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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 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Concurrent implementation of the Crank-Nicolson method for heat transfer analysis

To exploit the significant gains in computing speed provided by Multiple Instruction Multiple Data (MIMD) computers, concurrent methods for practical problems need to be investigated and test problems implemented on actual hardware. One such problem class is heat transfer analysis which is important in many aerospace applications. This paper compares the efficiency of two alternate implementations of heat transfer analysis on an experimental MIMD computer called the Finite Element Machine (FEM). The implicit Crank-Nicolson method is used to solve concurrently the heat transfer equations by both iterative and direct methods. Comparison of actual timing results achieved for the two methods and their significance relative to more complex problems are discussed.

Ransom, J. B.↗
NASA NTRS2006

In-Space Radiator Shape Optimization using Genetic Algorithms

Future space exploration missions will require the development of more advanced in-space radiators. These radiators should be highly efficient and lightweight, deployable heat rejection systems. Typical radiators for in-space heat mitigation commonly comprise a substantial portion of the total vehicle mass. A small mass savings of even 5-10% can greatly improve vehicle performance. The objective of this paper is to present the development of detailed tools for the analysis and design of in-space radiators using evolutionary computation techniques. The optimality criterion is defined as a two-dimensional radiator with a shape demonstrating the smallest mass for the greatest overall heat transfer, thus the end result is a set of highly functional radiator designs. This cross-disciplinary work combines topology optimization and thermal analysis design by means of a genetic algorithm The proposed design tool consists of the following steps; design parameterization based on the exterior boundary of the radiator, objective function definition (mass minimization and heat loss maximization), objective function evaluation via finite element analysis (thermal radiation analysis) and optimization based on evolutionary algorithms. The radiator design problem is defined as follows: the input force is a driving temperature and the output reaction is heat loss. Appropriate modeling of the space environment is added to capture its effect on the radiator. The design parameters chosen for this radiator shape optimization problem fall into two classes, variable height along the width of the radiator and a spline curve defining the -material boundary of the radiator. The implementation of multiple design parameter schemes allows the user to have more confidence in the radiator optimization tool upon demonstration of convergence between the two design parameter schemes. This tool easily allows the user to manipulate the driving temperature regions thus permitting detailed design of in-space radiators for unique situations. Preliminary results indicate an optimized shape following that of the temperature distribution regions in the "cooler" portions of the radiator. The results closely follow the expected radiator shape.

Hull, Patrick V.↗
NASA NTRS1998

Experimental Performance of a Micromachined Heat Flux Sensor

Steady-state and frequency response calibration of a microfabricated heat-flux sensor have been completed. This sensor is batch fabricated using standard, micromachining techniques, allowing both miniaturization and the ability to create arrays of sensors and their corresponding interconnects. Both high-frequency and spatial response is desired, so the sensors are both thin and of small cross-sectional area. Thin-film, temperature-sensitive resistors are used as the active gauge elements. Two sensor configurations are investigated: (1) a Wheatstone-bridge using four resistors; and (2) a simple, two-resistor design. In each design, one resistor (or pair) is covered by a thin layer (5000 A) thermal barrier; the other resistor (or pair) is covered by a thick (5 microns) thermal barrier. The active area of a single resistor is 360 microns by 360 microns; the total gauge area is 1.5 mm square. The resistors are made of 2000 A-thick metal; and the entire gauge is fabricated on a 25 microns-thick flexible, polyimide substrate. Heat flux through the surface changes the temperature of the resistors and produces a corresponding change in resistance. Sensors were calibrated using two radiation heat sources: (1) a furnace for steady-state, and (2) a light and chopper for frequency response.

TEMPERATURE SENSITIVE ELEMENTS↗
DOE OSTI2018

Heat-and-Mass Transfer Intensification in Saturated-Steam Generators in NPP with VVER as a Means for Increasing Efficiency and Reliability

The intensification of steam generation in combination with improvement of the temperature regime, specifically, with the elimination of temperature fluctuations of the loaded components of the apparatus (heat-exchange tubes, warming-medium headers) increases the steam-generation capacity and eliminates the factors causing damage to the structural elements of steam generators. The possibility of intensifying heat-and-mass transfer on the basis of the experience gained in operating steam generators in NPP with VVER (horizontal) and NPP in foreign countries (vertical) is examined. It is concluded on the basis of the analysis that it is expedient to develop a domestically produced apparatus of the vertical type, which will make possible well-founded production of steam generators for NPP with VVER in the future.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRS1972

A modified Monte Carlo model for the ionospheric heating rates

A Monte Carlo method is adopted as a basis for the derivation of the photoelectron heat input into the ionospheric plasma. This approach is modified in an attempt to minimize the computation time. The heat input distributions are computed for arbitrarily small source elements that are spaced at distances apart corresponding to the photoelectron dissipation range. By means of a nonlinear interpolation procedure their individual heating rate distributions are utilized to produce synthetic ones that fill the gaps between the Monte Carlo generated distributions. By varying these gaps and the corresponding number of Monte Carlo runs the accuracy of the results is tested to verify the validity of this procedure. It is concluded that this model can reduce the computation time by more than a factor of three, thus improving the feasibility of including Monte Carlo calculations in self-consistent ionosphere models.

