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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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Fluid Dynamic and Stability Analysis of a Thin Liquid Sheet

Interest in thin sheet flows has recently been renewed due to their potential application in space radiators. Theoretical and experimental studies of the fluid dynamics and stability of thin liquid sheet flows have been carried out in this thesis. A computer program was developed to determine the cross-sectional shape of the edge cylinder given the cross-sectional area of the edge cylinder. A stability analysis was performed on a non-planer liquid sheet. A study was conducted to determine the effects of air resistance on the sheet.

McMaster, Matthew S.↗
DOE OSTI2014

Liquid 1-propanol studied by neutron scattering, near-infrared, and dielectric spectroscopy

Liquid monohydroxy alcohols exhibit unusual dynamics related to their hydrogen bonding induced structures. The connection between structure and dynamics is studied for liquid 1-propanol using quasi-elastic neutron scattering, combining time-of-flight and neutron spin-echo techniques, with a focus on the dynamics at length scales corresponding to the main peak and the pre-peak of the structure factor. At the main peak, the structural relaxation times are probed. These correspond well to mechanical relaxation times calculated from literature data. At the pre-peak, corresponding to length scales related to H-bonded structures, the relaxation times are almost an order of magnitude longer. According to previous work [C. Gainaru, R. Meier, S. Schildmann, C. Lederle, W. Hiller, E. Rössler, and R. Böhmer, Phys. Rev. Lett. 105, 258303 (2010)] this time scale difference is connected to the average size of H-bonded clusters. The relation between the relaxation times from neutron scattering and those determined from dielectric spectroscopy is discussed on the basis of broad-band permittivity data of 1-propanol. Moreover, in 1-propanol the dielectric relaxation strength as well as the near-infrared absorbance reveal anomalous behavior below ambient temperature. A corresponding feature could not be found in the polyalcohols propylene glycol and glycerol.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1993

Colorimetric qualification of shear sensitive liquid crystal coatings

The work that has been done to date on the Shear Sensitive Liquid Crystal Project demonstrated that cholesteric liquid crystal coatings respond to both the direction and magnitude of a shearing force. The response of the coating is to selectively scatter incident white light into a spectrum of colors. Discernible color changes at a fixed angle of observation and illumination are the result of an applied shear stress. The intention was to be able to convert these observable color patterns from a flow visualization technique into a quantitative tool. One of the earlier intentions was to be able to use liquid crystals in dynamic flow fields. This was assumed possible because liquid crystals had made it possible to visualize transients in surface shear forces. Although the transients were visualized by color changes to an order one micro second, the time response of a coating to align to a shearing force is dependent on the magnitude of the change between its initial and final states. Unfortunately, the response is not instantaneous. It is for this reason any future attempt at quantifying the magnitude and directions of a shearing force are limited to surface shear stress vector fields in three dimensional steady state flows. This limitation does not significantly detract from the utility of liquid crystal coatings. The measurement of skin friction in the study of transition on wings, prediction of drag forces, performance assessment, and the investigation of boundary layer behavior is of great importance in aerodynamics. There exist numerous examples of techniques for the measurement of surface shear stress. Most techniques require arduous calibrations and necessitate extensive preparation of the receiving surfaces. However, the main draw back of instruments such as Preston tubes, hot films, buried wire gages, and floating element balances is that they only provide a point measurement. The advantages of capturing global shear data would be appreciable when compared with conventional point measurement sensors. It has yet to be determined if a repeatable correlation exists between the measured color of a liquid crystal coating and the magnitude/directional components of a shear vector imposed onto it.

