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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 NTRS1986

HOST structural analysis program overview

Hot-section components of aircraft gas turbine engines are subjected to severe thermal structural loading conditions, especially during the startup and takeoff portions of the engine cycle. The most severe and damaging stresses and strains are those induced by the steep thermal gradients induced during the startup transient. These transient stresses and strains are also the most difficult to predict, in part because the temperature gradients and distributions are not well known or readily predictable and, in part, because the cyclic elastic-viscoplastic behavior of the materials at these extremes of temperature and strain are not well known or readily predictable. A broad spectrum of structures related technology programs is underway to address these deficiencies at the basic as well as the applied level. The three key program elements in the HOST structural analysis program are computations, constitutive modeling, and experiments for each research activity. Also shown are tables summarizing each of the activities.

Thompson, Robert L.↗
NASA NTRS1999

Validation of Modified Wine-Rack Thermal Design for Nickel-Hydrogen Batteries in Landsat-7 Spacecraft Thermal Vacuum Test and in Flight

A heritage wine-rack thermal/mechanical design for the nickel-hydrogen batteries was the baseline at the Landsat-7 Preliminary Design Review. An integrated thermal and power analysis of the batteries performed by the author in 1994 revealed that the maximum cell-to-cell gradient was 6.6 C. The author proposed modifying the heritage wine-rack design by enhancing heat conduction from cells to cells, and from cells to battery frame. At the 1995 Intersociety Energy Conversion Engineering Conference (IECEC), the author presented a paper on methods of modifying the wine-rack design. It showed that the modified wine-rack option, which uses a metallic filler, could reduce the maximum cell-to-cell temperature gradient to 1.30 C, and could also reduce the maximum cell temperature by as much as 80 C. That design concept was adopted by the Landsat7 Project Office, and a design change was made at the Critical Design Review. Results of the spacecraft thermal vacuum and thermal balance tests, and temperature data in flight show that the temperatures of the battery cells are very uniform. The maximum cell-to-cell gradient is 1.50 C. They validate the modified wine-rack thermal design.

Choi, Michael K.↗
DOE OSTI2023

Micro-tearing mode dominated electron heat transport in DIII-D H-mode pedestal

Abstract A new, comprehensive set of evidence reveals that Micro-Tearing Modes (MTMs) dominate pedestal electron heat transport in an H-mode experiment in the DIII-D tokamak. The experiment investigates the role of MTMs by scanning pedestal collisionality, a main drive of MTM instability, from 0.43 to 0.84 on the pedestal top. Broadband (150–800 kHz) magnetic and density fluctuations originating from the pedestal gradient region and highly consistent with MTMs are observed, with amplitude increasing during the scan. The higher magnetic fluctuation amplitude correlates with a lower pedestal electron temperature gradient, implying MTMs may regulate the pedestal electron heat transport. The collisionality scan results in profile and transport changes consistent with predicted transport capability of MTMs: (1) experimentally-determined electron heat diffusivity increases ∼40% at the location where the broadband density fluctuations peak; (2) ion heat diffusivity has less increase (<20%); and (3) a locally flattened region in the electron temperature pedestal is observed at high collisionality. A local, linear gyrokinetic simulation finds MTMs as the most unstable mode in the pedestal gradient region. In addition, local, nonlinear simulations suggest MTMs can dominate and drive experimentally-relevant, megawatt-level electron heat flux. This result establishes MTMs as an effective transport mechanism in the H-mode pedestal, in particular at high collisionality.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1990

Thermocapillary convection in a model float-zone

A finite-element method has been used to study thermocapillary convection in a model of relevance to the float-zone, crystal-growth process. The geometry consists of a pair of horizontal isothermal surfaces with a Boussinesq liquid suspended between them. Because of the variation of surface tension with temperature, the temperature gradient along the free surface drives thermocapillary convection. The free surface is allowed to deform and its location is calculated along with the velocity and temperature fields. Cases in which thermocapillarity dominates and others in which it interacts with an unstable axial buoyancy gradient are treated. In order to obtain information of possible interest to potential microgravity applications, the influence of the Grashof number is investigated.

