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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 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Numerical Simulations of Time-Resolved Photoluminescence in CdSexTe1-x/CdTe Solar Cells

We present initial time-resolved photoluminescence (TRPL) simulations in graded CdSexTe1-e thin-film solar cells to quantify the front-interface recombination velocity, S int,front . Our model includes several composition dependences: bandgap energy, absorption coefficient, electron affinity, and carrier lifetime. Cathodoluminescence spectrum imaging measurements on bevels provide an estimate of the bandgap and the CdSe x Te 1-x alloy composition through the absorber thickness. TRPL decays are simulated as a function of the laser power, S int,front , front-interface band offset, and bulk Shockley-Read-Hall lifetime. We find the impact of S intf,ront on the PL decay increases as the band offset shifts from a "spike" to a "cliff". Recombination rate analysis shows that back-interface recombination could potentially dictate the later part of the TRPL decay "t 2" in high-lifetime CdSe x Te 1-x cells. We briefly discuss ongoing work to determine TRPL measurement conditions that maximize sensitivity to S itnt,front.

CdTe solar cells↗
DOE OSTI2016

Experimental Stress Characterization and Numerical Simulation for Copper Pumping Analysis of Through-Silicon Vias

A 3-D thermomechanical model of through-silicon vias (TSVs) has been analyzed and verified with in situ microscale strain measurements by synchrotron X-ray microdiffraction will be discussed in this paper. Thereafter, a comprehensive stress/strain analysis on copper pumping and back-end-of-line (BEOL) cracking issues has been carried out. In addition, a design-of-experiments-based approach has been used to understand the effect of various parameters on copper pumping and BEOL stress. The results show that the smaller TSV diameter and thinner silicon die help reduce the copper pumping and thus mitigate BEOL stress.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Numerical Simulation of Irradiation Induced Swelling for STAR 4.1 Blanket

Here, this article presents the preliminary results of FEM implementation of irradiation-induced swelling, hardening, and creep effect using ANSYS user programmable features (UPFs) applied to material properties. The first liquid metal breeding blanket model for STAR 4.1 tokamak as a part of the virtual prototyping system is under development at Princeton Plasma Physics Laboratory (PPPL). Intense neutron irradiation produces significant changes in the physical and mechanical properties of Fe-(8%–9%)Cr-based reduced activation ferritic martensitic (RAFM) steels. An ANSYS model of the breeding blanket was built to involve these irradiation-induced material property changes with neutron fluence distribution mapped from the MCNP model. Simulation results show that significant structure deformation forms from nuclear swelling, stress, and plastic strain arising from DPA gradient through wall thickness. The material degradation effect is not negligible. This modeling feature can either assist in analyzing the structural behaviors with the influence of nuclear swelling or provide guidance to design the structure to withstand irradiation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Numerical Simulation of an Industrial Fluid Catalytic Cracking Regenerator

Fluid catalytic cracking (FCC) is one of the most important conversion processes in petroleum refineries, and the FCC regenerator is a key part of an FCC unit utilized in the recovery of solid catalyst reactivity by burning off the deposited coke on the catalyst surface. Furthermore, a three-dimensional multiphase, multispecies reacting flow computational fluid dynamics (CFD) model was established to simulate the flow and reactions inside an FCC regenerator. The Euler–Euler approach, where the two phases (gas and solid) are considered to be continuous and fully interpenetrating, is employed. The model includes gas–solid momentum exchange, gas–solid heat exchange, gas–solid mass exchange, and chemical reactions. Chemical reactions incorporated into the model simulate the combustion of coke which is present on the catalyst surface. We validated the simulation results using plant data.

42 ENGINEERING↗
DOE OSTI2016

Numerical Simulation Comparison of Two Reactor Configurations for Chemical Looping Combustion and Chemical Looping With Oxygen Uncoupling

Chemical looping with oxygen uncoupling (CLOU) is a carbon capture technology that utilizes a metal oxide as an oxygen carrier to selectively separate oxygen from air and release gaseous O 2 into a reactor where fuel, such as coal, is combusted. Previous research has addressed reactor design for CLOU systems, but little direct comparison between different reactor designs has been performed. This study utilizes Barracuda-VR® for comparison of two system configurations, one uses circulating fluidized beds (CFB) for both the air reactor (AR) and fuel reactor (FR) and another uses bubbling fluidized beds for both reactors. Initial validation of experimental and computational fluid dynamic (CFD) simulations was performed to show that basic trends are captured with the CFD code. The CFD simulations were then used to perform comparison of key performance parameters such as solids circulation rate and reactor residence time, pressure profiles in the reactors and loopseals, and particle velocities in different locations of the reactor as functions of total solids inventory and reactor gas flows. Here, using these simulation results, it was determined that the dual CFB system had larger range for solids circulation rate before choked flow was obtained. Both systems had similar particle velocities for the bottom 80% of particle mass, but the bubbling bed (BB) obtained higher particle velocities as compared to the circulating fluidized-bed FR, due to the transport riser. As a system, the results showed that the dual CFB configuration allowed better control over the range of parameters tested.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2021

Numerical Simulation of Container Breach and Airborne Release of Solids Due to Mechanical Insults

