WorldWideScience

Sample records for brayton cycle

  1. Exergy analysis for combined regenerative Brayton and inverse Brayton cycles

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Zelong; Chen, Lingen; Sun, Fengrui [College of Naval Architecture and Power, Naval University of Engineering, Wuhan 430033 (China)

    2012-07-01

    This paper presents the study of exergy analysis of combined regenerative Brayton and inverse Brayton cycles. The analytical formulae of exergy loss and exergy efficiency are derived. The largest exergy loss location is determined. By taking the maximum exergy efficiency as the objective, the choice of bottom cycle pressure ratio is optimized by detailed numerical examples, and the corresponding optimal exergy efficiency is obtained. The influences of various parameters on the exergy efficiency and other performances are analyzed by numerical calculations.

  2. Exergy analysis for combined regenerative Brayton and inverse Brayton cycles

    Directory of Open Access Journals (Sweden)

    Zelong Zhang, Lingen Chen, Fengrui Sun

    2012-01-01

    Full Text Available This paper presents the study of exergy analysis of combined regenerative Brayton and inverse Brayton cycles. The analytical formulae of exergy loss and exergy efficiency are derived. The largest exergy loss location is determined. By taking the maximum exergy efficiency as the objective, the choice of bottom cycle pressure ratio is optimized by detailed numerical examples, and the corresponding optimal exergy efficiency is obtained. The influences of various parameters on the exergy efficiency and other performances are analyzed by numerical calculations.

  3. Quantum Brayton cycle with coupled systems as working substance

    Science.gov (United States)

    Huang, X. L.; Wang, L. C.; Yi, X. X.

    2013-01-01

    We explore the quantum version of the Brayton cycle with a composite system as the working substance. The actual Brayton cycle consists of two adiabatic and two isobaric processes. Two pressures can be defined in our isobaric process; one corresponds to the external magnetic field (characterized by Fx) exerted on the system, while the other corresponds to the coupling constant between the subsystems (characterized by Fy). As a consequence, we can define two types of quantum Brayton cycle for the composite system. We find that the subsystem experiences a quantum Brayton cycle in one quantum Brayton cycle (characterized by Fx), whereas the subsystem's cycle is quantum Otto cycle in another Brayton cycle (characterized by Fy). The efficiency for the composite system equals to that for the subsystem in both cases, but the work done by the total system is usually larger than the sum of the work done by the two subsystems. The other interesting finding is that for the cycle characterized by Fy, the subsystem can be a refrigerator, while the total system is a heat engine. The result in this paper can be generalized to a quantum Brayton cycle with a general coupled system as the working substance.

  4. Advanced Supercritical Carbon Dioxide Brayton Cycle Development

    Energy Technology Data Exchange (ETDEWEB)

    Anderson, Mark [Univ. of Wisconsin, Madison, WI (United States); Sienicki, James [Argonne National Lab. (ANL), Argonne, IL (United States); Moisseytsev, Anton [Argonne National Lab. (ANL), Argonne, IL (United States); Nellis, Gregory [Univ. of Wisconsin, Madison, WI (United States); Klein, Sanford [Univ. of Wisconsin, Madison, WI (United States)

    2015-10-21

    -through labyrinth seals was proposed. A stepped labyrinth seal, which mimics the behavior of the labyrinth seal used in the Sandia National Laboratory (SNL) S-CO2 Brayton cycle, was also tested in the experiment along with simulations performed. The rest of this study demonstrates the difference of valves' behavior under supercritical fluid and normal fluid conditions. A small-scale valve was tested in the experiment facility using S-CO2. Different percentages of opening valves were tested, and the measured mass flow rate agreed with simulation predictions. Two transients from a real S-CO2 Brayton cycle design provided the data for valve selection. The selected valve was studied using numerical simulation, as experimental data is not available.

  5. Thermodynamic Optimization of Supercritical CO{sub 2} Brayton Cycles

    Energy Technology Data Exchange (ETDEWEB)

    Rhim, Dong-Ryul; Park, Sung-Ho; Kim, Su-Hyun; Yeom, Choong-Sub [Institute for Advanced Engineering, Yongin (Korea, Republic of)

    2015-05-15

    The supercritical CO{sub 2} Brayton cycle has been studied for nuclear applications, mainly for one of the alternative power conversion systems of the sodium cooled fast reactor, since 1960's. Although the supercritical CO{sub 2} Brayton cycle has not been expected to show higher efficiency at lower turbine inlet temperature over the conventional steam Rankine cycle, the higher density of supercritical CO{sub 2} like a liquid in the supercritical region could reduce turbo-machinery sizes, and the potential problem of sodium-water reaction with the sodium cooled fast reactor might be solved with the use of CO{sub 2} instead of water. The supercritical CO{sub 2} recompression Brayton cycle was proposed for the better thermodynamic efficiency than for the simple supercritical CO{sub 2} Brayton cycle. Thus this paper presents the efficiencies of the supercritical CO{sub 2} recompression Brayton cycle along with several decision variables for the thermodynamic optimization of the supercritical CO{sub 2} recompression Brayton cycle. The analytic results in this study show that the system efficiency reaches its maximum value at a compressor outlet pressure of 200 bars and a recycle fraction of 30 %, and the lower minimum temperature approach at the two heat exchangers shows higher system efficiency as expected.

  6. Thermodynamic Optimization of Supercritical CO2 Brayton Cycles

    International Nuclear Information System (INIS)

    The supercritical CO2 Brayton cycle has been studied for nuclear applications, mainly for one of the alternative power conversion systems of the sodium cooled fast reactor, since 1960's. Although the supercritical CO2 Brayton cycle has not been expected to show higher efficiency at lower turbine inlet temperature over the conventional steam Rankine cycle, the higher density of supercritical CO2 like a liquid in the supercritical region could reduce turbo-machinery sizes, and the potential problem of sodium-water reaction with the sodium cooled fast reactor might be solved with the use of CO2 instead of water. The supercritical CO2 recompression Brayton cycle was proposed for the better thermodynamic efficiency than for the simple supercritical CO2 Brayton cycle. Thus this paper presents the efficiencies of the supercritical CO2 recompression Brayton cycle along with several decision variables for the thermodynamic optimization of the supercritical CO2 recompression Brayton cycle. The analytic results in this study show that the system efficiency reaches its maximum value at a compressor outlet pressure of 200 bars and a recycle fraction of 30 %, and the lower minimum temperature approach at the two heat exchangers shows higher system efficiency as expected

  7. Systems Analyses of Advanced Brayton Cycles

    Energy Technology Data Exchange (ETDEWEB)

    A.D. Rao; D.J. Francuz; J.D. Maclay; J. Brouwer; A. Verma; M. Li; G.S. Samuelsen

    2008-09-30

    The main objective is to identify and assess advanced improvements to the Brayton Cycle (such as but not limited to firing temperature, pressure ratio, combustion techniques, intercooling, fuel or combustion air augmentation, enhanced blade cooling schemes) that will lead to significant performance improvements in coal based power systems. This assessment is conducted in the context of conceptual design studies (systems studies) that advance state-of-art Brayton cycles and result in coal based efficiencies equivalent to 65% + on natural gas basis (LHV), or approximately an 8% reduction in heat rate of an IGCC plant utilizing the H class steam cooled gas turbine. H class gas turbines are commercially offered by General Electric and Mitsubishi for natural gas based combined cycle applications with 60% efficiency (LHV) and it is expected that such machine will be offered for syngas applications within the next 10 years. The studies are being sufficiently detailed so that third parties will be able to validate portions or all of the studies. The designs and system studies are based on plants for near zero emissions (including CO{sub 2}). Also included in this program is the performance evaluation of other advanced technologies such as advanced compression concepts and the fuel cell based combined cycle. The objective of the fuel cell based combined cycle task is to identify the desired performance characteristics and design basis for a gas turbine that will be integrated with an SOFC in Integrated Gasification Fuel Cell (IGFC) applications. The goal is the conceptualization of near zero emission (including CO{sub 2} capture) integrated gasification power plants producing electricity as the principle product. The capability of such plants to coproduce H{sub 2} is qualitatively addressed. Since a total systems solution is critical to establishing a plant configuration worthy of a comprehensive market interest, a baseline IGCC plant scheme is developed and used to study

  8. Back work ratio of Brayton cycle; La relacion de trabajo de retroceso de un ciclo Brayton

    Energy Technology Data Exchange (ETDEWEB)

    Malaver de la Fuente, M. [Universidad Maritima del Caribe (Venezuela)]. E-mail: mmf_umc@hotmail.com

    2010-07-15

    This paper analyzes the existing relation between temperatures, back work ratio and net work of Brayton cycle, a cycle that describes gas turbine engines performance. The application of computational software helps to show the influence of back work ratio or coupling ratio, compressor and turbine inlet temperatures in an ideal thermodynamical cycle. The results lead to deduce that the maximum value reached in back work ratio will depend on the ranges of maximum and minimal temperatures of Brayton cycle. [Spanish] En este articulo se estudia la relacion que existe entre las temperaturas, la relacion de trabajo de retroceso y el trabajo neto en el ciclo Brayton, que es el ciclo ideal que describe el comportamiento de los motores de turbina de gas. La aplicacion de programas computarizados ayuda a mostrar la influencia de la relacion de trabajo de retroceso o relacion de acoplamiento, la temperatura de entrada al compresor y la temperatura de entrada a la turbina en este ciclo termodinamico ideal. Los resultados obtenidos permiten deducir que el valor maximo que alcanza la relacion de trabajo de retroceso dependera de los limites de temperatura maxima y minima impuestos en el ciclo Brayton.

  9. Power enhancement of the Brayton cycle by steam utilization

    Science.gov (United States)

    Jesionek, Krzysztof; Chrzczonowski, Andrzej; Ziółkowski, Paweł; Badur, Janusz

    2012-09-01

    The paper presents thermodynamic analysis of the gas-steam unit of the 65 MWe combined heat and power station. Numerical analyses of the station was performed for the nominal operation conditions determining the Brayton and combined cycle. Furthermore, steam utilization for the gas turbine propulsion in the Cheng cycle was analysed. In the considered modernization, steam generated in the heat recovery steam generator unit is directed into the gas turbine combustion chamber, resulting in the Brayton cycle power increase. Computational flow mechanics codes were used in the analysis of the thermodynamic and operational parameters of the unit.

  10. Multi-objective optimization of combined Brayton and inverse Brayton cycles using advanced optimization algorithms

    Science.gov (United States)

    Venkata Rao, R.; Patel, Vivek

    2012-08-01

    This study explores the use of teaching-learning-based optimization (TLBO) and artificial bee colony (ABC) algorithms for determining the optimum operating conditions of combined Brayton and inverse Brayton cycles. Maximization of thermal efficiency and specific work of the system are considered as the objective functions and are treated simultaneously for multi-objective optimization. Upper cycle pressure ratio and bottom cycle expansion pressure of the system are considered as design variables for the multi-objective optimization. An application example is presented to demonstrate the effectiveness and accuracy of the proposed algorithms. The results of optimization using the proposed algorithms are validated by comparing with those obtained by using the genetic algorithm (GA) and particle swarm optimization (PSO) on the same example. Improvement in the results is obtained by the proposed algorithms. The results of effect of variation of the algorithm parameters on the convergence and fitness values of the objective functions are reported.

  11. Combined-Brayton cycle, space nuclear power systems

    International Nuclear Information System (INIS)

    Because it is a widely recognized dynamic space conversion system, the Brayton cycle has been studied in France since several years, especially within the framework of a limited space program. A recuperated cycle of 20 to 30 kWe has been considered so far. However, possible applications could evolve and the need for an extended, diversified utilization of the Brayton cycle could appear. So, for Lunar or Mars bases which would accept large radiators and can benefit from a certain gravity level, combined cycle systems could be proposed. Following a reference to past works on space combined cycles, a possible association of a Brayton cycle with a thermoionic reactor is presented. The power level of a 'Topaz-2' type space nuclear system can be boosted from 8 kWe to around 36 to 53 kWe, at the expense of a large radiator of course. Furthermore, combined Brayton-Rankine, organic (toluene) or steam, cycles can pave the way to a simpler gas-cooled, particle bed reactor concept. A particular arrangement of HeXe heater and boiler or steam generator in series is proposed. It makes it possible to lower the reactor inlet temperature, which is quite adequate for the use of light water as moderator. Oustanding net efficiencies of 25.8 to 27.6 per cent, given the reactor temperature profile, are obtained. Consequences on the reactor design are mentioned

  12. Power conversion systems based on Brayton cycles for fusion reactors

    Energy Technology Data Exchange (ETDEWEB)

    Linares, J.I., E-mail: linares@upcomillas.es [Rafael Marino Chair on New Energy Technologies. Comillas Pontifical University, Alberto Aguilera, 25-28015 Madrid (Spain); Herranz, L.E. [Unit of Nuclear Safety Research. CIEMAT, Madrid (Spain); Moratilla, B.Y.; Serrano, I.P. [Rafael Marino Chair on New Energy Technologies. Comillas Pontifical University, Alberto Aguilera, 25-28015 Madrid (Spain)

    2011-10-15

    This paper investigates Brayton power cycles for fusion reactors. Two working fluids have been explored: helium in classical configurations and CO{sub 2} in recompression layouts (Feher cycle). Typical recuperator arrangements in both cycles have been strongly constrained by low temperature of some of the energy thermal sources from the reactor. This limitation has been overcome in two ways: with a combined architecture and with dual cycles. Combined architecture couples the Brayton cycle with a Rankine one capable of taking advantage of the thermal energy content of the working fluid after exiting the turbine stage (iso-butane and steam fitted best the conditions of the He and CO{sub 2} cycles, respectively). Dual cycles set a specific Rankine cycle to exploit the lowest quality thermal energy source, allowing usual recuperator arrangements in the Brayton cycle. The results of the analyses indicate that dual cycles could reach thermal efficiencies around 42.8% when using helium, whereas thermal performance might be even better (46.7%), if a combined CO{sub 2}-H{sub 2}O cycle was set.

  13. Nuclear reactor closed Brayton cycle space power conversion systems

    International Nuclear Information System (INIS)

    This paper presents the past history, present status and future prospects for closed Brayton cycle power conversion systems to be used in space when requirements have been established. Since there is a classic lack of coordination between advanced technology and its perceived need that can be strongly affected by associated factors, recommendations will be made to assist in the current situation. 4 refs

  14. Operation and analysis of a supercritical CO2 Brayton cycle.

    Energy Technology Data Exchange (ETDEWEB)

    Wright, Steven Alan; Radel, Ross F.; Vernon, Milton E.; Pickard, Paul S.; Rochau, Gary Eugene

    2010-09-01

    Sandia National Laboratories is investigating advanced Brayton cycles using supercritical working fluids for use with solar, nuclear or fossil heat sources. The focus of this work has been on the supercritical CO{sub 2} cycle (S-CO2) which has the potential for high efficiency in the temperature range of interest for these heat sources, and is also very compact, with the potential for lower capital costs. The first step in the development of these advanced cycles was the construction of a small scale Brayton cycle loop, funded by the Laboratory Directed Research & Development program, to study the key issue of compression near the critical point of CO{sub 2}. This document outlines the design of the small scale loop, describes the major components, presents models of system performance, including losses, leakage, windage, compressor performance, and flow map predictions, and finally describes the experimental results that have been generated.

  15. Performance evaluation of space solar Brayton cycle power systems

    Science.gov (United States)

    Diao, Zheng-Gang

    1992-06-01

    Unlike gas turbine power systems which consume chemical or nuclear energy, the energy consumption and/or cycle efficiency should not be a suitable criterion for evaluating the performance of space solar Brayton cycle power. A new design goal, life cycle cost, can combine all the power system characteristics, such as mass, area, and station-keeping propellant, into a unified criterion. Effects of pressure ratio, recuperator effectiveness, and compressor inlet temperature on life cycle cost were examined. This method would aid in making design choices for a space power system.

  16. Modeling and Simulation of a Desiccant Assisted Brayton Refrigeration Cycle

    OpenAIRE

    Nobrega, Carlos E.L.; Sphaier, Leandro Alcoforado

    2012-01-01

    The phase-out of CFCs has shed a new light over natural refrigerants, which have null global warming potentials. Air would be a natural choice, and although the Brayton cycle usually exhibits a lower coefficient of performance when compared to vapor-compression systems of same capacity, it has been considered in applications other than aircraft cooling. These include gas separation, food processing and preservation, refrigerated containers and train air-conditioning. Price perspectives in the...

  17. Supercritical Carbon Dioxide Brayton Cycle Energy Conversion System

    International Nuclear Information System (INIS)

    This report contains the description of the S-CO2 Brayton cycle coupled to KALIMER-600 as an alternative energy conversion system. For system development, a computer code was developed to calculate heat balance of 100% power operation condition. Based on the computer code, the S-CO2 Brayton cycle energy conversion system was constructed for the KALIMER-600. Using the developed turbomachinery models, the off-design characteristics and the sensitivities of the S-CO2 turbomachinery were investigated. For the development of PCHE models, a one-dimensional analysis computer code was developed to evaluate the performance of the PCHE. Possible control schemes for power control in the KALIMER-600 S-CO2 Brayton cycle were investigated by using the MARS code. Simple power reduction and recovery event was selected and analyzed for the transient calculation. For the evaluation of Na/CO2 boundary failure event, a computer was developed to simulate the complex thermodynamic behaviors coupled with the chemical reaction between liquid sodium and CO2 gas. The long term behavior of a Na/CO2 boundary failure event and its consequences which lead to a system pressure transient were evaluated

  18. Supercritical Carbon Dioxide Brayton Cycle Energy Conversion System

    Energy Technology Data Exchange (ETDEWEB)

    Cha, Jae Eun; Kim, S. O.; Seong, S. H.; Eoh, J. H.; Lee, T. H.; Choi, S. K.; Han, J. W.; Bae, S. W

    2007-12-15

    This report contains the description of the S-CO{sub 2} Brayton cycle coupled to KALIMER-600 as an alternative energy conversion system. For system development, a computer code was developed to calculate heat balance of 100% power operation condition. Based on the computer code, the S-CO{sub 2} Brayton cycle energy conversion system was constructed for the KALIMER-600. Using the developed turbomachinery models, the off-design characteristics and the sensitivities of the S-CO{sub 2} turbomachinery were investigated. For the development of PCHE models, a one-dimensional analysis computer code was developed to evaluate the performance of the PCHE. Possible control schemes for power control in the KALIMER-600 S-CO{sub 2} Brayton cycle were investigated by using the MARS code. Simple power reduction and recovery event was selected and analyzed for the transient calculation. For the evaluation of Na/CO{sub 2} boundary failure event, a computer was developed to simulate the complex thermodynamic behaviors coupled with the chemical reaction between liquid sodium and CO{sub 2} gas. The long term behavior of a Na/CO{sub 2} boundary failure event and its consequences which lead to a system pressure transient were evaluated.

  19. Thermodynamic Modeling for Open Combined Regenerative Brayton and Inverse Brayton Cycles with Regeneration before the Inverse Cycle

    Directory of Open Access Journals (Sweden)

    Lingen Chen

    2012-01-01

    Full Text Available A thermodynamic model of an open combined regenerative Brayton and inverse Brayton cycles with regeneration before the inverse cycle is established in this paper by using thermodynamic optimization theory. The flow processes of the working fluid with the pressure drops and the size constraint of the real power plant are modeled. There are 13 flow resistances encountered by the working fluid stream for the cycle model. Four of these, the friction through the blades and vanes of the compressors and the turbines, are related to the isentropic efficiencies. The remaining nine flow resistances are always present because of the changes in flow cross-section at the compressor inlet of the top cycle, regenerator inlet and outlet, combustion chamber inlet and outlet, turbine outlet of the top cycle, turbine outlet of the bottom cycle, heat exchanger inlet, and compressor inlet of the bottom cycle. These resistances associated with the flow through various cross-sectional areas are derived as functions of the compressor inlet relative pressure drop of the top cycle, and control the air flow rate, the net power output and the thermal efficiency. The analytical formulae about the power output, efficiency and other coefficients are derived with 13 pressure drop losses. It is found that the combined cycle with regenerator can reach higher thermal efficiency but smaller power output than those of the base combined cycle at small compressor inlet relative pressure drop of the top cycle.

  20. Closed Brayton cycle power conversion systems for nuclear reactors :

    Energy Technology Data Exchange (ETDEWEB)

    Wright, Steven A.; Lipinski, Ronald J.; Vernon, Milton E.; Sanchez, Travis

    2006-04-01

    This report describes the results of a Sandia National Laboratories internally funded research program to study the coupling of nuclear reactors to gas dynamic Brayton power conversion systems. The research focused on developing integrated dynamic system models, fabricating a 10-30 kWe closed loop Brayton cycle, and validating these models by operating the Brayton test-loop. The work tasks were performed in three major areas. First, the system equations and dynamic models for reactors and Closed Brayton Cycle (CBC) systems were developed and implemented in SIMULINKTM. Within this effort, both steady state and dynamic system models for all the components (turbines, compressors, reactors, ducting, alternators, heat exchangers, and space based radiators) were developed and assembled into complete systems for gas cooled reactors, liquid metal reactors, and electrically heated simulators. Various control modules that use proportional-integral-differential (PID) feedback loops for the reactor and the power-conversion shaft speed were also developed and implemented. The simulation code is called RPCSIM (Reactor Power and Control Simulator). In the second task an open cycle commercially available Capstone C30 micro-turbine power generator was modified to provide a small inexpensive closed Brayton cycle test loop called the Sandia Brayton test-Loop (SBL-30). The Capstone gas-turbine unit housing was modified to permit the attachment of an electrical heater and a water cooled chiller to form a closed loop. The Capstone turbine, compressor, and alternator were used without modification. The Capstone systems nominal operating point is 1150 K turbine inlet temperature at 96,000 rpm. The annular recuperator and portions of the Capstone control system (inverter) and starter system also were reused. The rotational speed of the turbo-machinery is controlled by adjusting the alternator load by using the electrical grid as the load bank. The SBL-30 test loop was operated at

  1. A Brayton cycle solar dynamic heat receiver for space

    Science.gov (United States)

    Sedgwick, L. M.; Nordwall, H. L.; Kaufmann, K. J.; Johnson, S. D.

    1989-01-01

    The detailed design of a heat receiver developed to meet the requirements of the Space Station Freedom, which will be assembled and operated in low earth orbit beginning in the mid-1990's, is described. The heat receiver supplies thermal energy to a nominal 25-kW closed-Brayton-cycle power conversion unit. The receiver employs an integral thermal energy storage system utilizing the latent heat of a eutectic-salt phase-change mixture to store energy for eclipse operation. The salt is contained within a felt metal matrix which enhances heat transfer and controls the salt void distribution during solidification.

  2. Operational Results of a Closed Brayton Cycle Test-Loop

    Science.gov (United States)

    Wright, Steven A.; Fuller, Robert; Lipinski, Ronald J.; Nichols, Kenneth; Brown, Nicholas

    2005-02-01

    A number of space and terrestrial power system designs plan to use nuclear reactors that are coupled to Closed-loop Brayton Cycle (CBC) systems to generate electrical power. Because very little experience exists regarding the operational behavior of these systems, Sandia National Laboratories (through its Laboratory Directed Research and Development program) is developing a closed-loop test bed that can be used to determine the operational behavior of these systems and to validate models for these systems. Sandia has contracted Barber-Nichols Corporation to design, fabricate, and assemble a Closed-loop Brayton Cycle (CBC) system. This system was developed by modifying commercially available hardware. It uses a 30 kWe Capstone C-30 gas-turbine unit (www.capstoneturbine.com) with a modified housing that permits the attachment of an electrical heater and a water cooled chiller that are connected to the turbo-machinery in a closed loop. The test-loop reuses the Capstone turbine, compressor, and alternator. The Capstone system's nominal operating point is 1150 K turbine inlet temperature at 96,000 rpm. The annular recuperator and portions of the Capstone control system (inverter) and starter system are also reused. The rotational speed of the turbo-machinery is controlled either by adjusting the alternator load by either using the electrical grid or a separate load bank. This report describes the test-loop hardware SBL-30 (Sandia Brayton Loop-30kWe). Also presented are results of early testing and modeling of the unit. The SBL-30 hardware is currently configured with a heater that is limited to 80 kWth with a maximum outlet temperature of ˜1000 K.

  3. Simulation of CO2 Brayton Cycle for Engine Exhaust Heat Recovery under Various Operating Loads

    Institute of Scientific and Technical Information of China (English)

    舒歌群; 张承宇; 田华; 高媛媛; 李团兵; 仇荣赓

    2015-01-01

    A bottoming cycle system based on CO2 Brayton cycle is proposed to recover the engine exhaust heat. Its performance is compared with the conventional air Brayton cycle under five typical engine conditions. The results show that CO2 Brayton cycle proves to be superior to the air Brayton cycle in terms of the system net output power, thermal efficiency and recovery efficiency. In most cases, the recovery efficiency of CO2 Brayton cycle can be higher than 9%and the system has a better performance at the engine’s high operating load. The thermal efficiency can be as large as 24.83%under 100%operating load, accordingly, the net output power of 14.86 kW is obtained.

  4. Potential impacts of Brayton- and Stirling-cycle engines

    Energy Technology Data Exchange (ETDEWEB)

    Heft, R.C.

    1980-11-15

    Two engine technologies (Brayton cycle and Stirling cycle) currently being pursued by the US Department of Energy were examined for their potential impacts if they achieved commercial viability. An economic analysis of the expected response of buyers to the attributes of the alternative engines was performed. Hedonic coefficients for vehicle fuel efficiency, performance and size were estimated for domestic cars based upon historical data. The marketplace value of the fuel efficiency enhancement provided by Brayton or Stirling engines was estimated. The effect upon various economic sectors of a large scale change-over from conventional to alternate engines was estimated using an economic input-output analysis. Primary effects were found in fuels refining, non-ferroalloy ores and ferroalloy smelting. Secondary effects were found in mining, transport, and capital financing. Under the assumption of 10 years for plant conversions and 1990 and 1995 as the introduction date for turine and Stirling engines respectively, the comparative fuel savings and present value of the future savings in fuel costs were estimated.

  5. Performance improvement options for the supercritical carbon dioxide brayton cycle

    International Nuclear Information System (INIS)

    The supercritical carbon dioxide (S-CO2) Brayton cycle is under development at Argonne National Laboratory as an advanced power conversion technology for Sodium-Cooled Fast Reactors (SFRs) as well as other Generation IV advanced reactors as an alternative to the traditional Rankine steam cycle. For SFRs, the S-CO2 Brayton cycle eliminates the need to consider sodium-water reactions in the licensing and safety evaluation, reduces the capital cost of the SFR plant, and increases the SFR plant efficiency. Even though the S-CO2 cycle has been under development for some time and optimal sets of operating parameters have been determined, those earlier development and optimization studies have largely been directed at applications to other systems such as gas-cooled reactors which have higher operating temperatures than SFRs. In addition, little analysis has been carried out to investigate cycle configurations deviating from the selected 'recompression' S-CO2 cycle configuration. In this work, several possible ways to improve S-CO2 cycle performance for SFR applications have been identified and analyzed. One set of options incorporates optimization approaches investigated previously, such as variations in the maximum and minimum cycle pressure and minimum cycle temperature, as well as a tradeoff between the component sizes and the cycle performance. In addition, the present investigation also covers options which have received little or no attention in the previous studies. Specific options include a 'multiple-recompression' cycle configuration, intercooling and reheating, as well as liquid-phase CO2 compression (pumping) either by CO2 condensation or by a direct transition from the supercritical to the liquid phase. Some of the options considered did not improve the cycle efficiency as could be anticipated beforehand. Those options include: a double recompression cycle, intercooling between the compressor stages, and reheating between the turbine stages. Analyses carried

  6. Sensitivity study on nitrogen Brayton cycle coupled with a small ultra-long cycle fast reactor

    Energy Technology Data Exchange (ETDEWEB)

    Seo, Seok Bin; Seo, Han; Bang, In Cheol [Ulsan National Institute of Science and Technology, Ulsan (Korea, Republic of)

    2014-10-15

    The main characteristics of UCFR are constant neutron flux and power density. They move their positions every moment at constant speed along with axial position of fuel rod for 60 years. Simultaneously with the development of the reactors, a new power conversion system has been considered. To solve existing issues of vigorous sodium-water reaction in SFR with steam power cycle, many researchers suggested a closed Brayton cycle as an alternative technique for SFR power conversion system. Many inactive gases are selected as a working fluid in Brayton power cycle, mainly supercritical CO{sub 2} (S-CO{sub 2}). However, S-CO{sub 2} still has potential for reaction with sodium. CO{sub 2}-sodium reaction produces solid product, which has possibility to have an auto ignition reaction around 600 .deg. C. Thus, instead of S-CO{sub 2}, CEA in France has developed nitrogen power cycle for ASTRID (Advanced Sodium Technological Reactor for Industrial Demonstration). In addition to inactive characteristic of nitrogen with sodium, its thermal and physical similarity with air enables to easily adopt to existing air Brayton cycle technology. In this study, for an optimized power conversion system for UCFR, a nitrogen Brayton cycle was analyzed in thermodynamic aspect. Based on subchannel analysis data of UCFR-100, a parametric study for thermal performance of nitrogen Brayton cycle was achieved. The system maximum pressure significantly affects to the overall efficiency of cycle, while other parameters show little effects. Little differences of the overall efficiencies for all cases between three stages (BOC, MOC, EOC) indicate that the power cycle of UCFR-100 maintains its performance during the operation.

  7. Sensitivity study on nitrogen Brayton cycle coupled with a small ultra-long cycle fast reactor

    International Nuclear Information System (INIS)

    The main characteristics of UCFR are constant neutron flux and power density. They move their positions every moment at constant speed along with axial position of fuel rod for 60 years. Simultaneously with the development of the reactors, a new power conversion system has been considered. To solve existing issues of vigorous sodium-water reaction in SFR with steam power cycle, many researchers suggested a closed Brayton cycle as an alternative technique for SFR power conversion system. Many inactive gases are selected as a working fluid in Brayton power cycle, mainly supercritical CO2 (S-CO2). However, S-CO2 still has potential for reaction with sodium. CO2-sodium reaction produces solid product, which has possibility to have an auto ignition reaction around 600 .deg. C. Thus, instead of S-CO2, CEA in France has developed nitrogen power cycle for ASTRID (Advanced Sodium Technological Reactor for Industrial Demonstration). In addition to inactive characteristic of nitrogen with sodium, its thermal and physical similarity with air enables to easily adopt to existing air Brayton cycle technology. In this study, for an optimized power conversion system for UCFR, a nitrogen Brayton cycle was analyzed in thermodynamic aspect. Based on subchannel analysis data of UCFR-100, a parametric study for thermal performance of nitrogen Brayton cycle was achieved. The system maximum pressure significantly affects to the overall efficiency of cycle, while other parameters show little effects. Little differences of the overall efficiencies for all cases between three stages (BOC, MOC, EOC) indicate that the power cycle of UCFR-100 maintains its performance during the operation

  8. Thermo-economic performance of HTGR Brayton power cycles

    International Nuclear Information System (INIS)

    High temperature reached in High and Very High Temperature Reactors (VHTRs) results in thermal efficiencies substantially higher than those of actual nuclear power plants. A number of studies mainly driven by achieving optimum thermal performance have explored several layout. However, economic assessments of cycle power configurations for innovative systems, although necessarily uncertain at this time, may bring valuable information in relative terms concerning power cycle optimization. This paper investigates the thermal and economic performance direct Brayton cycles. Based on the available parameters and settings of different designs of HTGR power plants (GTHTR-300 and PBMR) and using the first and second laws of thermodynamics, the effects of compressor inter-cooling and of the compressor-turbine arrangement (i.e., single vs. multiple axes) on thermal efficiency have been estimated. The economic analysis has been based on the El-Sayed methodology and on the indirect derivation of the reactor capital investment. The results of the study suggest that a 1-axis inter-cooled power cycle has a similar thermal performance to the 3-axes one (around 50%) and, what's more, it is substantially less taxed. A sensitivity study allowed assessing the potential impact of optimizing several variables on cycle performance. Further than that, the cycle components costs have been estimated and compared. (authors)

  9. Solar/gas Brayton/Rankine cycle heat pump assessment

    Science.gov (United States)

    Rousseau, J.; Liu, A. Y.

    1982-05-01

    A 10-ton gas-fired heat pump is currently under development at AiResearch under joint DOE and GRI sponsorship. This heat pump features a highly efficient, recuperated, subatmospheric Brayton-cycle engine which drives the centrifugal compressor of a reversible vapor compression heat pump. The investigations under this program were concerned initially with the integration of this machine with a parabolic dish-type solar collector. Computer models were developed to accurately describe the performance of the heat pump packaged in this fashion. The study determined that (1) only a small portion (20 to 50 percent) of the available solar energy could be used because of a fundamental mismatch between the heating and cooling demand and the availability of solar energy, and (2) the simple pay back period, by comparison to the baseline non-solar gas-fired heat pump, was unacceptable (15 to 36 years).

  10. Calculation principles of humid air in a reversed Brayton cycle

    Energy Technology Data Exchange (ETDEWEB)

    Backman, J. [Lappeenranta Univ. of Technology (Finland). Dept. of Energy Technology

    1997-12-31

    The article presents a calculation method for reversed Brayton cycle that uses humid air as working medium. The reversed Brayton cycle can be employed as an air dryer, a heat pump or a refrigerating machine. In this research the use of humid air as a working fluid has an environmental advantage, as well. In this method especially the expansion process in the turbine is important because of the condensation of the water vapour in the humid air. This physical phenomena can have significant effects on the level of performance of the application. The expansion process differs physically from the compression process, when the water vapour in the humid air begins to condensate. In the thermodynamic equilibrium of the flow, the water vapour pressure in humid air cannot exceed the pressure of saturated water vapour in corresponding temperature. Expansion calculation during operation around the saturation zone is based on a quasistatic expansion, in which the system after the turbine is in thermodynamical equilibrium. The state parameters are at every moment defined by the equation of state, and there is no supercooling in the vapour. Following simplifications are used in the calculations: The system is assumed to be adiabatic. This means that there is no heat transfer to the surroundings. This is a common practice, when the temperature differences are moderate as here; The power of the cooling is omitted. The cooling construction is very dependent on the machine and the distribution of the losses; The flow is assumed to be one-dimensional, steady-state and homogenous. The water vapour condensing in the turbine can cause errors, but the errors are mainly included in the efficiency calculation. (author) 11 refs.

  11. Brayton-Cycle Baseload Power Tower CSP System

    Energy Technology Data Exchange (ETDEWEB)

    Anderson, Bruce [Wilson Solarpower Corporation, Boston, MA (United States)

    2013-12-31

    The primary objectives of Phase 2 of this Project were:1. Engineer, fabricate, and conduct preliminary testing on a low-pressure, air-heating solar receiver capable of powering a microturbine system to produce 300kWe while the sun is shining while simultaneously storing enough energy thermally to power the system for up to 13 hours thereafter. 2. Cycle-test a high-temperature super alloy, Haynes HR214, to determine its efficacy for the system’s high-temperature heat exchanger. 3. Engineer the thermal energy storage system. This Phase 2 followed Wilson’s Phase 1, which primarily was an engineering feasibility study to determine a practical and innovative approach to a full Brayton-cycle system configuration that could meet DOE’s targets. Below is a summary table of the DOE targets with Wilson’s Phase 1 Project results. The results showed that a Brayton system with an innovative (low pressure) solar receiver with ~13 hours of dry (i.e., not phase change materials or molten salts but rather firebrick, stone, or ceramics) has the potential to meet or exceed DOE targets. Such systems would consist of pre-engineered, standardized, factory-produced modules to minimize on-site costs while driving down costs through mass production. System sizes most carefully analyzed were in the range of 300 kWe to 2 MWe. Such systems would also use off-the-shelf towers, blowers, piping, microturbine packages, and heliostats. Per DOE’s instructions, LCOEs are based on the elevation and DNI levels of Daggett, CA, for a 100 MWe power plant following 2 GWe of factory production of the various system components.

  12. Innovative open air brayton combined cycle systems for the next generation nuclear power plants

    Science.gov (United States)

    Zohuri, Bahman

    The purpose of this research was to model and analyze a nuclear heated multi-turbine power conversion system operating with atmospheric air as the working fluid. The air is heated by a molten salt, or liquid metal, to gas heat exchanger reaching a peak temperature of 660 0C. The effects of adding a recuperator or a bottoming steam cycle have been addressed. The calculated results are intended to identify paths for future work on the next generation nuclear power plant (GEN-IV). This document describes the proposed system in sufficient detail to communicate a good understanding of the overall system, its components, and intended uses. The architecture is described at the conceptual level, and does not replace a detailed design document. The main part of the study focused on a Brayton --- Rankine Combined Cycle system and a Recuperated Brayton Cycle since they offer the highest overall efficiencies. Open Air Brayton power cycles also require low cooling water flows relative to other power cycles. Although the Recuperated Brayton Cycle achieves an overall efficiency slightly less that the Brayton --- Rankine Combined Cycle, it is completely free of a circulating water system and can be used in a desert climate. Detailed results of modeling a combined cycle Brayton-Rankine power conversion system are presented. The Rankine bottoming cycle appears to offer a slight efficiency advantage over the recuperated Brayton cycle. Both offer very significant advantages over current generation Light Water Reactor steam cycles. The combined cycle was optimized as a unit and lower pressure Rankine systems seem to be more efficient. The combined cycle requires a lot less circulating water than current power plants. The open-air Brayton systems appear to be worth investigating, if the higher temperatures predicted for the Next Generation Nuclear Plant do materialize.

  13. Parametric Investigation and Thermoeconomic Optimization of a Combined Cycle for Recovering the Waste Heat from Nuclear Closed Brayton Cycle

    Directory of Open Access Journals (Sweden)

    Lihuang Luo

    2016-01-01

    Full Text Available A combined cycle that combines AWM cycle with a nuclear closed Brayton cycle is proposed to recover the waste heat rejected from the precooler of a nuclear closed Brayton cycle in this paper. The detailed thermodynamic and economic analyses are carried out for the combined cycle. The effects of several important parameters, such as the absorber pressure, the turbine inlet pressure, the turbine inlet temperature, the ammonia mass fraction, and the ambient temperature, are investigated. The combined cycle performance is also optimized based on a multiobjective function. Compared with the closed Brayton cycle, the optimized power output and overall efficiency of the combined cycle are higher by 2.41% and 2.43%, respectively. The optimized LEC of the combined cycle is 0.73% lower than that of the closed Brayton cycle.

  14. Automatic Control Strategy Development for the Supercritical CO2 Brayton Cycle for LFR Autonomous Load Following

    International Nuclear Information System (INIS)

    The supercritical carbon dioxide (S-CO2) Brayton cycle is a promising advanced alternative to the Rankine saturated steam cycle and ideal gas Brayton cycle for the energy converters of specific reactor concepts belonging to the U.S. Department of Energy Generation IV Nuclear Energy Systems Initiative. A new plant dynamics analysis computer code has been developed for simulation of the S-CO2 Brayton cycle coupled to an autonomous Lead-Cooled Fast Reactor (LFR). The plant dynamics code was used to develop an automatic control strategy for the whole plant in response to changes in the demand from the electrical grid. The specific features of the S-CO2 Brayton cycle that result in limitations on the control range and speed of specific control mechanisms are discussed. Calculations of whole-plant responses to plant operational transients involving step and continuous changes in grid demand are demonstrated. (authors)

  15. A treatment of thermal efficiency improvement in the Brayton cycle

    International Nuclear Information System (INIS)

    So far, as the working fluid for power-generating plants, mainly water and air (combustion gas) have been used. In this study, in regeneration and isothermal compression processes being considered as the means for the efficiency improvement in Brayton cycle, the investigation of equivalent graphical presentation method with T-S diagrams, the introduction of the new characteristic number expressing the possibility of thermal efficiency improvement by regeneration, and the investigation of the effect of the difference of working fluid on thermal efficiency were carried out. Next, as the cycle approximately realizing isothermal compression process with condensation process, the super-critical pressure cycle with liquid phase compression was rated, and four working fluids, NH3, SO2, CO2 and H2O were examined as perfect gas and real gas. The advantage of CO2 regeneration for the thermal efficiency improvement was clarified by using the dimensionless characteristic number. The graphical presentation of effective work, the thermal efficiency improvement by regeneration, the thermal efficiency improvement by making compression process isothermal, the effect on thermal efficiency due to various factors and working fluids, the characteristic number by regeneration, and the application to real working fluids are reported. (Kako, I.)

  16. Exergy analyses of an endoreversible closed regenerative Brayton cycle CCHP plant

    OpenAIRE

    Bo Yang, Lingen Chen, Fengrui Sun

    2014-01-01

    An endoreversible closed regenerative Brayton cycle CCHP (combined cooling, heating and power) plant coupled to constant-temperature heat reservoirs is presented using finite time thermodynamics (FTT). The CCHP plant includes an endoreversible closed regenerative Brayton cycle, an endoreversible four-heat-reservoir absorption refrigerator and a heat recovery device of thermal consumer. The heat-resistance losses in the hot-, cold-, thermal consumer-, generator-, condenser-, evaporator- and ab...

  17. Preliminary design for a reverse Brayton cycle cryogenic cooler

    Science.gov (United States)

    Swift, Walter L.

    1993-01-01

    A long life, single stage, reverse Brayton cycle cryogenic cooler is being developed for applications in space. The system is designed to provide 5 W of cooling at a temperature of 65 Kelvin with a total cycle input power of less than 200 watts. Key features of the approach include high speed, miniature turbomachines; an all metal, high performance, compact heat exchanger; and a simple, high frequency, three phase motor drive. In Phase 1, a preliminary design of the system was performed. Analyses and trade studies were used to establish the thermodynamic performance of the system and the performance specifications for individual components. Key mechanical features for components were defined and assembly layouts for the components and the system were prepared. Critical materials and processes were identified. Component and brassboard system level tests were conducted at cryogenic temperatures. The system met the cooling requirement of 5 W at 65 K. The system was also operated over a range of cooling loads from 0.5 W at 37 K to 10 W at 65 K. Input power to the system was higher than target values. The heat exchanger and inverter met or exceeded their respective performance targets. The compresssor/motor assembly was marginally below its performance target. The turboexpander met its aerodynamic efficiency target, but overall performance was below target because of excessive heat leak. The heat leak will be reduced to an acceptable value in the engineering model. The results of Phase 1 indicate that the 200 watt input power requirement can be met with state-of-the-art technology in a system which has very flexible integration requirements and negligible vibration levels.

  18. Optimization of the performance characteristics in an irreversible regeneration magnetic Brayton refrigeration cycle

    Science.gov (United States)

    Wang, Hao; Wu, GuoXing

    2012-02-01

    A model of the irreversible regenerative Brayton refrigeration cycle working with paramagnetic materials is established, in which the regeneration problem in two constant-magnetic field processes and the irreversibility in two adiabatic processes are considered synthetically. Expressions for the COP, cooling rate, power input, the minimum ratio of the two magnetic fields, etc., are derived. It is found that the influence of the irreversibility and the regeneration on the main performance parameters of the magnetic Brayton refrigerator is remarkable. It is important that we have obtained several optimal criteria, which may provide some theoretical basis for the optimal design and operation of the Brayton refrigerator. The results obtained in the paper can provide some new theoretical information for the optimal design and performance improvement of real Brayton refrigerators.

  19. Exergy analyses of an endoreversible closed regenerative Brayton cycle CCHP plant

    Directory of Open Access Journals (Sweden)

    Bo Yang, Lingen Chen, Yanlin Ge, Fengrui Sun

    2014-01-01

    Full Text Available An endoreversible closed regenerative Brayton cycle CCHP (combined cooling, heating and power plant coupled to constant-temperature heat reservoirs is presented using finite time thermodynamics (FTT. The CCHP plant includes an endoreversible closed regenerative Brayton cycle, an endoreversible four-heat-reservoir absorption refrigerator and a heat recovery device of thermal consumer. The heat-resistance losses in the hot-, cold-, thermal consumer-, generator-, condenser-, evaporator- and absorber-side heat exchangers and regenerator are considered. The performance of the CCHP plant is studied from the exergetic perspective, and the analytical formulae about exergy output rate and exergy efficiency are derived. Through numerical calculations, the pressure ratio of regenerative Brayton cycle is optimized, the effects of heat conductance of regenerator and ratio of heat demanded by the thermal consumer to power output on dimensionless exergy output rate and exergy efficiency are analyzed.

  20. Exergy Analysis and Second Law Efficiency of a Regenerative Brayton Cycle with Isothermal Heat Addition

    Directory of Open Access Journals (Sweden)

    Naser M. Jubeh

    2005-07-01

    Full Text Available Abstract: The effect of two heat additions, rather than one, in a gas turbine engine is analyzed from the second law of thermodynamics point of view. A regenerative Brayton cycle model is used for this study, and compared with other models of Brayton cycle. All fluid friction losses in the compressor and turbine are quantified by an isentropic efficiency term. The effect of pressure ratio, turbine inlet temperature, ambient temperature, altitude, and altitude with variable ambient temperature on irreversibility "exergy destroyed" and second law efficiency was investigated and compared for all models. The results are given graphically with the appropriate discussion and conclusion.

  1. Computational analysis of supercritical CO2 Brayton cycle power conversion system for fusion reactor

    International Nuclear Information System (INIS)

    Highlights: ► Computational analysis of S-CO2 Brayton cycle power conversion system. ► Validation of numerical model with literature data. ► Recompression S-CO2 Brayton cycle thermal efficiency of 42.44%. ► Reheating concept to enhance the cycle thermal efficiency. ► Higher efficiency achieved by the proposed concept. - Abstract: The Optimized Supercritical Cycle Analysis (OSCA) code is being developed to analyze the design of a supercritical carbon dioxide (S-CO2) driven Brayton cycle for a fusion reactor as part of the Modular Optimal Balance Integral System (MOBIS). This system is based on a recompression Brayton cycle. S-CO2 is adopted as the working fluid for MOBIS because of its easy availability, high density and low chemical reactivity. The reheating concept is introduced to enhance the cycle thermal efficiency. The helium-cooled lithium lead model AB of DEMO fusion reactor is used as reference in this paper.

  2. Thermodynamic analysis of the double Brayton cycle with the use of oxy combustion and capture of CO2

    Science.gov (United States)

    Ziółkowski, Paweł; Zakrzewski, Witold; Kaczmarczyk, Oktawia; Badur, Janusz

    2013-06-01

    In this paper, thermodynamic analysis of a proposed innovative double Brayton cycle with the use of oxy combustion and capture of CO2, is presented. For that purpose, the computation flow mechanics (CFM) approach has been developed. The double Brayton cycle (DBC) consists of primary Brayton and secondary inverse Brayton cycle. Inversion means that the role of the compressor and the gas turbine is changed and firstly we have expansion before compression. Additionally, the workingfluid in the DBC with the use of oxy combustion and CO2 capture contains a great amount of H2O and CO2, and the condensation process of steam (H2O) overlaps in negative pressure conditions. The analysis has been done for variants values of the compression ratio, which determines the lowest pressure in the double Brayton cycle.

  3. Brayton-Cycle Heat Recovery System Characterization Program. Glass-furnace facility test plan

    Energy Technology Data Exchange (ETDEWEB)

    1980-08-29

    The test plan for development of a system to recover waste heat and produce electricity and preheated combustion air from the exhaust gases of an industrial glass furnace is described. The approach is to use a subatmospheric turbocompressor in a Brayton-cycle system. The operational furnace test requirements, the operational furnace environment, and the facility design approach are discussed. (MCW)

  4. Techno-economic studies of environmentally friendly Brayton cycles in the petrochemical industry

    OpenAIRE

    Nkoi, Barinyima

    2014-01-01

    Brayton cycles are open gas turbine cycles extensively used in aviation and industrial applications because of their advantageous volume and weight characteristics. With the bulk of waste exhaust heat and engine emissions associated, there is need to be mindful of environmentally-friendliness of these engine cycles, not compromising good technical performance, and economic viability. This research considers assessment of power plants in helicopters, and aeroderivative ind...

  5. Optimal analysis on the performance of an irreversible harmonic quantum Brayton refrigeration cycle.

    Science.gov (United States)

    Lin, Bihong; Chen, Jincan

    2003-11-01

    An irreversible model of a quantum refrigeration cycle working with many noninteracting harmonic oscillators is established. The refrigeration cycle consists of two adiabatic and two constant-frequency processes. The general performance characteristics of the cycle are investigated, based on the quantum master equation and the semigroup approach. The expressions for several important performance parameters such as the coefficient of performance, cooling rate, power input, and rate of entropy production are derived. By using numerical solutions, the cooling rate of the refrigeration cycle subject to finite cycle duration is optimized. The maximum cooling rate and the corresponding parameters are calculated numerically. The optimal region of the coefficient of performance and the optimal ranges of temperatures of the working substance and times spent on the two constant-frequency processes are determined. Moreover, the optimal performance of the cycle in the high-temperature limit is compared with that of a classical Brayton refrigerator working with an ideal gas. The results obtained here show that in the high-temperature limit a harmonic quantum Brayton cycle may be equivalent to a classical Brayton cycle. PMID:14682856

  6. Preliminary Design of S-CO{sub 2} Brayton Cycle for KAIST Micro Modular Reactor

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Seong Gu; Kim, Min Gil; Bae, Seong Jun; Lee, Jeong Ik [Korea Advanced Institue of Science and Technology, Daejeon (Korea, Republic of)

    2013-10-15

    This paper suggests a complete modular reactor with an innovative concept of reactor cooling by using a supercritical carbon dioxide directly. Authors propose the supercritical CO{sub 2} Brayton cycle (S-CO{sub 2} cycle) as a power conversion system to achieve small volume of power conversion unit (PCU) and to contain the core and PCU in one vessel for the full modularization. This study suggests a conceptual design of small modular reactor including PCU which is named as KAIST Micro Modular Reactor (MMR). As a part of ongoing research of conceptual design of KAIST MMR, preliminary design of power generation cycle was performed in this study. Since the targets of MMR are full modularization of a reactor system with S-CO{sub 2} coolant, authors selected a simple recuperated S-CO{sub 2} Brayton cycle as a power conversion system for KAIST MMR. The size of components of the S-CO{sub 2} cycle is much smaller than existing helium Brayton cycle and steam Rankine cycle, and whole power conversion system can be contained with core and safety system in one containment vessel. From the investigation of the power conversion cycle, recompressing recuperated cycle showed higher efficiency than the simple recuperated cycle. However the volume of heat exchanger for recompressing cycle is too large so more space will be occupied by heat exchanger in the recompressing cycle than the simple recuperated cycle. Thus, authors consider that the simple recuperated cycle is more suitable for MMR. More research for the KAIST MMR will be followed in the future and detailed information of reactor core and safety system will be developed down the road. More refined cycle layout and design of turbomachinery and heat exchanger will be performed in the future study.

  7. Preliminary design of S-CO{sub 2} Brayton cycle for APR-1400 with power generation and desalination process

    Energy Technology Data Exchange (ETDEWEB)

    Bae, Seong Jun; Lee, Won Woong; Jeong, Yong Hoon; Lee, Jeong Ik [KAIST, Daejeon (Korea, Republic of); Yoon, Ho Joon [KUSTAR, Abu Dhabi (United Arab Emirates)

    2015-10-15

    This study was conducted to explore the capabilities of the S-CO{sub 2} Brayton cycle for a cogeneration system for APR-1400 application. Three concepts of the S-CO{sub 2} simple recuperated co-generation cycle were designed. A supercritical CO{sub 2} (S-CO{sub 2}) Brayton cycle is recently receiving significant attention as a promising power conversion system in wide range of energy applications due to its high efficiency and compact footprint. The main reason why the S-CO{sub 2} Brayton cycle has these advantages is that the compressor operates near the critical point of CO{sub 2} (30.98 .deg. C, 7.38MPa) to reduce the compression work significantly compared to the other Brayton cycles. In this study, the concept of replacing the entire steam cycle of APR-1400 with the S-CO{sub 2} Brayton cycle is evaluated. The power generation purpose S-CO{sub 2} Brayton cycles are redesigned to generate power and provide heat to the desalination system at the same time. The performance of these newly suggested cycles are evaluated in this paper. The target was to deliver 147MW heat to the desalination process. The thermal efficiencies of the three concepts are not significantly different, but the 3{sup rd} concept is relatively simpler than other cycles because only an additional heat exchanger is required. Although the 2{sup nd} concept is relatively complicated in comparison to other concepts, the temperatures at the inlet and outlet of the DHX are higher than that of the others. As shown in the results, the S-CO{sub 2} Brayton cycles are not easy to outperform the steam cycle with very simple layout and general design points under APR-1400 operating condition. However, this study shows that the S-CO{sub 2} Brayton cycles can be designed as a co-generation cycle while producing the target desalination heat with a simple configuration. In addition, it was also found that the S-CO{sub 2} Brayton cycle can achieve higher cycle thermal efficiency than the steam power cycle under

  8. Features of supercritical carbon dioxide Brayton cycle coupled with reactor

    International Nuclear Information System (INIS)

    In order to obtain acceptable cycle efficiency, current helium gas turbine power cycle technology needs high cycle temperature which means that the cycle needs high core-out temperature. The technology has high requirements on reactor structure and fuel elements materials, and also on turbine manufacture. While utilizing CO2 as cycle working fluid, it can guarantee to lower the cycle temperature and turbo machine Janume but achieve the same cycle efficiency, so as to enhance the safety and economy of reactor. According to the laws of thermodynamics, a calculation model of supercritical CO2 power cycle was established to analyze the feature, and the decisive parameters of the cycle and also investigate the effect of each parameter on the cycle efficiency in detail were obtained. The results show that supercritical CO2 power cycle can achieve quite satisfied efficiency at a lower cycle highest temperature than helium cycle, and CO2 is a promising working fluid. (authors)

  9. Preheating of fluid in a supercritical Brayton cycle power generation system at cold startup

    Energy Technology Data Exchange (ETDEWEB)

    Wright, Steven A.; Fuller, Robert L.

    2016-07-12

    Various technologies pertaining to causing fluid in a supercritical Brayton cycle power generation system to flow in a desired direction at cold startup of the system are described herein. A sensor is positioned at an inlet of a turbine, wherein the sensor is configured to output sensed temperatures of fluid at the inlet of the turbine. If the sensed temperature surpasses a predefined threshold, at least one operating parameter of the power generation system is altered.

  10. Supercritical CO2 Brayton Cycle Energy Conversion System Coupled with SFR

    International Nuclear Information System (INIS)

    This report contains the description of the S-CO2 Brayton cycle coupled to KALIMER-600 as an alternative energy conversion system. For a system development, a computer code was developed to calculate heat balance of normal operation condition. Based on the computer code, the S-CO2 Brayton cycle energy conversion system was constructed for the KALIMER-600. Computer codes were developed to analysis for the S-CO2 turbomachinery. Based on the design codes, the design parameters were prepared to configure the KALIMER-600 S-CO2 turbomachinery models. A one-dimensional analysis computer code was developed to evaluate the performance of the previous PCHE heat exchangers and a design data for the typical type PCHE was produced. In parallel with the PCHE-type heat exchanger design, an airfoil shape fin PCHE heat exchanger was newly designed. The new design concept was evaluated by three-dimensional CFD analyses. Possible control schemes for power control in the KALIMER-600 S-CO2 Brayton cycle were investigated by using the MARS code. The MMS-LMR code was also developed to analyze the transient phenomena in a SFR with a supercritical CO2 Brayton cycle to develop the control logic. Simple power reduction and recovery event was selected and analyzed for the transient calculation. For the evaluation of Na-CO2 boundary failure event, a computer was developed to simulate the complex thermodynamic behaviors coupled with the chemical reaction between liquid sodium and CO2 gas. The long term behavior of a Na-CO2 boundary failure event and its consequences which lead to a system pressure transient were evaluated

  11. Coupling a Supercritical Carbon Dioxide Brayton Cycle to a Helium-Cooled Reactor.

    Energy Technology Data Exchange (ETDEWEB)

    Middleton, Bobby [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Pasch, James Jay [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Kruizenga, Alan Michael [Sandia National Lab. (SNL-CA), Livermore, CA (United States); Walker, Matthew [Sandia National Lab. (SNL-CA), Livermore, CA (United States)

    2016-01-01

    This report outlines the thermodynamics of a supercritical carbon dioxide (sCO2) recompression closed Brayton cycle (RCBC) coupled to a Helium-cooled nuclear reactor. The baseline reactor design for the study is the AREVA High Temperature Gas-Cooled Reactor (HTGR). Using the AREVA HTGR nominal operating parameters, an initial thermodynamic study was performed using Sandia's deterministic RCBC analysis program. Utilizing the output of the RCBC thermodynamic analysis, preliminary values of reactor power and of Helium flow rate through the reactor were calculated in Sandia's HelCO2 code. Some research regarding materials requirements was then conducted to determine aspects of corrosion related to both Helium and to sCO2 , as well as some mechanical considerations for pressures and temperatures that will be seen by the piping and other components. This analysis resulted in a list of materials-related research items that need to be conducted in the future. A short assessment of dry heat rejection advantages of sCO2> Brayton cycles was also included. This assessment lists some items that should be investigated in the future to better understand how sCO2 Brayton cycles and nuclear can maximally contribute to optimizing the water efficiency of carbon free power generation

  12. The Brayton Cycle heat pump for solvent recovery and pollution control

    International Nuclear Information System (INIS)

    The Brayton Cycle heat pump technology for the recovery of solvent and prevention of emissions is relatively new. Like most new technologies, it is a combination of older concepts, ideas and types of processes put together in a unique way. As a result, proven equipment enables achievement of extremely low condensing temperatures at relatively low cost. The Brayton Cycle is a thermodynamic principle. It was used first for a turbine engine, but more recently it has been used for a variety of other kinds of processes including refrigeration. A great variety of methods are used for emission control including adsorption, direct condensation, absorption in a fluid, and incineration or destruction. The Brayton Cycle technology actually fits into two of these categories, adsorption and direct condensation. Since it is a refrigeration process, it can be used to condense solvents from a solvent-laden air stream. The advantage of this particular process over other refrigeration methods is that lower temperatures can be achieved more easily. In fact, temperatures as low as -150 degrees F have been used to recover solvents in this manner. That happens to be the freezing point of methylene chloride which is a very volatile compound. High recovery efficiencies can be obtained for a whole variety of organic materials. 8 figs., 1 tab

  13. Identified corrosion and erosion mechanisms in SCO2 Brayton Cycles.

    Energy Technology Data Exchange (ETDEWEB)

    Fleming, Darryn D.; Kruizenga, Alan Michael

    2014-06-01

    Supercritical Carbon Dioxide (S-CO2) is an efficient and flexible working fluid for power production. Research to interface S-CO2 systems with nuclear, thermal solar, and fossil energy sources is currently underway. To proceed, we must address concerns regarding compatibility of materials, at high temperature, and compatibility between significantly different heat transfer fluids. Dry, pure S-CO2 is thought to be relatively inert [1], while the addition of ppm levels of water and oxygen result in formation of a protective chromia layer and iron oxide [2]. Thin oxides are favorable as diffusion barriers, and for their minimal impact on heat transfer. While S-CO2 is typically understood to be the secondary fluid, many varieties of primary fluids exist for nuclear applications. Molten salts, for use in the Molten Salt Reactor concept, are given as an example to contrast the materials requirements of primary and secondary fluids. Thin chromia layers are soluble in molten salt systems (nitrate, chloride, and fluoride based salts) [3-8], making materials selection for heat exchangers a precarious balancing act between high temperature oxidation (S-CO2) and metal dissolution (salt side of heat exchanger). Because concerns have been raised regarding component lifetimes, S-CO2 work has begun to characterize starting materials and to establish a baseline by analysis of 1) as-received stainless steel piping, and 2) piping exposed to S-CO2 under typical operating conditions with Sandia National Laboratories Brayton systems. A second issue discovered by SNL involves substantial erosion in the turbine blade and inlet nozzle. It is believed that this is caused by small particulates that originate from different materials around the loop that are entrained by the S-CO2 to the nozzle, where they impact the inlet nozzle vanes, causing erosion. We believe that, in some way, this is linked to the purity of the S-CO2, the corrosion contaminants, and the metal particulates that

  14. Design Development Analyses in Support of a Heatpipe-Brayton Cycle Heat Exchanger

    Science.gov (United States)

    Steeve, Brian E.; Kapernick, Richard J.

    2004-01-01

    One of the power systems under consideration for nuclear electric propulsion or as a planetary surface power source is a heatpipe-cooled reactor coupled to a Brayton cycle. In this system, power is transferred from the heatpipes to the Brayton gas via a heat exchanger attached to the heatpipes. This paper discusses the fluid, thermal and structural analyses that were performed in support of the design of the heat exchanger to be tested in the SAFE-100 experimental program at the Marshall Space Flight Center: An important consideration throughout the design development of the heat exchanger w its capability to be utilized for higher power and temperature applications. This paper also discusses this aspect of the design and presents designs for specific applications that are under consideration.