Neitzel, G. P.↗
DOE OSTI2025

CFD modeling of natural circulation in LiCl-KCl molten salt closed loop

Characterizing flow within a molten salt closed-loop system is crucial for assessing system requirements, evaluating performance, and identifying potential flaws. Direct flow measurement using instrumentation is challenging due to extreme environmental conditions and the limitations associated with measuring molten salt flow under natural convection. Here, this study aims to provide comprehensive insights into the thermal-hydraulic behavior of a closed loop, with a particular focus on temperature distribution and velocity prediction. The Computational Fluid Dynamics (CFD) model demonstrated the capability to effectively simulate and predict both temperature distributions and flow velocities within the molten salt loop. The CFD model's predictive capability was validated by its ability to replicate temperature measurements under varying boundary conditions. The analysis revealed that the CFD model tends to underpredict temperatures in the cold leg and overpredict them in the hot leg, highlighting the need for continuous model refinement and acknowledging the limitations of using a steady-state approach. Furthermore, the potential of using external temperature measurements to estimate internal molten salt temperatures and predict flow velocity was explored, revealing that this approach could introduce up to a 5.5% error in flow velocity calculations. Line probes mapping temperature distributions across the tube's cross-section and molten salt provided valuable insights into temperature gradients, emphasizing the need for a thermal conductivity equation for molten salt with lower uncertainty to achieve more accurate temperature predictions of the system.

22 - GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2024

Theoretical and global simulation analysis of collisional microtearing modes

Microtearing modes (MTMs) are suggested as a candidate for anomalous thermal transport in tokamak H-mode discharges. This study investigates MTMs in tokamak plasmas, employing simulations in the BOUT++ framework. It simplifies and linearizes the governing equations in detailed linear simulations. The study meticulously evaluates various conductivity models under diverse plasma conditions and collision regimes. The research thoroughly assesses different conductivity models across a range of plasma conditions and collision regimes. A unified dispersion relation that includes both MTM and Drift-Alfvén Wave (DAW) instabilities is derived, showing that DAW and MTM instabilities occur at varying distances from the rational surface. Specifically, MTMs become unstable near the rational surface but stabilize farther away, while drift-Alfvén instability appears farther from the rational surface. The study also re-derives MTM dispersion relations using Ohm's law and the vorticity equation, providing a thorough analysis of electromagnetic and electrostatic interactions in tokamaks. Global simulations demonstrate an inverse correlation between MTM growth rates and collisionality, and a direct correlation with temperature gradients. The nonalignment of the rational surface with the peak ω*e stabilizes the MTMs. Nonlinear simulations highlight electron temperature relaxation as the primary saturation mechanism for MTMs, with magnetic flutter identified as the dominant mode of electron thermal transport.

Fan, K. (ORCID:0000000227518809)↗
NASA NTRS1977

Development of the data base for a degradation model of a selenide RTG

The paper is concerned with the evaluation of the materials used in a selenide radioisotope thermoelectric generator (RTG). These materials are composed of n-type gadolinium selenide and n-type copper selenide. A three-fold evaluation approach is being used: (1) the study of the rate of change of the thermal conductivity of the material, (2) the investigation of the long-term stability of the material's Seebeck voltage and electrical resistivity under current and temperature gradient conditions, and (3) determination of the physical behavior and compatibility of the material with surrounding insulation at elevated temperatures. Programmatically, the third category of characteristic evaluation is being emphasized.

Stapfer, G.↗
NASA NTRS1979

A field study of air flow and turbulent features of advection fog

The setup and initial operation of a set of specialized meteorological data collection hardware are described. To study the life cycle of advection fogs at a lake test site, turbulence levels in the fog are identified, and correlated with the temperature gradients and mean wind profiles. A meteorological tower was instrumented to allow multiple-level measurements of wind and temperature on a continuous basis. Additional instrumentation was: (1)hydrothermograph, (2)microbarograph, (3)transmissometers, and (4)a boundary layer profiler. Two types of fogs were identified, and important differences in the turbulence scales were noted.

