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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS2010

Modeling of the Orbital Debris Population of RORSAT Sodium-Potassium Droplets

A large population resident in the orbital debris environment is composed of eutectic sodium-potassium (NaK) droplets, released during the reactor core ejection of 16 nuclear-powered Radar Ocean Reconnaissance Satellites (RORSATs) launched in the 1980s by the former Soviet Union. These electrically conducting RORSAT debris objects are spherical in shape, generating highly polarized radar returns. Their diameters are mostly in the centimeter and millimeter size regimes. Since the Space Surveillance Network catalog is limited to objects greater than 5 cm in low Earth orbit, our current knowledge about this special class of orbital debris relies largely on the analysis of Haystack radar data. This paper elaborates the simulation of the RORSAT debris populations in the new NASA Orbital Debris Engineering Model ORDEM2010, which replaces ORDEM2000. The estimation of the NaK populations uses the NASA NaK-module as a benchmark. It follows the general statistical approach to developing all other ORDEM2010-required LEO populations (for various types of debris and across a wide range of object sizes). This paper describes, in detail, each major step in the NaK-population derivation, including a specific discussion on the conversion between Haystack-measured radar-cross-sections and object-size distribution for the NaK droplets. Modeling results show that the RORSAT debris population is stable for the time period under study and that Haystack data sets are fairly consistent over the observations of multiple years.

Xu, Y.-L.↗
DOE OSTI2025

Nuclear Magnetic Resonance Dynamics of LiTFSI–Pyrazole Eutectic Solvents

Deep Eutectic Solvents (DESs) have emerged as promising candidates to replace conventional organic solvents in various technological applications due to their low vapor pressure, non-flammability, and ease of preparation at low costs. In particular, Type IV DESs, which are composed of metal salts and hydrogen bond donors, are possible replacements for lithium-ion battery electrolytes. In this study, we investigate the molecular dynamics of solvents of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and pyrazole (PYR) at varying LiTFSI:PYR molar ratios (1:2, 1:3, 1:4, 1:5) using Nuclear Magnetic Resonance Dispersion (NMRD) and Pulsed Field Gradient (PFG) Nuclear Magnetic Resonance (NMR). PFG NMR reveals composition-dependent diffusion trends, while NMRD provides molecular-level insights into the longitudinal relaxation rate (R 1 = 1/T 1 ). Notably, the LiTFSI:PYR (1:2) sample shows distinct behavior across both techniques, exhibiting enhanced relaxation rates and lower self-diffusion for 1 H compared to the other nuclei ( 19 F and 7 Li), suggestive of stronger and more efficient Li + –pyrazole interactions, as confirmed by the modeling of the relaxation profiles. Our study advances understanding of ion dynamics in azole-based eutectic solvents, supporting their potential use in safer battery electrolytes.

FFC-NMR↗
DOE OSTI2021

Influence of fine-scale B2 precipitation on dynamic compression and wear properties in hypo-eutectic Al0.5CoCrFeNi high-entropy alloy

The near equiatomic high-entropy alloys based on Al, Co, Cr, Fe, Ni have provided a novel microstructural template for alloy design. The face-centered cubic (FCC) matrix strengthened by body-centered cubic (BCC) based ordered B2 precipitates can be used to develop a new generation of precipitation strengthened alloys. The present study focuses on an Al0.5CoCrFeNi hypo-eutectic alloy consisting of an as-solidified FCC+B2 microstructure. Guided by solution thermodynamic modeling, this alloy has been isothermally aged for solid-state precipitation of a high fraction of fine-scale intragranular B2 particles. The dynamic compressive strength, hardness, and sliding wear response of the alloy as a function of B2 phase fraction is examined. The flow stress at 0.02% true strain increased from ~ 670 MPa to ~1350 (102%) MPa, the ultimate compressive strength increased from ~1160 MPa to 1500 MPa (20%), and the wear resistance increased more than 5 times with progressively increasing phase fraction of B2 precipitates.

