A5022283446- Material Dynamics and Properties
- Nuclear Materials and Properties
- Nanofluid Flow and Heat Transfer
- Thermal properties of materials
- Graphite, nuclear technology, radiation studies
- Nuclear and radioactivity studies
- Phase Equilibria and Thermodynamics
- Fusion materials and technologies
- Ion-surface interactions and analysis
- Solid-state spectroscopy and crystallography
- Advanced Condensed Matter Physics
- Glass properties and applications
- Semiconductor materials and devices
- Nuclear reactor physics and engineering
- Theoretical and Computational Physics
- Heat Transfer and Optimization
- Silicon Carbide Semiconductor Technologies
- Thermal Radiation and Cooling Technologies
- Radioactive element chemistry and processing
- Thermodynamic and Structural Properties of Metals and Alloys
- Nuclear materials and radiation effects
- Inorganic Fluorides and Related Compounds
- Molten salt chemistry and electrochemical processes
- Advancements in Battery Materials
- Advanced Thermoelectric Materials and Devices
North Carolina State University
2015-2025
University of Illinois Chicago
2023
Idaho National Laboratory
2011
Los Alamos National Laboratory
2007-2008
Massachusetts Institute of Technology
2005-2007
This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which thermal conductivity of identical samples colloidally stable dispersions nanoparticles “nanofluids,” was measured by over 30 organizations worldwide, using a variety experimental approaches, including transient hot wire method, steady-state methods, and optical methods. The nanofluids tested exercise were comprised aqueous nonaqueous basefluids, metal oxide particles, near-spherical elongated...
We show that a large set of nanofluid thermal conductivity data falls within the upper and lower Maxwell bounds for homogeneous systems. This indicates nanofluids is largely dependent on whether nanoparticles stay dispersed in base fluid, form aggregates, or assume percolating fractal configuration. The experimental data, which are strikingly analogous to those most solid composites liquid mixtures, provide strong evidence classical nature conduction nanofluids.
Transient hot-wire data on thermal conductivity of suspensions silica and perfluorinated particles show agreement with the mean-field theory Maxwell but not recently postulated microconvection mechanism. The influence interfacial resistance, convective effects at microscales, possibility enhancements beyond limit are discussed.
Thermal conduction modes in a nanocolloid (nanofluid) are quantitatively assessed by combining linear response theory with molecular dynamics simulations. The microscopic heat flux is decomposed into three additive fluctuation modes, namely, kinetic, potential, and collision. For low volume fractions ($<1%$) of nanosized platinum clusters which interact strongly xenon host liquid, significant thermal conductivity enhancement results from the self correlation potential flux. Our findings...
We describe an atomistic method for computing the viscosity of highly viscous liquids based on activated state kinetics. A basin-filling algorithm allowing system to climb out deep energy minima through a series activation and relaxation is proposed first benchmarked problem adatom diffusion metal surface. It then used generate transition pathway trajectories in potential landscape binary Lennard-Jones system. Analysis sampled trajectory shows moves from one minimum another by process that...
In a well-dispersed nanofluid with strong cluster-fluid attraction, thermal conduction paths can arise through percolating amorphouslike interfacial structures. This results in conductivity enhancement beyond the Maxwell limit of 3phi, phi being nanoparticle volume fraction. Our findings from nonequilibrium molecular dynamics simulations, which are amenable to experimental verification, provide theoretical basis for development future nanofluids.
Abstract Among the superionic conductors that show a Faraday transition – continuous increase in ionic conductivity over range of temperatures fluorite structures have enjoyed incisive examinations past four decades; yet fundamental nature superionicity has remained largely inconclusive. Departing from traditional quasi-static defect framework, we provide weighty evidence for string-like dynamical govern fast ion conduction process fluorites. We lower encourage growth longer but slowly...
<title>Abstract</title> For the next-generation high temperature microreactors, yttrium dihydride (YH2) is an attractive solid state neutron moderator. Despite a number of recent investigations, mechanism hydrogen transport remains poorly understood. Experimental evaluations diffusivity are inconclusive with large variations in diffusivities and activation energies. In this work, we perform ab initio molecular dynamics (AIMD) simulations on YH2 for temperatures spanning 300 K to 1200 K. Our...
