Expressions for the effective diffusivity in materials with interphase boundaries

2004 ◽  
Vol 819 ◽  
Author(s):  
Irina V. Belova ◽  
Graeme E. Murch
Keyword(s):  
Polycrystalline Material ◽  
Effective Diffusivity ◽  
Poor Agreement ◽  
Two Phase ◽  
Interphase Boundaries ◽  
Long Time ◽  
Simulation Results ◽  
The Individual ◽  
Individual Grains ◽  
Good Agreement

AbstractWe address the problem of calculating the long-time-limit effective diffusivity in stable two- phase polycrystalline material. A phenomenological model is used where the high diffusivity interphase boundaries are treated as connected “coatings” of the individual grains. Derivation of expressions for the effective diffusivity with segregation is made along Maxwell lines. Monte Carlo simulation using lattice-based random walks is used to test the validity of the expressions. It is shown that for the case analysed the derived expressions for the effective diffusivity are in very good agreement with simulation results. The equivalent of the Hart equation is also derived. It is shown to be in poor agreement with simulation results.

Theory of Superplastic Flow in Two-Phase Materials: Roles of Interphase-Boundary Dislocations, Ledges, and Diffusion

1977 ◽  
Vol 99 (3) ◽  
pp. 244-251 ◽  
Author(s):  
J. H. Gittus
Keyword(s):  
Energy Barrier ◽  
Domain Boundary ◽  
Antiphase Domain ◽  
Superplastic Flow ◽  
Two Phase ◽  
Pile Up ◽  
Interphase Boundaries ◽  
And Diffusion ◽  
Good Agreement ◽  
Disordered Regions

A new theory is developed to explain superplastic flow in two-phase materials. It is postulated that boundary-dislocations, piled up in dislocation-Interphase-Boundaries (IPBs) climb away into disordered regions of the IPB. Sliding then occurs at an IPB as dislocations glide toward the head of the pile up to replace those which have climbed into disordered regions of the boundary. An energy barrier which would otherwise render sliding virtually impossible on dislocation-IPBs can, it is shown, be largely eliminated if the dislocations glide in pairs. The disorder (actually an antiphase domain boundary) which is created by the passage of the leading dislocation is then repaired by passage of its successor. The threshold stress for superplastic flow is provisionally identified with the stress which pins IPB dislocations to boundary ledges. The activation energy is theoretically that for IPB diffusion. Good agreement is obtained between the theoretical equation for superplastic flow and the results of published experiments.

An Application of Multigrain Approaches to the Structural Solution of Grains from Polycrystalline Samples

2019 ◽  
Vol 288 ◽  
pp. 119-123 ◽  
Author(s):  
Jav Davaasambuu ◽  
Jon Wright ◽  
Henning O. Soerensen ◽  
Soeren Schmidt ◽  
Henning F. Poulsen ◽  
...  
Keyword(s):  
Structural Refinement ◽  
X Ray Diffraction ◽  
X Ray ◽  
Experimental Parameters ◽  
Resolution Level ◽  
Diffraction Patterns ◽  
The Individual ◽  
Individual Grains ◽  
Comparison Of The Results ◽  
Good Agreement

The overlap of diffraction spots from different grains was investigated to understand the influence of experimental factors on the x-ray diffraction data quality and to optimize the experimental parameters for data collection on polycrystalline samples. Diffraction patterns for photoactive polycrystals were indexed and sorted with respect to grains using multigrain approaches. The indexing of diffraction spots and the identification of grains for tetrathiafulvalene-p-chloranil samples were performed using the ImageD11, GrainSpotter, GRAINDEX and Cell_now programs. In many cases, comparison of the results from these programs shows good agreement. For the individual grains from polycrystalline samples, the crystal structure was solved and refined using the SHELXTL program. After the structural refinement of the grains, the best and the average R1 values were 1.93% and 2.06%, respectively, which are on a comparable resolution level with that obtained from the x-ray single crystal measurements.