  15. Improvement of supercritical CO2 Brayton cycle using binary gas mixture

    International Nuclear Information System (INIS)

    A Sodium-cooled Fast Reactor (SFR) is one of the strongest candidates for the next generation nuclear reactor. However, the conventional design of a SFR concept with an indirect Rankine cycle is inevitably subjected to a sodium-water reaction. To prevent hazardous situation caused by sodium-water reaction, the SFR with Brayton cycle using Supercritical Carbon dioxide (S-CO2 cycle) as a working fluid can be an alternative approach. The S-CO2 Brayton cycle is more sensitive to the critical point of working fluids than other Brayton cycles. This is because compressor work significantly decreases at slightly above the critical point due to high density near the boundary between the supercritical state and the subcritical state. For this reason, the minimum temperature and pressure of cycle are just above the CO2 critical point. The critical point acts as a limitation of the lowest operating condition of the cycle. In general, lowering the rejection temperature of a thermodynamic cycle increases the efficiency and thus, changing the critical point of CO2 can result in an improvement of the total cycle efficiency with the same cycle layout. Modifying the critical point of the working fluid can be done by adding other gases to CO2. The direction and range of the CO2 critical point variation depends on the mixed component and its amount. In particular, chemical reactivity of the gas mixture itself and the gas mixture with sodium at high temperatures are of interest. To modify the critical point of the working fluid, several gases were chosen as candidates by which chemical stability with sodium within the interested range of cycle operating condition was assured: CO2 was mixed with N2, O2, He, Ar and Xe. To evaluate the effect of shifting the critical point and changes in the properties of the S-CO2 Brayton cycle, a supercritical Brayton cycle analysis code connected with the REFPROP program from the NIST was developed. The developed code is for evaluating simple

  16. Thermal analysis on N2 and S-CO2 Brayton cycle for the energy conversion system of small scale ultra-long cycle fast reactor

    International Nuclear Information System (INIS)

    An ultra-long cycle fast reactor (UCFR) is one of the SFR designs operating in a long cycle without refueling. The operational mechanism of long cycle fast reactor is once-through fuel cycle through breed and burn system. The benefits of long cycle fast reactor include capital/operation cost reductions, low proliferation risk, and the interim storage of light water reactor (LWR) spent fuel. For the power conversion system of next generation nuclear reactor, Brayton cycle has been mainly considered. Brayton cycle not only increases overall thermal efficiency in corresponding temperature range of GenIV reactors, but also solves sodium-water reaction issues. As a working fluid in Brayton cycle, many inactive gases are selected. For the power conversion system of next generation nuclear reactor, Brayton cycle has been mainly considered. Among the candidates for working fluid in Brayton power cycle, S-CO2 and N2 are analyzed in thermal aspect. For the major parameters including maximum system pressure, isentropic efficiencies of compressor and turbine, and pinch point, S-CO2 cycle shows the highest thermal performance. However, N2 cycle without intermediate loop gives comparable thermal performance, if high pressure around 70 bar and high isentropic efficiency of each component are maintained

  17. Scaling considerations for a multi-megawatt class supercritical CO2 brayton cycle and commercialization.

    Energy Technology Data Exchange (ETDEWEB)

    Fleming, Darryn D.; Holschuh, Thomas Vernon,; Conboy, Thomas M.; Pasch, James Jay; Wright, Steven A; Rochau, Gary E; Fuller, Robert Lynn

    2013-11-01

    Small-scale supercritical CO2 demonstration loops are successful at identifying the important technical issues that one must face in order to scale up to larger power levels. The Sandia National Laboratories supercritical CO2 Brayton cycle test loops are identifying technical needs to scale the technology to commercial power levels such as 10 MWe. The small size of the Sandia 1 MWth loop has demonstration of the split flow loop efficiency and effectiveness of the Printed Circuit Heat Exchangers (PCHXs) leading to the design of a fully recuperated, split flow, supercritical CO2 Brayton cycle demonstration system. However, there were many problems that were encountered, such as high rotational speeds in the units. Additionally, the turbomachinery in the test loops need to identify issues concerning the bearings, seals, thermal boundaries, and motor controller problems in order to be proved a reliable power source in the 300 kWe range. Although these issues were anticipated in smaller demonstration units, commercially scaled hardware would eliminate these problems caused by high rotational speeds at small scale. The economic viability and development of the future scalable 10 MWe solely depends on the interest of DOE and private industry. The Intellectual Property collected by Sandia proves that the ~10 MWe supercritical CO2 power conversion loop to be very beneficial when coupled to a 20 MWth heat source (either solar, geothermal, fossil, or nuclear). This paper will identify a commercialization plan, as well as, a roadmap from the simple 1 MWth supercritical CO2 development loop to a power producing 10 MWe supercritical CO2 Brayton loop.

  18. Exergetic efficiency optimization for an irreversible heat pump working on reversed Brayton cycle

    Indian Academy of Sciences (India)

    Yuehong Bi; Lingen Chen; Fengrui Sun

    2010-03-01

    This paper deals with the performance analysis and optimization for irreversible heat pumps working on reversed Brayton cycle with constant-temperature heat reservoirs by taking exergetic efficiency as the optimization objective combining exergy concept with finite-time thermodynamics (FTT). Exergetic efficiency is defined as the ratio of rate of exergy output to rate of exergy input of the system. The irreversibilities considered in the system include heat resistance losses in the hot- and cold-side heat exchangers and non-isentropic losses in the compression and expansion processes. The analytical formulas of the heating load, coefficient of performance (COP) and exergetic efficiency for the heat pumps are derived. The results are compared with those obtained for the traditional heating load and coefficient of performance objectives. The influences of the pressure ratio of the compressor, the allocation of heat exchanger inventory, the temperature ratio of two reservoirs, the effectiveness of the hot- and cold-side heat exchangers and regenerator, the efficiencies of the compressor and expander, the ratio of hot-side heat reservoir temperature to ambient temperature, the total heat exchanger inventory, and the heat capacity rate of the working fluid on the exergetic efficiency of the heat pumps are analysed by numerical calculations. The results show that the exergetic efficiency optimization is an important and effective criterion for the evaluation of an irreversible heat pump working on reversed Brayton cycle.

  19. Conceptual Design of S-CO2 Brayton Cycle Radial Turbomachinery for KAIST Micro Modular Reactor

    International Nuclear Information System (INIS)

    KAIST proposed a new SMR design, which utilizes S-CO2 as the working fluid. It was named as KAIST MMR. Compared with existing SMR concepts, KAIST MMR has advantages of achieving smaller volume of power conversion unit (PCU) and containing the core and PCU in one vessel for the complete modularization. Authors noticed that the compressor and turbine assumed performances of KAIST MMR were conservatively selected previously. Thus, this paper tries to address the best estimate values of each turbomachinery in 10MWe class KAIST MMR. The turbomachinery size of the S-CO2 cycle is smaller than helium Brayton cycle and steam Rankine cycle. The suggested SMR concept adopts passive cooling system by using air. This method can cool reactor without external electricity supply. Small size and more flexible installation in the inland area will be necessary characteristics for the future nuclear application in the water limited region. KAIST MMR meets all these requirements by utilizing S-CO2 as a working fluid. This paper presents the work for further increasing the system performance by estimating the component efficiency more realistically. The cycle layout adopted for the application is S-CO2 recuperated Brayton cycle. The best efficiency of compressor and turbine was evaluated to be 84.94% and 90.94%, respectively. By using KAIST in-house code, thermal efficiency and net output were increased to 35.81% and 12.45MWe, respectively, for the same core thermal power. More refined cycle layout and suitable turbomachinery design will be performed in the near future

  20. Concept Design for a High Temperature Helium Brayton Cycle with Interstage Heating and Cooling

    Energy Technology Data Exchange (ETDEWEB)

    Wright, Steven A. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Vernon, Milton E. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Pickard, Paul S. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2013-12-01

    The primary metric for the viability of these next generation nuclear power plants will be the cost of generated electricity. One important component in achieving these objectives is the development of power conversion technologies that maximize the electrical power output of these advanced reactors for a given thermal power. More efficient power conversion systems can directly reduce the cost of nuclear generated electricity and therefore advanced power conversion cycle research is an important area of investigation for the Generation IV Program. Brayton cycles using inert or other gas working fluids, have the potential to take advantage of the higher outlet temperature range of Generation IV systems and allow substantial increases in nuclear power conversion efficiency, and potentially reductions in power conversion system capital costs compared to the steam Rankine cycle used in current light water reactors. For the Very High Temperature Reactor (VHTR), Helium Brayton cycles which can operate in the 900 to 950 C range have been the focus of power conversion research. Previous Generation IV studies examined several options for He Brayton cycles that could increase efficiency with acceptable capital cost implications. At these high outlet temperatures, Interstage Heating and Cooling (IHC) was shown to provide significant efficiency improvement (a few to 12%) but required increased system complexity and therefore had potential for increased costs. These scoping studies identified the potential for increased efficiency, but a more detailed analysis of the turbomachinery and heat exchanger sizes and costs was needed to determine whether this approach could be cost effective. The purpose of this study is to examine the turbomachinery and heat exchanger implications of interstage heating and cooling configurations. In general, this analysis illustrates that these engineering considerations introduce new constraints to the design of IHC systems that may require

  1. Optimization of Brayton cycles for low-to-moderate grade thermal energy sources

    International Nuclear Information System (INIS)

    Future electricity generation will involve low or moderate temperature technologies. In such a scenario, optimisation of thermodynamic cycles will be a key task. This work presents a systematic analysis to find the operating regime where Brayton cycles reach the highest efficiency, using real substances and given heat source and sink temperatures. Several configurations using fluids close to its critical point at the compressor inlet are considered. Irreversibility sources are carefully analysed, as well as the type of working fluid. The analysis is performed by means of a theoretical approach to obtain some trends, which are afterwards validated with real gases. Results show that the efficiency and the specific work improve if the compressor inlet is close to the critical point. Furthermore, these cycles are less sensitive to pressure drops and politropic efficiencies than those working with ideal gases. The above features are more evident when the ratio of heat source and heat sink temperatures is low. The selection of the gas becomes a fundamental issue in this quest. Critical temperature should be close to ambient temperature, low critical pressure is advisable and the R/cp factor measured at the ideal gas condition should be low to further enhance the efficiency. - Highlights: • Performance analysis of Brayton cycles with the compressor inlet close to the critical point. • Cycles are not very sensitive to pressure drops and isentropic efficiencies of the compressor. • Gas selection becomes important, regarding the critical pressure and temperature as well as the kind of fluid. • R/cp factor measured at the ideal gas condition should be as low as possible

  2. Second-law analysis and optimization of reverse brayton cycles of different configurations for cryogenic applications

    Science.gov (United States)

    Streit, James Ryder; Razani, Arsalan

    2012-06-01

    Second-law of thermodynamics (2nd law) and exergy analyses and optimization offour Reverse Brayton Refrigeration (RBR) cryogenic cycle configurations: Conventional 1-stage compression cycle; Conventional 2-stage compression cycle; 1-stage compressionModified cycle with intermediate cooling of the recuperator using an auxiliary cooler; andan Integrated 2-stage expansion RBR cycle are performed. The conventional RBR cyclesare analyzed for low and high pressure ratio applications using multistage compressorswith intercooling. Analytical solutions for the conventional cycles are developed includingthermal and fluid flow irreversibilities of the recuperators and all heat exchangers inaddition to the compression and expansion processes. Analytical solutions are used to findthe thermodynamic bounds for the performance of the cycles. Exergy irreversibilitydiagrams of the cycles are developed and the effects of important system parameters onRBR cycle performance are investigated. 2nd law/exergy analyses, and optimization of thecycles with intermediate cooling of the recuperator, considering the cooling temperatureand the recuperator effectiveness and pressure drop, are included. The effect of the 2ndlaw/exergy efficiency of the auxiliary cooler on the total system efficiencies is presented.

  3. Creep Property Characterization of Potential Brayton Cycle Impeller and Duct Materials

    Science.gov (United States)

    Gabb, Timothy P.; Gayda, John; Garg, Anita

    2007-01-01

    Cast superalloys have potential applications in space as impellers within closed-loop Brayton cycle nuclear power generation systems. Likewise wrought superalloys are good candidates for ducts and heat exchangers transporting the inert working gas in a Brayton-based power plant. Two cast superalloys, Mar-M247LC and IN792, and a NASA GRC powder metallurgy superalloy, LSHR, have been screened to compare their respective capabilities for impeller applications. Mar-M247LC has been selected for additional long term evaluations. Initial tests in helium indicate this inert environment may debit long term creep resistance of this alloy. Several wrought superalloys including Hastelloy® X, Inconel® 617, Inconel® 740, Nimonic® 263, Incoloy® MA956, and Haynes 230 are also being screened to compare their capabilities for duct applications. Haynes 230 has been selected for additional long term evaluations. Initial tests in helium are just underway for this alloy. These proposed applications would require sufficient strength and creep resistance for long term service at temperatures up to 1200 K, with service times to 100,000 h or more. Therefore, long term microstructural stability is also being screened.

  4. Creep Property Characterization of Potential Brayton Cycle Impeller and Duct Materials

    Science.gov (United States)

    Gabb, Timothy P.; Gayda, john; Garg, Anita

    2007-01-01

    Cast superalloys have potential applications in space as impellers within closed-loop Brayton cycle nuclear power generation systems. Likewise wrought superalloys are good candidates for ducts and heat exchangers transporting the inert working gas in a Brayton-based power plant. Two cast superalloys, Mar-M247LC and IN792, and a NASA GRC powder metallurgy superalloy, LSHR, have been screened to compare their respective capabilities for impeller applications. Mar-M247LC has been selected for additional long term evaluations. Initial tests in helium indicate this inert environment may debit long term creep resistance of this alloy. Several wrought superalloys including Hastelloy(Registered TradeMark) X, Inconel(Registered TradeMark) 617, Inconel(Registered TradeMark) 740, Nimonic(Registered TradeMark) 263, Incoloy(Registered TradeMark) MA956, and Haynes 230 are also being screened to compare their capabilities for duct applications. Haynes 230 has been selected for additional long term evaluations. Initial tests in helium are just underway for this alloy. These proposed applications would require sufficient strength and creep resistance for long term service at temperatures up to 1200 K, with service times to 100,000 h or more. Therefore, long term microstructural stability is also being screened.

  5. Tensile and Creep Property Characterization of Potential Brayton Cycle Impeller and Duct Materials

    Science.gov (United States)

    Gabb, Timothy P.; Gayda, John

    2006-01-01

    This paper represents a status report documenting the work on creep of superalloys performed under Project Prometheus. Cast superalloys have potential applications in space as impellers within closed-loop Brayton cycle nuclear power generation systems. Likewise wrought superalloys are good candidates for ducts and heat exchangers transporting the inert working gas in a Brayton-based power plant. Two cast superalloys, Mar-M247LC and IN792, and a NASA GRC powder metallurgy superalloy, LSHR, are being screened to compare their respective capabilities for impeller applications. Several wrought superalloys including Hastelloy X, (Haynes International, Inc., Kokomo, IN), Inconel 617, Inconel 740, Nimonic 263, and Incoloy MA956 (Special Metals Corporation, Huntington, WV) are also being screened to compare their capabilities for duct applications. These proposed applications would require sufficient strength and creep resistance for long term service at temperatures up to 1200 K, with service times to 100,000 h or more. Conventional tensile and creep tests were performed at temperatures up to 1200 K on specimens extracted from the materials. Initial microstructure evaluations were also undertaken.

  6. Brayton-cycle heat recovery-system characterization program. Subatmospheric-system test report

    Energy Technology Data Exchange (ETDEWEB)

    Burgmeier, L.; Leung, S.

    1981-07-31

    The turbine tests and results for the Brayton cycle subatmospheric system (SAS) are summarized. A scaled model turbine was operated in the same environment as that which a full-scale SAS machine would experience from the hot effluent flue gas from a glass container furnace. The objective of the testing was to evaluate the effects of a simulated furnace flue gas stream on the turbine nozzles and blades. The following specific areas were evaluated: erosion of the turbine nozzles and blades from the dust in the flue gas, hot corrosion from alkali metal salts in the dust and acid vapor (sulfur trioxide and hydrogen chloride) in the flue gas, and fouling and flow blockage due to deposition and/or condensation from the flue gas constituents.

  7. Heat exchanger optimization of a closed Brayton cycle for nuclear space propulsion

    Energy Technology Data Exchange (ETDEWEB)

    Ribeiro, Guilherme B.; Guimaraes, Lamartine N.F.; Braz Filho, Francisco A., E-mail: gbribeiro@ieav.cta.br, E-mail: guimarae@ieav.cta.br, E-mail: braz@ieav.cta.br [Instituto de Estudos Avancados (IEAV), Sao Jose dos Campos, SP (Brazil). Divisao de Energia Nuclear

    2015-07-01

    Nuclear power systems turned to space electric propulsion differs strongly from usual ground-based power systems regarding the importance of overall size and weight. For propulsion power systems, weight and efficiency are essential drivers that should be managed during conception phase. Considering that, this paper aims the development of a thermal model of a closed Brayton cycle that applies the thermal conductance of heat exchangers in order to predict the energy conversion performance. The centrifugal-flow turbine and compressor characterization were achieved using algebraic equations from literature data. The binary mixture of He-Xe with molecular weight of 40 g/mole is applied and the impact of heat exchanger optimization in thermodynamic irreversibilities is evaluated in this paper. (author)

  8. Dynamic response simulation for high temperature gas-cooled reactor with indirect closed Brayton cycle

    International Nuclear Information System (INIS)

    A transient simulation program is developed in order to study dynamic characteristics of high temperature gas-cooled reactor with indirect closed Brayton cycle. After the brief introduction to such a plant, detailed mathematical models for important installations are described in the paper. By inducing step positive reactivity into the reactor, it looks like that the powers of turbo machine installations have a different growth rate accompanied with small increase of reactor power. Furthermore, this paper shows the temperature changes of reactor and heat exchangers. For the heat exchangers of the whole secondary loop, the pressure changes behave quite differently for those three sections divided by turbine, low pressure compressor and high pressure compressor. For all these equipments, the simulation program gives reasonable results and is in accordance with dynamic characteristics of their own. (authors)

  9. Enhanced arrangement for recuperators in supercritical CO2 Brayton power cycle for energy conversion in fusion reactors

    International Nuclear Information System (INIS)

    Highlights: •We propose an enhanced power conversion system layout for a Model C fusion reactor. •Proposed layout is based on a modified recompression supercritical CO2 Brayton cycle. •New arrangement in recuperators regards to classical cycle is used. •High efficiency is achieved, comparable with the best obtained in complex solutions. -- Abstract: A domestic research program called TECNOFUS was launched in Spain in 2009 to support technological developments related to a dual coolant breeding blanket concept for fusion reactors. This concept of blanket uses Helium (300 °C/400 °C) to cool part of it and a liquid metal (480 °C/700 °C) to cool the rest; it also includes high temperature (700 °C/800 °C) and medium temperature (566 °C/700 °C) Helium cooling circuits for divertor. This paper proposes a new layout of the classical recompression supercritical CO2 Brayton cycle which replaces one of the recuperators (the one with the highest temperature) by another which by-passes the low temperature blanket source. This arrangement allows reaching high turbine inlet temperatures (around 600 °C) with medium pressures (around 225 bar) and achieving high cycle efficiencies (close to 46.5%). So, the proposed cycle reveals as a promising design because it integrates all the available thermal sources in a compact layout achieving high efficiencies with the usual parameters prescribed in classical recompression supercritical CO2 Brayton cycles

  10. Use of Multiple Reheat Helium Brayton Cycles to Eliminate the Intermediate Heat Transfer Loop for Advanced Loop Type SFRs

    Energy Technology Data Exchange (ETDEWEB)

    Haihua Zhao; Hongbin Zhang; Samuel E. Bays

    2009-05-01

    The sodium intermediate heat transfer loop is used in existing sodium cooled fast reactor (SFR) plant design as a necessary safety measure to separate the radioactive primary loop sodium from the water of the steam Rankine power cycle. However, the intermediate heat transfer loop significantly increases the SFR plant cost and decreases the plant reliability due to the relatively high possibility of sodium leakage. A previous study shows that helium Brayton cycles with multiple reheat and intercooling for SFRs with reactor outlet temperature in the range of 510°C to 650°C can achieve thermal efficiencies comparable to or higher than steam cycles or recently proposed supercritical CO2 cycles. Use of inert helium as the power conversion working fluid provides major advantages over steam or CO2 by removing the requirement for safety systems to prevent and mitigate the sodium-water or sodium-CO2 reactions. A helium Brayton cycle power conversion system therefore makes the elimination of the intermediate heat transfer loop possible. This paper presents a pre-conceptual design of multiple reheat helium Brayton cycle for an advanced loop type SFR. This design widely refers the new horizontal shaft distributed PBMR helium power conversion design features. For a loop type SFR with reactor outlet temperature 550°C, the design achieves 42.4% thermal efficiency with favorable power density comparing with high temperature gas cooled reactors.

  11. Innovative biomass to power conversion systems based on cascaded supercritical CO2 Brayton cycles

    International Nuclear Information System (INIS)

    In the small to medium power range the main technologies for the conversion of biomass sources into electricity are based either on reciprocating internal combustion or organic Rankine cycle engines. Relatively low energy conversion efficiencies are obtained in both systems due to the thermodynamic losses in the conversion of biomass into syngas in the former, and to the high temperature difference in the heat transfer between combustion gases and working fluid in the latter. The aim of this paper is to demonstrate that higher efficiencies in the conversion of biomass sources into electricity can be obtained using systems based on the supercritical closed CO2 Brayton cycles (s-CO2). The s-CO2 system analysed here includes two cascaded supercritical CO2 cycles which enable to overcome the intrinsic limitation of the single cycle in the effective utilization of the whole heat available from flue gases. Both part-flow and simple supercritical CO2 cycle configurations are considered and four boiler arrangements are investigated to explore the thermodynamic performance of such systems. These power plant configurations, which were never explored in the literature for biomass conversion into electricity, are demonstrated here to be viable options to increase the energy conversion efficiency of small-to-medium biomass fired power plants. Results of the optimization procedure show that a maximum biomass to electricity conversion efficiency of 36% can be achieved using the cascaded configuration including a part flow topping cycle, which is approximately 10%-points higher than that of the existing biomass power plants in the small to medium power range. - Highlights: • Supercritical CO2 cycles are proposed for biomass to electricity conversion. • Four boiler design options are considered. • High total system efficiency is due to the part-flow cascaded configuration. • The efficiency is higher than that of other small/medium size alternative systems

  12. Brayton cycle for internal combustion engine exhaust gas waste heat recovery

    Directory of Open Access Journals (Sweden)

    J Galindo

    2015-06-01

    Full Text Available An average passenger car engine effectively uses about one-third of the fuel combustion energy, while the two-thirds are wasted through exhaust gases and engine cooling. It is of great interest to automotive industry to recover some of this wasted energy, thus increasing the engine efficiency and lowering fuel consumption and contamination. Waste heat recovery for internal combustion engine exhaust gases using Brayton cycle machine was investigated. The principle problems of application of such a system in a passenger car were considered: compressor and expander machine selection, machine size for packaging under the hood, efficiency of the cycle, and improvement of engine efficiency. Important parameters of machines design have been determined and analyzed. An average 2-L turbocharged gasoline engine’s New European Driving Cycle points were taken as inlet points for waste heat recovery system. It is theoretically estimated that the recuperated power of 1515 W can be achieved along with 5.7% improvement in engine efficiency, at the point where engine power is 26550 W.

  13. Application of exergetic sustainability index to a nano-scale irreversible Brayton cycle operating with ideal Bose and Fermi gasses

    International Nuclear Information System (INIS)

    Highlights: • An irreversible Brayton cycle operating quantum gasses is considered. • Exergetic sustainability index is derived for nano-scale cycles. • Nano-scale effects are considered. • Calculation are conducted for irreversible cycles. • Numerical results are presented and discussed. - Abstract: In this study, a nano-scale irreversible Brayton cycle operating with quantum gasses including Bose and Fermi gasses is researched. Developments in the nano-technology cause searching the nano-scale machines including thermal systems to be unavoidable. Thermodynamic analysis of a nano-scale irreversible Brayton cycle operating with Bose and Fermi gasses was performed (especially using exergetic sustainability index). In addition, thermodynamic analysis involving classical evaluation parameters such as work output, exergy output, entropy generation, energy and exergy efficiencies were conducted. Results are submitted numerically and finally some useful recommendations were conducted. Some important results are: entropy generation and exergetic sustainability index are affected mostly for Bose gas and power output and exergy output are affected mostly for the Fermi gas by x. At the high temperature conditions, work output and entropy generation have high values comparing with other degeneracy conditions

  14. Application of exergetic sustainability index to a nano-scale irreversible Brayton cycle operating with ideal Bose and Fermi gasses

    Energy Technology Data Exchange (ETDEWEB)

    Açıkkalp, Emin, E-mail: eacikkalp@gmail.com [Department of Mechanical and Manufacturing Engineering, Engineering Faculty, Bilecik S.E. University, Bilecik (Turkey); Caner, Necmettin [Department of Chemistry, Faculty of Arts and Sciences, Eskisehir Osmangazi University, Eskisehir (Turkey)

    2015-09-25

    Highlights: • An irreversible Brayton cycle operating quantum gasses is considered. • Exergetic sustainability index is derived for nano-scale cycles. • Nano-scale effects are considered. • Calculation are conducted for irreversible cycles. • Numerical results are presented and discussed. - Abstract: In this study, a nano-scale irreversible Brayton cycle operating with quantum gasses including Bose and Fermi gasses is researched. Developments in the nano-technology cause searching the nano-scale machines including thermal systems to be unavoidable. Thermodynamic analysis of a nano-scale irreversible Brayton cycle operating with Bose and Fermi gasses was performed (especially using exergetic sustainability index). In addition, thermodynamic analysis involving classical evaluation parameters such as work output, exergy output, entropy generation, energy and exergy efficiencies were conducted. Results are submitted numerically and finally some useful recommendations were conducted. Some important results are: entropy generation and exergetic sustainability index are affected mostly for Bose gas and power output and exergy output are affected mostly for the Fermi gas by x. At the high temperature conditions, work output and entropy generation have high values comparing with other degeneracy conditions.

  15. Nuclear Air-Brayton Combined Cycle Power Conversion Design, Physical Performance Estimation and Economic Assessment

    Science.gov (United States)

    Andreades, Charalampos

    The combination of an increased demand for electricity for economic development in parallel with the widespread push for adoption of renewable energy sources and the trend toward liberalized markets has placed a tremendous amount of stress on generators, system operators, and consumers. Non-guaranteed cost recovery, intermittent capacity, and highly volatile market prices are all part of new electricity grids. In order to try and remediate some of these effects, this dissertation proposes and studies the design and performance, both physical and economic, of a novel power conversion system, the Nuclear Air-Brayton Combined Cycle (NACC). The NACC is a power conversion system that takes a conventional industrial frame type gas turbine, modifies it to accept external nuclear heat at 670°C, while also maintaining its ability to co-fire with natural gas to increase temperature and power output at a very quick ramp rate. The NACC addresses the above issues by allowing the generator to gain extra revenue through the provision of ancillary services in addition to energy payments, the grid operator to have a highly flexible source of capacity to back up intermittent renewable energy sources, and the consumer to possibly see less volatile electricity prices and a reduced probability of black/brown outs. This dissertation is split into six sections that delve into specific design and economic issues related to the NACC. The first section describes the basic design and modifications necessary to create a functional externally heated gas turbine, sets a baseline design based upon the GE 7FB, and estimates its physical performance under nominal conditions. The second section explores the off-nominal performance of the NACC and characterizes its startup and shutdown sequences, along with some of its safety measures. The third section deals with the power ramp rate estimation of the NACC, a key performance parameter in a renewable-heavy grid that needs flexible capacity. The

  16. Analysis of Superimposed Elementary Thermodynamic Cycles: from the Brayton-Joule to Advanced Mixed (Auto-Combined Cycles

    Directory of Open Access Journals (Sweden)

    Giovanni Manente

    2009-09-01

    Full Text Available

    The need for efficiency improvement in energy conversion systems leads to a stricter functional integration among system components. This results in structures of increasing complexity, the high performance of which are often difficult to be understood easily. To make the comprehension of these structures easier, a new approach is followed in this paper, consisting in their representation as partial or total superimposition of elementary thermodynamic cycles. Although system performance cannot, in general, be evaluated as the sum of the performance of the separate thermodynamic cycles, this kind of representation and analysis can be of great help in understanding directions of development followed in the literature for the construction of advanced energy systems, and could suggest new potential directions of work. The evolution from the simple Brayton-Joule cycle to the so called “mixed” cycles, in which heat at the turbine discharge is exploited using internal heat sinks only without using a separate bottoming section, is used to demonstrate the potentiality of the approach. Mixed cycles are named here "auto-combined cycles” to highlight the combination of different (gas and steam cycles within the same system components.

    • This paper is an updated version of a paper published in the ECOS'08 proceedings. 

  17. Evaluation of Active Working Fluids for Brayton Cycles in Space Applications

    Science.gov (United States)

    Conklin, J. C.; Courville, G. E.; Scott, J. H.

    2004-02-01

    The main parameter of interest for space thermal power conversion to electricity is specific power, defined as the total electric power output per unit of system mass, rather than the cycle thermal efficiency. For a closed Brayton cycle, performance with two active working fluids, nitrogen tetroxide and aluminum chloride, is compared to that with an inert mixture of helium and xenon having a molecular mass of 40. A chemically active working fluid is defined here as a chemical compound that has a relatively high molecular weight at temperatures appropriate for the compressor inlet and dissociates to a lighter molecular weight fluid at typical turbine inlet temperatures. The active working fluids may have the advantage of a higher net turbomachinery work output and an advantageous enhancement of the heat transfer coefficient in the heat exchangers. The fundamental theory of the active working fluid concept is presented to demonstrate these potential advantages. Scoping calculations of the heat exchanger mass for a selected spacecraft application of 36.4 kW of electrical power output show that the nitrogen tetroxide active working fluid has an advantageous 7% to 30% lower mass-to-power ratio than that for the inert noble gas mixture, depending on the allowable turbine inlet temperature. The calculations for the aluminum chloride system suggest only a slight improvement in performance relative to the inert noble gas mixture.

  18. High Temperature Fusion Reactor Cooling Using Brayton Cycle Based Partial Energy Conversion

    Science.gov (United States)

    Juhasz, Albert J.; Sawicki, Jerzy T.

    2003-01-01

    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.

  19. A Mass Computation Model for Lightweight Brayton Cycle Regenerator Heat Exchangers

    Science.gov (United States)

    Juhasz, Albert J.

    2010-01-01

    Based on a theoretical analysis of convective heat transfer across large internal surface areas, this paper discusses the design implications for generating lightweight gas-gas heat exchanger designs by packaging such areas into compact three-dimensional shapes. Allowances are made for hot and cold inlet and outlet headers for assembly of completed regenerator (or recuperator) heat exchanger units into closed cycle gas turbine flow ducting. Surface area and resulting volume and mass requirements are computed for a range of heat exchanger effectiveness values and internal heat transfer coefficients. Benefit cost curves show the effect of increasing heat exchanger effectiveness on Brayton cycle thermodynamic efficiency on the plus side, while also illustrating the cost in heat exchanger required surface area, volume, and mass requirements as effectiveness is increased. The equations derived for counterflow and crossflow configurations show that as effectiveness values approach unity, or 100 percent, the required surface area, and hence heat exchanger volume and mass tend toward infinity, since the implication is that heat is transferred at a zero temperature difference. To verify the dimensional accuracy of the regenerator mass computational procedure, calculation of a regenerator specific mass, that is, heat exchanger weight per unit working fluid mass flow, is performed in both English and SI units. Identical numerical values for the specific mass parameter, whether expressed in lb/(lb/sec) or kg/ (kg/sec), show the dimensional consistency of overall results.

  20. Dynamic neutronic and stability analysis of a burst mode, single cavity gas core reactor Brayton cycle space power system

    Science.gov (United States)

    Dugan, Edward T.; Kutikkad, Kiratadas

    The conceptual, burst-mode gaseous-core reactor (GCR) space nuclear power system presently subjected to reactor-dynamics and system stability studies operates on a closed Brayton cycle, via disk MHD generator for energy conversion. While the gaseous fuel density power coefficient of reactivity is found to be capable of rapidly stabilizing the GCR system, the power of this feedback renders standard external reactivity insertions inadequate for significant power-level changes during normal operation.

  1. Modeling the small-scale dish-mounted solar thermal Brayton cycle

    Science.gov (United States)

    Le Roux, Willem G.; Meyer, Josua P.

    2016-05-01

    The small-scale dish-mounted solar thermal Brayton cycle (STBC) makes use of a sun-tracking dish reflector, solar receiver, recuperator and micro-turbine to generate power in the range of 1-20 kW. The modeling of such a system, using a turbocharger as micro-turbine, is required so that optimisation and further development of an experimental setup can be done. As a validation, an analytical model of the small-scale STBC in Matlab, where the net power output is determined from an exergy analysis, is compared with Flownex, an integrated systems CFD code. A 4.8 m diameter parabolic dish with open-cavity tubular receiver and plate-type counterflow recuperator is considered, based on previous work. A dish optical error of 10 mrad, a tracking error of 1° and a receiver aperture area of 0.25 m × 0.25 m are considered. Since the recuperator operates at a very high average temperature, the recuperator is modeled using an updated ɛ-NTU method which takes heat loss to the environment into consideration. Compressor and turbine maps from standard off-the-shelf Garrett turbochargers are used. The results show that for the calculation of the steady-state temperatures and pressures, there is good comparison between the Matlab and Flownex results (within 8%) except for the recuperator outlet temperature, which is due to the use of different ɛ-NTU methods. With the use of Matlab and Flownex, it is shown that the small-scale open STBC with an existing off-the-shelf turbocharger could generate a positive net power output with solar-to-mechanical efficiency of up to 12%, with much room for improvement.

  2. Transient analysis of an FHR coupled to a helium Brayton power cycle

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Minghui [The Ohio State Univ., Columbus, OH (United States). Nuclear Engineering Program; Kim, In Hun [The Ohio State Univ., Columbus, OH (United States). Nuclear Engineering Program; Sun, Xiaodong [The Ohio State Univ., Columbus, OH (United States). Nuclear Engineering Program; Christensen, Richard [The Ohio State Univ., Columbus, OH (United States). Nuclear Engineering Program; Utgikar, Vivek [Univ. of Idaho, Idaho Falls, ID (United States); Sabharwall, Piyush [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2015-08-01

    The Fluoride salt-cooled High-temperature Reactor (FHR) features a passive decay heat removal system and a high-efficiency Brayton cycle for electricity generation. It typically employs an intermediate loop, consisting of an intermediate heat exchanger (IHX) and a secondary heat exchanger (SHX), to couple the primary system with the power conversion unit (PCU). In this study, a preliminary dynamic system model is developed to simulate transient characteristics of a prototypic 20-MWth Fluoride salt-cooled High-temperature Test Reactor (FHTR). The model consists of a series of differential conservation equations that are numerically solved using the MATLAB platform. For the reactor, a point neutron kinetics model is adopted. For the IHX and SHX, a fluted tube heat exchanger and an offset strip-fin heat exchanger are selected, respectively. Detailed geometric parameters of each component in the FHTR are determined based on the FHTR nominal steady-state operating conditions. Three initiating events are simulated in this study, including a positive reactivity insertion, a step increase in the mass flow rate of the PCU helium flow, and a step increase in the PCU helium inlet temperature to the SHX. The simulation results show that the reactor has inherent safety features for those three simulated scenarios. It is observed that the increase in the temperatures of the fuel pebbles and primary coolant is mitigated by the decrease in the reactor power due to negative temperature feedbacks. The results also indicate that the intermediate loop with the two heat exchangers plays a significant role in the transient progression of the integral reactor system.

  3. Use of RELAP5-3D for Dynamic Analysis of a Closed-Loop Brayton Cycle Coupled To a Nuclear Reactor

    Science.gov (United States)

    McCann, Larry D.

    2007-01-01

    This paper describes results of a dynamic system model for a pair of closed Brayton-cycle (CBC) loops running in parallel that are connected to a nuclear gas reactor. The model assumes direct coupling between the reactor and the Brayton-cycle loops. The RELAP5-3D (version 2.4.1) computer program was used to perform the analysis. Few reactors have ever been coupled to closed Brayton-cycle systems. As such their behavior under dynamically varying loads, startup and shut down conditions, and requirements for safe and autonomous operation are largely unknown. The model described in this paper represents the reactor, turbine, compressor, recuperator, heat rejection system and alternator. The initial results of the model indicate stable operation of the reactor-driven Brayton-cycle system. However, for analysts with mostly pressurized water reactor experience, the Brayton cycle loops coupled to a gas-cooled reactor also indicate some counter-intuitive behavior for the complete coupled system. This model has provided crucial information in evaluating the reactor design and would have been further developed for use in developing procedures for safe start up, shut down, safe-standby, and other autonomous operating modes had the plant development cycle been completed.

  4. Development of a Supercritical Carbon Dioxide Brayton Cycle: Improving VHTR Efficiency and Testing Material Compatibility - Final Report

    Energy Technology Data Exchange (ETDEWEB)

    Chang H. Oh

    2006-06-01

    Generation IV reactors will need to be intrinsically safe, having a proliferation-resistant fuel cycle and several advantages relative to existing light water reactor (LWR). They, however, must still overcome certain technical issues and the cost barrier before it can be built in the U.S. The establishment of a nuclear power cost goal of 3.3 cents/kWh is desirable in order to compete with fossil combined-cycle, gas turbine power generation. This goal requires approximately a 30 percent reduction in power cost for stateof-the-art nuclear plants. It has been demonstrated that this large cost differential can be overcome only by technology improvements that lead to a combination of better efficiency and more compatible reactor materials. The objectives of this research are (1) to develop a supercritical carbon dioxide Brayton cycle in the secondary power conversion side that can be applied to the Very-High-Temperature Gas-Cooled Reactor (VHTR), (2) to improve the plant net efficiency by using the carbon dioxide Brayton cycle, and (3) to test material compatibility at high temperatures and pressures. The reduced volumetric flow rate of carbon dioxide due to higher density compared to helium will reduce compression work, which eventually increase plant net efficiency.

  5. Development of 0.5-5 W, 10K Reverse Brayton Cycle Cryocoolers - Phase II Final Report

    Energy Technology Data Exchange (ETDEWEB)

    Doty, F. D.; Boman, A.; Arnold, S.; Spitzmesser, J. B.; Jones, D.; McCree, D.; Hacker, L. J.

    2001-10-15

    Miniature cryocoolers for the 8-30 K range are needed to provide 0.5-5 w of cooling to high sensitivity detectors (for long-wave-length IR, magnetism, mm-wave, X-ray, dark matter, and possibly y-ray detection) while maintaining low mass, ultra-low vibration, and good efficiency. This project presents a new approach to eliminating the problems normally encountered in efforts to build low-vibration, fieldable, miniature cryocoolers. Using the reverse Brayton Cycle (RBC), the approach applies and expands on existing spinner technology previously used only in Nuclear Magnetic Resonance (NMR) probes.

  6. The efficiency of an open-cavity tubular solar receiver for a small-scale solar thermal Brayton cycle

    International Nuclear Information System (INIS)

    Highlights: • Results show efficiencies of a low-cost stainless steel tubular cavity receiver. • Optimum ratio of 0.0035 is found for receiver aperture area to concentrator area. • Smaller receiver tube and higher mass flow rate increase receiver efficiency. • Larger tube and smaller mass flow rate increase second law efficiency. • Large-tube receiver performs better in the small-scale solar thermal Brayton cycle. - Abstract: The first law and second law efficiencies are determined for a stainless steel closed-tube open rectangular cavity solar receiver. It is to be used in a small-scale solar thermal Brayton cycle using a micro-turbine with low compressor pressure ratios. There are many different variables at play to model the air temperature increase of the air running through such a receiver. These variables include concentrator shape, concentrator diameter, concentrator rim angle, concentrator reflectivity, concentrator optical error, solar tracking error, receiver aperture area, receiver material, effect of wind, receiver tube diameter, inlet temperature and mass flow rate through the receiver. All these variables are considered in this paper. The Brayton cycle requires very high receiver surface temperatures in order to be successful. These high temperatures, however, have many disadvantages in terms of heat loss from the receiver, especially radiation heat loss. With the help of ray-tracing software, SolTrace, and receiver modelling techniques, an optimum receiver-to-concentrator-area ratio of A′ ≈ 0.0035 was found for a concentrator with 45° rim angle, 10 mrad optical error and 1° tracking error. A method to determine the temperature profile and net heat transfer rate along the length of the receiver tube is presented. Receiver efficiencies are shown in terms of mass flow rate, receiver tube diameter, pressure drop, maximum receiver surface temperature and inlet temperature of the working fluid. For a 4.8 m diameter parabolic dish, the

  7. Ecological Optimization and Parametric Study of an Irreversible Regenerative Modified Brayton Cycle with Isothermal Heat Addition

    OpenAIRE

    Vivek Tiwari; Subhash Chandra Kaushik; Sudhir Kumar Tyagi

    2003-01-01

    Abstract: An ecological optimization along with a detailed parametric study of an irreversible regenerative Brayton heat engine with isothermal heat addition have been carried out with external as well as internal irreversibilities. The ecological function is defined as the power output minus the power loss (irreversibility) which is ambient temperature times the entropy generation rate. The external irreversibility is due to finite temperature difference between the heat engine and the exter...

  8. Development and validation of models for simulation of supercritical carbon dioxide Brayton cycles and application to self-propelling heat removal systems in boiling water reactors

    OpenAIRE

    Venker, Jeanne

    2015-01-01

    The objective of the current work was to develop a model that is able to describe the transient behavior of supercritical carbon dioxide (sCO2) Brayton cycles, to be applied to self-propelling residual heat removal systems in boiling water reactors. The developed model has been implemented into the thermohydraulic system code ATHLET. By means of this improved ATHLET version, novel residual heat removal systems, which are based on closed sCO2 Brayton cycles, can be assessed as a retrofit measu...

  9. Conceptual Design of S-CO{sub 2} Brayton Cycle Radial Turbomachinery for KAIST Micro Modular Reactor

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Seongkuk; Kim, Seong Gu; Lee, Jekyoung; Lee, Jeong Ik [Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of)

    2014-05-15

    KAIST proposed a new SMR design, which utilizes S-CO{sub 2} as the working fluid. It was named as KAIST MMR. Compared with existing SMR concepts, KAIST MMR has advantages of achieving smaller volume of power conversion unit (PCU) and containing the core and PCU in one vessel for the complete modularization. Authors noticed that the compressor and turbine assumed performances of KAIST MMR were conservatively selected previously. Thus, this paper tries to address the best estimate values of each turbomachinery in 10MWe class KAIST MMR. The turbomachinery size of the S-CO{sub 2} cycle is smaller than helium Brayton cycle and steam Rankine cycle. The suggested SMR concept adopts passive cooling system by using air. This method can cool reactor without external electricity supply. Small size and more flexible installation in the inland area will be necessary characteristics for the future nuclear application in the water limited region. KAIST MMR meets all these requirements by utilizing S-CO{sub 2} as a working fluid. This paper presents the work for further increasing the system performance by estimating the component efficiency more realistically. The cycle layout adopted for the application is S-CO{sub 2} recuperated Brayton cycle. The best efficiency of compressor and turbine was evaluated to be 84.94% and 90.94%, respectively. By using KAIST in-house code, thermal efficiency and net output were increased to 35.81% and 12.45MWe, respectively, for the same core thermal power. More refined cycle layout and suitable turbomachinery design will be performed in the near future.

  10. Investigation on the performance of the supercritical Brayton cycle with CO2-based binary mixture as working fluid for an energy transportation system of a nuclear reactor

    International Nuclear Information System (INIS)

    In this study, the performance of a SBC (supercritical gas Brayton cycle) using CO2-based binary mixtures as the working fluids have been studied. Based on the thermodynamic analyses, an in-house code has been developed to determine the cycle efficiency and the amounts of heat transfer in the HTR (high temperature recuperator) and the LTR (low temperature recuperator) with different CO2/additive gas ratios. Several gases are selected as potential additives, including O2, He, Ar, Kr, butane and cyclohexane. Compared with the Brayton cycle with pure S–CO2 (supercritical carbon dioxide) as the working fluid, it is found that both CO2–He and CO2–Kr mixtures can improve the thermodynamic performances of the SBC by increasing the cycle efficiency and decreasing the amounts of heat transfer in the HTR and LTR. For the cycles with the pure S–CO2 mixture, CO2–butane mixture and CO2–cyclohexane mixture as the working fluids, the cycle efficiencies decrease with increasing main compressor inlet temperature. However, when the main compressor inlet temperature is above the critical temperature of pure CO2, the cycle efficiencies of the cycles with CO2–butane mixture and CO2–cyclohexane mixture are higher than that of the cycle with pure CO2 as the working fluid. For the cycles with CO2-based binary mixtures and pure S–CO2 as the working fluids, the higher reactor outlet temperature always results into higher cycle efficiencies and larger amount of heat transfer in the HTR and smaller amount of heat transfer in the LTR. - Highlights: • The Brayton cycle performance with different mixtures as working fluids is studied. • Thermodynamic analysis is carried out to evaluate cycle efficiency and heat transfer in HTR and LTR. • The optimum working parameters of the Brayton cycle is proposed to improve working performance

  11. Detailed analysis of the effect of the turbine and compressor isentropic efficiency on the thermal and exergy efficiency of a Brayton cycle

    Directory of Open Access Journals (Sweden)

    Živić Marija

    2014-01-01

    Full Text Available Energy and exergy analysis of a Brayton cycle with an ideal gas is given. The irreversibility of the adiabatic processes in turbine and compressor is taken into account through their isentropic efficiencies. The net work per cycle, the thermal efficiency and the two exergy efficiencies are expressed as functions of the four dimensionless variables: the isentropic efficiencies of turbine and compressor, the pressure ratio, and the temperature ratio. It is shown that the maximal values of the net work per cycle, the thermal and the exergy efficiency are achieved when the isentropic efficiencies and temperature ratio are as high as possible, while the different values of pressure ratio that maximize the net work per cycle, the thermal and the exergy efficiencies exist. These pressure ratios increase with the increase of the temperature ratio and the isentropic efficiency of compressor and turbine. The increase of the turbine isentropic efficiency has a greater impact on the increase of the net work per cycle and the thermal efficiency of a Brayton cycle than the same increase of compressor isentropic efficiency. Finally, two goal functions are proposed for thermodynamic optimization of a Brayton cycle for given values of the temperature ratio and the compressor and turbine isentropic efficiencies. The first maximizes the sum of the net work per cycle and thermal efficiency while the second the net work per cycle and exergy efficiency. In both cases the optimal pressure ratio is closer to the pressure ratio that maximizes the net work per cycle.

  12. Operating conditions of an open and direct solar thermal Brayton cycle with optimised cavity receiver and recuperator

    International Nuclear Information System (INIS)

    The small-scale open and direct solar thermal Brayton cycle with recuperator has several advantages, including low cost, low operation and maintenance costs and it is highly recommended. The main disadvantages of this cycle are the pressure losses in the recuperator and receiver, turbomachine efficiencies and recuperator effectiveness, which limit the net power output of such a system. The irreversibilities of the solar thermal Brayton cycle are mainly due to heat transfer across a finite temperature difference and fluid friction. In this paper, thermodynamic optimisation is applied to concentrate on these disadvantages in order to optimise the receiver and recuperator and to maximise the net power output of the system at various steady-state conditions, limited to various constraints. The effects of wind, receiver inclination, rim angle, atmospheric temperature and pressure, recuperator height, solar irradiance and concentration ratio on the optimum geometries and performance were investigated. The dynamic trajectory optimisation method was applied. Operating points of a standard micro-turbine operating at its highest compressor efficiency and a parabolic dish concentrator diameter of 16 m were considered. The optimum geometries, minimum irreversibility rates and maximum receiver surface temperatures of the optimised systems are shown. For an environment with specific conditions and constraints, there exists an optimum receiver and recuperator geometry so that the system produces maximum net power output. -- Highlights: → Optimum geometries exist such that the system produces maximum net power output. → Optimum operating conditions are shown. → Minimum irreversibility rates and minimum entropy generation rates are shown. → Net power output was described in terms of total entropy generation rate. → Effects such as wind, recuperator height and irradiance were investigated.

  13. The design and fabrication of a reverse Brayton cycle cryocooler system for the high temperature superconductivity cable cooling

    Science.gov (United States)

    Park, Jae Hong; Kwon, Yong Ha; Kim, Young Soo

    2005-01-01

    A high temperature superconductivity cable must be cooled below the nitrogen liquefaction temperature to apply the cable to power generation and transmission systems under superconducting state. To maintain the superconducting state, a reliable cryocooler system is also required. The design and fabrication of a cryocooler system have been performed with a reverse Brayton cycle using neon gas as a refrigerant. The system consists of a compressor, a recuperator, a cold-box, and control valves. The design of the system is made to have 1 kW cooling capacity. The heat loss through multilayer insulators is calculated. Conduction heat loss is about 7 W through valves and access ports and radiation heat loss is about 18 W on the surface of a cryocooler. The design factors are discussed in detail.

  14. An open reversed Brayton cycle with regeneration using moist air for deep freeze cooled by circulating water

    Energy Technology Data Exchange (ETDEWEB)

    Hou, Shaobo [Guangdong Ocean University, College of Engineering, East Jiefang Rd. No. 40, Xiashan, Zhanjiang, Guangdong 524006 (China); Northwestern Polytechnical University, School of Aeroengine and Thermal Power Engineering, Xi' an, Shaanxi 710072 (China); Zhang, Hefei [Northwestern Polytechnical University, School of Aeroengine and Thermal Power Engineering, Xi' an, Shaanxi 710072 (China)

    2009-01-15

    This paper presents an open reversed Brayton cycle with regeneration using moist air for deep freeze cooled by circulating water, and proves its feasibility through performance simulation. Pinch technology is used to analyze the cooling of the wet air after compressor and the water used for cooling wet air after compressor. Its refrigeration depends mainly on the sensible heat of air and the latent heat of water vapor, its performance is more efficient than a conventional air-cycle, and the utilization of turbo-machinery makes it possible. The adoption of this cycle will make deep freeze easily and reduce initial cost because very low temperature, about -55 C, air is obtained. The sensitivity analysis of coefficient of performance to the efficiency of compressor and the efficiency of compressor, and the results of the cycle are also given. The simulation results show that the COP of this system depends on the temperature before turbine, the efficiency of compressor and the efficiency of compressor, and varies with the wet bulb temperature of the outdoor air. Humid air is a perfect working fluid for deep freeze with no cost to the user. (author)

  15. Waste heat recovery from adiabatic diesel engines by exhaust-driven Brayton cycles

    Energy Technology Data Exchange (ETDEWEB)

    Khalifa, H.E.

    1983-12-01

    This report presents an evaluation of Brayton Bottoming Systems (BBS) as waste heat recovery devices for future adiabatic diesel engines in heavy duty trucks. Parametric studies were performed to evaluate the influence of external and internal design parameters on BBS performance. Conceptual design and trade-off studies were undertaken to estimate the optimum configuration, size, and cost of major hardware components. The potential annual fuel savings of long-haul trucks equipped with BBS were estimated. The addition of a BBS to a turbocharged, nonaftercooled adiabatic engine would improve fuel economy by as much as 12%. In comparison with an aftercooled, turbocompound engine, the BBS-equipped turbocharged engine would offer a 4.4% fuel economy advantage. It is also shown that, if installed in tandem with an aftercooled turbocompound engine, the BBS could effect a 7.2% fuel economy improvement. The cost of a mass-produced 38 Bhp BBS is estimated at about $6460 or $170/Bhp. Technical and economic barriers that would hinder the commercial introduction of bottoming systems were identified.

  16. Transient Accident Analysis of a Supercritical Carbon Dioxide Brayton Cycle Energy Converter Coupled to an Autonomous Lead-Cooled Fast Reactor

    International Nuclear Information System (INIS)

    The Supercritical Carbon Dioxide (S-CO2) Brayton Cycle is a promising advanced alternative to the Rankine saturated steam cycle and recuperated gas Brayton cycle for the energy converters of specific reactor concepts belonging to the U.S. Department of Energy Generation IV Nuclear Energy Systems Initiative. A new plant dynamics analysis computer code has been developed for simulation of the S-CO2 Brayton cycle coupled to an autonomous, natural circulation Lead-Cooled Fast Reactor (LFR). The plant dynamics code was used to simulate the whole-plant response to accident conditions. The specific design features of the reactor concept influencing passive safety are discussed and accident scenarios are identified for analysis. Results of calculations of the whole-plant response to loss-of-heat sink, loss-of-load, and pipe break accidents are demonstrated. The passive safety performance of the reactor concept is confirmed by the results of the plant dynamics code calculations for the selected accident scenarios. (authors)

  17. Integrated solar thermal Brayton cycles with either one or two regenerative heat exchangers for maximum power output

    International Nuclear Information System (INIS)

    The main objective of this paper is to optimise the open-air solar-thermal Brayton cycle by considering the implementation of the second law of thermodynamics and how it relates to the design of the heat exchanging components within it. These components included one or more regenerators (in the form of cross-flow heat exchangers) and the receiver of a parabolic dish concentrator where the system heat was absorbed. The generation of entropy was considered as it was associated with the destruction of exergy or available work. The dimensions of some components were used to optimise the cycles under investigation. EGM (Entropy Generation Minimisation) was employed to optimise the system parameters by considering their influence on the total generation of entropy (destruction of exergy). Various assumptions and constraints were considered and discussed. The total entropy generation rate and irreversibilities were determined by considering the individual components and ducts of the system, as well as their respective inlet and outlet conditions. The major system parameters were evaluated as functions of the mass flow rate to allow for a proper discussion of the system performance. The performances of both systems were investigated, and characteristics were listed for both. Finally, a comparison is made to shed light on the differences in performance. - Highlights: • Implementation of the second law of thermodynamics. • Design of heat exchanging and collecting equipment. • Utilisation of Entropy Generation Minimization. • Presentation of a multi-objective optimization. • Raise efficiency with more regeneration

  18. Development of the ANL plant dynamics code and control strategies for the supercritical carbon dioxide Brayton cycle and code validation with data from the Sandia small-scale supercritical carbon dioxide Brayton cycle test loop.

    Energy Technology Data Exchange (ETDEWEB)

    Moisseytsev, A.; Sienicki, J. J. (Nuclear Engineering Division)

    2011-11-07

    Significant progress has been made in the ongoing development of the Argonne National Laboratory (ANL) Plant Dynamics Code (PDC), the ongoing investigation and development of control strategies, and the analysis of system transient behavior for supercritical carbon dioxide (S-CO{sub 2}) Brayton cycles. Several code modifications have been introduced during FY2011 to extend the range of applicability of the PDC and to improve its calculational stability and speed. A new and innovative approach was developed to couple the Plant Dynamics Code for S-CO{sub 2} cycle calculations with SAS4A/SASSYS-1 Liquid Metal Reactor Code System calculations for the transient system level behavior on the reactor side of a Sodium-Cooled Fast Reactor (SFR) or Lead-Cooled Fast Reactor (LFR). The new code system allows use of the full capabilities of both codes such that whole-plant transients can now be simulated without additional user interaction. Several other code modifications, including the introduction of compressor surge control, a new approach for determining the solution time step for efficient computational speed, an updated treatment of S-CO{sub 2} cycle flow mergers and splits, a modified enthalpy equation to improve the treatment of negative flow, and a revised solution of the reactor heat exchanger (RHX) equations coupling the S-CO{sub 2} cycle to the reactor, were introduced to the PDC in FY2011. All of these modifications have improved the code computational stability and computational speed, while not significantly affecting the results of transient calculations. The improved PDC was used to continue the investigation of S-CO{sub 2} cycle control and transient behavior. The coupled PDC-SAS4A/SASSYS-1 code capability was used to study the dynamic characteristics of a S-CO{sub 2} cycle coupled to a SFR plant. Cycle control was investigated in terms of the ability of the cycle to respond to a linear reduction in the electrical grid demand from 100% to 0% at a rate of 5

  19. Reactor dynamics and stability analysis of a burst-mode gas core reactor, Brayton cycle space power system

    International Nuclear Information System (INIS)

    Reactor dynamics and system stability studies are performed on a conceptual burst-mode gaseous core reactor space nuclear power system. This concept operates on a closed Brayton cycle in the burst mode (on the order of 100-MW output for a few thousand seconds) using a disk magnetohydrodynamic generator for energy conversion. The fuel is a gaseous mixture of UF4 or UF6 and helium. Nonlinear dynamic analysis is performed using circulating-fuel, point-reactor-kinetics equations along with thermodynamic, lumped-parameter heat transfer and one-dimensional isentropic flow equations. The gaseous nature of the fuel plus the fact that the fuel is circulating lead to dynamic behavior that is quite different from that of conventional solid-core systems. For the transients examined, Doppler fuel temperature and moderator temperature feedbacks are insignificant when compared with reactivity feedback associated with fuel gas density variations. The gaseous fuel density power coefficient of reactivity is capable of rapidly stabilizing the system, within a few seconds, even when large positive reactivity insertions are imposed; however, because of the strength of this feedback, standard external reactivity insertions alone are inadequate to bring about significant power level changes during normal reactor operation. Additional methods of reactivity control, such as changes in the gaseous of fuel mass flow rate or core inlet pressure, are required to achieve desired power level control. Finally, linear stability analysis gives results that are qualitatively in agreement with the nonlinear analysis

  20. Simulation of operational an accidental behaviour of modular high temperature reactors with Brayton cycle Power Conversion Unit

    International Nuclear Information System (INIS)

    The present work analyses and investigates the behaviour of a High Temperature Reactor (HTR) with a Pebble Bed core connected to a Brayton cycle Power Conversion Unit (PCU) during operational and accident conditions. The modelling of a complete circuit including both the PCU and the Pebble Bed Reactor has been performed with the commercial thermal-fluid analysis simulation code Flownex. Flownex has been developed for High Temperature Pebble Bed Reactor applications, and has been exten-sively validated against other codes. As the reactor core model incorporated in Flownex is a simplified model based on 0D point kinetics, the extended 1D WKIND core model was implemented in the analysis calculations using a special coupling methodology. This study introduces a new sub-routine which enables the cou-pling of the WKIND reactor core model to the Flownex PCU model via an external interface. The interface facilitates the data exchange between the two codes, allowing for necessary manipulations and synchronisation of the coupled codes. By doing so, the 1D diffusion equation solution implemented in WKIND core model replaces the point kinetics model implemented in Flownex. This replacement allows for a detailed accurate solution even for very fast transients, through the treatment of the space-dependent heat conduction from the graphite matrix to helium. Flownex component models have been validated against the experimental results of the 50 MWel direct helium turbine facility Energieversorgung Oberhausen (EVO II). This provided the opportunity to validate Flownex calculations against experimental data derived from a large-scale helium Brayton cycle installation. Small differences observed in the results could be explained. Based upon steady state and transient analysis it is concluded that Flownex models simulate accurately the behaviour of the components integrated in the EVO II plant. Such models could be applied to analyse the transient behaviour of the total system of the

  1. Modeling and sizing of the heat exchangers of a new supercritical CO{sub 2} Brayton power cycle for energy conversion for fusion reactors

    Energy Technology Data Exchange (ETDEWEB)

    Serrano, I.P.; Cantizano, A.; Linares, J.I., E-mail: linares@upcomillas.es; Moratilla, B.Y.

    2014-10-15

    Highlights: •We propose a procedure to model the heat exchangers of a S-CO2 Brayton power cycle. •Discretization in sub-heat exchangers is performed due to complex behavior of CO{sub 2}. •Different correlations have been tested, verifying them with CFD when necessary. •Obtained sizes are agree with usual values of printed circuit heat exchangers. -- Abstract: TECNO{sub F}US is a research program financed by the Spanish Government to develop technologies related to a dual-coolant (He/Pb–Li) breeding blanket design concept including the auxiliary systems for a future power reactor (DEMO). One of the main issues of this program is the optimization of heat recovery from the reactor and its conversion into electrical power. This paper is focused on the methodology employed for the design and sizing of all the heat exchangers of the supercritical CO{sub 2} Brayton power cycle (S-CO2) proposed by the authors. Due to the large pressure difference between the fluids, and also to their compactness, Printed Circuit Heat Exchangers (PCHE) are suggested in literature for these type of cycles. Because of the complex behavior of CO{sub 2}, their design is performed by a numerical discretization into sub-heat exchangers, thus a higher precision is reached when the thermal properties of the fluids vary along the heat exchanger. Different empirical correlations for the pressure drop and the Nusselt number have been coupled and assessed. The design of the precooler (PC) and the low temperature recuperator (LTR) is also verified by simulations using CFD because of the near-critical behavior of CO{sub 2}. The size of all of the heat exchangers of the cycle have been assessed.

