitional beam power condition between Microwave Supported Combustion and Microwave Supported Detonation regimes.

In order to reduce the size and mass of the single‐shaft turbo‐machines, with little impact on the size of the heat transfer components in the CBC loop, He‐Xe binary mixture with a molecular weight of 40 g/mole has been the working fluid of choice in space nuclear reactor power systems with Close Brayton Cycle (CBC) for energy conversion. This working fluid is also a suitable coolant for the fission reactors heat source designed with fast neutron energy spectra. For space nuclear reactors with thermal neutron energy spectra, however, the high capture neutron cross‐section of Xe will reduce the beginning‐of‐life excess reactivity of the reactor, decreasing its effective operation lifetime. In addition, the neutron activation of Xe in the reactor will introduce a radioactivity source term in the CBC loop. Alternative working fluids with no activation concerns and comparable performance are N2 and the binary mixtures of He‐N2. This paper calculates the transport properties of these working fluids and compare...

The subject of this paper is the current energy challenge and its relation to the entropy challenge. I will summarize the first in the context of the depletion of a finite resource and the rising concern over its environmental impact, and the second in terms of the need to radically improve energy conversion efficiency. Efficiency of chemical and combustion engines is discussed and an approach to reduce entropy generation in combustion is suggested. Related results from some fluid dynamic phenomena are discussed.

Thermophotovoltaic (TPV) cells hold great promise for lightweight, reliable energy conversion for deep space missions. A new method for developing a realistic model of any type of solar cell, with application to Thermophotovoltaic devices, is presented in this paper. Taking into account the high cost of research and experimentation involved with the development of advanced cells, we present here this novel methodology. An example model of an InGaP/GaAs/Ge multi‐junction cell is prepared and is fully simulated. The major stages of the process are explained and the simulation results are compared to published experimental data. An example of cell parameters optimization is also presented. The flexibility of the proposed methodology is demonstrated and example results are shown throughout the whole process. One of the big problems for use of TPV devices in any space mission is heat removal. Currently, many TPV designs assume a low temperature radiator, which equates to large areas and masses. As an application to demonstrate the advantage of this approach. The Silvaco Virtual Wafer Fabrication Software is used as a tool to examine TPV optimization and performance at high temperatures in an attempt to reduce the mass cost associated with large radiators. Results are shown for InGaAs cells optimized to a 1300K black body at 350 K, 400 K, 450 K, and, 500 K.

This paper presents the hydrodynamic efficiency of ablation plasma produced by pulsed ion beam on the basis of the ion beam‐target interaction. We used a one‐dimensional hydrodynamic fluid compressible to study the physics involved namely an ablation acceleration behavior and analyzed it as a rocketlike model in order to investigate its hydrodynamic variables for propulsion applications. These variables were estimated by the concept of ablation driven implosion in terms of ablated mass fraction, implosion efficiency, and hydrodynamic energy conversion. Herein, the energy conversion efficiency of 17.5% was achieved. In addition, the results show maximum energy efficiency of the ablation process (ablation efficiency) of 67% meaning the efficiency with which pulsed ion beam energy‐ablation plasma conversion. The effects of ion beam energy deposition depth to hydrodynamic efficiency were briefly discussed. Further, an evaluation of propulsive force with high specific impulse of 4000s, total impulse of 34mN and momentum to energy ratio in the range of μN/W was also analyzed.

The S∧4 reactor has a sectored, Mo‐14%Re solid core for avoidance of single point failures in reactor cooling and Closed Brayton Cycle (CBC) energy conversion. The reactor is loaded with UN fuel, cooled with a He‐Xe gas mixture at ∼1200 K and operates at steady thermal power of 550 kW. Following a launch abort accident, the axial and radial BeO reflectors easily disassemble upon impact so that the bare reactor is subcriticial when submerged in wet sand or seawater and the core voids are filled with seawater. Spectral Shift Absorber (SSA) additives have been shown to increase the UN fuel enrichment and significantly reduce the total mass of the reactor. This paper investigates the effects of SSA additions on the temperature and burnup reactivity coefficients and the operational lifetime of the S∧4 reactor. SSAs slightly decrease the temperature reactivity feedback coefficient, but significantly increase the operating lifetime by decreasing the burnup reactivity coefficient. With no SSAs, fuel enrichment is only 58.5 wt% and the estimated operating lifetime is the shortest (7.6 years) with the highest temperature and burnup reactivity feedback coefficients (−0.2709 ¢/K and −1.3470 $/atom%). With europium‐151 and gadolinium‐155 additions, the enrichment (91.5 and 94 wt%) and operating lifetime (9.9 and 9.8 years) of the S∧4 reactor are the highest while the temperature and burnup reactivity coefficients (−0.2382 and −0.2447 ¢/K; −0.9073 and 0.8502 $/atom%) are the lowest.

