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Results for “THERMAL DIFFUSION”

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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Venus ionosphere - Photochemical and thermal diffusion control of ion composition

The major photochemical sources and sinks for ten of the ions measured by the ion mass spectrometer on the Pioneer Venus bus and orbiter spacecraft that are consistent with the neutral gas composition measured on the same spacecraft are identified. The neutral gas temperature (as a function of solar zenith angle) derived from measured ion distributions in photochemical equilibrium is given. Above 200 kilometers, the altitude behavior of ions is generally controlled by plasma diffusion, with important modifications for minor ions due to thermal diffusion resulting from the observed gradients of plasma temperatures. The dayside equilibrium distributions of ions are sometimes perturbed by plasma convection, while lateral transport of ions from the dayside seems to be a major source of the nightside ionosphere.

Bauer, S. J.↗
NASA NTRS1996

Thermal Diffusivity and Conductivity of Hg(1-x)Zn(x)Te Solids and Melts

The thermal diffusivity of pseudobinary Hg(1-x)Zn(x)Te solids and melts was measured by the laser flash method. The measured diffusivities for the solids of 0.10 less than or equal to x less than or equal to 0.30 are about 60% of that of the HgTe solid. Those for the melts rise rapidly with temperature but less so with increasing x. For x = 0.30, the diffusivity of the melt is about one third of that of the HgTe melt. Using the calculated beat capacity data from the associated solution model and measured density values, the thermal conductivity for the pseudobinary Hg(1-x)Zn(x)Te solids of 0.10 less than or equal to x less than or equal to 0.30 and for the melts of x = O.10, 0.16, and 0.30 was determined.

Sha, Yi-Gao↗
DOE OSTI2025

Remarks on the thesis of Aitor Bengoechea Fernández: Generalization of Doppler effect processing using S(α,β) thermal diffusion laws

The thesis titled “Generalization of Doppler effect processing using S(α,β) thermal diffusion laws” addresses a critical gap in the modeling of neutron scattering phenomena in nuclear materials, particularly where crystal lattice effects intersect with low-energy resonances. Conducted within the Doctoral School ED 352 at Aix-Marseille Université and hosted at CEA Cadarache, the research presents a theoretical and numerical framework for extending the applicability of Thermal Scattering Laws (TSLs) using higher-order correlation functions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1980

Ice crystal growth in a dynamic thermal diffusion chamber

Ice crystals were grown in a supersaturated environment produced by a dynamic thermal diffusion chamber, which employed two horizontal plates separated by a distance of 2.5 cm. Air was circulated between and along the 1.2 m length of the plates past ice crystals which nucleated and grew from a fiber suspended vertically between the two plates. A zoom stereo microscope with a magnification which ranged from 3X to 80X and both 35 mm still photographs and 16 mm time lapse cine films taken through the microscope were used to study the variation of the shape and linear growth rate of ice crystals as a function of the ambient temperature, the ambient supersaturation, and the forced ventilation velocity. The ambient growth conditions were varied over the range of temperature 0 to -40 C, over the range of supersaturation 4% to 50% with respect to ice, and over the range of forced ventilation velocities 0 cm/s to 20 cm/s.

Keller, V. W.↗
NASA NTRS1991

Experimental thermal conductivity, thermal diffusivity, and specific heat values for mixtures of nitrogen, oxygen, and argon

Experimental measurements of thermal conductivity and thermal diffusivity obtained with a transient hot-wire apparatus are reported for three mixtures of nitrogen, oxygen, and argon. Values of the specific heat, Cp, are calculated from these measured values and the density calculated with an equation of state. The measurements were made at temperatures between 65 and 303 K with pressures between 0.1 and 70 MPa. The data cover the vapor, liquid, and supercritical gas phases for the three mixtures. The total reported points are 1066 for the air mixture (78.11 percent nitrogen, 20.97 percent oxygen, and 0.92 percent argon), 1058 for the 50 percent nitrogen, 50 percent oxygen mixture, and 864 for the 25 percent nitrogen, 75 oxygen mixture. Empirical thermal conductivity correlations are provided for the three mixtures.