  2. Analysis of transient coolant void formation during a guillotine-type HX tube rupture event in the Star-LM system employing a supercritical CO2 Brayton cycle

    International Nuclear Information System (INIS)

    One proposed concept for the STAR-LM Lead Fast Reactor (LFR) incorporates a supercritical CO2 gas turbine Brayton cycle to achieve high cycle efficiency and reduced plant footprint. In this design, 100+% of core full power is transferred by natural circulation from the core, located at the bottom of the reactor vessel, to in-vessel heat exchangers (HXs) located at the top of the vessel in the annulus between the core shroud and vessel inner wall. Although this approach extremely simplifies the plant design, the presence of the HXs within the vessel raises concerns regarding the potential rupture of a HX tube that would initiate a high-pressure blowdown of CO2 into the lead coolant. The principal issue is to what extent, if any, is void entrained downwards with the coolant and then upwards through the core where adverse reactivity effects or degraded heat removal could result. To address this question, a scoping analysis of transient void formation during a guillotine-type HX tube rupture event in the STAR-LM employing a supercritical CO2 Brayton cycle has been performed. The void formation process is evaluated by solving a coupled set of ordinary differential equations describing: i) the supercritical CO2 blowdown, ii) bubble center-of-mass trajectory, iii) bubble growth rate, iv) bubble gas internal energy, and v) discrete bubble formation rate due to Taylor instability at the bubble/coolant interface. The results indicate that for thermal hydraulic conditions consistent with the current STAR-LM design, the peak blowdown rate from a single tube rupture is ∼ 2.5 kg/sec. The void formation process is dominated by large coherent gas bubbles that penetrate minimally downwards into the coolant due to the large coolant density. Rather, the gas pockets are predicted to periodically rise due to buoyancy and vent to the core cover gas region, as opposed to being swept downwards with the coolant. Moreover, the total CO2 fraction that is rendered in the form of discrete

  3. Off-design performance prediction of Radial Compressor of Supercritical CO{sub 2} Brayton Cycle for KAIST Micro Modular Reactor

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Seongkuk; Lee, Jekyoung; Kim, Seong Gu; Lee, Jeong Ik [Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of)

    2014-10-15

    KAIST research team suggested a new concept of SMR, which utilizes S-CO{sub 2} as the operating fluid and coolant. It was named as KAIST MMR(Micro Modular Reactor). Compared with existing SMR concepts, this reactor has advantages of achieving smaller volume of power conversion unit (PCU) containing the core and PCU in one vessel for the complete modularization passive air-cooling system more flexible installation in the inland area. In previous study, performance of turbomachinery in PCU was considered only on-design. But, off-design performances of each component can affect not only PCU but also the core because this reactor adopts the direct S-CO{sub 2} loop in GFR. Nuclear system is applied by relatively conservative criteria of safety. Thus, off-design performances of each component should be considered in order to be more realistic reactor. The suggested turbomachinery size of the S-CO{sub 2} cycle is relatively smaller than those of helium Brayton cycle and steam Rankine cycle. Performance analysis of compressor is conducted by KAIST-TMD in case of on-design and off-design. Compressor efficiency in on-design conditions is obtained 84.51 %. But compressor performance in off-design conditions decreases certainly. This means that more heat than existing prediction is rejected by air-cooling system. KAIST-TMD will be verified with more experiment data for providing the results of more accurate analysis. Also, this code will be modified to couple with safety analysis codes and S-CO{sub 2} cycle analysis codes in the future. Furthermore, authors will consider aerodynamic performance analysis and various losses for more realization.

  4. Selection of a closed Brayton cycle gas turbine for an intermediate-duty solar-electric power plant

    Science.gov (United States)

    Vieth, G. L.; Plummer, D. F.

    1980-03-01

    Subsystem and system analyses were performed to select the preferred working gas, performance characteristics and size of a closed cycle gas turbine for an intermediate-duty solar-electric power plant. Capital costs for all major subsystems were evaluated, but the principal selection criterion was the projected cost of electricity produced by the plant. Detailed analyses of the power conversion loop were conducted for both air and helium systems. Since the plant was intended for use on an intermediate-duty cycle, thermal storage was required. The coupling of the storage and power conversion loops in combination with the daily operating cycle influenced plant performance and energy costs in addition to the selection of the power conversion cycle.

  5. Closed Brayton Cycle power system with a high temperature pellet bed reactor heat source for NEP applications

    Science.gov (United States)

    Juhasz, Albert J.; El-Genk, Mohamed S.; Harper, William B., Jr.

    1992-01-01

    Capitalizing on past and future development of high temperature gas reactor (HTGR) technology, a low mass 15 MWe closed gas turbine cycle power system using a pellet bed reactor heating helium working fluid is proposed for Nuclear Electric Propulsion (NEP) applications. Although the design of this directly coupled system architecture, comprising the reactor/power system/space radiator subsystems, is presented in conceptual form, sufficient detail is included to permit an assessment of overall system performance and mass. Furthermore, an attempt is made to show how tailoring of the main subsystem design characteristics can be utilized to achieve synergistic system level advantages that can lead to improved reliability and enhanced system life while reducing the number of parasitic load driven peripheral subsystems.

  6. Development of a plant dynamics computer code for analysis of a supercritical carbon dioxide Brayton cycle energy converter coupled to a natural circulation lead-cooled fast reactor.

    Energy Technology Data Exchange (ETDEWEB)

    Moisseytsev, A.; Sienicki, J. J.

    2007-03-08

    STAR-LM is a lead-cooled pool-type fast reactor concept operating under natural circulation of the coolant. The reactor core power is 400 MWt. The open-lattice core consists of fuel pins attached to the core support plate, (the does not consist of removable fuel assemblies). The coolant flows outside of the fuel pins. The fuel is transuranic nitride, fabricated from reprocessed LWR spent fuel. The cladding material is HT-9 stainless steel; the steady-state peak cladding temperature is 650 C. The coolant is single-phase liquid lead under atmospheric pressure; the core inlet and outlet temperatures are 438 C and 578 C, respectively. (The Pb coolant freezing and boiling temperatures are 327 C and 1749 C, respectively). The coolant is contained inside of a reactor vessel. The vessel material is Type 316 stainless steel. The reactor is autonomous meaning that the reactor power is self-regulated based on inherent reactivity feedbacks and no external power control (through control rods) is utilized. The shutdown (scram) control rods are used for startup and shutdown and to stop the fission reaction in case of an emergency. The heat from the reactor is transferred to the S-CO{sub 2} Brayton cycle in in-reactor heat exchangers (IRHX) located inside the reactor vessel. The IRHXs are shell-and-tube type heat exchangers with lead flowing downwards on the shell side and CO{sub 2} flowing upwards on the tube side. No intermediate circuit is utilized. The guard vessel surrounds the reactor vessel to contain the coolant, in the very unlikely event of reactor vessel failure. The Reactor Vessel Auxiliary Cooling System (RVACS) implementing the natural circulation of air flowing upwards over the guard vessel is used to cool the reactor, in the case of loss of normal heat removal through the IRHXs. The RVACS is always in operation. The gap between the vessels is filled with liquid lead-bismuth eutectic (LBE) to enhance the heat removal by air by significantly reducing the thermal

  7. A hybrid Brayton engine concept

    Science.gov (United States)

    Six, L. D.; Elkins, R.

    1980-01-01

    A first generation open cycle Brayton engine concept for use in full scale solar module testing was defined. The concept extended to include solar/fossil hybrid capability. The combustion system defined for hybrid operation consists of a wide range combustor liner, a single airblast atomizer, an ignitor and a high-voltage ignition unit. Wide range combustor operation would be achieved through combining pilot and primary zones. The hybrid control mode and the solar only control mode are both based on the concept of maintaining constant turbine inlet temperature and varying the engine speed for part-power operation. In addition, the hybrid control concept will allow the operator to set a minimum thermal power input to the engine by setting a corresponding minimum engine speed. When the solar thermal power input falls below this minimum, fossil fuel would be utilized to augment the solar thermal power input.

  8. Development of a 77K Reverse-Brayton Cryocooler with Multiple Coldheads Project

    Data.gov (United States)

    National Aeronautics and Space Administration — RTI will design and optimize an 80 W, 77K cryocooler based on the reverse turbo Brayton cycle (RTBC) with four identical coldheads for distributed cooling. Based on...

  9. Performance Optimization of a Solar-driven Irreversible Intercooled Regenerated Brayton Cycle%不可逆中冷回热太阳能布雷顿循环系统的优化分析

    Institute of Scientific and Technical Information of China (English)

    许益霖; 黄跃武

    2011-01-01

    建立了由太阳能集热器模型和不可逆中冷回热布雷顿循环模型组成的恒温热源条件下太阳能布雷顿循环系统,以系统总效率为目标函数,考虑了高低温侧换热器、回热器和中冷器的热阻损失以及压缩机和涡轮机的不可逆损失,借助数值计算对太阳能集热器的工作温度进行了优化,并分析了主要特征参数对总效率的影响.结果表明:太阳能布雷顿循环系统中存在一个最佳的太阳能集热器工作温度和相应的最大总效率及最大总输出功率;在此基础上,通过优化中间压比可使循环系统的总效率和相应的总输出功率达到双重最大值;系统总效率随着回热器传热有效度和光学效率的增加而提高;系统运行时存在一个最佳的总压比.%An irreversible solar-driven heat engine system with constant-temperature heat-reservoirs has been built up, which consists of the model of a solar collector and an intercooled regenerated Brayton cycle. Taking the overall efficiency as the objective function, and considering both the heat resistance in high/low temperature-side heat exchanger, regenerative heater and intercooler, and the irreversible loss in compressor and turbine, the operating temperature of solar collector has been optimized with the help of numerical simulation, while influence of the main parameters on its overall efficiency analyzed. Results show that for the solar-driven Brayton cycle, there exists an optimum collector operating temperature, a corresponding maximum overall efficiency and a maximum total output power; on this basis, both the overall efficiency and the total output power may reach their maximum value by optimizing the intermediate pressure ratio; the overall efficiency increases with the rise of thermal and optical efficiency of regenerative heater; there exists an optimum total pressure ratio for the system.

  10. A comparison between molten carbonate fuel cells based hybrid systems using air and supercritical carbon dioxide Brayton cycles with state of the art technology

    Science.gov (United States)

    Sánchez, D.; Muñoz de Escalona, J. M.; Chacartegui, R.; Muñoz, A.; Sánchez, T.

    A proposal for high efficiency hybrid systems based on molten carbonate fuel cells is presented in this paper. This proposal is based on adopting a closed cycle bottoming gas turbine using supercritical carbon dioxide as working fluid as opposed to open cycle hot air turbines typically used in this type of power generators. First, both bottoming cycles are compared for the same operating conditions, showing that their performances do not differ as much as initially expected, even if the initial objective of reducing compression work is accomplished satisfactorily. In view of these results, a profound review of research and industrial literature is carried out in order to determine realistic specifications for the principal components of the bottoming systems. From this analysis, it is concluded that an appropriate set of specifications must be developed for each bottoming cycle as the performances of compressor, turbine and recuperator differ significantly from one working fluid to another. Thus, when the operating conditions are updated, the performances of the resulting systems show a remarkable advantage of carbon dioxide based systems over conventional air units. Actually, the proposed hybrid system shows its capability to achieve 60% net efficiency, what represents a 10% increase with respect to the reference system.

  11. Dynamic simulation of a reverse Brayton refrigerator

    International Nuclear Information System (INIS)

    A test refrigerator based on the modified Reverse Brayton cycle has been developed in the Chinese Academy of Sciences recently. To study the behaviors of this test refrigerator, a dynamic simulation has been carried out. The numerical model comprises the typical components of the test refrigerator: compressor, valves, heat exchangers, expander and heater. This simulator is based on the oriented-object approach and each component is represented by a set of differential and algebraic equations. The control system of the test refrigerator is also simulated, which can be used to optimize the control strategies. This paper describes all the models and shows the simulation results. Comparisons between simulation results and experimental data are also presented. Experimental validation on the test refrigerator gives satisfactory results

  12. Rankine-Brayton engine powered solar thermal aircraft

    Science.gov (United States)

    Bennett, Charles L.

    2009-12-29

    A solar thermal powered aircraft powered by heat energy from the sun. A Rankine-Brayton hybrid cycle heat engine is carried by the aircraft body for producing power for a propulsion mechanism, such as a propeller or other mechanism for enabling sustained free flight. The Rankine-Brayton engine has a thermal battery, preferably containing a lithium-hydride and lithium mixture, operably connected to it so that heat is supplied from the thermal battery to a working fluid. A solar concentrator, such as reflective parabolic trough, is movably connected to an optically transparent section of the aircraft body for receiving and concentrating solar energy from within the aircraft. Concentrated solar energy is collected by a heat collection and transport conduit, and heat transported to the thermal battery. A solar tracker includes a heliostat for determining optimal alignment with the sun, and a drive motor actuating the solar concentrator into optimal alignment with the sun based on a determination by the heliostat.

  13. Rankline-Brayton engine powered solar thermal aircraft

    Science.gov (United States)

    Bennett, Charles L.

    2012-03-13

    A solar thermal powered aircraft powered by heat energy from the sun. A Rankine-Brayton hybrid cycle heat engine is carried by the aircraft body for producing power for a propulsion mechanism, such as a propeller or other mechanism for enabling sustained free flight. The Rankine-Brayton engine has a thermal battery, preferably containing a lithium-hydride and lithium mixture, operably connected to it so that heat is supplied from the thermal battery to a working fluid. A solar concentrator, such as reflective parabolic trough, is movably connected to an optically transparent section of the aircraft body for receiving and concentrating solar energy from within the aircraft. Concentrated solar energy is collected by a heat collection and transport conduit, and heat transported to the thermal battery. A solar tracker includes a heliostat for determining optimal alignment with the sun, and a drive motor actuating the solar concentrator into optimal alignment with the sun based on a determination by the heliostat.

  14. 逆布雷顿空气制冷机动态降温特性数值研究%Numerical study on dynamic cooling performance of reverse Brayton cycle air cryocooler

    Institute of Scientific and Technical Information of China (English)

    赵祥雄; 孙皖; 刘炅辉; 侯予

    2013-01-01

    建立了逆布雷顿空气制冷机系统时间相关数学模型,对系统动态降温过程进行了数值分析.详细阐述了系统主要部件板翅式换热器及透平膨胀机动态回热及降温数学模型.以该模型为基础,分析了逆布雷顿空气制冷系统不同入口压力、温度、流量及不同换热面积和膨胀机效率下的动态温降特性曲线,讨论了部分参数对系统动态降温性能的影响.结果表明:对于确定的入口流量,提高系统入口压力可以加快系统降温速度和最大温降;此外,系统设计时采用较大的回热换热器面积和提高膨胀机效率也是实现更大温降的有效手段.%In order to study the dynamic cooling process performance of a reverse Brayton cycle air cryocooler, a system time-dependent numerical model was set up and described, including the dynamic thermal performance model of a plate-fin heat exchanger and a turbo expander. The dynamic cooling process of the air cryocooler was discussed under different system inlet parameters, including pressure, temperature, volume flowrate, different heat exchange area and different turbo expander efficiency. The theoretical results shown that the higher the system inlet pressure the faster the system temperature decreases in case of low system inlet temperature and small system inlet flowrate, the increase of heat exchange area and turbo expander thermal efficiency can promote the system cooling performance.

  15. Thermodynamic design of 10 kW Brayton cryocooler for HTS cable

    Science.gov (United States)

    Chang, Ho-Myung; Park, C. W.; Yang, H. S.; Sohn, Song Ho; Lim, Ji Hyun; Oh, S. R.; Hwang, Si Dole

    2012-06-01

    Thermodynamic design of Brayton cryocooler is presented as part of an ongoing governmental project in Korea, aiming at 1 km HTS power cable in the transmission grid. The refrigeration requirement is 10 kW for continuously sub-cooling liquid nitrogen from 72 K to 65 K. An ideal Brayton cycle for this application is first investigated to examine the fundamental features. Then a practical cycle for a Brayton cryocooler is designed, taking into account the performance of compressor, expander, and heat exchangers. Commercial software (Aspen HYSYS) is used for simulating the refrigeration cycle with real fluid properties of refrigerant. Helium is selected as a refrigerant, as it is superior to neon in thermodynamic efficiency. The operating pressure and flow rate of refrigerant are decided with a constraint to avoid the freezing of liquid nitrogen

  16. Experimental and Analytical Performance of a Dual Brayton Power Conversion System

    Science.gov (United States)

    Lavelle, Thomas A.; Hervol, David S.; Briggs, Maxwell; Owen, A. Karl

    2009-01-01

    The interactions between two closed Brayton cycle (CBC) power conversion units (PCU) which share a common gas inventory and heat source have been studied experimentally using the Dual Brayton Power Conversion System (DBPCS) and analytically using the Closed- Cycle System Simulation (CCSS) computer code. Selected operating modes include steady-state operation at equal and unequal shaft speeds and various start-up scenarios. Equal shaft speed steady-state tests were conducted for heater exit temperatures of 840 to 950 K and speeds of 50 to 90 krpm, providing a system performance map. Unequal shaft speed steady-state testing over the same operating conditions shows that the power produced by each Brayton is sensitive to the operating conditions of the other due to redistribution of gas inventory. Startup scenarios show that starting the engines one at a time can dramatically reduce the required motoring energy. Although the DBPCS is not considered a flight-like system, these insights, as well as the operational experience gained from operating and modeling this system provide valuable information for the future development of Brayton systems.

  17. On Brayton and Moser's missing stability theorem

    NARCIS (Netherlands)

    Jeltsema, D.; Scherpen, J. M. A.

    2005-01-01

    In the early 1960s, Brayton and Moser proved three theorems concerning the stability of nonlinear electrical circuits. The applicability of each theorem depends on three different conditions on the type of admissible nonlinearities in circuit. Roughly speaking, this means that the theorems apply to

  18. Phase 2 Brayton/Rankine 10-ton gas-fired space-conditioning system

    Science.gov (United States)

    1982-07-01

    The technical accomplishments to date in the design, development, and demonstration program leading to commercialization of a 10 ton heat actuated space conditioning system for light commercialization of a 10 ton heat actuated space conditioning system for light commercial building applications are summarized. The system consists of a natural gas powered Brayton cycle engine and a Rankine cycle heat pump, combined in a single roof top package. The heat actuated space conditioning system provides more efficient use of natural gas and is intended as an all gas alternative to the electric heat pump. The system employs a subatmospheric natural gas fired heat pump. A centrifugal R-12 refrigerant compressor is driven directly from the Brayton engine rotating group through a hermetically sealed coupling. Unique features that offer high life cycle performance include a permanent magnet coupling, foil bearings, an atmospheric in-line combustor, and a high temperature recuperator.

  19. Performance and Operational Characteristics for a Dual Brayton Space Power System With Common Gas Inventory

    Science.gov (United States)

    Johnson, Paul K.; Mason, Lee S.

    2006-01-01

    This paper provides an analytical evaluation on the operation and performance of a dual Brayton common gas system. The NASA Glenn Research Center in-house computer program Closed Cycle System Simulation (CCSS) was used to construct a model of two identical 50 kWe-class recuperated closed-Brayton-cycle (CBC) power conversion units that share a common gas inventory and single heat source. As operating conditions for each CBC change, the total gas inventory is redistributed between the two units and overall system performance is affected. Several steady-state off-design operating points were analyzed by varying turbine inlet temperature and turbo-alternator shaft rotational speed to investigate the interaction of the two units.

  20. Numerical Comparison of NASA's Dual Brayton Power Generation System Performance Using CO2 or N2 as the Working Fluid

    Science.gov (United States)

    Ownens, Albert K.; Lavelle, Thomas M.; Hervol, David S.

    2010-01-01

    A Dual Brayton Power Conversion System (DBPCS) has been tested at the NASA Glenn Research Center using Nitrogen (N2) as the working fluid. This system uses two closed Brayton cycle systems that share a common heat source and working fluid but are otherwise independent. This system has been modeled using the Numerical Propulsion System Simulation (NPSS) environment. This paper presents the results of a numerical study that investigated system performance changes resulting when the working fluid is changed from gaseous (N2) to gaseous carbon dioxide (CO2).

  1. Exergy performance analysis for irreversible closed Brayton cycle combined cooling, heating and power generation plant driven by residual energy and heat of blast furnace%高炉余能余热驱动的不可逆闭式布雷顿热电冷联产装置(炯)性能分析

    Institute of Scientific and Technical Information of China (English)

    冯辉君; 陈林根; 孙丰瑞

    2013-01-01

    A combined cooling,heating and power (CCHP) generation plant model composing by one irreversible closed Brayton cycle driven by residual energy and heat of blast furnace and one endoreversible four-heat-reservoir absorption refrigeration cycle was established by using finite time thermodynamics.The expressions of the exergy output rate and exergy efficiency were derived.The effects of the cycle parameters on the characteristics of exergy output rate and exergy efficiency versus pressure ratio were analyzed by using numerical calculations.The performances of the maximum exergy output rate was compared with that of the maximum exergy efficiency and some suggestions on the designs and operations of actual CCHP plants were proposed.%用有限时间热力学理论建立了由一个高炉余能余热驱动的不可逆闭式布雷顿循环和一个内可逆四热源吸收式制冷循环组成的热电冷联产循环模型,导出了其(娴)输出率和(炯)效率的表达式.利用数值计算方法,分析了循环各参数对(炯)输出率和(炯)效率与压比关系的影响,比较了最大(炯)输出率和最大(炯)效率性能,给出了实际热电冷联产装置设计和运行的建议.

  2. Compressor and Turbine Models of Brayton Units for Space Nuclear Power Systems

    Science.gov (United States)

    Gallo, Bruno M.; El-Genk, Mohamed S.; Tournier, Jean-Michel

    2007-01-01

    Closed Brayton Cycles with centrifugal flow, single-shaft turbo-machines are being considered, with gas cooled nuclear reactors, to provide 10's to 100's of electrical power to support future space exploration missions and Lunar and Mars outposts. Such power system analysis is typically based on the cycle thermodynamics, for given operating pressures and temperatures and assumed polytropic efficiencies of the compressor and turbine of the Brayton energy conversion units. Thus the analysis results not suitable for modeling operation transients such as startup and changes in the electric load. To simulate these transients, accurate models of the turbine and compressor in the Brayton rotating unit, which calculate the changes in the compressor and turbine efficiencies with system operation are needed. This paper presents flow models that account for the design and dimensions of the compressor impeller and diffuser, and the turbine stator and rotor blades. These models calculate the various enthalpy losses and the polytropic efficiencies along with the pressure ratios of the turbine and compressor. The predictions of these models compare well with reported performance data of actual hardware. In addition, the results of a parametric analysis to map the operations of the compressor and turbine, as functions of the rotating shaft speed and inlet Mach number of the gas working fluid, are presented and discussed. The analysis used a binary mixture of He-Xe with a molecular weight of 40 g/mole as the working fluid.

  3. Comparison of Analytical Predictions and Experimental Results for a Dual Brayton Power System (Discussion on Test Hardware and Computer Model for a Dual Brayton System)

    Science.gov (United States)

    Johnson, Paul K.

    2007-01-01

    NASA Glenn Research Center (GRC) contracted Barber-Nichols, Arvada, CO to construct a dual Brayton power conversion system for use as a hardware proof of concept and to validate results from a computational code known as the Closed Cycle System Simulation (CCSS). Initial checkout tests were performed at Barber- Nichols to ready the system for delivery to GRC. This presentation describes the system hardware components and lists the types of checkout tests performed along with a couple issues encountered while conducting the tests. A description of the CCSS model is also presented. The checkout tests did not focus on generating data, therefore, no test data or model analyses are presented.

  4. Performance analysis of a large-scale helium Brayton cryo-refrigerator with static gas bearing turboexpander

    International Nuclear Information System (INIS)

    Highlights: • A 2 kW at 20.0 K helium Brayton cryo-refrigerator is built in China. • A series of tests have been systematically conducted to investigate the performance of the cryo-refrigerator. • Maximum heat conductance proportion (90.7%) appears in the heat exchangers of cold box rather than those of heat reservoirs. • A model of helium Brayton cryo-refrigerator/cycle is presented according to finite-time thermodynamics. - Abstract: Large-scale helium cryo-refrigerator is widely used in superconducting systems, nuclear fusion engineering, and scientific researches, etc., however, its energy efficiency is quite low. First, a 2 kW at 20.0 K helium Brayton cryo-refrigerator is built, and a series of tests have been systematically conducted to investigate the performance of the cryo-refrigerator. It is found that maximum heat conductance proportion (90.7%) appears in the heat exchangers of cold box rather than those of heat reservoirs, which is the main characteristic of the helium Brayton cryo-refrigerator/cycle different from the air Brayton refrigerator/cycle. Other three characteristics also lie in the configuration of refrigerant helium bypass, internal purifier and non-linearity of specific heat of helium. Second, a model of helium Brayton cryo-refrigerator/cycle is presented according to finite-time thermodynamics. The assumption named internal purification temperature depth (PTD) is introduced, and the heat capacity rate of whole cycle is divided into three different regions in accordance with the PTD: room temperature region, upper internal purification temperature region and lower one. Analytical expressions of cooling capacity and COP are obtained, and we found that the expressions are piecewise functions. Further, comparison between the model and the experimental results for cooling capacity of the helium cryo-refrigerator shows that error is less than 7.6%. The PTD not only helps to achieve the analytical formulae and indicates the working

  5. Comparison of Analytical Predictions and Experimental Results for a Dual Brayton Power System

    Science.gov (United States)

    Johnson, Paul

    2007-01-01

    NASA Glenn Research Center (GRC) contracted Barber- Nichols, Arvada, CO to construct a dual Brayton power conversion system for use as a hardware proof of concept and to validate results from a computational code known as the Closed Cycle System Simulation (CCSS). Initial checkout tests were performed at Barber- Nichols to ready the system for delivery to GRC. This presentation describes the system hardware components and lists the types of checkout tests performed along with a couple issues encountered while conducting the tests. A description of the CCSS model is also presented. The checkout tests did not focus on generating data, therefore, no test data or model analyses are presented.

  6. Design and Off-Design Performance of 100 kWe-Class Brayton Power Conversion Systems

    Science.gov (United States)

    Johnson, Paul K.; Mason, Lee S.

    2005-02-01

    The NASA Glenn Research Center in-house computer model Closed Cycle Engine Program (CCEP) was used to explore the design trade space and off-design performance characteristics of 100 kWe-class recuperated Closed Brayton Cycle (CBC) power conversion systems. Input variables for a potential design point included the number of operating units (1, 2, 4), cycle peak pressure (0.5, 1, 2 MPa), and turbo-alternator shaft speed (30,45, 60 kRPM). The design point analysis assumed a fixed turbine inlet temperature (1150 K), compressor inlet temperature (400 K), helium-xenon working-fluid molecular weight (40 g/mol), compressor pressure ratio (2.0), recuperator effectiveness (0.95), and a Sodium-Potassium (NaK) pumped-loop radiator. The design point options were compared on the basis of thermal input power, radiator area, and mass. For a nominal design point with defined Brayton components and radiator area, off-design cases were examined by reducing turbine inlet temperature (as low as 900 K), reducing shaft speed (as low as 50% of nominal), and circulating a percentage (up to 20%) of the compressor exit flow back to the gas cooler. The off-design examination sought approaches to reduce thermal input power without freezing the radiator.

  7. Detonation Jet Engine. Part 1--Thermodynamic Cycle

    Science.gov (United States)

    Bulat, Pavel V.; Volkov, Konstantin N.

    2016-01-01

    We present the most relevant works on jet engine design that utilize thermodynamic cycle of detonative combustion. The efficiency advantages of thermodynamic detonative combustion cycle over Humphrey combustion cycle at constant volume and Brayton combustion cycle at constant pressure were demonstrated. An ideal Ficket-Jacobs detonation cycle, and…

  8. Heat exchanger design for hot air ericsson-brayton piston engine

    Directory of Open Access Journals (Sweden)

    Ďurčanský P.

    2014-03-01

    Full Text Available One of the solutions without negative consequences for the increasing energy consumption in the world may be use of alternative energy sources in micro-cogeneration. Currently it is looking for different solutions and there are many possible ways. Cogeneration is known for long time and is widely used. But the installations are often large and the installed output is more suitable for cities or industry companies. When we will speak about decentralization, the small machines have to be used. The article deals with the principle of hot-air engines, their use in combined heat and electricity production from biomass and with heat exchangers as primary energy transforming element. In the article is hot air engine presented as a heat engine that allows the conversion of heat into mechanical energy while heat supply can be external. In the contribution are compared cycles of hot-air engine. Then are compared suitable heat exchangers for use with hot air Ericsson-Brayton engine. In the final part is proposal of heat exchanger for use in closed Ericsson-Brayton cycle.

  9. Plate-fin Heat-exchangers for a 10 kW Brayton Cryocooler and a 1 km HTS Cable

    Science.gov (United States)

    Chang, Ho-Myung; Gwak, Kyung Hyun; Jung, Seyong; Yang, Hyung Suk; Hwang, Si-Dole

    Plate-fin heat exchangers (PFHX) are designed and fabricated for a cryogenic cooling system, serving for a 10 kW Brayton cryocooler and a 1 km HTS transmission cable under development in Korea. To achieve compactness and thermal efficiency at the same time, a recuperative HX for Brayton cycle and a sub-cooling HX of liquid nitrogen for HTS cable are designed as integrated parts. A key design feature is focused on the coldest part of sub-cooling HX, where the streams of liquid nitrogen and refrigerant (helium gas) are arranged as two-pass cross-flow so that the risk of freeze-out of liquid nitrogen can be reduced. Details of hardware PFHX design are presented and discussed towards its immediate application to the HTS cable system.

  10. Effects of backlash and dead band on temperature control of the primary loop of a conceptual nuclear Brayton space powerplant

    Science.gov (United States)

    Petrick, E. J.

    1973-01-01

    An analytical study was made of the stability of a closed-loop liquid-lithium temperature control of the primary loop of a conceptual nuclear Brayton space powerplant. The operating point was varied from 20 to 120 percent of design. A describing-function technique was used to evaluate the effects of temperature dead band and control coupling backlash. From the system investigation, it was predicted that a limit cycle will not exist with a temperature dead band, but a limit cycle will not exist when backlash is present. The results compare favorably with a digital computer simulation.

  11. An isothermal model of a hybrid Stirling/reverse-Brayton cryocooler

    Science.gov (United States)

    Nellis, G. F.; Maddocks, J. R.

    2003-01-01

    This paper presents a model of a cryogenic refrigerator that integrates a reverse-Brayton lower temperature stage with a 2-piston Stirling upper temperature stage using a rectification system of check valves and buffer volumes. The numerical model extends the isothermal Schmidt analysis of the Stirling cycle by deriving the additional dimensionless governing equations that characterize the recuperative system. Numerical errors are quantified and the results are verified against analytical solutions in the appropriate limits. The model is used to explore the effect of the rectification system's characteristics on the overall cycle's behavior. Finally, the model is used to optimize the hybrid system's design by varying the swept volume ratio and phase angle in order to maximize the refrigeration per unit of heat transfer in the recuperator and regenerator.

  12. Variations on the Zilch Cycle

    Science.gov (United States)

    Binder, P.-M.; Tanoue, C. K. S.

    2013-01-01

    Thermo dynamic cycles in introductory physics courses are usually made up from a small number of permutations of isothermal, adiabatic, and constant-pressure and volume quasistatic strokes, with the working fluid usually being an ideal gas. Among them we find the Carnot, Stirling, Otto, Diesel, and Joule-Brayton cycles; in more advanced courses,…

  13. Brayton Power Conversion System Study to Advance Technology Readiness for Nuclear Electric Propulsion — Phase I

    Science.gov (United States)

    Frye, Patrick E.; Allen, Robert; Delventhal, Rex

    2005-02-01

    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 potential missions with a sound technology plan for TRL (Technical Readiness Level) advancement identified. The studies assumed a turbine inlet temperature ˜ 100C above the current the state of the art capabilities with materials issues identified and an approach for resolution developed. Analyses and evaluations of six HRS (heat rejection subsystem) concepts and PMAD (Power Management and Distribution) architecture trades will be discussed in the paper.

  14. Brayton Power Conversion System Study to Advance Technology Readiness for Nuclear Electric Propulsion

    Science.gov (United States)

    Allen, Bog; Delventhal, Rex; Frye, Patrick

    2004-01-01

    Recently, there has been significant interest within the aerospace community to develop space based nuclear power conversion technologies especially for exploring the outer planets of our solar system where the solar energy density is very low. To investigate these technologies NASA awarded several contracts under Project 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 investigation 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 and a lifetime of 15 years (10 years full power). For the radiation environment, the system was to be capable of operation in the generic space environment and withstand the extreme environments surrounding Jupiter. The studies defined a BPCS design traceable to NEP (Nuclear Electric Propulsion) requirements and suitable for future missions with a sound technology plan for technology readiness level (TRL) advancement identified. The studies assumed a turbine inlet temperature approx. 100 C above the current the state of the art capabilities with materials issues and related development tasks identified. Analyses and evaluations of six different HRS (heat rejection system) designs and three primary power management and distribution (PMAD) configurations will be discussed in the paper.

  15. Study on the matching performance of a low temperature reverse Brayton air refrigerator

    International Nuclear Information System (INIS)

    Highlights: • A relation between operation parameters of expander and brake pressure was obtained. • A matching model was got based on the theoretical analysis and simulation. • Brake pressure feedback control was proposed and applied in the experiment. • The minimum free-load refrigerating temperature of 99.6 K was reached. - Abstract: A small reverse Brayton cycle air refrigerator was designed and fabricated. Bump-type air journal foil bearing, pressurized thrust gas bearing and centrifugal blower as brake were employed in the turboexpander. Usually, constant brake inlet pressure is set in a reverse Brayton refrigerator. However, the unchanged brake inlet pressure cannot adapt to the changing temperature and expansion ratio during the cooling down process, which could go against the system performance. In this article, the relationship between the turboexpander operation parameters and brake pressure was disclosed through theoretical analysis. The performance curve was analyzed through numerical simulation using CFX. A matching model was established based on the theoretical analysis and numerical simulation. Brake pressure feedback control was then proposed and applied in the experimental study. Thermal performance of the refrigerator was tested under varied operating conditions (different expansion ratios, temperatures and brake pressures). The results indicated that the appropriate brake pressure facilitated system good thermal performance under both design and off-design conditions, and the theoretical results agreed well with the experimental data

  16. Brayton Isotope Power System (BIPS). Phase I. First annual technical report

    Energy Technology Data Exchange (ETDEWEB)

    1976-10-27

    The objective of the BIPS program is to develop a closed gas turbine dynamic conversion system for space application. The baseline system is a 7-year life, 450 lb, 1300 W(e) unit using Brayton cycle hardware developed for the NASA LeRC and two 2400 W(t) Multi-Hundred Watt isotope heat sources developed for the ERDA. Phase I of the three-phase BIPS program is the conceptual design of the flight system, the design, development, and testing of a prototype Ground Demonstration System (GDS). The Mini-Brayton Rotating Unit (Mini-BRU), Mini-BRU Recuperator (MBR), and Heat Source Assembly (HSA) will be integrated into the ground demonstrator loop, and the system will be tested under simulated space conditions at the AiResearch Space Power Laboratory. Successful completion of the Phase I effort in mid 1978 is expected to lead to the Phase II and Phase III follow-on efforts. Phase II is a 24-month effort for the development and qualification of a flight system. Qualification will include testing with an isotope heat source. Phase III is a 12-month effort to fabricate flight-qualified hardware for delivery in April 1981.

  17. Comparison Between helium cycle and Supercritical CO2 Cycle for MMR and AMR

    International Nuclear Information System (INIS)

    Korea Atomic Energy Research Institute (KAERI) started the development of Mobile Multi-Purpose Reactor (MMR), which is a 10MWth gas-cooled reactor. MMR is aiming for maximizing mobility, high performance, durability and safety. This is in order to use the MMR for many purposes such as ship propulsion, train engine and so on. MMR generally uses helium Brayton cycle as a power conversion system since it can obtain very simple system arrangement with direct cycle. However, some researchers have proposed that the supercritical carbon dioxide (S-CO2) Brayton cycle can be more efficient energy converting cycle for the high temperature gas cooled reactor (HTGR) and the very high temperature reactor (VHTR) system as well. Thus, this paper is to compare helium Brayton cycle to the S-CO2 Brayton cycle in terms of the efficiency while varying turbine inlet temperature (T. I. T). A cascaded S-CO2 cycle which had been proposed by Argonne National laboratory (ANL) was used as the S-CO2 Brayton cycle configuration. This cycle is to overcome the mismatch of temperature drop between reactor coolant and CO2 through the reactor heat exchanger (RHX). Our research team reviewed the ANL research by using the in-house codes developed by the Korea Advanced institute of Science and Technology (KAIST) research team. The calculation error between the in-house code and previous result was -0.36%

  18. Isotope Brayton ground demonstration testing and flight qualification. Volume 1. Technical program

    Energy Technology Data Exchange (ETDEWEB)

    1974-12-09

    A program is proposed for the ground demonstration, development, and flight qualification of a radioisotope nuclear heated dynamic power system for use on space missions beginning in the 1980's. This type of electrical power system is based upon and combines two aerospace technologies currently under intense development; namely, the MHW isotope heat source and the closed Brayton cycle gas turbine. This power system represents the next generation of reliable, efficient economic electrical power equipment for space, and will be capable of providing 0.5 to 2.0 kW of electric power to a wide variety of spacecraft for earth orbital and interplanetary missions. The immediate design will be based upon the requirements for the Air Force SURVSATCOM mission. The proposal is presented in three volumes plus an Executive Summary. This volume describes the tasks in the technical program.

  19. An Advanced Turbo-Brayton Converter for Radioisotope Power Systems

    Science.gov (United States)

    Zagarola, Mark V.; Izenson, Michael G.; Breedlove, Jeffrey J.; O'Connor, George M.; Ketchum, Andrew C.; Jetley, Richard L.; Simons, James K.

    2005-02-01

    Past work has shown that Brayton power converters are an attractive option for high power, long-duration space missions. More recently, Creare has shown that Brayton technology could be scaled with high efficiency and specific power to lower power levels suitable for radioisotope power conversion systems. Creare is currently leading the development of an advanced turbo-Brayton converter under NASA's Prometheus Program. The converter design is based on space-proven cryocooler technologies that have been shown to be safe; to provide long, maintenance-free lifetimes; and to have high reliability, negligible vibration emittance, and low EMI/EMC. The predicted performance of a converter at the beginning of life is greater than 20% (including electronic inefficiencies and overhead) with a converter specific power of greater than 8 We/kg for a test unit and greater than 15 We/kg for a flight unit. The degradation in performance over a 14-year mission lifetime is predicted to be negligible, and the primary life limiting factor is not expected to be an issue for greater than twice the mission duration. Work during the last year focused on the material and fabrication issues associated with a high temperature turbine and a lightweight recuperator, and the performance issues associated with the high-temperature insulation and power conversion electronics. The development of the converter is on schedule. Thermal vacuum testing to demonstrate a technology readiness level of 5 is currently planned for 2006.

  20. State space model extraction of thermohydraulic systems Part II: a linear graph approach applied to a Brayton cycle–based power conversion unit

    OpenAIRE

    Uren, Kenneth Richard; Schoor, George van

    2013-01-01

    This second paper in a two part series presents the application of a developed state space model extraction methodology applied to a Brayton cycle-based PCU (power conversion unit) of a PBMR (pebble bed modular reactor). The goal is to investigate if the state space extraction methodology can cope with larger and more complex thermohydraulic systems. In Part I the state space model extraction methodology for the purpose of control was described in detail and a state space represen...

  1. Control system options and strategies for supercritical CO2 cycles.

    Energy Technology Data Exchange (ETDEWEB)

    Moisseytsev, A.; Kulesza, K. P.; Sienicki, J. J.; Nuclear Engineering Division; Oregon State Univ.

    2009-06-18

    The Supercritical Carbon Dioxide (S-CO{sub 2}) Brayton Cycle is a promising alternative to Rankine steam cycle and recuperated gas Brayton cycle energy converters for use with Sodium-Cooled Fast Reactors (SFRs), Lead-Cooled Fast Reactors (LFRs), as well as other advanced reactor concepts. The S-CO{sub 2} Brayton Cycle offers higher plant efficiencies than Rankine or recuperated gas Brayton cycles operating at the same liquid metal reactor core outlet temperatures as well as reduced costs or size of key components especially the turbomachinery. A new Plant Dynamics Computer Code has been developed at Argonne National Laboratory for simulation of a S-CO{sub 2} Brayton Cycle energy converter coupled to an autonomous load following liquid metal-cooled fast reactor. The Plant Dynamics code has been applied to investigate the effectiveness of a control strategy for the S-CO{sub 2} Brayton Cycle for the STAR-LM 181 MWe (400 MWt) Lead-Cooled Fast Reactor. The strategy, which involves a combination of control mechanisms, is found to be effective for controlling the S-CO{sub 2} Brayton Cycle over the complete operating range from 0 to 100 % load for a representative set of transient load changes. While the system dynamic analysis of control strategy performance for STARLM is carried out for a S-CO{sub 2} Brayton Cycle energy converter incorporating an axial flow turbine and compressors, investigations of the S-CO{sub 2} Brayton Cycle have identified benefits from the use of centrifugal compressors which offer a wider operating range, greater stability near the critical point, and potentially further cost reductions due to fewer stages than axial flow compressors. Models have been developed at Argonne for the conceptual design and performance analysis of centrifugal compressors for use in the SCO{sub 2} Brayton Cycle. Steady state calculations demonstrate the wider operating range of centrifugal compressors versus axial compressors installed in a S-CO{sub 2} Brayton Cycle as

  2. Mini-Brayton economic RTG study. Final report

    Energy Technology Data Exchange (ETDEWEB)

    1974-01-01

    The objective of this study is to demonstrate the applicability of a radioisotope heated Mini-Brayton power system to the 1973 USAF/AEC requirements established for the SURVSATCOM Mission. The principal requiremenets of the power system, are: 400 We power level; maximum weight 205 lbs.; $1.2 to 2.0 million per unit cost; and 5y mission duration. A radioisotope heat source that meets the ACE Nuclear Safety Criteria is presented. The major aspects of the Reference Design MB-ERTG are summarized. The Reference Design, utilizes a flexible Brayton rotating unit (BRU), a /sup 244/Cm heat source with ceramic clad fuel cylinders and an aluminum radiator. The flexible BRU has a variable power output capability, from 400 We to 3000 We, and is an important factor in the formulation of a cost effective development plan. The system weight is 186 lb and unit cost, including the /sup 244/Cm fuel, acceptance testing and delivery is $748,000. The total development cost for the 5-yr program is estimated at $16.4M with an additional $6.5M required for /sup 244/Cm heat source development support, /sup 244/Cm fuel, heat source fabrication and capital equipment expenditures. (LCL)

  3. Optimization of a Brayton cryocooler for ZBO liquid hydrogen storage in space

    Science.gov (United States)

    Deserranno, D.; Zagarola, M.; Li, X.; Mustafi, S.

    2014-11-01

    NASA is evaluating and developing technology for long-term storage of cryogenic propellant in space. A key technology is a cryogenic refrigerator which intercepts heat loads to the storage tank, resulting in a reduced- or zero-boil-off condition. Turbo-Brayton cryocoolers are particularly well suited for cryogen storage applications because the technology scales well to high capacities and low temperatures. In addition, the continuous-flow nature of the cycle allows direct cooling of the cryogen storage tank without mass and power penalties associated with a cryogenic heat transport system. To quantify the benefits and mature the cryocooler technology, Creare Inc. performed a design study and technology demonstration effort for NASA on a 20 W, 20 K cryocooler for liquid hydrogen storage. During the design study, we optimized these key components: three centrifugal compressors, a modular high-capacity plate-fin recuperator, and a single-stage turboalternator. The optimization of the compressors and turboalternator were supported by component testing. The optimized cryocooler has an overall flight mass of 88 kg and a specific power of 61 W/W. The coefficient of performance of the cryocooler is 23% of the Carnot cycle. This is significantly better performance than any 20 K space cryocooler existing or under development.

  4. Brayton power conversion system parametric design modelling for nuclear electric propulsion

    Science.gov (United States)

    Ashe, Thomas L.; Otting, William D.

    1993-11-01

    The parametrically based closed Brayton cycle (CBC) computer design model was developed for inclusion into the NASA LeRC overall Nuclear Electric Propulsion (NEP) end-to-end systems model. The code is intended to provide greater depth to the NEP system modeling which is required to more accurately predict the impact of specific technology on system performance. The CBC model is parametrically based to allow for conducting detailed optimization studies and to provide for easy integration into an overall optimizer driver routine. The power conversion model includes the modeling of the turbines, alternators, compressors, ducting, and heat exchangers (hot-side heat exchanger and recuperator). The code predicts performance to significant detail. The system characteristics determined include estimates of mass, efficiency, and the characteristic dimensions of the major power conversion system components. These characteristics are parametrically modeled as a function of input parameters such as the aerodynamic configuration (axial or radial), turbine inlet temperature, cycle temperature ratio, power level, lifetime, materials, and redundancy.

  5. Key Factors Influencing the Decision on the Number of Brayton Units for the Prometheus Space Reactor

    Science.gov (United States)

    Ashcroft, John; Belanger, Sean; Burdge, Wayne; Clementoni, Eric; Jensen, Krista; Proctor, N. Beth; Zemo-Fulkerson, Annie

    2007-01-01

    The Naval Reactors (NR) Program and its DOE Laboratories, KAPL and Bettis, were assigned responsibility to develop space reactor systems for the Prometheus Program. After investigating all of the potential reactor and energy conversion options, KAPL and Bettis selected a direct gas Brayton system as the reference approach for the nuclear electric propulsion missions, including the Jupiter Icy Moons Orbiter (JIMO). In order to determine the optimal plant architecture for the direct gas system, KAPL and Bettis investigated systems with one or two active Brayton units and up to two spare units. No final decision was made on the optimal system configuration for the NEP gas-Brayton system prior to closeout of the project. The two most promising options appear to be a single system without spares and a three Brayton system with two operating units, each producing half of the required load, with a single spare unit. The studies show that a single Brayton system, without spares, offers the lowest mass system, with potential for lower operating temperature, and a minimum of system and operational complexity. The lower required mass and increased system efficiency inherent in the single Brayton system may be exploited to satisfy other design objectives such as reduced reactor and radiator operating temperatures. While Brayton system lifetimes applicable to a JIMO or other nuclear electric propulsion (NEP) mission have not been demonstrated, there is no fundamental limit on the lifetime of the Brayton hardware. Use of additional Brayton units with installed spares will allow for continued operation in the event of a failure of an individual Brayton unit. However, preliminary system reliability evaluations do not point to any substantial reliability benefit provided by carrying spare Brayton units. If a spare unit is used, operating two of the units at full power with an unpowered spare proved more efficient than operating all three units at a reduced power and temperature

  6. Brayton isotope power system. Volume II. System evaluation attributes

    Energy Technology Data Exchange (ETDEWEB)

    1978-03-15

    This volume of the Brayton Isotope Power System, Phase II Plan, contains the self-evaluation by AiResearch, GE, and TECO, addressing Section 3 of The Dynamic Systems Evaluation Criteria and Procedures established by the Department of Energy. These evaluation criteria addresses: Component Feasibility; Flight System Design Performance; GDS Test Results; Reliability and Practicality; Safety; Spacecraft Integration; and Cost and Risk. Included in each of these general categories are several attributes, each of which addresses a separate component, feature, or area of interest related to the power system, its development status, degree of preparedness for proceeding into a flight program, and/or the contractors' performance during Phase I. The key elements which indicate the readiness of a radioisotope power system to progress into a flight qualification program are: an advanced state of development of the power conversion system; demonstrated or exhibited potential for space systems standards of reliability; evident capability of meeting system safety requirements; favorable cost/benefit tradeoff considering projected missions and technology advancement potential; and proven feasibility of fabricating and qualifying a flight system and integrating it with a candidate spacecraft and launch vehicle. As a result of considerable government investment in Brayton system component development, the MHW isotope heat source and the BIPS Phase I Ground Demonstration System, the BIPS is a more advanced state of development than any previous radioisotope power system technology. Evidence of this is presented along with a complete review of the attributes, the contractor recommended ratings, and the rationale for the self-evaluation.

  7. Test Results from a Direct Drive Gas Reactor Simulator Coupled to a Brayton Power Conversion Unit

    Science.gov (United States)

    Hervol, David S.; Briggs, Maxwell H.; Owen, Albert K.; Bragg-Sitton, Shannon M.; Godfroy, Thomas J.

    2010-01-01

    Component level testing of power conversion units proposed for use in fission surface power systems has typically been done using relatively simple electric heaters for thermal input. These heaters do not adequately represent the geometry or response of proposed reactors. As testing of fission surface power systems transitions from the component level to the system level it becomes necessary to more accurately replicate these reactors using reactor simulators. The Direct Drive Gas-Brayton Power Conversion Unit test activity at the NASA Glenn Research Center integrates a reactor simulator with an existing Brayton test rig. The response of the reactor simulator to a change in Brayton shaft speed is shown as well as the response of the Brayton to an insertion of reactivity, corresponding to a drum reconfiguration. The lessons learned from these tests can be used to improve the design of future reactor simulators which can be used in system level fission surface power tests.

  8. Advanced thermal-energy-storage concept-definition study for solar Brayton power plants. Final technical report, Volume I

    Energy Technology Data Exchange (ETDEWEB)

    1976-01-01

    The detailed results are presented of a technical and economic assessment of phase change and thermochemical energy storage systems in a solar power plant employing a high temperature Brayton cycle thermal engine with helium as the heat transport fluid. The assessment included an examination of the storage system operation, efficiency, power plant interaction, design, materials, safety, maintenance, environmental impact, system life, and economics. These considerations are implemented in the conceptual design of three baseline storage systems and their components for use in a solar power plant module of 50 megawatt electrical power output. Rationale is provided to support the configuration, operation and material choices. A preliminary assessment of the technology development and experimental test program requirements are also included. The report is contained in four separate volumes. This volume is the technical report.

  9. Brayton isotope power system. Phase I (Ground demonstration system) configuration control document (CCD)

    Energy Technology Data Exchange (ETDEWEB)

    1975-09-25

    The Brayton Isotope Power System (BIPS) Ground Demonstration System (GDS) configuration is defined. The GDS is configured to be similar to a conceptual flight system design referred to herein as the BIPS Flight System (FS). The Brayton Isotope Power System is being developed by the ERDA as a 500 to 2000 W/sub e/, 7 year life 3.5 W/sub e/ per pound space power system. The system was a closed Brayton dynamic system to convert energy from an isotope heat source at a net efficiency exceeding 25%. This CCD is for the first phase of the ERDA program to have a qualified system ready for launch by June 30, 1981. Phase I is a 36 month effort to provide a conceptual design of the flight system and design, fabricate and test a ground demonstration system. The baseline system is predicated on using two of the multihundred-watt isotope heat sources being developed for the ERDA by GE. The Ground Demonstration System will simulate, as closely as possible, the Brayton Isotope Power Flight System and will utilize components and technology being developed by NASA for the Mini-Brayton rotating unit (AIRPHX), recuperator (AIRLA) and heat source assembly (GE). The Ground Demonstration System includes a performance test and a 1000-hour endurance test.

  10. Preliminary Failure Modes, Effects and Criticality Analysis (FMECA) of the conceptual Brayton Isotope Power System (BIPS) Flight System

    International Nuclear Information System (INIS)

    A failure modes, effects and criticality analysis (FMECA) was made of the Brayton Isotope Power System Flight System (BIPS-FS) as presently conceived. The components analyzed include: Mini-BRU; Heat Source Assembly (HSA); Mini-Brayton Recuperator (MBR); Space Radiator; Ducts and Bellows, Insulation System; Controls; and Isotope Heat Source (IHS)

  11. Comparison of Direct and Indirect Gas Reactor Brayton Systems for Nuclear Electric Space Propulsion

    International Nuclear Information System (INIS)

    Gas reactor systems are being considered as candidates for use in generating power for the Prometheus-1 spacecraft, along with other NASA missions as part of the Prometheus program. Gas reactors offer a benign coolant, which increases core and structural materials options. However, the gas coolant has inferior thermal transport properties, relative to other coolant candidates such as liquid metals. This leads to concerns for providing effective heat transfer and for minimizing pressure drop within the reactor core. In direct gas Brayton systems, i.e. those with one or more Brayton turbines in the reactor cooling loop, the ability to provide effective core cooling and low pressure drop is further constrained by the need for a low pressure, high molecular weight gas, typically a mixture of helium and xenon. Use of separate primary and secondary gas loops, one for the reactor and one or more for the Brayton system(s) separated by heat exchanger(s), allows for independent optimization of the pressure and gas composition of each loop. The reactor loop can use higher pressure pure helium, which provides improved heat transfer and heat transport properties, while the Brayton loop can utilize lower pressure He-Xe. However, this approach requires a separate primary gas circulator and also requires gas to gas heat exchangers. This paper focuses on the trade-offs between the direct gas reactor Brayton system and the indirect gas Brayton system. It discusses heat exchanger arrangement and materials options and projects heat exchanger mass based on heat transfer area and structural design needs. Analysis indicates that these heat exchangers add considerable mass, but result in reactor cooling and system resiliency improvements

  12. Optimization and Comparison of Direct and Indirect Supercritical Carbon Dioxide Power Plant Cycles for Nuclear Applications

    Energy Technology Data Exchange (ETDEWEB)

    Edwin A. Harvego; Michael G. McKellar

    2011-11-01

    There have been a number of studies involving the use of gases operating in the supercritical mode for power production and process heat applications. Supercritical carbon dioxide (CO2) is particularly attractive because it is capable of achieving relatively high power conversion cycle efficiencies in the temperature range between 550 C and 750 C. Therefore, it has the potential for use with any type of high-temperature nuclear reactor concept, assuming reactor core outlet temperatures of at least 550 C. The particular power cycle investigated in this paper is a supercritical CO2 Recompression Brayton Cycle. The CO2 Recompression Brayton Cycle can be used as either a direct or indirect power conversion cycle, depending on the reactor type and reactor outlet temperature. The advantage of this cycle when compared to the helium Brayton cycle is the lower required operating temperature; 550 C versus 850 C. However, the supercritical CO2 Recompression Brayton Cycle requires an operating pressure in the range of 20 MPa, which is considerably higher than the required helium Brayton cycle operating pressure of 8 MPa. This paper presents results of analyses performed using the UniSim process analyses software to evaluate the performance of both a direct and indirect supercritical CO2 Brayton Recompression cycle for different reactor outlet temperatures. The direct supercritical CO2 cycle transferred heat directly from a 600 MWt reactor to the supercritical CO2 working fluid supplied to the turbine generator at approximately 20 MPa. The indirect supercritical CO2 cycle assumed a helium-cooled Very High Temperature Reactor (VHTR), operating at a primary system pressure of approximately 7.0 MPa, delivered heat through an intermediate heat exchanger to the secondary indirect supercritical CO2 Brayton Recompression cycle, again operating at a pressure of about 20 MPa. For both the direct and indirect cycles, sensitivity calculations were performed for reactor outlet temperature

  13. Steady-state temperature distribution within a Brayton rotating unit operating in a power conversion system using helium-xenon gas

    Science.gov (United States)

    Johnsen, R. L.; Namkoong, D.; Edkin, R. A.

    1971-01-01

    The Brayton rotating unit (BRU), consisting of a turbine, an alternator, and a compressor, was tested as part of a Brayton cycle power conversion system over a side range of steady state operating conditions. The working fluid in the system was a mixture of helium-xenon gases. Turbine inlet temperature was varied from 1200 to 1600 F, compressor inlet temperature from 60 to 120 F, compressor discharge pressure from 20 to 45 psia, rotative speed from 32 400 to 39 600 rpm, and alternator liquid-coolant flow rate from 0.01 to 0.27 pound per second. Test results indicated that the BRU internal temperatures were highly sensitive to alternator coolant flow below the design value of 0.12 pound per second but much less so at higher values. The armature winding temperature was not influenced significantly by turbine inlet temperature, but was sensitive, up to 20 F per kVA alternator output, to varying alternator output. When only the rotational speed was changed (+ or - 10% of rated value), the BRU internal temperatures varied directly with the speed.

  14. Preliminary Study of the Supercritical CO{sub 2} Hybrid Cycle for the HTGR Application

    Energy Technology Data Exchange (ETDEWEB)

    Bae, Seong Jun; Ahn, Yoonhan; Lee, Jeong Ik [Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of)

    2014-05-15

    This study was conducted to explore the potential of Supercritical Carbon Dioxide (S-CO{sub 2}) Brayton cycle for the HTGR application. The S-CO{sub 2} cycle is being considered as a PCS due to its high thermal efficiency, simplicity, compactness and so on. Generally, the S-CO{sub 2} Brayton cycle is characterized as a highly recuperated cycle which means that to achieve high thermal efficiency, the cycle requires a highly effective recuperator. Argonne National Laboratory (ANL) showed that direct application of the standard S-CO{sub 2} recompressing Brayton cycle to the HTGR or the Very High Temperature Reactor (VHTR) is difficult to achieve high thermal efficiency due to the mismatch of the temperature difference between the temperature drop of helium as the primary reactor coolant and the temperature rise of CO{sub 2} as the PCS coolant through an Intermediate Heat Exchanger (IHX). Therefore, our research team suggests a novel S-CO{sub 2} cycle configuration, the S-CO{sub 2} Brayton and Rankine hybrid cycle, to solve this limitation. This S-CO{sub 2} hybrid concept is utilizing the waste heat of the S-CO{sub 2} Brayton cycle as heat input to the S-CO{sub 2} Rankine cycle. Dividing the thermal capacity of the heat source in to the Brayton cycle part and Rankine cycle part of the S-CO{sub 2} hybrid cycle appropriately, the temperature difference at the IHX could be reduced, therefore the net system performance and operating range can be improved. In this study, the ANL research is reviewed by the in-house cycle analysis codes developed by the Korea Advanced Institute of Science and Technology (KAIST) research team. And the S-CO{sub 2} Brayton and Rankine hybrid cycle is studied as a PCS for the VHTR condition which was utilized by ANL research team; it was assumed that the core outlet temperature to be 850 .deg. C and the core inlet temperature of 400 .deg. C.

  15. Cooling, freezing and heating with the air cycle: air as the ultimate green refrigerant

    NARCIS (Netherlands)

    Verschoor, M.J.E.

    2000-01-01

    Due to the recent concern about the damage that CFCs cause to the environment (ozone layer, global warming) and the absence of commonly acceptable alternative refrigerants, the search for alternative refrigeration concepts is going on. Air as refrigerant in the Joule-Brayton cycle (air cycle) is one

  16. Reactor/Brayton power systems for nuclear electric spacecraft

    International Nuclear Information System (INIS)

    Studies are currently underway to assess the technological feasibility of a nuclear-reactor-powered spacecraft propelled by electric thrusters. The purpose of this study was to provide comparative information on a closed cycle gas turbine power conversion system

  17. Exergoeconomic performance optimization of an endoreversible intercooled regenerated Brayton cogeneration plant. Part 1: Thermodynamic model and parameter analyses

    Directory of Open Access Journals (Sweden)

    Lingen Chen, Bo Yang, Fengrui Sun

    2011-03-01

    Full Text Available A thermodynamic model of an endoreversible intercooled regenerative Brayton heat and power cogeneration plant coupled to constant-temperature heat reservoirs is established by using finite time thermodynamics in Part 1 of this paper. The heat resistance losses in the hot-, cold- and consumer-side heat exchangers, the intercooler and the regenerator are taken into account. The finite time exergoeconomic performance of the cogeneration plant is investigated. The analytical formulae about dimensionless profit rate and exergetic efficiency are derived. The numerical examples show that there exists an optimal value of intercooling pressure ratio which leads to an optimal value of dimensionless profit rate for the fixed total pressure ratio. There also exists an optimal total pressure ratio which leads to a maximum profit rate for the variable total pressure ratio. The effects of intercooling, regeneration and the ratio of the hot-side heat reservoir temperature to environment temperature on dimensionless profit rate and the corresponding exergetic efficiency are analyzed. At last, it is found that there exists an optimal consumer-side temperature which leads to a double-maximum dimensionless profit rate. The profit rate of the model cycle is optimized by optimal allocation of the heat conductance of the heat exchangers in Part 2 of this paper.

  18. Systems Analyses of Advanced Brayton Cycles For High Efficiency Zero Emission Plants

    Energy Technology Data Exchange (ETDEWEB)

    A. D. Rao; J. Francuz; H. Liao; A. Verma; G. S. Samuelsen

    2006-11-01

    Table 1 shows that the systems efficiency, coal (HHV) to power, is 35%. Table 2 summarizes the auxiliary power consumption within the plant. Thermoflex was used to simulate the power block and Aspen Plus the balance of plant. The overall block flow diagram is presented in Figure A1.3-1 and the key unit process flow diagrams are shown in subsequent figures. Stream data are given in Table A1.3-1. Equipment function specifications are provided in Tables A1.3-2 through 17. The overall plant scheme consists of a cryogenic air separation unit supplying 95% purity O{sub 2} to GE type high pressure (HP) total quench gasifiers. The raw gas after scrubbing is treated in a sour shift unit to react the CO with H{sub 2}O to form H{sub 2} and CO{sub 2}. The gas is further treated to remove Hg in a sulfided activated carbon bed. The syngas is desulfurized and decarbonized in a Selexol acid gas removal unit and the decarbonized syngas after humidification and preheat is fired in GE 7H type steam cooled gas turbines. Intermediate pressure (IP) N{sub 2} from the ASU is also supplied to the combustors of the gas turbines as additional diluent for NOx control. A portion of the air required by the ASU is extracted from the gas turbines. The plant consists of the following major process units: (1) Air Separation Unit (ASU); (2) Gasification Unit; (3) CO Shift/Low Temperature Gas Cooling (LTGC) Unit; (4) Acid Gas Removal Unit (AGR) Unit; (5) Fuel Gas Humidification Unit; (6) Carbon Dioxide Compression/Dehydration Unit; (7) Claus Sulfur Recovery/Tail Gas Treating Unit (SRU/TGTU); and (8) Power Block.

  19. Waste heat recovery from adiabatic diesel engines by exhaust-driven Brayton cycles

    Science.gov (United States)

    Khalifa, H. E.

    1983-01-01

    An evaluation of Bryton Bottoming Systems (BBS) as waste heat recovery devices for future adiabatic diesel engines in heavy duty trucks is presented. Parametric studies were performed to evaluate the influence of external and internal design parameters on BBS performance. Conceptual design and trade-off studies were undertaken to estimate the optimum configuration, size, and cost of major hardware components. The potential annual fuel savings of long-haul trucks equipped with BBS were estimated. The addition of a BBS to a turbocharged, nonaftercooled adiabatic engine would improve fuel economy by as much as 12%. In comparison with an aftercooled, turbocompound engine, the BBS-equipped turbocharged engine would offer a 4.4% fuel economy advantage. If installed in tandem with an aftercooled turbocompound engine, the BBS could effect a 7.2% fuel economy improvement. The cost of a mass-produced 38 Bhp BBS is estimated at about $6460 or 170/Bhp. Technical and economic barriers that hinder the commercial introduction of bottoming systems were identified. Related studies in the area of waste heat recovery from adiabatic diesel engines and NASA-CR-168255 (Steam Rankine) and CR-168256 (Organic Rankine).