Muratore, Joseph J., Jr.↗
DOE OSTI2018

Ion-specific Confined Water Dynamics in Convex Nanopores of Gemini Surfactant Lyotropic Liquid Crystals

The impact of pore geometry and functionality on the dynamics of water nanoconfined in porous media are the subject of some debate. Here, we report the synthesis and small-angle X-ray scattering (SAXS) characterization of a series of perdeuterated gemini surfactant lyotropic liquid crystals (LLCs), in which convex, water-filled nanopores of well-defined dimensions are lined with carboxylate functionalities. Quasielastic neutron scattering (QENS) measurements of the translational water dynamics in these dicarboxylate LLC nanopores as functions of the surfactant hydration state and the charge compensating counterion (Na + , K + , NMe 4 + ) reveal that the measured dynamics depend primarily on surfactant hydration, with an unexpected counterion dependence that varies with hydration number. We rationalize these trends in terms of a balance between counterion-water attractions and the nanopore volume excluded by the counterions. On the basis of electron density maps derived from SAXS analyses of these LLCs, we directly show that the volume excluded by the counterions depends on both their size and spatial distribution in the water-filled channels. The translational water dynamics in the convex pores of these LLCs are also slower than those reported in the concave pores of AOT reverse micelles, implying that water dynamics also depend on the nanopore curvature.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The Kinetics of the Liquid Phase Nucleation in a Stretched FCC Crystal: A Molecular Dynamics Simulation

The kinetics of a spontaneous formation of liquid phase in a stretched (superheated) Lennard-Jones fcc crystal is studied. Molecular dynamics experiments are used to determine the main parameters of the nucleation process: nucleation frequency J, diffusion coefficient of nuclei D{sub *}, nonequilibrium Zel’dovich factor Z, and critical nucleus size R{sub *}. The calculations are performed at negative pressures from the endpoint of the melting line and at positive pressures that are higher by a factor of eight than the critical pressure. The simulation results are compared to the classical homogeneous nucleation theory. It is found that the theory qualitatively correctly reproduces the dynamics of developing the process. The theory and the simulation demonstrate good quantitative agreement for the transition rate of the liquid phase nucleus through the critical size, but there is large difference in the numbers of critical nuclei in the unit volume of the metastable phase. In the case of significant superheatings and negative pressures, the contribution of the energy of elastic stresses to the moving force of the phase transformation is small and it can be neglected in a first approximation. The mismatch between the theory and the simulation results can be eliminated taking that the surface free energy of a curved “crystal–liquid droplet” interface is smaller than that of a plane interface by 30–35%.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

MO-A-BRD-01: An Investigation of the Dynamic Response of a Novel Acousto-Optic Liquid Crystal Detector for Full-Field Transmission Ultrasound Breast Imaging

Purpose: To characterize the dynamic response of a novel acousto-optic (AO) liquid crystal detector for high-resolution transmission ultrasound breast imaging. Transient and steady-state lesion contrast were investigated to identify optimal transducer settings for our prototype imaging system consistent with the FDA limits of 1 W/cm{sup 2} and 50 J/cm{sup 2} on the incident acoustic intensity and the transmitted acoustic energy flux density. Methods: We have developed a full-field transmission ultrasound breast imaging system that uses monochromatic plane-wave illumination to acquire projection images of the compressed breast. The acoustic intensity transmitted through the breast is converted into a visual image by a proprietary liquid crystal detector operating on the basis of the AO effect. The dynamic response of the AO detector in the absence of an imaged breast was recorded by a CCD camera as a function of the acoustic field intensity and the detector exposure time. Additionally, a stereotactic needle biopsy breast phantom was used to investigate the change in opaque lesion contrast with increasing exposure time for a range of incident acoustic field intensities. Results: Using transducer voltages between 0.3 V and 0.8 V and exposure times of 3 minutes, a unique one-to-one mapping of incident acoustic intensity to steady-state optical brightness in the AO detector was observed. A transfer curve mapping acoustic intensity to steady-state optical brightness shows a high-contrast region analogous to the linear portion of the Hurter-Driffield curves of radiography. Using transducer voltages between 1 V and 1.75 V and exposure times of 90 s, the lesion contrast study demonstrated increasing lesion contrast with increasing breast exposure time and acoustic field intensity. Lesion-to-background contrast on the order of 0.80 was observed. Conclusion: Maximal lesion contrast in our prototype system can be obtained using the highest acoustic field intensity and the longest breast exposure time allowable under FDA standards. Department of Defense (DOD) Breast Cancer Research Program IDEA Award W81XWH-11-1-0332; National Institutes of Health (NIH) Grant T32 EB002103-21 from the National Institute of Biomedical Imaging and Bioengineering (NIBIB)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Nonuniversal Coupling of Cage Scale Hopping and Collective Elastic Distortion as the Origin of Dynamic Fragility Diversity in Glass-Forming Polymer Liquids