Mayr, H. G.↗
NASA NTRSDate not supplied

Solar Coronal Phenomenon: Imaging Spectroscopy

The Sun's outer atmosphere, known as the corona, is significantly hotter than its surface, presenting a long-standing scientific mystery. One hypothesis is that small, frequent bursts of energy, called nanoflares, may be responsible for this heating, though the exact mechanism remains unclear. Additionally, certain elements in the corona appear more abundant than expected, a phenomenon termed the "FIP effect," which might also be linked to coronal heating processes. Imaging X-ray spectroscopy offers a powerful method for investigating these solar mysteries. In this talk, we will explore these intriguing questions about the Sun and discuss how imaging X-ray spectroscopy can provide insights. We will introduce the Marshall Grazing Incidence X-ray Imaging Spectrometer (MaGIXS) sounding rocket experiment and its recent successful flight, designed to probe these enigmatic aspects of the Sun.

solar corona↗
DOE OSTI2019

Magnetic and Thermal Design of HTS Quadrupole Magnet for Newly Developed Superconducting Proton Cyclotron Beam Line

A magnetic and thermal design of high-temperature superconducting (HTS) quadrupole magnet for newly developed superconducting proton cyclotron was presented in this research. With superconducting technology, the design can reduce the magnet size and remove the heat loads more efficiently. Calculations are conducted with finite element method (FEM) to study the quadrupole magnet’s magnetic and thermal properties. For the magnet cold-mass and cryostat system, the heat load is mainly generated by conduction and radiation. Multilayer thermal insulation and G10 supports are used to restrict them. The magnetic field distribution in the HTS coils is calculated to consider the critical current degradation of the YBCO tapes. The effects on the field gradient quality in relation to the pole tip profile and end chamfer are analyzed. The sixth multipole component in the integral field can be improved with end chamfer. Finally, a 20 T/m HTS quadrupole magnet with integral field uniformity less than 0.05% out to 75% of the inscribed radius is proposed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1987

Determination of the cross-sectional temperature distribution and boiling limitation of a heat pipe

A computer model is developed and verified which is capable of determining the cross-sectional temperature distribution within a heat pipe with an attached radiator fin; such heat pipes would be plugged into contact heat exchangers designed to carry heat from a space station habitation module to the radiator elements through a centralized fluid loop. The model can furnish information for determining the susceptibility of the monogroove heat pipe to boiling, as well as the location and magnitude of that boiling.

Peterson, G. P.↗
DOE OSTI2017

Considerations for Use of Am-241 for Heat Source Material for Radioisotope Power Systems.

There have been several efforts made over the last 60 years to examine the entire periodic table of the elements to determine the best isotope/element for use as a heat source for radioisotope power systems (RPS). Am-241 is typically not in the final group being considered due to its 432-year half-life. The window of isotopes considered has usually been kept to 15-100 year half-life. The criteria in down selecting an isotope for use as a heat source material have been: 1) radiation characteristics (easy to shield), 2) specific power (higher is better), 3) fuel form considerations (chemically compatible with cladding, chemically inert with respect to the environment, robust mechanically, high melting point), and 4) available at a reasonable cost and suitable quantities. There have been a few efforts examining Am-241 for use in RPS during the past 2 decades. None of these has advanced beyond comparison of known chemical or material properties. No heat sources have been made and none have been placed into RPS for testing. No tests have been conducted of the various americium oxides (AmO, Am 2 O 3 , AmO 2 nor nonstoichiometric phases between these oxides) for their behavior with the environment to confirm inert behavior or compatibility with cladding materials. From a crystallographic point of view americium and oxygen can form crystal phases that exhibit face-centered cubic, monoclinic, cubic or tetragonal characteristics. A simple point to make here is that the chemistry of americium and oxygen is complicated and not well understood at this point compared to plutonium and oxygen.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2020