Optimization on the Structure of Ceramic Nozzles by FLUENT Simulation

2013 ◽  
Vol 397-400 ◽  
pp. 213-217
Author(s):  
Ming Wei Ding ◽  
Chang Jing Fu ◽  
Si Bei Yin
Keyword(s):  
Cone Angle ◽  
Two Phase ◽  
Abrasive Particles ◽  
Outflow Velocity ◽  
Fluent Simulation ◽  
Fluent Software ◽  
Simulation Results ◽  
Through Hole ◽  
Hole Structure ◽  
Good Agreement

Based on the theory of gas-solid two-phase flow, abrasive flows in ceramic nozzles with different structures are simulated by FLUENT software and the outflow velocity of particles is compared. The results show: the abrasive outflow velocity of ceramic nozzle with cone angle is large than that of ceramic nozzle with through-hole structure, and the distribution of abrasive particles is more uniform for the ceramic nozzle with cone angle. The best entrance cone angle of ceramic nozzle is 10o30o, and the maximum abrasive outflow velocity of the ceramic nozzle with cone angle of 20o is 90.16 m/s. The simulation results have a good agreement with the experimental results.

scholarly journals Hydraulic Transients Induced by Pigging Operation in Pipeline with a Long Slope

2013 ◽  
Vol 2013 ◽  
pp. 1-9 ◽  
Author(s):  
Tao Deng ◽  
Jing Gong ◽  
Haihao Wu ◽  
Yu Zhang ◽  
Siqi Zhang ◽  
...  
Keyword(s):  
Field Data ◽  
Water Pressure ◽  
Severe Damage ◽  
Cavitation Model ◽  
Two Phase ◽  
Vapor Cavity ◽  
The Third ◽  
Simulation Results ◽  
Water Pressure Testing ◽  
Good Agreement

Pigging in pipelines basically performs operations for five reasons including cleaning the pipe interior, batching or separating dissimilar products, displacement, measurement, and internal inspection. A model has been proposed for the dynamic simulation of the pigging process after water pressure testing in a long slope pipeline. In this study, an attempt has been made to analyze two serious accidents during pigging operation in 2010 by the model which is developed by the method of characteristic (MOC) by Wylie et al. (1993) and the two-phase homogeneous equilibrium vaporous cavitation model deveoped by Shu (2003) for vaporous cavitation. Moreover, simulation results of the third operation show good agreement with field data from the previous field trial. After investigation, it was showed that the impulse pressures produced during collapse of a vapor cavity result in severe damage of tubes.

Numerical Investigations on the Explosion Effects of Fuel Air Mixtures

2002 ◽  
Author(s):  
Tian Zhou ◽  
Yonghui Guo ◽  
Haibo Zhang
Keyword(s):  
Gas Phase ◽  
Fuel Droplet ◽  
Tvd Schemes ◽  
Propagation Process ◽  
Two Phase ◽  
Fuel Gas ◽  
Reaction Velocity ◽  
Numerical Investigations ◽  
Simulation Results ◽  
Good Agreement

To investigate the explosion parameters of Fuel Air Mixtures, the two-phase gas-droplet conservation equations are used. The model includes the following aspects: the deformation and fragmentation of the fuel droplet, the formation of fuel gas through evaporation and stripping of the boundary layer of the fuel droplet, the chemical delay and chemical reaction velocity between fuel gas and oxygen in the air. The high-resolution implicit TVD schemes are applied to gas phase equations and MacCormack schemes to liquid phase equations. The formation and propagation process of gas-droplet detonation wave inside the fuel air cloud and the attenuation process of the shock wave outside the cloud are simulated numerically. The simulation results keep good agreement with others’ study. The explosion effects of the height of the second ignition inside the cloud and the ratio of the cloud height to the cloud diameter are investigated numerically, too.

Modeling of Two-Phase Boiling Flow and Critical Heat Flux With the NEK-2P CFD Code

2017 ◽  
Author(s):  
Adrian Tentner ◽  
Prasad Vegendla ◽  
Ananias Tomboulides ◽  
Aleks Obabko ◽  
Elia Merzari ◽  
...  
Keyword(s):  
Heat Flux ◽  
Wall Temperature ◽  
Measured Data ◽  
Two Phase ◽  
Initial Validation ◽  
Hydraulic Conditions ◽  
Boiling Flow ◽  
Simulation Results ◽  
Two Fluid ◽  
Good Agreement

The paper focuses on the development, implementation, and initial validation of the NEK-2P two-fluid two-phase model. Recent extensions of the Extended Boiling Framework (EBF) models are presented, including the implementation of a four-field two-phase topology which replaces the previous two-field two-phase approach. The paper presents results of recent NEK-2P analyses of several CHF experiments. Good agreement between the simulated wall temperatures and measured data is observed. The simulation results predict well both the dryout location and post dryout wall temperature magnitudes, illustrating the ability of the NEK-2P code and extended EBF models to simulate the CHF phenomena for a range of thermal-hydraulic conditions.