Gwalani, Bharat↗
DOE OSTI2022

Thermodynamic assessment of lithium halide reciprocal salt systems for energy applications

Lithium halides are of interest because of their unique applications as fuel or coolants in molten salt reactors (MSRs) and electrolytes in thermally activated batteries. Because iodine is an important fission product for MSRs, the Molten Salt Thermal Properties Database-Thermochemical (MSTDB-TC) is being expanded to include relevant iodide reciprocal salt systems. In this work, we assess the thermochemical properties of lithium halide pseudobinary systems based on reported experimental phase diagrams, eutectic temperatures, and enthalpies of mixing. Within the framework of the modified quasi-chemical model in the quadruplet approximation (MQMQA), extrapolations to the related pseudoternary and pseudoquaternary systems have been performed. The pseudoquaternary representations of phase equilibria, enthalpy, entropy, and heat capacity are represented in the resultant models. Of interest for generating source terms for accident analysis is the ability to compute the vapor pressures of the dominant iodide species for the systems at any composition. Here, an example of such calculations is provided for the LiF-LiI system at x LiI = 0.01 and x LiI = 0.70, in this case indicating that the LiI vapor species are predominant.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

SAM Code Enhancements for Modeling of Liquid Metal-Cooled Fast Reactor Concepts

The SAM code is under development and supported by DOE-NE’s Nuclear Energy Advanced Modeling and Simulation program as a modern system-level modeling and simulation tool for advanced non-light water reactor safety analyses. These advanced reactor concepts incorporate novel and improved approaches to achieve safety and economic feasibility. This report summarizes two major efforts in addressing the modeling gaps in SAM for liquid-metal-cooled fast reactor (LMFR) applications, i.e. thermal mixing and stratification phenomena in large pools and corrosion-oxidation of components in flowing lead. A new one-dimensional model for thermal mixing and stratification effects in large pools and enclosures is developed and implemented. Thermal mixing and stratification occur when fluid enters a pool at a temperature different than the bulk fluid itself, a scenario often encountered during transients in pool-type systems. These phenomena are critical for the safety of reactors, impacting phenomena like natural circulation, which is essential for passive cooling. The improved model in SAM addresses limitations of state-of-the-art approaches by combining one-dimensional (1D) channels, representing the coolant jet flow, with lumped-parameter zero-dimensional (0D) pools, representing the rest of coolant in the tank. Energy exchange between the 1D jet and the 0D pools is based on heat transfer correlations calibrated against 3D simulations. It is verified that this model can handle various flow configurations, including hot jets in colder pools, cold jets in hotter pools, and the presence of features like ceilings, free surfaces, and obstacles. Additionally, validation against experimental data demonstrates the ability of the model to capture mixing and stratification effects in a wide range of conditions. The flexibility and improved accuracy of the new model make it a valuable tool for reactor safety analysis, allowing for the simulation of different geometries encountered in advanced reactors. A system-level corrosion modeling capability is developed and implemented in SAM to support Lead Fast Reactor (LFR) development. Although the initial focus of this capability will be on LFR application, this can later be expanded to include other liquid metals such as Lead-Bismuth Eutectic (LBE) and PbLi. This report summarizes the common corrosion mitigation strategies and outlines the progress on implementing and validating a corrosion-oxidation model in SAM. Verification and validation of the corrosion-oxidation portion of the model was performed using analytical solution and measured data from samples tested in the non-isothermal pumped lead loop at IPPE Obninsk. The iron transport and corrosion/precipitation portion of the model was assessed using an analytical model and measured corrosion depths from a natural convection lead loop experiment performed at CEA. It is demonstrated that the model implemented in SAM performed well in these assessments.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2023

Power Electronics Materials and Bonded Interfaces - Reliability and Lifetime

High temperature operation of wide bandgap devices continue to be a challenge for the power electronics packages. Thermal performance and reliability are important factors that determine the viability of a bonded interface for operation at high temperatures. In this presentation, we present the technical approach and key results from the research on sintered silver, transient liquid phase alloy, and polymeric materials. A lifetime prediction model that incorporates the thermomechanical behavior of sintered silver at 200C was developed. The copper-aluminum transient alloy completed 350 thermal cycles from -40C to 200C and little increase in the defect level was observed. In addition to material research, we initiated a time-series analysis on the scanning acoustic microscope images of eutectic solder to explore statistical forecasting methods and machine learning techniques. Initial results that report the accuracy of a few different statistical models are presented.

ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2025

Effect of Soluble Corrosion Products on Electrical Double Layer in LiCl-KCl Molten Salts

Corrosion in molten salts greatly hampers the application for renewable energy applications like molten salt reactors. To develop effective strategies for corrosion mitigation, understanding the interfacial structures and properties such as specific ion adsorption and electrical double layer capacitance are crucial. Using cyclic voltammetry and electrochemical impedance spectroscopy, we systematically studied the interfaces on various model electrodes including W (solid), Bi (liquid), and the stainless steel 316 in LiCl-KCl eutectic molten salts with the addition of corrosion species CrCl 2 and FeCl 2 . Both Cr 2+ and Fe 2+ ions increased electrical double layer capacitance, with Cr 2+ showing specific adsorption behavior and shifting the potential of zero charge, while Fe 2+ had minimal effect on point of zero charge. Two-working electrode measurements revealed increasing open-circuit potential and electrical double layer capacitance during the exposure of stainless steel 316, indicating its progressive corrosion and ion accumulation at the interface. X-ray photoelectron spectroscopy and Raman confirmed Cr enrichment at the interface. This work highlights the strong correlation between electrical double layer behavior and corrosion dynamics in molten salts and suggests electrical double layer capacitance as a sensitive, in situ indicator for corrosion monitoring.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2022

Broadband NMR relaxometry of electrolytes for energy storage

An increasing use of the fast field cycling nuclear magnetic resonance relaxometry technique to investigate dynamics in electrolytes for energy storage has been evidenced during the last decade. Therefore, this review article describes some of the research carried out on electrolytes during the last ten years using this technique. These studies include various types of liquid electrolytes, such as ionic liquids and deep eutectic solvents, semi-solid-state electrolytes, in particular ionogels and polymer gels, and solid electrolytes such as glasses, glass ceramics and polymers. Here, an extended description of the different models used to explain the relaxation rate profiles is presented throughout this article.

25 ENERGY STORAGE↗
NASA NTRS1994

Influence of convection on microstructure

The primary motivation for this research was to determine the cause for space processing altering the microstructure of some eutectics, especially the MnBi-Bi eutectic. Four primary hypotheses were to be tested under this current grant: (1) A fibrous microstructure is much more sensitive to convection than a lamellar microstructure, which was assumed in our prior theoretical treatment. (2) An interface with one phase projecting out into the melt is much more sensitive to convection than a planar interface, which was assumed in our prior theoretical treatment. (3) The Soret effect is much more important in the absence of convection and has a sufficiently large influence on microstructure that its action can explain the flight results. (4) The microstructure is much more sensitive to convection when the composition of the bulk melt is off eutectic. These hypotheses were tested. It was concluded that none of these can explain the Grumman flight results. Experiments also were performed on the influence of current pulses on MnBi-Bi microstructure. A thorough review was made of all experimental results on the influence of convection on the fiber spacing in rod eutectics, including results from solidification in space or at high gravity, and use of mechanical stirring or a magnetic field. Contradictory results were noted. The predictions of models for convective influences were compared with the experimental results. Vigorous mechanical stirring appears to coarsen the microstructure by altering the concentration field in front of the freezing interface. Gentle convection is believed to alter the microstructure of a fibrous eutectic only when it causes a fluctuating freezing rate with a system for which the kinetics of fiber branching differs from that for fiber termination. These fluctuations may cause the microstructure to coarsen or to become finer, depending on the relative kinetics of these processes. The microstructure of lamellar eutectics is less sensitive to freezing rate fluctuations and to gentle convection.