Wireless Instrumented RB Experiment Preliminary Design and Analysis

The ability to deploy new nuclear fuels for current or future reactor concepts requires carefully designed experiments to generate data to support fuel qualification. Ideally these experiments would include state of-the-art sensing to maximize the amount of in situ data that can be collected during operation. Furthermore, advanced reactor systems can take advantage of integrated in-core sensing technologies to maximize fuel utilization, reduce unnecessary conservativism in design margins, and improve operator’s understanding of limiting peaking factors. Before any novel sensing technologies can be readily adopted for nuclear applications, they must first demonstrate acceptable performance in test reactors. This report summarizes the preliminary design and analysis of the most highly instrumented irradiation experiment ever performed in the removable beryllium (RB) positions of the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL). The Wireless Instrumented RB Experiment 2021 (WIRE-21) will test a wide range of sensors including wireless sensors being developed by Westinghouse Electric Company (WEC) that could provide in situ measurements of peak fuel temperatures and fuel rod pressurization due to fission gas release. The ability to wirelessly transmit a signal through the fuel rod’s cladding is critical to improving fuel monitoring capabilities without requiring signal penetrations through the cladding pressure boundary, which would significantly impact fuel fabrication, handling, and operation. Other sensors that will be tested in WIRE-21 include an array of thermocouples, self-powered neutron detectors (SPNDs), and spatially distributed fiber-optic temperature sensors. More generally, WIRE-21 will establish a flexible irradiation vehicle design to allow accelerated, economical testing of advanced sensor technologies while leveraging the extremely high neutron flux that is available in HFIR. This report summarizes the mechanical design for WIRE-21, the experimental test matrix, initial neutronic and thermal design analyses, and the active monitoring and control system enhancements necessary to support testing of advanced sensor technologies. The containment for WIRE-21 is similar to previous RB irradiation vehicles but includes a few modifications, most notably the use of integrated compression seals to pass a larger number of sensor leads through the experiment’s pressure boundary. In addition to the sensor leads, inert gas lines are passed into the experiment to enable active temperature control and the ability to pneumatically actuate a bellows-driven pressure sensor. WIRE-21 is targeting temperatures (300–350°C) and neutron fluence levels (~10 22 n/cm 2 ) relevant to light water reactors (LWRs), but the flexible design of the experiment vehicle allows much higher operating temperatures (>1,100°C). Neutronic calculations determine the neutron flux conditions as well as the nuclear heating within the experiments. These results are used as inputs to detailed thermal finite element calculations, which are required to evaluate the complex, three-dimensional heat transfer that occurs within WEC’s wireless sensor enclosures. Initial results show that the temperatures of the sensors’ enclosures and the metal bellows can be operated near the temperature range of LWR coolants and cladding while simultaneously increasing the temperature of a surrogate fuel material to values in the range of 800–1200°C to simulate centerline fuel temperatures during LWR operation.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1973

A modified Monte Carlo model for the ionospheric heating rates.

A Monte Carlo method is adopted as a basis for the derivation of the photoelectron-heat input into the ionospheric plasma. Since a great number of Monte Carlo runs are required normally for the computation of the heating rates, this approach is modified in an attempt to minimize the computation time. The heat-input distributions are computed for arbitrarily small source elements that are spaced apart at distances corresponding to the photoelectron dissipation range. By means of a nonlinear interpolation procedure their individual heating-rate distributions are utilized to produce synthetic ones that fill the gaps between the Monte Carlo generated distributions. By varying these gaps and the corresponding number of Monte Carlo runs the accuracy of the results is tested to verify the validity of this procedure. It is concluded that this model can reduce the computation time by as much as an order of magnitude, thus improving the feasibility of including Monte Carlo calculations in self-consistent ionosphere models.

Mayr, H. G.↗
NASA NTRS1996

Evaporation on/in Capillary Structures of High Heat Flux Two-Phase Devices

Two-phase devices (heat pipes, capillary pumped loops, loop heat pipes, and evaporators) have become recognized as key elements in thermal control systems of space platforms. Capillary and porous structures are necessary and widely used in these devices, especially in high heat flux and zero-g applications, to provide fluid transport and enhanced heat transfer during vaporization and condensation. However, some unexpected critical phenomena, such as dryout in long heat pipe evaporators and high thermal resistance of loop heat pipe evaporators with high heat fluxes, are possible and have been encountered in the use of two-phase devices in the low gravity environment. Therefore, a detailed fundamental investigation is proposed to better understand the fluid behavior in capillary-porous structures during vaporization at high heat fluxes. The present paper addresses some theoretical aspects of this investigation.

Faghri, Amir↗
NASA NTRS1973

Abundances in the Crab Nebula

The bright visual-wavelength emission lines in spectra of filaments in the Crab Nebula cannot be used to derive unique values for the relative abundances of elements there, even under a simplifying assumption that heating is due entirely to photoionization by the Crab's nonthermal continuum. However, a range of possibilities may be estimated. By mass, helium is more abundant than hydrogen; but the mass fraction of heavier elements may be surprisingly small. Such conclusions are subject to modification if a noticeable fraction of the energy density involves fast particles around 1 MeV.