Nuclear power will play an important role in future exploration efforts. Its benefits pertain to practically all the different timeframes associated with the Exploration Vision, from robotic investigation of potential lunar landing sites to long‐duration crewed missions on the lunar surface. However, the implementation of nuclear technology must follow a logical progression in capability that meets but does not overwhelm the power requirements for the missions in each exploration timeframe. It is likely that the surface power infrastructure, particularly for early missions, will be distributed in nature. Thus, nuclear sources will have to operate in concert with other types of power and energy storage systems, and must mesh well with the power architectures envisioned for each mission phase. Most importantly, they must demonstrate a clear advantage over other non‐nuclear options (e.g., solar power, fuel cells) for their particular function. This paper describes a strategy that does this in the form of three sequential system developments. It begins with use of radioisotope generators currently under development, and applies the power conversion technology developed for these units to the design of a simple, robust reactor power system. The products from these development efforts would eventually serve as the foundation for application of nuclear power systems for exploration of Mars and beyond.

Thermionic energy converters are based on electron emission through thermal excitation and collection where the thermal energy is directly converted into electrical power. Conventional thermionic energy converters based on emission from planar metal emitters have been limited due to space charge. This paper presents a novel approach to thermionic energy conversion by focusing on nanostructured carbon materials, sulfur doped nanocrystalline diamond and carbon nanotube films as emitters. These materials exhibit intrinsic field enhancement which can be exploited in lowering the emission barrier, i.e. the effective work function. Moreover, emission from these materials is described in terms of emission sites as a result of a non‐uniform spatial distribution of the field enhancement factor. This phenomenon can prove advantageous in a converter configuration to mitigate space charge effects by reducing the transit time of electrons in the gap due to an accelerated charge carrier transport.

To investigate and mature space based nuclear power conversion technologies NASA awarded several contracts under Prometheus, the Nuclear Systems Program. The studies described in this paper were performed under one of those contracts, which was to investigate the use of a nuclear power conversion system based on the closed Brayton cycle (CBC). The conceptual design effort performed included BPCS (Brayton power conversion system) trade studies to minimize system weight and radiator area and advance the state of the art of BPCS technology. The primary requirements for studies were a power level of 100 kWe (to the PPU), a low overall power system mass (with a target of less than 3000 kg), and a lifetime of 15 years (10 years full power). For the radiation environment, the system was to operate in the generic space environment and withstand the extreme environments within the Jovian system. The studies defined a BPCS design traceable to NBP (Nuclear Electric Propulsion) requirements and suitable for future po...

A Dynamic simulation Model (DynMo) for space reactor power systems is developed using the SIMULINK® platform. DynMo is modular and could be applied to power systems with different types of reactors, energy conversion, and heat pipe radiators. This paper presents a general description of DynMo‐TE for a space power system powered by a Sectored Compact Reactor (SCoRe) and that employs off‐the‐shelf SiGe thermoelectric converters. SCoRe is liquid metal cooled and designed for avoidance of a single point failure. The reactor core is divided into six equal sectors that are neutronically, but not thermal‐hydraulically, coupled. To avoid a single point failure in the power system, each reactor sector has its own primary and secondary loops, and each loop is equipped with an electromagnetic (EM) pump. A Power Conversion assembly (PCA) and a Thermoelectric Conversion Assembly (TCA) of the primary and secondary EM pumps thermally couple each pair of a primary and a secondary loop. The secondary loop transports the h...

