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81 records · Page 5

All sources NASA NTRS DOE OSTI

NASA NTRS2006

Heat Rejection Concepts for Lunar Fission Surface Power Applications

This paper describes potential heat rejection design concepts for lunar surface Brayton power conversion systems. Brayton conversion systems are currently under study by NASA for surface power applications. Surface reactors may be used for the moon to power human outposts enabling extended stays and closed loop life support. The Brayton Heat Rejection System (HRS) must dissipate waste heat generated by the power conversion system due to inefficiencies in the thermal-to-electric conversion process. Space Brayton conversion system designs tend to optimize at efficiencies of about 20 to 25 percent with radiator temperatures in the 400 K to 600 K range. A notional HRS was developed for a 100 kWe-class Brayton power system that uses a pumped water heat transport loop coupled to a water heat pipe radiator. The radiator panels employ a tube and fin construction consisting of regularly-spaced circular heat pipes contained within two composite facesheets. The water heat pipes interface to the coolant through curved sections partially contained within the cooling loop. The paper evaluates various design parameters including radiator panel orientation, coolant flow path, and facesheet thickness. Parameters were varied to compare design options on the basis of H2O pump pressure rise and required power, heat pipe unit power and radial flux, radiator area, radiator panel areal mass, and overall HRS mass.

Siamidis, John↗

NASA NTRS2005

Heat Rejection Concepts for Brayton Power Conversion Systems

This paper describes potential heat rejection design concepts for closed Brayton cycle (CBC) power conversion systems. Brayton conversion systems are currently under study by NASA for Nuclear Electric Propulsion (NEP) applications. The Heat Rejection Subsystem (HRS) must dissipate waste heat generated by the power conversion system due to inefficiencies in the thermal-to-electric conversion process. Space Brayton conversion system designs tend to optimize at efficiencies of about 20 to 25 percent with radiator temperatures in the 400 to 600 K range. A notional HRS was developed for a 100 kWe-class Brayton power system that uses a pumped sodium-potassium (NaK) heat transport loop coupled to a water heat pipe radiator. The radiator panels employ a sandwich construction consisting of regularly-spaced circular heat pipes contained within two composite facesheets. Heat transfer from the NaK fluid to the heat pipes is accomplished by inserting the evaporator sections into the NaK duct channel. The paper evaluates various design parameters including heat pipe diameter, heat pipe spacing, and facesheet thickness. Parameters were varied to compare design options on the basis of NaK pump pressure rise and required power, heat pipe unit power and radial flux, radiator panel areal mass, and overall HRS mass.

Siamidis, John↗

NASA NTRSDate not supplied

Convertor Development for Dynamic Radioisotope Power Systems

Dynamic power conversion technologies are being developed for future space science and exploration missions by NASA’s Radioisotope Power Systems (RPS) Program, in collaboration with the U.S. Department of Energy (DOE). The Dynamic Radioisotope Power Systems (DRPS) Project is working to mature dynamic power convertors and controllers for infusion into a potential future flight generators.1,2 Maturation of power conversion technologies is being executed by the DRPS Project and the Thermal Energy Conversion Branch, located at NASA’s Glenn Research Center (GRC), and includes convertor technology development contracts and in-house controller development. The convertor technology development contracts consist of three contractors tasked to design, fabricate, and complete performance testing before the units are delivered to GRC for independent assessment. All contractors have completed convertor designs and are fabricating convertors to enable performance testing, while one has demonstrated initial performance of their design. The contractors also have provided generator conceptual designs, which utilize their respective convertor technologies being developed.

Dynamic↗

NASA NTRSDate not supplied

Mass Modeling of NEP Power Conversion Concepts for Human Mars Exploration

The specific mass (mass per unit of electric power output) of an NEP power conversion system is an important metric for the performance and feasibility of a crewed NEP vehicle. This work explores a component level buildup of the specific mass for a crewed NEP vehicle. The buildup is highly parametric and avoids being tied to specific technologies where practical. This allows the specific mass to be calculated for a variety of assumptions and operating conditions and be used to optimize particular design variables or compare different system configurations. The values of specific mass are dependent on assumptions with significant uncertainty; comparison between cases and trends observed in the models are the main goal of the work presented here. To demonstrate the level of insight this type of modeling can provide, the impacts of compressor inlet temperature, turbine inlet temperature, and radiator pressure drop on specific mass are explored. In addition, the specific mass can be used to assess the benefit of separating the radiator and reactor loop from the power conversion cycle.