Connell, J. D.↗
NASA NTRS1979

An energy-balance model of glaciation cycles

A one dimensional energy balance model is presented which contains a time lagged albedo to account for the delayed dependence of continental ice sheets on temperature; it also includes a smoothing of temperature gradients in the tropics to account for the effect of the Hadley circulation on the strong flattening of meridional temperature profiles there. The model exhibits finite amplitude, sustained free oscillations; these oscillations are triggered by a change in the insulation parameter and occur in the absence of any external forcing. This model behavior strongly suggests the possibility of an almost-intransitive mechanism playing a role in glaciation cycles. This behavior also occurs on shorter time scales which might be relevant to the interannual variability of the atmosphere.

Ghil, M.↗
NASA NTRS1985

Effects of dynamic heat fluxes on model climate sensitivity Meridional sensible and latent heat fluxes

The high- and low-latitude radiative-dynamic (HLRD) climatic model of Wang et al. (1984) was used to study the effect of meridional heat (MH) fluxes on climate changes caused by increases of CO2 abundance and solar constant variations. However, the empirical MH parameterization of the HLRD model was replaced by physically based parameterization, which gives separate meridional sensible and latent heat fluxes and provides a complete representation of the dependence of the flux on the mean temperature field. Both parameterization methods yielded about the same changes in global mean surface temperature and ice line, and both produced only small changes in meridional temperature gradient, although the latter were even smaller with the physically based parameterizations. At any latitude, the hemispheric mean surface temperature, rather than MH fluxes, dominates the surface temperature changes.

Gutowski, W. J., Jr.↗
NASA NTRS1987

The behavior of multiphase systems in low gravity

The motion of drops and bubbles due to interfacial tension gradients is studied. It is noted that, when a drop or bubble is inserted into a fluid possessing a temperature gradient, the resulting gradient of interfacial tension will, through viscous traction on the neighboring fluid, cause it to move. In response, the drop will propel itself in the direction of the pole with the lower interfacial tension. This phenomenon, thermocapillary migration, is discussed in detail.

Subramanian, R. Shankar↗
NASA NTRS1992

Finite difference solution for transient cooling of a radiating-conducting semitransparent layer

Transient solutions were obtained for cooling a semitransparent material by radiation and conduction. The layer is in a vacuum environment so the only means for heat dissipation is by radiation from within the medium leaving through the boundaries. Heat conduction serves only to partially equalize temperatures across the layer. As the optical thickness is increased, steep temperature gradients exist near the boundaries when conduction is relatively small. A solution procedure is required that will provide accurate temperature distributions adjacent to the boundaries, or radiative heat losses will be in error. The approach utilized numerical Gaussian integration to obtain the local radiative source term, and a finite difference procedure with variable space and time increments to solve the transient energy equation.

Siegel, Robert↗
NASA NTRS1992

Spatial and temporal temperature distribution optimization for a geostationary antenna

The Geostationary Microwave Precipitation Radiometer antenna is considered and a thermal design analysis is performed to determine a design that would minimize on-orbit antenna temporal and spatial temperature gradients. The final design is based on an optically opaque radome which covered the antenna. The average orbital antenna temperature is found to be 9 C with maximum temporal and spatial variations of 34 C and 1 C, respectively. An independent thermal distortion analysis showed that this temporal variation would give an antenna figure error of 14 microns.

Tsuyuki, G.↗
NASA NTRS2019

Twentieth Century Redistribution in Climatic Drivers of Global Tree Growth

Energy and water limitations of tree growth remain insufficiently understood at large spatiotemporal scales, hindering model representation of interannual or longer-term ecosystem processes. By assessing and statistically scaling the climatic drivers from 2710 tree-ring sites, we identified the boreal and temperate land areas where tree growth during 1930–1960 CE responded positively to temperature (20.8 ± 3.7 Mio km2; 25.9 ± 4.6%), precipitation (77.5 ± 3.3 Mio km2; 96.4 ± 4.1%), and other parameters. The spatial manifestation of this climate response is determined by latitudinal and altitudinal temperature gradients, indicating that warming leads to geographic shifts in growth limitations. We observed a significant (P < 0.001) decrease in temperature response at cold-dry sites between 1930–1960 and 1960–1990 CE, and the total temperature-limited area shrunk by −8.7 ± 0.6 Mio km2. Simultaneously, trees became more limited by atmospheric water demand almost worldwide. These changes occurred under mild warming, and we expect that continued climate change will trigger a major redistribution in growth responses to climate.