Multi‐bandgap, photonic energy conversion is under investigation for nearly every class of photovoltaic materials, with monolithic, series‐connected device structures being the preferred mode of implementation. For TPV energy conversion systems, such an approach represents the next wave in TPV converter advancement. In this paper, we focus on a rigorous analysis of series‐connected, multi‐bandgap, tandem (SCMBT) converter structures according to Kirchhoff’s circuit laws. A general formulation is presented, followed by an application of the general formulation to a typical, semi‐realistic model for well‐behaved, p‐n junction, photovoltaic devices. Using results generated from a computer code written in Visual Basic, we then present example calculations for SCMBT TPV converters with two subcells, for a TPV system utilizing a blackbody radiator operating at 954°C (1750°F). A comparison of the results obtained using the rigorous analysis, with those obtained by using the commonly adopted subcell‐photocurrent‐matching design rule, is discussed in detail. An output power density increase of ∼ 5% is realized in the solution determined by the rigorous analysis, as compared to that obtained with the subcell‐photocurrent‐matching rule. Additional interesting, non‐intuitive results are also highlighted.

The development of lightweight, efficient power for emerging NASA missions and recent advances in thermophotovoltaic (TPV) conversion technology have renewed interest in combining radioisotope heat sources with photovoltaic energy conversion. Thermophotovoltaic power conversion uses advanced materials able to utilize a broader, spectrally tuned range of wavelengths for more efficient power conversion than solar cells. Spectral control, including selective emitters, TPV module, and filters, are key to high‐efficiency operation. This paper outlines the mechanical, thermal, and optical designs for the converter, including the heat source, the selective emitter, filters, photovoltaic (PV) cells, and optical cavity components. Focus is on the emitter type and the band‐gap of InGaAs PV cells in developing the design. Any component and converter data available at the time of publication will also be presented.

For some future space power systems using high temperature nuclear heat sources most of the output energy will be used in other than electrical form, and only a fraction of the total thermal energy generated will need to be converted to electrical work. The paper describes the conceptual design of such a partial energy conversion system, consisting of a high temperature fusion reactor operating in series with a high temperature radiator and in parallel with dual closed cycle gas turbine (CCGT) power systems, also referred to as closed Brayton cycle (CBC) systems, which are supplied with a fraction of the reactor thermal energy for conversion to electric power. Most of the fusion reactor's output is in the form of charged plasma which is expanded through a magnetic nozzle of the interplanetary propulsion system. Reactor heat energy is ducted to the high temperature series radiator utilizing the electric power generated to drive a helium gas circulation fan. In addition to discussing the thermodynamic aspects of the system design the authors include a brief overview of the gas turbine and fan rotor-dynamics and proposed bearing support technology along with performance characteristics of the three phase AC electric power generator and fan drive motor.

Previously studied electromagnetic launchers have contained either copper magnets or superconducting magnets wound from tape. However, an attractive alternative to use of wound magnets is use of monolithic magnets made by improved melt-texturing techniques. Melt-textured monolithic magnets can have good energy density and very high effective power when converting magnetic to kinetic energy. One of the difficulties associated with monolithic magnets, which is addressed in this paper, is their nonuniform current density. We have measured the energy conversion efficiency for 28 YBCO magnet combinations. A scaling parameter for predicting efficiency as a function of geometry and critical current is proposed. We then searched for an optimally shaped magnet by using a numerical model with a genetic algorithm. The best individuals were found to be shaped like an hourglass. A magnet of this shape was fabricated, and measured to have a conversion efficiency of 84%.

Biological molecular motors drive unidirectional transport and transduce chemical energy to mechanical work. In order to identify this energy conversion which is a common feature of molecular motors, many workers have studied various physical models, which consist of Brownian particles in spatially periodic potentials. Most of the models are, however, based on “single-particle” dynamics and too simple as models for biological motors, especially for actin-myosin motors, which cause muscle contraction. In this paper, particles coupled by elastic strings in an asymmetric periodic potential are considered as a model for the motors. We investigate the dynamics of the model and calculate the efficiency of energy conversion with the use of molecular dynamical method. In particular, we find that the velocity and efficiency of the elastically coupled particles where the natural length of the springs is incommensurable with the period of the periodic potential are larger than those of the corresponding single particle model.

