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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Thermal transport in defective and disordered materials

With significant recent advancements in thermal sciences—such as the development of new theoretical and experimental techniques, and the discovery of new transport mechanisms—it is helpful to revisit the fundamentals of vibrational heat conduction to formulate an updated and informed physical understanding. The increasing maturity of simulation and modeling methods sparks the desire to leverage these techniques to rapidly improve and develop technology through digital engineering and multi-scale, electro-thermal models. With that vision in mind, this review attempts to build a holistic understanding of thermal transport by focusing on the often unaddressed relationships between subfields, which can be critical for multi-scale modeling approaches. For example, we outline the relationship between mode-specific (computational) and spectral (analytical) models. We relate thermal boundary resistance models based on perturbation approaches and classic transmissivity based models. We discuss the relationship between lattice dynamics and molecular dynamics approaches along with two-channel transport frameworks that have emerged recently and that connect crystal-like and amorphous-like heat conduction. Throughout, we discuss best practices for modeling experimental data and outline how these models can guide material-level and system-level design.

42 ENGINEERING↗
NASA NTRS2009

Narrow Radiative Recombination Continua: A Signature of Ions Crossing the Contact Discontinuity of Astrophysical Shocks

X-rays from planetary nebulae (PNs) are believed to originate from a shock driven into the fast stellar wind (v ~ 1000 kilometers per second) as it collides with an earlier circumstellar slow wind (v ~ 10 kilometers per second). In theory, the shocked fast wind (hot hubble) and the ambient cold nebula can remain separated by magnetic fields along a surface referred to as the contact discontinuity (CD) that inhibits diffusion and heat conduction. The CD region is extremely difficult to probe directly owing to its small size and faint emission. This has largely left the study of CDs, stellar-shocks, and the associated micro-physics in the realm of theory. This paper presents spectroscopic evidence for ions from the hot bubble (kT approximately equal to 100 eV) crossing the CD and penetrating the cold nebular gas (kT approximately equal to 1 eV). Specifically, a narrow radiative recombination continuum (RRC) emission feature is identified in the high resolution X-ray spectrum of the PN BD+30degree3639 indicating bare C VII ions are recombining with cool electrons at kT(sub e) = 1.7 plus or minus 1.3 eV. An upper limit to the flux of the narrow RRC of H-like C VI is obtained as well. The RRCs are interpreted as due to C ions from the hot bubble of BD+30degree3639 crossing the CD into the cold nebula, where they ultimately recombine with its cool electrons. The RRC flux ratio of C VII to C VI constrains the temperature jump across the CD to deltakT greater than 80 eV, providing for the first time direct evidence for the stark temperature disparity between the two sides of an astrophysical CD, and constraining the role of magnetic fields and heat conduction accordingly. Two colliding-wind binaries are noted to have similar RRCs suggesting a temperature jump and CD crossing by ions may be common feature of stellar wind shocks.

Behar, Ehud↗
DOE OSTI2020

Multiphase representation of hotspot formation and growth

Multiphase reacting flow approach has been adopted for modeling of hotspot formation and growth on sub-zonal scale. Mechanical response of the high explosive (HE) is modeled by the Visco-Plastic SCRAM model which includes plastic work, crack growth, and frictional heating along the cracks. In this work a sub-zonal regions with high temperature, hotspots, are modeled as a new phase. Formation and growth of the hotspot phase from the cold phase is modeled as a phase change. Each phase has its own temperature and pressure. Chemical reactions also progress in both phases. The growth of hotspots are determined by the solution of the heat conduction equation with appropriate heat sources due to friction and plastic heating. Sample calculations using the BABBO code show successful detonation calculations with hotspot formation and growth.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1974

Thermal preparation of foods in space-vehicle environments

Convection is the primary heat transfer mechanism for most foods heated in an earth-based environment. In contrast, in the low-gravity environment of space flight, the primary heat transfer mechanism is conduction (or radiation in the absence of a conducting medium). Conduction heating is significantly slower and less efficient than convection heating. This fact poses a problem for food heating during space flight. A numerical model has been developed to evaluate this problem. This model simulates the food-heating process for Skylab. The model includes the effect of a thermally controlled on/off heat flux. Parametric studies using this model establish how the required heating time is affected by: the thermal diffusivity of the nutrient materials, the power level of the heater, the initial food temperatures, and the food container dimensions.

