Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Liquid dynamics”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Dynamics of fluorinated imide-based ionic liquids using nuclear magnetic resonance techniques

There is increasing interest in studying molecular motions in ionic liquids to gain better insights into their transport properties and to expand their applications. Here, in this study, we have employed the fast field cycling relaxometry and pulsed field gradient nuclear magnetic resonance techniques to investigate the rotational and translational dynamics of fluorinated imide-based ionic liquids (ILs) at different temperatures. We have studied a total of six ILs composed of the 1-butyl-3-methylimidazolium cation ([BMIM] + ) combined with chemically modified analogs of the bis((trifluoromethyl)sulfonyl)imide anion ([NTf 2 ] − or [TFSI] − ). The primary objective of this paper is to broaden the understanding of how the anion's conformational flexibility, fluorination, and mass affect the molecular dynamics of cations and anions. Our results indicate that flexibility has the most significant impact on the rotational and translational motions of ions. Meanwhile, the effect of fluorination and mass is only relevant when conformational flexibility does not change significantly between the ILs being compared.

25 ENERGY STORAGE↗
DOE OSTI2019

Structure and dynamics of short-chain polymerized ionic liquids

Combining experimental results obtained with X-ray scattering and field-gradient nuclear magnetic resonance (NMR) and an assessment of new and previous dielectric and rheology data, our study focuses on the molecular weight (M w ) evolution of local structure and dynamics in a homologous series of covalently bonded ionic liquids. Performed on a family of electrolytes with a tailored degree of ionic decoupling, this study reveals the differences between monomeric and oligomeric melts with respect to their structural organization, mass and charge transport, and molecular diffusion. Our work demonstrates that for the monomeric compound, the broadband conductivity and mechanical spectra reflect the same underlying distribution of activation barriers and that the Random Barrier Model describes fairly well both the ionic and structural relaxation processes in these materials. Moreover, the oligomers with chains comprising ten segments only exhibit both structural and dynamical fingerprints of a genuine polymer. A comparison of conductivity levels estimated using the self-diffusion coefficients probed via NMR and those probed directly with dielectric spectroscopy reflects the emerging of ion correlations which are affecting the macroscopic charge transport in these materials in a chain-length dependent manner.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Pair dynamics and the intermolecular nuclear Overhauser effect (NOE) in liquids analysed by simulation and model theories: Application to an ionic liquid

Combining simulation and model theories, this paper analyses the impact of pair dynamics on the intermolecular nuclear Overhauser effect (NOE) in liquids. For the first time, we give a distance resolved NOE. When applied to the ionic liquid 1-ethyl-3-methyl-imidazolium tetrafluoroborate the NOE turns out to be of long-range nature. This behaviour translates to the experimentally measured cross- and longitudinal relaxation rates. We were able to calculate the heteronuclear NOE from simulation data, despite the high computational effort. Model theories are computationally less demanding and cover the complete frequency range of the respective spectral density function, they are usually based on a very simple pair distribution function and the solution of the diffusion equation. In order to model the simulated data sufficiently, these simplifications in structure and dynamics have to be generalised considerably.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Effect of Silicon, Carbon, and Sulfur on Structure of Liquid Iron and Implications for Structure-Property Relations in Liquid Iron-Light Element Alloys

Planetary cores are considered to be composed of iron (Fe) and light elements. Extensive studies on structure and properties of crystalline Fe–light element alloys have been carried out to discuss composition and structure of the solid inner core. In contrast, structure and properties of liquid Fe–light element alloys, which are important to discuss nature and dynamics of the liquid outer core, remain poorly understood. Here we conducted series of liquid structure measurements to systematically understand effect of silicon (Si), carbon (C), and sulfur (S) on structure of liquid Fe. We found that incorporation of Si in liquid Fe shortens the nearest (r 1 ) and second (r 2 ) neighbor distances, while incorporation of C and small amount of S expands these distances. The different structural behavior is interpreted in view of different light–element incorporation mechanisms: substitutional incorporation of Si and interstitial incorporation of C and S. All light elements lower density of liquid Fe regardless of shortening or expansion of the r 1 and r 2 distances, while P–wave velocities of liquid Fe–light element alloys show linear increase with shortening of the r 1 and r 2 . The different light–element incorporation behavior in the structure of liquid Fe and the resultant variation in the properties of liquid Fe–light element alloys should be important in understanding behavior of liquid Fe–light element alloys in the planetary cores.

58 GEOSCIENCES↗
DOE OSTI2014

Is there a third order phase transition for supercritical fluids?

We prove that according to Molecular Dynamics (MD) simulations of liquid mixtures of Lennard-Jones (L-J) particles, there is no third order phase transition in the supercritical regime beyond Andrew's critical point. This result is in open contrast with recent theoretical studies and experiments which instead suggest not only its existence but also its universality regarding the chemical nature of the fluid. We argue that our results are solid enough to go beyond the limitations of MD and the generic character of L-J models, thus suggesting a rather smooth liquid-vapor thermodynamic behavior of fluids in supercritical regime.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Effects of confinement on anomalies and phase transitions of core-softened fluids