Davidson, K.↗
NASA NTRS1994

Analysis of high speed flow, thermal and structural interactions

Research for this grant focused on the following tasks: (1) the prediction of severe, localized aerodynamic heating for complex, high speed flows; (2) finite element adaptive refinement methodology for multi-disciplinary analyses; (3) the prediction of thermoviscoplastic structural response with rate-dependent effects and large deformations; (4) thermoviscoplastic constitutive models for metals; and (5) coolant flow/structural heat transfer analyses.

Thornton, Earl A.↗
NASA NTRS2004

Thermal Buckling Analysis of Rectangular Panels Subjected to Humped Temperature Profile Heating

This research investigates thermal buckling characteristics of rectangular panels subjected to different types of humped temperature profile heating. Minimum potential energy and finite-element methods are used to calculate the panel buckling temperatures. The two methods give fairly close thermal buckling solutions. 'Buckling temperature magnification factor of the first kind, eta' is established for the fixed panel edges to scale up the buckling solution of uniform temperature loading case to give the buckling solution of the humped temperature profile loading cases. Also, 'buckling temperature magnification factor of the second kind, xi' is established for the free panel edges to scale up the buckling solution of humped temperature profile loading cases with unheated boundary heat sinks to give the buckling solutions when the boundary heat sinks are heated up.

Ko, William I.↗
NASA NTRS1985

Finite element algorithms for compressible flow computation on a supercomputer

Methods of applying computational fluid dynamics techniques to engineering problems are discussed. The linking factors between theoretical and applied research are the shape and weight functions which produce the Galerkin finite element schemes. The flow is unsteady, viscous, heat conducting and compressible, and steady-state flows are the asymptotic limit of unsteady flows. All flows are described by the time-averaged Navier-Stokes equations (NSE) with mass and energy conservation. Local curvilinear intrinsic coordinates are applied to discretize the NSE in arbitrary geometric domains. A modified weighted residuals approach defines the discrete analogs of the physical systems modeled and a general interpolants method is used to derive families of numerical models, both implicit and explicit, finite difference and finite elemnt, from a single point of departure. Time-dependent element approximations are achieved with a progressive assembly of generalized elements method. Hyperbolic steady-state Euler algorithms and quasi-parabolic are spatial marching algorithms for solving the discretized equations. Application of the techniques is illustrated through calculation of the compressible flow around a hypersonic flight vehicle at 100,000 ft at zero angle of attack at speeds of Mach 4-10.

Spradley, L. W.↗
DOE OSTI2021

Thermal conductivity modeling of monodispersed microspheres using discrete element method

Particle beds are widely used in various systems and processes, such as particle heat exchangers, granular flow reactors, and additive manufacturing. Accurate modeling of the thermal conductivity of particle beds and understanding of their heat transfer mechanisms are important. However, previous models were based on simple cubic packing of particles, which could not accurately represent the actual heat transfer processes under certain conditions. Here, we examine the effect of the packing structure on the thermal conductivity of particle beds. We use monodispersed silica microspheres with average particle sizes ranging from 23 to 330 μm as a model material. We employ a transient hot-wire technique to measure the thermal conductivity of the particle beds with packing density of 43%–57% within a temperature range of room temperature to 500 °C and under N2 gaseous pressures of 20–760 Torr. We then use a discrete element method (DEM) to obtain the realistic packing structure of the particles, which is then fed into a finite-element model (FEM) to calculate the thermal conductivity, with the consideration of solid conduction, gas conduction, and radiation heat transfer. Our results show that the thermal conductivity model based on the more realistic random packing structure derived from the DEM shows better agreement with the experimental data compared to that based on the simple cubic-packing structure. The combined DEM and FEM methodology can serve as a useful tool to predict the effective thermal conductivity of particle beds and to quantify different heat transfer mechanisms under various conditions.

14 SOLAR ENERGY↗
NASA NTRS1998

Finite Element Modeling of Magnetically-Damped Convection during Solidification

A fully 3-D, transient finite element model is developed to represent the magnetic damping effects on complex fluid flow, heat transfer and electromagnetic field distributions in a Sn- 35.5%Pb melt undergoing unidirectional solidification. The model is developed based on our in- house finite element code for the fluid flow, heat transfer and electromagnetic field calculations. The numerical model is tested against numerical and experimental results for water as reported in literature. Various numerical simulations are carried out for the melt convection and temperature distribution with and without the presence of a transverse magnetic field. Numerical results show that magnetic damping can be effectively applied to stabilize melt flow, reduce turbulence and flow levels in the melt and over a certain threshold value a higher magnetic field resulted in a greater reduction in velocity. Also, for the study of melt flow instability, a long enough running time is needed to ensure the final fluid flow recirculation pattern. Moreover, numerical results suggest that there seems to exist a threshold value of applied magnetic field, above which magnetic damping becomes possible and below which the 0 convection in the melt is actually enhanced.

deGroh, H. C.↗