Radioisotope power systems are an enabling and essential technology for missions to the outer planets. Previous planetary missions such as Voyagers I and II, Galileo, Ulysses, and Cassini have relied on Radioisotope Thermoelectric Generators (RTGs). These RTGs, while demonstrating outstanding reliability and extremely long life, have relatively low power conversion efficiency. Advanced power systems now being developed offer the prospect of significant improvement in efficiency with corresponding reduction in the plutonium fuel required. The Advanced Radioisotope Power System (ARPS) being developed by Lockheed Martin under contract from DOE, utilizes cells that rely on Alkali Metal Thermal to Electric Conversion (AMTEC) as a means of energy conversion. AMTEC cells currently under development are fabricated from refractory alloys, capable of matching the elevated temperature of the General Purpose Heat Source previously used in RTGs. Preliminary design of the power system is based on the requirement to provide two generators for each mission, with each generator capable of providing a minimum of 105 watts of electrical power, six years after launch. The selected generator configuration includes a stack of four GPHS modules, with 16 AMTEC cells arranged on four sides surrounding the stack. This paper will describe the preliminary design of the generator, and will provide estimates of the mass, performance, and thermal characteristics.

The principles and techniques of reversible thermodynamics are unable to describe the process and phenomena that occur in AMTEC devices. The process of energy conversion, in general, and in particular the operation of the beta alumina solid electrolyte (BASE) produce dynamic changes of state. In this paper irreversible thermodynamics is used in an attempt to describe these dynamic changes through the derivation of the appropriate entropy balance equation. To describe the transport (diffusion) of sodium cations through the BASE the Onsager reciprocal relations are used. The phenomenological equations derived from Onsager Relations are of limited value in practical calculations. Therefore the dissipation function is transformed to obtain the forces related to the fluxes by simple parameters, some of which are constant in range of AMTEC operation as shown by experiment.

This paper summarizes the recent experience with high temperature MULTI-FOIL thermal insulation and compares the results with those obtained in the 1960s. In contrast to other energy conversion systems such as Brayton, thermoelectric, AMTEC, or thermo photovoltaic, the thermionic ISUS (Integrated Solar Upper Stage) operates at high temperatures, up to 2500 K. The ISUS uses a solar receiver, a concentrator heating a graphite absorber, which is part of the RAC (Receiver Absorber Converter) module, further described by Rochow (1996) and Westerman (1995). The MULTI-FOIL surrounds the absorber and minimizes the heat losses from it. During the propulsion phase of the mission the thermionic converters, the third part of the RAC, are thermally shielded from the absorber by a movable Multi-Foil assembly. For the lower phase the insulation at the converter is lowered, exposing the converters to the hot absorber.

This paper reports recent progress on thermophotovoltaic (TPV) devices for space power applications. Previous investigations (Schock 1994 and Ewell 1993) indicate that the TPV approach may offer greater efficiency than conventional thermoelectric conversion. We discuss an approach based on photovoltaic (PV) devices made from ternary and quaternary III‐V alloys, using dielectric and plasma filters. The objective is to develop a TPV cell and filter which is ‘‘tunable’’ to the emission spectrum of radioisotope or reactor heat sources, at temperatures in the range of 1273–1473 K. An advantage of quaternary III‐V semiconductors is that devices can be fabricated by molecular beam epitaxy (MBE) on a suitable binary substrate, such as GaSb or InAs, and the band gap and lattice constant can be adjusted independently to match requirements. Energy gaps from 0.5 to 0.72 eV can be obtained. The use of Al as one component of a III‐V quaternary provides exceptional adjustability of the gap, while the use of Sb as one component reduces surface recombination velocity—enhancing collection efficiency.

As a result of its 1993–94 work, NII NPO ‘‘LUCH’’ developed a thermionic fuel element (TFE) SC‐320 intended for use as part of a nuclear thermionic reactor‐converter known as SPACE‐R designed in the US and rated at 40 kW of output electric power. This paper presents the results of the demonstration electric power tests of the SC‐320 TFE mock‐up conducted in the US at the TSET testing facility located at the University of New Mexico. The data obtained are compared to the calculated characteristics as well as the output parameters of the Topaz‐2 NPS TFEs.

This paper discusses the nuclear and thermal analysis of two fission‐powered concepts: the Heatpipe Power Systems (HPS) that provides power only, and the Heatpipe Bimodal System (HBS) that provides both power and thermal propulsion. The HPS and HBS systems can provide substantial levels of power and propulsion at low mass, with a high degree of safety and reliability. The systems have been designed to utilize existing technology and facilities, which will make the development cost relatively low.