A recently developed atomistic method capable of calculating the fragile (non-Arrhenius) temperature behavior highly viscous liquids is further tested by studying a model SiO(2), glass former well known for its Arrhenius (strong). The predicts an variation, in agreement with experiments, origin which revealed both quantitative and qualitative results on transition state pathways, activation barrier analysis, energy landscape connectivity, mechanisms. Also predicted from to strong at lower...
Using Raman and X-ray photoelectron spectroscopy, we delineate the bond defect structures in nuclear block graphite (NBG-18) under neutron ion irradiation. The strengthening of (D) peak spectra irradiation is attributed to an increase topological, sp2-hybridized defects. transmission electron microscopy, provide evidence for prismatic dislocations as well a number basal dissociating into Shockley partials. non-vanishing D spectra, together with generous dislocations, even at low doses,...
The microscopic origin of glass transition, when liquid viscosity changes continuously by more than ten orders magnitude, is challenging to explain from first principles. Here we describe the detailed derivation and implementation a Markovian Network model calculate shear deeply supercooled liquids based on numerical sampling an atomistic energy landscape, which sheds some light this transition. Shear stress relaxation calculated master-equation description in system follows transition-state...
Multicomponent diffusional mechanisms in the ternary LiCl-KCl system are elucidated using Green-Kubo formalism and equilibrium molecular dynamics simulations. The Maxwell-Stefan (MS) diffusion matrix is evaluated from Onsager dynamical that contains flux correlation functions. From temporal behavior of functions, we observe Li-Li Li-Cl ion pairs have a pronounced cage remains noticeably strong even at high temperatures. Even though coefficients, which time integrals portray relatively smooth...
Using molecular dynamics simulations of UO2-a type II superionic conductor-we identify a well-defined onset dynamic disorder (Tα), which is remarkably correlated to nontrivial advance dynamical heterogeneity (DH). Quantified by the correlations in propensity and van Hove self-correlation function, DH shown grow with increasing temperature from Tα, peak at an intermediate between Tα Tλ-the transition temperature-and then recede. Surprisingly, attributes are not uniform across temperatures-our...
We show that the absolute thermodynamic properties of molten salts (mixtures KCl and LiCl) can be accurately determined from two-phase (2PT) method is based on superpositioning solid-like gas-like (hard-sphere) vibrational density states (DoS). The 2PT predictions are in excellent accordance with those integration method; melting point evaluated free energy entropy shows close conformity experimental/NIST data. DoS partitioning Li+ ions eutectic LiCl–KCl mixture largely solid-like, unlike K+...
In an earlier work [V. A. Annamareddy et al., Phys. Rev. E 89, 010301(R) (2014)], we showed the manifestation of dynamical heterogeneity (DH)—the presence clustered mobile and immobile regions—in UO2, a model type II superionic conductor. current work, demonstrate mechanism dynamic facilitation (DF) in two conductors (CaF2 UO2) using atomistic simulations. Using mobility transfer function, DF is shown to vary non-monotonically with temperature intensity peaking at temperatures close...
Li2O belongs to the family of antifluorites that show superionic behavior at high temperatures. While some characteristics are well-known, mechanistic details ionic conduction processes somewhat nebulous. In this work, we first establish an onset is emblematic a gradual disordering process among Li ions characteristic temperature Tα (~1000 K) using reported neutron diffraction data and atomistic simulations. state, observed portray dynamic disorder by hopping between tetrahedral lattice...
Two dynamic transitions or crossovers, one at a low temperature (T${}^{*}$ \ensuremath{\approx} 1006 K) and the other high (T${}^{0}$ 1384 K), are shown to emerge in supercooled liquid silicon using molecular dynamics simulations. The high-temperature transition (T${}^{0}$) marks decoupling of stress, density, energy relaxation mechanisms. At low-temperature (T${}^{*}$), depending on cooling rate, can either undergo high-density-liquid low-density-liquid (HDL-LDL) phase experience an HDL-HDL...