Perkins, R. A.↗
NASA NTRS2000

Vapor Transport Within the Thermal Diffusion Cloud Chamber

A review of the equations used to determine the 1-D vapor transport in the thermal diffusion cloud chamber (TDCC) is presented. These equations closely follow those of the classical Stefan tube problem in which there is transport of a volatile species through a noncondensible, carrier gas. In both cases, the very plausible assumption is made that the background gas is stagnant. Unfortunately, this assumption results in a convective flux which is inconsistent with the momentum and continuity equations for both systems. The approximation permits derivation of an analytical solution for the concentration profile in the Stefan tube, but there is no computational advantage in the case of the TDCC. Furthermore, the degree of supersaturation is a sensitive function of the concentration profile in the TD CC and the stagnant background gas approximation can make a dramatic difference in the calculated supersaturation. In this work, the equations typically used with a TDCC are compared with very general transport equations describing the 1-D diffusion of the volatile species. Whereas no pressure dependence is predicted with the typical equations, a strong pressure dependence is present with the more general equations given in this work. The predicted behavior is consistent with observations in diffusion cloud experiments. It appears that the new equations may account for much of the pressure dependence noted in TDCC experiments, but a comparison between the new equations and previously obtained experimental data are needed for verification.

Ferguson, Frank T.↗
NASA NTRS1987

Thermal diffusive conductivity of dilute superfluid (He-3)-(He-4) mixtures

A new technique is described for measuring the effective thermal conductivity of superfluid (He-3)-(He-4) mixtures. The results confirm the large departures from hydrodynamic theory reported previously. The analysis suggests that the measured conductivity is the finite thermal diffusive conductivity of superfluid helium in the absence of counterflow. This conductivity need not diverge in the limit of small He-3 concentration.

Chui, T. C. P.↗
NASA NTRS2016

Comparison of Turbulent Thermal Diffusivity and Scalar Variance Models

This paper will include a detailed comparison of heat transfer models that rely upon the thermal diffusivity. The goals are to inform users of the development history of the various models and the resulting differences in model formulations, as well as to evaluate the models on a variety of validation cases so that users might better understand which models are more broadly applicable.

turbulence models↗
DOE OSTI2025

X-ray thermal diffuse scattering as a texture-robust temperature diagnostic for dynamically compressed solids

We present a model of x-ray thermal diffuse scattering (TDS) from a cubic polycrystal with an arbitrary crystallographic texture, based on the classic approach of Warren [B. E. Warren, Acta Crystallogr. 6, 803 (1953)]. We compare the predictions of our model with femtosecond x-ray diffraction patterns gathered from ambient and dynamically compressed rolled copper foils obtained at the High Energy Density instrument of the European X-Ray Free-Electron Laser facility and find that the texture-aware TDS model yields more accurate results than does the conventional powder model owed to Warren. Nevertheless, we further show: with sufficient angular detector coverage, the TDS signal is largely unchanged by sample orientation and in all cases strongly resembles the signal from a perfectly random powder; shot-to-shot fluctuations in the TDS signal resulting from grain-sampling statistics are at the percent level, in stark contrast to the fluctuations in the Bragg-peak intensities (which are over an order of magnitude greater); and TDS is largely unchanged even following texture evolution caused by compression-induced plastic deformation. We conclude that TDS is robust against texture variation, making it a flexible temperature diagnostic applicable just as well to off-the-shelf commercial foils as to ideal powders.

Crystal lattices↗
NASA NTRS2016

Comparison of Turbulent Thermal Diffusivity and Scalar Variance Models

In this study, several variable turbulent Prandtl number formulations are examined for boundary layers, pipe flow, and axisymmetric jets. The model formulations include simple algebraic relations between the thermal diffusivity and turbulent viscosity as well as more complex models that solve transport equations for the thermal variance and its dissipation rate. Results are compared with available data for wall heat transfer and profile measurements of mean temperature, the root-mean-square (RMS) fluctuating temperature, turbulent heat flux and turbulent Prandtl number. For wall-bounded problems, the algebraic models are found to best predict the rise in turbulent Prandtl number near the wall as well as the log-layer temperature profile, while the thermal variance models provide a good representation of the RMS temperature fluctuations. In jet flows, the algebraic models provide no benefit over a constant turbulent Prandtl number approach. Application of the thermal variance models finds that some significantly overpredict the temperature variance in the plume and most underpredict the thermal growth rate of the jet. The models yield very similar fluctuating temperature intensities in jets from straight pipes and smooth contraction nozzles, in contrast to data that indicate the latter should have noticeably higher values. For the particular low subsonic heated jet cases examined, changes in the turbulent Prandtl number had no effect on the centerline velocity decay.

computational fluid dynamics↗
NASA NTRS1980

Thermal diffusion calculations for the ionosphere of Venus

Simplified multicomponent diffusion calculations are made for the ionosphere of Venus. Large differences in temperature between electrons and ions and appreciable temperature gradients that are near those of recent measurements are used. Compositions for which binary thermal diffusion coefficients for ions are the same as multi-ion ones are examined as well as those that are quite different. An attempt to combine binary coefficients to give multi-ions ones has not been particularly successful.

