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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Supercritical CO2 Power Cycles Design Basis – Brayton Cycle Analysis - Update

Fundamental sCO2 cycle analyses. This is an ESPA/Noblis presentation of a study made to look at indirect sCO2 Brayton cycles using a generic heat source from a fundamental thermodynamic prospective. Included are overviews of factors impacting cycle configurations, heat sources and outlines of both indirect and direct Brayton Cycles. Sensitivity Analyses are performed on a number of items that include working fluids, cycle pressure ratios and pressures, turbine inlet temperatures, and turbomachinery efficiencies. The study includes testing various equation of state (EOS) to arrive at reasonable and accurate thermodynamic values for fluids in the critical point region. The results are presented in many summary plots to illustrate the findings to the reader. Additional discussion is available in a final report.

Generic heat source↗
DOE OSTI2011

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

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 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 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 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 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 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 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%/minute. It was determined that utilization of turbine throttling control below 50% load improves the cycle efficiency significantly. Consequently, the cycle control strategy has been updated to include turbine throttle valve control. The new control strategy still relies on inventory control in the 50%-90% load range and turbine bypass for fine and fast generator output adjustments, but it now also includes turbine throttling control in the 0%-50% load range. In an attempt to investigate the feasibility of using the S-CO 2 cycle for normal decay heat removal from the reactor, the cycle control study was extended beyond the investigation of normal load following. It was shown that such operation is possible with the extension of the inventory and the turbine throttling controls. However, the cycle operation in this range is calculated to be so inefficient that energy would need to be supplied from the electrical grid assuming that the generator could be capable of being operated in a motoring mode with an input electrical energy from the grid having a magnitude of about 20% of the nominal plant output electrical power level in order to maintain circulation of the CO 2 in the cycle. The work on investigation of cycle operation at low power level will be continued in the future. In addition to the cycle control study, the coupled PDC-SAS4A/SASSYS-1 code system was also used to simulate thermal transients in the sodium-to-CO 2 heat exchanger. Several possible conditions with the potential to introduce significant changes to the heat exchanger temperatures were identified and simulated. The conditions range from reactor scram and primary sodium pump failure or intermediate sodium pump failure on the reactor side to pipe breaks and valve malfunctions on the S-CO 2 side. It was found that the maximum possible rate of the heat exchanger wall temperature change for the particular heat exchanger design assumed is limited to ±7 C/s for less than 10 seconds. Modeling in the Plant Dynamics Code has been compared with available data from the Sandia National Laboratories (SNL) small-scale S-CO 2 Brayton cycle demonstration that is being assembled in a phased approach currently at Barber-Nichols Inc. and at SNL in the future. The available data was obtained with an earlier configuration of the S-CO 2 loop involving only a single-turbo-alternator-compressor (TAC) instead of two TACs, a single low temperature recuperator (LTR) instead of both a LTR and a high temperature recuperator (HTR), and fewer than the later to be installed full set of electric heaters. Due to the absence of the full heating capability as well as the lack of a high temperature recuperator providing additional recuperation, the temperature conditions obtained with the loop are too low for the loop conditions to be prototypical of the S-CO 2 cycle.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2017

Enhancing power cycle efficiency for a supercritical Brayton cycle power system using tunable supercritical gas mixtures

Various technologies pertaining to tuning composition of a fluid mixture in a supercritical Brayton cycle power generation system are described herein. Compounds, such as Alkanes, are selectively added or removed from an operating fluid of the supercritical Brayton cycle power generation system to cause the critical temperature of the fluid to move up or down, depending upon environmental conditions. As efficiency of the supercritical Brayton cycle power generation system is substantially optimized when heat is rejected near the critical temperature of the fluid, dynamically modifying the critical temperature of the fluid based upon sensed environmental conditions improves efficiency of such a system.