  20. MELCOR Extensions for Simulation of Modular Power Cycles and Thermochemical Cycles for the Generation of Hydrogen via Nuclear Reactors

    Energy Technology Data Exchange (ETDEWEB)

    Sal B Rodriguez; Randall O Gauntt; Randy Cole; Marcos Modesto; Katherine McFadden; Len Malczynski; Billy Martin [Sandia National Laboratories, P.O. Box 5800, MS 0748, Albuquerque, NM 87123 (United States); Shripad T Revankar; Karen Vierow [Purdue University, 355 North Lansing Street, West Lafayette, IN 46202 (United States); Dave Louie; Louis Archuleta [Omicron, Inc., 2500 Louisiana Blvd. NE, Suite 410, Albuquerque, NM 87110 (United States)

    2006-07-01

    Sandia National Laboratories (SNL) is currently extending MELCOR so that it can be used to simulate high-temperature nuclear reactors with modular secondary-side power components that are coupled to thermochemical cycles such as sulfur iodine (SI), the Westinghouse hybrid sulfur (HyS), and a generalized thermochemical cycle. To this extent, we will begin by extending MELCOR models for high-temperature gas cooled reactors, Brayton power cycles, an SI thermochemical cycle, and a graphical user interface (GUI). In addition, future versions of MELCOR will include a Monte Carlo module for uncertainty and optimization studies, modular components for major power cycles, a financial module, and a generalized thermochemical cycle. (authors)

  1. Technology for Bayton-cycle powerplants using solar and nuclear energy

    Science.gov (United States)

    English, R. E.

    1986-01-01

    Brayton cycle gas turbines have the potential to use either solar heat or nuclear reactors for generating from tens of kilowatts to tens of megawatts of power in space, all this from a single technology for the power generating system. Their development for solar energy dynamic power generation for the space station could be the first step in an evolution of such powerplants for a very wide range of applications. At the low power level of only 10 kWe, a power generating system has already demonstrated overall efficiency of 0.29 and operated 38 000 hr. Tests of improved components show that these components would raise that efficiency to 0.32, a value twice that demonstrated by any alternate concept. Because of this high efficiency, solar Brayton cycle power generators offer the potential to increase power per unit of solar collector area to levels exceeding four times that from photovoltaic powerplants using present technology for silicon solar cells. The technologies for solar mirrors and heat receivers are reviewed and assessed. This Brayton technology for solar powerplants is equally suitable for use with the nuclear reactors. The available long time creep data on the tantalum alloy ASTAR-811C show that such Brayton cycles can evolve to cycle peak temperatures of 1500 K (2240 F). And this same technology can be extended to generate 10 to 100 MW in space by exploiting existing technology for terrestrial gas turbines in the fields of both aircraft propulsion and stationary power generation.

  2. Cooling, freezing and heating with the air cycle: air as the ultimate green refrigerant

    OpenAIRE

    Verschoor, M.J.E.

    2000-01-01

    Due to the recent concern about the damage that CFCs cause to the environment (ozone layer, global warming) and the absence of commonly acceptable alternative refrigerants, the search for alternative refrigeration concepts is going on. Air as refrigerant in the Joule-Brayton cycle (air cycle) is one of the most natural refrigerants, and it meets all criteria for a refrigerant being environmentally benign. For this reason the air cycle is one of the most promising long-term alternatives for re...

  3. Recent technology advances in the NASA-Lewis Research Center Brayton program.

    Science.gov (United States)

    Vernon, R.

    1972-01-01

    A review of the progress and milestones passed in the Brayton program during the past year is presented. The 2-to-15 kWe power system was successfully operated in a vacuum with a space-type radiator. Gas loop and electrical subsystem endurance tests have continued to demonstrate long-term operation with one rotating unit surpassing 10,000 hours of failure-free operation. Simplified gas-bearing designs for the rotating unit are being evaluated. Fabrication of an improved design of heat exchanger is nearing completion, and a study of more advanced heat exchanger technology is being conducted.

  4. Dynamic simulation of 10 kW Brayton cryocooler for HTS cable

    Energy Technology Data Exchange (ETDEWEB)

    Chang, Ho-Myung; Park, Chan Woo [Hong Ik University, Department of Mechanical Engineering, Seoul, 121-791 (Korea, Republic of); Yang, Hyung Suk; Hwang, Si Dole [KEPCO Research Institute, Daejeon, 305-760 (Korea, Republic of)

    2014-01-29

    Dynamic simulation of a Brayton cryocooler is presented as a partial effort of a Korean governmental project to develop 1∼3 km HTS cable systems at transmission level in Jeju Island. Thermodynamic design of a 10 kW Brayton cryocooler was completed, and a prototype construction is underway with a basis of steady-state operation. This study is the next step to investigate the transient behavior of cryocooler for two purposes. The first is to simulate and design the cool-down process after scheduled or unscheduled stoppage. The second is to predict the transient behavior following the variation of external conditions such as cryogenic load or outdoor temperature. The detailed specifications of key components, including plate-fin heat exchangers and cryogenic turbo-expanders are incorporated into a commercial software (Aspen HYSYS) to estimate the temporal change of temperature and flow rate over the cryocooler. An initial cool-down scenario and some examples on daily variation of cryocooler are presented and discussed, aiming at stable control schemes of a long cable system.

  5. Progress Towards a 6-10 K Turbo-Brayton Cryocooler

    Science.gov (United States)

    Zagarola, M. V.; Cragin, K. J.; Breedlove, J. J.; Davis, T. M.

    2006-04-01

    Turbomachine-based Brayton (turbo-Brayton) cryocoolers are an ideal option for long-duration space missions. Key attributes inherent to the technology are high reliability, extremely low vibration emittance, and flexible packaging and integration with instruments and spacecraft systems. The first space implementation of the technology was the NICMOS Cryocooler, which is a single-stage unit that was installed on the Hubble Space Telescope in March 2002. This cryocooler provides 7 W of cooling at 70 K and has been operating for 3.3 years (July 2005) without degradation in performance. New developments at Creare are focused on two-stage configurations with load temperatures as low as 6 K. The lower temperatures and loads have required advances in component technologies to meet aggressive targets for cryocooler mass, size and performance. The development of the electronics, compressors and intermediate turboalternator for a 6-10 K cryocooler are complete. This paper summarizes our accomplishments on the completed components, and reviews our progress towards the development of the remaining critical components, a lightweight recuperator and a high performance low temperature turboalternator.

  6. Dynamic simulation of 10 kW Brayton cryocooler for HTS cable

    Science.gov (United States)

    Chang, Ho-Myung; Park, Chan Woo; Yang, Hyung Suk; Hwang, Si Dole

    2014-01-01

    Dynamic simulation of a Brayton cryocooler is presented as a partial effort of a Korean governmental project to develop 1˜3 km HTS cable systems at transmission level in Jeju Island. Thermodynamic design of a 10 kW Brayton cryocooler was completed, and a prototype construction is underway with a basis of steady-state operation. This study is the next step to investigate the transient behavior of cryocooler for two purposes. The first is to simulate and design the cool-down process after scheduled or unscheduled stoppage. The second is to predict the transient behavior following the variation of external conditions such as cryogenic load or outdoor temperature. The detailed specifications of key components, including plate-fin heat exchangers and cryogenic turbo-expanders are incorporated into a commercial software (Aspen HYSYS) to estimate the temporal change of temperature and flow rate over the cryocooler. An initial cool-down scenario and some examples on daily variation of cryocooler are presented and discussed, aiming at stable control schemes of a long cable system.

  7. Carbon-Carbon Composites as Recuperator Material for Direct Gas Brayton Systems

    Energy Technology Data Exchange (ETDEWEB)

    RA Wolf

    2006-07-19

    Of the numerous energy conversion options available for a space nuclear power plant (SNPP), one that shows promise in attaining reliable operation and high efficiency is the direct gas Brayton (GB) system. In order to increase efficiency, the GB system incorporates a recuperator that accounts for nearly half the weight of the energy conversion system (ECS). Therefore, development of a recuperator that is lighter and provides better performance than current heat exchangers could prove to be advantageous. The feasibility of a carbon-carbon (C/C) composite recuperator core has been assessed and a mass savings of 60% and volume penalty of 20% were projected. The excellent thermal properties, high-temperature capabilities, and low density of carbon-carbon materials make them attractive in the GB system, but development issues such as material compatibility with other structural materials in the system, such as refractory metals and superalloys, permeability, corrosion, joining, and fabrication must be addressed.

  8. Thermodynamic cycles optimised for medium enthalpy units of concentrating solar power

    International Nuclear Information System (INIS)

    Concentrated solar power presents the drawback of decreasing radiation capture efficiency as the temperature of the receiver increases, because thermal losses increase as well. Low temperature at the receiver is an advantage for radiation concentrators, as they present high capture efficiency, but this fact changes into a drawback because of the low efficiency of the thermodynamic cycles working with a low temperature heat source. An analysis is presented on the performance of real fluids working with such a type of heat sources that can be generated in simple solar thermal units. Both Joule–Brayton cycles and dry-turbine Rankine cycles are considered, using regenerative heat exchangers for heat recovering. The driving force of this research is to look for working fluids with actual thermodynamic characteristics which fit well with temperatures of the heat source and sink. Some unconventional substances, as refrigerant R-125 or SF6, show good performance. They may be suitable at certain regimes of Rankine and Brayton cycles and could work in fast-reacting systems. Of course, differences in the performance of Brayton and Rankine cycles convey differences in the complexity and cost of the components, but they offer a wide field for coherently choosing the working fluid and thermal conditions. - Highlights: • Analysis of Brayton and Rankine cycles close to the critical point. • Performance of transcritical and supercritical cycles. • The close to critical point region is a promising region for low-to-moderate temperature applications. • Fluid selection becomes important. SF6 and R-125 present good performance

  9. The universal power and efficiency characteristics for irreversible reciprocating heat engine cycles

    CERN Document Server

    Qin Xiao Yong; Sun Feng Rui; Wu Chih

    2003-01-01

    The performance of irreversible reciprocating heat engine cycles with heat transfer loss and friction-like term loss is analysed using finite-time thermodynamics. The universal relations between the power output and the compression ratio, between the thermal efficiency and the compression ratio, and the optimal relation between power output and the efficiency of the cycles are derived. Moreover, analysis and optimization of the model were carried out in order to investigate the effect of cycle processes on the performance of the cycle using numerical examples. The results obtained herein include the performance characteristics of irreversible reciprocating Diesel, Otto, Atkinson and Brayton cycles.

  10. Parametric thermodynamic analysis of closed-cycle gas-laser operation in space

    Science.gov (United States)

    Burns, R. K.

    1974-01-01

    Cycle efficiency and radiator area required were calculated for thermally and electrically pumped lasers operating in closed cycles with a compressor and the required heat exchangers. A thermally pumped laser included within a Brayton cycle was also analyzed. Performance of all components, including the laser, was parametrically varied. For the thermally pumped laser the cycle efficiencies range below 10 percent and are very sensitive to the high-pressure losses associated with the supersonic diffuser required at the laser cavity exit. The efficiencies predicted for the electrically pumped laser cycles range slightly higher, but radiator area also tends to be larger.

  11. On the thermal efficiency of power cycles in finite time thermodynamics

    Science.gov (United States)

    Momeni, Farhang; Morad, Mohammad Reza; Mahmoudi, Ashkan

    2016-09-01

    The Carnot, Diesel, Otto, and Brayton power cycles are reconsidered endoreversibly in finite time thermodynamics (FTT). In particular, the thermal efficiency of these standard power cycles is compared to the well-known results in classical thermodynamics. The present analysis based on FTT modelling shows that a reduction in both the maximum and minimum temperatures of the cycle causes the thermal efficiency to increase. This is antithetical to the existing trend in the classical references. Under the assumption of endoreversibility, the relation between the efficiencies is also changed to {η }{{Carnot}}\\gt {η }{{Brayton}}\\gt {η }{{Diesel}}\\gt {η }{{Otto}}, which is again very different from the corresponding classical results. The present results benefit a better understanding of the important role of irreversibility on heat engines in classical thermodynamics.

  12. HTR-Based Power Plants’ Performance Analysis Applied on Conventional Combined Cycles

    Directory of Open Access Journals (Sweden)

    José Carbia Carril

    2015-01-01

    Full Text Available In high temperature reactors including gas cooled fast reactors and gas turbine modular helium reactors (GT-MHR specifically designed to operate as power plant heat sources, efficiency enhancement at effective cost under safe conditions can be achieved. Mentioned improvements concern the implementation of two cycle structures: (a, a stand alone Brayton operating with helium and a stand alone Rankine cycle (RC with regeneration, operating with carbon dioxide at ultrasupercritical pressure as working fluid (WF, where condensation is carried out at quasicritical conditions, and (b, a combined cycle (CC, in which the topping closed Brayton cycle (CBC operates with helium as WF, while the bottoming RC is operated with one of the following WFs: carbon dioxide, xenon, ethane, ammonia, or water. In both cases, an intermediate heat exchanger (IHE is proposed to provide thermal energy to the closed Brayton or to the Rankine cycles. The results of the case study show that the thermal efficiency, through the use of a CC, is slightly improved (from 45.79% for BC and from 50.17% for RC to 53.63 for the proposed CC with He-H2O operating under safety standards.

  13. Gas-injection-start and shutdown characteristics of a 2-kilowatt to 15-kilowatt Brayton power system

    Science.gov (United States)

    Cantoni, D. A.

    1972-01-01

    Two methods of starting the Brayton power system have been considered: (1) using the alternator as a motor to spin the Brayton rotating unit (BRU), and (2) spinning the BRU by forced gas injection. The first method requires the use of an auxiliary electrical power source. An alternating voltage is applied to the terminals of the alternator to drive it as an induction motor. Only gas-injection starts are discussed in this report. The gas-injection starting method requires high-pressure gas storage and valves to route the gas flow to provide correct BRU rotation. An analog computer simulation was used to size hardware and to determine safe start and shutdown procedures. The simulation was also used to define the range of conditions for successful startups. Experimental data were also obtained under various test conditions. These data verify the validity of the start and shutdown procedures.

  14. Thermodynamic Analysis of Supplementary-Fired Gas Turbine Cycles

    DEFF Research Database (Denmark)

    Elmegaard, Brian; Henriksen, Ulrik Birk; Qvale, Einar Bjørn

    2002-01-01

    demonstration of a two-stage gasification process through construction of several plants.} A preliminary analysis of the ideal recuperated Brayton cycle shows that for this cycle any supplementary firing will have a marginal efficiency of unity per extra unit of fuel. The same result is obtained...... for the indirectly fired gas turbine (IFGT) and for the supplementary-fired IFGT. Both results show that the combination of external firing and internal firing have the potential of reducing or solving some problems with the use of biomass both in the recuperated and the indirectly fired gas turbine: The former...... to be independent of temperature ratio and lower than for the recuperated gas turbine....

  15. Design and optimization of a single stage centrifugal compressor for a solar dish-Brayton system

    Science.gov (United States)

    Wang, Yongsheng; Wang, Kai; Tong, Zhiting; Lin, Feng; Nie, Chaoqun; Engeda, Abraham

    2013-10-01

    According to the requirements of a solar dish-Brayton system, a centrifugal compressor stage with a minimum total pressure ratio of 5, an adiabatic efficiency above 75% and a surge margin more than 12% needs to be designed. A single stage, which consists of impeller, radial vaned diffuser, 90° crossover and two rows of axial stators, was chosen to satisfy this system. To achieve the stage performance, an impeller with a 6:1 total pressure ratio and an adiabatic efficiency of 90% was designed and its preliminary geometry came from an in-house one-dimensional program. Radial vaned diffuser was applied downstream of the impeller. Two rows of axial stators after 90° crossover were added to guide the flow into axial direction. Since jet-wake flow, shockwave and boundary layer separation coexisted in the impeller-diffuser region, optimization on the radius ratio of radial diffuser vane inlet to impeller exit, diffuser vane inlet blade angle and number of diffuser vanes was carried out at design point. Finally, an optimized centrifugal compressor stage fulfilled the high expectations and presented proper performance. Numerical simulation showed that at design point the stage adiabatic efficiency was 79.93% and the total pressure ratio was 5.6. The surge margin was 15%. The performance map including 80%, 90% and 100% design speed was also presented.

  16. Numerical simulations of LNG vapor dispersion in Brayton Fire Training Field tests with ANSYS CFX

    International Nuclear Information System (INIS)

    Federal safety regulations require the use of validated consequence models to determine the vapor cloud dispersion exclusion zones for accidental liquefied natural gas (LNG) releases. One tool that is being developed in industry for exclusion zone determination and LNG vapor dispersion modeling is computational fluid dynamics (CFD). This paper uses the ANSYS CFX CFD code to model LNG vapor dispersion in the atmosphere. Discussed are important parameters that are essential inputs to the ANSYS CFX simulations, including the atmospheric conditions, LNG evaporation rate and pool area, turbulence in the source term, ground surface temperature and roughness height, and effects of obstacles. A sensitivity analysis was conducted to illustrate uncertainties in the simulation results arising from the mesh size and source term turbulence intensity. In addition, a set of medium-scale LNG spill tests were performed at the Brayton Fire Training Field to collect data for validating the ANSYS CFX prediction results. A comparison of test data with simulation results demonstrated that CFX was able to describe the dense gas behavior of LNG vapor cloud, and its prediction results of downwind gas concentrations close to ground level were in approximate agreement with the test data.

  17. A thermodynamic review of cryogenic refrigeration cycles for liquefaction of natural gas

    Science.gov (United States)

    Chang, Ho-Myung

    2015-12-01

    A thermodynamic review is presented on cryogenic refrigeration cycles for the liquefaction process of natural gas. The main purpose of this review is to examine the thermodynamic structure of various cycles and provide a theoretical basis for selecting a cycle in accordance with different needs and design criteria. Based on existing or proposed liquefaction processes, sixteen ideal cycles are selected and the optimal conditions to achieve their best thermodynamic performance are investigated. The selected cycles include standard and modified versions of Joule-Thomson (JT) cycle, Brayton cycle, and their combined cycle with pure refrigerants (PR) or mixed refrigerants (MR). Full details of the cycles are presented and discussed in terms of FOM (figure of merit) and thermodynamic irreversibility. In addition, a new method of nomenclature is proposed to clearly identify the structure of cycles by abbreviation.

  18. Supercritical CO2 Brayton power cycles for DEMO (demonstration power plant) fusion reactor based on dual coolant lithium lead blanket

    OpenAIRE

    Linares, José Ignacio; Cantizano González, Alexis; Moratilla, Beatriz Y.; Martin Palacios, Victor; Batet Miracle, Lluís

    2016-01-01

    The purpose of this website is to provide information about fusion and fusion research, particularly the research activities related to EUROfusion. Neither EUROfusion, the EUROfusion Research Units, the European Commission, nor anyone acting on their behalf, is responsible for any damage resulting from the use of information contained on this website. Unless otherwise explicitly stated, all information, text and electronic images contained on this website are the intellectual property of ...

  19. Combined Turbine and Cycle Optimization for Organic Rankine Cycle Power Systems—Part B

    DEFF Research Database (Denmark)

    La Seta, Angelo; Meroni, Andrea; Andreasen, Jesper Graa;

    2016-01-01

    Organic Rankine cycle (ORC) power systems have recently emerged as promising solutions for waste heat recovery in low- and medium-size power plants. Their performance and economic feasibility strongly depend on the expander. The design process and efficiency estimation are particularly challenging...... power output of 8.3% compared to the case when the turbine efficiency is assumed to be 80%. This work also demonstrates that this approach can support the plant designer in the selection of the optimal size of the organic Rankine cycle unit when multiple exhaust gas streams are available....... due to the peculiar physical properties of the working fluid and the gas-dynamic phenomena occurring in the machine. Unlike steam Rankine and Brayton engines, organic Rankine cycle expanders combine small enthalpy drops with large expansion ratios. These features yield turbine designs with few highly...

  20. Air bottoming cycle, an alternative to combined cycles. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Kaikko, J. [Royal Inst. of Techn., Stockholm (Sweden). Dept. of Energy Technology

    2001-10-01

    In this work, the idea of Air Bottoming Cycle (ABC) has been studied. The objectives for the work have been to establish an understanding of the concept for power and heat generation as well as to find - if possible - feasible concepts for future use in the Swedish energy system. Combined cycle in power generation is an established technology. In the conventional combined cycle, a gas turbine works as a topping cycle together with the steam (Rankine) bottoming cycle. In the ABC the steam bottoming cycle is replaced with a gas turbine (Brayton) bottoming cycle having air as a working fluid. The two gas turbines are thermally connected over a gas-to-gas heat exchanger. This concept promises savings in weight and cost, as well as operating benefits, compared to the Rankine bottoming technology. The ABC has been modelled using a heat balance program, and a parametric study for the concept optimisation as well as for off-design analysis has been performed. Performance of the ABC has been compared to other, established technologies. A preliminary economic evaluation has been made. As a result of the study, it is clarified that the Rankine bottoming cycle with steam remains superior to the ABC as regards electrical efficiency in the medium and large power scale. For small-scale applications (<10 MW{sub e}) where the thermodynamic advantage of the Rankine cycle is not dominating any longer and its economy is burdened by the heavy investment structure, the ABC becomes the better alternative for energy utilisation. A preliminary economic evaluation shows that (at energy prices autumn 2000) the ABC is at the same level as the comparable small-scale cogeneration installations. Due to high power-to-heat ratio however, higher electricity prices will favour the ABC. One interesting feature of the ABC is that about 50% of the dissipated low-value heat from the cycle is carried by clean (sterile) air at the temperature around 200 deg C. This air can be utilised for space heating or

  1. Air bottoming cycle, an alternative to combined cycles. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Kaikko, J. [Royal Inst. of Tech., Stockholm (Sweden). Dept. of Energy Technology

    2002-02-01

    In this work, the idea of Air Bottoming Cycle (ABC) has been studied. The objectives for the work have been to establish an understanding of the concept for power and heat generation as well as to find - if possible - feasible concepts for future use in the Swedish energy system. Combined cycle in power generation is an established technology. In the conventional combined cycle, a gas turbine works as a topping cycle together with the steam (Rankine) bottoming cycle. In the ABC the steam bottoming cycle is replaced with a gas turbine (Brayton) bottoming cycle having air as a working fluid. The two gas turbines are thermally connected over a gas-to-gas heat exchanger. This concept promises savings in weight and cost, as well as operating benefits, compared to the Rankine bottoming technology. The ABC has been modelled using a heat balance program, and a parametric study for the concept optimisation as well as for off-design analysis has been performed. Performance of the ABC has been compared to other, established technologies. A preliminary economic evaluation has been made. As a result of the study, it is clarified that the Rankine bottoming cycle with steam remains superior to the ABC as regards electrical efficiency in the medium and large power scale. For small-scale applications (<10 MW{sub e}) where the thermodynamic advantage of the Rankine cycle is not dominating any longer and its economy is burdened by the heavy investment structure, the ABC becomes the better alternative for energy utilisation. A preliminary economic evaluation shows that (at energy prices autumn 2000) the ABC is at the same level as the comparable small-scale cogeneration installations. Due to high power-to-heat ratio however, higher electricity prices will favour the ABC. One interesting feature of the ABC is that about 50% of the dissipated low-value heat from the cycle is carried by clean (sterile) air at the temperature around 200 deg C. This air can be utilised for space heating or

  2. Proposal for an advanced heat source assembly for the Isotope Brayton Power System. Volume 1. Technical program and statement of work

    Energy Technology Data Exchange (ETDEWEB)

    1974-12-09

    The technical program plan for evaluating the performance and safety of a radioisotope-fueled Brayton power system for space vehicles is presented with schedules for evaluating heat source design and safety, for specifying power system requirements, and for the development and operation of a ground demonstration system. (LCL)

  3. Comparative evaluation of three alternative power cycles for waste heat recovery from the exhaust of adiabatic diesel engines

    Energy Technology Data Exchange (ETDEWEB)

    Bailey, M.M.

    1985-07-01

    Three alternative power cycles were compared in application as an exhaust-gas heat-recovery system for use with advanced ''adiabatic'' diesel engines. The power cycle alternatives considered were steam Rankine, organic Rankine with RC-1 as the working fluid, and variations of an air Brayton cycle. The comparison was made in terms of fuel economy and economic payback potential for heavy-duty trucks operating in line-haul service. The results indicate that, in terms of engine rated specific fuel consumption, a diesel/alternative-power-cycle engine offers a significant improvement over the turbocompound diesel used as the baseline for comparison. The maximum improvement resulted from the use of a Rankine cycle heat-recovery system in series with turbocompounding. The air Brayton cycle alternatives studied, which included both simple-cycle and compression-intercooled configurations, were less effective and provided about half the fuel consumption improvement of the Rankine cycle alternatives under the same conditions. Capital and maintenance cost estimates were also developed for each of the heat-recovery power cycle systems. These costs were integrated with the fuel savings to identify the time required for net annual savings to pay back the initial capital investment. The sensitivity of capital payback time to arbitrary increases in fuel price, not accompanied by corresponding hardware cost inflation, was also examined. The results indicate that a fuel price increase is required for the alternative power cycles to pay back capital within an acceptable time period.

  4. Comparative evaluation of three alternative power cycles for waste heat recovery from the exhaust of adiabatic diesel engines

    Science.gov (United States)

    Bailey, M. M.

    1985-01-01

    Three alternative power cycles were compared in application as an exhaust-gas heat-recovery system for use with advanced adiabatic diesel engines. The power cycle alternatives considered were steam Rankine, organic Rankine with RC-1 as the working fluid, and variations of an air Brayton cycle. The comparison was made in terms of fuel economy and economic payback potential for heavy-duty trucks operating in line-haul service. The results indicate that, in terms of engine rated specific fuel consumption, a diesel/alternative-power-cycle engine offers a significant improvement over the turbocompound diesel used as the baseline for comparison. The maximum imporvement resulted from the use of a Rankine cycle heat-recovery system in series with turbocompounding. The air Brayton cycle alternatives studied, which included both simple-cycle and compression-intercooled configurations, were less effective and provided about half the fuel consumption improvement of the Rankine cycle alternatives under the same conditions. Capital and maintenance cost estimates were also developed for each of the heat-recovery power cycle systems. These costs were integrated with the fuel savings to identify the time required for net annual savings to pay back the initial capital investment. The sensitivity of capital payback time to arbitrary increases in fuel price, not accompanied by corresponding hardware cost inflation, was also examined. The results indicate that a fuel price increase is required for the alternative power cycles to pay back capital within an acceptable time period.

  5. Feasibility of Ericsson type isothermal expansion/compression gas turbine cycle for nuclear energy use

    International Nuclear Information System (INIS)

    A gas turbine with potential demand for the next generation nuclear energy use such as HTGR power plants, a gas cooled FBR, a gas cooled nuclear fusion reactor uses helium as working gas and with a closed cycle. Materials constituting a cycle must be set lower than allowable temperature in terms of mechanical strength and radioactivity containment performance and so expansion inlet temperature is remarkably limited. For thermal efficiency improvement, isothermal expansion/isothermal compression Ericsson type gas turbine cycle should be developed using wet surface of an expansion/compressor casing and a duct between stators without depending on an outside heat exchanger performing multistage re-heat/multistage intermediate cooling. Feasibility of an Ericsson cycle in comparison with a Brayton cycle and multi-stage compression/expansion cycle was studied and technologies to be developed were clarified. (author)

  6. Supercritical CO2 Power Cycles: Design Considerations for Concentrating Solar Power

    Energy Technology Data Exchange (ETDEWEB)

    Neises, Ty; Turchi, Craig

    2014-09-01

    A comparison of three supercritical CO2 Brayton cycles: the simple cycle, recompression cycle and partial-cooling cycle indicates the partial-cooling cycle is favored for use in concentrating solar power (CSP) systems. Although it displays slightly lower cycle efficiency versus the recompression cycle, the partial-cooling cycle is estimated to have lower total recuperator size, as well as a lower maximum s-CO2 temperature in the high-temperature recuperator. Both of these effects reduce recuperator cost. Furthermore, the partial-cooling cycle provides a larger temperature differential across the turbine, which translates into a smaller, more cost-effective thermal energy storage system. The temperature drop across the turbine (and by extension, across a thermal storage system) for the partial-cooling cycle is estimated to be 23% to 35% larger compared to the recompression cycle of equal recuperator conductance between 5 and 15 MW/K. This reduces the size and cost of the thermal storage system. Simulations by NREL and Abengoa Solar indicate the partial-cooling cycle results in a lower LCOE compared with the recompression cycle, despite the former's slightly lower cycle efficiency. Advantages of the recompression cycle include higher thermal efficiency and potential for a smaller precooler. The overall impact favors the use of a partial-cooling cycle for CSP compared to the more commonly analyzed recompression cycle.

  7. Exergy Analysis for Combined Brayton and Inverse Brayton Cycles%布雷顿、逆布雷顿循环组成的联合循环(火用)分析

    Institute of Scientific and Technical Information of China (English)

    张万里; 陈林根; 孙丰瑞

    2005-01-01

    利用热力学第二定律分析了布雷顿、逆布雷顿循环组成的联合循环,得出了联合循环各部分的(火用)损失及系统的(火用)效率表达式,确定了循环中(火用)损失最大的位置,并由数值计算分析了各种参数对联合循环(火用)效率和其他特性的影响.

  8. Exergy Analysis of Combined Cycle Power Plant: NTPC Dadri, India

    Directory of Open Access Journals (Sweden)

    Arvind Kumar Tiwari

    2012-12-01

    Full Text Available The aim of the present paper is to exergy analysis of combined Brayton/Rankine power cycle of NTPC Dadri India. Theoretical exergy analysis is carried out for different components of dadri combined cycle power plant which consists of a gas turbine unit, heat recovery steam generator without extra fuel consumption and steam turbine unit. The results pinpoint that more exergy losses occurred in the gas turbine combustion chamber. Its reached 35% of the total exergy losses while the exergy losses in other plant components are between 7% -21% of the total exergy losses at 1400o C turbine inlet temperature and pressure ratio 10 .This paper also considered the effect of the pressure ratio, turbine inlet temperature, pressure drop in combustion chamber and heat recovery steam generator on the exergy losses in the plant, there are a clear effects in the exergy losses when changing pressure ratio, turbine inlet temperature.

  9. Evaluation of technical feasibility of closed-cycle non-equilibrium MHD power generation with direct coal firing. Final report, Task I

    Energy Technology Data Exchange (ETDEWEB)

    1981-11-01

    Program accomplishments in a continuing effort to demonstrate the feasibility of direct coal-fired, closed-cycle MHD power generation are reported. This volume contains the following appendices: (A) user's manual for 2-dimensional MHD generator code (2DEM); (B) performance estimates for a nominal 30 MW argon segmented heater; (C) the feedwater cooled Brayton cycle; (D) application of CCMHD in an industrial cogeneration environment; (E) preliminary design for shell and tube primary heat exchanger; and (F) plant efficiency as a function of output power for open and closed cycle MHD power plants. (WHK)

  10. Exergoeconomic performance optimization of an endoreversible intercooled regenerated Brayton cogeneration plant. Part 2: Heat conductance allocation and pressure ratio optimization

    Directory of Open Access Journals (Sweden)

    Bo Yang, Lingen Chen, Fengrui Sun

    2011-03-01

    Full Text Available Finite time exergoeconomic performance of an endoreversible intercooled regenerative Brayton cogeneration plant is optimized based on the model which is established using finite time thermodynamic in Part 1 of this paper. It is found that the optimal heat conductance allocation of the regenerator is zero. When the total pressure ratio and the heat conductance allocation of the regenerator are fixed, it is shown that there exist an optimal intercooling pressure ratio, and a group of optimal heat conductance allocations among the hot-, cold- and consumer-side heat exchangers and the intercooler, which correspond to a maximum dimensionless profit rate. When the total pressure ratio is variable, there exists an optimal total pressure ratio which corresponds to a double-maximum dimensionless profit rate, and the corresponding exergetic efficiency is obtained. The effects of the total heat exchanger conductance, price ratios and the consumer-side temperature on the double-maximum dimensionless profit rate and the corresponding exergetic efficiency are discussed. It is found that there exists an optimal consumer-side temperature which corresponds to a thrice-maximum dimensionless profit rate.

  11. An important feature of air heat pump cycle: Heating capacity in line with heating load

    International Nuclear Information System (INIS)

    In the conventional vapor-compression heat pumps, the heating capacity and the heating load usually vary in opposite directions, which results in a mismatch of the heating capacity and the heating load at off-design conditions. Air (reversed Brayton) cycle is a potential substitute for the conventional vapor-compression cycles. This paper proved that in theory the air heat pump cycle can make the heating capacity in line with the heating load at a stable level of heating COP (coefficient of performance). A thermodynamic model for the air heat pump cycle with practical compressor and expander was developed. The optimal heating COP and the corresponding pressure ratio were derived from the model. Then the cycle performance was analytically expressed under the optimal COP conditions. The heating capacity under different operating conditions was found in line with the heating load. Comparisons between the air heat pump cycle and two typical vapor-compression heat pump cycles were numerically done for further verification. It also turned out that the energy efficiency of air heat pump is comparable to the transcritical CO2 heat pump, particularly at large temperature difference. - Highlights: • We developed a thermodynamic model for air heat pump cycle. • The optimal COP (coefficient of performance) was derived and the corresponding cycle performance was analyzed. • Comparison of air heat pump cycle and vapor-compression cycles was numerically done. • We proved air heat pump cycle can make heating capacity in line with heating load

  12. Carbon dioxide direct cycle modular reactor

    International Nuclear Information System (INIS)

    Recently, as the micro gas-turbine power generation is clean for environment and has high convenience, it is focused as a small size dispersion electric source for super markets, hospitals, factories, and so on. And, a modular high temperature gas reactor (PBMR) adopting the gas turbine is also focused recently, and is progressed on its construction in South Africa and reported on construction plan of the Exelon Inc. in U.S.A. PBMR has specific safety for a small size and pebble-bed reactor and also has some characters on low construction cost similar to that of LWR due to simplification and small size module adoption of its plant. The PBMR uses helium for its coolants, of which exit temperature is set for at 900degC to get higher thermal efficiency. This is because of its adoption of Brayton cycle to fast reduce the efficiency with falling temperature. However, as helium is a costly and easy-emission vapor, it is desired to alternate to cheaper and more difficult-emission vapor. Here were introduced on carbon dioxide (CO2) direct cycle using carbon dioxide with extremely higher thermal efficiency than helium and its applicability to nuclear reactors. (G.K.)

  13. Biogeochemical Cycling

    Science.gov (United States)

    Bebout, Brad; Fonda, Mark (Technical Monitor)

    2002-01-01

    This lecture will introduce the concept of biogeochemical cycling. The roles of microbes in the cycling of nutrients, production and consumption of trace gases, and mineralization will be briefly introduced.

  14. Supercritical CO2 direct cycle Gas Fast Reactor (SC-GFR) concept.

    Energy Technology Data Exchange (ETDEWEB)

    Wright, Steven Alan; Parma, Edward J., Jr.; Suo-Anttila, Ahti Jorma (Computational Engineering Analysis, Albuquerque, NM); Al Rashdan, Ahmad (Texas A& M University, College Station, TX); Tsvetkov, Pavel Valeryevich (Texas A& M University, College Station, TX); Vernon, Milton E.; Fleming, Darryn D.; Rochau, Gary Eugene

    2011-05-01

    This report describes the supercritical carbon dioxide (S-CO{sub 2}) direct cycle gas fast reactor (SC-GFR) concept. The SC-GFR reactor concept was developed to determine the feasibility of a right size reactor (RSR) type concept using S-CO{sub 2} as the working fluid in a direct cycle fast reactor. Scoping analyses were performed for a 200 to 400 MWth reactor and an S-CO{sub 2} Brayton cycle. Although a significant amount of work is still required, this type of reactor concept maintains some potentially significant advantages over ideal gas-cooled systems and liquid metal-cooled systems. The analyses presented in this report show that a relatively small long-life reactor core could be developed that maintains decay heat removal by natural circulation. The concept is based largely on the Advanced Gas Reactor (AGR) commercial power plants operated in the United Kingdom and other GFR concepts.

  15. 对某布雷顿循环燃烧器专利进行分析研究%Analysis of a Brayton Cycle Burner Patent

    Institute of Scientific and Technical Information of China (English)

    党娟; 苏铁熊

    2014-01-01

    本文对某布雷顿循环燃烧器专利进行研究,给定相关参数,对此燃烧器进行完全燃烧、过量空气系数、燃空比等计算.将计算结果与现在大部分发动机的数据相比,说明此燃烧器降低污染,提高效率.

  16. FES cycling.

    Science.gov (United States)

    Newham, D J; Donaldson, N de N

    2007-01-01

    Spinal cord injury (SCI) leads to a partial or complete disruption of motor, sensory, and autonomic nerve pathways below the level of the lesion. In paraplegic patients, functional electrical stimulation (FES) was originally widely considered as a means to restore walking function but this was proved technically very difficult because of the numerous degrees of freedom involved in walking. FES cycling was developed for people with SCI and has the advantages that cycling can be maintained for reasonably long periods in trained muscles and the risk of falls is low. In the article, we review research findings relevant to the successful application of FES cycling including the effects on muscle size, strength and function, and the cardiovascular and bone changes. We also describe important practical considerations in FES cycling regarding the application of surface electrodes, training and setting up the stimulator limitations, implanted stimulators and FES cycling including FES cycling in groups and other FES exercises such as FES rowing.

  17. Cycling more for safer cycling

    OpenAIRE

    VAN HOUT, Kurt

    2009-01-01

    Cycling presents a lot of benefits to the individual and to society. Health, environment, accessibility, local businesses, … all gain when more people cycle. Yet many governments are reluctant when it comes to promoting cycling, mainly because of (perceived) safety issues. Since studies have established a clear and consistent relationship between bicycle use and cyclist accident risk, this lack of bicycle promotion will influence the safety outcome of bicyclists. In this paper the relation be...

  18. Preliminary Studies of Na2CO3 Elimination from Na/CO2 Reaction in S-CO2 Power Cycle coupled to SFR System

    International Nuclear Information System (INIS)

    In order to avoid the SWR, the supercritical CO2 (S-CO2) Brayton cycle was proposed as a design alternative to the steam Rankine cycle. The S-CO2 Brayton cycle has good features such as improved thermal efficiency, reduced total plant size by having compact turbomachinery and heat exchangers and relatively simplified cycle layout. However, several technical challenges are still remaining for application of S-CO2 Brayton cycle to SFR. This is because when the pressure boundary in sodium-CO2 heat exchanger (HX) fails then leaked CO2 reacts with sodium, although the SWR is eliminated. The reaction between sodium and CO2 is much milder than SWR but more complex. The reaction is affected by the reaction temperature and there is the possibility of sodium ignition at very high temperature. So far, some research works on Na/CO2 reaction has been done. The experiments for Na/CO2 surface reaction, wastage phenomenon and self-plugging of narrow flow channel of Na/CO2 HXs were successfully conducted in KAERI. CEA proposed the major Na/CO2 reaction formulas and performed the calorimetric studies. JAEA experimentally investigated reaction behavior of CO2 with a liquid sodium pool. However, any research works for treatment and removal of reaction products from Na/CO2 reaction has not been done so far. Generally, when the pressure boundary fails CO2 will be released to sodium side and the amount of leakage will be depending on the rupture size. CO2 will react with sodium in the sodium-CO2 HX. It will lead to an economical problem if the channel is plugged by the solid reaction products of Na/CO2 reaction. Since the whole system operation should be stopped or some sort of bypass system should be applied to replace the plugged channel, which will affect the system economics. Therefore, it needs a material which can clean up the solid reaction products of Na/CO2 reaction and contaminated system while minimizing the impact on economics. If there is a material that can act as a

  19. Preliminary performance of a 4.97-inch radial turbine operating in a Brayton power system with a helium-xenon gas mixture

    Science.gov (United States)

    Leroy, M. J., Jr.; Ream, L. W.; Curreri, J. S.

    1971-01-01

    The performance characteristics of the Brayton-rotating-unit's 4.97-inch radial turbine were investigated with the turbine part of a power conversion system. The following system parameters were varied: turbine inlet temperature from 1200 to 1600 F, compressor inlet temperature from 60 to 120 F, compressor outlet pressure from 20 to 45 psia, and shaft speed from 90-110 percent of rated speed (36000 rpm). The working fluid of the system was a gas mixture of helium-xenon with a nominal molecular weight of 83.8. Test results indicate that changes in system conditions have little effect on the turbine efficiency. At the design turbine inlet temperature of 1600 F and compressor inlet temperature of 80 F, an average turbine efficiency of 91 percent was obtained.

  20. Selection of components for the IDEALHY preferred cycle for the large scale liquefaction of hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Quack, H.; Seemann, I.; Klaus, M.; Haberstroh, Ch. [Technische Universitaet Dresden, Dresden (Germany); Berstad, D.; Walnum, H. T.; Neksa, P. [SINTEF Energy Research, Trondheim (Norway); Decker, L. [Linde Kryotechnik AG, Pfungen (Switzerland)

    2014-01-29

    In a future energy scenario, in which storage and transport of liquid hydrogen in large quantities will be used, the efficiency of the liquefaction of hydrogen will be of utmost importance. The goal of the IDEALHY working party is to identify the most promising process for a 50 t/d plant and to select the components, with which such a process can be realized. In the first stage the team has compared several processes, which have been proposed or realized in the past. Based on this information a process has been selected, which is thermodynamically most promising and for which it could be assumed that good components already exist or can be developed in the foreseeable future. Main features of the selected process are the compression of the feed stream to a relatively high pressure level, o-p conversion inside plate-fin heat exchangers and expansion turbines in the supercritical region. Precooling to a temperature between 150 and 100 K will be obtained from a mixed refrigerant cycle similar to the systems used successfully in natural gas liquefaction plants. The final cooling will be produced by two Brayton cycles, both having several expansion turbines in series. The selected overall process has still a number of parameters, which can be varied. The optimum, i.e. the final choice will depend mainly on the quality of the available components. Key components are the expansion turbines of the two Brayton cycles and the main recycle compressor, which may be common to both Brayton cycles. A six-stage turbo-compressor with intercooling between the stages is expected to be the optimum choice here. Each stage may consist of several wheels in series. To make such a high efficient and cost-effective compressor feasible, one has to choose a refrigerant, which has a higher molecular weight than helium. The present preferred choice is a mixture of helium and neon with a molecular weight of about 8 kg/kmol. Such an expensive refrigerant requires that the whole refrigeration loop

  1. Fuel cycles

    International Nuclear Information System (INIS)

    AECL publications, from the open literature, on fuels and fuel cycles used in CANDU reactors are listed in this bibliography. The accompanying index is by subject. The bibliography will be brought up to date periodically

  2. Fes cycling

    Directory of Open Access Journals (Sweden)

    Berkelmans Rik

    2008-01-01

    Full Text Available Many research with functional electrical stimulation (FES has been done to regain mobility and for health benefits. Better results have been reported for FES-cycling than for FES-walking. The majority of the subjects during such research are people with a spinal cord injury (SCI, cause they often lost skin sensation. Besides using surface stimulation also implanted stimulators can be used. This solves the skin sensation problem, but needs a surgery. Many physiological effects of FES-cycling has been reported, e.g., increase of muscles, better blood flow, reduction of pressure ulcers, improved self-image and some reduction of bone mineral density (BMD loss. Also people with an incomplete SCI benefit by FES-cycling, e.g. cycling time without FES, muscle strength and also the walking abilities increased. Hybrid exercise gives an even better cardiovascular training. Presently 4 companies are involved in FES-cycling. They all have a stationary mobility trainer. Two of them also use an outdoor tricycle. One combined with voluntary arm cranking. By optimizing the stimulation parameters the power output and fatigue resistance will increase, but will still be less compared to voluntary cycling.

  3. Progress in Finite Time Thermodynamic Studies for Internal Combustion Engine Cycles

    Directory of Open Access Journals (Sweden)

    Yanlin Ge

    2016-04-01

    Full Text Available On the basis of introducing the origin and development of finite time thermodynamics (FTT, this paper reviews the progress in FTT optimization for internal combustion engine (ICE cycles from the following four aspects: the studies on the optimum performances of air standard endoreversible (with only the irreversibility of heat resistance and irreversible ICE cycles, including Otto, Diesel, Atkinson, Brayton, Dual, Miller, Porous Medium and Universal cycles with constant specific heats, variable specific heats, and variable specific ratio of the conventional and quantum working fluids (WFs; the studies on the optimum piston motion (OPM trajectories of ICE cycles, including Otto and Diesel cycles with Newtonian and other heat transfer laws; the studies on the performance limits of ICE cycles with non-uniform WF with Newtonian and other heat transfer laws; as well as the studies on the performance simulation of ICE cycles. In the studies, the optimization objectives include work, power, power density, efficiency, entropy generation rate, ecological function, and so on. The further direction for the studies is explored.

  4. Exergoeconomic performance optimization for a steady-flow endoreversible refrigeration model including six typical cycles

    Directory of Open Access Journals (Sweden)

    Lingen Chen, Xuxian Kan, Fengrui Sun, Feng Wu

    2013-01-01

    Full Text Available The operation of a universal steady flow endoreversible refrigeration cycle model consisting of a constant thermal-capacity heating branch, two constant thermal-capacity cooling branches and two adiabatic branches is viewed as a production process with exergy as its output. The finite time exergoeconomic performance optimization of the refrigeration cycle is investigated by taking profit rate optimization criterion as the objective. The relations between the profit rate and the temperature ratio of working fluid, between the COP (coefficient of performance and the temperature ratio of working fluid, as well as the optimal relation between profit rate and the COP of the cycle are derived. The focus of this paper is to search the compromised optimization between economics (profit rate and the utilization factor (COP for endoreversible refrigeration cycles, by searching the optimum COP at maximum profit, which is termed as the finite-time exergoeconomic performance bound. Moreover, performance analysis and optimization of the model are carried out in order to investigate the effect of cycle process on the performance of the cycles using numerical example. The results obtained herein include the performance characteristics of endoreversible Carnot, Diesel, Otto, Atkinson, Dual and Brayton refrigeration cycles.

  5. Exergoeconomic performance optimization for a steady-flow endoreversible refrigeration model including six typical cycles

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Lingen; Kan, Xuxian; Sun, Fengrui; Wu, Feng [College of Naval Architecture and Power, Naval University of Engineering, Wuhan 430033 (China)

    2013-07-01

    The operation of a universal steady flow endoreversible refrigeration cycle model consisting of a constant thermal-capacity heating branch, two constant thermal-capacity cooling branches and two adiabatic branches is viewed as a production process with exergy as its output. The finite time exergoeconomic performance optimization of the refrigeration cycle is investigated by taking profit rate optimization criterion as the objective. The relations between the profit rate and the temperature ratio of working fluid, between the COP (coefficient of performance) and the temperature ratio of working fluid, as well as the optimal relation between profit rate and the COP of the cycle are derived. The focus of this paper is to search the compromised optimization between economics (profit rate) and the utilization factor (COP) for endoreversible refrigeration cycles, by searching the optimum COP at maximum profit, which is termed as the finite-time exergoeconomic performance bound. Moreover, performance analysis and optimization of the model are carried out in order to investigate the effect of cycle process on the performance of the cycles using numerical example. The results obtained herein include the performance characteristics of endoreversible Carnot, Diesel, Otto, Atkinson, Dual and Brayton refrigeration cycles.

  6. Supercritical Water Reactor Cycle for Medium Power Applications

    Energy Technology Data Exchange (ETDEWEB)

    BD Middleton; J Buongiorno

    2007-04-25

    Scoping studies for a power conversion system based on a direct-cycle supercritical water reactor have been conducted. The electric power range of interest is 5-30 MWe with a design point of 20 MWe. The overall design objective is to develop a system that has minimized physical size and performs satisfactorily over a broad range of operating conditions. The design constraints are as follows: Net cycle thermal efficiency {ge}20%; Steam turbine outlet quality {ge}90%; and Pumping power {le}2500 kW (at nominal conditions). Three basic cycle configurations were analyzed. Listed in order of increased plant complexity, they are: (1) Simple supercritical Rankine cycle; (2) All-supercritical Brayton cycle; and (3) Supercritical Rankine cycle with feedwater preheating. The sensitivity of these three configurations to various parameters, such as reactor exit temperature, reactor pressure, condenser pressure, etc., was assessed. The Thermoflex software package was used for this task. The results are as follows: (a) The simple supercritical Rankine cycle offers the greatest hardware simplification, but its high reactor temperature rise and reactor outlet temperature may pose serious problems from the viewpoint of thermal stresses, stability and materials in the core. (b) The all-supercritical Brayton cycle is not a contender, due to its poor thermal efficiency. (c) The supercritical Rankine cycle with feedwater preheating affords acceptable thermal efficiency with lower reactor temperature rise and outlet temperature. (d) The use of a moisture separator improves the performance of the supercritical Rankine cycle with feedwater preheating and allows for a further reduction of the reactor outlet temperature, thus it was selected for the next step. Preliminary engineering design of the supercritical Rankine cycle with feedwater preheating and moisture separation was performed. All major components including the turbine, feedwater heater, feedwater pump, condenser, condenser pump

  7. Koszul cycles

    CERN Document Server

    Bruns, Winfreid; Römer, Tim

    2010-01-01

    We prove regularity bounds for Koszul cycles holding for every ideal of dimension at most 1 in a polynomial ring. We generalize the lower bound for the Green-Lazarsfeld index of Veronese rings we proved in arXiv:0902.2431 to the multihomogeneous setting.

  8. Happy Cycling

    DEFF Research Database (Denmark)

    Geert Jensen, Birgitte; Nielsen, Tom

    2013-01-01

    og Interaktions Design, Aarhus Universitet under opgave teamet: ”Happy Cycling City – Aarhus”. Udfordringen i studieopgaven var at vise nye attraktive løsningsmuligheder i forhold til cyklens og cyklismens integration i byrum samt at påpege relationen mellem design og overordnede diskussioner af...

  9. Glacial cycles

    DEFF Research Database (Denmark)

    Kaufmann, R. K.; Juselius, Katarina

    and compare the accuracy of their in-sample simulations. Results indicate that strong statistical associations between endogenous climate variables are not enough for statistical models to reproduce glacial cycles. Rather, changes in solar insolation associated with changes in Earth's orbit are needed...

  10. Efficient cycles for carbon capture CLC power plants based on thermally balanced redox reactors

    KAUST Repository

    Iloeje, Chukwunwike

    2015-10-01

    © 2015 Elsevier Ltd. The rotary reactor differs from most alternative chemical looping combustion (CLC) reactor designs because it maintains near-thermal equilibrium between the two stages of the redox process by thermally coupling channels undergoing oxidation and reduction. An earlier study showed that this thermal coupling between the oxidation and reduction reactors increases the efficiency by up to 2% points when implemented in a regenerative Brayton cycle. The present study extends this analysis to alternative CLC cycles with the objective of identifying optimal configurations and design tradeoffs. Results show that the increased efficiency from reactor thermal coupling applies only to cycles that are capable of exploiting the increased availability in the reduction reactor exhaust. Thus, in addition to the regenerative cycle, the combined CLC cycle and the combined-regenerative CLC cycle are suitable for integration with the rotary reactor. Parametric studies are used to compare the sensitivity of the different cycle efficiencies to parameters like pressure ratio, turbine inlet temperature, carrier-gas fraction and purge steam generation. One of the key conclusions from this analysis is that while the optimal efficiency for regenerative CLC cycle was the highest of the three (56% at 3. bars, 1200. °C), the combined-regenerative cycle offers a trade-off that combines a reasonably high efficiency (about 54% at 12. bars, 1200. °C) with much lower gas volumetric flow rate and consequently, smaller reactor size. Unlike the other two cycles, the optimal compressor pressure ratio for the regenerative cycle is weakly dependent on the design turbine inlet temperature. For the regenerative and combined regenerative cycles, steam production in the regenerator below 2× fuel flow rate improves exhaust recovery and consequently, the overall system efficiency. Also, given that the fuel side regenerator flow is unbalanced, it is more efficient to generate steam from the

  11. Quasi-static Cycle Performance Analysis of Micro Modular Reactor for Heat Sink Temperature Variation

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Seong Kuk; Lee, Jekyoung; Ahn, Yoonhan; Lee, Jeong Ik [KAIST, Daejeon (Korea, Republic of); Cha, Jae Eun [KAERI, Daejeon (Korea, Republic of)

    2015-10-15

    A Supercritical CO{sub 2} (S-CO{sub 2}) cycle has potential for high thermal efficiency in the moderate turbine inlet temperature (450 - 750 .deg. C) and achieving compact system size because of small specific volume and simple cycle layouts. Owing to small specific volume of S-CO{sub 2} and the development of heat exchanger technology, it can accomplish complete modularization of the system. The previous works focused on the cycle performance analysis for the design point only. However, the heat sink temperature can be changed depending on the ambient atmosphere condition, i.e. weather, seasonal change. This can influence the compressor inlet temperature, which alters the cycle operating condition overall. To reflect the heat sink temperature variation, a quasi-static analysis code for a simple recuperated S-CO{sub 2} Brayton cycle has been developed by the KAIST research team. Thus, cycle performance analysis is carried out with a compressor inlet temperature variation in this research. In the case of dry air-cooling system, the ambient temperature of the local surrounding can affect the compressor inlet temperature. As the compressor inlet temperature increases, thermal efficiency and generated electricity decrease. As further works, the experiment of S-CO{sub 2} integral test loop will be performed to validate in-house codes, such as KAIST{sub T}MD and the quasi-static code.

  12. Sulfur cycle

    Digital Repository Service at National Institute of Oceanography (India)

    LokaBharathi, P.A.

    Ecological Society Symposium held jointly with the Linnean Society of London. Oxford: Blackwell. Huston MH and Smith T (1987) Plant succession: Life history and competition. American Naturalist 130: 168–198. Sulfur Cycle P A Loka Bharathi, National Institute.... Vegetatio 110: 115–147. Odum EP (1969) The strategy of ecosystem development. Science 164: 262–270. Walker KR and Alberstadt LP(1975) Ecological succession asan aspect of structure in fossil communities. Paleobiology 1: 238–257. Author's personal copy S 4 O...

  13. 脉冲爆震发动机热力循环性能分析%The Analysis of Pulse Detonation Engine Thermodynamic Cycle Performance

    Institute of Scientific and Technical Information of China (English)

    陈鑫; 于锦禄; 何立明; 杨帆

    2011-01-01

    The propagation mechanism of detonation wave procreant in mixed gas is analyzed.The basic relation between the parameters of the detonation wave in propagation process is established.At the different pressure ratios, the detonation wave characteristic parameters are calculated, the backwards and forwards mach numbers of the detonation wave are obtained.The calculation method of thermal efficiency and entropy production with detonating combustion is deduced.At the different pressure ratios, the variety rule of thermal efficiency and entropy production are calculated.Finally, the detonation cycle is compared with Brayton cycle and Humphrey cycle, the results show that the detonation cycle is higher than the Brayton cycle and the Humphrey cycle in cycle thermal efficiency.%分析了混合气体中燃烧产生的爆震波的传播机理,建立了爆震波传播过程中参数的基本关系.在不同进气增压比条件下,对爆震波的特性参数进行了计算,得出了爆震波前后气流参数的变化关系;并计算了爆震燃烧循环过程的热效率和爆震燃烧不可逆过程中熵增随爆震波前马赫数的变化规律.最后将爆震燃烧循环与布莱顿循环、甘福利循环进行比较,结果表明:爆震燃烧循环具有更高的有效循环功和循环热效率.

  14. Metal corrosion in a supercritical carbon dioxide - liquid sodium power cycle.

    Energy Technology Data Exchange (ETDEWEB)

    Moore, Robert Charles; Conboy, Thomas M.

    2012-02-01

    A liquid sodium cooled fast reactor coupled to a supercritical carbon dioxide Brayton power cycle is a promising combination for the next generation nuclear power production process. For optimum efficiency, a microchannel heat exchanger, constructed by diffusion bonding, can be used for heat transfer from the liquid sodium reactor coolant to the supercritical carbon dioxide. In this work, we have reviewed the literature on corrosion of metals in liquid sodium and carbon dioxide. The main conclusions are (1) pure, dry CO{sub 2} is virtually inert but can be highly corrosive in the presence of even ppm concentrations of water, (2) carburization and decarburization are very significant mechanism for corrosion in liquid sodium especially at high temperature and the mechanism is not well understood, and (3) very little information could be located on corrosion of diffusion bonded metals. Significantly more research is needed in all of these areas.

  15. Exergoeconomic performance optimization of an endoreversible intercooled regenerative Brayton combined heat and power plant coupled to variable-temperature heat reservoirs

    Directory of Open Access Journals (Sweden)

    Bo Yang, Lingen Chen, Fengrui Sun

    2012-01-01

    Full Text Available An endoreversible intercooled regenerative Brayton combined heat and power (CHP plant model coupled to variable-temperature heat reservoirs is established. The exergoeconomic performance of the CHP plant is investigated using finite time thermodynamics. The analytical formulae about dimensionless profit rate and exergy efficiency of the CHP plant with the heat resistance losses in the hot-, cold- and consumer-side heat exchangers, the intercooler and the regenerator are deduced. By taking the maximum profit rate as the objective, the heat conductance allocation among the five heat exchangers and the choice of intercooling pressure ratio are optimized by numerical examples, the characteristic of the optimal dimensionless profit rate versus corresponding exergy efficiency is investigated. When the optimization is performed further with respect to the total pressure ratio, a double-maximum profit rate is obtained. The effects of the design parameters on the double-maximum dimensionless profit rate and corresponding exergy efficiency, optimal total pressure ratio and optimal intercooling pressure ratio are analyzed in detail, and it is found that there exist an optimal consumer-side temperature and an optimal thermal capacitance rate matching between the working fluid and the heat reservoir, respectively, corresponding to a thrice-maximum dimensionless profit rate.

  16. Exergoeconomic performance optimization of an endoreversible intercooled regenerative Brayton combined heat and power plant coupled to variable-temperature heat reservoirs

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Bo; Chen, Lingen; Sun, Fengrui [College of Naval Architecture and Power, Naval University of Engineering, Wuhan 430033 (China)

    2012-07-01

    An endoreversible intercooled regenerative Brayton combined heat and power (CHP) plant model coupled to variable-temperature heat reservoirs is established. The exergoeconomic performance of the CHP plant is investigated using finite time thermodynamics. The analytical formulae about dimensionless profit rate and exergy efficiency of the CHP plant with the heat resistance losses in the hot-, cold- and consumer-side heat exchangers, the intercooler and the regenerator are deduced. By taking the maximum profit rate as the objective, the heat conductance allocation among the five heat exchangers and the choice of intercooling pressure ratio are optimized by numerical examples, the characteristic of the optimal dimensionless profit rate versus corresponding exergy efficiency is investigated. When the optimization is performed further with respect to the total pressure ratio, a double-maximum profit rate is obtained. The effects of the design parameters on the double-maximum dimensionless profit rate and corresponding exergy efficiency, optimal total pressure ratio and optimal intercooling pressure ratio are analyzed in detail, and it is found that there exist an optimal consumer-side temperature and an optimal thermal capacitance rate matching between the working fluid and the heat reservoir, respectively, corresponding to a thrice-maximum dimensionless profit rate.

  17. Safe cycling!

    CERN Document Server

    Anaïs Schaeffer

    2012-01-01

    The HSE Unit will be running a cycling safety campaign at the entrances to CERN's restaurants on 14, 15 and 16 May. Pop along to see if they can persuade you to get back in the saddle!   With summer on its way, you might feel like getting your bike out of winter storage. Well, the HSE Unit has come up with some original ideas to remind you of some of the most basic safety rules. This year, the prevention campaign will be focussing on three themes: "Cyclists and their equipment", "The bicycle on the road", and "Other road users". This is an opportunity to think about the condition of your bike as well as how you ride it. From 14 to 16 May, representatives of the Swiss Office of Accident Prevention and the Touring Club Suisse will join members of the HSE Unit at the entrances to CERN's restaurants to give you advice on safe cycling (see box). They will also be organising three activity stands where you can test your knowle...

  18. Thermal analysis of heat and power plant with high temperature reactor and intermediate steam cycle

    Science.gov (United States)

    Fic, Adam; Składzień, Jan; Gabriel, Michał

    2015-03-01

    Thermal analysis of a heat and power plant with a high temperature gas cooled nuclear reactor is presented. The main aim of the considered system is to supply a technological process with the heat at suitably high temperature level. The considered unit is also used to produce electricity. The high temperature helium cooled nuclear reactor is the primary heat source in the system, which consists of: the reactor cooling cycle, the steam cycle and the gas heat pump cycle. Helium used as a carrier in the first cycle (classic Brayton cycle), which includes the reactor, delivers heat in a steam generator to produce superheated steam with required parameters of the intermediate cycle. The intermediate cycle is provided to transport energy from the reactor installation to the process installation requiring a high temperature heat. The distance between reactor and the process installation is assumed short and negligable, or alternatively equal to 1 km in the analysis. The system is also equipped with a high temperature argon heat pump to obtain the temperature level of a heat carrier required by a high temperature process. Thus, the steam of the intermediate cycle supplies a lower heat exchanger of the heat pump, a process heat exchanger at the medium temperature level and a classical steam turbine system (Rankine cycle). The main purpose of the research was to evaluate the effectiveness of the system considered and to assess whether such a three cycle cogeneration system is reasonable. Multivariant calculations have been carried out employing the developed mathematical model. The results have been presented in a form of the energy efficiency and exergy efficiency of the system as a function of the temperature drop in the high temperature process heat exchanger and the reactor pressure.