Nakada, M. P.↗
NASA NTRS1985

Computerized data acquisition and analysis for measuring thermal diffusivity

JPL has been leading a concentrated effort to develop improved thermoelectric materials for space applications. Thermoelectric generators are an attractive source of electrical energy for space power because of lack of moving parts and slow degradation of performance. Thermoelectric material is characterized by: Seebeck coefficient, electrical resistivity and thermal conductivity. To measure the high temperature thermal conductivity is experimentally very difficult. However, it can be calculated from the specific heat and thermal diffusivity which are easier to measure at high temperatures, especially using the flash method. Data acquisition and analysis for this experiment were automated at JPL using inexpensive microcomputer equipment. This approach is superior to tedious and less accurate manual analysis of data. It is also preferred to previously developed systems utilizing expensive minicomputers or mainframes.

Chmielewski, A.↗
DOE OSTI2024

Thermal diffusion, exhaust gas recirculation and blending effects on lean premixed hydrogen flames

Thermodiffusively-unstable lean premixed hydrogen flames are investigated using two-dimensional direct numerical simulation employing finite-rate chemical kinetics. Three databases are generated focussing on the inclusion of the Soret effect, the recirculation of exhaust gas, and blending with methane. A simple rescaling of a classic thermal diffusion model is presented and shown to mimic multicomponent diffusion with very low computational cost and little-to-no loss in accuracy. It is also shown that a previously developed model for mean local flame speeds in lean premixed hydrogen flames can still be used provided Soret effects are taken into account in one-dimensional calculations. The addition of exhaust gas to the unburned mixture is found to enhance thermodiffusive instability; the primary mechanism for this was shown to be the highly-efficient third-body nature of water, with the reduction of adiabatic flame temperature a second-order effect. Again, the existing mean local flame speed model proved sufficient. Finally, blending with methane was found to reduce the thermodiffusive response of the flame, more so than the existing model suggests, despite adjustment of the fuel Lewis number; an adapted model is presented to account for this.

08 HYDROGEN↗
NASA NTRS2014

Analytic Couple Modeling Introducing Device Design Factor, Fin Factor, Thermal Diffusivity Factor, and Inductance Factor

A set of convenient thermoelectric device solutions have been derived in order to capture a number of factors which are previously only resolved with numerical techniques. The concise conversion efficiency equations derived from governing equations provide intuitive and straight-forward design guidelines. These guidelines allow for better device design without requiring detailed numerical modeling. The analytical modeling accounts for factors such as i) variable temperature boundary conditions, ii) lateral heat transfer, iii) temperature variable material properties, and iv) transient operation. New dimensionless parameters, similar to the figure of merit, are introduced including the device design factor, fin factor, thermal diffusivity factor, and inductance factor. These new device factors allow for the straight-forward description of phenomenon generally only captured with numerical work otherwise. As an example a device design factor of 0.38, which accounts for thermal resistance of the hot and cold shoes, can be used to calculate a conversion efficiency of 2.28 while the ideal conversion efficiency based on figure of merit alone would be 6.15. Likewise an ideal couple with efficiency of 6.15 will be reduced to 5.33 when lateral heat is accounted for with a fin factor of 1.0.

Seebeck effect↗
DOE OSTI2025

Measurement of turbulent velocity and bounds for thermal diffusivity in laser shock compressed foams by x-ray photon correlation spectroscopy

Experimental benchmarking of transport coefficients under extreme conditions is required for validation of differing theoretical models. To date, measurement of transport properties of dynamically compressed samples remains a challenge with only a limited number of studies able to quantify transport in high pressure and temperature matter. x-ray photon correlation spectroscopy utilizes coherent x-ray sources to measure time correlations of density fluctuations, thus providing measurements of length and timescale-dependent transport properties. Here, we present a first-of-a-kind experiment to conduct x-ray photon correlation spectroscopy in laser shock compression experiments. We report measurement of the turbulent velocity in the wake of a laser driven supersonic shock and place an upper bound on thermal diffusivity in a solid density plasma on nanosecond timescales.

High-energy-density plasmas↗