Here, we formulate a theoretical mechanism for the physical origin of the massive dynamic fragility range observed in long chain glass-forming polymer melts within the context of the force-level elastically collective nonlinear Langevin equation theory of coupled local nonlocal activated segmental relaxation. The hypothesis involves how the cage scale barrier hopping process on the three Kuhn segment length scale is quantitatively coupled to the longer range collective elastic distortion required to sterically allow large-amplitude events to occur. The key nonuniversal aspect is proposed to be an effective microscopic jump distance, a dynamical quantity associated with the activation barrier, which is influenced by nanometer-scale conformational transition physics and monomer chemistry. Furthermore, by introducing a single numerical factor that breaks the universality of the jump distance in our mapping of polymers to liquids of disconnected Kuhn-sized hard spheres, one can account rather well, and simultaneously, for the vitrification temperatures and dynamic fragilities of 17 polymer liquids of diverse chemistry. The very low fragilities of polyisobutylene (PIB) and polyethylene are suggested to be a consequence of suppression of the collective elastic distortion effect. The large fragility variations displayed by polymeric materials appears special to long chain melts, consistent with their absence in molecular and oligomer liquids. Connections between cooperativity and fragility are identified. The theory very accurately captures segmental relaxation time experimental data for PIB, polypropylene, and polycarbonate melts over 11 13 decades. Our present work sets the stage for attempting to understand the failure of time temperature superposition in the deeply supercooled regime.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effects of fuel viscosity on the primary breakup dynamics of a high-speed liquid jet with comparison to X-ray radiography

One of the major concerns in combustion engines is the sensitivity of engine performance to fuel prop- erties. Recent works have shown that even slight differences in fuel properties can cause significant changes in performance and emission of an engine. In order to design the combustion engines with multi-fuel flexi- bilities, the precise assessment of fuel sensitivity on liquid jet atomization process is a prerequisite since the resulting fuel/air mixture is critical to the subsequent combustion process. The present study is focusing on the effect of physical fuel properties, mostly viscosity difference, on the breakup process of the liquid jet injected into still air. Two different jet fuels, CAT-A2 and CAT-C3, are considered here as surrogates for a fossil-based fuel and a bio-derived high-viscosity alternative fuel. The simulations are performed using the volume-of-fluid (VoF) interface tracking method coupled to Lagrangian particle method in order to capture the breakup instabilities of jets and the resulting droplets. The investigations take the actual geometry of the injector into account to resolve the unsteady flow phenomena inside the nozzle that impact the turbu- lence transition and atomization. The simulation results are compared to the experimental measurement using X-ray radiography. Both simulation and X-ray measurements consistently describe the effects of different fuels on the fundamental properties of atomization including the breakup length, transverse liquid volume fraction and the droplet sauter-mean-diameter. The application of a Detailed Numerical Simulation approach complemented by unique X-ray diagnostics is novel and providing new understanding and research directions in engine spray dynamics