42 ENGINEERING↗
DOE OSTI2017

Heat Storage for Peak Power with Base-Load Rankine-Cycle LWRs nd Brayton-Cycle High-Temperature Reactors

The world is transitioning to a low-carbon energy system. Variable electricity and industrial energy demands have been met with storable fossil fuels-systems with low-capital costs and high-operating costs. In contrast, the low-carbon energy sources (nuclear, wind and solar) are characterized by high-capital-costs and low-operating costs. High utilization is required to produce economic energy. The addition of large quantities of wind or solar changes the market. The Massachusetts Institute of Technology (MIT) Future of Solar Energy study provides an examination of the solar option and the challenge of moving from an electricity grid dominated by fossil fuel generation to a grid with significant solar capacity. As more solar plants are built, electricity prices at times of high solar output collapse; thus, solar revenue collapses as solar production increases. This limits unsubsidized solar capacity to a relatively small fraction of total electricity production even if there are large decreases in solar capital costs. The same occurs with the large-scale use of wind. This results in increasing number of hours of near-zero wholesale prices for electricity that has been seen in multiple electricity markets in Europe and the United States. This is bad economic news for nuclear, wind and solar for revenue collapse limits the use of low-carbon technologies. It favors lower-capital-cost higher-operating- cost natural gas plants with their capability to cycle up and down quickly. New technologies are required to store or use this electricity at times of low prices to produce electricity at times of high prices. We describe two strategies to improve nuclear power economics based on heat storage. Heat storage is less expensive than electricity storage. The reactor operates at full capacity all the time but the electricity to the grid varies with time depending upon electricity prices. Each option allows sending heat to industry.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
NASA NTRS2007

Gas Foil Bearing Technology Advancements for Closed Brayton Cycle Turbines

Closed Brayton Cycle (CBC) turbine systems are under consideration for future space electric power generation. CBC turbines convert thermal energy from a nuclear reactor, or other heat source, to electrical power using a closed-loop cycle. The operating fluid in the closed-loop is commonly a high pressure inert gas mixture that cannot tolerate contamination. One source of potential contamination in a system such as this is the lubricant used in the turbomachine bearings. Gas Foil Bearings (GFB) represent a bearing technology that eliminates the possibility of contamination by using the working fluid as the lubricant. Thus, foil bearings are well suited to application in space power CBC turbine systems. NASA Glenn Research Center is actively researching GFB technology for use in these CBC power turbines. A power loss model has been developed, and the effects of a very high ambient pressure, start-up torque, and misalignment, have been observed and are reported here.

Howard, Samuel A.↗
DOE OSTI2019

Cogeneration using multi-effect distillation and a solar-powered supercritical carbon dioxide Brayton cycle

Supercritical carbon dioxide (sCO 2 ) Brayton cycles are considered to be a potentially viable option for reducing the cost of electricity generation from solar power tower plants, owing to theoretically high efficiency, low compressor work, and compact turbomachinery. These cycles have relatively high heat rejection temperatures (>70 degrees C), which are ideal for integration with multi-effect distillation (MED) for distillate generation from seawater, without being a parasitic load to the power plant as compared to cogeneration with steam Rankine cycle. The intermittency of solar radiation reduces the annual capacity factor of concentrating solar power (CSP) plants to about 50-60% even with a molten salt storage tank of 10-h. This reduces the annual distillate generation and increases the cost of the distillate. A novel concept to reduce distillate cost is introduced, whereby the waste heat from the sCO 2 Brayton cycle is stored. A two-tank demineralized water storage tank is selected and is shown to allow for the integration of a smaller MED system operating at an increased capacity factor. The optimal storage tank design reduces the distillate cost by 19% and increase the MED capacity factor from 46.4% to 75%. Different coastal locations with good solar resource are studied for cogeneration with the CSP-sCO 2 Brayton cycle. Techno-economic analysis shows the cost of distillate produced by MED is 16% cheaper than the distillate produced from reverse osmosis system for Yanbu, Saudi Arabia.

14 SOLAR ENERGY↗
DOE OSTI2017

Corrosion of Structural Materials for Advanced Supercritical Carbon- Dioxide Brayton Cycle