Wilcox, William R.↗
DOE OSTI2023

Validation of MFUEL Metal Fuel Performance Models of SAS4A/SASSYS-1

The fuel characterization models of SAS4A/SASSYS-1 (SAS) have recently been extended to include a new U-Pu-Zr metal fuel model, MFUEL. MFUEL is equipped with mechanistic physics based models to predict the pre-transient characterization and transient response of metal fuel, with emphasis on fuel melting, cladding failure, and the metal fuel’s impact on core reactivity. The MFUEL model will be available in the full version of SAS4A/SASSYS-1 5.7, which is scheduled to be released in June 2023. Fast reactor fuel pins that operated in EBR-II and FFTF with low smear density U-Zr and U-Pu-Zr metal fuels and irradiation resistant ferritic-martensitic cladding showed significant advantages in achieving high burnups and assuring inherent safety characteristics during anticipated transients, design basis events, and beyond design basis events. For safety analysis, a fuel performance model must be able to predict (1) Fuel pin mechanics and compositional and dimensional changes, (2) Clad failure, and (3) Fuel pin thermal resistance. Achieving these high level goals accurately is strongly related to the model performance of individual physical processes taking place within a fuel pin during its lifetime. Metal fuels typically operate above the mid-point temperature of melting during normal, as well as off-normal, conditions. At these elevated temperatures, the availability of thermal activation provides a driving force for various diffusional processes leading to complex phase transformations, micro-structure evolution, significant amounts of fuel swelling, interconnected porosity formation, excessive amounts of fission gas release, and fuel clad chemical interactions. Clad failure in fast reactors primarily occurs as a result of creep rupture augmented by clad wastage formation. The reaction is driven by thermal creep induced dislocation motion, grain boundary cavity nucleation, growth and breakup of grain boundaries. The high level complexity and limited available data requires introducing physics-based modeling approaches to gain extrapolation ability and sensitivity with respect to various conditions. The objective of this report is to perform validation of MFUEL using the experimental data for (1) Normal operation EBR-II fuel behavior, (2) Normal operation PHENIX fuel behavior, (3) HT9 Pressure tube ramp-and-hold creep rupture tests, (4) Whole Pin Furnace (WPF) creep strain, creep rupture and eutectic tests, (5) Fuel Behavior Test Apparatus (FBTA) eutectic tests, and (6) TREAT M5-7 OverPower tests up to clad failure. Section-2 includes a brief description of the MFUEL models. A detailed description of the MFUEL physics-based, semi-empirical models will be presented in the SAS V 5.7 theory manual. Section-3, 4, and 5 describes the validation effort for the pre-transient irradiation, furnace transients, and TREAT M-Series transients, respectively.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Demonstration of RELAP5-3D for transient analysis of a dual coolant lead lithium fusion blanket concept

Our research aims to build a multiphysics framework for transient analysis of the Dual- Coolant Lead-Lithium (DCLL) blanket design of the proposed Fusion Nuclear Science Facility (FNSF) for all Onticipated Operational Occurrences (AOOs) using Reduced Order Models (ROMs). This paper presents an assessment of using RELAP5-3D for transient thermal-hydraulic blanket analysis of the DCLL design. Preliminary validation studies for the RELAP5-3D properties were conducted using a representative vertical flow loop model and a comparison study using experimental data from the thermal convection corrosion loops at ORNL. These studies inspected the thermal hydraulic response of Lead-Lithium Eutectic (PbLi) systems within the RELAP5-3D code; mainly pressure drop and heat transfer, as compared to analytical calculations and experimental data. The Magnetohydrodynamic (MHD) pressure drop effect for liquid metal under the effects of a uniform magnetic field was implemented into our models using an equivalent forms loss coefficient based on the phasic momentum equations. We verified our implementation of MHD pressure drop within RELAP5-3D using a systematic approach consisting of two studies. Models were developed to perform comparison studies based on experimental data from the Argonne Liquid metal EXperiment (ALEX) facility and the Magnetohydrodynamic PbLi Experiment (MaPLE) facility. Using the developed validation basis, we built a simplified DCLL channel model within RELAP5-3D, inspected MHD pressure drop and performed transient temperature analysis. The DCLL channel model used radial heating data from the International Thermonuclear Experimental Reactor (ITER) which was normalized to the FNSF design. Here, a representative startup transient was performed using a relative power curve from the initial ramp up of a long-term power pulse of the Tore Supra reactor. This study demonstrated that RELAP5-3D ROMs are capable of accurate transient analysis of the DCLL blanket. We have since utilized MCNP to develop heating profiles based on the FNSF design and are working toward implementing them into our DCLL model.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Assessment of thermodynamic stability of sapphire in eutectic molten chloride environment