  19. Thermal analysis of heat and power plant with high temperature reactor and intermediate steam cycle

    Directory of Open Access Journals (Sweden)

    Fic Adam

    2015-03-01

    Full Text Available Thermal analysis of a heat and power plant with a high temperature gas cooled nuclear reactor is presented. The main aim of the considered system is to supply a technological process with the heat at suitably high temperature level. The considered unit is also used to produce electricity. The high temperature helium cooled nuclear reactor is the primary heat source in the system, which consists of: the reactor cooling cycle, the steam cycle and the gas heat pump cycle. Helium used as a carrier in the first cycle (classic Brayton cycle, which includes the reactor, delivers heat in a steam generator to produce superheated steam with required parameters of the intermediate cycle. The intermediate cycle is provided to transport energy from the reactor installation to the process installation requiring a high temperature heat. The distance between reactor and the process installation is assumed short and negligable, or alternatively equal to 1 km in the analysis. The system is also equipped with a high temperature argon heat pump to obtain the temperature level of a heat carrier required by a high temperature process. Thus, the steam of the intermediate cycle supplies a lower heat exchanger of the heat pump, a process heat exchanger at the medium temperature level and a classical steam turbine system (Rankine cycle. The main purpose of the research was to evaluate the effectiveness of the system considered and to assess whether such a three cycle cogeneration system is reasonable. Multivariant calculations have been carried out employing the developed mathematical model. The results have been presented in a form of the energy efficiency and exergy efficiency of the system as a function of the temperature drop in the high temperature process heat exchanger and the reactor pressure.

  20. Thermogravitational cycles: theoretical framework and example of an electric thermogravitational generator based on balloon inflation/deflation

    CERN Document Server

    Aouane, Kamel; Ford, Ian J; Elson, Tim P; Nightingale, Christopher

    2015-01-01

    Several studies have combined heat and gravitational energy exchanges to create novel heat engines. A common theoretical framework is developed here to describe thermogravitational cycles which have the same efficiencies as the Carnot, Rankine or Brayton cycles. Considering a working fluid, enclosed in a balloon, inside a column filled with a transporting fluid, the cycle is composed of four steps. Starting from the top of the column, the balloon goes down, receives heat from a hot source at the bottom, rises and delivers heat to a cold source at the top. Unlike classic power cycles which need external work to operate the compressor, thermogravitational cycles can operate as "pure power cycle" where no work is provided to drive the cycle. To illustrate this concept, the prototype of a thermogravitational electrical generator is presented. It uses a hot source of low temperature (average temperature near 57{\\deg}C) and relies on the gravitational energy exchanges of an organic fluid inside a balloon attached t...

  1. Design consideration of supercritical CO2 power cycle integral experiment loop

    International Nuclear Information System (INIS)

    Supercritical-CO2 Brayton cycle has been recently gaining a lot of attention for the mild temperature (450–650 °C) heat source application due to its high efficiency and compact footprint as the system layout of S–CO2 cycle is simple and small turbomachinery and compact micro-channel heat exchangers are utilized. As CO2 properties behave more like an incompressible fluid near the critical point (30.98 °C, 7.38 MPa), the control of compressor operating condition and stability is the key technology that influences the cycle efficiency. Based on the previous works on the S–CO2 test facilities from various research institutions, a Korean research team designed the SCIEL (Supercritical CO2 Integral Experiment Loop) to achieve higher efficiency with higher pressure ratio with S–CO2 power cycle compared to other pre-existing facilities. This paper will describe the underlying design principles of the integral experiment facility and the current status of SCIEL which is being constructed in KAERI (Korea Atomic Energy Research Institute). - Highlights: • Previous studies of small scale S–CO2 test loops are reviewed thoroughly. • High pressure ratio S–CO2 experiment facility was designed and constructed. • The S–CO2 compressor operation stability was checked. • Preliminary data were obtained

  2. Applicability of the minimum entropy generation method for optimizing thermodynamic cycles

    Institute of Scientific and Technical Information of China (English)

    Cheng Xue-Tao; Liang Xin-Gang

    2013-01-01

    Entropy generation is often used as a figure of merit in thermodynamic cycle optimizations.In this paper,it is shown that the applicability of the minimum entropy generation method to optimizing output power is conditional.The minimum entropy generation rate and the minimum entropy generation number do not correspond to the maximum output power when the total heat into the system of interest is not prescribed.For the cycles whose working medium is heated or cooled by streams with prescribed inlet temperatures and prescribed heat capacity flow rates,it is theoretically proved that both the minimum entropy generation rate and the minimum entropy generation number correspond to the maximum output power when the virtual entropy generation induced by dumping the used streams into the environment is considered.However,the minimum principle of entropy generation is not tenable in the case that the virtual entropy generation is not included,because the total heat into the system of interest is not fixed.An irreversible Carnot cycle and an irreversible Brayton cycle are analysed.The minimum entropy generation rate and the minimum entropy generation number do not correspond to the maximum output power if the heat into the system of interest is not prescribed.

  3. Evaluation of High-Temperature Tensile Property of Diffusion Bond of Austenitic Alloys for S-CO2 Cycle Heat Exchangers

    International Nuclear Information System (INIS)

    To improve the inherent safety of the sodium-cooled fast reactor (SFR), the supercritical CO2 (S-CO2) Brayton cycle is being considered as an alternative power conversion system to steam the Rankine cycle. In the S-CO2 system, a PCHE (printed circuit heat exchanger) is being considered. In this type of heat exchangers, diffusion bonding is used for joining the thin plates. In this study, the diffusion bonding characteristics of various austenitic alloys were evaluated. The tensile properties were measured at temperatures starting from the room temperature up to 650℃. For the 316H and 347H types of stainless steel, the tensile ductility was well maintained up to 550℃. However, the Incoloy 800HT showed lower strength and ductility at all temperatures. The microstructure near the bond line was examined to understand the reason for the loss of ductility at high temperatures

  4. Investigation of CO{sub 2} Recovery System Design in Supercritical Carbon Dioxide Power Cycle for Sodium-cooled Fast Reactor

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Min Seok; Jung, Hwa-Young; Ahn, Yoonhan; Cho, Seong Kuk; Lee, Jeong Ik [KAIST, Daejeon (Korea, Republic of)

    2015-10-15

    These are mainly possible because the S-CO{sub 2} Brayton cycle has lower compressing work than other Brayton cycles due to its high density and low compressibility near the critical point. These attributes make easier to achieve higher turbine inlet temperature. Furthermore, the coolant chemistry control and component cooling systems are relatively simple for the S-CO{sub 2} cycle unlike the steam Rankine cycle, and therefore the total plant footprint can be greatly reduced further. However, certain amount of leakage flow is inevitable in the rotating turbo-machinery since the S-CO{sub 2} power cycle is a highly pressurized system. A computational model of critical flow in turbo-machinery seal is essential to predict the leakage flow and calculate the required total mass of working fluid in S-CO{sub 2} power system. Before designing a computational model of critical flow in turbo-machinery seal, this paper will identify what the issues are in predicting leakage flow and how these issues can be successfully addressed. Also, suitability of this solution in a large scale S-CO{sub 2} power cycle will be discussed, because this solution is for the small scale. S-CO{sub 2} power cycle has gained interest especially for the SFR application as an alternative to the conventional steam Rankine cycle, since S-CO{sub 2} power cycle can provide better performance and enhance safety. This paper discussed what the problem in leakage flow is and how to deal with this problem at present. High cavity pressure causing instability of gas foil bearing and large windage losses can be reduced by booster pump used to scavenge the gas in the rotor cavity. Also, labyrinth seals can be another good solution to decrease the rotor cavity pressure. Additionally, difference between large and small scale S-CO{sub 2} power cycle in turbo-machinery leakage is addressed. It is shown that optimization of CO{sub 2} recovery system design is more important to large scale S-CO{sub 2} power cycle. For

  5. 基于爆震燃烧的燃气轮机理想热力循环分析%Ideal Thermodynamic Cycle Analysis of Gas Turbine Based on Detonation Combustion

    Institute of Scientific and Technical Information of China (English)

    李晓丰; 肖俊峰; 王玮; 王峰; 郑龙席

    2016-01-01

    鉴于爆震燃烧具有自增压、传播速度快等优点,提出了将燃气轮机中等压燃烧替换为爆震燃烧的理念,并建立了基于爆震燃烧的燃气轮机理想热力循环模型,对比研究了DCGT( detonation cycle of gas turbine)、Brayton和Humphrey 3种循环燃气轮机的综合性能。在压气机压比、吸热量和透平背压相同的条件下,数据分析结果表明DCGT循环燃气轮机较其他2种循环更具优势,在压比为16时其循环热效率较Brayton循环提高15�4%,燃料消耗率降低13�5%;DCGT循环燃气轮机在压比为6�6时的总体性能与压比为16时的Brayton循环相当。%In view of self⁃pressurized, high flame propagation speed and other characteristics of detonation combus⁃tion, it was proposed that the constant pressure combustor of gas turbine was replaced by the detonation combustor, and the ideal thermodynamic cycle model of gas turbine based on detonation combustion was established; then the performances of DCGT( Detonation Cycle of Gas Turbine) , Brayton and Humphrey thermodynamic cycle were com⁃paratively analyzed. On condition that the parameters of combustor inlet, the fuel and the turbine backpressure are the same, the results show that the performance of DCGT is, compared with the other two, better. When the com⁃pressor pressure ratio is 16, the cycle thermal efficiency of detonation gas turbine is increased by 15�4% compared with Brayton cycle and the fuel consumption rate is decreased by 13�5%. The performance of DCGT at pressure ra⁃tio 6�6 is equivalent to that of Brayton cycle gas turbine at pressure ratio 16.

  6. Alternative analysis to increase the power in combined-cycle power plants; Analisis de alternativas para el incremento de potencia en plantas termoelectricas de Ciclo Combinado

    Energy Technology Data Exchange (ETDEWEB)

    Pacheco Cruz, Hector; Arriola Medellin, Alejandro M. [Gerencia de Procesos Termicos, Instituto de Investigaciones Electricas, Cuernavaca, Morelos (Mexico)]. E-mail: hpacheco@iie.org.mx; aarriola@iie.org.mx

    2010-11-15

    The electricity industry traditionally had two thermodynamic cycles for power generation: conventional steam turbine (Rankine cycle) used to supply a base load during the day, and gas turbines (Brayton cycle), for its speed response, normally used to cover peak loads. However, to provide variable peak loads, the gas turbine, as a volumetric machine is affected by the change in air density by changing the combustion temperature. This paper shows the scheme of integration of both systems, that it's known as combined cycle and the different options that would have these power plants, to maintain or increase their power in variable ambient conditions. It analyzes different options, such as: 1. Supplementary fire in the stove. 2. Air cooling intake in the gas turbine (evaporation system or mechanical system). 3. Steam injection in the combustion chamber. [Spanish] La industria electrica tradicionalmente a contado con dos ciclos termodinamicos para generacion electrica: las turbinas convencionales de vapor (ciclo de Rankine) se utilizan para suministrar una carga base durante el dia, y las turbinas de gas (ciclo de Brayton), por su rapidez de respuesta, se utilizan normalmente para cubrir las cargas pico. Sin embargo, para suministrar las cargas variables pico, la turbina a gas, por ser una maquina volumetrica, se ve afectada por el cambio de la densidad del aire de combustion al cambiar la temperatura ambiente. En este trabajo se muestra el esquema de integracion de ambos sistemas, en lo que se conoce como ciclo combinado y las diferentes opciones que tendrian estas plantas de generacion electrica para mantener o incrementar su potencia en condiciones ambiente variable. Para ello se analizan diferentes opciones, tales como: 1.- Combustion suplementaria en el recuperador de calor. 2.- Enfriamiento del aire de admision a la turbina de gas (mediante un sistema de evaporacion o mediante un sistema mecanico). 3.- Inyeccion de vapor a la camara de combustion. Palabras

  7. Finite time exergoeconomic performance optimization for an irreversible universal steady flow variable-temperature heat reservoir heat pump cycle model

    Directory of Open Access Journals (Sweden)

    Huijun Feng, Lingen Chen, Fengrui Sun

    2010-11-01

    Full Text Available An irreversible universal steady flow heat pump cycle model with variable-temperature heat reservoirs and the losses of heat-resistance and internal irreversibility is established by using the theory of finite time thermodynamics. The universal heat pump cycle model consists of two heat-absorbing branches, two heat-releasing branches and two adiabatic branches. Expressions of heating load, coefficient of performance (COP and profit rate of the universal heat pump cycle model are derived, respectively. By means of numerical calculations, heat conductance distributions between hot- and cold-side heat exchangers are optimized by taking the maximum profit rate as objective. There exist an optimal heat conductance distribution and an optimal thermal capacity rate matching between the working fluid and heat reservoirs which lead to a double maximum profit rate. The effects of internal irreversibility, total heat exchanger inventory, thermal capacity rate of the working fluid and heat capacity ratio of the heat reservoirs on the optimal finite time exergoeconomic performance of the cycle are discussed in detail. The results obtained herein include the optimal finite time exergoeconomic performances of endoreversible and irreversible, constant- and variable-temperature heat reservoir Brayton, Otto, Diesel, Atkinson, Dual, Miller and Carnot heat pump cycles.

  8. Combined Turbine and Cycle Optimization for Organic Rankine Cycle Power Systems—Part B: Application on a Case Study

    Directory of Open Access Journals (Sweden)

    Angelo La Seta

    2016-05-01

    Full Text Available Organic Rankine cycle (ORC power systems have recently emerged as promising solutions for waste heat recovery in low- and medium-size power plants. Their performance and economic feasibility strongly depend on the expander. The design process and efficiency estimation are particularly challenging due to the peculiar physical properties of the working fluid and the gas-dynamic phenomena occurring in the machine. Unlike steam Rankine and Brayton engines, organic Rankine cycle expanders combine small enthalpy drops with large expansion ratios. These features yield turbine designs with few highly-loaded stages in supersonic flow regimes. Part A of this two-part paper has presented the implementation and validation of the simulation tool TURAX, which provides the optimal preliminary design of single-stage axial-flow turbines. The authors have also presented a sensitivity analysis on the decision variables affecting the turbine design. Part B of this two-part paper presents the first application of a design method where the thermodynamic cycle optimization is combined with calculations of the maximum expander performance using the mean-line design tool described in part A. The high computational cost of the turbine optimization is tackled by building a model which gives the optimal preliminary design of an axial-flow turbine as a function of the cycle conditions. This allows for estimating the optimal expander performance for each operating condition of interest. The test case is the preliminary design of an organic Rankine cycle turbogenerator to increase the overall energy efficiency of an offshore platform. For an increase in expander pressure ratio from 10 to 35, the results indicate up to 10% point reduction in expander performance. This corresponds to a relative reduction in net power output of 8.3% compared to the case when the turbine efficiency is assumed to be 80%. This work also demonstrates that this approach can support the plant designer

  9. Essays on economic cycles

    NARCIS (Netherlands)

    Groot, de E.A. (Bert)

    2006-01-01

    Schumpeter’s line of thought of multiple economic cycles is further investigated. The existence of multiple cycles in economic variables is demonstrated. In basic innovations five different cycles are found. Multiple cycle structures are shown in various macro-economic variables from the United King

  10. The business cycle and the life cycle

    OpenAIRE

    Paul Gomme; Richard Rogerson; Peter Rupert; Randall Wright

    2004-01-01

    The paper documents how cyclical fluctuations in market work vary over the life cycle and then assesses the predictions of a life-cycle version of the growth model for those observations. The analysis yields a simple but striking finding. The main discrepancy between the model and that data lies in the inability of the model to account for fluctuations in hours for individuals in the first half of their life cycle. The predictions for those in the latter half of the life cycle are quite close...

  11. The Solar Cycle

    CERN Document Server

    Hathaway, David H

    2015-01-01

    The Solar Cycle is reviewed. The 11-year cycle of solar activity is characterized by the rise and fall in the numbers and surface area of sunspots. A number of other solar activity indicators also vary in association with the sunspots including; the 10.7cm radio flux, the total solar irradiance, the magnetic field, flares and coronal mass ejections, geomagnetic activity, galactic cosmic ray fluxes, and radioisotopes in tree rings and ice cores. Individual solar cycles are characterized by their maxima and minima, cycle periods and amplitudes, cycle shape, the equatorward drift of the active latitudes, hemispheric asymmetries, and active longitudes. Cycle-to-cycle variability includes the Maunder Minimum, the Gleissberg Cycle, and the Gnevyshev-Ohl (even-odd) Rule. Short-term variability includes the 154-day periodicity, quasi-biennial variations, and double-peaked maxima. We conclude with an examination of prediction techniques for the solar cycle and a closer look at cycles 23 and 24.

  12. Solar cycle 25: another moderate cycle?

    CERN Document Server

    Cameron, Robert H; Schuessler, Manfred

    2016-01-01

    Surface flux transport simulations for the descending phase of cycle 24 using random sources (emerging bipolar magnetic regions) with empirically determined scatter of their properties provide a prediction of the axial dipole moment during the upcoming activity minimum together with a realistic uncertainty range. The expectation value for the dipole moment around 2020 $(2.5\\pm1.1\\,$G) is comparable to that observed at the end of cycle 23 (about $2\\,$G). The empirical correlation between the dipole moment during solar minimum and the strength of the subsequent cycle thus suggests that cycle 25 will be of moderate amplitude, not much higher than that of the current cycle. However, the intrinsic uncertainty of such predictions resulting from the random scatter of the source properties is considerable and fundamentally limits the reliability with which such predictions can be made before activity minimum is reached.

  13. Solar Cycle 25: Another Moderate Cycle?

    Science.gov (United States)

    Cameron, R. H.; Jiang, J.; Schüssler, M.

    2016-06-01

    Surface flux transport simulations for the descending phase of Cycle 24 using random sources (emerging bipolar magnetic regions) with empirically determined scatter of their properties provide a prediction of the axial dipole moment during the upcoming activity minimum together with a realistic uncertainty range. The expectation value for the dipole moment around 2020 (2.5 ± 1.1 G) is comparable to that observed at the end of Cycle 23 (about 2 G). The empirical correlation between the dipole moment during solar minimum and the strength of the subsequent cycle thus suggests that Cycle 25 will be of moderate amplitude, not much higher than that of the current cycle. However, the intrinsic uncertainty of such predictions resulting from the random scatter of the source properties is considerable and fundamentally limits the reliability with which such predictions can be made before activity minimum is reached.

  14. Cycling in Sydney, Australia

    Directory of Open Access Journals (Sweden)

    Alexis Zander

    2013-01-01

    Full Text Available Introduction. Cycling can be an enjoyable way to meet physical activity recommendations and is suitable for older people; however cycling participation by older Australians is low. This qualitative study explored motivators, enablers, and barriers to cycling among older people through an age-targeted cycling promotion program. Methods. Seventeen adults who aged 50–75 years participated in a 12-week cycling promotion program which included a cycling skills course, mentor, and resource pack. Semistructured interviews at the beginning and end of the program explored motivators, enablers, and barriers to cycling. Results. Fitness and recreation were the primary motivators for cycling. The biggest barrier was fear of cars and traffic, and the cycling skills course was the most important enabler for improving participants’ confidence. Reported outcomes from cycling included improved quality of life (better mental health, social benefit, and empowerment and improved physical health. Conclusions. A simple cycling program increased cycling participation among older people. This work confirms the importance of improving confidence in this age group through a skills course, mentors, and maps and highlights additional strategies for promoting cycling, such as ongoing improvement to infrastructure and advertising.

  15. Life cycle assessment (LCA)

    DEFF Research Database (Denmark)

    Thrane, Mikkel; Schmidt, Jannick Andresen

    2004-01-01

    The chapter introduces Life Cycle Assessment (LCA) and its application according to the ISO 1404043 standards.......The chapter introduces Life Cycle Assessment (LCA) and its application according to the ISO 1404043 standards....

  16. HIV Life Cycle

    Science.gov (United States)

    HIV Overview The HIV Life Cycle (Last updated 9/22/2015; last reviewed 9/22/2015) Key Points HIV gradually destroys the immune ... life cycle. What is the connection between the HIV life cycle and HIV medicines? Antiretroviral therapy (ART) ...

  17. Cycling To Awareness.

    Science.gov (United States)

    Kozak, Stan

    1999-01-01

    Encourages environmental and outdoor educators to promote bicycling. In the community and the curriculum, cycling connects environmental issues, health and fitness, law and citizenship, appropriate technology, and the joy of being outdoors. Describes the Ontario Cycling Association's cycling strategy and its four components: school cycling…

  18. POWER CYCLE AND STRESS ANALYSES FOR HIGH TEMPERATURE GAS-COOLED REACTOR

    International Nuclear Information System (INIS)

    The Department of Energy and the Idaho National Laboratory are developing a Next Generation Nuclear Plant (NGNP) to serve as a demonstration of state-of-the-art nuclear technology. The purpose of the demonstration is two fold (1) efficient low cost energy generation and (2) hydrogen production. Although a next generation plant could be developed as a single-purpose facility, early designs are expected to be dual-purpose. While hydrogen production and advanced energy cycles are still in its early stages of development, research towards coupling a high temperature reactor, electrical generation and hydrogen production is under way. Many aspects of the NGNP must be researched and developed in order to make recommendations on the final design of the plant. Parameters such as working conditions, cycle components, working fluids, and power conversion unit configurations must be understood. Three configurations of the power conversion unit were demonstrated in this study. A three-shaft design with three turbines and four compressors, a combined cycle with a Brayton top cycle and a Rankine bottoming cycle, and a reheated cycle with three stages of reheat were investigated. An intermediate heat transport loop for transporting process heat to a High Temperature Steam Electrolysis (HTSE) hydrogen production plant was used. Helium, CO2, and a 80% nitrogen, 20% helium mixture (by weight) were studied to determine the best working fluid in terms cycle efficiency and development cost. In each of these configurations the relative component size were estimated for the different working fluids. The relative size of the turbomachinery was measured by comparing the power input/output of the component. For heat exchangers the volume was computed and compared. Parametric studies away from the baseline values of the three-shaft and combined cycles were performed to determine the effect of varying conditions in the cycle. This gives some insight into the sensitivity of these cycles to

  19. Predicting the ultimate potential of natural gas SOFC power cycles with CO2 capture - Part A: Methodology and reference cases

    Science.gov (United States)

    Campanari, Stefano; Mastropasqua, Luca; Gazzani, Matteo; Chiesa, Paolo; Romano, Matteo C.

    2016-08-01

    Driven by the search for the highest theoretical efficiency, in the latest years several studies investigated the integration of high temperature fuel cells in natural gas fired power plants, where fuel cells are integrated with simple or modified Brayton cycles and/or with additional bottoming cycles, and CO2 can be separated via chemical or physical separation, oxy-combustion and cryogenic methods. Focusing on Solid Oxide Fuel Cells (SOFC) and following a comprehensive review and analysis of possible plant configurations, this work investigates their theoretical potential efficiency and proposes two ultra-high efficiency plant configurations based on advanced intermediate-temperature SOFCs integrated with a steam turbine or gas turbine cycle. The SOFC works at atmospheric or pressurized conditions and the resulting power plant exceeds 78% LHV efficiency without CO2 capture (as discussed in part A of the work) and 70% LHV efficiency with substantial CO2 capture (part B). The power plants are simulated at the 100 MW scale with a complete set of realistic assumptions about fuel cell (FC) performance, plant components and auxiliaries, presenting detailed energy and material balances together with a second law analysis.

  20. Predicting the ultimate potential of natural gas SOFC power cycles with CO2 capture - Part A: Methodology and reference cases

    Science.gov (United States)

    Campanari, Stefano; Mastropasqua, Luca; Gazzani, Matteo; Chiesa, Paolo; Romano, Matteo C.

    2016-08-01

    Driven by the search for the highest theoretical efficiency, in the latest years several studies investigated the integration of high temperature fuel cells in natural gas fired power plants, where fuel cells are integrated with simple or modified Brayton cycles and/or with additional bottoming cycles, and CO2 can be separated via chemical or physical separation, oxy-combustion and cryogenic methods. Focusing on Solid Oxide Fuel Cells (SOFC) and following a comprehensive review and analysis of possible plant configurations, this work investigates their theoretical potential efficiency and proposes two ultra-high efficiency plant configurations based on advanced intermediate-temperature SOFCs integrated with a steam turbine or gas turbine cycle. The SOFC works at atmospheric or pressurized conditions and the resulting power plant exceeds 78% LHV efficiency without CO2 capture (as discussed in part A of the work) and 70% LHV efficiency with substantial CO2 capture (part B). The power plants are simulated at the 100 MW scale with a complete set of realistic assumptions about fuel cell (FC) performance, plant components and auxiliaries, presenting detailed energy and material balances together with a second law analysis.

  1. Thermodynamic Analysis of Supplementary-Fired Gas Turbine Cycles

    Directory of Open Access Journals (Sweden)

    Bjørn Qvale

    2003-06-01

    Full Text Available

    This paper presents an analysis of the possibilities for improving the efficiency of an indi-rectly biomass-fired gas turbine (IBFGT by supplementary direct gas-firing. The supplementary firing may be based on natural gas, biogas or pyrolysis gas. Intuitively, supplementary firing is expected to result in a high marginal efficiency. The paper shows that depending on the application, this is not always the case.

    The interest in this cycle arises from a recent demonstration of the feasibility of a two-stage gasification process through construction of several plants. The gas from this process could be divided into two streams, one for primary and one for supplementary firing. A preliminary analysis of the ideal, recuperated Brayton cycle shows that for this cycle any supplementary firing will have a marginal efficiency of unity per extra unit of fuel. The same result is obtained for the indirectly fired gas turbine (IFGT and for the supplementary-fired IFGT. These results show that the combination of external firing and internal firing have the potential of reducing or solving some problems associated with the use of biomass both in the recuperated and the indirectly fired gas turbine: The former requires a clean, expensive fuel. The latter is limited in efficiency due to limitations in material temperature of the heat exchanger. Thus, in the case of an IBFGT, it would appear be very appropriate to use a cheap biomass or waste fuel for low temperature combustion and external firing and use natural gas at a high marginal efficiency for high temperature heating. However, it is shown that this is not the case for a simple IBFGT supplementary-fired with natural gas. The marginal efficiency of the natural gas is in this case found to be independent of temperature ratio and lower than for the recuperated gas turbine. Instead, other process changes may be considered in order to obtain a high marginal efficiency on natural gas. Two possibilities

  2. -150℃逆布雷顿空气制冷机动态温降特性研究%Study on the Dynamic Cooling Performance of a-150 ℃ Reverse Brayton Cycle Air Cryocooler

    Institute of Scientific and Technical Information of China (English)

    蔡君伟; 孙皖; 李斌; 李涛; 侯予

    2013-01-01

    A turboexpander having a working wheel with a diameter of 24mm and a plate-fin heat exchanger were applied in a retrofitted -150 ℃ air cryocooler system. A vacuum cryogenic trap (absolute pressure < 10-3 Pa) was used for insulation. The dynamic cooling performance of the whole system was studied under the conditions of different brake wheel configurations. A numerical model in respect of the dynamic cooling performance of the - 150 ℃ air cryocooler system was established. The results show that the brake wheel size significantly affects the cooling performance of the cryocooler, and the lowest system temperature is under -150 ℃. Additionally, the numerical results agree well with the experimental data.%为了研究空气制冷机的动态温降特性,对采用工作轮直径为24 mm的小型透平膨胀机和板翅式换热器的逆布雷顿循环空气制冷机实验台进行了改进.采用高真空绝热冷箱对制冷机进行绝热,可使绝对压力低于10-3 Pa,得到的设计制冷温度为-150℃.对不同进口参数和采用不同直径风机轮的制冷机工况进行了实验研究,获得了透平膨胀机的实际温降曲线;以实验系统为基础建立了数学模型,得到了相应的理论温降曲线.研究结果表明:风机轮尺寸对空气制冷机动态温降过程的影响较大,实验的最低温度低于-150℃;所建理论模型能够较好地预测实际系统温降的过程.

  3. The performance analysis and optimization of helium cryogenic cooling system with reverse Brayton cycle for cold neutron source%冷中子源逆布雷顿循环氦制冷机性能分析和优化

    Institute of Scientific and Technical Information of China (English)

    余锋; 厉彦忠; 陈二锋; 徐嘉

    2007-01-01

    运用能量守恒和(火用)分析方法,对冷中子源氦制冷逆布雷顿循环过程进行热力分析和(火用)分析.找出了系统(火用)效率和各部件(火用)损失随着压缩机压比、膨胀机等熵效率、跑冷量、换热器冷热流体平均温差变化的规律,并提出减小循环跑冷量、换热器内冷热流体温差,以及提高压缩机压比、膨胀机等熵效率、物料分配均匀度以提高循环性能和系统(火用)效率的措施.基于换热器内部冷热流体温差分布对循环性能影响的分析,设计了膨胀机预冷循环方案,该方案的(火用)效率相对于基本循环提高了24 %.

  4. 带涡轮进气冷却的燃气轮机循环(火用)分析%Exergy Analysis of a Brayton Cycle with Turbine Gas Cooling

    Institute of Scientific and Technical Information of China (English)

    赵雄飞; 陈贤冲; 贾小权

    2012-01-01

    对带涡轮进气冷却的燃气轮机循环进行了(火用)分析,导出了循环(火用)效率和(火用)损失的表达式,分析了循环温比和质量流率比对循环(火用)效率和循环输出比功的影响.得到了该循环的(火用)效率特性和输出比功特性,确定了(火用)损失最大的位置,研究对燃气轮机循环的设计有一定指导意义.

  5. The Solar Cycle

    Directory of Open Access Journals (Sweden)

    David H. Hathaway

    2015-09-01

    Full Text Available The solar cycle is reviewed. The 11-year cycle of solar activity is characterized by the rise and fall in the numbers and surface area of sunspots. A number of other solar activity indicators also vary in association with the sunspots including; the 10.7 cm radio flux, the total solar irradiance, the magnetic field, flares and coronal mass ejections, geomagnetic activity, galactic cosmic ray fluxes, and radioisotopes in tree rings and ice cores. Individual solar cycles are characterized by their maxima and minima, cycle periods and amplitudes, cycle shape, the equatorward drift of the active latitudes, hemispheric asymmetries, and active longitudes. Cycle-to-cycle variability includes the Maunder Minimum, the Gleissberg Cycle, and the Gnevyshev–Ohl (even-odd Rule. Short-term variability includes the 154-day periodicity, quasi-biennial variations, and double-peaked maxima. We conclude with an examination of prediction techniques for the solar cycle and a closer look at cycles 23 and 24.

  6. [Cycling in Zagreb].

    Science.gov (United States)

    Matos, Stipan; Krapac, Ladislav; Krapac, Josip

    2007-01-01

    Cycling in Zagreb, as means of urban transport inside and outside the city, has a bright past, hazy presence but a promising future. Every day, aggressive citizens who lack urban traffic culture mistreat many cyclists but also many pedestrians. Sedentary way of living, unhealthy eating habits and inadequate recreation would surely be reduced if Zagreb had a network of cycling tracks (190 cm) or lanes (80 cm). Main city roads were constructed at the beginning of the 20th century. Today, the lack of cycling tracks is particularly evident in terms of missing connections between northern and southern parts of the city. Transportation of bikes in public vehicles, parking of bikes as well as cycling along the foot of the mountains Medvednica and Zumberacko gorje is not adequately organized. Better organization is necessary not only because of the present young generation but also because of the young who will shortly become citizens of the EU, where cycling is enormously popular. Cycling tourism is not known in Zagreb, partly due to inadequate roads. The surroundings of Zagreb are more suitable for cycling tourism and attractive brochures and tourist guides offer information to tourists on bikes. Professional, acrobatic and sports cycling do not have a tradition in Zagreb and in Croatia. The same holds true for recreational cycling and indoor exercise cycling. The authors discuss the impact of popularization of cycling using print and electronic media. The role of district and local self-government in the construction and improvement of traffic roads in Zagreb is very important. It is also significant for the implementation of legal regulations that must be obeyed by all traffic participants in order to protect cyclists, the most vulnerable group of traffic participants besides passengers. Multidisciplinary action of all benevolent experts would surely increase safety and pleasure of cycling in the city and its surroundings. This would also help reduce daily stress and

  7. Real business cycle realizations

    OpenAIRE

    Smith, Gregor W.; Stanley E. Zin

    1997-01-01

    Much recent business cycle research focuses on moments of macroeconomic aggregates. We construct examples of real business cycle sample paths for output, consumption, and employment for the U.S. economy. Annual sample paths are generated from an initial condition in 1925, measured technology and government spending shocks since then, and a standard, calibrated, one-sector model of the business cycle. Quarterly sample paths are generated similarly, from an initial condition in 1955. The law of...

  8. Fictitious Supercontinent Cycles

    CERN Document Server

    Herndon, J Marvin

    2013-01-01

    Descriptions of phenomena, events, or processes made on the basis of problematic paradigms can be unreasonably complex (e.g. epicycles) or simply wrong (e.g. ultraviolet catastrophe). Supercontinent cycles, also called Wilson cycles, are, I submit, artificial constructs, like epicycles. Here I provide the basis for that assertion and describe published considerations from a fundamentally different, new, indivisible geoscience paradigm which obviate the necessity for assuming supercontinent cycles.

  9. Alternative fuel cycles

    International Nuclear Information System (INIS)

    Uranium resource utilization and economic considerations provide incentives to study alternative fuel cycles as future options to the PHWR natural uranium cycle. Preliminary studies to define the most favourable alternatives and their possible introduction dates are discussed. The important and uncertain components which influence option selection are reviewed, including nuclear capacity growth, uranium availability and demand, economic potential, and required technological developments. Finally, a summary of Ontario Hydro's program to further assess cycle selection and define development needs is given. (auth)

  10. Fast breeder fuel cycle

    International Nuclear Information System (INIS)

    Basic elements of the ex-reactor part of the fuel cycle (reprocessing, fabrication, waste handling and transportation) are described. Possible technical and proliferation measures are evaluated, including current methods of accountability, surveillance and protection. The reference oxide based cycle and advanced cycles based on carbide and metallic fuels are considered utilizing conventional processes; advanced nonaqueous reprocessing is also considered. This contribution provides a comprehensive data base for evaluation of proliferation risks

  11. Friction Generated Limit Cycles

    OpenAIRE

    Ohlsson, Henrik; Åström, Karl Johan

    2001-01-01

    This paper treats limit cycles caused by friction. The goal has been to explain phenomena that have been observed experimentally in mechatronic systems. Experiments have shown that oscillations of qualitatively different types can be obtained simply by changing controller specifications. Stiction is important in some cases but not in others. Necessary conditions for limit cycle are given for the case where stiction is important. Conditions for local stability of the limit cycles are also pres...

  12. Historicising the Hydrosocial Cycle

    OpenAIRE

    Jeremy J. Schmidt

    2014-01-01

    This paper examines the historical claims made in support of the hydrosocial cycle. In particular, it considers how arguments advancing the hydrosocial cycle make historical claims regarding modernist conceptions of what water is (i.e. H2O) and its fit with society. The paper gives special emphasis to the society/nature dualism and to the notion of agency as key sites of contest in arguments regarding the hydrosocial cycle. It finds that, while several versions of the hydrosocial cycle seek t...

  13. Edgeworth cycles revisited

    Energy Technology Data Exchange (ETDEWEB)

    Doyle, Joseph [MIT Sloan School of Management, 50 Memorial Drive, E52-447, Cambridge MA 02142 (United States); Muehlegger, Erich [John F. Kennedy School of Government, Harvard University, Mailbox 25, 79 JFK Street, Cambridge, MA 02138 (United States); Samphantharak, Krislert [Graduate School of International Relations and Pacific Studies, University of California at San Diego, 9500 Gilman Drive 1519, La Jolla, CA 92093 (United States)

    2010-05-15

    Some gasoline markets exhibit remarkable price cycles, where price spikes are followed by a series of small price declines: a pattern consistent with a model of Edgeworth cycles described by Maskin and Tirole. We extend the model and empirically test its predictions with a new dataset of daily station-level prices in 115 US cities. Consistent with the theory, and often in contrast with previous empirical work, we find the least and most concentrated markets are much less likely to exhibit cycling behavior both within and across cities; areas with more independent convenience-store gas stations are also more likely to cycle. (author)

  14. Evaluation of technical feasibility of closed-cycle non-equilibrium MHD power generation with direct coal firing. Final report, Task 1

    Energy Technology Data Exchange (ETDEWEB)

    1981-11-01

    Program accomplishments in a continuing effort to demonstrate the feasibility of direct coal fired, closed cycle, magnetohydrodynamic power generation are detailed. These accomplishments relate to all system aspects of a CCMHD power generation system including coal combustion, heat transfer to the MHD working fluid, MHD power generation, heat and cesium seed recovery and overall systems analysis. Direct coal firing of the combined cycle has been under laboratory development in the form of a high slag rejection, regeneratively air cooled cyclone coal combustor concept, originated within this program. A hot bottom ceramic regenerative heat exchanger system was assembled and test fired with coal for the purposes of evaluating the catalytic effect of alumina on NO/sub x/ emission reduction and operability of the refractory dome support system. Design, procurement, fabrication and partial installation of a heat and seed recovery flow apparatus was accomplished and was based on a stream tube model of the full scale system using full scale temperatures, tube sizes, rates of temperature change and tube geometry. Systems analysis capability was substantially upgraded by the incorporation of a revised systems code, with emphasis on ease of operator interaction as well as separability of component subroutines. The updated code was used in the development of a new plant configuration, the Feedwater Cooled (FCB) Brayton Cycle, which is superior to the CCMHD/Steam cycle both in performance and cost. (WHK)

  15. Optimized, Competitive Supercritical-CO2 Cycle GFR for Gen IV Service

    International Nuclear Information System (INIS)

    An overall plant design was developed for a gas-cooled fast reactor employing a direct supercritical Brayton power conversion system. The most important findings were that (1) the concept could be capital-cost competitive, but startup fuel cycle costs are penalized by the low core power density, specified in large part to satisfy the goal of significant post-accident passive natural convection cooling; (2) active decay heat removal is preferable as the first line of defense, with passive performance in a backup role; (3) an innovative tube-in-duct fuel assembly, vented to the primary coolant, appears to be practicable; and (4) use of the S-Co2 GFR to support hydrogen production is a synergistic application, since sufficient energy can be recuperated from the product H2 and 02 to allow the electrolysis cell to run 250 C hotter than the reactor coolant, and the water boilers can be used for reactor decay heat removal. Increasing core power density is identified as the top priority for future work on GFRs of this type

  16. Optimized, Competitive Supercritical-CO2 Cycle GFR for Gen IV Service

    Energy Technology Data Exchange (ETDEWEB)

    M.J. Driscoll; P. Hejzlar; G. Apostolakis

    2008-09-08

    An overall plant design was developed for a gas-cooled fast reactor employing a direct supercritical Brayton power conversion system. The most important findings were that (1) the concept could be capital-cost competitive, but startup fuel cycle costs are penalized by the low core power density, specified in large part to satisfy the goal of significatn post-accident passive natural convection cooling; (2) active decay heat removal is preferable as the first line of defense, with passive performance in a backup role; (3) an innovative tube-in-duct fuel assembly, vented to the primpary coolant, appears to be practicable; and (4) use of the S-Co2 GFR to support hydrogen production is a synergistic application, since sufficient energy can be recuperated from the product H2 and 02 to allow the electrolysis cell to run 250 C hotter than the reactor coolant, and the water boilers can be used for reactor decay heat removal. Increasing core poer density is identified as the top priority for future work on GFRs of this type.

  17. Teaching the Krebs Cycle.

    Science.gov (United States)

    Akeroyd, F. Michael

    1983-01-01

    Outlines a simple but rigorous treatment of the Krebs Cycle suitable for A-level Biology students. The importance of the addition of water molecules in various stages of the cycle is stressed as well as the removal of hydrogen atoms by the oxidizing enzymes. (JN)

  18. Life Cycle Environmental Management

    DEFF Research Database (Denmark)

    Pedersen, Claus Stig; Jørgensen, Jørgen; Pedersen, Morten Als

    1996-01-01

    processes. The discipline of life cycle environmental management (LCEM) focuses on the incorporation of environmental criteria from the life cycles of products and other company activities into the company management processes. This paper introduces the concept of LCEM as an important element...

  19. Life cycle management (LCM)

    DEFF Research Database (Denmark)

    Remmen, Arne; Thrane, Mikkel

    2004-01-01

    The chapter gives an introduction to Life Cycle Management (LCM) and shows how LCM can be practiced in different contexts and at different ambition levels.......The chapter gives an introduction to Life Cycle Management (LCM) and shows how LCM can be practiced in different contexts and at different ambition levels....

  20. Power Plant Cycling Costs

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, N.; Besuner, P.; Lefton, S.; Agan, D.; Hilleman, D.

    2012-07-01

    This report provides a detailed review of the most up to date data available on power plant cycling costs. The primary objective of this report is to increase awareness of power plant cycling cost, the use of these costs in renewable integration studies and to stimulate debate between policymakers, system dispatchers, plant personnel and power utilities.

  1. Thermal analysis of the heat recuperator of a combined cycle thermoelectric central; Analisis termico del recuperador de calor de una central termoelectrica de ciclo combinado

    Energy Technology Data Exchange (ETDEWEB)

    Romero Paredes, Hernando; Sanchez, I.; Lazcano, L. C.; Ambriz, Juan Jose; Alvarez, M. [Universidad Autonoma Metropolitana-Iztapalapa, Mexico, D. F. (Mexico); Gonzalez, O. [Comision Federal de Electricidad, Tula (Mexico)

    1996-12-31

    The thermoelectric centrals of the combined cycle type (Brayton Cycle and Rankine Cycle) present a series of opportunities to increase the efficiency of the combined cycle or of the generated power. This paper shows the methodology for the performance of energy balances in a heat recuperator (H. R.), typically employed in the combined cycle stations operating in Mexico, for the assessment of the energy harnessing in the different sections conforming a H. R. The effect of the installation of evaporative coolers and/or an absorption cooling system at the gas turbine compressor intake on the steam generation in the heat recuperator, is evaluated. This extra generation of steam is quantified for its potential use in the same absorption refrigeration system. From the assessment, it follows up that the steam generation in the H.R. is inversely proportional to the ambient temperature and that, although the increased amount of steam generated can not be harnessed in total by the steam turbine, the remaining fraction is good enough to cover the heat demand for the operation of the refrigeration system. [Espanol] Las centrales termoelectricas del tipo ciclo combinado (ciclo Brayton y ciclo Rankine) presentan un conjunto de oportunidades para incrementar la eficiencia del ciclo combinado o bien la potencia generada. En el presente trabajo se expone la metodologia para realizar los balances de energia en un recuperador de calor (R.C.) tipicamente utilizado en las Centrales de Ciclo Combinado (CCC) que operan en Mexico, para evaluar el aprovechamiento de la energia en las diferentes secciones que conforman un R.C. Se evalua el efecto que tiene la instalacion de enfriadores evaporativos y/o un sistema de enfriamiento por absorcion en la succion del compresor de la turbina de gas sobre la generacion de vapor en el recuperador de calor. Se cuantifica esta generacion extra de vapor para su posible utilizacion en el mismo sistema de refrigeracion por absorcion. De la evaluacion se

  2. Predicting the Sunspot Cycle

    Science.gov (United States)

    Hathaway, David H.

    2009-01-01

    The 11-year sunspot cycle was discovered by an amateur astronomer in 1844. Visual and photographic observations of sunspots have been made by both amateurs and professionals over the last 400 years. These observations provide key statistical information about the sunspot cycle that do allow for predictions of future activity. However, sunspots and the sunspot cycle are magnetic in nature. For the last 100 years these magnetic measurements have been acquired and used exclusively by professional astronomers to gain new information about the nature of the solar activity cycle. Recently, magnetic dynamo models have evolved to the stage where they can assimilate past data and provide predictions. With the advent of the Internet and open data policies, amateurs now have equal access to the same data used by professionals and equal opportunities to contribute (but, alas, without pay). This talk will describe some of the more useful prediction techniques and reveal what they say about the intensity of the upcoming sunspot cycle.

  3. Assessing Cycling Participation in Australia

    OpenAIRE

    Chris Rissel; Cameron Munro; Adrian Bauman

    2013-01-01

    Planning and evaluating cycling programs at a national or state level requires accurate measures of cycling participation. However, recent reports of cycling participation have produced very different estimates. This paper examines the reported rates of cycling in five recent population surveys of cycling. Three surveys (one national and two from Sydney) asking respondents when they last rode a bicycle generated cycling participation (cycled in the past year) estimates of 29.7%, 34.1% and 28....

  4. Bimodality and the Hale cycle

    Science.gov (United States)

    Wilson, Robert M.

    1988-01-01

    Evidence is provided of a modulation of between 20 and 24 yr for the Hale cycle, and comparison of consecutive pairs of cycles strongly suggests that even-numbered cycles are preferentially paired with odd-numbered following cycles. The results indicate that cycles 22 and 23 form a new cyle pair. The sum of monthly mean sunspot numbers over consecutively paired sunspot cycles for Hale cycle 12 is found to be about 19,100 + or - 3000.

  5. The Anderson Quin Cycle

    Energy Technology Data Exchange (ETDEWEB)

    Anderson, J.H.; Bilbow, W.M.

    1993-03-18

    The objective of this study was to make a more refined evaluation of the Anderson Quin Cycle based on most recent information on the performance of various elements that will be used in the Anderson Quin Cycle. My original estimate of the work plan for evaluating and optimizing the Anderson Quin Cycle called for 7000 man hours of work. Since this grant was limited to 2150 man hours, we could not expect to achieve all the objectives within the allotted period of work. However, the most relevant program objectives have been completed as reported here. The analysis generally confirms the results originally estimated in my paper on the subject. (Ref. 2) Further optimizations should show even higher efficiencies. The Anderson Quin Cycle (US Patent applied for) basically consists of 5 elements in the power cycle: A refrigeration system to cool and clean the inlet air before it enters the compressor that supplies air for the gas turbine; a gas turbine consisting of a compressor, combustor, and turbine; a steam boiler and steam turbine system using the heat from the exhaust gas out of the gas turbine; a vapor turbine cycle, which utilizes the condensed heat from the exhaust of the steam turbine and the exhaust gas heat leaving the steam boiler to operate a vapor turbine cycle which utilizes another fluid than water, in this case isobutane; and the fifth element consists of a gas cooler and heat pump system, which removes the heat from the exhaust gas to lower its temperature essentially to atmospheric temperature, and at the same time permits treatment of the exhaust gas to remove acid components such as sulfur dioxide and nitrogen oxides. Current industry accepted component characteristics were incorporated in the performance analysis of the overall cycle, ensuring accurate and meaningful operating predictions. The characteristics and performance of each of the elements are described. The thermal efficiency of the optimized calculated Anderson Quin Cycle is 62 percent.

  6. Future fuel cycles

    International Nuclear Information System (INIS)

    A fuel cycle must offer both financial and resource savings if it is to be considered for introduction into Ontario's nuclear system. The most promising alternative CANDU fuel cycles are examined in the context of both of these factors over a wide range of installed capacity growth rates and economic assumptions, in order to determine which fuel cycle, or cycles, should be introduced, and when. It is concluded that the optimum path for the long term begins with the prompt introduction of the low-enriched-uranium fuel cycle. For a wide range of conditions, this cycle remains the optimum throughout the very long term. Conditions of rapid nuclear growth and very high uranium price escalation rates warrant the supersedure of the low-enriched-uranium cycle by either a plutonium-topped thorium cycle or plutonium recycle, beginning between 2010 and 2025. It is also found that the uranium resource position is sound in terms of both known resources and production capability. Moreover, introduction of the low-enriched-uranium fuel cycle and 1250 MWe reactor units will assure the economic viability of nuclear power until at least 2020, even if uranium prices increase at a rate of 3.5% above inflation. The interrelationship between these two conclusions lies in the tremendous incentive for exploration which will occur if the real uranium price escalation rate is high. From a competitive viewpoint, nuclear power can withstand increases in the price of uranium. However, such increases will likely further expand the resource base, making nuclear an even more reliable energy source. (auth)

  7. Cycling across borders

    Directory of Open Access Journals (Sweden)

    Jože Kos

    1999-01-01

    Full Text Available The article describes the intent and content of the international Velo-City conference 1999, Maribor–Graz and the organisation of this cycling development planning meeting. It focuses on the resolution of the conference concerning cycling traffic policies, the emerging network of European cycling connections and the traffic planning workshop about a difficult square in Maribor. The content framework of particular papers is shown, as well as other post-conference events. In the conclusion certain useful addresses for obtaining added data on sustainable traffic planning are given.

  8. Life Cycle Sustainability Dashboard

    DEFF Research Database (Denmark)

    Traverso, Marzia; Finkbeiner, Matthias; Jørgensen, Andreas;

    2012-01-01

    One method to assess the sustainability performance of products is life cycle sustainability assessment (LCSA), which assesses product performance considering the environmental,economic, and social dimensions of the life cycle. The results of LCSA can be used to compare different products...... of sustainability is the communicability of the results by means of a graphical representation (a cartogram), characterized by a suitable chromatic scale and ranking score. The integration of LCSA and the dashboard of sustainability into a so-called Life Cycle Sustainability Dashboard (LCSD) is described here...

  9. Fuel cycle data survey

    International Nuclear Information System (INIS)

    A survey of the fuel cycle cost data published during 1977 and 1978 is presented in tabular and graphical form. Cost trends for the period 1965 onwards are presented for yellow cake, conversion, uranium enrichment, fuel fabrication and reprocessing

  10. Cycles in graphs

    CERN Document Server

    Alspach, BR

    1985-01-01

    This volume deals with a variety of problems involving cycles in graphs and circuits in digraphs. Leading researchers in this area present here 3 survey papers and 42 papers containing new results. There is also a collection of unsolved problems.

  11. Fuel cycle studies

    International Nuclear Information System (INIS)

    Programs are being conducted in the following areas: advanced solvent extraction techniques, accident consequences, fuel cycles for nonproliferation, pyrochemical and dry processes, waste encapsulation, radionuclide transport in geologic media, hull treatment, and analytical support for LWBR

  12. Resuscitating Real Business Cycles

    OpenAIRE

    Robert G. King; Sergio T. Rebelo

    2000-01-01

    The Real Business Cycle (RBC) research program has grown spectacularly over the last decade, as its concepts and methods have diffused into mainstream macroeconomics. Yet, there is increasing skepticism that technology shocks are a major source of business fluctuations. This chapter exposits the basic RBC model and shows that it requires large technology shocks to produce realistic business cycles. While Solow residuals are sufficiently volatile, these imply frequent technological regress. Pr...

  13. Quantifying the adaptive cycle

    Science.gov (United States)

    Angeler, David G.; Allen, Craig R.; Garmestani, Ahjond S.; Gunderson, Lance H.; Hjerne, Olle; Winder, Monika

    2015-01-01

    The adaptive cycle was proposed as a conceptual model to portray patterns of change in complex systems. Despite the model having potential for elucidating change across systems, it has been used mainly as a metaphor, describing system dynamics qualitatively. We use a quantitative approach for testing premises (reorganisation, conservatism, adaptation) in the adaptive cycle, using Baltic Sea phytoplankton communities as an example of such complex system dynamics. Phytoplankton organizes in recurring spring and summer blooms, a well-established paradigm in planktology and succession theory, with characteristic temporal trajectories during blooms that may be consistent with adaptive cycle phases. We used long-term (1994–2011) data and multivariate analysis of community structure to assess key components of the adaptive cycle. Specifically, we tested predictions about: reorganisation: spring and summer blooms comprise distinct community states; conservatism: community trajectories during individual adaptive cycles are conservative; and adaptation: phytoplankton species during blooms change in the long term. All predictions were supported by our analyses. Results suggest that traditional ecological paradigms such as phytoplankton successional models have potential for moving the adaptive cycle from a metaphor to a framework that can improve our understanding how complex systems organize and reorganize following collapse. Quantifying reorganization, conservatism and adaptation provides opportunities to cope with the intricacies and uncertainties associated with fast ecological change, driven by shifting system controls. Ultimately, combining traditional ecological paradigms with heuristics of complex system dynamics using quantitative approaches may help refine ecological theory and improve our understanding of the resilience of ecosystems.

  14. Solar Cycle Prediction

    CERN Document Server

    Petrovay, K

    2010-01-01

    A review of solar cycle prediction methods and their performance is given, including forecasts for cycle 24 and focusing on aspects of the solar cycle prediction problem that have a bearing on dynamo theory. The scope of the review is further restricted to the issue of predicting the amplitude (and optionally the epoch) of an upcoming solar maximum no later than right after the start of the given cycle. Prediction methods form three main groups. Precursor methods rely on the value of some measure of solar activity or magnetism at a specified time to predict the amplitude of the following solar maximum. Their implicit assumption is that each numbered solar cycle is a consistent unit in itself, while solar activity seems to consist of a series of much less tightly intercorrelated individual cycles. Extrapolation methods, in contrast, are based on the premise that the physical process giving rise to the sunspot number record is statistically homogeneous, i.e., the mathematical regularities underlying its variati...

  15. Prospects for Nuclear Electric Propulsion Using Closed-Cycle Magnetohydrodynamic Energy Conversion

    Science.gov (United States)

    Litchford, R. J.; Bitteker, L. J.; Jones, J. E.

    2001-01-01

    Nuclear electric propulsion (NEP) has long been recognized as a major enabling technology for scientific and human exploration of the solar system, and it may conceivably form the basis of a cost-effective space transportation system suitable for space commerce. The chief technical obstacles to realizing this vision are the development of efficient, high-power (megawatt-class) electric thrusters and the development of low specific mass (less than 1 kg/kWe) power plants. Furthermore, comprehensive system analyses of multimegawatt class NEP systems are needed in order to critically assess mission capability and cost attributes. This Technical Publication addresses some of these concerns through a systematic examination of multimegawatt space power installations in which a gas-cooled nuclear reactor is used to drive a magnetohydrodynamic (MHD) generator in a closed-loop Brayton cycle. The primary motivation for considering MHD energy conversion is the ability to transfer energy out of a gas that is simply too hot for contact with any solid material. This has several intrinsic advantages including the ability to achieve high thermal efficiency and power density and the ability to reject heat at elevated temperatures. These attributes lead to a reduction in system specific mass below that obtainable with turbine-based systems, which have definite solid temperature limits for reliable operation. Here, the results of a thermodynamic cycle analysis are placed in context with a preliminary system analysis in order to converge on a design space that optimizes performance while remaining clearly within established bounds of engineering feasibility. MHD technology issues are discussed including the conceptual design of a nonequilibrium disk generator and opportunities for exploiting neutron-induced ionization mechanisms as a means of increasing electrical conductivity and enhancing performance and reliability. The results are then used to make a cursory examination of piloted

  16. Helium process cycle

    Science.gov (United States)

    Ganni, Venkatarao

    2007-10-09

    A unique process cycle and apparatus design separates the consumer (cryogenic) load return flow from most of the recycle return flow of a refrigerator and/or liquefier process cycle. The refrigerator and/or liquefier process recycle return flow is recompressed by a multi-stage compressor set and the consumer load return flow is recompressed by an independent consumer load compressor set that maintains a desirable constant suction pressure using a consumer load bypass control valve and the consumer load return pressure control valve that controls the consumer load compressor's suction pressure. The discharge pressure of this consumer load compressor is thereby allowed to float at the intermediate pressure in between the first and second stage recycle compressor sets. Utilizing the unique gas management valve regulation, the unique process cycle and apparatus design in which the consumer load return flow is separate from the recycle return flow, the pressure ratios of each recycle compressor stage and all main pressures associated with the recycle return flow are allowed to vary naturally, thus providing a naturally regulated and balanced floating pressure process cycle that maintains optimal efficiency at design and off-design process cycle capacity and conditions automatically.

  17. Helium process cycle

    Science.gov (United States)

    Ganni, Venkatarao

    2008-08-12

    A unique process cycle and apparatus design separates the consumer (cryogenic) load return flow from most of the recycle return flow of a refrigerator and/or liquefier process cycle. The refrigerator and/or liquefier process recycle return flow is recompressed by a multi-stage compressor set and the consumer load return flow is recompressed by an independent consumer load compressor set that maintains a desirable constant suction pressure using a consumer load bypass control valve and the consumer load return pressure control valve that controls the consumer load compressor's suction pressure. The discharge pressure of this consumer load compressor is thereby allowed to float at the intermediate pressure in between the first and second stage recycle compressor sets. Utilizing the unique gas management valve regulation, the unique process cycle and apparatus design in which the consumer load return flow is separate from the recycle return flow, the pressure ratios of each recycle compressor stage and all main pressures associated with the recycle return flow are allowed to vary naturally, thus providing a naturally regulated and balanced floating pressure process cycle that maintains optimal efficiency at design and off-design process cycle capacity and conditions automatically.

  18. Advanced heat pump cycle

    Energy Technology Data Exchange (ETDEWEB)

    Groll, E.A.; Radermacher, R.

    1993-07-01

    The desorption and absorption process of a vapor compression heat pump with a solution circuit (VCHSC) proceeds at gliding temperature intervals, which can be adjusted over a wide range. In case that the gliding temperature intervals in the desorber and the absorber overlap, a modification of the VCHSC employing a desorber/absorber heat exchange (DAHX) can be introduced, which results in an extreme reduction of the pressure ratio. Although the DAHX-cycle has features of a two-stage cycle, it still requires only one solution pump, one separator and one compressor. Such a cycle for the working pair ammonia/water is built in the Energy Laboratory of the Center for Environmental Energy Engineering at the University of Maryland. The experimental results obtained with the research plant are discussed and compared to those calculated with a simulation program. The possible temperature lift between heat source and heat sink depending on the achievable COP are presented.

  19. Superfluid thermodynamic cycle refrigerator

    Science.gov (United States)

    Swift, Gregory W.; Kotsubo, Vincent Y.

    1992-01-01

    A cryogenic refrigerator cools a heat source by cyclically concentrating and diluting the amount of .sup.3 He in a single phase .sup.3 He-.sup.4 He solution. The .sup.3 He in superfluid .sup.4 He acts in a manner of an ideal gas in a vacuum. Thus, refrigeration is obtained using any conventional thermal cycle, but preferably a Stirling or Carnot cycle. A single phase solution of liquid .sup.3 He at an initial concentration in superfluid .sup.4 He is contained in a first variable volume connected to a second variable volume through a superleak device that enables free passage of .sup.4 He while restricting passage of .sup.3 He. The .sup.3 He is compressed (concentrated) and expanded (diluted) in a phased manner to carry out the selected thermal cycle to remove heat from the heat load for cooling below 1 K.

  20. The global sulfur cycle

    Science.gov (United States)

    Sagan, D. (Editor)

    1985-01-01

    The results of the planetary biology microbial ecology's 1984 Summer Research Program, which examined various aspects of the global sulfur cycle are summarized. Ways in which sulfur flows through the many living and chemical species that inhabit the surface of the Earth were investigated. Major topics studied include: (1) sulfur cycling and metabolism of phototropic and filamentous sulfur bacteria; (2) sulfur reduction in sediments of marine and evaporite environments; (3) recent cyanobacterial mats; (4) microanalysis of community metabolism in proximity to the photic zone in potential stromatolites; and (5) formation and activity of microbial biofilms on metal sulfides and other mineral surfaces. Relationships between the global sulfur cycle and the understanding of the early evolution of the Earth and biosphere and current processes that affect global habitability are stressed.

  1. Cycles in fossil diversity

    Energy Technology Data Exchange (ETDEWEB)

    Rohde, Robert A.; Muller, Richard A.

    2004-10-20

    It is well-known that the diversity of life appears to fluctuate during the course the Phanerozoic, the eon during which hard shells and skeletons left abundant fossils (0-542 Ma). Using Sepkoski's compendium of the first and last stratigraphic appearances of 36380 marine genera, we report a strong 62 {+-} 3 Myr cycle, which is particularly strong in the shorter-lived genera. The five great extinctions enumerated by Raup and Sepkoski may be an aspect of this cycle. Because of the high statistical significance, we also consider contributing environmental factors and possible causes.

  2. Revenue cycle management.

    Science.gov (United States)

    Manley, Ray; Satiani, Bhagwan

    2009-11-01

    With the widening gap between overhead expenses and reimbursement, management of the revenue cycle is a critical part of a successful vascular surgery practice. It is important to review the data on all the components of the revenue cycle: payer contracting, appointment scheduling, preregistration, registration process, coding and capturing charges, proper billing of patients and insurers, follow-up of accounts receivable, and finally using appropriate benchmarking. The industry benchmarks used should be those of peers in identical groups. Warning signs of poor performance are discussed enabling the practice to formulate a performance improvement plan.

  3. Global water cycle

    Science.gov (United States)

    Robertson, Franklin; Goodman, Steven J.; Christy, John R.; Fitzjarrald, Daniel E.; Chou, Shi-Hung; Crosson, William; Wang, Shouping; Ramirez, Jorge

    1993-01-01

    This research is the MSFC component of a joint MSFC/Pennsylvania State University Eos Interdisciplinary Investigation on the global water cycle extension across the earth sciences. The primary long-term objective of this investigation is to determine the scope and interactions of the global water cycle with all components of the Earth system and to understand how it stimulates and regulates change on both global and regional scales. Significant accomplishments in the past year are presented and include the following: (1) water vapor variability; (2) multi-phase water analysis; (3) global modeling; and (4) optimal precipitation and stream flow analysis and hydrologic processes.