Throughout U.S. Department of Energy (DOE) complexes, safety engineers employ the five-factor formula to calculate the source term (ST) that includes parameters of airborne release fraction (ARF), respirable fraction (RF) and damage ratio (DR). Limited experimental data on fragmentation of solids, such as ceramic pellets (i.e., PuO2), and container breach due to mechanical insults (i.e., drop and forklift impact), can be supplemented by modeling and simulation using high fidelity computational tools to estimate these parameters. This paper presents the use of Sandia National Laboratories' SIERRA solid mechanics (SM) finite element code to investigate the behavior of the widely utilized waste container (such as 7A Drum) subject to a range of free fall impact and puncture scenarios. The resulting behavior of the container is assessed, and the estimates are presented for bounding DRs from calculated breach areas for the various accident conditions considered. This paper also describes a novel multiscale constitutive model recently implemented in SIERRA/SM that simulates the fracture of brittle materials such as PuO 2 and determines ARF during the fracture process. Furthermore, comparisons are made between model predictions and simple bench-top experiments.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2011

Numerical simulation of the electromagnetic fields excited by loop antennas in plasma in the whistler frequency range

The electromagnetic fields excited by circular loop antennas in a magnetized plasma in the whistler frequency range are simulated by the finite-difference time-domain method. The spatial structure of quasi-monochromatic fields excited in the near- and far-field zones by an antenna with a harmonic current, as well as the dynamics of the electromagnetic field excited by an antenna with a current in the form of a single video pulse, is studied. Simulations performed for a uniform plasma and uniform ambient magnetic field agree well with the results of theoretical analysis and model laboratory experiments performed on large-scale plasma devices.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Study of the development of relativistic plasma bunches in a long mirror trap by optical and X-ray imaging and numerical simulations

The work presents experimental results demonstrating the feasibility of autoresonance acceleration of electrons in a long mirror trap with a reverse magnetic field. It is shown that gyromagnetic autoresonance results in the formation of a plasma bunch with average electron energy of several hundred keV, which is confined for a long time in the trap. The results of computer simulations of the regime of reverse gyromagnetic autoresonance agree well with the experimental data.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Numerical simulation of optical feedback on a quantum dot lasers

We use multi-population rate equations model to study feedback oscillations in the quantum dot laser. This model takes into account all peculiar characteristics in the quantum dots such as inhomogeneous broadening of the gain spectrum, the presence of the excited states on the quantum dot and the non-confined states due to the presence of wetting layer and the barrier. The contribution of quantum dot groups, which cannot follow by other models, is simulated. The results obtained from this model show the feedback oscillations, the periodic oscillations which evolves to chaos at higher injection current of higher feedback levels. The frequency fluctuation is attributed mainly to wetting layer with a considerable contribution from excited states. The simulation shows that is must be not using simple rate equation models to express quantum dots working at excited state transition.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Numerical Simulation of the Structure and Mechanical Properties of Silicene Layers on Graphite during the Lithium Ion Motion

The molecular dynamics method is applied to study structural and mechanical effects appearing during the lithium ion motion in a dc electric field along a planar channel formed by perfect silicene sheets and sheets containing vacancy-type defects. Mono-, di-, tri-, and hexavacancies of rather densely and uniformly filled silicene sheets are arranged one above the other on a graphite substrate. The times of Li{sup +} ion passage through silicene channels with various gaps are determined. The construction of Voronoi polyhedra and truncated polyhedrons, whose centers coincide with the moving ion position allowed revealing the structural features inherent to the two-dimensional layered structure. The nature of stresses appearing in silicene sheets most critical to ion motion over the channel is determined.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Numerical Simulation of Thermodynamic Parameters of High-Porosity Copper

We propose that a modified equation of state be used for calculating the thermodynamically equilibrium TEC2 model for improving the reliability of description of thermodynamic parameters of shock loading of pure materials and heterogeneous mixtures of various porosities. For copper, the parameters of a thermally consistent equation of state have been determined. A reliable description of shock-wave loading of copper has been obtained using a small number of fitting parameters determined from the concordance with experimental data. Thermodynamic parameters have been simulated for copper with various porosities; the compression ratio and the temperature along the shock adiabat have been determined, and the value of heat capacity along the normal isobar has been calculated. The results of calculations are compared with available experimental results obtained by different authors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Short-Range Order and Charge Transport in SiO{sub x}: Experiment and Numerical Simulation

The structure of nonstoichiometric silicon oxide (SiO{sub x}) has been studied by the methods of highresolution X-ray photoelectron spectroscopy and fundamental optical-absorption spectroscopy. The conductivity of SiO{sub x} (x = 1.4 and 1.6) films has been measured in a wide range of electric fields and temperatures. Experimental data are described in terms of the proposed SiO{sub x} structure model based on the concept of fluctuating chemical composition leading to nanoscale fluctuations in the electric potential. The maximum amplitude of potential fluctuations amounts to 2.6 eV for electrons and 3.8 eV for holes. In the framework of this model, the observed conductivity of SiO{sub x} is described by the Shklovskii–Efros theory of percolation in inhomogeneous media. The characteristic spatial scale of potential fluctuations in SiO{sub x} films is about 3 nm. The electron-percolation energy in SiO{sub 1.4} and SiO{sub 1.6} films is estimated to be 0.5 and 0.8 eV, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