Bannerot, R. B.↗
NASA NTRS1975

Space shuttle/food system study. Volume 1: Technical volume, oven study

The baseline space shuttle galley was designed to utilize lightweight rehydratable foods, to be prepared for consumption by rehydration with chilled or hot water. The impact is examined of an extension of food types to include thermostabilized food, at ambient temperature, and frozen foods on the baseline design of the shuttle galley. Weight, volume, and power penalities associated with heating thermostabilized and frozen foods by means of a hot air convection heating system and a conduction heating system are determined along with the impact on crew/galley interface and meal preparation.

Source record↗
NASA NTRS1975

Design of a heat pipe governed thermal control system for the Solar Electric Propulsion Stage /SEPS/

A 2200-w capacity spacecraft heat rejection system designed for the SEPS and utilizing heat pipe radiator panels has been investigated. The total thermal control system consists of two radiator panels connected to the heat source by variable conductance heat pipes (VCHP's). The system was designed to operate in the 223 to 333 temperature range. The radiators have an emittance of 0.88 at their operational temperature and a fin efficiency of approximately 80 percent. The radiators are thermally isolated from the SEPS and environment by multilayer insulation and thermal shields. Butane was selected as the working fluid for the VCHP because of its low freezing point (135), which is necessary to prevent diffusion freezeout of the liquid during the cold outbond missions. Helium was selected for the control gas. This paper describes the VCHP system, discusses the system design parameters and presents the results of the analyses.

Ruttner, L. E.↗
NASA NTRS1982

Heat Pipe Blocks Return Flow

Metal-foil reed valve in conventional slab-wick heat pipe limits heat flow to one direction only. With sink warmer than source, reed is forced closed and fluid returns to source side through annular transfer wick. When this occurs, wick slab on sink side of valve dries out and heat pipe ceases to conduct heat.

Eninger, J. E.↗
NASA NTRS1981

Numerical treatment of nonlinear latent heat boundary conditions at moving interfaces in genuine two dimensional solidification problems

The proposed method for the treatment of two dimensional solidification problems is based on quasilinearization of the transformed heat conduction equation and latent heat condition at the interface and an iterative sequence in which these are solved simultaneously. Modern algorithms for solving such sparse systems mean that most of the storage advantage of other methods are reduced and the speed of solution can be improved.

Beckett, P. M.↗
NASA NTRS1984

Variable-Conductance Heat-Transfer Module

Working lengths of heat pipes electronically controlled. Rate of heat transfer controlled by electrical heaters shorten effective working lengths of heat pipes. Concept not limited to right circular cylindrical shape. Concept adaptable to terrestrial instruments or processes in which atmospheres or fluids must be cooled and returned to instruments or processes at fixed lower temperatures.

Hewitt, D. R.↗
NASA NTRS1983

Saturn's icy satellites - Thermal and structural models

Thermal history models which assume formation as homogeneous ice-silicate mixtures are constructed for the small, icy Saturnian satellites Mimas, Tethys, Dione, Rhea, and Iapetus, including the effects of radiogenic and accretional heating, conductive and subsolidus convective heat transfer, and lithosphgeric growth. Accretional heating is not likely to have melted the water ice in the interiors of these bodies, and solid state creep of the ice-dominated material precludes melting by radiogenic heating. The four largest satellites are sufficiently large and rich in heat-producing silicates to possess a solid state convection system beneath a rigid lithosphere, irrespective of initial conditions. The model thermal histories are qualitatively consistent with the present appearances of these satellites.

Ellsworth, K.↗
NASA NTRS1983

Acoustical modes of arbitrary volumes using NASTRAN transient heat transfer RF9

An equivalence between temperature and pressure, heat conduction and stiffness and heat capacity and mass is defined, enabling acoustical modal analysis of arbitrary three dimensional volumes. The transient heat transfer analysis rigid format in NASTRAN, RF9, has been altered providing the acoustical analysis capability. Examples and ALTERs are included.

Elchuri, V.↗
NASA NTRS1984

Numerical modeling of laser thermal propulsion flows

An review of the problems associated with modeling laser thermal propulsion flows, a synopsis of the status of such models, and the attributes of a successful model are presented. The continuous gaseous hydrogen laser-supported combustion wave (LSCW) thruster, for which a high-energy laser system (preferably space-based) should exist by the time the propulsion technology is developed, is considered in particular. The model proposed by Raizer (1970) is based on the assumptions of one-dimensional flow at constant pressure with heat conduction as the principal heat transfer mechanism. Consideration is given to subsequent models which account for radiative transfer into the ambient gas; provide a two-dimensional generalization of Raizer's analysis for the subsonic propagation of laser sparks in air; include the effect of forward plasma radiation in a one-dimensional model; and attempt a time-dependent (elliptic) solution of the full Navier-Stokes equations for the flow in a simple axisymmetric thruster. Attention is also given to thruster and nozzle flow models and thermodynamic and transport properties.