nep↗

NASA NTRSDate not supplied

Mass Modeling of NEP Power Conversion Concepts for Human Mars Exploration

NEP↗

DOE OSTI2025

Printed circuit primary heat exchanger for power conversion in heat pipe microreactor applications

Here, in the present study, a model was developed for a recuperated air Brayton cycle for heat pipe microreactors, and the effect of the primary heat exchanger type assessed. An annular flow heat exchanger and a printed circuit heat exchanger (PCHE) were evaluated. A sub-sized diffusion bonded, PCHE test specimen was manufactured and tested with nitrogen as the working fluid to validate and improve the PCHE model. A comparison of the thermal cycle efficiency for the Brayton cycle coupled to a heat pipe microreactor using each of the two primary heat exchangers showed competitive performance for both options, with achievable cycle efficiencies of 34 % and 35 % for the annular and printed circuit heat exchangers, respectively. The impact of heat pipe length and additional reheating stages on cycle efficiency was studied. Increasing the heat pipe condenser length from 0.8 to 2.0 m resulted in an increase in cycle efficiency of 3.5 % and 3.2 % for the annular and printed circuit heat exchangers, respectively. The use of additional reheating stages showed a reduction in cycle efficiency since the heat pipe surface area limits the primary heat exchanger size and effectiveness. These results highlight the importance of the primary heat exchanger on the performance of a heat pipe microreactor. Overall, the cycle model, testing, and heat exchanger model showed the potential for the PCHE to improve the economics of a heat pipe microreactor relative to the annular flow heat exchanger, which also opens the possibility to use different heat transfer fluids such as supercritical CO 2 .

PCHE↗

NASA NTRS2018

Dynamic Power Convertor Development for Radioisotope Power Systems at NASA GRC

The Thermal Energy Conversion Branch at NASA Glenn Research Center (GRC) is supporting the development of high-efficiency power convertors in support of Radioisotope Power System (RPS) development. Significant progress was made towards such a system that utilized Stirling conversion machines during the 2001 to 2015 timeframe. Flight development of the Advanced Stirling Radioisotope Generator (ASRG) was cancelled in 2013 by the Department of Energy (DOE) and NASA Headquarters primarily due to budget constraints, and the Advanced Stirling Convertor (ASC) technology contract was subsequently concluded in 2015. A new chapter of technology development has recently been initiated by the NASA RPS Program. This new effort is considering all dynamic power convertor options, such as Stirling and Brayton cycles. Four convertor development contracts supporting this effort were awarded in 2017. The awarded contracts include two free-piston Stirling, one thermoacoustic Stirling, and one turbo-Brayton designs. The technology development contracts each consist of up to three phases: Design, Fabricate, and Test. As of May 2018, all contracts have completed the Design Phase, and each underwent a design review with an independent review board. Two of the contracts have been awarded the Phase 2 option for fabrication. Convertors manifesting from these development efforts will then undergo independent validation and verification at NASA facilities, which will consist of convertor performance and RPS viability demonstrations. Example tests include launch vibration simulation, performance mapping over the environmental temperature range, and static acceleration exposure. In parallel with this renewed development effort, NASA GRC is still demonstrating free-piston Stirling convertor technology using assets from previous projects. The Stirling Research Laboratory (SRL) is still operating 10 convertors from previous development projects. Four of which are flexure-bearing based, and the other six are gas-bearing based. One of the flexure-bearing convertors has accumulated over 110,000 hours of operation, and holds the current maintenance-free heat-engine run-time record. Another flexure-bearing convertor was recently manually shutdown after 105,620 hours of operation, then disassembled and inspected. This inspection produced a wealth of information about the effects of this amount of runtime on the technology's components. One of the engineering unit flexure-bearing convertors recently underwent launch simulation vibration test, a static acceleration exposure up to 20 g, and was then placed on extended operation. Amongst the gas-bearing convertors, the longest running unit has accumulated over 70,000 hours of operation. Four high-fidelity gas-bearing convertors from the ASRG project are still operating continuously, for which the longest runtime has reached 26,000 hours.

