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Results for “Temperature Gradient”

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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Finite element study of plate buckling induced by spatial temperature gradients

Finite element analyses of thermal buckling of thin metallic plates with prescribed spatial temperature distributions are described. Thermally induced compressive membrane stresses and transverse plate displacement imperfections initiate plates buckling. A finite element formulation based on von Karman plate theory is presented. The resulting nonlinear equations are solved for incremental temperature increases by Newton-Raphson iteration. The computational method is used to investigate the buckling response of rectangular plates with steady and unsteady spatially varying temperature distributions. The role of initial plate imperfections and temperature distributions on the nonlinear response of plate displacements and stresses is described. The relatively high levels of stress induced by spatial temperature gradients should be considered carefully in the postbuckling design of panels for aerospace vehicles subjected to combined mechanical and thermal loads.

Thornton, Earl A.↗
DOE OSTI2018

Thin-Film In{sub x}Al{sub y}Ga{sub 1–} {sub x–} {sub y}As{sub z}Sb{sub 1–} {sub z}/GaSb Heterostructures Grown in a Temperature Gradient

The thin-film In{sub x}Al{sub y}Ga{sub 1–} {sub x–} {sub y}As{sub z}Sb{sub 1–} {sub z}/GaSb heterostructures have been grown from liquid phase in a temperature gradient. The growth kinetics, the composition, the structural perfection, and the luminescence properties of the InAlGaAsSb thin films grown on a GaSb substrate have been studied.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Control of Stratification in Drying Particle Suspensions via Temperature Gradients

A potential strategy for controlling stratification in a drying suspension of bidisperse particles is studied using molecular dynamics simulations. When the suspension is maintained at a constant temperature during fast drying, it can exhibit “small-on-top” stratification with an accumulation (depletion) of smaller (larger) particles in the top region of the drying film, consistent with the prediction of current theories based on diffusiophoresis. However, when only the region near the substrate is thermalized at a constant temperature, a negative temperature gradient develops in the suspension because of evaporative cooling at the liquid–vapor interface. Since the associated thermophoresis is stronger for larger nanoparticles, a higher fraction of larger nanoparticles migrate to the top of the drying film at fast evaporation rates. As a result, stratification is converted to “large-on-top”. Very strong small-on-top stratification can be produced with a positive thermal gradient in the drying suspension. Here, we explore a way to produce a positive thermal gradient by thermalizing the vapor at a temperature higher than that of the solvent. Possible experimental approaches to realize various thermal gradients in a suspension undergoing solvent evaporation and thus to produce different stratification states in the drying film are suggested.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Ecophotonics: assessment of temperature gradient in aquatic organisms using up-conversion luminescent particles

In the frameworks of developing ecophotonics, we consider the possibility of applying luminescence spectroscopy for monitoring conditions of aquatic organisms, aimed at the study and prognosis of the effect of human activity and climate changes on the environment. The method of luminescence spectroscopy in combination with anti-Stokes luminophores (up-conversion particles) used as optical sensors is used for the noninvasive assessment of the temperature gradient in the internal tissues of aquatic organisms. It is shown that the temperature dependence of the intensity ratio observed in the maxima of the luminescence spectrum bands of the particles Y{sub 2}O{sub 3} : Yb, Er, administered in a biological object, is linear. This fact offers a possibility of using the up-conversion particles for assessing the metabolic activity of different tissues, including those in the framework of ecological monitoring. (paper)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Ion-temperature-gradient stability near the magnetic axis of quasisymmetric stellarators

Abstract The stability of the ion-temperature gradient mode in quasisymmetric stellarators is assessed. This is performed using a set of analytical estimates together with linear gyrokinetic simulations. The peak growth rates, their corresponding real frequencies and wave-vectors are identified. A comparison is made between a first-order near-axis expansion model and eleven realistic designs obtained using numerical optimization methods. It is found that while the near-axis expansion is able to replicate the growth rates, real frequencies and perpendicular wave-vector at the inner core (both using simplified dispersion relations and first-principle gyrokinetic simulations), it leads to an overestimation of the growth rate at larger radii. An approximate analytic solution of the ITG dispersion relation for the non-resonant limit suggests growth rates could be systematically higher in quasi-axisymmetric (QA) configurations compared to quasi-helically (QH) symmetric ones. However except for very close to the axis, linear gyrokinetic simulations do not show systematic differences between QA and QH configurations.