The continued development of molten salt reactors requires highly efficient and stable instruments that can efficiently track monitor conditions of the molten salt during long-term application operation in both the fuel and coolant/heat transfer fluid loops. Sapphire (Al 2 O 3 ) fibers have shown tremendous potential by enabling radiation resistance and a broader operational range of temperature . Thermodynamic modeling using the ThermoCalc and the SGTE Molten Salts (SALT1) and Pure Substances (Pure5) database is done performed to understand the compatibility of Al 2 O 3 fibers with NaCl-MgCl 2 eutectic molten salt in the temperature range of 600 to 1000°C. The thermodynamic calculations show that sapphire fibers are not expected to be compatible with long term exposure to molten chloride salts within this temperature range. Furthermore, various pure metallic elements were evaluated as potential cladding materials for part of the Al 2 O 3 fibers. Based on the thermodynamic analysis, molybdenum (Mo) and nickel (Ni) could be effective cladding materials to enhance the stability of Al 2 O 3 in NaCl and MgCl 2 chloride salt molten bath in the desired temperature range. The presence of a metallic cladding leads to the suppression of aluminum dissolution from Al 2 O 3 , thus improving its stability in chloride salts. Additionally, it is also shown that Al 2 O 3 remains stable up to 2300 K in the presence of pre-existing Al 2 MgO 4 and Al 2 NiO 4 in the eutectic molten chloride bath environment.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2023

The role of cellular structure, non-equilibrium eutectic phases and precipitates on quasi-static strengthening mechanisms of as-built AlSi10Mg parts 3D printed via laser powder bed fusion

The quasi-static loading strengthening mechanism in the as-built state of an AlSi10Mg alloy 3D-printed via Laser Powder Bed Fusion (LPBF) was thoroughly identified and quantified using state-of-the-art electron microscopy and synchrotron X-ray diffraction techniques. The yield strength was comprehensively modelled through an in-depth characterization and quantification of the microstructural features as well as their effective volumes for strengthening. In particular, the non-equilibrium eutectic network was characterized with a two-fold structure: cell boundary particles as well as intracellular lamellar/fibrous networks, each consisting of discrete phases exhibiting a thru-thickness compositional gradient, a semi-coherent interface with the matrix and an abundance of crystal defects such as nano-sized sub-grains, microstrains and stacking faults. Further, these altogether made the eutectic phase the most potent contributor to the yield strength accounting for ~30–40% of the estimated value (i.e., cell boundary and eutectic network strengthening combined). Precipitates strengthening was identified as the second most potent mechanism via a shearing process only. Moreover, the presented methodology was able to capture the effect of LPBF processing variables on the individual strengthening contributions, e.g., the effect of a lower laser scanning speed on increasing the cell size as well as the mean precipitate size, which are shown to exhibit opposing impacts on strengthening.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Testing to Evaluate Processes Expected to Occur during MSR Salt Spill Accidents

Obtaining a license for a new nuclear reactor requires the identification and assessment of the potential consequences of specified accident scenarios, which are achieved using accident progression models. Those models need to be parameterized and validated using experimental data, but existing experimental data addressing processes relevant to molten salt reactor accidents are sparse. Specifically, experimental data that quantify the sensitives of important processes to the initial conditions of the spill, the ambient environment, and the containment features are needed to parameterize individual process models. Integrated experiments that simulate accident scenarios are also needed to provide data for model validation, but these experiments will require the use of proven methods to quantify the processes under evaluation. The overarching objectives of this work are to develop the methods for simulating the targeted processes, to determine the effectiveness of the methods in producing the data required for model development, to generate data that can be used to parameterize individual process models, and to provide key insights into the behavior of spilled molten salt that should be considered in models. Experimental methods were designed to quantify aspects of individual processes expected to occur during or after a molten salt spill accident that will affect the fate of spilled molten salt and the radionuclides within. These processes include 1) molten salt spreading and heat transfer, 2) molten salt flowing and freezing in tubing, 3) stainless steel corrosion kinetics in molten salt, and 4) molten salt splashing and aerosol generation. The initial tests described in this report were conducted using eutectic FLiNaK to demonstrate the test methods, the data that are generated, and the analyses of the data to derive values needed for modeling. The primary variables that were tested include initial salt temperature and the presence of volatile surrogate fission products (e.g., cesium and iodine). The developed methods are shown to be effective in quantifying the desired processes and can be applied to study more complex salt compositions of interest to molten salt reactor developers, a wide range of environmental conditions of interest to modelers, and additional variables relevant to salt spill accidents. The developed methods and insights gained from laboratory tests can also be incorporated in future large-scale integrated tests used to simulate molten salt spill accidents.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
NASA NTRS1987