Mccay, T. D.↗
NASA NTRS1987

Electrically Conductive, Heat-Resistant Paint

Improved, sprayable, thermal- and electrostatic-discharge-control coating for titanium possesses excellent adhesion and high resistance to both vibration and thermal shock. Coating is improved formulation of one described in "High-Temperature Coatings for Titanium" (NPO-16222).

Hribar, V. F.↗
NASA NTRS1991

Structured background grids for generation of unstructured grids by advancing front method

A new method of background grid construction is introduced for generation of unstructured tetrahedral grids using the advancing-front technique. Unlike the conventional triangular/tetrahedral background grids which are difficult to construct and usually inadequate in performance, the new method exploits the simplicity of uniform Cartesian meshes and provides grids of better quality. The approach is analogous to solving a steady-state heat conduction problem with discrete heat sources. The spacing parameters of grid points are distributed over the nodes of a Cartesian background grid by interpolating from a few prescribed sources and solving a Poisson equation. To increase the control over the grid point distribution, a directional clustering approach is used. The new method is convenient to use and provides better grid quality and flexibility. Sample results are presented to demonstrate the power of the method.

Pirzadeh, Shahyar↗
NASA NTRS1993

Refractive Index Effects on Radiation in an Absorbing, Emitting, and Scattering Laminated Layer

A simple set of equations is derived for predicting temperature radiative energy flow in a two-region semitransparent laminated layer in the limit of zero heat conduction. The composite is heated on its two sides by unequal amounts of incident radiation. The two layers of the composite have different refractive indices, and each material absorbs, emits, and isotropically scatters radiation. The interfaces are diffuse, and all interface reflections are included. To illustrate the thermal behavior that is readily calculated from the equations, typical results an given for various optical thicknesses and refractive indices of the layers. Internal reflections have a substantial effect on the temperature distribution and radiative heat flow.

Siegel, R.↗
NASA NTRS1994

Aerothermodynamics of Pyrolizing Surfaces in Hypersonic Rarefied Flows

Direct simulation Monte Carlo (DSMC) calculations of rarefied flows about entry bodies typically employ a fixed surface temperature or a radiative-equilibrium energy balance to compute that temperature. Such boundary conditions neglect any effects of heat capacitance and heat conduction in the spacecraft heat shield and, therefore, provide an upper bound for the surface temperature. Such calculations also neglect pyrolysis from the heat shield which can be significant for a high-energy incident flow at very low densities. Accurate prediction of both heating and aerodynamic forces requires including pyrolysis and surface heat transfer in the models for gas-surface interaction employed in DSMC methods. Although these physical models have long appeared in various continuum flow calculation codes, they have only recently appeared in DSMC codes which are required to simulate rarefied flows during entry at high altitudes. In the current implementation, routines from the widely distributed Charring Material Thermal Response and Ablation (CMA) program are coupled into a DSMC code to calculate the one-dimensional heat transfer into the carbon phenolic heat shield at each point on a vehicle surface. Temperature-dependent material properties, surface re-radiation, and in-depth pyrolysis were included in the calculation, but surface ablation was neglected. Sample calculations for entry of the Galileo probe into the atmosphere of Jupiter demonstrate that including pyrolysis in the model leads to significant differences in predicted aerodynamics. Granted, the drag coefficient does not depend strongly on the surface temperature which can itself be significantly below the radiative equilibrium value during entry. However, the surface mass flux due to pyrolysis of the material is significant once the probe drops to altitudes characterized by transition flow. This leads to a noticeable increase in drag and a decrease in heating compared to a body without pyrolysis.

Haas, Brian L.↗
NASA NTRS2004

Micro-Scale Regenerative Heat Exchanger

A micro-scale regenerative heat exchanger has been designed, optimized and fabricated for use in a micro-Stirling device. Novel design and fabrication techniques enabled the minimization of axial heat conduction losses and pressure drop, while maximizing thermal regenerative performance. The fabricated prototype is comprised of ten separate assembled layers of alternating metal-dielectric composite. Each layer is offset to minimize conduction losses and maximize heat transfer by boundary layer disruption. A grating pattern of 100 micron square non-contiguous flow passages were formed with a nominal 20 micron wall thickness, and an overall assembled ten-layer thickness of 900 microns. Application of the micro heat exchanger is envisioned in the areas of micro-refrigerators/coolers, micropower devices, and micro-fluidic devices.

Moran, Matthew E.↗