The supercritical carbon-dioxide (referred to as SC-CO 2 hereon) Brayton cycle is being considered for power conversion systems for a number of nuclear reactor concepts, including the sodium fast reactor (SFR), fluoride saltcooled high temperature reactor (FHR), and high temperature gas reactor (HTGR), and several types of small modular reactors (SMR). The SC-CO 2 direct cycle gas fast reactor has also been recently proposed. The SC-CO 2 Brayton cycle (discussed in Chapter 1) provides higher efficiencies compared to the Rankine steam cycle due to less compression work stemming from higher SC-CO 2 densities, and allows for smaller components size, fewer components, and simpler cycle layout. For example, in the case of a SFR using a SC-CO 2 Brayton cycle instead of a steam cycle would also eliminate the possibility of sodium-water interactions. The SC-CO 2 cycle has a higher efficiency than the helium Brayton cycle, with the additional advantage of being able to operate at lower temperatures and higher pressures. In general, the SC-CO 2 Brayton cycle is well-suited for any type of nuclear reactor (including SMR) with core outlet temperature above ~ 500°C in either direct or indirect versions. In all the above applications, materials corrosion in high temperature SC-CO 2 is an important consideration, given their expected lifetimes of 20 years or longer. Our discussions with National Laboratories and private industry early on in this project indicated materials corrosion to be one of the significant gaps in the implementation of SC-CO 2 Brayton cycle. Corrosion can lead to a loss of effective load-bearing wall thickness of a component and can potentially lead to the generation of oxide particulate debris which can lead to three-body wear in turbomachinery components. Another environmental degradation effect that is rather unique to CO 2 environment is the possibility for simultaneous occurrence of carburization during oxidation of the material. Carburization can potentially lead to embrittlement of structural alloys in SC-CO 2 Brayton cycle. An important consideration in regards to corrosion is that the temperatures can vary widely across the various sections of the SC-CO 2 Brayton cycle, from room temperature to 750°C, with even higher temperatures being desirable for higher efficiencies. Thus the extent of corrosion and corrosion mechanisms in various components and SC-CO 2 Brayton cycle will be different, requiring a judicious selection of materials for different sections of the cycle. The goal of this project was to address materials corrosion-related challenges, identify appropriate materials, and advance the body of scientific knowledge in the area of high temperature SC-CO 2 corrosion. The focus was on corrosion of materials in SC-CO 2 environment in the temperature range of 450°C to 750°C at a pressure of 2900 psi for exposure duration for up to 1000 hours. The Table below lists the materials tested in the project. The materials were selected based on their high temperature strength, their code certification status, commercial availabilities, and their prior or current usage in the nuclear reactor industry. Additionally, pure Fe, Fe-12%Cr, and Ni-22%Cr were investigated as simple model materials to more clearly understand corrosion mechanisms. This first phase of the project involved testing in research grade SC-CO 2 (99.999% purity). Specially designed autoclaves with high fidelity temperature, pressure, and flow control capabilities were built or modified for this project.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Operation and analysis of a supercritical CO2 Brayton cycle.

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.

42 ENGINEERING↗
DOE OSTI2014

Superficial Carbon Dioxide Brayton Cycle Energy Conversion Research and Development Program

A closed Brayton cycle recirculates the working fluid, and the turbine exhaust is used in a recuperating heat exchanger to heat the turbine feed. A "supercritical cycle' is a closed Brayton cycle in which the working fluid, such as supercritical carbon dioxide (s-0O2), is maintained near the critical point during the compression phase of the cycle. The key property of the fluid near its critical point is its higher gas density, closer to that of a liquid than of a gas, allowing for the pumping power in the compressor to be significantly reduced, which results in thermal efficiency that is significantly improved over the efficiency attainable in an ideal-gas Brayton cycle. Another advantage of using a supercritical cycle is that the overall footprint of the power-conversion system can be significantly reduced, as compared to the same power output of a steam-Rankine cycle, due to the high pressure in the system and resulting low volumetric flow rate. This allows for the heat-rejection heat exchanger and turbine to be orders of magnitude smaller than for similar power output steam-Rankine systems. Other potential advantages are the reduced use of water, not only due to the increased efficiency, but due also to the fact that the heat rejection temperature is significantly higher than for steam-Rankine systems, allowing for significant heat rejection directly to air. In 2006, Sandia National Laboratories (SNL), recognizing these potentially significant advantages of a higher efficiency power cycle, used internal funds to establish a testing capability and began partnering with the U.S. Department of Energy Office of Nuclear Energy to develop a laboratory-scale test assembly to show the viability of the underlying science and demonstrate system performance. Since that time, SNL has generated over 100 kW-hours of energy, verified cycle performance, and developed cycle controls and maintenance procedures. The test assembly has successfully operated in different configurations (simple Brayton, waste heat cycle, and recompression) and tested additives to the s-CO 2 working fluid. However, challenges remain to confirm viability of existing components and suitability of materials, demonstrate that theoretical efficiencies are achievable, and integrate and scale up existing technologies to be suitable for a range of applications.