  4. Marine nitrogen cycle

    Digital Repository Service at National Institute of Oceanography (India)

    Naqvi, S.W.A.

    and particulate organic forms, respectively) and atmospheric deposition (~50 Tg N a -1 ), a substantial fraction of which is believed to be of anthropogenic (human-made) origin. Of the various loss terms of combined nitrogen from the ocean, emission of N 2 O... and nitrous oxide budgets: Moving targets as we enter the anthropocene?, Sci. Mar., 65, 85-105, 2001. Page 2 of 3Marine nitrogen cycle - Encyclopedia of Earth 11/20/2006http://www.eoearth.org/article/Marine_nitrogen_cycle square6 Gruber, N.: The dynamics...

  5. Carbon cycle makeover

    DEFF Research Database (Denmark)

    Canfield, Donald Eugene; Kump, Lee R.

    2013-01-01

    remaining in sediments after respiration leave a residual of oxygen in the atmosphere. The source of oxygen to the atmosphere represented by organic matter burial is balanced by oxygen sinks associated with rock weathering and chemical reaction with volcanic gases. This is the long-term carbon and oxygen...... geochemical cycle. But Earth is an old planet, and oxygen levels have changed through time (2). On page 540 of this issue, Schrag et al. (3) challenge the most commonly used geochemical approach to assess long-term changes in the coupled oxygen and carbon cycles....

  6. Menstrual cycle pattern and fertility

    DEFF Research Database (Denmark)

    Kolstad, Henrik A.; Bonde, Jens Peter; Hjøllund, Niels Henrik;

    1999-01-01

    To characterize how the menstrual cycle pattern relates to fertility regardless of potential biases caused by inappropriate coital timing during the menstrual cycle or early embryonal loss.......To characterize how the menstrual cycle pattern relates to fertility regardless of potential biases caused by inappropriate coital timing during the menstrual cycle or early embryonal loss....

  7. The Science of Cycling

    Science.gov (United States)

    Crompton, Zoe; Daniels, Shelley

    2014-01-01

    Children are engaged by finding out about science in the real world (Harlen, 2010). Many children will be cyclists or will have seen or heard about the success of British cyclists in the Olympics and the Tour de France. This makes cycling a good hook to draw children into learning science. It is also a good cross-curricular topic, with strong…

  8. Assisted Cycling Tours

    Science.gov (United States)

    Hollingsworth, Jan Carter

    2008-01-01

    This article discusses Assisted Cycling Tours (ACT), a Westminster, Colorado based 501(c)3, non-profit that is offering the joy of bicycle tours in breathtaking, scenic locations to children and adults with developmental and physical disabilities and their families. ACT was founded by Bob Matter and his son David with a goal of opening up the…

  9. Re-Cycling

    Science.gov (United States)

    Brown, Robert W.; Covault, Corbin E.

    2015-01-01

    An old comedy routine on Saturday Night Live by Father Guido Sarducci introduced a "Five-Minute University," because five minutes is all that's remembered after graduation anyway. In counterpoint, we discuss "cycling," a teaching method for memory enhancement. Our principal implementation consists of offering a simple version…

  10. Educational Business Cycles

    DEFF Research Database (Denmark)

    Tepe, Markus; Vanhuysse, Pieter

    Strong institutional constraints and better-informed voters may lead re-election seeking incumbents to shift the use of political business cycle mechanisms away from monetary and fiscal policy towards other policy domains that are more easily manipulable, targetable, and timeable. We investigate...

  11. Educational Business Cycles

    DEFF Research Database (Denmark)

    Tepe, Markus; Vanhuysse, Pieter

    2009-01-01

    Strong institutional constraints and better-informed voters may lead re-election seeking incumbents to shift the use of political business cycle mechanisms away from monetary and fiscal policy towards other policy domains that are more easily manipulable, targetable, and timeable. We investigate...

  12. Boundedly rational credit cycles

    OpenAIRE

    S??ez, Mar??a

    1996-01-01

    We propose an evolutionary model of a credit market. We show that the economy exhibits credit cycles. The model predicts dynamics which are consistent with some evidence about the Great Depression. Real shocks trigger episodes of credit--crunch which are observed in the process of adjustment towards the post shock equilibrium.

  13. Life Cycle Collection Management

    Directory of Open Access Journals (Sweden)

    Helen Shenton

    2003-09-01

    Full Text Available Life cycle collection management is a way of taking a long-term approach to the responsible stewardship of the British Library's collections and is one of the Library's strategic strands. It defines the different stages in a collection item's existence over time. These stages range from selection and acquisitions processing, cataloguing and press marking, through to preventive conservation, storage and retrieval. Life cycle collection management seeks to identify the costs of each stage in order to show the economic interdependencies between the phases over time. It thereby aims to demonstrate the long-term consequences of what the library takes into its collections, by making explicit the financial and other implications of decisions made at the beginning of the life cycle for the next 100 plus years. This paper describes the work over the past year at the British Library on this complex and complicated subject. It presents the emerging findings and suggests how it can be used for practical reasons (by individual curators and selectors and for economic, governance and political purposes. The paper describes the next steps in the project, for example, on a predictive data model. The British Library is seeking to benchmark itself against comparable organisations in this area. It intends to work with others on specific comparison for example, of life cycle costing of electronic and paper journals, as a prelude to eliding digital and 'traditional' formats.

  14. Skills, sunspots and cycles

    DEFF Research Database (Denmark)

    Busato, Francesco; Marchetti, Enrico

    This paper explores the ability of a class of one-sector,multi-input models to generate indeterminate equilibrium paths, andendogenous cycles, without relying on factors' hoarding. The modelpresents a novel theoretical economic mechanism that supportssunspot-driven expansions without requiring up...

  15. The Pneumocystis life cycle

    Directory of Open Access Journals (Sweden)

    Cécile-Marie Aliouat-Denis

    2009-05-01

    Full Text Available First recognised as "schizonts" of Trypanosoma cruzi, Pneumocystis organisms are now considered as part of an early-diverging lineage of Ascomycetes. As no robust long-term culture model is available, most data on the Pneumocystis cell cycle have stemmed from ultrastructural images of infected mammalian lungs. Although most fungi developing in animals do not complete a sexual cycle in vivo, Pneumocystis species constitute one of a few exceptions. Recently, the molecular identification of several key players in the fungal mating pathway has provided further evidence for the existence of conjugation and meiosis in Pneumocystisorganisms. Dynamic follow-up of stage-to-stage transition as well as studies of stage-specific proteins and/or genes would provide a better understanding of the still hypothetical Pneumocystislife cycle. Although difficult to achieve, stage purification seems a reasonable way forward in the absence of efficient culture systems. This mini-review provides a comprehensive overview of the historical milestones leading to the current knowledge available on the Pneumocystis life cycle.

  16. Stellar magnetic cycles

    Science.gov (United States)

    Baliunas, S. L.

    2004-05-01

    Is hope for understanding the solar magnetic cycle to be found in stars? Observations of stars with significant sub-surface convective zones -- masses smaller than about 1.5 solar masses on the lower main sequence and many types of cool, post-main-sequence stars -- indicate the presence of surface and atmospheric inhomogeneities analogous to solar magnetic features, making stellar magnetic activity a cosmically widespread phenomenon. Observations have been made primarily in visible wavelengths, and important information has also been derived from the ultraviolet and x-ray spectrum regions. Interannual to interdecadal variability of spectrum indicators of stellar magnetic features is common, and in some cases similar in appearance to the 11-year sunspot cycle. Successful models of the physical processes responsible for stellar magnetic cycles, typically cast as a magnetohydrodynamic dynamo, require advances in understanding not only convection but also the magnetic field's interaction with it. The observed facts that underpin the hope for models will be summarized. Properties of stellar magnetic cycles will be compared and contrasted with those of the sun, including inferences from paleo-environmental reservoirs that contain information on solar century- to millennial-scale magnetic variability. Partial support of this research came from NASA NAG5-7635, NRC COBASE, CRDF 322, MIT-MSG 5710001241, JPL 1236821, AF 49620-02-1-0194, Richard Lounsberry Foundation, Langley-Abbot, Rollins, Scholarly Studies and James Arthur Funds (Smithsonian Institution) and several generous individuals.

  17. Big Data and Cycling

    NARCIS (Netherlands)

    Romanillos, Gustavo; Zaltz Austwick, Martin; Ettema, Dick; De Kruijf, Joost

    2016-01-01

    Big Data has begun to create significant impacts in urban and transport planning. This paper covers the explosion in data-driven research on cycling, most of which has occurred in the last ten years. We review the techniques, objectives and findings of a growing number of studies we have classified

  18. The Geologic Nitrogen Cycle

    Science.gov (United States)

    Johnson, B. W.; Goldblatt, C.

    2013-12-01

    N2 is the dominant gas in Earth's atmosphere, and has been so through the majority of the planet's history. Originally thought to only be cycled in significant amounts through the biosphere, it is becoming increasingly clear that a large degree of geologic cycling can occur as well. N is present in crustal rocks at 10s to 100s of ppm and in the mantle at 1s to perhaps 10s of ppm. In light of new data, we present an Earth-system perspective of the modern N cycle, an updated N budget for the silicate Earth, and venture to explain the evolution of the N cycle over time. In an fashion similar to C, N has a fast, biologically mediated cycle and a slower cycle driven by plate tectonics. Bacteria fix N2 from the atmosphere into bioavailable forms. N is then cycled through the food chain, either by direct consumption of N-fixing bacteria, as NH4+ (the primary waste form), or NO3- (the most common inorganic species in the modern ocean). Some organic material settles as sediment on the ocean floor. In anoxic sediments, NH4+ dominates; due to similar ionic radii, it can readily substitute for K+ in mineral lattices, both in sedimentary rocks and in oceanic lithosphere. Once it enters a subduction zone, N may either be volatilized and returned to the atmosphere at arc volcanoes as N2 or N2O, sequestered into intrusive igneous rocks (as NH4+?), or subducted deep into the mantle, likely as NH4+. Mounting evidence indicates that a significant amount of N may be sequestered into the solid Earth, where it may remain for long periods (100s m.y.) before being returned to the atmosphere/biosphere by volcanism or weathering. The magnitude fluxes into the solid Earth and size of geologic N reservoirs are poorly constrained. The size of the N reservoirs contained in the solid Earth directly affects the evolution of Earth's atmosphere. It is possible that N now sequestered in the solid Earth was once in the atmosphere, which would have resulted in a higher atmospheric pressure, and

  19. Stirling cycle cryogenic cooler

    Science.gov (United States)

    Gasser, M. G.; Sherman, A.; Studer, P. A.; Daniels, A.; Goldowsky, M. P. (Inventor)

    1983-01-01

    A long lifetime Stirling cycle cryogenic cooler particularly adapted for space applications is described. It consists of a compressor section centrally aligned end to end with an expansion section, and respectively includes a reciprocating compressor piston and displacer radially suspended in interconnecting cylindrical housings by active magnetic bearings and has adjacent reduced clearance regions so as to be in noncontacting relationship therewith and wherein one or more of these regions operate as clearance seals. The piston and displacer are reciprocated in their housings by linear drive motors to vary the volume of respectively adjacent compression and expansion spaces which contain a gaseous working fluid and a thermal regenerator to effect Stirling cycle cryogenic cooling.

  20. Stirling cycle cryogenic cooler

    Science.gov (United States)

    Gasser, M. G.; Sherman, A.; Studer, P. A.; Daniels, A.; Goldowsky, M. P.

    1983-06-01

    A long lifetime Stirling cycle cryogenic cooler particularly adapted for space applications is described. It consists of a compressor section centrally aligned end to end with an expansion section, and respectively includes a reciprocating compressor piston and displacer radially suspended in interconnecting cylindrical housings by active magnetic bearings and has adjacent reduced clearance regions so as to be in noncontacting relationship therewith and wherein one or more of these regions operate as clearance seals. The piston and displacer are reciprocated in their housings by linear drive motors to vary the volume of respectively adjacent compression and expansion spaces which contain a gaseous working fluid and a thermal regenerator to effect Stirling cycle cryogenic cooling.

  1. Gap Cycling for SWIFT

    CERN Document Server

    Corum, Curtis A; Snyder, Carl J; Garwood, Michael

    2013-01-01

    Purpose: SWIFT (SWeep Imaging with Fourier Transformation) is a non- Cartesian MRI method with unique features and capabilities. In SWIFT, radiofrequency (RF) excitation and reception are performed nearly simultaneously, by rapidly switching between transmit and receive during a frequency-swept RF pulse. Because both the transmitted pulse and data acquisition are simultaneously amplitude-modulated in SWIFT (in contrast to continuous RF excitation and uninterrupted data acquisition in more familiar MRI sequences), crosstalk between different frequency bands occurs in the data. This crosstalk leads to a "bulls-eye" artifact in SWIFT images. We present a method to cancel this inter-band crosstalk by cycling the pulse and receive gap positions relative to the un-gapped pulse shape. We call this strategy "gap cycling." Methods: We carry out theoretical analysis, simulation and experiments to characterize the signal chain, resulting artifacts, and their elimination for SWIFT. Results: Theoretical analysis reveals t...

  2. Archaea in biogeochemical cycles.

    Science.gov (United States)

    Offre, Pierre; Spang, Anja; Schleper, Christa

    2013-01-01

    Archaea constitute a considerable fraction of the microbial biomass on Earth. Like Bacteria they have evolved a variety of energy metabolisms using organic and/or inorganic electron donors and acceptors, and many of them are able to fix carbon from inorganic sources. Archaea thus play crucial roles in the Earth's global geochemical cycles and influence greenhouse gas emissions. Methanogenesis and anaerobic methane oxidation are important steps in the carbon cycle; both are performed exclusively by anaerobic archaea. Oxidation of ammonia to nitrite is performed by Thaumarchaeota. They represent the only archaeal group that resides in large numbers in the global aerobic terrestrial and marine environments on Earth. Sulfur-dependent archaea are confined mostly to hot environments, but metal leaching by acidophiles and reduction of sulfate by anaerobic, nonthermophilic methane oxidizers have a potential impact on the environment. The metabolisms of a large number of archaea, in particular those dominating the subsurface, remain to be explored.

  3. Menstrual cycle pattern and fertility

    DEFF Research Database (Denmark)

    Kolstad, Henrik A.; Bonde, Jens Peter; Hjøllund, Niels Henrik;

    1999-01-01

    OUTCOME MEASURE(S): The probability of pregnancy occurring within one menstrual cycle (fecundity). RESULT(S): In women who had a cycle length that differed by >10 days from the usual cycle length, fecundity was approximately 25% that of women who had no variation (odds ratio 0.25, 95% confidence interval...... 0.09-0.68). When the combined effect of cycle variation and cycle length was assessed, cycle variation was a persistent strong predictor of fecundity. CONCLUSION(S): The mechanisms of the present findings probably are female functional disturbances in ovulation, conception, implantation......, or sustained pregnancy, linked with variable menstrual cycle length. Thus, identification of medical and environmental causes of abnormal menstrual cycle patterns may provide clues to the causes of infertility. Moreover, the menstrual cycle pattern also should be taken into consideration in the clinical...

  4. Assessing Cycling Participation in Australia

    Directory of Open Access Journals (Sweden)

    Chris Rissel

    2013-01-01

    Full Text Available Planning and evaluating cycling programs at a national or state level requires accurate measures of cycling participation. However, recent reports of cycling participation have produced very different estimates. This paper examines the reported rates of cycling in five recent population surveys of cycling. Three surveys (one national and two from Sydney asking respondents when they last rode a bicycle generated cycling participation (cycled in the past year estimates of 29.7%, 34.1% and 28.9%. Two other national surveys which asked participants to recall (unprompted any physical activity done for exercise, recreation or sport in the previous 12 months, estimated cycling in the past year as 11.1% and 6.5%. While unprompted recall of cycling as a type of physical activity generates lower estimates of cycling participation than specific recall questions, both assessment approaches produced similar patterns of cycling by age and sex with both approaches indicating fewer women and older adults cycling. The different question styles most likely explain the substantial discrepancies between the estimates of cycling participation. Some differences are to be expected due to sampling variability, question differences, and regional variation in cycling.

  5. The nuclear fuel cycle

    International Nuclear Information System (INIS)

    The papers presented at the International Conference on The Nuclear Fuel Cycle, held at Stockholm, 28 to 31 October 1975, are reviewed. The meeting, organised by the U.S. Atomic Industrial Forum, and the Swedish Nuclear Forum, was concerned more particularly with economic, political, social and commercial aspects than with tecnology. The papers discussed were considered under the subject heading of current status, uranium resources, enrichment, and reprocessing. (U.K.)

  6. Concordance in Business Cycles

    OpenAIRE

    C. John McDermott; Alasdair Scott

    2000-01-01

    We study the properties of a test that determines whether two time series comove. The test computes a simple nonparametric statistic for “concordance,” which describes the proportion of time that the cycles of two series spend in the same phase. We establish the size and power properties of this test. As an illustration, the procedures are applied to output series from selected major industrial countries. We find limited evidence of widespread concordance for these countries.

  7. Cycles in Nonlinear Macroeconomics

    OpenAIRE

    Voronin, Anatoly V.; Chernyshov, Sergey I.

    2007-01-01

    The monograph is concerned with some key problems of the theory of nonlinear economic dynamics. The authors' concept consists in analyzing the problem of structural instability of economic systems within the framework of the synergetic paradigm. As examples, the classical models of macroeconomics are considered. The authors present the results of the study of the phenomenon of self-organization in open and nonequilibrium economic systems. The generation of limit cycles, as well as of more com...

  8. Steps and cycles

    OpenAIRE

    Chadwick, Andy

    2015-01-01

    Andy Chadwick* explains how interaction between continuous trend with natural climate cycles produces the observed stepped pattern of global warming Climate-change ‘sceptics’ have made great mileage out of the current hiatus in observed global warming. Atmospheric temperatures have not really increased since the turn of the 21st Century, a fact frequently cited as incompatible with, or even disproving, global warming. These same commentators draw a discreet veil over the fact that temper...

  9. FUZZY REASONING IN CYCLES

    Institute of Scientific and Technical Information of China (English)

    曹立明

    1990-01-01

    By the similarity between the syllogism in logic and a path proposition in graph theory,a new concept,fuzzy reasoning graph G has been given in this paper. Transitive closure has been studied and used to do reasoning related to self-loop in G,and an algorithm has been designed to cope with reasoning in other cycles in G. Both approaches are applicable and efficient.

  10. Nuclear Fuel Cycle

    Energy Technology Data Exchange (ETDEWEB)

    Dale, Deborah J. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2014-10-28

    These slides will be presented at the training course “International Training Course on Implementing State Systems of Accounting for and Control (SSAC) of Nuclear Material for States with Small Quantity Protocols (SQP),” on November 3-7, 2014 in Santa Fe, New Mexico. The slides provide a basic overview of the Nuclear Fuel Cycle. This is a joint training course provided by NNSA and IAEA.

  11. International Business Cycle

    Directory of Open Access Journals (Sweden)

    Marek Lubiński

    2007-06-01

    Full Text Available Prime stylized facts of international business cycle theory refer to positive correlation in the cyclical components of important macroeconomic variables across countries. However a number of indicators of business cycle synchronization do not point to clear trends. It can be ascribed to the fact that different forces influence level of business cycle correlation. When investigating into the forces behind the commonness in aggregate fluctuations economic research seems to have pointed in two directions. One strand of the literature examines the idea of common exogenous shocks that affect economies simultaneously. In addition to that economic interdependencies such as trade in goods and services or capital account transactions may serve as the channels through which disturbances spill over across countries.The observed degree of output co movement reflects both the nature of the shocks that have occurred and the degree of economic interdependence. In the periods when common shocks prevail level of synchronization is usually higher than in times of transmission dominance.

  12. Terrestrial Carbon Cycle Variability

    Science.gov (United States)

    Baldocchi, Dennis; Ryu, Youngryel; Keenan, Trevor

    2016-01-01

    A growing literature is reporting on how the terrestrial carbon cycle is experiencing year-to-year variability because of climate anomalies and trends caused by global change. As CO 2 concentration records in the atmosphere exceed 50 years and as satellite records reach over 30 years in length, we are becoming better able to address carbon cycle variability and trends. Here we review how variable the carbon cycle is, how large the trends in its gross and net fluxes are, and how well the signal can be separated from noise. We explore mechanisms that explain year-to-year variability and trends by deconstructing the global carbon budget. The CO 2 concentration record is detecting a significant increase in the seasonal amplitude between 1958 and now. Inferential methods provide a variety of explanations for this result, but a conclusive attribution remains elusive. Scientists have reported that this trend is a consequence of the greening of the biosphere, stronger northern latitude photosynthesis, more photosynthesis by semi-arid ecosystems, agriculture and the green revolution, tropical temperature anomalies, or increased winter respiration. At the global scale, variability in the terrestrial carbon cycle can be due to changes in constituent fluxes, gross primary productivity, plant respiration and heterotrophic (microbial) respiration, and losses due to fire, land use change, soil erosion, or harvesting. It remains controversial whether or not there is a significant trend in global primary productivity (due to rising CO 2, temperature, nitrogen deposition, changing land use, and preponderance of wet and dry regions). The degree to which year-to-year variability in temperature and precipitation anomalies affect global primary productivity also remains uncertain. For perspective, interannual variability in global gross primary productivity is relatively small (on the order of 2 Pg-C y -1) with respect to a large and uncertain background (123 +/- 4 Pg-C y -1), and

  13. Bifurcation of limit cycles near equivariant compound cycles

    Institute of Scientific and Technical Information of China (English)

    Mao-an HAN; Tong-hua ZHANG; Hong ZANG

    2007-01-01

    In this paper we study some equivariant systems on the plane. We first give some criteria for the outer or inner stability of compound cycles of these systems. Then we investigate the number of limit cycles which appear near a compound cycle of a Hamiltonian equivariant system under equivariant perturbations. In the last part of the paper we present an application of our general theory to show that a Z3 equivariant system can have 13 limit cycles.

  14. Cycle-to-cycle variability as an optimal behavioral strategy

    OpenAIRE

    Brezina, Vladimir; Proekt, Alex; Weiss, Klaudiusz R.

    2006-01-01

    Aplysia feeding behavior is highly variable from cycle to cycle. In some cycles, when the variability causes a mismatch between the animal's movements and the requirements of the feeding task, the variability makes the behavior unsuccessful. We propose that the behavior is variable nevertheless because the variability serves a higher-order functional purpose. When the animal is faced with a new and only imperfectly known feeding task in each cycle, the variability implements a trial-and-error...

  15. How well can business cycle accounting account for business cycles?

    OpenAIRE

    Otsu, Keisuke

    2012-01-01

    The business cycle accounting method introduced by Chari, Kehoe and McGrattan (2007) is a useful tool to decompose business cycle fluctuations into their contributing factors. However, the model estimated by the maximum likelihood method cannot replicate business cycle moments computed from data. Moment-based estimation might be an attractive alternative if the purpose of the research is to study business cycle properties such as volatility, persistence and cross-correlation of variables inst...

  16. Research and development of an air-cycle heat-pump water heater. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Dieckmann, J.T.; Erickson, A.J.; Harvey, A.C.; Toscano, W.M.

    1979-10-01

    A prototype reverse Brayton air cycle heat pump water heater has been designed and built for residential applications. The system consists of a compressor/expander, an air-water heat exchanger, an electric motor, a water circulation pump, a thermostat, and fluid management controls. The prototype development program consisted of a market analysis, design study, and development testing. A potential residential market for the new high-efficiency water heater of approximately 480,000 units/y was identified. The retail and installation cost of this water heater is estimated to be between $500 and $600 which is approximately $300 more than a conventional electric water heater. The average payback per unit is less than 3-1/2 y and the average recurring energy cost savings after the payback period is approximately $105/y at the average seasonal coefficient of performance (COP) of 1.7. As part of the design effort, a thermodynamic parametric analysis was performed on the water heater system. It was determined that to obtain a coefficient of performance of 1.7, the isentropic efficiency of both the compressor and the expander must be at least 85%. The selected mechanical configuration is described. The water heater has a diameter of 25 in. and a height of 73 in. The results of the development testing of the prototype water heater system showed: the electrical motor maximum efficiency of 78%; the compressor isentropic efficiency is 95 to 119% and the volumetric efficiency is approximately 85%; the expander isentropic efficiency is approximately 58% and the volumetric efficiency is 92%; a significant heat transfer loss of approximately 16% occurred in the expander; and the prototype heat pump system COP is 1.26 which is less than the design goal of at least 1.7. Future development work is recommended.

  17. The software life cycle

    CERN Document Server

    Ince, Darrel

    1990-01-01

    The Software Life Cycle deals with the software lifecycle, that is, what exactly happens when software is developed. Topics covered include aspects of software engineering, structured techniques of software development, and software project management. The use of mathematics to design and develop computer systems is also discussed. This book is comprised of 20 chapters divided into four sections and begins with an overview of software engineering and software development, paying particular attention to the birth of software engineering and the introduction of formal methods of software develop

  18. Geomicrobiological cycling of antimony

    Science.gov (United States)

    Kulp, T. R.; Terry, L.; Dovick, M. A.; Braiotta, F.

    2013-12-01

    Microbiologically catalyzed oxidation and reduction of toxic metalloids (e.g., As, Se, and Te) generally proceeds much faster than corresponding abiotic reactions. These microbial transformations constitute biogeochemical cycles that control chemical speciation and environmental behavior of metalloids in aqueous environments. Particular progress has been made over the past two decades in documenting microbiological biotransformations of As, which include anaerobic respiratory reduction of As(V) to As(III), oxidation of As(III) to As(V) linked to chemoautotrophy or photoautotrophy, and cellular detoxification pathways. By contrast, microbial interactions with Sb, As's group 15 neighbor and a toxic element of emerging global concern, are poorly understood. Our work with sediment microcosms, enrichment cultures, and bacterial isolates suggests that prokaryotic metabolisms may be similarly important to environmental Sb cycling. Enrichment cultures and isolates from a Sb-contaminated mine site in Idaho exhibited Sb(V)-dependent heterotrophic respiration under anaerobic conditions and Sb(III)-dependent autotrophic growth in the presence of air. Live, anoxic cultures reduced 2 mM Sb(V) to Sb(III) within 5 d, while no activity occurred in killed controls. Sb(V) reduction was stimulated by lactate or acetate and was quantitatively coupled to the oxidation of lactate. The oxidation of radiolabeled 14C-acetate (monitored by GC-GPC) demonstrated Sb(V)-dependent oxidation to 14CO2, suggesting a dissimilatory process. Sb(V) dependent growth in cultures was demonstrated by direct counting. Microbiological reduction of Sb(V) also occurred in anerobic sediment microcosms from an uncontaminated suburban lake, but did not appear to be linked to growth and is interpreted as a mechanism of biological detoxification. Aerobic microcosms and cultures from the Idaho mine oxidized 2 mM Sb(III) to Sb(V) within 7 d and coupled this reaction to cell growth quantified by direct counting. An

  19. Revenue cycle management: part I.

    Science.gov (United States)

    Crew, Matt

    2006-01-01

    The revenue cycle starts long before a patient is seen and continues until a claim is completely resolved. Each step in the revenue cycle must be clearly defined and easy to follow. Use of various tools such as templates, forms, reports, spreadsheets, and components of your practice management system will help to provide the consistency you need for profitable revenue cycle management.

  20. Sometimes "Newton's Method" Always "Cycles"

    Science.gov (United States)

    Latulippe, Joe; Switkes, Jennifer

    2012-01-01

    Are there functions for which Newton's method cycles for all non-trivial initial guesses? We construct and solve a differential equation whose solution is a real-valued function that two-cycles under Newton iteration. Higher-order cycles of Newton's method iterates are explored in the complex plane using complex powers of "x." We find a class of…

  1. Paths and cycles of hypergraphs

    Institute of Scientific and Technical Information of China (English)

    王建方; Tony; T.Lee

    1999-01-01

    Hypergraphs are the most general structures in discrete mathematics. Acyclic hypergraphs have been proved very useful in relational databases. New systems of axioms for paths, connectivity and cycles of hypergraphs are constructed. The systems suit the structure properties of relational databases. The concepts of pseudo cycles and essential cycles of hypergraphs are introduced. They are relative to each other. Whether a family of cycles of a hypergraph is dependent or independent is defined. An enumeration formula for the maximum number of independent essential cycles of a hypergraph is given.

  2. Part 5. Fuel cycle options

    International Nuclear Information System (INIS)

    The results of the FBR fuel cycle study that supported US contributions to the INFCE are presented. Fuel cycle technology is reviewed from both generic and historical standpoints. Technology requirements are developed within the framework of three deployment scenarios: the reference international, the secured area, and the integral cycle. Reprocessing, fabrication, waste handling, transportation, and safeguards are discussed for each deployment scenario. Fuel cycle modifications designed to increase proliferation defenses are described and assessed for effectiveness and technology feasibility. The present status of fuel cycle technology is reviewed and key issues that require resolution are identified

  3. Exfoliation Propensity of Oxide Scale in Heat Exchangers Used for Supercritical CO2 Power Cycles

    Energy Technology Data Exchange (ETDEWEB)

    Sabau, Adrian S [ORNL; Shingledecker, John P. [Electric Power Research Institute (EPRI); Kung, Steve [Electric Power Research Institute (EPRI); Wright, Ian G. [WrightHT, Inc.; Nash, Jim [Brayton Energy, LLC, Hampton, NH

    2016-01-01

    Supercritical CO2 (sCO2) Brayton cycle systems offer the possibility of improved efficiency in future fossil energy power generation plants operating at temperatures of 650 C and above. As there are few data on the oxidation/corrosion behavior of structural alloys in sCO2 at these temperatures, modeling to predict the propensity for oxide exfoliation is not well developed, thus hindering materials selection for these novel cycles. The ultimate goal of this effort is to provide needed data on scale exfoliation behavior in sCO2 for confident alloy selection. To date, a model developed by ORNL and EPRI for the exfoliation of oxide scales formed on boiler tubes in high-temperature, high-pressure steam has proven useful for managing exfoliation in conventional steam plants. A major input provided by the model is the ability to predict the likelihood of scale failure and loss based on understanding of the evolution of the oxide morphologies and the conditions that result in susceptibility to exfoliation. This paper describes initial steps taken to extend the existing model for exfoliation of steam-side oxide scales to sCO2 conditions. The main differences between high-temperature, high-pressure steam and sCO2 that impact the model involve (i) significant geometrical differences in the heat exchangers, ranging from standard pressurized tubes seen typically in steam-producing boilers to designs for sCO2 that employ variously-curved thin walls to create shaped flow paths for extended heat transfer area and small channel cross-sections to promote thermal convection and support pressure loads; (ii) changed operating characteristics with sCO2 due to the differences in physical and thermal properties compared to steam; and (iii) possible modification of the scale morphologies, hence properties that influence exfoliation behavior, due to reaction with carbon species from sCO2. The numerical simulations conducted were based on an assumed sCO2 operating schedule and several

  4. Krebs Cycle Wordsearch

    Science.gov (United States)

    Helser, Terry L.

    2001-04-01

    This puzzle embeds 46 names, terms, abbreviations, and acronyms about the citric acid (Krebs) cycle in a 14- x 17-letter matrix. A descriptive narrative beside it describes important features of the pathway. All the terms a student needs to find are embedded there with the first letter followed by underlined blanks to be completed. Therefore, the students usually must find the terms to know how to spell them, correctly fill in the blanks in the narrative with the terms, and then find and highlight the terms in the letter matrix. When all are found, the 24 unused letters complete a sentence that describes a major feature of this central pathway. The puzzle may be used as homework, an extra-credit project, or a group project in the classroom in any course where basic metabolism is learned. It disguises as fun the hard work needed to learn the names of the intermediates, enzymes, and cofactors.

  5. Open cycle thermoacoustics

    Energy Technology Data Exchange (ETDEWEB)

    Reid, Robert Stowers

    2000-01-01

    A new type of thermodynamic device combining a thermodynamic cycle with the externally applied steady flow of an open thermodynamic process is discussed and experimentally demonstrated. The gas flowing through this device can be heated or cooled in a series of semi-open cyclic steps. The combination of open and cyclic flows makes possible the elimination of some or all of the heat exchangers (with their associated irreversibility). Heat is directly exchanged with the process fluid as it flows through the device when operating as a refrigerator, producing a staging effect that tends to increase First Law thermodynamic efficiency. An open-flow thermoacoustic refrigerator was built to demonstrate this concept. Several approaches are presented that describe the physical characteristics of this device. Tests have been conducted on this refrigerator with good agreement with a proposed theory.

  6. HTGR fuel cycle

    International Nuclear Information System (INIS)

    In the spring of 1987, the HTGR fuel cycle project has been existing for ten years, and for this reason a status seminar has been held on May 12, 1987 in the Juelich Nuclear Research Center, that gathered the participants in this project for a discussion on the state of the art in HTGR fuel element development, graphite development, and waste management. The papers present an overview of work performed so far and an outlook on future tasks and goals, and on taking stock one can say that the project has been very successful so far: The HTGR fuel element now available meets highest requirements and forms the basis of today's HTGR safety philosophy; research work on graphite behaviour in a high-temperature reactor has led to complete knowledge of the temperature or neutron-induced effects, and with the concept of direct ultimate waste disposal, the waste management problem has found a feasible solution. (orig./GL)

  7. The supercontinent cycle

    Energy Technology Data Exchange (ETDEWEB)

    Nance, R.D.; Worsley, T.R.; Moody, J.B.

    1988-07-01

    This paper discusses a new theory of plate tectonics which proposes that Pangaea was only the most recent in a series of supercontinents that have been breaking up and reassembling every 500 million years or so. The cycle, driven by heat percolating up from the mantle, splits continents and drives interrelated processes that shape the earth's geology and climate and play a role in biological evolution. The framework of the supercontinent theory makes it possible to understand the timing of changes in sea level that have taken place in the past 570 million years, and also helps to explain periods of intense mountain building, episodes of glaciation, and changes in the nature of life on the earth.

  8. The uranium cycle

    International Nuclear Information System (INIS)

    In identifying uranium provinces, and, more importantly, mineralized zones within these provinces, it is of paramount importance to attempt to trace the geochemical behaviour of an element through all stages of Earth's evolution. Aspects that need to be addressed in this regard include solar abundance levels and fractionation processes during accretion, changing patterns of crustal evolution, effects of an evolving atmosphere, and the weathering cycle. Abundance patterns and partition coefficients of some of the siderophile elements in mantle rocks lend support to a multistage accretionary process. Lack of a terrestrial record in the first 500 Ma necessitates that lunar models be invoked, which suggests that early fractionation of a mafic/ultramafic magma resulted in an anorthositic crust. Fractionation of the mantle and transfer of materials to the upper levels must be central to any model invoked for development of the crust. Given high heat flow conditions in the early Archaean it would seem inescapable that the process of sea floor spreading and plate tectonics was an ongoing process. If the plate tectonic model is taken back to 3500 Ma, and assuming current speading rates, then about half of the mantle has passed through the irreversible differentiation cycle. Arguments in support of recycled material must be balanced against mantle metasomatism effects. With the associated advent of partial melting of the mantle material a partitioning of minor and trace elements into the melt fraction would take place. The early primitive mafic and ultramafic komatiites exemplify this feature by concentrating U and Th by a factor of 5 compared to chondritic abundances. It is of tantamount importance to understand the generation of the magmas in order to predict which are the 'fertile' bodies in terms of radioelement concentrations. In that the granitoid magmas image their source compositions, the association of high radioelements will primarily be source-dependent. Uranium

  9. Measurement of single cycle and sub-cycle pulse duration

    Institute of Scientific and Technical Information of China (English)

    Zhenglie Gong(龚正烈); Wenzhuo Ge(葛文卓); Guizhong Zhang(张贵忠); Wanghua Xiang(向望华)

    2004-01-01

    This paper suggests that the linear interferometric correlation (LFC) can be used to measure pulse duration of a few cycles, single cycle or even sub-cycle light pulse. The relations between pulsewidth and LFC curve are derived for Gaussian- and hyperbolic secant-shaped pules. This new method abandons focusing,frequency doubling and filtering in the traditional second order correlation method, meanwhile the signalto-noise ratio (SNR) is improved.

  10. Overview of cycling injuries: results of a cycling club survey.

    Science.gov (United States)

    Decalzi, Javier F; Narvy, Steven J; Vangsness, C Thomas

    2013-04-01

    Participation in competitive bicycling has increased substantially over the past decade, and bicycle injuries have increased accordingly. Cycling has been reported in several studies to have higher rates of injury than other sports and recreational activities; accordingly, riders must be cognizant of the potential for injury and protect themselves appropriately. The purpose of the current study was to survey an established competitive Los Angeles-based road cycling team to determine the epidemiology of and circumstances for traumatic cycling injuries.

  11. Removing Cycles in Esterel Programs

    Directory of Open Access Journals (Sweden)

    Reinhard von Hanxleden

    2007-05-01

    Full Text Available Esterel belongs to the family of synchronous programming languages, which are affected by cyclic signal dependencies. This prohibits a static scheduling, limiting the choice of available compilation techniques for programs with such cycles. This work proposes an algorithm that, given a constructive synchronous Esterel program, performs a semantics-preserving source code level transformation that removes cyclic signal dependencies. The transformation is divided into two parts: detection of cycles and iterative resolution of these cycles. It is based on the replacement of cycle signals by a signal expression involving no other cycle signals, thereby breaking the cycle. This transformation of cyclic Esterel programs enables the use of efficient compilation techniques, which are only available for acyclic programs. Furthermore, experiments indicate that the code transformation can even improve code quality produced by compilers that can already handle cyclic programs.

  12. Reproductive cycles of buffalo.

    Science.gov (United States)

    Perera, B M A O

    2011-04-01

    The domestic water buffalo (Bubalus bubalis) has an important role in the agricultural economy of many developing countries in Asia, providing milk, meat and draught power. It is also used in some Mediterranean and Latin American countries as a source of milk and meat for specialized markets. Although the buffalo can adapt to harsh environments and live on poor quality forage, reproductive efficiency is often compromised by such conditions, resulting in late sexual maturity, long postpartum anoestrus, poor expression of oestrus, poor conception rates and long calving intervals. The age at puberty is influenced by genotype, nutrition, management and climate, and under favourable conditions occurs at 15-18 months in river buffalo and 21-24 months in swamp buffalo. The ovaries are smaller than in cattle and contain fewer primordial follicles. Buffalo are capable of breeding throughout the year, but in many countries a seasonal pattern of ovarian activity occurs. This is attributed in tropical regions to changes in rainfall resulting in feed availability or to temperature stress resulting in elevated prolactin secretion, and in temperate regions to changes in photoperiod and melatonin secretion. The mean length of the oestrous cycle is 21 days, with greater variation than observed in cattle. The signs of oestrus in buffalo are less overt than in cattle and homosexual behaviour between females is rare. The duration of oestrus is 5-27 h, with ovulation occurring 24-48 h (mean 34 h) after the onset of oestrus. The hormonal changes occurring in peripheral circulation are similar to those observed in cattle, but the peak concentrations of progesterone and oestradiol-17β are less. The number of follicular waves during an oestrous cycle varies from one to three and influences the length of the luteal phase as well as the inter-ovulatory interval. Under optimal conditions, dairy types managed with limited or no suckling resume oestrus cyclicity by 30-60 days after calving

  13. Entrepreneurship and the business cycle

    OpenAIRE

    Thurik, Roy

    2014-01-01

    Entrepreneurship has a cyclical component, raising two questions. Is the entrepreneurship cycle related to the business cycle? And is there causality? A two-way relationship between entrepreneurship and the business cycle would be in line with the two faces of entrepreneurs: as agents of change creating upswings (opportunity entrepreneurship) and as rational actors escaping unemployment by setting up a business (necessity entrepreneurship). Nascent entrepreneurship can indeed be precyclical, ...

  14. Rethinking the Ancient Sulfur Cycle

    Science.gov (United States)

    Fike, David A.; Bradley, Alexander S.; Rose, Catherine V.

    2015-05-01

    The sulfur biogeochemical cycle integrates the metabolic activity of multiple microbial pathways (e.g., sulfate reduction, disproportionation, and sulfide oxidation) along with abiotic reactions and geological processes that cycle sulfur through various reservoirs. The sulfur cycle impacts the global carbon cycle and climate primarily through the remineralization of organic carbon. Over geological timescales, cycling of sulfur is closely tied to the redox state of Earth's exosphere through the burial of oxidized (sulfate) and reduced (sulfide) sulfur species in marine sediments. Biological sulfur cycling is associated with isotopic fractionations that can be used to trace the fluxes through various metabolic pathways. The resulting isotopic data provide insights into sulfur cycling in both modern and ancient environments via isotopic signatures in sedimentary sulfate and sulfide phases. Here, we review the deep-time δ34S record of marine sulfates and sulfides in light of recent advances in understanding how isotopic signatures are generated by microbial activity, how these signatures are encoded in marine sediments, and how they may be altered following deposition. The resulting picture shows a sulfur cycle intimately coupled to ambient carbon cycling, where sulfur isotopic records preserved in sedimentary rocks are critically dependent on sedimentological and geochemical conditions (e.g., iron availability) during deposition.

  15. Regenerative superheated steam turbine cycles

    Science.gov (United States)

    Fuller, L. C.; Stovall, T. K.

    1980-01-01

    PRESTO computer program was developed to analyze performance of wide range of steam turbine cycles with special attention given to regenerative superheated steam turbine cycles. It can be used to model standard turbine cycles, including such features as process steam extraction, induction and feedwater heating by external sources, peaking, and high back pressure. Expansion line efficiencies, exhaust loss, leakages, mechanical losses, and generator losses are used to calculate cycle heat rate and generator output. Program provides power engineer with flexible aid for design and analysis of steam turbine systems.

  16. Organic rankine cycle fluid

    Science.gov (United States)

    Brasz, Joost J.; Jonsson, Ulf J.

    2006-09-05

    A method of operating an organic rankine cycle system wherein a liquid refrigerant is circulated to an evaporator where heat is introduced to the refrigerant to convert it to vapor. The vapor is then passed through a turbine, with the resulting cooled vapor then passing through a condenser for condensing the vapor to a liquid. The refrigerant is one of CF.sub.3CF.sub.2C(O)CF(CF.sub.3).sub.2, (CF.sub.3).sub.2 CFC(O)CF(CF.sub.3).sub.2, CF.sub.3(CF.sub.2).sub.2C(O)CF(CF.sub.3).sub.2, CF.sub.3(CF.sub.2).sub.3C(O)CF(CG.sub.3).sub.2, CF.sub.3(CF.sub.2).sub.5C(O)CF.sub.3, CF.sub.3CF.sub.2C(O)CF.sub.2CF.sub.2CF.sub.3, CF.sub.3C(O)CF(CF.sub.3).sub.2.

  17. The earth's hydrological cycle

    CERN Document Server

    Bonnet, R-M; Calisto, M; Destouni, G; Gurney, R; Johannessen, J; Kerr, Y; Lahoz, WA; Rast, M

    2014-01-01

    This book gives a comprehensive presentation of our present understanding of the Earth's Hydrological cycle and the problems, consequences and impacts that go with this topic. Water is a central component in the Earth's system. It is indispensable for life on Earth in its present form and influences virtually every aspect of our planet's life support system. On relatively short time scales, atmospheric water vapor interacts with the atmospheric circulation and is crucial in forming the Earth's climate zones. Water vapor is the most powerful of the greenhouse gases and serves to enhance the tropospheric temperature. The dominant part of available water on Earth resides in the oceans. Parts are locked up in the land ice on Greenland and Antarctica and a smaller part is estimated to exist as groundwater. If all the ice over the land and all the glaciers were to melt, the sea level would rise by some 80 m. In comparison, the total amount of water vapor in the atmosphere is small; it amounts to ~ 25 kg/m2, or the ...

  18. Biomass Gasification Combined Cycle

    Energy Technology Data Exchange (ETDEWEB)

    Judith A. Kieffer

    2000-07-01

    Gasification combined cycle continues to represent an important defining technology area for the forest products industry. The ''Forest Products Gasification Initiative'', organized under the Industry's Agenda 2020 technology vision and supported by the DOE ''Industries of the Future'' program, is well positioned to guide these technologies to commercial success within a five-to ten-year timeframe given supportive federal budgets and public policy. Commercial success will result in significant environmental and renewable energy goals that are shared by the Industry and the Nation. The Battelle/FERCO LIVG technology, which is the technology of choice for the application reported here, remains of high interest due to characteristics that make it well suited for integration with the infrastructure of a pulp production facility. The capital cost, operating economics and long-term demonstration of this technology area key input to future economically sustainable projects and must be verified by the 200 BDT/day demonstration facility currently operating in Burlington, Vermont. The New Bern application that was the initial objective of this project is not currently economically viable and will not be implemented at this time due to several changes at and around the mill which have occurred since the inception of the project in 1995. The analysis shows that for this technology, and likely other gasification technologies as well, the first few installations will require unique circumstances, or supportive public policies, or both to attract host sites and investors.

  19. The closed fuel cycle

    International Nuclear Information System (INIS)

    Available in abstract form only. Full text of publication follows: The fast growth of the world's economy coupled with the need for optimizing use of natural resources, for energy security and for climate change mitigation make energy supply one of the 21. century most daring challenges. The high reliability and efficiency of nuclear energy, its competitiveness in an energy market undergoing a new oil shock are as many factors in favor of the 'renaissance' of this greenhouse gas free energy. Over 160,000 tHM of LWR1 and AGR2 Used Nuclear Fuel (UNF) have already been unloaded from the reactor cores corresponding to 7,000 tons discharged per year worldwide. By 2030, this amount could exceed 400,000 tHM and annual unloading 14,000 tHM/year. AREVA believes that closing the nuclear fuel cycle through the treatment and recycling of Used Nuclear Fuel sustains the worldwide nuclear power expansion. It is an economically sound and environmentally responsible choice, based on the preservation of natural resources through the recycling of used fuel. It furthermore provides a safe and secure management of wastes while significantly minimizing the burden left to future generations. (authors)

  20. Life Cycle of Stars

    Science.gov (United States)

    1999-01-01

    In this stunning picture of the giant galactic nebula NGC 3603, the crisp resolution of NASA's Hubble Space Telescope captures various stages of the life cycle of stars in one single view. To the upper left of center is the evolved blue supergiant called Sher 25. The star has a unique circumstellar ring of glowing gas that is a galactic twin to the famous ring around the supernova 1987A. The grayish-bluish color of the ring and the bipolar outflows (blobs to the upper right and lower left of the star) indicates the presence of processed (chemically enriched) material. Near the center of the view is a so-called starburst cluster dominated by young, hot Wolf-Rayet stars and early O-type stars. A torrent of ionizing radiation and fast stellar winds from these massive stars has blown a large cavity around the cluster. The most spectacular evidence for the interaction of ionizing radiation with cold molecular-hydrogen cloud material are the giant gaseous pillars to the right of the cluster. These pillars are sculptured by the same physical processes as the famous pillars Hubble photographed in the M16 Eagle Nebula. Dark clouds at the upper right are so-called Bok globules, which are probably in an earlier stage of star formation. To the lower left of the cluster are two compact, tadpole-shaped emission nebulae. Similar structures were found by Hubble in Orion, and have been interpreted as gas and dust evaporation from possibly protoplanetary disks (proplyds). This true-color picture was taken on March 5, 1999 with the Wide Field Planetary Camera 2.

  1. The LifeCycle model

    DEFF Research Database (Denmark)

    Krink, Thiemo; Løvbjerg, Morten

    2002-01-01

    Adaptive search heuristics are known to be valuable in approximating solutions to hard search problems. However, these techniques are problem dependent. Inspired by the idea of life cycle stages found in nature, we introduce a hybrid approach called the LifeCycle model that simultaneously applies...

  2. Nuclear fuel cycle information workshop

    International Nuclear Information System (INIS)

    This overview of the nuclear fuel cycle is divided into three parts. First, is a brief discussion of the basic principles of how nuclear reactors work; second, is a look at the major types of nuclear reactors being used and world-wide nuclear capacity; and third, is an overview of the nuclear fuel cycle and the present industrial capability in the US

  3. Economic growth and business cycles

    NARCIS (Netherlands)

    Canton, E.J.F.

    1997-01-01

    This thesis contains five essays on economic growth and business cycles. The main focus is on the interaction between economic growth and the cycle: is cyclical variability good or bad for the long-run rate of economic growth? The introduction aims to provide some empirical evidence for an investmen

  4. The water cycle for kids

    Science.gov (United States)

    Neno, Stephanie; Morgan, Jim; Zonolli, Gabriele; Perlman, Howard; Gonthier, Gerard

    2013-01-01

    The U.S. Geological Survey (USGS) and the Food and Agriculture Organization of the United Nations (FAO) have created a water-cycle diagram for use in elementary and middle schools. The diagram is available in many languages. This diagram is part of the USGS's Water Science School, in which the water cycle is described in detail.

  5. Activity Cycle of Solar Filaments

    Indian Academy of Sciences (India)

    K. J. Li; Q. X. Li; P. X. Gao; J. Mu; H. D. Chen; T. W. Su

    2007-06-01

    Long-term variation in the distribution of the solar filaments observed at the Observatorie de Paris, Section de Meudon from March 1919 to December 1989 is presented to compare with sunspot cycle and to study the periodicity in the filament activity, namely the periods of the coronal activity with the Morlet wavelet used. It is inferred that the activity cycle of solar filaments should have the same cycle length as sunspot cycle, but the cycle behavior of solar filaments is globally similar in profile with, but different in detail from, that of sunspot cycles. The amplitude of solar magnetic activity should not keep in phase with the complexity of solar magnetic activity. The possible periods in the filament activity are about 10.44 and 19.20 years. The wavelet local power spectrum of the period 10.44 years is statistically significant during the whole consideration time. The wavelet local power spectrum of the period 19.20 years is under the 95% confidence spectrum during the whole consideration time, but over the mean red-noise spectrum of = 0.72 before approximate Carrington rotation number 1500, and after that the filament activity does not statistically show the period. Wavelet reconstruction indicates that the early data of the filament archive (in and before cycle 16) are more noiseful than the later (in and after cycle 17).

  6. MOTHER MK II: An advanced direct cycle high temperature gas reactor

    International Nuclear Information System (INIS)

    The MOTHER (MOdular Thermal HElium Reactor) power plant concepts employ high temperature gas reactors utilizing TRISO fuel, graphite moderator, and helium coolant, in combination with a direct Brayton cycle for electricity generation. The helium coolant from the reactor vessel passes through a Power Conversion Unit (PCU), which includes a turbine-generator, recuperator, precooler, intercooler and turbine-compressors, before being returned to the reactor vessel. The PCU substitutes for the reactor coolant system pumps and steam generators and most of the Balance Of Plant (BOP), including the steam turbines and condensers, employed by conventional nuclear power plants utilizing water cooled reactors. This provides a compact, efficient, and relatively simple plant configuration. The MOTHER MK I conceptual design, completed in the 1987 - 1989 time frame, was developed to economically meet the energy demands for extracting and processing heavy oil from the tar sands of western Canada. However, considerable effort was made to maximize the market potential beyond this application. Consistent with the remote and very high labour rate environment in the tar sands region, simplification of maintenance procedures and facilitation of 'change-out' in lieu of in situ repair was a design focus. MOTHER MK I had a thermal output of 288 MW and produced 120 MW electrical when operated in the electricity only production mode. An annular Prismatic reactor core was utilized, largely to minimize day-to-day operations activities. Key features of the power conversion system included two Power Conversion Units (144 MWth each), the horizontal orientation of all rotating machinery and major heat exchangers axes, high speed rotating machinery (17,030 rpm for the turbine-compressors and 10,200 rpm for the power turbine-generator), gas (helium) bearings for all rotating machinery, and solid state frequency conversion from 170 cps (at full power) to the grid frequency. Recognizing that the on

  7. Prospects for Predicting Cycle 24

    Indian Academy of Sciences (India)

    Arnab Rai Choudhuri

    2008-03-01

    Although we have reliable data of solar polar fields only from the mid-1970s, it seems that the polar field at a minimum is well correlated with the next cycle, but the strength of the cycle is not correlated with the polar field produced at its end. We explain this by suggesting that the Babcock–Leighton mechanism of poloidal field generation from tilted active regions involves randomness, whereas the other aspects of the dynamo process are more ordered. To model actual cycles, we have to ‘correct’ our theoretical dynamo model by ‘feeding’ information about the polar field at the minima. Following this process, we find that our model fits the observed sunspot numbers of cycles 21–23 reasonably well and predicts that cycle 24 will be the weakest in a century.

  8. Super- and Transcritical Fluid Expansions for Next-Generation Energy Conversion Systems

    NARCIS (Netherlands)

    Harinck, J.

    2010-01-01

    The next generation of thermodynamic power cycles offers great potential as the conceptual basis for sustainable energy converters. Examples are the supercritical and superheated Organic Rankine cycle, the transcritical condensation cycle, the supercritical Brayton cycle, the Organic Stirling cycle

  9. Limit cycles in quantum systems

    Energy Technology Data Exchange (ETDEWEB)

    Niemann, Patrick

    2015-04-27

    In this thesis we investigate Limit Cycles in Quantum Systems. Limit cycles are a renormalization group (RG) topology. When degrees of freedom are integrated out, the coupling constants flow periodically in a closed curve. The presence of limit cycles is restricted by the necessary condition of discrete scale invariance. A signature of discrete scale invariance and limit cycles is log-periodic behavior. The first part of this thesis is concerned with the study of limit cycles with the similarity renormalization group (SRG). Limit cycles are mainly investigated within conventional renormalization group frameworks, where degrees of freedom, which are larger than a given cutoff, are integrated out. In contrast, in the SRG potentials are unitarily transformed and thereby obtain a band-diagonal structure. The width of the band structure can be regarded as an effective cutoff. We investigate the appearance of limit cycles in the SRG evolution. Our aim is to extract signatures as well as the scaling factor of the limit cycle. We consider the 1/R{sup 2}-potential in a two-body system and a three-body system with large scattering lengths. Both systems display a limit cycle. Besides the frequently used kinetic energy generator we apply the exponential and the inverse generator. In the second part of this thesis, Limit Cycles at Finite Density, we examine the pole structure of the scattering amplitude for distinguishable fermions at zero temperature in the medium. Unequal masses and a filled Fermi sphere for each fermion species are considered. We focus on negative scattering lengths and the unitary limit. The properties of the three-body spectrum in the medium and implications for the phase structure of ultracold Fermi gases are discussed.

  10. Power and Efficiency Analysis of a Solar Central Receiver Combined Cycle Plant with a Small Particle Heat Exchanger Receiver

    Science.gov (United States)

    Virgen, Matthew Miguel

    Two significant goals in solar plant operation are lower cost and higher efficiencies. To achieve those goals, a combined cycle gas turbine (CCGT) system, which uses the hot gas turbine exhaust to produce superheated steam for a bottoming Rankine cycle by way of a heat recovery steam generator (HRSG), is investigated in this work. Building off of a previous gas turbine model created at the Combustion and Solar Energy Laboratory at SDSU, here are added the HRSG and steam turbine model, which had to handle significant change in the mass flow and temperature of air exiting the gas turbine due to varying solar input. A wide range of cases were run to explore options for maximizing both power and efficiency from the proposed CSP CCGT plant. Variable guide vanes (VGVs) were found in the earlier model to be an effective tool in providing operational flexibility to address the variable nature of solar input. Combined cycle efficiencies in the range of 50% were found to result from this plant configuration. However, a combustor inlet temperature (CIT) limit leads to two distinct Modes of operation, with a sharp drop in both plant efficiency and power occurring when the air flow through the receiver exceeded the CIT limit. This drawback can be partially addressed through strategic use of the VGVs. Since system response is fully established for the relevant range of solar input and variable guide vane angles, the System Advisor Model (SAM) from NREL can be used to find what the actual expected solar input would be over the course of the day, and plan accordingly. While the SAM software is not yet equipped to model a Brayton cycle cavity receiver, appropriate approximations were made in order to produce a suitable heliostat field to fit this system. Since the SPHER uses carbon nano-particles as the solar absorbers, questions of particle longevity and how the particles might affect the flame behavior in the combustor were addressed using the chemical kinetics software Chemkin

  11. Hydrogen-or-Fossil-Combustion Nuclear Combined-Cycle Systems for Base- and Peak-Load Electricity Production

    Energy Technology Data Exchange (ETDEWEB)

    Forsberg, Charles W [ORNL; Conklin, Jim [ORNL

    2007-09-01

    A combined-cycle power plant is described that uses (1) heat from a high-temperature nuclear reactor to meet base-load electrical demands and (2) heat from the same high-temperature reactor and burning natural gas, jet fuel, or hydrogen to meet peak-load electrical demands. For base-load electricity production, fresh air is compressed; then flows through a heat exchanger, where it is heated to between 700 and 900 C by heat provided by a high-temperature nuclear reactor via an intermediate heat-transport loop; and finally exits through a high-temperature gas turbine to produce electricity. The hot exhaust from the Brayton-cycle gas turbine is then fed to a heat recovery steam generator that provides steam to a steam turbine for added electrical power production. To meet peak electricity demand, the air is first compressed and then heated with the heat from a high-temperature reactor. Natural gas, jet fuel, or hydrogen is then injected into the hot air in a combustion chamber, combusts, and heats the air to 1300 C-the operating conditions for a standard natural-gas-fired combined-cycle plant. The hot gas then flows through a gas turbine and a heat recovery steam generator before being sent to the exhaust stack. The higher temperatures increase the plant efficiency and power output. If hydrogen is used, it can be produced at night using energy from the nuclear reactor and stored until needed. With hydrogen serving as the auxiliary fuel for peak power production, the electricity output to the electric grid can vary from zero (i.e., when hydrogen is being produced) to the maximum peak power while the nuclear reactor operates at constant load. Because nuclear heat raises air temperatures above the auto-ignition temperatures of the various fuels and powers the air compressor, the power output can be varied rapidly (compared with the capabilities of fossil-fired turbines) to meet spinning reserve requirements and stabilize the electric grid. This combined cycle uses the

  12. Hydrogen or Fossil Combustion Nuclear Combined Cycle Systems for Baseload and Peak Load Electricity Production. Annex X

    International Nuclear Information System (INIS)

    A combined cycle power plant is described that uses: (i) heat from a high temperature nuclear reactor to meet baseload electrical demands; and (ii) heat from the same high temperature reactor and burning natural gas, jet fuel or hydrogen to meet peak load electrical demands. For baseload electricity production, fresh air is compressed, then flows through a heat exchanger, where it is heated to between 700 and 900oC by using heat provided by a high temperature nuclear reactor via an intermediate heat transport loop, and finally exits through a high temperature gas turbine to produce electricity. The hot exhaust from the Brayton cycle gas turbine is then fed to a heat recovery steam generator that provides steam to a steam turbine for added electrical power production. To meet peak electricity demand, the air is first compressed and then heated with the heat from a high temperature reactor. Natural gas, jet fuel or hydrogen is then injected into the hot air in a combustion chamber, combusts and heats the air to 1300oC - the operating conditions for a standard natural gas fired combined cycle plant. The hot gas then flows through a gas turbine and a heat recovery steam generator before being sent to the exhaust stack. The higher temperatures increase the plant efficiency and power output. If hydrogen is used, it can be produced at night using energy from the nuclear reactor and stored until required. With hydrogen serving as the auxiliary fuel for peak power production, the electricity output to the electrical grid can vary from zero (i.e. when hydrogen is being produced) to the maximum peak power while the nuclear reactor operates at constant load. As nuclear heat raises air temperatures above the auto-ignition temperatures of the various fuels and powers the air compressor, the power output can be varied rapidly (compared with the capabilities of fossil fired turbines) to meet spinning reserve requirements and stabilize the electrical grid. This combined cycle uses

  13. Life cycle of mobile devices

    Directory of Open Access Journals (Sweden)

    T.V. Rohal

    2011-12-01

    Full Text Available Article is devoted features of life cycle of mobile devices. The article highlighted a number of disadvantages associated with managing the life cycle of the product. Disadvantages include the orientation is not on the quality of mobile devices and their design, the obsolescence of digital products. The article drew attention to the need for process improvement life cycle management of mobile devices. For since this type of product is now the most popular among the population, consumers are interested, first of all, quality, and only then, look good.

  14. Introducing Life Cycle Impact Assessment

    DEFF Research Database (Denmark)

    Hauschild, Michael Zwicky; Huijbregts, Mark AJ

    2015-01-01

    methodology projects and presents the international scientific discussions and methodological consensus attempts in consecutive working groups under the auspices of the Society of Environmental Toxicology and Chemistry (SETAC) as well as the UNEP/ SETAC Life Cycle Initiative, and the (almost) parallel......This chapter serves as an introduction to the presentation of the many aspects of life cycle impact assessment (LCIA) in this volume of the book series ‘LCA Compendium’. It starts with a brief historical overview of the development of life cycle impact assessment driven by numerous national LCIA...

  15. Prospects for predicting cycle 24

    OpenAIRE

    Choudhuri, Arnab Rai

    2008-01-01

    Although we have reliable data of solar polar fields only from the mid-1970s, it seems that the polar field at a minimum is well correlated with the next cycle, but the strength of the cycle is not correlated with the polar field produced at its end. We explain this by suggesting that the Babcock–Leighton mechanism of poloidal field generation from tilted active regions involves randomness, whereas the other aspects of the dynamo process are more ordered. To model actual cycles, we have to 'c...