Breakup instability↗
NASA NTRS2021

Modeling the Effects of Liquid-to-Gas Density Ratio on Slosh Dynamics

Mechanical models are commonly used in Guidance, Navigation and Controls (GN&C) system-level models to represent propellant slosh forces on launch vehicles and spacecraft. The slosh model parameters are typically predicted using semi-empirical analytical methods that are based on experimental data for high liquid-to-gas density ratios (such as water and air at standard sea level conditions). Model parameter calculations typically neglect any contribution to slosh dynamics from the gas phase. However, some cryogenic propellant systems operate in conditions where the density ratio can be orders of magnitude smaller. Analytical and computational modeling was used in this effort to investigate the effects of liquid-to-gas density ratio on slosh dynamics. No experimental data nor previous studies are available at this time that quantify the effect of liquid-to-gas density ratio on slosh dynamics. However, in a recent CFD study, results showed that density ratio can have a significant effect on slosh model parameters. In this study, a dual pendulum slosh model was created that distinctly represents both liquid and gas phase dynamics. Solution of the model, which invokes the Euler-Lagrange equations of motion, demonstrates that slosh frequency is a combination of liquid slosh frequency and gas phase slosh frequency. Additionally, it shows that slosh mass is reduced due to the opposing motion of the gas phase with respect to that of the liquid phase. The slosh model parameter trends were verified using Computational Fluid Dynamics (CFD) analysis results for various liquid-to-gas density ratios, tanks, and fill levels.

Christopher D Moore↗
DOE OSTI2014

Effects of sub-Tg annealing on Cu64.5Zr35.5 glasses: A molecular dynamics study

Creating metallic glasses by cooling liquid melts in molecular dynamics simulations faces a well-known challenge that the cooling rate is too fast compared with experiments. Taking the prototypical Cu 64.5Zr35.5 glasses as an example, we propose an efficient cooling strategy in which most of the computer time is spent on a prolonged isothermal process slightly below the glass-transition temperature, Tg . The glassy sample prepared in this way demonstrates significant energetic stability, slow dynamics, and well-developed short-range icosahedral order. By conventional uniform cooling, similar properties can only be obtained using a cooling rate more than 15 times slower.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Temperature-driven motion of liquid crystals confined in a microvolume

The theoretical description of the reorientational dynamics in microsized liquid crystal (LC) cell, where the nematic sample is confined by two horizontal and two lateral surfaces, under the influence of a temperature gradient ∇T, caused by a laser beam focused on the bounding surface with and without the orientational defect, whereas the rest of the bounding surfaces of the LC cell are kept at constant temperature, has been presented. Our calculations, based on the appropriate nonlinear extension of the classical Ericksen-Leslie theory, show that due to interaction between ∇T and the gradient of the director field ∇n-circumflex in the LC sample, a thermally excited vortical fluid flow is maintained in the vicinity of the orientational defect, with the motion in the positive sense (clockwise) around the middle part of that defect. In the case of the same LC cell, but without the orientational defect on the lower hotter boundary, the heating regime can also produce the vortical flow in the vicinity of the lower boundary, but with the motion in the negative sense (anti-clockwise) around the middle part of that boundary. At that, the second vortex is characterized by a much slower speed than the vortical flow in the first case.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1993

Natural and thermocapillary convection in multiple liquid layers

A numerical and experimental investigation is conducted of the fluid dynamics of immiscible liquid layers, as encountered in the liquid encapsulation of electronic melts. Attention is given to the convective flow in multiple liquid layers that are driven by temperature gradients that are either parallel or perpendicular to the liquid/liquid interfaces. The experimental and theoretical results obtained are noted not to be in agreement for differential side-heating of a three-layer system.

Prakash, A.↗
DOE OSTI2016

Simulations of the infrared, Raman, and 2D-IR photon echo spectra of water in nanoscale silica pores