Two Phase Flow Modeling of the Interior Ballistics for a Naval Medium Caliber Gun with Guided Projectile

2013 ◽  
Vol 465-466 ◽  
pp. 531-535
Author(s):  
Hazem Elsadek ◽  
Xiao Bing Zhang ◽  
Mahmod M. Rashad ◽  
Cheng Cheny
Keyword(s):  
Fluid Dynamics ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Flow Modeling ◽  
Governing Equations ◽  
Ballistic Performance ◽  
Two Phase ◽  
Interior Ballistics ◽  
Simulation Results ◽  
Good Agreement

This paper discusses the two phase (gas/Particles) flow effect of interior ballistic performance in a 76 mm naval medium caliber gun with guided projectile, using granular seven-perforated propellant. The theoretical and numerical simulation of the two phase flow in the interior ballistic cycle is carried out by using MacCromack technique depending on the governing equations of the two phase flow. This simulation is considered to be helpful for the prediction of the interior ballistic parameters which are required for endurance of guided projectile. A good agreement between the simulation results compared to the experimental results is fulfilled. Keywords: Guided projectile, two phase flow modeling, Interior ballistic, Computational fluid dynamics.

Numerical Modeling of Evolution of Boundary Between Incompressible Gas and Liquid in Two-Dimensional Region

2006 ◽  
Vol 4 ◽  
pp. 224-236
Author(s):  
A.S. Topolnikov
Keyword(s):  
Numerical Modeling ◽  
Interphase Boundary ◽  
Incompressible Liquid ◽  
Stokes Equations ◽  
Numerical Code ◽  
Navier Stokes ◽  
Two Phase ◽  
Navier Stokes Equations ◽  
Incompressible Media ◽  
Good Agreement

The paper is devoted to numerical modeling of Navier–Stokes equations for incompressible media in the case, when there exist gas and liquid inside the rectangular calculation region, which are separated by interphase boundary. The set of equations for incompressible liquid accounting for viscous, gravitational and surface (capillary) forces is solved by finite-difference scheme on the spaced grid, for description of interphase boundary the ideology of Level Set Method is used. By developed numerical code the set of hydrodynamic problems is solved, which describe the motion of two-phase incompressible media with interphase boundary. As a result of numerical simulation the solutions are obtained, which are in good agreement with existing analytical and experimental solutions.

ADHD with Comorbid Bipolar Disorders: A Systematic Review of Neurobiological, Clinical and Pharmacological Aspects Across the Lifespan

2019 ◽  
Vol 26 (38) ◽  
pp. 6942-6969 ◽  
Author(s):  
Federico Mucci ◽  
Maria Teresa Avella ◽  
Donatella Marazziti
Keyword(s):  
Clinical Features ◽  
Adult Adhd ◽  
Neurodevelopmental Disorder ◽  
Bipolar Disorders ◽  
Mood Stabilizers ◽  
Disruptive Behaviour ◽  
Single Individual ◽  
Pharmacological Management ◽  
Long Time ◽  
The Individual

Background: Attention deficit hyperactivity (ADHD) disorder is a neurodevelopmental disorder characterized by inattention, hyperactivity, disruptive behaviour, and impulsivity. Despite considered typical of children for a long time, the persistence of ADHD symptoms in adulthood gained increasing interest during the last decades. Indeed, its diagnosis, albeit controversial, is rarely carried out even because ADHD is often comorbid with several other psychiatric diosrders, in particular with bipolar disorders (BDs), a condition that complicates the clinical picture, assessment and treatment. Aims: The aim of this paper was to systematically review the scientific literature on the neurobiological, clinical features and current pharmacological management of ADHD comorbid with BDs across the entire lifespan, with a major focus on the adulthood. Discussion: The pharmacology of ADHD-BD in adults is still empirical and influenced by the individual experience of the clinicians. Stimulants are endowed of a prompt efficacy and safety, whilst non-stimulants are useful when a substance abuse history is detected, although they require some weeks in order to be fully effective. In any case, an in-depth diagnostic and clinical evaluation of the single individual is mandatory. Conclusions: The comorbidity of ADHD with BD is still a controversial matter, as it is the notion of adult ADHD as a distinct nosological category. Indeed, some findings highlighted the presence of common neurobiological mechanisms and overlapping clinical features, although disagreement does exist. In any case, while expecting to disentangle this crucial question, a correct management of this comorbidity is essential, which requires the co-administration of mood stabilizers. Further controlled clinical studies in large samples of adult ADHD-BD patients appear extremely urgent in order to better define possible therapeutic guidelines, as well as alternative approaches for this potentially invalidating condition.

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