  16. (Auto)Ethnographies and Cycling

    DEFF Research Database (Denmark)

    Larsen, Jonas

    2014-01-01

    , habits and affective capacities of cycling are cultivated and performed. The article argues that autoethnography is particularly apt at illuminating the embodied qualities of movement, and it sits within established ethnographies of ‘excising’ and ‘mobile bodies’. In the second part of the article, I...... draw upon ongoing autoethnographies of cycling in a familiar place (my hometown, Copenhagen) and by learning to cycle ‘out-of-place’ (in London) and ‘in-a-new–way’ (when commuting long distance on a racer bike). The study challenges static notions of the body by analysing how cyclists’ (and researchers...

  17. BWROPT: A multi-cycle BWR fuel cycle optimization code

    Energy Technology Data Exchange (ETDEWEB)

    Ottinger, Keith E.; Maldonado, G. Ivan, E-mail: Ivan.Maldonado@utk.edu

    2015-09-15

    Highlights: • A multi-cycle BWR fuel cycle optimization algorithm is presented. • New fuel inventory and core loading pattern determination. • The parallel simulated annealing algorithm was used for the optimization. • Variable sampling probabilities were compared to constant sampling probabilities. - Abstract: A new computer code for performing BWR in-core and out-of-core fuel cycle optimization for multiple cycles simultaneously has been developed. Parallel simulated annealing (PSA) is used to optimize the new fuel inventory and placement of new and reload fuel for each cycle considered. Several algorithm improvements were implemented and evaluated. The most significant of these are variable sampling probabilities and sampling new fuel types from an ordered array. A heuristic control rod pattern (CRP) search algorithm was also implemented, which is useful for single CRP determinations, however, this feature requires significant computational resources and is currently not practical for use in a full multi-cycle optimization. The PSA algorithm was demonstrated to be capable of significant objective function reduction and finding candidate loading patterns without constraint violations. The use of variable sampling probabilities was shown to reduce runtime while producing better results compared to using constant sampling probabilities. Sampling new fuel types from an ordered array was shown to have a mixed effect compared to random new fuel type sampling, whereby using both random and ordered sampling produced better results but required longer runtimes.

  18. Life-cycle cost analysis of adsorption cycles for desalination

    KAUST Repository

    Thu, Kyaw

    2010-08-01

    This paper presents the thermo-economic analysis of the adsorption desalination (AD) cycle that is driven by low-temperature waste heat from exhaust of industrial processes or renewable sources. The AD cycle uses an adsorbent such as the silica gel to desalt the sea or brackish water. Based on an experimental prototype AD plant, the life-cycle cost analysis of AD plants of assorted water production capacities has been simulated and these predictions are translated into unit cost of water production. Our results show that the specific energy consumption of the AD cycle is 1.38 kWh/m3 which is the lowest ever reported. For a plant capacity of 1000 m3/d, the AD cycle offers a unit cost of $0.457/m3 as compared to more than $0.9 for the average RO plants. Besides being cost-effective, the AD cycle is also environment-friendly as it emits less CO2 emission per m3 generated, typically 85% less, by comparison to an RO process. © 2010 Desalination Publications.

  19. Heat exchanger temperature response for duty-cycle transients in the NGNP/HTE

    International Nuclear Information System (INIS)

    the reference NGNP/HTE plant can be found in the body of this report. The outcome is an integrated plant/control system design. The following conclusions are drawn from the analysis: (1) The plant load schedule can be managed to maintain near-constant hot side temperatures over the load range in both the nuclear and chemical plant. (2) The reactor open-loop response is inherently stable resulting mainly from a large Doppler temperature coefficient compared to the other reactivity temperature feedbacks. (3) The typical controller used to manage reactor power production to maintain reactor outlet temperature at a setpoint introduces a feedback path that tends to destabilize reactor power production in the NGNP. (4) A primary loop flow controller that forces primary flow to track PCU flow rate is effective in minimizing spatial temperature differentials within the IHX. (5) Inventory control in both the primary and PCU system during ramp load change transients is an effective means of maintaining high NGNP thermal efficiency while at reduced electric load. (6) Turbine bypass control is an effective means for responding to step changes in generator load when equipment capacity limitations prevent inventory control from being effective. (7) Turbine bypass control is effective in limiting PCU shaft over speed for the loss of generator load upset event. (8) The proposed control strategy is effective in limiting time variation of the differential spatial temperature distribution in the IHX during transients. Essentially the IHX can be made to behave in a manner where each point in the IHX experiences approximately the same temperature rate of change during a transient. (9) The stability of the closed-loop Brayton cycle was found to be sensitive to where one operates on the turbo-machine performance maps. There are competing interests: more stable operation means operating on the curves at points that reduce overall cycle efficiency. Future work should address in greater detail

  20. Corporate governance cycles during transition

    DEFF Research Database (Denmark)

    Mygind, Niels; Demina, Natalia; Gregoric, Aleksandra;

    2004-01-01

    -nancial system. To provide simple hypothesis tests, we use Russian enterprise data for 1995-2003 and Slovenian data covering 1998-2003. In spite of differences in institutional development, con-cerning privatization and development of corporate governance institutions, we find that govern-ance cycles are broadly...... of ownership on managers, external domestic and foreign owners. JEL-codes: G3, J5, P2, P3 - Keywords: corporate governance, life-cycle, privatization, ownership change, transition economies, Russia and Slovenia.......Ownership is determined by firm specific factors and the environment. Firms change over their life-cycle. The governance cycle - here defined as changes in identity of the dominant owner and own-ership concentration - is marked by key phases including start-up, growth, and possibly a restructur...

  1. Revenue cycle management, Part II.

    Science.gov (United States)

    Crew, Matt

    2007-01-01

    The proper management of your revenue cycle requires the application of "best practices" and the continual monitoring and measuring of the entire cycle. The correct technology will enable you to gain the insight and efficiencies needed in the ever-changing healthcare economy. The revenue cycle is a process that begins when you negotiate payor contracts, set fees, and schedule appointments and continues until claims are paid in full. Every single step in the cycle carries equal importance. Monitoring all phases and a commitment to continually communicating the results will allow you to achieve unparalleled success. In part I of this article, we explored the importance of contracting, scheduling, and case management as well as coding and clinical documentation. We will now take a closer look at the benefits charge capture, claim submission, payment posting, accounts receivable follow-up, and reporting can mean to your practice.

  2. Total Product Life Cycle (TPLC)

    Data.gov (United States)

    U.S. Department of Health & Human Services — The Total Product Life Cycle (TPLC) database integrates premarket and postmarket data about medical devices. It includes information pulled from CDRH databases...

  3. Mirador - Carbon Cycle and Ecosystems

    Data.gov (United States)

    National Aeronautics and Space Administration — Earth Science data access made simple. This Focus Area deals with the cycling of carbon in reservoirs and ecosystems as it changes naturally, is changed by humans,...

  4. Mirador - Water and Energy Cycles

    Data.gov (United States)

    National Aeronautics and Space Administration — Earth Science data access made simple. Through water and energy cycle research we can improve hurricane prediction, quantify tropical rainfall and eventually begin...

  5. Cycling in multimodal transport behaviours

    DEFF Research Database (Denmark)

    Olafsson, Anton Stahl; Nielsen, Thomas Sick; Carstensen, Trine Agervig

    2016-01-01

    explores how cycling forms part of multimodal transport behaviour based on survey data on transport modes and travel purposes and the weekly frequency of out-of-home activities and travel mode use in a representative sample of adult Danes (n = 1957). The following five distinct multimodal travel segments......Multimodality is important for achieving less car dependent lifestyles and more sustainable transport behaviours. It is widely recognised that cycling plays a prominent role in sustainable transport. However, research has largely focused on cycling substituting motorised transport. This study...... or 'modality styles' are identified: 'education transport'; 'public-based transport'; 'limited transport'; 'bicycle-based transport'; and 'car-based transport'. Travel behaviour is predominantly multimodal with few unimodal car-drivers being identified. Substantial cycling takes place in all modality styles...

  6. Towards Life Cycle Sustainability Assessment

    Directory of Open Access Journals (Sweden)

    Marzia Traverso

    2010-10-01

    Full Text Available Sustainability is nowadays accepted by all stakeholders as a guiding principle for both public policy making and corporate strategies. However, the biggest challenge for most organizations remains in the real and substantial implementation of the sustainability concept. The core of the implementation challenge is the question, how sustainability performance can be measured, especially for products and processes. This paper explores the current status of Life Cycle Sustainability Assessment (LCSA for products and processes. For the environmental dimension well established tools like Life Cycle Assessment are available. For the economic and social dimension, there is still need for consistent and robust indicators and methods. In addition to measuring the individual sustainability dimensions, another challenge is a comprehensive, yet understandable presentation of the results. The “Life Cycle Sustainability Dashboard” and the “Life Cycle Sustainability Triangle” are presented as examples for communication tools for both experts and non expert stakeholders.

  7. Venus Altitude Cycling Balloon Project

    Data.gov (United States)

    National Aeronautics and Space Administration — The ISTAR Group ( IG) and team mate Thin Red Line Aerospace (TRLA) propose a Venus altitude cycling balloon (Venus ACB), an innovative superpressure balloon...

  8. Endogenous, Imperfectly Competitive Business Cycles

    DEFF Research Database (Denmark)

    Whitta-Jacobsen, Hans Jørgen

    We investigate how imperfect competition affects the occurrence and the properties of endogenous, rational expectations business cycles in an overlapping generations model with constant returns to scale in production. The model has explicit product and labor markets all characterized...... by monopolistic competition. An implicit assumption of barriers to entry justifies that the number of firms is fixed even when positive profits occur. It turns out that both market power of firms on the product markets and market power of unions on the labor markets make the occurrence of cycles more likely....... In particular, imperfect competition on the product markets and the positive profits associated with it may have the effect that there is a cycle even if the labor supply curve is increasing in the real-wage rate. For competitive cycles is required not only a decreasing labor supply curve, but a wage elasticity...

  9. Stability ordering of cycle expansions

    CERN Document Server

    Dettmann, C P

    1997-01-01

    We propose that cycle expansions be ordered with respect to stability rather than orbit length for many chaotic systems, particularly those exhibiting crises. This is illustrated with the strong field Lorentz gas, where we obtain significant improvements over traditional approaches.

  10. Glacial Cycles and Milankovitch Forcing

    CERN Document Server

    Raghuraman, Shiv Priyam

    2015-01-01

    Using a recent conceptual model of the glacial-interglacial cycles we present more evidence of Milankovitch cycles being the trigger for retreat and forming of ice sheets in the cycles. This model is based on a finite approximation of an infinite dimensional model which has three components: Budyko's energy balance model describing the annual mean temperatures at latitudes, Widiasih's ODE which describes the behavior of the edge of the ice sheet, and Walsh et al. who introduced a snow line to account for glacial accumulation and ablation zones. Certain variables in the model are made to depend on the Milankovitch cycles, in particular, the obliquity of the Earth's axis and the eccentricity of the Earth's orbit. We see as a result that deglaciation and glaciation do occur mostly due to obliquity and to some extent eccentricity.

  11. On acyclicity of games with cycles

    DEFF Research Database (Denmark)

    Andersson, Klas Olof Daniel; Hansen, Thomas Dueholm; Gurvich, Vladimir

    2010-01-01

    We study restricted improvement cycles (ri-cycles) in finite positional n-person games with perfect information modeled by directed graphs (di-graphs) that may contain directed cycles (di-cycles). We assume that all these di-cycles form one outcome c, for example, a draw. We obtain criteria of re...

  12. No News in Business Cycles

    OpenAIRE

    Forni, Mario; Gambetti, Luca; Sala, Luca

    2011-01-01

    This paper uses a structural, large dimensional factor model to evaluate the role of 'news' shocks (shocks with a delayed effect on productivity) in generating the business cycle. We find that (i) existing small-scale VECM models are affected by 'non-fundamentalness' and therefore fail to recover the correct shock and impulse response functions; (ii) news shocks have a limited role in explaining the business cycle; (iii) their effects are in line with what predicted by standard neoclassical t...

  13. Business Cycle Theory and Econometrics

    OpenAIRE

    Allan W. Gregory; Smith, Gregor W.

    1995-01-01

    We outline in turn criticisms made by econometricians of the methods used in empirical business-cycle research and then criticisms made by business-cycle researchers of some methods used by econometricians. The aim is to clarify and in some cases correct these criticisms. Overall there is no conflict in using rigourous statistical procedures to study modern dynamic stochastic general equilibrium models. We also provide a concise bibliography of recent research on statistical methods for busin...

  14. Limit cycles of effective theories

    OpenAIRE

    Glazek, Stanislaw D.

    2006-01-01

    A simple example is used to show that renormalization group limit cycles of effective quantum theories can be studied in a new way. The method is based on the similarity renormalization group procedure for Hamiltonians. The example contains a logarithmic ultraviolet divergence that is generated by both real and imaginary parts of the Hamiltonian matrix elements. Discussion of the example includes a connection between asymptotic freedom with one scale of bound states and the limit cycle with a...

  15. Social learning and innovation cycles

    OpenAIRE

    Garfagnini, Umberto; Strulovici, Bruno

    2012-01-01

    We study social learning and innovation in an overlapping generations model, emphasizing the trade-off between marginal innovation (combining existing technologies) and radical innovation (breaking new ground). We characterize both short-term and long-term dynamics of innovation, and the intergenerational accumulation of knowledge. Innovation cycles emerge endogenously, but the number of cycles is finite almost surely, and radical innovation terminates in finite time. We identify a negative r...

  16. Animal spirits and business cycles

    OpenAIRE

    Bidder, Rhys

    2015-01-01

    Animal spirits are often suggested as a cause of business cycles, but they are very difficult to define. Recent research proposes a novel explanation based on the changing level of risk over time and people’s uncertainty about how the world works. The interaction of these two can lead to significant business cycle fluctuations in response to spikes in volatility. This finding gives researchers an alternative to irrational behavior as an explanation for why swings in consumer sentiment appear ...

  17. The NEWS Water Cycle Climatology

    Science.gov (United States)

    Rodell, Matthew; Beaudoing, Hiroko Kato; L'Ecuyer, Tristan; William, Olson

    2012-01-01

    NASA's Energy and Water Cycle Study (NEWS) program fosters collaborative research towards improved quantification and prediction of water and energy cycle consequences of climate change. In order to measure change, it is first necessary to describe current conditions. The goal of the first phase of the NEWS Water and Energy Cycle Climatology project was to develop "state of the global water cycle" and "state of the global energy cycle" assessments based on data from modern ground and space based observing systems and data integrating models. The project was a multi-institutional collaboration with more than 20 active contributors. This presentation will describe the results of the water cycle component of the first phase of the project, which include seasonal (monthly) climatologies of water fluxes over land, ocean, and atmosphere at continental and ocean basin scales. The requirement of closure of the water budget (i.e., mass conservation) at various scales was exploited to constrain the flux estimates via an optimization approach that will also be described. Further, error assessments were included with the input datasets, and we examine these in relation to inferred uncertainty in the optimized flux estimates in order to gauge our current ability to close the water budget within an expected uncertainty range.

  18. Fuel cycles using adulterated plutonium

    Energy Technology Data Exchange (ETDEWEB)

    Brooksbank, R. E.; Bigelow, J. E.; Campbell, D. O.; Kitts, F. G.; Lindauer, R. B.

    1978-01-01

    Adjustments in the U-Pu fuel cycle necessitated by decisions made to improve the nonproliferation objectives of the US are examined. The uranium-based fuel cycle, using bred plutonium to provide the fissile enrichment, is the fuel system with the highest degree of commercial development at the present time. However, because purified plutonium can be used in weapons, this fuel cycle is potentially vulnerable to diversion of that plutonium. It does appear that there are technologically sound ways in which the plutonium might be adulterated by admixture with /sup 238/U and/or radioisotopes, and maintained in that state throughout the fuel cycle, so that the likelihood of a successful diversion is small. Adulteration of the plutonium in this manner would have relatively little effect on the operations of existing or planned reactors. Studies now in progress should show within a year or two whether the less expensive coprocessing scheme would provide adequate protection (coupled perhaps with elaborate conventional safeguards procedures) or if the more expensive spiked fuel cycle is needed as in the proposed civex pocess. If the latter is the case, it will be further necessary to determine the optimum spiking level, which could vary as much as a factor of a billion. A very basic question hangs on these determinations: What is to be the nature of the recycle fuel fabrication facilities. If the hot, fully remote fuel fabrication is required, then a great deal of further development work will be required to make the full cycle fully commercial.

  19. Optimization of the fuel cycle

    International Nuclear Information System (INIS)

    The nuclear fuel cycle can be optimized subject to a wide range of criteria. Prime amongst these are economics, sustainability of resources, environmental aspects, and proliferation-resistance of the fuel cycle. Other specific national objectives will also be important. These criteria, and their relative importance, will vary from country to country, and with time. There is no single fuel cycle strategy that is optimal for all countries. Within the short term, the industry is attached to dominant thermal reactor technologies, which themselves have two main variants, a cycle closed by reprocessing of spent fuel and subsequent recycling and a once through one where spent fuel is stored in advance of geological disposal. However, even with current technologies, much can be done to optimize the fuel cycles to meet the relevant criteria. In the long term, resource sustainability can be assured for centuries through the use of fast breeder reactors, supporting high-conversion thermal reactors, possibly also utilizing the thorium cycle. These must, however, meet the other key criteria by being both economic and safe. (author)

  20. A biogeochemical cycle for aluminium?

    Science.gov (United States)

    Exley, Christopher

    2003-09-15

    The elaboration of biogeochemical cycles for elements which are known to be essential for life has enabled a broad appreciation of the homeostatic mechanisms which underlie element essentiality. In particular they can be used effectively to identify any part played by human activities in element cycling and to predict how such activities might impact upon the lithospheric and biospheric availability of an element in the future. The same criteria were the driving force behind the construction of a biogeochemical cycle for aluminium, a non-essential element which is a known ecotoxicant and a suspected health risk in humans. The purpose of this exercise was to examine the concept of a biogeochemical cycle for aluminium and not to review the biogeochemistry of this element. The cycle as presented is rudimentary and qualitative though, even in this nascent form, it is informative and predictive and, for these reasons alone, it is deserving of future quantification. A fully fledged biogeochemical cycle for aluminium should explain the biospheric abundance of this element and whether we should expect its (continued) active involvement in biochemical evolution.

  1. The Water Cycle Solutions Network

    Science.gov (United States)

    Houser, P.; Belvedere, D.; Imam, B.; Schiffer, R.; Schlosser, C.; Gupta, H.; Welty, C.; Vörösmarty, C.; Matthews, D.; Lawford, R.

    2006-12-01

    The goal of the Water cycle Solutions Network is to improve and optimize the sustained ability of water cycle researchers, stakeholders, organizations and networks to interact, identify, harness, and extend research results to augment decision support tools and meet national needs. WaterNet will engage relevant NASA water cycle research resources and community-of-practice organizations, to develop what we term an "actionable database" that can be used to communicate and connect water cycle research results (WCRs) towards the improvement of water-related Decision Support Tools (DSTs). An actionable database includes enough sufficient knowledge about its nodes and their heritage so that connections between these nodes are identifiable and robust. Recognizing the many existing highly valuable water-related science and application networks, we will focus the balance of our efforts on enabling their interoperability in a solutions network context. We will initially focus on identification, collection, and analysis of the two end points, these being the WCRs and water related DSTs. We will then develop strategies to connect these two end points via innovative communication strategies, improved user access to NASA resources, improved water cycle research community appreciation for DST requirements, improved policymaker, management and stakeholder knowledge of NASA research and application products, and improved identification of pathways for progress. Finally, we will develop relevant benchmarking and metrics, to understand the network's characteristics, to optimize its performance, and to establish sustainability. The WaterNet will deliver numerous pre-evaluation reports that will identify the pathways for improving the collective ability of the water cycle community to routinely harness WCRs that address crosscutting water cycle challenges.

  2. GT-MHR international project of high-temperature helium cooled reactor with direct gas-turbine power conversion cycle

    International Nuclear Information System (INIS)

    Full text: The international project of gas-turbine modular helium-cooled reactor (GT-MHR) presented in the report is a realization of high-temperature technology and is based on the experience with helium-cooled reactors with ceramic fuel particles and on innovative solutions concerning power conversion system with closed gas-turbine cycle and turbomachine with electromagnetic bearings. The international GT-MHR Project is currently being jointly developed by USA and Russia for disposition of excessive weapon-grade plutonium. For commercial electricity generation, the reactor will use uranium fuel. The GT-MHR combines a gas-cooled modular helium reactor (MHR) and a highly efficient integrated gas-turbine power conversion system (Brayton cycle) with expected cycle efficiency up to 48%. The reactor and power conversion unit are located in an underground concrete silo. The GT-MHR technical characteristics and design features assure: high level of passive safety that completely prevents core melting in accidents with any scenario, including full loss of inert coolant; low level of thermal and radiation impact to the environment; capability to use various fuels in the core (e.g. low-enriched uranium, mixed uranium-thorium and uranium-plutonium fuel, or plutonium fuel) without modifying the core design; meeting the non-proliferation requirements through technology and properties of ceramic fuel particles; capability to achieve coolant temperatures of up to 1000 deg. C, which is needed for various industrial processes; high efficiency of electricity generation. A whole complex of research and development activities is being carried out by RRC KI, OKBM, VNIINM, 'Lutch', and other Russian organizations in order to support key design solutions, primarily on fuel, turbomachine with electromagnetic bearings, structural materials, vessels and computer codes. At present, the GT-MHR capability to generate high-grade heat at temperatures up to 1000 deg. C makes it the only

  3. Focused training boosts revenue cycle skills, accountability.

    Science.gov (United States)

    Richmond, Craig

    2011-09-01

    In 2009, the MetroHealth System took its first steps toward creating a comprehensive revenue cycle university, with the goal of developing revenue cycle staff talent and achieving best-in-class revenue cycle operations. MetroHealth became a beta site for HFMA's online Credentialed Revenue Cycle Representative (CRCR) program, and asked its revenue cycle leaders to present classes on key revenue cycle issues. As of June 2011, 62 percent of 122 revenue cycle employees who had taken the CRCR course passed the exam. The CRCR designation is now a prerequisite for career advancement in certain revenue cycle areas at MetroHealth.

  4. Antifreeze life cycle assessment (LCA

    Directory of Open Access Journals (Sweden)

    Kesić Jelena

    2005-01-01

    Full Text Available Antifreeze based on ethylene glycol is a commonly used commercial product The classification of ethylene glycol as a toxic material increased the disposal costs for used antifreeze and life cycle assessment became a necessity. Life Cycle Assessment (LCA considers the identification and quantification of raw materials and energy inputs and waste outputs during the whole life cycle of the analyzed product. The objectives of LCA are the evaluation of impacts on the environment and improvements of processes in order to reduce and/or eliminate waste. LCA is conducted through a mathematical model derived from mass and energy balances of all the processes included in the life cycle. In all energy processes the part of energy that can be transformed into some other kind of energy is called exergy. The concept of exergy considers the quality of different types of energy and the quality of different materials. It is also a connection between energy and mass transformations. The whole life cycle can be described by the value of the total loss of exergy. The physical meaning of this value is the loss of material and energy that can be used. The results of LCA are very useful for the analyzed products and processes and for the determined conditions under which the analysis was conducted. The results of this study indicate that recycling is the most satisfactory solution for the treatment of used antifreeze regarding material and energy consumption but the re-use of antifreeze should not be neglected as a solution.

  5. Analysis of supercritical CO{sub 2} cycle control strategies and dynamic response for Generation IV Reactors.

    Energy Technology Data Exchange (ETDEWEB)

    Moisseytsev, A.; Sienicki, J. J. (Nuclear Engineering Division)

    2011-04-12

    The analysis of specific control strategies and dynamic behavior of the supercritical carbon dioxide (S-CO{sub 2}) Brayton cycle has been extended to the two reactor types selected for continued development under the Generation IV Nuclear Energy Systems Initiative; namely, the Very High Temperature Reactor (VHTR) and the Sodium-Cooled Fast Reactor (SFR). Direct application of the standard S-CO{sub 2} recompression cycle to the VHTR was found to be challenging because of the mismatch in the temperature drop of the He gaseous reactor coolant through the He-to-CO{sub 2} reactor heat exchanger (RHX) versus the temperature rise of the CO{sub 2} through the RHX. The reference VHTR features a large temperature drop of 450 C between the assumed core outlet and inlet temperatures of 850 and 400 C, respectively. This large temperature difference is an essential feature of the VHTR enabling a lower He flow rate reducing the required core velocities and pressure drop. In contrast, the standard recompression S-CO{sub 2} cycle wants to operate with a temperature rise through the RHX of about 150 C reflecting the temperature drop as the CO{sub 2} expands from 20 MPa to 7.4 MPa in the turbine and the fact that the cycle is highly recuperated such that the CO{sub 2} entering the RHX is effectively preheated. Because of this mismatch, direct application of the standard recompression cycle results in a relatively poor cycle efficiency of 44.9%. However, two approaches have been identified by which the S-CO{sub 2} cycle can be successfully adapted to the VHTR and the benefits of the S-CO{sub 2} cycle, especially a significant gain in cycle efficiency, can be realized. The first approach involves the use of three separate cascaded S-CO{sub 2} cycles. Each S-CO{sub 2} cycle is coupled to the VHTR through its own He-to-CO{sub 2} RHX in which the He temperature is reduced by 150 C. The three respective cycles have efficiencies of 54, 50, and 44%, respectively, resulting in a net cycle

  6. Analysis of supercritical CO{sub 2} cycle control strategies and dynamic response for Generation IV Reactors.

    Energy Technology Data Exchange (ETDEWEB)

    Moisseytsev, A.; Sienicki, J. J. (Nuclear Engineering Division)

    2011-04-12

    The analysis of specific control strategies and dynamic behavior of the supercritical carbon dioxide (S-CO{sub 2}) Brayton cycle has been extended to the two reactor types selected for continued development under the Generation IV Nuclear Energy Systems Initiative; namely, the Very High Temperature Reactor (VHTR) and the Sodium-Cooled Fast Reactor (SFR). Direct application of the standard S-CO{sub 2} recompression cycle to the VHTR was found to be challenging because of the mismatch in the temperature drop of the He gaseous reactor coolant through the He-to-CO{sub 2} reactor heat exchanger (RHX) versus the temperature rise of the CO{sub 2} through the RHX. The reference VHTR features a large temperature drop of 450 C between the assumed core outlet and inlet temperatures of 850 and 400 C, respectively. This large temperature difference is an essential feature of the VHTR enabling a lower He flow rate reducing the required core velocities and pressure drop. In contrast, the standard recompression S-CO{sub 2} cycle wants to operate with a temperature rise through the RHX of about 150 C reflecting the temperature drop as the CO{sub 2} expands from 20 MPa to 7.4 MPa in the turbine and the fact that the cycle is highly recuperated such that the CO{sub 2} entering the RHX is effectively preheated. Because of this mismatch, direct application of the standard recompression cycle results in a relatively poor cycle efficiency of 44.9%. However, two approaches have been identified by which the S-CO{sub 2} cycle can be successfully adapted to the VHTR and the benefits of the S-CO{sub 2} cycle, especially a significant gain in cycle efficiency, can be realized. The first approach involves the use of three separate cascaded S-CO{sub 2} cycles. Each S-CO{sub 2} cycle is coupled to the VHTR through its own He-to-CO{sub 2} RHX in which the He temperature is reduced by 150 C. The three respective cycles have efficiencies of 54, 50, and 44%, respectively, resulting in a net cycle

  7. Proliferation resistance fuel cycle technology

    Energy Technology Data Exchange (ETDEWEB)

    Lee, J. S.; Ko, W. I

    1999-02-01

    The issues of dual use in nuclear technology are analysed for nuclear fuel cycle with special focus on uranium enrichment and spent fuel reprocessing which are considered as the most sensitive components in terms of vulnerability to diversion. Technical alternatives to mitigrate the vulnerability, as has been analysed in depth during the NASAP and INFCE era in the late seventies, are reviewed to characterize the DUPIC fuel cycle alternative. On the other hand, the new realities in nuclear energy including the disposition of weapon materials as a legacy of cold war are recast in an angle of nuclear proliferation resistance and safeguards with a discussion on the concept of spent fuel standard concept and its compliance with the DUPIC fuel cycle technology. (author)

  8. Corporate governance cycles during transition

    DEFF Research Database (Denmark)

    Jones, Derek C.; Mygind, Niels

    2004-01-01

    is faster in Estonia and this can be explained by the relatively fast pace of institutional change and evolution of important gov-ernance institutions, including tough bankruptcy legislation and advances in the financial system. JEL-codes: G3, J5, P2, P3 Keywords: corporate governance, life......We begin by identifying a typical governance life-cycle, defined as changes in ownership structure, and including both the identity of the major owner and ownership concentration. The cycle is marked by key events and phases including start-up, initial growth, mature growth, and possibly a crisis...... and restructuring stage or exit stage. The governance cycle for transitional countries reflects some specific characteristics -e.g. often privatization produces specific initial ownership structures, with an unusually high proportion of insider, especially, employee ownership. Subsequently pres...

  9. Measuring risky adolescent cycling behaviour.

    Science.gov (United States)

    Feenstra, Hans; Ruiter, Robert A C; Schepers, Jan; Peters, Gjalt-Jorn; Kok, Gerjo

    2011-09-01

    Adolescents are at a greater risk of being involved in traffic accidents than most other age groups, even before they start driving cars. This article aims to determine the factor structure of a self-report questionnaire measuring adolescent risky cycling behaviour, the ACBQ (Adolescent Cycling Behaviour Questionnaire). The questionnaire's structure was based on the widely used Driver Behaviour Questionnaire (DBQ). A sample of secondary school students (N = 1749; age range: 13-18 years) filled out the questionnaire. Factor analysis revealed a three-factor structure underlying the questionnaire, which was confirmed on two equally large portions of the entire sample. These three underlying factors were identified as errors, common violations and exceptional violations. The ACBQ is a useful instrument for measuring adolescents' risky cycling behaviour.

  10. Proliferation resistance fuel cycle technology

    International Nuclear Information System (INIS)

    The issues of dual use in nuclear technology are analysed for nuclear fuel cycle with special focus on uranium enrichment and spent fuel reprocessing which are considered as the most sensitive components in terms of vulnerability to diversion. Technical alternatives to mitigrate the vulnerability, as has been analysed in depth during the NASAP and INFCE era in the late seventies, are reviewed to characterize the DUPIC fuel cycle alternative. On the other hand, the new realities in nuclear energy including the disposition of weapon materials as a legacy of cold war are recast in an angle of nuclear proliferation resistance and safeguards with a discussion on the concept of spent fuel standard concept and its compliance with the DUPIC fuel cycle technology. (author)

  11. Optimization of data life cycles

    Science.gov (United States)

    Jung, C.; Gasthuber, M.; Giesler, A.; Hardt, M.; Meyer, J.; Rigoll, F.; Schwarz, K.; Stotzka, R.; Streit, A.

    2014-06-01

    Data play a central role in most fields of science. In recent years, the amount of data from experiment, observation, and simulation has increased rapidly and data complexity has grown. Also, communities and shared storage have become geographically more distributed. Therefore, methods and techniques applied to scientific data need to be revised and partially be replaced, while keeping the community-specific needs in focus. The German Helmholtz Association project "Large Scale Data Management and Analysis" (LSDMA) aims to maximize the efficiency of data life cycles in different research areas, ranging from high energy physics to systems biology. In its five Data Life Cycle Labs (DLCLs), data experts closely collaborate with the communities in joint research and development to optimize the respective data life cycle. In addition, the Data Services Integration Team (DSIT) provides data analysis tools and services which are common to several DLCLs. This paper describes the various activities within LSDMA and focuses on the work performed in the DLCLs.

  12. ALMA Cycle 0 Publication Statistics

    CERN Document Server

    Stoehr, Felix; Meakins, Silvia; Bishop, Marsha; Uchida, Ayako; Testi, Leonardo; Iono, Daisuke; Tatematsu, Kenichi; Wootten, Al

    2016-01-01

    The scientific impact of a facility is the most important measure of its success. Monitoring and analysing the scientific return can help to modify and optimise operations and adapt to the changing needs of scientific research. The methodology that we have developed to monitor the scientific productivity of the ALMA Observatory, as well as the first results, are described. We focus on the outcome of the first cycle (Cycle 0) of ALMA Early Science operations. Despite the fact that only two years have passed since the completion of Cycle 0 and operations have already changed substantially, this analysisconfirms the effectiveness of the underlying concepts. We find that ALMA is fulfilling its promise as a transformational facility for the observation of the Universe in the submillimetre.

  13. Modeling road-cycling performance.

    Science.gov (United States)

    Olds, T S; Norton, K I; Lowe, E L; Olive, S; Reay, F; Ly, S

    1995-04-01

    This paper presents a complete set of equations for a "first principles" mathematical model of road-cycling performance, including corrections for the effect of winds, tire pressure and wheel radius, altitude, relative humidity, rotational kinetic energy, drafting, and changed drag. The relevant physiological, biophysical, and environmental variables were measured in 41 experienced cyclists completing a 26-km road time trial. The correlation between actual and predicted times was 0.89 (P road-cycling performance are maximal O2 consumption, fractional utilization of maximal O2 consumption, mechanical efficiency, and projected frontal area. The model is then applied to some practical problems in road cycling: the effect of drafting, the advantage of using smaller front wheels, the effects of added mass, the importance of rotational kinetic energy, the effect of changes in drag due to changes in bicycle configuration, the normalization of performances under different conditions, and the limits of human performance.

  14. SIRTF Cycle-1 Research Opportunities

    Science.gov (United States)

    Soifer, B. T.; Bicay, M. D.

    2003-12-01

    The Space InfraRed Telescope Facility (SIRTF), the fourth and final element in NASA's family of Great Observatories, was successfully launched into an Earth-trailing heliocentric orbit on August 25, 2003. The SIRTF Science Center (SSC) at Caltech is now soliciting Cycle-1 research proposals from the worldwide scientific community. Proposals must be submitted electronically to the SSC by February 14, 2004. A preliminary version of the Cycle-1 Call for Proposals (CP) was issued by the SSC in November 2002. A CP Update and supporting technical documentation, which incorporates the on-orbit performance of the observatory, were released in December 2003. Investigations may be proposed for new SIRTF observations, through the General Observer (GO) program, or for archival research. About 3700 hours of observing time is being offered for the Cycle-1 GO Program, in small (less than 50 hours) and medium (50 to 200 hours) categories. More than \\15 million in NASA data analysis support is available to qualified GO investigators. For GO proposals, a detailed list of proposed observations, generated by the SIRTF Planning Observations Tool, must accompany the research proposal. The Archival Research (AR) Program in Cycle-1 is limited to the analysis of data from the First-Look Survey, a 100-hour program to be executed by the SSC at the start of the science mission. Up to \\750,000 in NASA data analysis support is available to qualified AR investigators. All documents supporting the Cycle-1 solicitation are available online in the Proposal Kit section of the SSC public Web site (http://sirtf.caltech.edu/SSC/). Questions pertaining to the Cycle-1 CP should be sent electronically to the SSC HelpDesk at sirtf@ipac.caltech.edu. SIRTF is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA.

  15. Tracing the glacial sulphur cycle

    Science.gov (United States)

    Hansson, M. E.; Jonsell, U.; Bigler, M.; de Angelis, M.; Fischer, H.; Siggaard-Andersen, M.-L.; Steffensen, J. P.; Udisti, R.; Wolff, E.

    2003-04-01

    Sulphate aerosols are playing a major role in climate forcing in the present atmosphere and therefore possibly also during other climatic stages. The deposition of sulphur-containing species onto polar ice sheets provides a tool for determining variations in the sulphur cycle in the past. Relatively short atmospheric residence times for sulphate aerosols cause spatial gradients and a high sensitivity to variations in the general circulation of the atmosphere and the hydrological cycle. Several factors may influence the air-snow transfer functions and post-depositional process may modify the deposited signal. Therefore, both a large spatial and temporal coverage is needed to identify significant changes in the sulphur cycle in the past. The EPICA Dome C ice core from Antarctica is providing the longest records ever, spanning several glacial cycles. Unique high-resolution chemical records, from discontinuous samples analysed by Ion Chromatography (IC), are gradually evolving from the cooperation between the laboratories in the EPICA Chemistry Consortium. The EPICA DML ice core is analysed in parallel by the same laboratories and the profiles are growing with the progress of the drilling each season. The sulphate and methane sulphonate records are here in focus and will be presented as far as they reach at present. High-resolution chemical records are now also available from the NorthGRIP ice core from Greenland spanning the last glacial cycle. An interhemispheric comparison of sulphur-containing species during the glacial period will be presented, using both new high-resolution data and previous ice core data from a few locations as well as initial results from sulphur isotope measurements, with the aim to increase our understanding of variations in the global sulphur cycle with climate change.

  16. Tricarboxylic-acid-cycle intermediates and cycle endurance capacity.

    Science.gov (United States)

    Brown, Amy C; Macrae, Holden S H; Turner, Nathan S

    2004-12-01

    The purpose of this study was to determine whether ingestion of a multinutrient supplement containing 3 tricarboxylic-acid-cycle intermediates (TCAIs; pyridoxine-alpha-ketoglutarate, malate, and succinate) and other substances potentially supporting the TCA cycle (such as aspartate and glutamate) would improve cyclists' time to exhaustion during a submaximal endurance-exercise test (approximately 70 % to 75 % VO2peak) and rate of recovery. Seven well-trained male cyclists (VO2max 67.4 2.1 mL x kg(-1) x in(-1), 28.6 +/- 2.4 y) participated in a randomized, double-blind crossover study for 7 wk. Each took either the treatment or a placebo 30 min before and after their normal training sessions for 3 wk and before submaximal exercise tests. There were no significant differences between the TCAI group (KI) and placebo group (P) in time to exhaustion during cycling (KI = 105 +/- 18, P = 113 +/- 11 min); respiratory-exchange ratio at 20-min intervals; blood lactate and plasma glucose before, after, and at 30-min intervals during exercise; perceived exertion at 20-min intervals during exercise; or time to fatigue after the 30-min recovery (KI = 16.1 +/- 3.2, P = 15 +/- 2 min). Taking a dietary sport supplement containing several TCAIs and supporting substances for 3 wk does not improve cycling performance at 75 % VO2peak or speed recovery from previously fatiguing exercise.

  17. Optimal Life Cycle Portfolio Choice with Housing Market Cycles

    DEFF Research Database (Denmark)

    Fischer, Marcel; Stamos, Michael Z.

    2013-01-01

    income, and pre-existing housing wealth but also the state of the housing market significantly affect household decisions. Consistently with the data, the model predicts that in good states of housing market cycles (1) homeownership rates increase, (2) households buying homes invest a larger share...

  18. Simple ocean carbon cycle models

    Energy Technology Data Exchange (ETDEWEB)

    Caldeira, K. [Lawrence Livermore National Lab., CA (United States); Hoffert, M.I. [New York Univ., NY (United States). Dept. of Earth System Sciences; Siegenthaler, U. [Bern Univ. (Switzerland). Inst. fuer Physik

    1994-02-01

    Simple ocean carbon cycle models can be used to calculate the rate at which the oceans are likely to absorb CO{sub 2} from the atmosphere. For problems involving steady-state ocean circulation, well calibrated ocean models produce results that are very similar to results obtained using general circulation models. Hence, simple ocean carbon cycle models may be appropriate for use in studies in which the time or expense of running large scale general circulation models would be prohibitive. Simple ocean models have the advantage of being based on a small number of explicit assumptions. The simplicity of these ocean models facilitates the understanding of model results.

  19. SNMR pulse sequence phase cycling

    Science.gov (United States)

    Walsh, David O; Grunewald, Elliot D

    2013-11-12

    Technologies applicable to SNMR pulse sequence phase cycling are disclosed, including SNMR acquisition apparatus and methods, SNMR processing apparatus and methods, and combinations thereof. SNMR acquisition may include transmitting two or more SNMR pulse sequences and applying a phase shift to a pulse in at least one of the pulse sequences, according to any of a variety cycling techniques. SNMR processing may include combining SNMR from a plurality of pulse sequences comprising pulses of different phases, so that desired signals are preserved and indesired signals are canceled.

  20. Ramsey Results for Cycle Spectra

    DEFF Research Database (Denmark)

    Brandt, S.; Joos, F.; Muttel, J.;

    2013-01-01

    Let C(G) denote the set of lengths of cycles of a graph G of order n and let (G) over bar denote the complement of G. We show that if n >= 6, then C(G) boolean OR C((G) over bar) contains all odd l with 3......Let C(G) denote the set of lengths of cycles of a graph G of order n and let (G) over bar denote the complement of G. We show that if n >= 6, then C(G) boolean OR C((G) over bar) contains all odd l with 3...

  1. Business Cycles in Developing Countries

    DEFF Research Database (Denmark)

    Rand, John; Tarp, Finn

    2002-01-01

    This paper demonstrates that developing countries differ considerably from their developed counterparts when focus is on the nature and characteristics of short run macroeconomic fluctuations. Cycles are generally shorter, and the stylized facts of business cycles across countries are more diverse...... than those of the rather uniform industrialized countries. Supply-side models are generally superior in explaining changes in output, but a “one-size fits all” approach in formulating policy is inappropriate. Our results also illustrate the critical importance of understanding business regularities...... as a stepping-stone in the process of designing appropriate stabilization policy and macroeconomic management in developing countries....

  2. Life cycle of remanufactured engines

    Institute of Scientific and Technical Information of China (English)

    YANG Ming; CHEN Ming

    2005-01-01

    The life cycle index of remanufactured engines was assessed by using the method of life cycle assessment (LCA). A remanufactured engine of a certain domestic brand was taken as researching object. Engine reproducing engineering was investigated from three aspects which were energy, material and environment. The application of LCA on remanufacturing engines was discussed in detail with a practical case. The results indicate that remanufackg CO2 , 6.09 kg CO, 1.01 kg NOx, 3. 985 kg SOx and 288. 725 kg solid waste. The remanufacturing of engines possesses great economic value and practicability.

  3. Digital calculations of engine cycles

    CERN Document Server

    Starkman, E S; Taylor, C Fayette

    1964-01-01

    Digital Calculations of Engine Cycles is a collection of seven papers which were presented before technical meetings of the Society of Automotive Engineers during 1962 and 1963. The papers cover the spectrum of the subject of engine cycle events, ranging from an examination of composition and properties of the working fluid to simulation of the pressure-time events in the combustion chamber. The volume has been organized to present the material in a logical sequence. The first two chapters are concerned with the equilibrium states of the working fluid. These include the concentrations of var

  4. Biogeochemical cycling and remote sensing

    Science.gov (United States)

    Peterson, D. L.

    1985-01-01

    Research is underway at the NASA Ames Research Center that is concerned with aspects of the nitrogen cycle in terrestrial ecosystems. An interdisciplinary research group is attempting to correlate nitrogen transformations, processes, and productivity with variables that can be remotely sensed. Recent NASA and other publications concerning biogeochemical cycling at global scales identify attributes of vegetation that could be related or explain the spatial variation in biologically functional variables. These functional variables include net primary productivity, annual nitrogen mineralization, and possibly the emission rate of nitrous oxide from soils.

  5. Properties of stellar activity cycles

    CERN Document Server

    Korhonen, Heidi

    2015-01-01

    The current photometric datasets, that span decades, allow for studying long-term cycles on active stars. Complementary Ca H&K observations give information also on the cycles of normal solar-like stars, which have significantly smaller, and less easily detectable, spots. In the recent years, high precision space-based observations, for example from the Kepler satellite, have allowed also to study the sunspot-like spot sizes in other stars. Here I review what is known about the properties of the cyclic stellar activity in other stars than our Sun.

  6. Properties of stellar activity cycles

    OpenAIRE

    Korhonen, Heidi

    2015-01-01

    The current photometric datasets, that span decades, allow for studying long-term cycles on active stars. Complementary Ca H&K observations give information also on the cycles of normal solar-like stars, which have significantly smaller, and less easily detectable, spots. In the recent years, high precision space-based observations, for example from the Kepler satellite, have allowed also to study the sunspot-like spot sizes in other stars. Here I review what is known about the properties of ...

  7. A short note on Reitlinger thermodynamic cycles

    CERN Document Server

    Sparavigna, Amelia Carolina

    2015-01-01

    It is well known that Carnot cycle is the thermodynamic cycle which has the best thermal efficiency. However, an entire class of cycles exists that can have the same maximum efficiency: this class is that of the regenerative Reitlinger cycles. Here we discuss them.

  8. Fundamental Cycles of Cognitive Growth.

    Science.gov (United States)

    Pegg, John

    Over recent years, various theories have arisen to explain and predict cognitive development in mathematics education. We focus on an underlying theme that recurs throughout such theories: a fundamental cycle of growth in the learning of specific concepts, which we frame within broader global theories of individual cognitive growth. Our purpose is…

  9. The product life cycle revisited

    DEFF Research Database (Denmark)

    Ulhøi, John Parm

    1995-01-01

    Efter et introduktionsafsnit følger afsnit II, hvor der gives en historisk analyse af Life Cycle Assessment (LCA) og Environmental Impact Assessment (EIA). I afsnit III munder analysen ud i en vurdering af ligheder og forskelle mellem LCA analyser og EIA analyser, og en diskussion følger af...

  10. Business Cycle Dependent Unemployment Insurance

    DEFF Research Database (Denmark)

    Andersen, Torben M.; Svarer, Michael

    The consequences of business cycle contingencies in unemployment insurance systems are considered in a search-matching model allowing for shifts between "good" and "bad" states of nature. We show that not only is there an insurance argument for such contingencies, but there may also be an incentive...

  11. Digital daily cycles of individuals

    DEFF Research Database (Denmark)

    Aledavood, Talayeh; Jørgensen, Sune Lehmann; Saramäki, Jari

    2015-01-01

    day-night pattern, there are individual differences: e.g., some of us are intrinsically morning-active, while others prefer evenings. In this article, we look at digital daily cycles: circadian patterns of activity viewed through the lens of auto-recorded data of communication and online activity. We...

  12. Nuclear fuel cycle. V. 2

    International Nuclear Information System (INIS)

    Nuclear fuel cycle information in some countries that develop, supply or use nuclear energy is presented. Data about Argentina, Australia, Belgium, Netherlands, Italy, Denmarmark, Norway, Sweden, Switzerland, Finland, Spain and India are included. The information is presented in a tree-like graphic way. (C.S.A.)

  13. Cycles and events in stratigraphy

    Energy Technology Data Exchange (ETDEWEB)

    Einsele, G.; Ricken, W.; Seilacher, A. (eds.)

    1991-01-01

    This book reviews and discusses the most up-to-date knowledge in the fields of cyclostratigraphy and event stratigraphy. The book contains 48 papers contributed by the most knowledgeable geologists and paleontologists in the fields of cycle and event stratigraphy. It is divided into two parts. Part one is concerned with the structure of individual beds and larger cycles and sequences and discusses; rhythmic stratification, event stratification, diagenetic overprint, cherts and phosphorites, and preservation and biologic destruction of laminated sediments. Part two, on larger cycles and sequences, looks at sequences, hierarchies, causes and environmental expression, and timing and correlation, i.e. the cycles of frequencies from millions of years to thousands of years (Milankovich band). Summaries on spectral analysis are also presented. There are 80 pages of references and a comprehensive index. It is extensively illustrated with line drawings and graphs. Practicing sedimentary geologists without access to a good library or find it hard to keep up with the plethora of journal articles and want a refresher in this area of stratigraphy will find the book particularly useful.

  14. Nuclear fuel cycle. V. 1

    International Nuclear Information System (INIS)

    Nuclear fuel cycle information in the main countries that develop, supply or use nuclear energy is presented. Data about Japan, FRG, United Kingdom, France and Canada are included. The information is presented in a tree-like graphic way. (C.S.A.)

  15. Sorption Refrigeration / Heat Pump Cycles

    Science.gov (United States)

    Saha, Bidyut Baran; Alam, K. C. Amanul; Hamamoto, Yoshinori; Akisawa, Atsushi; Kashiwagi, Takao

    Over the past few decades there have been considerable efforts to use adsorption (solid/vapor) for cooling and heat pump applications, but intensified efforts were initiated only since the imposition of international restrictions on the production and use of CFCs (chlorofluorocarbons) and HCFCs (hydrochlorofluorocarbons). Up to now, only the desiccant evaporative cooling system of the open type has achieved commercial use, predominantly in the United States. Closed-type adsorption refrigeration and heat pump systems are rarely seen in the market, or are still in the laboratory testing stage. Promising recent development have been made in Japan for the use of porous metal hydrides and composite adsorbents. In this paper, a short description of adsorption theories along with an overview of present status and future development trends of thermally powered adsorption refrigeration cycles are outlined putting emphasis on experimental achievements. This paper also addressed some advanced absorption cycles having relatively higher COP, and also summarizes fundamental concepts of GAX cycles and various GAX cycles developed for heat pump applications.

  16. H gas turbine combined cycle

    Energy Technology Data Exchange (ETDEWEB)

    Corman, J. [General Electric Co., Schenectady, NY (United States)

    1995-10-01

    A major step has been taken in the development of the Next Power Generation System - {open_quotes}H{close_quotes} Technology Combined Cycle. This new gas turbine combined-cycle system increases thermal performance to the 60% level by increasing gas turbine operating temperature to 1430 C (2600 F) at a pressure ratio of 23 to 1. Although this represents a significant increase in operating temperature for the gas turbine, the potential for single digit NOx levels (based upon 15% O{sub 2}, in the exhaust) has been retained. The combined effect of performance increase and environmental control is achieved by an innovative closed loop steam cooling system which tightly integrates the gas turbine and steam turbine cycles. The {open_quotes}H{close_quotes} Gas Turbine Combined Cycle System meets the goals and objectives of the DOE Advanced Turbine System Program. The development and demonstration of this new system is being carried out as part of the Industrial/Government cooperative agreement under the ATS Program. This program will achieve first commercial operation of this new system before the end of the century.

  17. Multilevel cycle of anthropogenic copper.

    Science.gov (United States)

    Graedel, T E; van Beers, D; Bertram, M; Fuse, K; Gordon, R B; Gritsinin, A; Kapur, A; Klee, R J; Lifset, R J; Memon, L; Rechberger, H; Spatari, S; Vexler, D

    2004-02-15

    A comprehensive contemporary cycle for stocks and flows of copper is characterized and presented, incorporating information on extraction, processing, fabrication and manufacturing, use, discard, recycling, final disposal, and dissipation. The analysis is performed on an annual basis, ca. 1994, at three discrete governmental unit levels--56 countries or country groups that together comprise essentially all global anthropogenic copper stocks and flows, nine world regions, and the planet as a whole. Cycles for all of these are presented and discussed, and a "best estimate" global copper cycle is constructed to resolve aggregation discrepancies. Among the most interesting results are (1) transformation rates and recycling rates in apparently similar national economies differ by factors of two or more (country level); (2) the discard flows that have the greatest potential for copper recycling are those with low magnitude flows but high copper concentrations--electronics, electrical equipment, and vehicles (regional level); (3) worldwide, about 53% of the copper that was discarded in various forms was recovered and reused or recycled (global level); (4) the highest rate of transfer of discarded copper to repositories is into landfills, but the annual amount of copper deposited in mine tailings is nearly as high (global level); and (5) nearly 30% of copper mining occurred merely to replace copper that was discarded. The results provide a framework for similar studies of other anthropogenic resource cycles as well as a basis for supplementary studies in resource stocks, industrial resource utilization, waste management, industrial economics, and environmental impacts. PMID:14998044

  18. Activity cycles of M dwarfs

    Science.gov (United States)

    Savanov, I. S.

    2012-09-01

    We have determined activity cycles for coolest M dwarfs using photometry from the ASAS survey. The time scales of brightness variations were determined for the program stars using calculated amplitude power spectra and wavelet spectra. Most of ther program stars display periodicities in their light-curve variations, with periods from hundreds of days to years. Analysis of diagrams plotting P cyc/ P rot versus 1/ P rot in logarithmic coordinates shows that the data for all our program objects fit the general relation quite well. No differences in the activity cycles are found for our sample stars, which have different masses and thus internal structures, some having convective envelopes and others being totally convective. Our analysis indicates that the slope i of this relation is close to unity, regardless of whether it is determined from all data, from data for the shortest cycles, or from data for the longest cycles. This value of i differs from values in the literature for stars of other spectral types. Our analysis of the P cyc- P rot relation indicates that the activity cycles for the studied sample of M dwarfs do not depend on the rotation periods of these objects. The data for the studied objects do not agree with any of the relations for relatively young (active) stars or older (less active) stars. The studied M dwarfs probably form another branch of low-mass stars that display more random, irregular magnetic activity on their surfaces, which is generated and supported by the distributed dynamo mechanism or a small-scale dynamo mechanism.

  19. The economics of thorium fuel cycles

    International Nuclear Information System (INIS)

    The individual cost components and the total fuel cycle costs for natural uranium and thorium fuel cycles are discussed. The thorium cycles are initiated by using either enriched uranium or plutonium. Subsequent thorium cycles utilize recycled uranium-233 and, where necessary, either uranium-235 or plutonium as topping. A calculation is performed to establish the economic conditions under which thorium cycles are economically attractive. (auth)

  20. When Product Life Cycle Meets Customer Activity Cycle

    DEFF Research Database (Denmark)

    Tan, Adrian Ronald

    2007-01-01

    Manufacturing companies have traditionally focused their efforts on designing, developing and producing products to offer on the market. Today global competition and demands for greater company responsibility of products throughout their entire life cycle are driving manufacturing companies...... to shift market strategies from a transactional approach to an approach based on the establishment and management of customer relationships (Grönroos, 1999). A growing number of studies and research programmes have focused on the potentials of business strategies based on providing the value of utility...... of products throughout their life cycle by designing integrated solutions of products and services. This approach has been dubbed ‘product/service-systems (PSS)’ (Mont, 2004). Although relationship marketing and product/service-system design have their roots in each their own research fields - marketing...

  1. Nitrogen cycling. Rapid nitrous oxide cycling in the suboxic ocean.

    Science.gov (United States)

    Babbin, Andrew R; Bianchi, Daniele; Jayakumar, Amal; Ward, Bess B

    2015-06-01

    Nitrous oxide (N2O) is a powerful greenhouse gas and a major cause of stratospheric ozone depletion, yet its sources and sinks remain poorly quantified in the oceans. We used isotope tracers to directly measure N2O reduction rates in the eastern tropical North Pacific. Because of incomplete denitrification, N2O cycling rates are an order of magnitude higher than predicted by current models in suboxic regions, and the spatial distribution suggests strong dependence on both organic carbon and dissolved oxygen concentrations. Furthermore, N2O turnover is 20 times higher than the net atmospheric efflux. The rapid rate of this cycling coupled to an expected expansion of suboxic ocean waters implies future increases in N2O emissions. PMID:26045434

  2. When Product Life Cycle Meets Customer Activity Cycle

    OpenAIRE

    Tan, Adrian Ronald

    2007-01-01

    Manufacturing companies have traditionally focused their efforts on designing, developing and producing products to offer on the market. Today global competition and demands for greater company responsibility of products throughout their entire life cycle are driving manufacturing companies to shift market strategies from a transactional approach to an approach based on the establishment and management of customer relationships (Grönroos, 1999). A growing number of studies and research progra...

  3. VISION - Verifiable Fuel Cycle Simulation of Nuclear Fuel Cycle Dynamics

    International Nuclear Information System (INIS)

    The U.S. DOE Advanced Fuel Cycle Initiative's (AFCI) fundamental objective is to provide technology options that--if implemented--would enable long-term growth of nuclear power while improving sustainability and energy security. The AFCI organization structure consists of four areas; Systems Analysis, Fuels, Separations and Transmutations. The Systems Analysis Working Group is tasked with bridging the program technical areas and providing the models, tools, and analyses required to assess the feasibility of design and deployment options and inform key decision makers. An integral part of the Systems Analysis tool set is the development of a system level model that can be used to examine the implications of the different mixes of reactors, implications of fuel reprocessing, impact of deployment technologies, as well as potential ''exit'' or ''off ramp'' approaches to phase out technologies, waste management issues and long-term repository needs. The Verifiable Fuel Cycle Simulation Model (VISION) is a computer-based simulation model that allows performing dynamic simulations of fuel cycles to quantify infrastructure requirements and identify key trade-offs between alternatives. It is based on the current AFCI system analysis tool ''DYMOND-US'' functionalities in addition to economics, isotopic decay, and other new functionalities. VISION is intended to serve as a broad systems analysis and study tool applicable to work conducted as part of the AFCI and Generation IV reactor development studies

  4. ITER-FEAT fuel cycle

    International Nuclear Information System (INIS)

    The Fuel Cycle, which includes plasma fuelling and exhaust, as well as exhaust processing and isotope separation, is one of the key elements on which the successful operation of ITER will depend. This paper provides an overview of this system, reviewing requirements, operational scenarios, and the integration of the various subsystems using the ITER fuel cycle dynamic simulation program CFTSIM. The requirements to provide a plasma fuelling rate of 200 Pam3s-1, with a flat-top burn of ∼400s and a repetition rate of two pulses per hour have the greatest influence on the design. However, while a flat-top burn of ∼400s is the initial design basis, the capability to extend the pulse to 3,000s in the longer term is essential from an operational perspective. (author)

  5. Soleus stretch reflex during cycling

    DEFF Research Database (Denmark)

    Grey, Michael James; Pierce, C. W.; Milner, T. E.;

    2001-01-01

    The modulation and strength of the human soleus short latency stretch reflex was investigated by mechanically perturbing the ankle during an unconstrained pedaling task. Eight subjects pedaled at 60 rpm against a preload of 10 Nm. A torque pulse was applied to the crank at various positions during...... the crank cycle, producing ankle dorsiflexion perturbations of similar trajectory. The stretch reflex was greatest during the power phase of the crank cycle and was decreased to the level of background EMG during recovery. Matched perturbations were induced under static conditions at the same crank angle...... and background soleus EMG as recorded during the power phase of active pedaling. The magnitude of the stretch reflex was not statistically different from that during the static condition throughout the power phase of the movement. The results of this study indicate that the stretch reflex is not depressed during...

  6. THE CANADIAN POLITICAL BUSINESS CYCLE

    Directory of Open Access Journals (Sweden)

    Barbara Libby

    2000-01-01

    Full Text Available This paper will discuss the existence of a Canadian Political Business Cycle (PBC during the period 1946-1989. Logit analysis was used to determine if changes in the unemployment rate, growth of real GNE and the rate of inflation are significantly different in the period before an election than during the rest of the electoral term. It was found that the rate of growth in the unemployment rate declines and the rate of growth of real GNP increases in the four quarters before an election. The behavior of these variables reverses in the period after an election. These findings are consistent with a political business cycle. Policy variables, under a majority government, also behave in a manner associated with a PBC, with the government stimulating the economy approximately two years into its term so that good economic news will occur before it has to call an election. Minority governments tend to simulate the economy immediately after taking office.

  7. Breaking the cycle of abuse.

    Science.gov (United States)

    Egeland, B; Jacobvitz, D; Sroufe, L A

    1988-08-01

    The aim of this study was to identify variables that distinguish mothers who broke the cycle of abuse from mothers who were abused as children and who also abused their own children. Based on maternal interviews and questionnaires completed over a 64-month period, measures of mothers' past and current relationship experiences, stressful life events, and personality characteristics were obtained. Abused mothers who were able to break the abusive cycle were significantly more likely to have received emotional support from a nonabusive adult during childhood, participated in therapy during any period of their lives, and to have had a nonabusive and more stable, emotionally supportive, and satisfying relationship with a mate. Abused mothers who reenacted their maltreatment with their own children experienced significantly more life stress and were more anxious, dependent, immature, and depressed. PMID:3168615

  8. Swimming as a limit cycle

    CERN Document Server

    Jacobs, Henry O

    2012-01-01

    Steady swimming can be characterized as both periodic and stable. These characteristics are the very definition of limit cycles, and so we ask "Can we view swimming as a limit cycle?" In this paper we will find that the answer is "yes". We will define a class of dissipative systems which correspond to the passive dynamics of a body immersed in a Navier-Stokes fluid (i.e. the dynamics of a dead fish). Upon performing reduction by symmetry we will find a hyperbolically stable fixed point which corresponds to the stability of a dead fish in stagnant water. Given a periodic force on the shape of the body we will invoke the persistence theorem to assert the existence of a loop which approximately satisfies the exact equations of motion. If we lift this loop with a phase reconstruction formula we will find that the lifted loops are not loops, but stable trajectories which represent regular periodic motion reminiscent of swimming.

  9. Carnot cycle for an oscillator

    CERN Document Server

    Arnaud, J; Philippe, F

    2002-01-01

    Carnot established in 1824 that the efficiency of cyclic engines operating between a hot bath at absolute temperature Th and a cold bath at temperature Tc cannot exceed 1-Tc/Th. This result implies the existence of an entropy function S(U) with the property that d^2S/dU^2 less equal 0, where U denotes the average energy. Linear single-mode systems alternately in contact with hot and cold baths obey these principles. A specific expression of the work done per cycle by an oscillator is derived from a prescription established by Einstein in 1906: heat baths may exchange energy with oscillators at angular frequency omega only by amounts hbar *omega, where 2*pi*hbar denotes the Planck constant. Non-reversible cycles are illustrated. The paper is essentially self-contained.