This paper describes the design of an experiment to demonstrate the feasibly of operating a cascade of a Thermionic Energy Converter (TEC) with an Alkali Metal Thermo Electric Converter (AMTEC). Both of these devices convert heat to electricity without moving mechanical parts and lend themselves to be incorporated into a cascade. Typically, the TEC operates from a hot temperature of 2000 K to 1700 K, rejecting heat at 1100 K to 700 K, while the AMTEC operates from a hot temperature of 1100 K to 900 K and a cold temperature of about 400 K. These temperature ranges form almost ideal cascade.

This paper presents an analysis of the performance of a selective emitter using small particles of rare earth compounds stable at high temperatures in a low emittance inert gas stream. An expression for the spectral emissive power excluding radiation scattering was derived to include the radiation in the emission band, produced by electronic transitions of the rare earth ion, and the continuum radiation outside the emission band produced by the rare earth host. Preliminary results suggest that a selective emitter based on suspended rare earth oxide particles will have high efficiency and merits further experimental investigation.

This paper presents the results of an investigation to demonstrate thermophotovoltaic energy conversion using InGaAs photovoltaic cells, yttrium‐aluminum‐garnet‐ (YAG‐) based selective emitters, and bandpass/reflector filters, with the heat source operating at 1100 °C. InGaAs cells were grown on InP by organometallic vapor phase epitaxy with bandgaps of 0.60 and 0.75 eV and coupled to Ho‐, Er‐, and Er‐Tm‐doped YAG selective emitters. Infrared reflector and/or shortpass filters were also used to increase the ratio of in‐band to out‐of‐band radiation from the selective emitters. Efficiencies as high as 13.2% were recorded for filtered converters.

The use of Solar Thermal Propulsion (STP) as an upper stage propulsion system requires the use of large primary concentrators. The size of the primary concentrators, ranging in size between 2–10 meters in diameter, depends upon the configuration of the propulsion system. Three concepts being pursued for the concentrators are inflatable, foam rigidized, and rigid concentrators. Inflatable concentrators are deployed by inflation, and their shape is maintained by a pressure inside the concentrator canopy. Foam rigidized concentrators are deployed by inflation. They differ from inflatable concentrators, in that they are rigidized by a foam which is injected between two membranes. This paper will discuss the current state of the technology for the fabrication and use of inflatable and foam rigidized concentrators and integration of these concentrators into an optic system. The use of a secondary concentrator to integrate the primary concentrator with an absorber system will also be presented.

The paper considers an ecological, solar, bimodal system with ultra‐high temperature thermionic energy converter (TEC). The solar bimodal Space Electric Propulsion System (SEPS) characteristics are presented.

This paper presents results of life tests of four conductively coupled thermoelectric cells. Two are on test at Lockheed Martin Astro Space and two at JPL. These cells were assembled in the summer of 1994 with modifications of the engineering cell design and fabrication processes aimed at extending life, improving performance and reducing costs. Testing commenced in September 1994. A brief history of cell design evolution is presented as well as earlier life test results. Previously tested cells had shown an abnormal increase in internal resistance between 500 and 3,500 hours at prototypic operating conditions. Diagnostic disassembly of these cells showed that the problem was void formation at the hot side graphite/SiGe bond. The existing silicon nitride coating was inadequate to prevent the escape of the highly volatile Ge species from the bond line into the vacuum environment. To prevent this an application of a thin glass layer was made over the silicon nitride. Accelerated coupon tests demonstrated equivalent life exceeding the seven year requirement. Life test results from the cells show normal internal resistance trends after 7,600 hours which exceeds any previous cell life test. This is a strong indication that the major life limiting degradation mechanisms are understood and the appropriate changes have been incorporated into the design.

R&D Technologies is developing thermophotovoltaic (TPV) technology based on the use of porous/fibrous ceramic broadband‐type emitter designs that utilize recuperative or regenerative techniques to improve thermal efficiency and power density. This paper describes preliminary estimates of what will be required to accomplish sufficient power density to develop a practical, commercially‐viable TPV generator. It addresses the needs for improved, thermal shock‐resistant, long‐life porous/fibrous ceramic emitters and provides information on the photocell technology required to achieve acceptable power density in broadband‐type (with selective filter) TPV systems. TPV combustors/systems operating at a temperature of 1500 °C with a broadband‐type emitter is proposed as a viable starting point for cost‐effective TPV conversion. Based on current projections for photocell cost, system power densities of 7.5–10 watts per square centimeter of emitter area will be required for TPV to become a commercially viable technology.