Physics↗
NASA NTRS1986

Stresses and deformations in composite tubes due to a circumferential temperature gradient

A linear elasticity solution for determining the response of composite tubes subjected to a circumferential temperature gradient is presented. Numerical examples are used to show that, in a single layer tube, fiber orientation strongly influences response. When the fibers are aligned axially, all stress components in the tube are small. When the fibers are aligned circumferentially, the hoop stress becomes large. This difference in behavior is due to the large difference between the radial and circumferential coefficients of thermal expansion when the fibers are oriented circumferentially. In multilayer tubes, stresses are quite high and just two constants characterize the overall bending and axial deformations of the tubes.

Hyer, M. W.↗
NASA NTRS2019

Evaluation of Temperature Gradients During Cure of a Thick Carbon Fiber/Epoxy Composite

The purpose of this study is to evaluate the development of thermal gradients throughout thick (1") carbon fiber composites and determine the effect of internal temperature distribution during cure on the observed mechanical properties in those composites. Composites up to 1.5" thick (56 plies) were fabricated with T700S/TC380 braided prepreg from Tencate following a modified vacuum bag layup procedure to include embedded thermocouples within the plies of the composite. Composite panels were cured in a programmable oven with thermocouple reading embedded throughout the panel thickness. Maximum temperature gradients measured between regions of the composite did not exceed 10 degrees C for any given composite thickness. The most significant temperature variation was measured between the mid-thickness plies and the tool-side surface plies. Although through thickness temperature variation during cure was small, a measureable variation in coupon glass transition temperature was recorded between the tool side plies and the remainder of the part, prior to post cure. Thermal and mechanical behavior of coupons taken from segments through the thickness of the part were comparable following a post-cure cycle.

Miller, Sandi↗
NASA NTRS1984

A current generation by Compton scattering in a relativistic plasma with velocity shear and temperature gradient

Current generation by Thomson scattering in a non-relativistic plasma with the velocity shear and the temperature gradient (Hinata and Daneshvar, 1983) is extended to a relativistic plasma by replacing Thomson cross section by the Klein-Nishina formula. Because of the energy dependence of the cross-section, a numerical rather than analytic result is presented. The present calculation may be applied to a supernova implosion where the temperature may reach several MeV and a strong differential rotation is expected. It may also find applications in the early universe, and laser-pellet interaction.

Hinata, S.↗
DOE OSTI2017

The two-dimensional kinetic ballooning theory for ion temperature gradient mode in tokamak

The two-dimensional (2D) kinetic ballooning theory is developed for the ion temperature gradient mode in an up-down symmetric equilibrium (illustrated via concentric circular magnetic surfaces). The ballooning transform converts the basic 2D linear gyro-kinetic equation into two equations: (1) the lowest order equation (ballooning equation) is an integral equation essentially the same as that reported by Dong et al., [Phys. Fluids B 4, 1867 (1992)] but has an undetermined Floquet phase variable, (2) the higher order equation for the rapid phase envelope is an ordinary differential equation in the same form as the 2D ballooning theory in a fluid model [Xie et al., Phys. Plasmas 23, 042514 (2016)]. The system is numerically solved by an iterative approach to obtain the (phase independent) eigen-value. The new results are compared here to the two earlier theories. We find a strongly modified up-down asymmetric mode structure, and non-trivial modifications to the eigen-value.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Two-dimensional Thomson scattering measurements of misaligned electron density and temperature gradients and associated Biermann battery produced fields