  10. Life cycle assessment of turbines

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2004-10-15

    This report forms part of the final reporting of the project 'LCA and turbines, which has been carried out as a cooperation between Vestas Wind Systems A/S and Tech-wise A/S on behalf of Elsam A/S. The goal of the project was to create a life cycle model for a big Vestas offshore turbine. Based on the offshore model an analysis has been prepared and this analysis will show the most significant environmental impacts a turbine will be subject to during its life cycle. Furthermore we have prepared a recommendation on how an improvement strategy on a selected area can be drafted. Finally, a preliminary environmental declaration of contents will be prepared for the turbine in question and 1 kWh generated from here. (BA)

  11. Business cycle synchronization in Europe

    DEFF Research Database (Denmark)

    Bergman, Ulf Michael; Jonung, Lars

    2011-01-01

    In this paper we study business cycle synchronization in the three Scandinavian countries Denmark, Norway and Sweden prior to, during and after the Scandinavian Currency Union 1873–1913. We find that the degree of synchronization tended to increase during the currency union, thus supporting earli...... empirical evidence. Estimates of factor models suggest that common Scandinavian shocks are important for these three countries. At the same time we find evidence suggesting that the importance of these shocks does not depend on the monetary regime.......In this paper we study business cycle synchronization in the three Scandinavian countries Denmark, Norway and Sweden prior to, during and after the Scandinavian Currency Union 1873–1913. We find that the degree of synchronization tended to increase during the currency union, thus supporting earlier...

  12. Single-cycle nonlinear optics

    Energy Technology Data Exchange (ETDEWEB)

    Max-Planck-Institut fur Quantenoptik; Goulielmakis, E.; Schultze, M.; Hofstetter, M.; Yakovlev, V. S.; Gagnon, J.; Uiberacker, M.; Aquila, A. L.; gullikson, E. M.; attwood, D. T.; Kienberger, R.; Krausz, F.; Kleineberg, U.

    2008-11-05

    Nonlinear optics plays a central role in the advancement of optical science and laser-based technologies. We report on the confinement of the nonlinear interaction of light with matter to a single wave cycle and demonstrate its utility for time-resolved and strong-field science. The electric field of 3.3-femtosecond, 0.72-micron laser pulses with a controlled and measured waveform ionizes atoms near the crests of the central wave cycle, with ionization being virtually switched off outside this interval. Isolated sub-100-attosecond pulses of extreme ultraviolet light (photon energy {approx} 80 electron volts), containing {approx} 0.5 nanojoule of energy, emerge from the interaction with a conversion efficiency of {approx} 10{sup -6}. These tools enable the study of the precision control of electron motion with light fields and electron-electron interactions with a resolution approaching the atomic unit of time ({approx} 24 attoseconds).

  13. HTGR fuel and fuel cycle technology

    Energy Technology Data Exchange (ETDEWEB)

    Lotts, A.L.; Coobs, J.H.

    1976-08-01

    The status of fuel and fuel cycle technology for high-temperature gas-cooled reactors (HTGRs) is reviewed. The all-ceramic core of the HTGRs permits high temperatures compared with other reactors. Core outlet temperatures of 740/sup 0/C are now available for the steam cycle. For advanced HTGRs such as are required for direct-cycle power generation and for high-temperature process heat, coolant temperatures as high as 1000/sup 0/C may be expected. The paper discusses the variations of HTGR fuel designs that meet the performance requirements and the requirements of the isotopes to be used in the fuel cycle. Also discussed are the fuel cycle possibilities, which include the low-enrichment cycle, the Th-/sup 233/U cycle, and plutonium utilization in either cycle. The status of fuel and fuel cycle development is summarized.

  14. National Policy on Nuclear Fuel Cycle

    International Nuclear Information System (INIS)

    National policy on nuclear fuel cycle is aimed at attaining the expected condition, i.e. being able to support optimality the national energy policy and other related Government policies taking into account current domestic nuclear fuel cycle condition and the trend of international nuclear fuel cycle development, the national strength, weakness, thread and opportunity in the field of energy. This policy has to be followed by the strategy to accomplish covering the optimization of domestic efforts, cooperation with other countries, and or purchasing licences. These policy and strategy have to be broken down into various nuclear fuel cycle programmes covering basically assesment of the whole cycle, performing research and development of the whole cycle without enrichment and reprocessing being able for weapon, as well as programmes for industrialization of the fuel cycle stepwisery commencing with the middle part of the cycle and ending with the edge of the back-end of the cycle

  15. Phase lags of solar hemispheric cycles

    CERN Document Server

    Muraközy, J

    2013-01-01

    The North-South asymmetry of solar activity is variable in time and strength. We analyse the long-term variation of the phase lags of hemispheric cycles and check a conjectured relationship between these phase lags and the hemispheric cycle strengths. Sunspot data are used from cycles 12-23 in which the separation of northern and southern hemispheres is possible. The centers of mass of the hemispheric cycle profiles were used to study the phase relations and relative strengths of the hemispheric cycles. This approach considers a cycle as a whole and disregards the short-term fluctuations of the cycle time profile. The phase of the hemispheric cycles shows an alternating variation: the northern cycle leads in 4 cycles and follows in 4 cycles. No significant relationship is found between the phase and strength differences of the hemispheric cycles. The period of 4+4 cycles appears to be close to the Gleissberg cycle and may provide a key to its physical background. It may raise a new aspect in the solar dynamo ...

  16. Biomechanics of Counterweighted One-Legged Cycling.

    Science.gov (United States)

    Elmer, Steven J; McDaniel, John; Martin, James C

    2016-02-01

    One-legged cycling has served as a valuable research tool and as a training and rehabilitation modality. Biomechanics of one-legged cycling are unnatural because the individual must actively lift the leg during flexion, which can be difficult to coordinate and cause premature fatigue. We compared ankle, knee, and hip biomechanics between two-legged, one-legged, and counterweighted (11.64 kg) one-legged cycling. Ten cyclists performed two-legged (240 W), one-legged (120 W), and counterweighted one-legged (120 W) cycling (80 rpm). Pedal forces and limb kinematics were recorded to determine work during extension and flexion. During counterweighted one-legged cycling relative ankle dorsiflexion, knee flexion, and hip flexion work were less than one-legged but greater than two-legged cycling (all P one-legged cycling were greater than one-legged but less than two-legged cycling (all P one-legged cycling reduced but did not eliminate differences in joint flexion and extension actions between one- and two-legged cycling. Even with these differences, counterweighted one-legged cycling seemed to have advantages over one-legged cycling. These results, along with previous work highlighting physiological characteristics and training adaptations to counterweighted one-legged cycling, demonstrate that this exercise is a viable alternative to one-legged cycling.

  17. Branes wrapped on coassociative cycles

    International Nuclear Information System (INIS)

    We obtain a supergravity solution arising when D6-branes are wrapped on coassociative four-cycles of constant curvature in seven manifolds of G2 holonomy. The solutions preserve two supercharges and thus represent supergravity duals of three dimensional Yang-Mills with N=1 supersymmetry. When uplifted to eleven dimensions our solution describes M-theory on the background of an eight manifold with Spin(7) holonomy. (author)

  18. Technology cycles and technology revolutions

    Energy Technology Data Exchange (ETDEWEB)

    Paganetto, Luigi; Scandizzo, Pasquale Lucio

    2010-09-15

    Technological cycles have been characterized as the basis of long and continuous periods economic growth through sustained changes in total factor productivity. While this hypothesis is in part consistent with several theories of growth, the sheer magnitude and length of the economic revolutions experienced by humankind seems to indicate surmise that more attention should be given to the origin of major technological and economic changes, with reference to one crucial question: role of production and use of energy in economic development.

  19. Entrepreneurship and the Business Cycle

    OpenAIRE

    KOELLINGER, Philipp; Thurik, Roy

    2009-01-01

    This discussion paper resulted in a publication in 'The Review of Economics and Statistics' (2012). Volume 94, issue 4, pages 1143-1156. We study the cyclical pattern of entrepreneurial activity. Results across 22 OECD countries for the period 1972-2007 show that entrepreneurial activity is a leading indicator of the business cycle in a Granger-causality sense. This contradicts existing theoretical hypotheses which predict that entrepreneurship is pro-cyclical or not cyclical. We discuss poss...

  20. Immigration, remittances, and business cycles

    OpenAIRE

    Federico S. Mandelman; Zlate, Andrei

    2010-01-01

    We use data on border enforcement and macroeconomic indicators from the United States and Mexico to estimate a two-country business cycle model of labor migration and remittances. The model matches the cyclical dynamics of labor migration to the United States and documents how remittances to Mexico serve an insurance role to smooth consumption across the border. During expansions in the destination economy, immigration increases with the expected stream of future wage gains, but it is dampene...

  1. Cycling Behavior and Memory Formation

    OpenAIRE

    Gerstner, Jason R.; Lyons, Lisa C.; Wright, Kenneth P.; Loh, Dawn H; Rawashdeh, Oliver; Eckel-Mahan, Kristin L.; Roman, Gregg W.

    2009-01-01

    Circadian research has spent considerable effort in the determining clock output pathways, including identifying both physiological and behavioral processes that demonstrate significant time-of-day variation. Memory formation and consolidation represent notable processes shaped by endogenous circadian oscillators. To date, very few studies on memory mechanisms have considered potential confounding effects of time-of-day and the organism’s innate activity cycles (e.g., nocturnal, diurnal, or c...

  2. Cardiac Biomarkers and Cycling Race

    OpenAIRE

    Caroline Le Goff, Jean-François Kaux, Sébastien Goffaux, Etienne Cavalier

    2015-01-01

    In cycling as in other types of strenuous exercise, there exists a risk of sudden death. It is important both to understand its causes and to see if the behavior of certain biomarkers might highlight athletes at risk. Many reports describe changes in biomarkers after strenuous exercise (Nie et al., 2011), but interpreting these changes, and notably distinguishing normal physiological responses from pathological changes, is not easy. Here we have focused on the kinetics of different cardiac bi...

  3. Miller cycle analysis using EGM

    OpenAIRE

    Ribeiro, Bernardo Sousa; Martins, Jorge

    2005-01-01

    The Entropy Generation Minimization (EGM) method is based on the analysis by three sciences (thermodynamics, fluid flow and heat transfer) of the different processes that may occur in a system or in an equipment. Herein the EGM method is applied to internal combustion engines to determine the entropy generation caused by different processes. A model incorporating entropy generation calculations is used to assess various engines configurations. Otto cycle was tested and...

  4. Creative Cycling of News Professionals

    OpenAIRE

    Astrid Gynnild, PhD.

    2007-01-01

    The theory of creative cycling emerged from my PhD study of news professionals in Norway. The study was carried out according to classic grounded theory principles (Glaser and Strauss 1967, Glaser 1978, 1998, 2001, 2005), and the area of interest was the performance of news journalism in the multimedia age. The theory runs counter to widespread tendencies of industrial age thinking in news media. It emphasizes news professionals’ search for meaning in their daily work, and suggests that their...

  5. Sickness Absence and Business Cycles

    OpenAIRE

    Jan Erik Askildsen; Espen Bratberg; Oivind Anti Nilsen

    2000-01-01

    Absenteeism is affected by the sickness benefit system. Countries with generous compensation during sick leaves also experience high numbers of sick leave. Sick leaves may vary over the business cycle due to unemployment disciplining effects or changes in labour force composition. The latter hypothesis maintains that sickness may be pro-cyclical due to employment of `marginal' workers with poorer health when demand increases. Using individual records of labour force participants in Norway, we...

  6. Containing revenue-cycle costs.

    Science.gov (United States)

    Geer, Robert; Burton, Eric

    2003-04-01

    Healthcare organizations can achieve revenue-cycle improvement while maintaining optimum staffing levels by taking a three-step approach-developing a plan, measuring costs, and using benchmarks to measure performance. Planned cost reductions can be achieved without a negative impact on the organization. Cost-reduction strategies should look at purchased services, staffing, and the cost-to-collect ratio. Healthcare organizations should reach target performance levels before implementing a cost-reduction strategy.

  7. Fundamental cycles and graph embeddings

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    In this paper, we investigate fundamental cycles in a graph G and their relations with graph embeddings. We show that a graph G may be embedded in an orientable surface with genus at least g if and only if for any spanning tree T , there exists a sequence of fundamental cycles C1, C2, . . . , C2g with C2i-1 ∩ C2i≠ф for 1≤ i ≤g. In particular, among β(G) fundamental cycles of any spanning tree T of a graph G, there are exactly 2γM (G) cycles C1, C2, . . . , C2γM (G) such that C2i-1 ∩ C2i≠ф for 1 ≤i≤γM (G), where β(G) and γM (G) are the Betti number and the maximum genus of G, respectively. This implies that it is possible to construct an orientable embedding with large genus of a graph G from an arbitrary spanning tree T (which may have very large number of odd components in G\\E(T )). This is different from the earlier work of Xuong and Liu, where spanning trees with small odd components are needed. In fact, this makes a common generalization of Xuong, Liu and Fu et al. Furthermore, we show that (1) this result is useful for locating the maximum genus of a graph having a specific edge-cut. Some known results for embedded graphs are also concluded; (2) the maximum genus problem may be reduced to the maximum matching problem. Based on this result and the algorithm of Micali-Vazirani, we present a new efficient algorithm to determine the maximum genus of a graph in O((β(G)) 25 ) steps. Our method is straight and quite different from the algorithm of Furst, Gross and McGeoch which depends on a result of Giles where matroid parity method is needed.

  8. Biogeochemical Cycles in Degraded Lands

    Science.gov (United States)

    Davidson, Eric A.; Vieira, Ima Celia G.; ReisdeCarvalho, Claudio Jose; DeanedeAbreuSa, Tatiana; deSouzaMoutinho, Paulo R.; Figueiredo, Ricardo O.; Stone, Thomas A.

    2004-01-01

    The objectives of this project were to define and describe the types of landscapes that fall under the broad category of "degraded lands" and to study biogeochemical cycles across this range of degradation found in secondary forests. We define degraded land as that which has lost part of its capacity of renovation of a productive ecosystem, either in the context of agroecosystems or as native communities of vegetation. This definition of degradation permits evaluation of biogeochemical constraints to future land uses.

  9. Product development cycle time reduction

    Science.gov (United States)

    Farran, Robin

    1992-05-01

    We are facing here today the key issues that face us in the competitive environment. North American companies are struggling to compete in the global marketplace. Gone are the days when presence ensured success. Then, sales and earnings were guaranteed. Today the competition is intense. Many manufacturing and service companies are no longer competitive. Traditionally, manufacturing companies have created the most wealth for the community and economy. Losing this ability to create wealth is tragic and unnecessary. A company can only be successful by focusing on customer satisfaction at competitive costs. Revenue growth and earnings growth require a continuous stream of products that anticipate the customers' needs, result from shorter and shorter innovation cycles, continually improve in quality, and are produced at improved costs on each cycle. The best opportunities for increased quality and decreased costs are with new products. Sure, work on quality and costs everyday. The biggest changes, however, will come through the new product development cycle. We must improve our development processes to provide leadership products which result in high levels of customer satisfaction. This is a prerequisite for business success. When presence in the marketplace was a virtual guarantee of success for a North American company, technology tended to drive the products, and the customers bought virtually everything that was produced. Functional excellence was stressed within companies ... and that was enough. Effective planning processes were not a prerequisite for success. Today success demands highly developed business research and planning processes, and functional excellence combined with organizational capabilities that ensure commercialization excellence.

  10. The parenting cycle of deployment.

    Science.gov (United States)

    DeVoe, Ellen R; Ross, Abigail

    2012-02-01

    Parents of dependent children comprise approximately 42% of Active Duty and National Guard/Reserve military members serving in Operation Iraqi Freedom/Operation Enduring Freedom. Recent estimates indicate that more than two million children have experienced parental deployment since the terrorist attacks on September 11, 2001. This article seeks to characterize the impact of the deployment life cycle on parenting roles among service members and at-home partners/caregivers of dependent children. Specifically, a new conceptual framework is presented for considering the ways in which parenting and co-parenting processes are affected by the demands and transitions inherent in contemporary deployment to a war zone. Although the phase-based emotional cycle of deployment continues to offer an instructive description of the broad challenges faced by military couples, a parenting cycle of deployment model shifts the perspective to the critical and largely ignored processes of parenting in the context of deployment and war, and to the realities faced by parents serving in the U.S. military. Implications for prevention, intervention, and future research related to military families are addressed. PMID:22360065

  11. Managing the strategic capital cycle.

    Science.gov (United States)

    Kaufman, K

    1997-12-01

    A healthcare organization's financial strategy should be defined within the context of the capital cycle and provide for the management of three critical components that will ensure the expansion and renewal of capital capacity--the design and implementation of the financial plan, the design and implementation of an appropriate capital structure, and a means to strategically utilize capital and reinvest it in the organization. The capital cycle comprises two parts--strategic planning and implementation, and the development of the support infrastructure that includes financial planning, capital structure, and capital allocation. The financial plan positions an organization within an area of financial equilibrium and defines its organizational capabilities. The financial infrastructure gives integrity and momentum to the capital cycle. Capital structure addresses critical funding and financing questions and is best defined as the combination of debt and equity that funds the strategic plan. In regard to capital allocation, healthcare organizations should follow a corporate "best practices" approach for such areas as financial objectives and policies, project review, and the capital expenditures approval process.

  12. ZPC Matrices and Zero Cycles

    Directory of Open Access Journals (Sweden)

    Marina Arav

    2009-01-01

    Full Text Available Let H be an m×n real matrix and let Zi be the set of column indices of the zero entries of row i of H. Then the conditions |Zk∩(∪i=1k−1Zi|≤1 for all k  (2≤k≤m are called the (row Zero Position Conditions (ZPCs. If H satisfies the ZPC, then H is said to be a (row ZPC matrix. If HT satisfies the ZPC, then H is said to be a column ZPC matrix. The real matrix H is said to have a zero cycle if H has a sequence of at least four zero entries of the form hi1j1,hi1j2,hi2j2,hi2j3,…,hikjk,hikj1 in which the consecutive entries alternatively share the same row or column index (but not both, and the last entry has one common index with the first entry. Several connections between the ZPC and the nonexistence of zero cycles are established. In particular, it is proved that a matrix H has no zero cycle if and only if there are permutation matrices P and Q such that PHQ is a row ZPC matrix and a column ZPC matrix.

  13. Endoreversible Meletis-Georgiou cycle

    Directory of Open Access Journals (Sweden)

    Chang Liu, Lingen Chen, Fengrui Sun

    2012-01-01

    Full Text Available An endoreversible Meletis-Georgiou (MG cycle model with constant specific heat of working fluid is established and the analytical formulae of performance parameters including working fluid temperatures, work output and efficiency are derived using the finite time thermodynamic theory. The performance of the endoreversible MG cycle is analyzed and optimized. The characteristics of the work output versus compression ratio, efficiency versus compression ratio, and work output versus efficiency are obtained, respectively, by detailed numerical examples, and the effects of changeover ratio, over-expansion ratio, heating value of fuel, heat transfer loss coefficient, initial temperature of working fluid, and the transferred volume ratio on the relationship mentioned above are also discussed. The maximum work output and the corresponding optimal compression ratio, changeover ratio, over-expansion ratio as well as the maximum efficiency and the corresponding optimal changeover ratio and over-expansion ratio are obtained by taking the cycle work output and efficiency as the optimization objectives, respectively. Moreover, the effects of the parameters such as the heating value of fuel, heat transfer loss coefficient, initial temperature of working fluid, and the transferred volume ratio on the maximum work output, the maximum efficiency and the corresponding optimal ratios are analyzed. The results may provide guidelines for the optimal design of practical MG engine.

  14. Nutrient cycling in mango trees

    Directory of Open Access Journals (Sweden)

    Cinara Xavier de Almeida

    2014-02-01

    Full Text Available Estimates of nutrient amounts both shedding and demanding replacement in the maintenance of productivity of fruit trees require studies on element dynamics within the many ecosystem components generally made up of nutrient cycling. Thus, it was the objective of this study to evaluate the nutrient biochemical cycling in a mango tree (Mangifera indica L. orchard, Palmer variety. Macronutrients [nitrogen (N, phosphorus (P, potassium (K, calcium (Ca, magnesium (Mg, and sulfur (S] had their contents evaluated in leaves at different stages: new, mature, senescent, and litter. First exploratory analysis was performed for main components which preserve the multivariate structure shown by the data. It was possible to observe the association of new leaves with N, P, K, Mg, and S; senescent leaves and the leaves from the litter were associated to Ca, while mature leaves, to K. As a complement, taking the independent variables into consideration, Tukey test (p?0.01 showed that the averages of N, P, and Ca differ between the new and the mature leaves; average of Mg in new leaves differs from the others, and S does not differ along the stages. Also observed was the re-translocation of 41%, 63% and 57% of N, P, and K, respectively, when comparison was made among the contents of the elements in mature leaves as well as in litter, which indicates that the biochemical cycling is important for the mango tree cultivation.

  15. Digital Daily Cycles of Individuals

    Science.gov (United States)

    Aledavood, Talayeh; Lehmann, Sune; Saramäki, Jari

    2015-10-01

    Humans, like almost all animals, are phase-locked to the diurnal cycle. Most of us sleep at night and are active through the day. Because we have evolved to function with this cycle, the circadian rhythm is deeply ingrained and even detectable at the biochemical level. However, within the broader day-night pattern, there are individual differences: e.g., some of us are intrinsically morning-active, while others prefer evenings. In this article, we look at digital daily cycles: circadian patterns of activity viewed through the lens of auto-recorded data of communication and online activity. We begin at the aggregate level, discuss earlier results, and illustrate differences between population-level daily rhythms in different media. Then we move on to the individual level, and show that there is a strong individual-level variation beyond averages: individuals typically have their distinctive daily pattern that persists in time. We conclude by discussing the driving forces behind these signature daily patterns, from personal traits (morningness/eveningness) to variation in activity level and external constraints, and outline possibilities for future research.

  16. Digital Daily Cycles of Individuals

    Directory of Open Access Journals (Sweden)

    Talayeh eAledavood

    2015-10-01

    Full Text Available Humans, like almost all animals, are phase-locked to the diurnal cycle. Most of us sleep at night and are active through the day. Because we have evolved to function with this cycle, the circadian rhythm is deeply ingrained and even detectable at the biochemical level. However, within the broader day-night pattern, there are individual differences: e.g., some of us are intrinsically morning-active, while others prefer evenings. In this article, we look at digital daily cycles: circadian patterns of activity viewed through the lens of auto-recorded data of communication and online activity. We begin at the aggregate level, discuss earlier results, and illustrate differences between population-level daily rhythms in different media. Then we move on to the individual level, and show that there is a strong individual-level variation beyond averages: individuals typically have their distinctive daily pattern that persists in time. We conclude by discussing the driving forces behind these signature daily patterns, from personal traits (morningness/eveningness to variation in activity level and external constraints, and outline possibilities for future research.

  17. Solar storms, cycles and topology

    Directory of Open Access Journals (Sweden)

    Lundstedt H.

    2010-12-01

    Full Text Available Solar storms are produced due to plasma processes inside and between coronal loops. These loops are topologically examined using knot and braid theory. Solar cycles are topologically explored with a complex generalization of the three ordinary differential equations studied by Lorenz. By studying the Poincaré map we give numerical evidence that the flow has an attractor with fractal structure. The period is defined as the time needed for a point on a hyperplane to return to the hyperplane again. The periods are distributed in an interval. For large values of the Dynamo number there is a long tail toward long periods and other interesting comet-like features. We also found a relationship between the intensity of a cycle and the length for the previous cycle. Maunder like minima are also appearing. These general relations found for periods can further be physically interpreted with improved helioseismic estimates of the parameters used by the dynamical systems. Solar Dynamic Observatory is expected to offer such improved measurements.

  18. Advanced Fuel Cycle Cost Basis

    Energy Technology Data Exchange (ETDEWEB)

    D. E. Shropshire; K. A. Williams; W. B. Boore; J. D. Smith; B. W. Dixon; M. Dunzik-Gougar; R. D. Adams; D. Gombert; E. Schneider

    2009-12-01

    This report, commissioned by the U.S. Department of Energy (DOE), provides a comprehensive set of cost data supporting a cost analysis for the relative economic comparison of options for use in the Advanced Fuel Cycle Initiative (AFCI) Program. The report describes the AFCI cost basis development process, reference information on AFCI cost modules, a procedure for estimating fuel cycle costs, economic evaluation guidelines, and a discussion on the integration of cost data into economic computer models. This report contains reference cost data for 25 cost modules—23 fuel cycle cost modules and 2 reactor modules. The cost modules were developed in the areas of natural uranium mining and milling, conversion, enrichment, depleted uranium disposition, fuel fabrication, interim spent fuel storage, reprocessing, waste conditioning, spent nuclear fuel (SNF) packaging, long-term monitored retrievable storage, near surface disposal of low-level waste (LLW), geologic repository and other disposal concepts, and transportation processes for nuclear fuel, LLW, SNF, transuranic, and high-level waste.

  19. Advanced Fuel Cycle Cost Basis

    Energy Technology Data Exchange (ETDEWEB)

    D. E. Shropshire; K. A. Williams; W. B. Boore; J. D. Smith; B. W. Dixon; M. Dunzik-Gougar; R. D. Adams; D. Gombert; E. Schneider

    2008-03-01

    This report, commissioned by the U.S. Department of Energy (DOE), provides a comprehensive set of cost data supporting a cost analysis for the relative economic comparison of options for use in the Advanced Fuel Cycle Initiative (AFCI) Program. The report describes the AFCI cost basis development process, reference information on AFCI cost modules, a procedure for estimating fuel cycle costs, economic evaluation guidelines, and a discussion on the integration of cost data into economic computer models. This report contains reference cost data for 25 cost modules—23 fuel cycle cost modules and 2 reactor modules. The cost modules were developed in the areas of natural uranium mining and milling, conversion, enrichment, depleted uranium disposition, fuel fabrication, interim spent fuel storage, reprocessing, waste conditioning, spent nuclear fuel (SNF) packaging, long-term monitored retrievable storage, near surface disposal of low-level waste (LLW), geologic repository and other disposal concepts, and transportation processes for nuclear fuel, LLW, SNF, transuranic, and high-level waste.

  20. Advanced Fuel Cycle Cost Basis

    Energy Technology Data Exchange (ETDEWEB)

    D. E. Shropshire; K. A. Williams; W. B. Boore; J. D. Smith; B. W. Dixon; M. Dunzik-Gougar; R. D. Adams; D. Gombert

    2007-04-01

    This report, commissioned by the U.S. Department of Energy (DOE), provides a comprehensive set of cost data supporting a cost analysis for the relative economic comparison of options for use in the Advanced Fuel Cycle Initiative (AFCI) Program. The report describes the AFCI cost basis development process, reference information on AFCI cost modules, a procedure for estimating fuel cycle costs, economic evaluation guidelines, and a discussion on the integration of cost data into economic computer models. This report contains reference cost data for 26 cost modules—24 fuel cycle cost modules and 2 reactor modules. The cost modules were developed in the areas of natural uranium mining and milling, conversion, enrichment, depleted uranium disposition, fuel fabrication, interim spent fuel storage, reprocessing, waste conditioning, spent nuclear fuel (SNF) packaging, long-term monitored retrievable storage, near surface disposal of low-level waste (LLW), geologic repository and other disposal concepts, and transportation processes for nuclear fuel, LLW, SNF, and high-level waste.

  1. BUSINESS CYCLES, ELECTORAL CYCLES. TOWARD A THEORETICAL FRAME OF INTERACTION

    Directory of Open Access Journals (Sweden)

    BOGDAN-LUCIAN DOSPINESCU

    2015-06-01

    Full Text Available The idea of cyclical movement of a system: be it political, economic, institutional, is one of the constants of critical thinking. In this sense, there is a natural cyclic movement that cannot be avoided (only amplified or diminished and is connected with the nature of these systems. The economy follows a cyclical movement; a period of growth follows a period of decline, and so on. So does popularity for political parties or leaders. In this paper, I explore the links between the business cycles and electoral cycles. For this purpose, I introduce the concept of electoral perception cycles. My hypothesis is that popularity of political parties and leaders follow a cyclical evolution, both on short and long term. I show how perception cycles can impact the “political business cycle theory”. There is great interest in political science literature for the factors that influence the fluctuations in Presidents’ popularity, especially from United States. However, very little has been said about Romania’s case. I investigate the hypothesis of electoral perception cycles looking at the popularity of former president Traian Basescu, over his two terms. The variable used to measure popularity is favorability, measured in national surveys, done face to face, on representative samplez, of around 1000 subjects. I’ve correlated the fluctuations in favorability over time, with key public events or political decisions taken by Traian Băsescu. The main findings are as follows. Firstly, there are significant short term fluctuations (short term perception cycles and they are correlated with major events on the agenda. I would point the following key moments: 1. The referendum for dismissal of the President in May 2007 – Traian Băsescu’s favorability increased by 7 percentage points; 2. The referendum for unicameral Parliament with 300 MPs in the fall of 2009. Coupled with victory in the presidential election, it lead to an increase of 10 percentage

  2. High performance heat pump absorption cycles

    Energy Technology Data Exchange (ETDEWEB)

    Lazzarin, R.; Longo, G.; Rossetto, L.

    1988-10-01

    Absorption heat pumps can provide high performances when operating in suitable cycles with multiple effects. This report describes some multistage cycles and evaluates the coefficient of performance realistically obtainable both in winter and summer working conditions.

  3. Not all counterclockwise thermodynamic cycles are refrigerators

    Science.gov (United States)

    Dickerson, R. H.; Mottmann, J.

    2016-06-01

    Clockwise cycles on PV diagrams always represent heat engines. It is therefore tempting to assume that counterclockwise cycles always represent refrigerators. This common assumption is incorrect: most counterclockwise cycles cannot be refrigerators. This surprising result is explored here for quasi-static ideal gas cycles, and the necessary conditions for refrigeration cycles are clarified. Three logically self-consistent criteria can be used to determine if a counterclockwise cycle is a refrigerator. The most fundamental test compares the counterclockwise cycle with a correctly determined corresponding Carnot cycle. Other criteria we employ include a widely accepted description of the functional behavior of refrigerators, and a corollary to the second law that limits a refrigerator's coefficient of performance.

  4. Biogeochemical cycles: Interactions in global metabolism

    Science.gov (United States)

    Moore, B., III; Morowitz, H.; Dastoor, M. N.

    1984-01-01

    A science that chooses the globe as it fundamental biogeophysical unit forces extraordinary conceptual difficulties. The roles of energy flow, matter cycles, carbon cycle, air pollution, global effects, air water interactions are discussed.

  5. Terminology gap in hydrological cycle

    Science.gov (United States)

    Zhuo, Lu; Han, Dawei

    2016-04-01

    Water is central to life on Earth. People have been trying to understand how water moves in the hydrosphere throughout the human history. In the 9th century BC, the famous Greek poet Homer described the hydrological cycle in Iliad as "okeanos whose stream bends back in a circle" with a belief that rivers are ocean-fed from subterranean seas. Later, Aristotle (4th century BC) claimed that most of the water came from underground caverns in which air was transformed into water. It was only until 1674, French scientist Perrault developed the correct concept of the water cycle. In modern times, scientists are interested in understanding the individual processes of the hydrological cycle with a keen focus on runoff which supplies water to rivers, lakes, and oceans. Currently, the prevailing concepts on runoff processes include 'infiltration excess runoff' and 'saturation excess runoff'. However, there is no term to describe another major runoff due to the excess beyond the soil water holding capacity (i.e., the field capacity). We argue that a new term should be introduced to fill this gap, and it could be called 'holding excess runoff' which is compatible with the convention. This new term is significant in correcting a half-century misnomer where 'holding excess runoff' has been incorrectly named as 'saturation excess runoff', which was introduced by the Xinanjiang model in China in 1960s. Similar concept has been adopted in many well-known hydrological models such as PDM and HBV in which the saturation refers to the field capacity. The term 'holding excess runoff' resolves such a common confusion in the hydrological community.

  6. Fundamental cycles and graph embeddings

    Institute of Scientific and Technical Information of China (English)

    REN Hani; ZHAO HongTao; LI HaoLing

    2009-01-01

    In this paper, we investigate fundamental cycles in a graph G and their relations with graph embeddings. We show that a graph G may be embedded in an orientable surface with genus at least g if and only if for any spanning tree T, there exists a sequence of fundamental cycles of any spanning tree T of a graph G, there are exactly 2γM(G) cycles G1,G2,…,C2γM(G) such that C2i-1 ∩ C2i≠ for 1≤I≤γM(G), where β(G) and γM(G) are the Betti number and the maximum genus of G, respectively. This implies that it is possible to construct an orientable embedding with large genus of a graph G from an arbitrary spanning tree T (which may have very large number of odd components in G\\E(T)). This is different from the earlier work of Xuong and Liu, where spanning trees with small odd components are needed. In fact, this makes a common generalization of Xuong, Liu and Fu et al. Furthermore, we show that (1) this result is useful for locating the maximum genus of a graph having a specific edge-cut. Some known results for embedded graphs are also concluded; (2) the maximum genus problem may be reduced to the maximum matching problem. Based on this result and the algorithm of Micali-Vazirani, we present a new efficient algorithm to determine the maximum genus of a graph in O((β(G))5/2) steps. Our method is straight and quite different from the algorithm of Furst, Gross and McGeoch which depends on a result of Giles where matroid parity method is needed.

  7. Rankine cycle system and method

    Energy Technology Data Exchange (ETDEWEB)

    Ernst, Timothy C.; Nelson, Christopher R.

    2014-09-09

    A Rankine cycle waste heat recovery system uses a receiver with a maximum liquid working fluid level lower than the minimum liquid working fluid level of a sub-cooler of the waste heat recovery system. The receiver may have a position that is physically lower than the sub-cooler's position. A valve controls transfer of fluid between several of the components in the waste heat recovery system, especially from the receiver to the sub-cooler. The system may also have an associated control module.

  8. The biogeochemistry of metal cycling

    Science.gov (United States)

    Nealson, Kenneth H. (Editor); Nealson, Molly (Editor); Dutcher, F. Ronald (Editor)

    1990-01-01

    The results of the Planetary Biology and Microbial Ecology's summer 1987 program are summarized. The purpose of the interdisciplinary PBME program is to integrate, via lectures and laboratory work, the contributions of university and NASA scientists and student interns. The 1987 program examined various aspects of the biogeochemistry of metal cycling, and included such areas as limnology, metal chemistry, metal geochemistry, microbial ecology, and interactions with metals. A particular area of focus was the use of remote sensing in the study of biogeochemistry. Abstracts and bibliographies of the lectures and reports of the laboratory projects are presented.

  9. Heteroclinic Cycles in Hopfield Networks

    Science.gov (United States)

    Chossat, Pascal; Krupa, Maciej

    2016-04-01

    It is widely believed that information is stored in the brain by means of the varying strength of synaptic connections between neurons. Stored patterns can be replayed upon the arrival of an appropriate stimulus. Hence, it is interesting to understand how an information pattern can be represented by the dynamics of the system. In this work, we consider a class of network neuron models, known as Hopfield networks, with a learning rule which consists of transforming an information string to a coupling pattern. Within this class of models, we study dynamic patterns, known as robust heteroclinic cycles, and establish a tight connection between their existence and the structure of the coupling.

  10. Search for relationship between duration of the extended solar cycles and amplitude of sunspot cycle

    CERN Document Server

    Tlatov, A G

    2007-01-01

    Duration of the extended solar cycles is taken into the consideration. The beginning of cycles is counted from the moment of polarity reversal of large-scale magnetic field in high latitudes, occurring in the sunspot cycle n till the minimum of the cycle n+2. The connection between cycle duration and its amplitude is established. Duration of the "latent" period of evolution of extended cycle between reversals and a minimum of the current sunspot cycle is entered. It is shown, that the latent period of cycles evolution is connected with the next sunspot cycle amplitude and can be used for the prognosis of a level and time of a sunspot maximum. The 24-th activity cycle prognosis is done. Long-term behavior of extended cycle's lengths is considered.

  11. Multiple Limit Cycles in an Immune System

    Institute of Scientific and Technical Information of China (English)

    Xun-cheng Huang; Le-min Zhu; Minaya Villasana

    2008-01-01

    The nonlinear oscillatory phenomenon has been observed in the system of immune response, which corresponds to the limit cycles in the mathematical models. We prove that the system simulating an immune response studied by Huang has at least three limit cycles in the system. The conditions for the multiple limit cycles are useful in analyzing the nonlinear oscillation in immune response.

  12. The next generation of revenue cycle management.

    Science.gov (United States)

    Hammer, David C

    2007-07-01

    The revenue cycle management environment is dynamic. Revenue cycle leaders are now responsible for additional functional areas and have to deal with new financing arrangements that expose the organization to greater financial risk. Financial managers can use key performance indicators and the suggested practice processes checklist to determine whether their revenue cycle operations are in good shape or need shaping up.

  13. Does It Have a Life Cycle?

    Science.gov (United States)

    Keeley, Page

    2010-01-01

    If life continues from generation to generation, then all plants and animals must go through a life cycle, even though it may be different from organism to organism. Is this what students have "learned," or do they have their own private conceptions about life cycles? The formative assessment probe "Does It Have a Life Cycle?" reveals some…

  14. Dormancy cycling in seeds: mechanisms and regulation

    NARCIS (Netherlands)

    Claessens, S.M.C.

    2012-01-01

    The life cycle of most plants starts, and ends, at the seed stage. In most species mature seeds are shed and dispersed on the ground. At this stage of its life cycle the seed may be dormant and will, by definition, not germinate under favourable conditions (Bewley, 1997). Seasonal dormancy cycling

  15. Combined cycles with gas turbine engines

    Energy Technology Data Exchange (ETDEWEB)

    Najjar, Y.S.H.; Akyurt, M. (King Abdulaziz Univ., Jeddah (Saudi Arabia). Mechanical Engineering Dept.)

    1994-03-01

    Simple cycle gas turbine engines suffer from limited efficiencies and consequential dominance of fuel prices on generation costs. Combined cycles, however. exploit the waste heat from exhaust gases to boost power output, resulting in overall efficiencies around 50%, which are significantly above those of steam power plants. This paper reviews various types of combined cycles, including repowering, integrated gasification and other advanced systems. (author)

  16. Kinetic models of conjugated metabolic cycles

    Science.gov (United States)

    Ershov, Yu. A.

    2016-01-01

    A general method is developed for the quantitative kinetic analysis of conjugated metabolic cycles in the human organism. This method is used as a basis for constructing a kinetic graph and model of the conjugated citric acid and ureapoiesis cycles. The results from a kinetic analysis of the model for these cycles are given.

  17. Hopf limit cycles estimation in power systems

    Energy Technology Data Exchange (ETDEWEB)

    Barquin, J.; Gomez, T.; Pagola, L.F. [Univ. Pontificia Comillas, Madrid (Spain). Inst. de Investigacion Tecnologica

    1995-11-01

    This paper addresses the computation of the Hopf limit cycle. This limit cycle is associated to the appearance of an oscillatory instability in dynamical power systems. An algorithm is proposed to estimate the dimensions and shape of this limit cycle. The algorithm is computationally efficient and is able to deal with large power systems. 7 refs, 4 figs, 1 tab

  18. On Acyclicity of Games with Cycles

    DEFF Research Database (Denmark)

    Andersson, Daniel; Gurvich, Vladimir; Hansen, Thomas Dueholm

    2009-01-01

    We study restricted improvement cycles (ri-cycles) in finite positional n-person games with perfect information modeled by directed graphs (digraphs) that may contain cycles. We obtain criteria of restricted improvement acyclicity (ri-acyclicity) in two cases: for n = 2 and for acyclic digraphs. We...

  19. Rock weathering and Carbon cycle

    Science.gov (United States)

    Strozza, Patrick

    2010-05-01

    In the history of the Earth system, we can find indicators of hot or glacial periods, as well as brutal climatic change… How can we explain those climate variations on a geological timescale ? One of the causative agents is probably the fluctuation of atmospheric CO2 amounts, (gas responsible for the greenhouse effect). A concrete study of some CO2 fluxes between Earth system reservoirs (atmo, hydro and lithosphere) is proposed in this poster. Hydrogencarbonate is the major ion in river surface waters and its amount is so high that it can not be explained by a simple atmospheric Carbon diffusion. From a simple measurement of river HCO3- concentration, we can estimate the consumption of atmospheric CO2 that arises from carbonate and silicate weathering processes. Practical experiments are proposed. These are carried out in the local environment, and are conform to the curriculums of Chemistry and Earth sciences. These tests enable us to outline long-term Carbon cycles and global climatic changes. Key words : Erosion, rock weathering, CO2 cycle, Hydrogencarbonate in waters, climatic changes

  20. Social Life Cycle Assessment Revisited

    Directory of Open Access Journals (Sweden)

    Ruqun Wu

    2014-07-01

    Full Text Available To promote the development of Social Life Cycle Assessment (SLCA, we conducted a comprehensive review of recently developed frameworks, methods, and characterization models for impact assessment for future method developers and SLCA practitioners. Two previous reviews served as our foundations for this review. We updated the review by including a comprehensive list of recently-developed SLCA frameworks, methods and characterization models. While a brief discussion from goal, data, and indicator perspectives is provided in Sections 2 to 4 for different frameworks/methods, the focus of this review is Section 5 where discussion on characterization models for impact assessment of different methods is provided. The characterization models are categorized into two types following the UNEP/SETAC guidelines: type I models without impact pathways and type II models with impact pathways. Different from methods incorporating type I/II characterization models, another LCA modeling approach, Life Cycle Attribute Assessment (LCAA, is also discussed in this review. We concluded that methods incorporating either type I or type II models have limitations. For type I models, the challenge lies in the systematic identification of relevant stakeholders and materiality issues; while for type II models, identification of impact pathways that most closely and accurately represent the real-world causal relationships is the key. LCAA may avoid these problems, but the ultimate questions differ from those asked by the methods using type I and II models.

  1. Life Cycle Assessment of Concrete

    Energy Technology Data Exchange (ETDEWEB)

    Sjunnesson, Jeannette

    2005-09-15

    This is an environmental study on concrete that follows the standard protocol of life cycle assessment (LCA). The study is done for two types of concrete, ordinary and frost-resistant concrete, and has an extra focus on the superplasticizers used as admixtures. The utilization phase is not included in this study since the type of construction for which the concrete is used is not defined and the concrete is assumed to be inert during this phase. The results show that it is the production of the raw material and the transports involved in the life cycle of concrete that are the main contributors to the total environmental load. The one single step in the raw material production that has the highest impact is the production of cement. Within the transportation operations the transportation of concrete is the largest contributor, followed by the transportation of the cement. The environmental impact of frost-resistant concrete is between 24-41 % higher than that of ordinary concrete due to its higher content of cement. Superplasticizers contribute with approximately 0.4-10.4 % of the total environmental impact of concrete, the least to the global warming potential (GWP) and the most to the photochemical ozone creation potential (POCP). Also the toxicity of the superplasticizers is investigated and the conclusion is that the low amount of leakage of superplasticizers from concrete leads to a low risk for the environment and for humans.

  2. Technology development life cycle processes.

    Energy Technology Data Exchange (ETDEWEB)

    Beck, David Franklin

    2013-05-01

    This report and set of appendices are a collection of memoranda originally drafted in 2009 for the purpose of providing motivation and the necessary background material to support the definition and integration of engineering and management processes related to technology development. At the time there was interest and support to move from Capability Maturity Model Integration (CMMI) Level One (ad hoc processes) to Level Three. As presented herein, the material begins with a survey of open literature perspectives on technology development life cycles, including published data on %E2%80%9Cwhat went wrong.%E2%80%9D The main thrust of the material presents a rational expose%CC%81 of a structured technology development life cycle that uses the scientific method as a framework, with further rigor added from adapting relevant portions of the systems engineering process. The material concludes with a discussion on the use of multiple measures to assess technology maturity, including consideration of the viewpoint of potential users.

  3. MHD Integrated Topping Cycle Project

    Energy Technology Data Exchange (ETDEWEB)

    1992-01-01

    The overall objective of the project is to design and construct prototypical hardware for an integrated MHD topping cycle, and conduct long duration proof-of-concept tests of integrated system at the US DOE Component Development and Integration Facility in Butte, Montana. The results of the long duration tests will augment the existing engineering design data base on MHD power train reliability, availability, maintainability, and performance, and will serve as a basis for scaling up the topping cycle design to the next level of development, an early commercial scale power plant retrofit. The components of the MHD power train to be designed, fabricated, and tested include: A slagging coal combustor with a rated capacity of 50 MW thermal input, capable of operation with an Eastern (Illinois {number sign}6) or Western (Montana Rosebud) coal, a segmented supersonic nozzle, a supersonic MHD channel capable of generating at least 1.5 MW of electrical power, a segmented supersonic diffuser section to interface the channel with existing facility quench and exhaust systems, a complete set of current control circuits for local diagonal current control along the channel, and a set of current consolidation circuits to interface the channel with the existing facility inverter.

  4. MHD Integrated Topping Cycle Project

    Energy Technology Data Exchange (ETDEWEB)

    1992-03-01

    The Magnetohydrodynamics (MHD) Integrated Topping Cycle (ITC) Project represents the culmination of the proof-of-concept (POC) development stage in the US Department of Energy (DOE) program to advance MHD technology to early commercial development stage utility power applications. The project is a joint effort, combining the skills of three topping cycle component developers: TRW, Avco/TDS, and Westinghouse. TRW, the prime contractor and system integrator, is responsible for the 50 thermal megawatt (50 MW{sub t}) slagging coal combustion subsystem. Avco/TDS is responsible for the MHD channel subsystem (nozzle, channel, diffuser, and power conditioning circuits), and Westinghouse is responsible for the current consolidation subsystem. The ITC Project will advance the state-of-the-art in MHD power systems with the design, construction, and integrated testing of 50 MW{sub t} power train components which are prototypical of the equipment that will be used in an early commercial scale MHD utility retrofit. Long duration testing of the integrated power train at the Component Development and Integration Facility (CDIF) in Butte, Montana will be performed, so that by the early 1990's, an engineering data base on the reliability, availability, maintainability and performance of the system will be available to allow scaleup of the prototypical designs to the next development level. This Sixteenth Quarterly Technical Progress Report covers the period May 1, 1991 to July 31, 1991.

  5. 塔式太阳能热发电中冷回热再热燃气轮机循环研究——功率与效率%Power and Efficiency of an Irreversible Closed Intercooling Reheating and Regenerated Brayton Cycle Coupler in Tower-typed Solar Energy Thermal Power Generation

    Institute of Scientific and Technical Information of China (English)

    黄德中; 方栋华; 许沧粟

    2012-01-01

    用热力学方法研究了塔式太阳能热发电中冷回热再热三级不可逆闭式燃气轮机循环的功率和效率.通过数值分析方法,计算了中冷度、回热度对循环最优功率、最优效率及其中间压比分配的关系.与闭式中冷回热燃气轮机循环的功率和效率比较,最大平均功率、最优功率和最优功率效率都有很大的提高.

  6. Water Cycling &the GPM Mission

    Science.gov (United States)

    Smith, E. A.

    2003-04-01

    The GPM mission is currently planned for start in the late'07 - early'08 time frame. Its main scientific goal is to help answer pressing scientific problems arising within the context of global and regional water cycles. These problems cut across a hierarchy of scales and include climate-water cycle interactions, techniques for improving weather and climate predictions, and better methods for combining observed precipitation with hydrometeorological prediction models for applications to hazardous flood-producing storms, seasonal flood/draught conditions, and fresh water resource assessments. The GPM mission will expand the scope of precipitation measurement through the use of a constellation of some 9 satellites, one of which will be an advanced TRMM-like "core" satellite carrying a dual-frequency Ku-Ka band precipitation radar and an advanced, multifrequency passive microwave radiometer with vertical-horizontal polarization discrimination. The other constellation members will include new dedicated satellites and co-existing operational/research satellites carrying similar (but not identical) passive microwave radiometers. The goal of the constellation is to achieve 3-hour sampling at any spot on the globe - continuously. The constellation's orbit architecture will consist of a mix of sun-synchronous and non-sun-synchronous satellites with the "core" satellite providing measurements of cloud-precipitation microphysical processes plus calibration-quality rainrates to be used with the other retrieval information to ensure bias-free constellation coverage. GPM is organized internationally, involving existing, pending, projected, and under-study partnerships which will link NASA and NOAA in the US, NASDA in Japan, ESA in Europe, ISRO in India, CNES in France, and possibly ASI in Italy, KARI in South Korea, CSA in Canada, and AEB in Brazil. Additionally, the program is actively pursuing agreements with other international collaborators and domestic scientific agencies

  7. Advanced Fuel Cycle Economic Sensitivity Analysis

    Energy Technology Data Exchange (ETDEWEB)

    David Shropshire; Kent Williams; J.D. Smith; Brent Boore

    2006-12-01

    A fuel cycle economic analysis was performed on four fuel cycles to provide a baseline for initial cost comparison using the Gen IV Economic Modeling Work Group G4 ECON spreadsheet model, Decision Programming Language software, the 2006 Advanced Fuel Cycle Cost Basis report, industry cost data, international papers, the nuclear power related cost study from MIT, Harvard, and the University of Chicago. The analysis developed and compared the fuel cycle cost component of the total cost of energy for a wide range of fuel cycles including: once through, thermal with fast recycle, continuous fast recycle, and thermal recycle.

  8. Design and Fabrication of Eu-Cycle

    Directory of Open Access Journals (Sweden)

    A.Venkat Sai

    2014-10-01

    Full Text Available EU-Cycle is a self balancing electric unicycle. A regular unicycle is powered by pedal and is balanced by a rider, whilst the EU-Cycle runs by an electric motor and balance by control system in the roll direction. The simple thing to do by rider is to lean forward for acceleration, to lean backward for braking. EU-Cycle is designed as to be a fast and portable means of transport among crowded area, home and office. Therefore, The EU-Cycle gives tough challenge to the unicycle. EU-Cycle has attracted print media including future stories in radio, television. Thus in addition to successful development of EU-Cycle in urban use, the project has to implement the EU-cycle as an educative device.

  9. A class of internally irreversible refrigeration cycles

    Science.gov (United States)

    Ait-Ali, Mohand A.

    1996-03-01

    A Carnot-like irreversible refrigeration cycle is modelled with two isothermal and two non-adiabatic, irreversible processes. The generic source of internal irreversibility, measured by the Clausius inequality, is a general irreversibility term which could include any heat leaks into the Joule - Thompson expansion valve, the evaporator and compressor cold boxes. This cycle is optimized first for maximum refrigeration power and maximum refrigeration load, then for maximum coefficient of performance. Its performances are compared with those of the endoreversible refrigeration cycle, based on a propane stage of a classical cascade liquefaction cycle example. Both cycle models achieve optimum power and maximum refrigeration load at nearly the same refrigeration temperature, but only the coefficient of performance of the irreversible refrigeration cycle reaches a maximum. Moreover, its prediction of heat conductance allocation between evaporator and condenser appears to be not only more conservative, but also more realistic for actual design considerations of refrigeration cycles.

  10. Search for relationship between duration of the extended solar cycles and amplitude of sunspot cycle

    OpenAIRE

    Tlatov, A. G.

    2007-01-01

    Duration of the extended solar cycles is taken into the consideration. The beginning of cycles is counted from the moment of polarity reversal of large-scale magnetic field in high latitudes, occurring in the sunspot cycle n till the minimum of the cycle n+2. The connection between cycle duration and its amplitude is established. Duration of the "latent" period of evolution of extended cycle between reversals and a minimum of the current sunspot cycle is entered. It is shown, that the latent ...

  11. Fuel Cycle System Analysis Handbook

    Energy Technology Data Exchange (ETDEWEB)

    Steven J. Piet; Brent W. Dixon; Dirk Gombert; Edward A. Hoffman; Gretchen E. Matthern; Kent A. Williams

    2009-06-01

    This Handbook aims to improve understanding and communication regarding nuclear fuel cycle options. It is intended to assist DOE, Campaign Managers, and other presenters prepare presentations and reports. When looking for information, check here. The Handbook generally includes few details of how calculations were performed, which can be found by consulting references provided to the reader. The Handbook emphasizes results in the form of graphics and diagrams, with only enough text to explain the graphic, to ensure that the messages associated with the graphic is clear, and to explain key assumptions and methods that cause the graphed results. Some of the material is new and is not found in previous reports, for example: (1) Section 3 has system-level mass flow diagrams for 0-tier (once-through), 1-tier (UOX to CR=0.50 fast reactor), and 2-tier (UOX to MOX-Pu to CR=0.50 fast reactor) scenarios - at both static and dynamic equilibrium. (2) To help inform fast reactor transuranic (TRU) conversion ratio and uranium supply behavior, section 5 provides the sustainable fast reactor growth rate as a function of TRU conversion ratio. (3) To help clarify the difference in recycling Pu, NpPu, NpPuAm, and all-TRU, section 5 provides mass fraction, gamma, and neutron emission for those four cases for MOX, heterogeneous LWR IMF (assemblies mixing IMF and UOX pins), and a CR=0.50 fast reactor. There are data for the first 10 LWR recycle passes and equilibrium. (4) Section 6 provides information on the cycle length, planned and unplanned outages, and TRU enrichment as a function of fast reactor TRU conversion ratio, as well as the dilution of TRU feedstock by uranium in making fast reactor fuel. (The recovered uranium is considered to be more pure than recovered TRU.) The latter parameter impacts the required TRU impurity limits specified by the Fuels Campaign. (5) Section 7 provides flows for an 800-tonne UOX separation plant. (6) To complement 'tornado' economic

  12. The effect of turbo trainer cycling on pedalling technique and cycling efficiency.

    Science.gov (United States)

    Arkesteijn, M; Hopker, J; Jobson, S A; Passfield, L

    2013-06-01

    Cycling can be performed on the road or indoors on stationary ergometers. The purpose of this study was to investigate differences in cycling efficiency, muscle activity and pedal forces during cycling on a stationary turbo trainer compared with a treadmill. 19 male cyclists cycled on a stationary turbo trainer and on a treadmill at 150, 200 and 250 W. Cycling efficiency was determined using the Douglas bags, muscle activity patterns were determined using surface electromyography and pedal forces were recorded with instrumented pedals. Treadmill cycling induced a larger muscular contribution from Gastrocnemius Lateralis, Biceps Femoris and Gluteus Maximus of respectively 14%, 19% and 10% compared with turbo trainer cycling (pcycling induced larger muscular contribution from Vastus Lateralis, Rectus Femoris and Tibialis Anterior of respectively 7%, 17% and 14% compared with treadmill cycling (pcycling was observed. These results suggest that cycling technique and type of ergometer can be altered without affecting cycling efficiency.

  13. The evolution of nitrogen cycling

    Science.gov (United States)

    Mancinelli, Rocco L.; Mckay, Christopher P.

    1988-01-01

    The energetics of nitrogen transformation reactions and the evolution of nitrogen cycling are examined. It is suggested that meteor impact-produced fixed nitrogen could have caused the entire reservoir of the earth's N2 to convert into fixed nitrogen at the end of accretion. The abiotic fixation rate on the early earth by lightning is estimated at about 1-3 X 10 to the 16th molecules of NO/J. It is found that biological nitrogen fixation may have evolved after the development of an aerobic atmosphere. It is shown that HNO could eventually become NO2(-) and NO3(-) after reaching the earth's surface. It is concluded that the evolutionary sequence for the biological transformation of nitrogen compounds is ammonification - denitrification - nitrification - nitrogen fixation.

  14. Thorium nuclear fuel cycle technology

    Energy Technology Data Exchange (ETDEWEB)

    Eom, Tae Yoon; Do, Jae Bum; Choi, Yoon Dong; Park, Kyoung Kyum; Choi, In Kyu; Lee, Jae Won; Song, Woong Sup; Kim, Heong Woo

    1998-03-01

    Since thorium produces relatively small amount of TRU elements after irradiation in the reactor, it is considered one of possible media to mix with the elements to be transmuted. Both solid and molten-salt thorium fuel cycles were investigated. Transmutation concepts being studied involved fast breeder reactor, accelerator-driven subcritical reactor, and energy amplifier with thorium. Long-lived radionuclides, especially TRU elements, could be separated from spent fuel by a pyrochemical process which is evaluated to be proliferation resistance. Pyrochemical processes of IFR, MSRE and ATW were reviewed and evaluated in detail, regarding technological feasibility, compatibility of thorium with TRU, proliferation resistance, their economy and safety. (author). 26 refs., 22 figs

  15. Business cycles in oil economies

    Energy Technology Data Exchange (ETDEWEB)

    Al-Mutairi, N.H.

    1991-01-01

    This study examines the impact of oil price shocks on output fluctuations of several oil-exporting economies. In most studies of business cycles, the role of oil price is ignored; the few studies that use oil price as one of the variables in the system focus on modeling oil-importing economies. The vector autoregression (VAR) technique is used to consider the cases of Norway, Nigeria, and Mexico. Both atheoretical and structural' VARs are estimated to determine the importance of oil price impulses on output variations. The study reports two types of results: variance decomposition and impulse response functions, with particular emphasis on the issues of stationarity and co-integration among the series. The empirical results suggest that shocks to oil price are important in explaining output variations. In most cases, shocks to oil price are shown to explain more than 20% of the forecast variance of output over a 40-quarter horizon.

  16. Violence as a Vicious Cycle

    Directory of Open Access Journals (Sweden)

    Huseyin Gulec

    2012-03-01

    Full Text Available Since the conclusion that the violence as a behavior is not (cannot be determined within an absolute genetic determinism has been reached for long years, environmental factors are increasingly examined. We witness that human behavior in society can easily convert into coping with stressful events with violence. Individual or social violence as a behavior has a similar pattern with violence committed in primitive society and by children. After a brief review of violence, its description, etiological theories and types, this article majorly focuses on children and their early and late response to violence. The purpose here is to draw attention to the individuals who were previously exposed to violence (either directly or indirectly resort to violence, perpetuating a vicious cycle.

  17. Canard cycles in global dynamics

    CERN Document Server

    Vidal, Alexandre

    2009-01-01

    Fast-slow systems are studied usually by "geometrical dissection". The fast dynamics exhibit attractors which may bifurcate under the influence of the slow dynamics which is seen as a parameter of the fast dynamics. A generic solution comes close to a connected component of the stable invariant sets of the fast dynamics. As the slow dynamics evolves, this attractor may lose its stability and the solution eventually reaches quickly another connected component of attractors of the fast dynamics and the process may repeat. This scenario explains quite well relaxation and bursting oscillations. More recently, in relation both with theory of dynamical systems and with applications to physiology, a new interest has emerged in canard cycles. These orbits share the property that they remain for a while close to an unstable invariant set (either singular set or periodic orbits of the fast dynamics). Although canards were first discovered when the transition points are folds, in this article, we focus on the case where...

  18. Fuel cycle of the AVR

    International Nuclear Information System (INIS)

    All the stages of development were secured by irradiation tests and by the use of the elements concerned in the AVR. Summarising, these were: The first charge with fuel elements from Union Carbide, with U-Th mixed carbide particles, wallpaper variants, U-Th mixed carbide particles, the pressed fuel element with U-Th mixed carbide particles, the pressed fuel element with U-Th mixed oxide particles, with an intermediate boundary layer; the present THTR element, the pressed fuel element with U-Th mixed oxide particles and low temperature PyC coating, the pressed fuel element with U-Th mixed oxide particles, with PyC and SiC layers, i.e.: TRISO particles, the pressed fuel element with pure uranium oxide particles for the low enrichment cycle, one coated only by 2 PyC layers, the other coated with PyC and SiC, i.e.: TRISO coating. (orig.)

  19. MAPK uncouples cell cycle progression from cell spreading and cytoskeletal organization in cycling cells

    OpenAIRE

    Margadant, Coert; Cremers, Lobke; Sonnenberg, Arnoud; Boonstra, Johannes

    2012-01-01

    Integrin-mediated cytoskeletal tension supports growth-factor-induced proliferation, and disruption of the actin cytoskeleton in growth factor-stimulated cells prevents the re-expression of cyclin D and cell cycle re-entry from quiescence. In contrast to cells that enter the cell cycle from G0, cycling cells continuously express cyclin D, and are subject to major cell shape changes during the cell cycle. Here, we investigated the cell cycle requirements for cytoskeletal tension and cell sprea...

  20. Solar Cycle Predictions Near Sunspot Minimum

    Science.gov (United States)

    Hathaway, David H.

    1997-01-01

    Observations of solar magnetic activity and the dynamics of the solar convection zone have produced severe constraints on models of the Sun's magnetic dynamo. These constraints are so severe that, at present, we do not have numerical models that can accept the current conditions and then march forward in time to predict future activity. Given this state of solar dynamo theory we are forced to examine previous behavior to discover patterns and trends that afford us some measure of predictability. Here we examine the behavior of several indicators of solar activity near solar minimum that are well correlated with the amplitude of the following solar maximum to predict the level of solar activity over cycle 23. Sunspot numbers, areas, and positions are useful for characterizing solar cycle behavior due to the extent of the data (12 cycles or more). These data exhibit several patterns that relate future activity to past behavior. With the Odd-Even effect the odd numbered cycles have been larger than their even numbered predecessors for each of the last six cycle pairs. With the Amplitude-Period effect short period cycles have been followed by large amplitude cycles and long period cycles have been followed by small amplitude cycles for 10 of the last 13 cycles. With the Maximum-Minimum effect the sunspot number at minimum is directly correlated with the sunspot number at maximum for a given cycle. The geomagnetic indices aa and Ap are also related to solar activity by the connections between disturbances in the solar wind and variations in the Earth's magnetic field. Like the Maximum-Minimum effect for sunspots, the size of the aa and Ap indices at minimum are directly related to the amplitude of the following maximum. The number of geomagnetically disturbed days (days with Ap >= 25) over the course of a cycle is another indicator for the size of the next cycle. The aa and Ap indices can each be separated into a component in phase with the current sunspot cycle and an