Containerless processing of undercooled melts

Containerless drop tube processing allows for significant levels of liquid undercooling through control of parameters such as sample size, surface coating and cooling rate. A laboratory scale (3 m) drop tube has been developed which allows the undercooling and solidification behavior of powder samples to be evaluated under low gravity free-fall conditions. The level of undercooling obtained in an InSb-Sb eutectic alloy has been evaluated by comparing the eutectic spacing in drop tube samples with a spacing/undercooling relationship established using thermal analysis techniques. Undercoolings of 0.17 and 0.23 T(e) were produced by processing under vacuum and He gas conditions respectively. Alternatively, the formation of an amorphous phase in a Ni-Nb eutectic alloy indicates that undercooling levels of approximately 500 C were obtained by drop tube processing. The influence of droplet size and gas environment on undercooling behavior in the Ni-Nb eutectic was evaluated through their effect on the amorphous/crystalline phase ratio. To supplement the structural analysis, heat flow modeling has been developed to describe the undercooling history during drop tube processing, and the model has been tested experimentally.

Shong, D. S.↗
NASA NTRS1991

Use of NH4Cl-H2O Analogue Castings to Model Aspects of Continuous Casting: Asymmetry in Inclined Moulds - Part 1

Crystallisation of NH4Cl from aqueous solutions has been used to examine grain formation in a configuration similar to that existing in the curved mould of a continuous, steel casting machine. The observations show how falling equiaxed crystals accumulate at the lower (outer) columnar front earlier than at the upper (inner) front and, thus, lead to an asymmetric grain structure. The usefulness of the aqueous system as a realistic model for steel casting is discussed in terms of relative temperature profiles, materials properties, and observed columnar and eutectic growth rates.

Jang, J.↗
NASA NTRS1997

Modeling Cyclic Phase Change and Energy Storage in Solar Heat Receivers

Numerical results pertaining to cyclic melting and freezing of an encapsulated phase change material (PCM), integrated into a solar heat receiver, have been reported. The cyclic nature of the present melt/freeze problem is relevant to latent heat thermal energy storage (LHTES) systems used to power solar Brayton engines in microgravity environments. Specifically, a physical and numerical model of the solar heat receiver component of NASA Lewis Research Center's Ground Test Demonstration (GTD) project was developed and results compared with available experimental data. Multi-conjugate effects such as the convective fluid flow of a low-Prandtl-number fluid, coupled with thermal conduction in the phase change material, containment tube and working fluid conduit were accounted for in the model. A single-band thermal radiation model was also included to quantify reradiative energy exchange inside the receiver and losses through the aperture. The eutectic LiF-CaF2 was used as the phase change material (PCM) and a mixture of He/Xe was used as the working fluid coolant. A modified version of the computer code HOTTube was used to generate results for comparisons with GTD data for both the subcooled and two-phase regimes. While qualitative trends were in close agreement for the balanced orbit modes, excellent quantitative agreement was observed for steady-state modes.

Hall, Carsie A., III↗
NASA NTRS1997

Parametric Analysis of Cyclic Phase Change and Energy Storage in Solar Heat Receivers

A parametric study on cyclic melting and freezing of an encapsulated phase change material (PCM), integrated into a solar heat receiver, has been performed. The cyclic nature of the present melt/freeze problem is relevant to latent heat thermal energy storage (LHTES) systems used to power solar Brayton engines in microgravity environments. Specifically, a physical and numerical model of the solar heat receiver component of NASA Lewis Research Center's Ground Test Demonstration (GTD) project was developed. Multi-conjugate effects such as the convective fluid flow of a low-Prandtl-number fluid, coupled with thermal conduction in the phase change material, containment tube and working fluid conduit were accounted for in the model. A single-band thermal radiation model was also included to quantify reradiative energy exchange inside the receiver and losses through the aperture. The eutectic LiF-CaF2 was used as the phase change material (PCM) and a mixture of He/Xe was used as the working fluid coolant. A modified version of the computer code HOTTube was used to generate results in the two-phase regime. Results indicate that parametric changes in receiver gas inlet temperature and receiver heat input effects higher sensitivity to changes in receiver gas exit temperatures.

Hall, Carsie A., III↗