We use molecular dynamics simulations to study how the confinement affects the dynamic, thermodynamic, and structural properties of a confined anomalous fluid. The fluid is modeled using an effective pair potential derived from the ST4 atomistic model for water. This system exhibits density, structural, and dynamical anomalies, and the vapor-liquid and liquid-liquid critical points similar to the quantities observed in bulk water. The confinement is modeled both by smooth and structured walls. The temperatures of extreme density and diffusion for the confined fluid show a shift to lower values while the pressures move to higher amounts for both smooth and structured confinements. In the case of smooth walls, the critical points and the limit between fluid and amorphous phases show a non-monotonic change in the temperatures and pressures when the nanopore size is increase. In the case of structured walls, the pressures and temperatures of the critical points varies monotonically with the pore size. Our results are explained on basis of the competition between the different length scales of the fluid and the wall-fluid interaction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Two-fluid dynamics of one-dimensional quantum liquids in the absence of Galilean invariance

Luttinger liquid theory of one-dimensional quantum systems ignores exponentially weak backscattering of particles. This endows Luttinger liquids with superfluid properties. The corresponding two-fluid hydrodynamic description available at present applies only to Galilean-invariant systems, whereas most experimental realizations of one-dimensional quantum liquids lack Galilean invariance. In this work, we develop the two-fluid theory of such quantum liquids. In the low-frequency limit the theory reduces to single-fluid hydrodynamics. However, the absence of Galilean invariance brings about three new transport coefficients. Lastly, we obtain expressions for these coefficients in terms of the backscattering rate.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Correlation between temperature variations of static and dynamic properties in glass-forming liquids

In this detailed analysis of the static structure factor S(Q) in several glass-forming liquids we show that the temperature variations of the width of the main diffraction peak Q(T ) correlate with the fragility of these liquids. Our observation suggests a direct connection between rather subtle structural changes and sharp slowing down of structural relaxation in glass-forming liquids. We also show that this observation can be rationalized using the Adam-Gibbs approach, through a connection between temperature variations of structural correlation length, lc 2 /Q, and the size of cooperatively rearranging regions.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Twist again: Dynamically and reversibly controllable chirality in liquid crystalline elastomer microposts

Photoresponsive liquid crystalline elastomers (LCEs) constitute ideal actuators for soft robots because their light-induced macroscopic shape changes can be harnessed to perform specific articulated motions. Conventional LCEs, however, do not typically exhibit complex modes of bending and twisting necessary to perform sophisticated maneuvers. Here, we model LCE microposts encompassing side-chain mesogens oriented along a magnetically programmed nematic director, and azobenzene cross-linkers, which determine the deformations of illuminated posts. On altering the nematic director orientation from vertical to horizontal, the post’s bending respectively changes from light-seeking to light-avoiding. Moreover, both modeling and subsequent experiments show that with the director tilted at 45°, the initially achiral post reversibly twists into a right- or left-handed chiral structure, controlled by the angle of incident light. We exploit this photoinduced chirality to design “chimera” posts (encompassing two regions with distinct director orientations) that exhibit simultaneous bending and twisting, mimicking motions exhibited by the human musculoskeletal system.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Memory effects in nuclear Fermi-liquid

The kinetic theory is applied to the nuclear Fermi liquid. The nuclear collective dynamics is treated in terms of the observable variables: particle density, current density, pressure etc. The influence of Fermi-surface distortion, relaxation processes and memory effects on the nuclear dynamics is studied. We show that the presence of the dynamic Fermi-surface distortion gives rise to some important consequences in the nuclear dynamics which are absent in classical liquids. We discuss the nuclear small amplitude excitations, the spinodal instability, the nuclear fission and the bubble instability in heated Fermi-liquid in presence of the memory effects.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS2001

How Does a Liquid Wet a Solid? Hydrodynamics of Dynamic Contact Angles

A contact line is defined at the intersection of a solid surface with the interface between two immiscible fluids. When one fluid displaces another immiscible fluid along a solid surface, the process is called dynamic wetting and a "moving" contact line (one whose position relative to the solid changes in time) often appears. The physics of dynamic wetting controls such natural and industrial processes as spraying of paints and insecticides, dishwashing, film formation and rupture in the eye and in the alveoli, application of coatings, printing, drying and imbibition of fibrous materials, oil recovery from porous rocks, and microfluidics.

Rame, Enrique↗
DOE OSTI2018

Comparative microscopic dynamics in a room-temperature ionic liquid confined in carbon pores characterized by reversible and irreversible ion immobilization

In search for the origin of irreversible ion immobilization under applied electric potential recently reported for a prototypical room-temperature ionic liquid electrolyte, [emim][Tf 2 N], confined in 1.5 nm carbon pores, here we compare the microscopic dynamics of cations in [emim][Tf 2 N] in the 1.5 nm and 6.7 nm carbon pores; in the latter, ion immobilization under applied electric potential is reversible. Using quasielastic neutron scattering, we find that the cation translational diffusivity is reasonably well defined on at least a nanometer length scale in the 6.7 nm pores, but not the 1.5 nm pores. Severely impeded microscopic dynamics of the confined electrolyte may be one of the factors differentiating the 1.5 nm pores from their larger counterparts and contributing to the irreversible immobilization of ions under applied electric potential.

Mamontov, Eugene↗
NASA NTRS1995

Computing Instability In Combustion Of Liquid Propellants

Computational fluid dynamics (CFD) code developed for use in design analyses of flow instabilities associated with combustion of sprayed liquid propellants in rocket engines. Code also contributes to design of improved commercial sprayed-fuel combustors in furnaces and jet engines. Proves robust, user-friendly software tool with comprehensive analysis capability. Enables characterization of stability or instability of engine in terms of such physically meaningful parameters as initial conditions of spray, spatial distribution of ratio between concentrations of fuel and oxidizer at injector faces, geometry of combustor, and configurations of baffles.

Chen, Yen-Sen↗