Babst, Flurin↗
NASA NTRS1994

SP-100 Thermoelectric Cell Testing at JPL

Three prototypic SP-100 thermoelectric cells, fabricated by Martin Marietta Astro Space in Valley Forge, Pennsylvania, were tested in vacuum at prototypic temperatures at JPL. Their thermal and electrical performance were characterized with 200, 300, 400, and 500 degree Celsius temperature gradients across the cell. The latter was representative of prototypic operating conditions with a 1050 degree Celsius hot side temperature and a 550 degree Celsius cold side temperature. The initial thermal and electrical performance of all three cells closely matched predictions.

thermoelectric↗
NASA NTRS1983

HOST structural analysis program overview

Hot section components of aircraft gas turbine engines are subjected to severe thermal structural loading conditions, especially during the start up and take off portions of the engine cycle. The most severe and damaging stresses and strains are those induced by the steep thermal gradients induced during the start up transient. These transient stresses and strains are also the most difficult to predict, in part because of the temperature gradients and distributions are not well known or readily predictable, and also because the cyclic elastic viscoplastic behavior of the materials at these extremes of temperature and strain are not well known or readily predictable. A broad spectrum of structures related technology programs is underway to address these deficiencies. One element of the structures program is developing improved time varying thermal mechanical load models for the entire engine mission cycle from start up to shutdown. Another major part of the program is the development of new and improved nonlinear 3-D finite elements and associated structural analysis programs, including the development of temporal elements with time dependent properties to account for creep effects in the materials and components.

Johns, R. H.↗
NASA NTRS1992

Nature of fluid flows in differentially heated cylindrical container filled with a stratified solution

Semiconductor crystals such as Hg(1-x)Cd(x)Te grown by unidirectional solidification Bridgmann method have shown compositional segregations in both the axial and radial directions. Due to the wide separation between the liquidus and the solidus of its pseudobinary phase diagram, there is a diffusion layer of higher HgTe content built up in the melt near the melt-solid interface which gives a solute concentration gradient in the axial direction. Because of the higher thermal conductivity in the melt than that in the crystal there is a thermal leakage through the fused silica crucible wall near the melt-solid interface. This gives a thermal gradient in the radial direction. Hart (1971), Thorpe, Hutt and Soulsby (1969) have shown that under such condition a fluid will become convectively unstable as a result of different diffusivities of temperature and solute. It is quite important to understand the effects of this thermosolute convection on the compositional segregation in the unidirectionally solidified crystals. To reach this goal, we start with a simplified problem. We study the nature of fluid flows of a stratified solution in a cylindrical container with a radial temperature gradient. The cylindrical container wall is considered to be maintained at a higher temperature than that at the center of the solution and the solution in the lower gravitational direction has higher solute concentration which decrease linearly to a lower concentration and then remain constant to the top of the solution. The sample solution is taken to be salt water.

Wang, Jai-Ching↗
DOE OSTI2021

Global Theory of Microtearing Modes in the Tokamak Pedestal

The pedestal of H-mode tokamaks displays strong magnetic fluctuations correlated with the evolution of the electron temperature. The microtearing mode (MTM), a temperature-gradient-driven instability that alters magnetic topology, is compatible with these observations. Here we extend the conventional theory of the MTM to include the global variation of the temperature and density profiles. The offset between the rational surface and the location of the pressure gradient maximum (μ) emerges as a crucial parameter for MTM stability. In conclusion, the extended theory matches observations on the Joint European Torus tokamak.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