Oriti, Salvatore↗

NASA NTRS2018

Dynamic Power Convertor Development for Radioisotope Power Systems at NASA Glenn Research Center

The Thermal Energy Conversion Branch at NASA Glenn Research Center (GRC) is supporting the development of high-efficiency power convertors for use in Radioisotope Power Systems (RPS). Significant progress was made towards such a system that utilized Stirling conversion during the 2001 to 2015 timeframe. Flight development of the Advanced Stirling Radioisotope Generator (ASRG) was cancelled in 2013 by the Department of Energy (DOE) and NASA Headquarters primarily due to budget constraints, and the Advanced Stirling Convertor (ASC) technology contract was subsequently concluded in 2015. A new chapter of technology development has recently been initiated by the NASA RPS Program. This effort is considering all dynamic power convertor options, such as Stirling and Brayton cycles. Four convertor development contracts supporting this effort were awarded in 2017. The awarded contracts include two free-piston Stirling, one thermoacoustic Stirling, and one turbo-Brayton designs. The technology development contracts each consist of up to three phases: Design, Fabricate, and Test. As of May 2018, all contracts have completed the Design Phase, and each underwent a design review with an independent review board. Three of the contracts are planned to execute the Phase 2 option for fabrication. Convertors manifesting from these development efforts will then undergo independent validation and verification at NASA facilities, which will consist of convertor performance and RPS viability demonstrations. Example tests include launch vibration simulation, performance mapping over the environmental temperature range, and static acceleration exposure. In parallel with this renewed development effort, NASA GRC is still demonstrating free-piston Stirling convertor technology using assets from previous projects. The Stirling Research Laboratory (SRL) is still operating several convertors from previous development projects which have similarities and relevance to current contract designs. Four of which are flexure-bearing based, and another six are gas-bearing based. One of the flexure-bearing convertors has accumulated over 110,000 hours of operation, and holds the current record for maintenance-free heat-engine run-time. Another flexure-bearing convertor was recently manually shutdown after 105,620 hours of operation, then disassembled and inspected. This inspection produced a wealth of information about the effects of this amount of runtime on the technology's components. One of the engineering unit flexure-bearing convertors recently underwent launch simulation vibration test, a static acceleration exposure up to 20 g, and was then placed on extended operation. Amongst the gas-bearing convertors, the longest running unit has accumulated over 70,000 hours of operation. Four high-fidelity gas-bearing convertors from the ASRG project are still operating continuously, for which the longest runtime has reached 28,000 hours.

Oriti, Salvatore M.↗

NASA NTRS2018

Dynamic Power Convertor Development for Radioisotope Power Systems at NASA Glenn Research Center

The Thermal Energy Conversion Branch at NASA Glenn Research Center is supporting the development of high-efficiency power convertors for use in radioisotope power systems (RPS). Significant progress was made toward such a system that utilized Stirling conversion during the 2001 to 2015 timeframe. Flight development of the Advanced Stirling Radioisotope Generator (ASRG) was canceled in 2013 by the U.S. Department of Energy (DOE) and NASA Headquarters primarily due to budget constraints, and the Advanced Stirling Convertor (ASC) technology contract was subsequently concluded in 2015. A new chapter of technology development has recently been initiated by the NASA RPS Program. This effort is considering all dynamic power convertor options, such as Stirling and Brayton cycles. Four convertor development contracts supporting this effort were awarded in 2017. The awarded contracts include two free-piston Stirling, one thermoacoustic Stirling, and one turbo-Brayton design. The technology development contracts each consist of up to three phases: design, fabrication, and test. As of May 2018, all contracts have completed the design phase, and each underwent a design review with an independent review board. Three of the contracts are planned to execute the phase 2 option for fabrication. Convertors manifesting from these development efforts will then undergo independent validation and verification (IV and V) at NASA facilities, which will consist of convertor performance and RPS viability demonstrations. Example tests include launch vibration simulation, performance mapping over the environmental temperature range, and static acceleration exposure. In parallel with this renewed development effort, Glenn is still demonstrating free-piston Stirling convertor technology using assets from previous projects. The Stirling Research Laboratory (SRL) is still operating several convertors from previous development projects, which have similarities and relevance to current contract designs. Four of these are flexure-bearing based and another six are gas bearing based. One of the flexure-bearing convertors has accumulated over 110,000 h of operation and holds the current record for maintenance-free heat-engine run time. Another flexure-bearing convertor was recently manually shut down after 105,620 h of operation, then disassembled and inspected. This inspection produced a wealth of information about the effects of this amount of run time on the technology's components. One of the engineering unit flexure-bearing convertors recently underwent a launch simulation vibration test, a static acceleration exposure up to 20 g, and was then placed on extended operation. Among the gas-bearing convertors, the longest running unit has accumulated over 70,000 h of operation. Four high-fidelity gas-bearing convertors from the ASRG project are still operating continuously for which the longest run time has reached 28,000 h.

Oriti, Salvatore M.↗