We present optical Thomson scattering measurements of electron density and temperature in high Mach number laser-driven blast waves in homogeneous gases. Taylor–Sedov blast waves are launched in nitrogen (N2) or helium (He) at pressures between 0.4 mTorr and 10 Torr by ablating a solid plastic target with a high energy laser pulse (10 J, 1012 W/cm2). Experiments are performed at high repetition rate (1 Hz), which allows one-dimensional and two-dimensional Thomson scattering measurements over an area of several cm2 by automatically translating the scattering volume between shots. Electron temperature and density in the blast wave fronts were seen to increase with increasing background gas pressure. Measured electron density and temperature gradients were used to calculate ∂B/∂t∝∇Te×∇ne. The experimentally measured ∂B/∂t showed agreement with the magnetic field probe (B-dot) measurements, revealing that magnetic fields are generated in the observed blast waves via the Biermann battery effect. The results are compared to numerical three-dimensional collisional magnetohydrodynamic simulations performed with FLASH, and are discussed in the context of spontaneous magnetic field generation via the Biermann battery effect.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1991

Characterization of thermotropism in primary roots of maize: dependence on temperature and temperature gradient, and interaction with gravitropism

Thermotropism in primary roots of Zea mays L. was studied with respect to gradient strength (degrees C cm-1), temperature of exposure within a gradient, pre-treatment temperature, and gravitropic stimulation. The magnitude of the response decreased with gradient strength. Maximum thermotropism was independent of gradient strength and pre-treatment temperature. The range of temperature for positive and negative thermotropism did not change with pre-treatment temperature. However, the exact range of temperatures for positive and negative thermotropism varied with gradient strengths. In general, temperatures of exposure lower than 25 degrees C resulted in positive tropic responses while temperatures of exposure of 39 degrees C or more resulted in negative tropic responses. Thermotropism was shown to modify and reverse the normal gravitropic curvature of a horizontal root when thermal gradients were applied opposite the 1 g vector. It is concluded that root thermotropism is a consequence of thermal sensing and that the curvature of the primary root results from the interaction of the thermal and gravitational sensing systems.

Non-NASA Center↗
DOE OSTI2022

Examination of stiff ion temperature gradient mode physics in simulations of DIII-D H-mode transport

A systematic evaluation of gyrokinetic and gyrofluid model predictions of ion temperature gradient (ITG) stability and transport using parameters from DIII-D high confinement mode (H-mode) plasmas has been performed. The nonlinear CGYRO code is used to make the gyrokinetic predictions, and the quasilinear TGLF model for the corresponding gyrofluid predictions. The assessments are made at three radii (normalized toroidal flux ρtor = 0.4, 0.55, and 0.7) in three different plasma scenarios with varying levels of neutral beam heating and torque. For each of the nine cases (3 radii × 3 scenarios) considered, ITG turbulence is found to be the dominant long-wavelength instability and transport mechanism. The inclusions of both transverse magnetic fluctuations and dynamic fast beam ions are stabilizing for all cases considered, with strongest effects seen at ρor = 0.4 where the fast ion population and normalized plasma pressure β = 2μ0nT/B2 are highest. The further inclusion of parallel magnetic fluctuations does not have a meaningful impact on the ITG turbulence in these scenarios, but does destabilize (in combination with fast ions) new high-frequency instabilities at ρtor = 0.4 in the high power scenarios. In each case the linear and nonlinear ITG critical gradients are predicted to be lower than the measured ITG scale lengths and their associated uncertainties. Inclusion of equilibrium flow shear in the transport predictions generally leads to an upshift in effective critical gradient rather than a qualitative change in the predicted stiffness, with stronger responses typically seen in the gyrokinetic predictions than in the gyrofluid results. However, in most cases these upshifted gradients still remain below the measured values and their uncertainties. Although the predicted critical gradients are below the measured gradients, both models predicted flux-matching gradients consistent with measured values in six of the nine cases considered, with no clear systematic over- or underprediction. Thus, while the experimental ion temperature profiles do not appear to be closely pinned to the ITG critical gradient, both gyrokinetic and gyrofluid models are able to accurately match the measured gradients reasonably well in most cases.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