Vibrational spectroscopy is frequently used to characterize nanoconfined liquids and probe the effect of the confining framework on the liquid structure and dynamics relative to the corresponding bulk fluid. However, it is still unclear what molecular-level information can be obtained from such measurements. In this paper, we address this question by using molecular dynamics (MD) simulations to reproduce the linear infrared (IR), Raman, and two-dimensional IR (2D-IR) photon echo spectra for water confined within hydrophilic (hydroxyl-terminated) silica mesopores. To simplify the spectra the OH stretching region of isotopically dilute HOD in D{sub 2}O is considered. An empirical mapping approach is used to obtain the OH vibrational frequencies, transition dipoles, and transition polarizabilities from the MD simulations. The simulated linear IR and Raman spectra are in good general agreement with measured spectra of water in mesoporous silica reported in the literature. The key effect of confinement on the water spectrum is a vibrational blueshift for OH groups that are closest to the pore interface. The blueshift can be attributed to the weaker hydrogen bonds (H-bonds) formed between the OH groups and silica oxygen acceptors. Non-Condon effects greatly diminish the contribution of these OH moieties to the linear IR spectrum, but these weaker H-bonds are readily apparent in the Raman spectrum. The 2D-IR spectra have not yet been measured and thus the present results represent a prediction. The simulated spectra indicates that it should be possible to probe the slower spectral diffusion of confined water compared to the bulk liquid by analysis of the 2D-IR spectra.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Structural transition in sputter-deposited amorphous germanium films by aging at ambient temperature

The structure of amorphous Ge (a-Ge) films prepared by sputter-deposition and the effects of aging at ambient temperature and pressure were studied by pair-distribution-function (PDF) analysis from electron scattering and molecular dynamics simulations. The PDFs of the as-deposited and aged samples for 3–13 months showed that the major peaks for Ge-Ge bonds decrease in intensity and broaden with aging for up to 7 months. In the PDFs of a-Ge of molecular dynamics simulation obtained by quenching liquid at different rates, the major peak intensities of a slowly cooled model are higher than those of a rapidly cooled model. Analyses on short- and medium-range configurations show that the slowly cooled model includes a certain amount of medium-range ordered (MRO) clusters, while the rapidly cooled model includes liquid-like configurations rather than MRO clusters. The similarity between experimental and computational PDFs implies that as-deposited films are similar in structure to the slowly cooled model, whereas the fully aged films are similar to the rapidly cooled model. It is assumed that as they undergo room-temperature aging, the MRO clusters disintegrate and transform into liquid-like regions in the same matrix. This transition in local configurations is discussed in terms of instability and the non-equilibrium of nanoclusters produced by a vapor-deposition process.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Fluctuations in the Dynamics of Glasses

This research program addressed the question of the presence of dynamical heterogeneities – strong spatial fluctuations in the dynamics – in glass forming liquids and jamming systems near dynamical arrest, with particular emphasis on aging systems, i.e. systems that are in the (non-equilibrium) glass regime. The main goals proposed for this research were: to perform numerical simulations of atomistic structural glass models to characterize dynamical heterogeneities in out of equilibrium (aging) glassy systems; to test the hypothesis that a certain symmetry (“time reparametrization symmetry”) is present in microscopic models of glassy systems and that this symmetry can explain the main features of dynamical heterogeneities; and to test to what extent these phenomena are universal across different glassy/jamming systems. It was found that: most of the important features of dynamical heterogeneities in the aging regime could be described in terms of simple scaling behaviors; that some of the most basic theoretical models of glassy systems indeed have time reparametrization symmetry; that all tests performed in numerical simulation data were consistent with the predictions from time reparametrization symmetry; and that to a large degree, the main features of dynamical heterogeneities were universal across different glassy systems. Most of the findings that came out of this research have been reported in detail in eight papers in high quality journals, two unpublished but publicly accessible manuscripts, and 27 invited and contributed talks.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Influence of Non-Equilibrium Conditions on Liquid Hydrogen Storage Tank Behavior [Slides]

Understanding liquid hydrogen tank fluid dynamics is key for modeling liquid hydrogen systems. The tank is the source for nearly all liquid hydrogen systems. Accurate flow modeling out of the tank is needed to predict flows through downstream components. Tank contains liquid and gas that may not be at equilibrium. Questions to be addressed are: Does heat and mass transfer between liquid and vapor affect the flow rate? Is boiling an important consideration? For what conditions is a pressure relief valve (PRV) sufficient to relieve pressure and when is the burst disc needed?

08 HYDROGEN↗