42 ENGINEERING↗
DOE OSTI2012

Advanced Multi-Effect Distillation System for Desalination Using Waste Heat fromGas Brayton Cycles

Generation IV high temperature reactor systems use closed gas Brayton Cycles to realize high thermal efficiency in the range of 40% to 60%. The waste heat is removed through coolers by water at substantially greater average temperature than in conventional Rankine steam cycles. This paper introduces an innovative Advanced Multi-Effect Distillation (AMED) design that can enable the production of substantial quantities of low-cost desalinated water using waste heat from closed gas Brayton cycles. A reference AMED design configuration, optimization models, and simplified economics analysis are presented. By using an AMED distillation system the waste heat from closed gas Brayton cycles can be fully utilized to desalinate brackish water and seawater without affecting the cycle thermal efficiency. Analysis shows that cogeneration of electricity and desalinated water can increase net revenues for several Brayton cycles while generating large quantities of potable water. The AMED combining with closed gas Brayton cycles could significantly improve the sustainability and economics of Generation IV high temperature reactors.

42 ENGINEERING↗
NASA NTRS1984

Subatmospheric Brayton-cycle Engine Program Review

A solar energy powered electrical generator utilizing a Subatmospheric Brayton cycle engine is examined. The generator consists of a subatmospheric, Brayton-cycle engine and a permanent magnet (PM) alternator. The electrical power is generated by an alternator driven directly by the Brayton-cycle engine rotating group. Features that enhance reliability and performance include air foil bearings on both the Brayton-cycle engine rotating group and the PM alternator, an atmospheric-pressure solar receiver and gas-fired trim heater, and a high temperature recuperator. The subatmospheric Brayton-cycle engine design is based on that of the gas fired heat pump engine.

Johnson, R. L.↗
DOE OSTI2019

Thermal desalination via supercritical CO 2 Brayton cycle: Optimal system design and techno-economic analysis without reduction in cycle efficiency

The supercritical carbon dioxide (sCO 2 ) Brayton cycle is an upcoming power cycle potentially providing higher energy efficiency and more compact turbomachinery compared to traditionally used Brayton and Rankine cycles. The heat rejected from the sCO 2 Brayton cycle is quite hot (>70 degrees C) and must be cooled before flowing back to the compressor. However, this heat is ideal for producing fresh water with a thermal desalination system. This paper focuses on integrating multi-effect distillation (MED) with the sCO 2 stream exiting the recuperator. A new methodology for integration of MED with the sCO 2 Brayton cycle is proposed for simultaneous production of power and fresh water. The distillate produced does not affect the sCO 2 cycle efficiency, i.e., distillate is produced without being a parasitic load to the power plant compared to conventional integration of MED with steam Rankine cycle. To maximize the energy recovery from the waste heat stream exiting the sCO 2 cycle, a new methodology is formulated and discussed in the Appendix. Integration of MED with a 115 MW e sCO 2 power plant (49.2% efficient) produces 2813 m3/day of distillate and the cost of distilled water is 1.1 $/m 3 . Further, to enhance the distillate production, an innovative MED configuration is proposed, and for the same cycle operating condition with an electrical output 115 MW e , the net distillate production increases by 59% to 4472 m 3 /day at 1 $/m 3 . The cost of desalinated water for the integrated system is 17.8% lower than that of a standalone reverse-osmosis plant having the same capacity. Parametric analysis is performed to calculate the optimal design parameters for the integrated MED-sCO 2 system.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
NASA NTRS2007

Heat Transfer Analysis of a Closed Brayton Cycle Space Radiator

This paper presents a mathematical analysis of the heat transfer processes taking place in a radiator for a closed cycle gas turbine (CCGT), also referred to as a Closed Brayton Cycle (CBC) space power system. The resulting equations and relationships have been incorporated into a radiator sub-routine of a numerical triple objective CCGT optimization program to determine operating conditions yielding maximum cycle efficiency, minimum radiator area and minimum overall systems mass. Study results should be of interest to numerical modeling of closed cycle Brayton space power systems and to the design of fluid cooled radiators in general.

Juhasz, Albert J.↗