scholarly journals Bridging Capillary-Driven Fragmentation and Grain Transport with Mixed Columnar-Equiaxed Solidification

2021 ◽  
Author(s):  
Christian M. G. Rodrigues ◽  
Menghuai Wu ◽  
Haijie Zhang ◽  
Andreas Ludwig ◽  
Abdellah Kharicha
Keyword(s):  
Flow Direction ◽  
Interfacial Area ◽  
Columnar Structure ◽  
Solidification Model ◽  
New Correlation ◽  
Equiaxed Solidification ◽  
Proposed Model ◽  
Interfacial Area Density ◽  
Columnar To Equiaxed Transition ◽  
Intrinsic Feature

AbstractIn this study, a first attempt is made to bridge capillary-driven fragmentation and grain transport using a mixed columnar-equiaxed solidification model. Grain transport is an intrinsic feature of the employed solidification model which has been extensively investigated over the years. Regarding the capillary-driven fragmentation event, a new correlation between the number of fragments and interfacial area density of the columnar structure was recently established by Cool and Voorhees (2017) based on experimental research under isothermal conditions. Here, we propose to modify Cool and Voorhees’ equation to extend its range of applicability to the solidification-dominant stage without destroying the agreement with the reported measurements in the coarsening-dominant stage. With this improvement in the mixed columnar-equiaxed solidification model, capillary effects can be isolated from the motion of the phases during fragmentation events, which facilitates understanding of the results. Under pure diffusive solidification conditions (no flow or crystal sedimentation), the simulation results were validated against phase-field simulations. In more realistic scenarios where liquid flow and fragment sedimentation are both considered, the simulations indicate very reasonable results for the detection of columnar-to-equiaxed transition, which suggests that the newly proposed model can be an important tool for industrial casting applications. Moreover, flow direction and intensity were shown to affect the potential for local fragmentation. Graphic Abstract

Relationships Between Mass Transfer and Morphology in Deformable Complex Interfacial Systems

2002 ◽  
Author(s):  
A. El Afif ◽  
D. De Kee ◽  
R. Cortez ◽  
D. P. Gaver
Keyword(s):  
Mass Transfer ◽  
Mass Flux ◽  
Complex Fluids ◽  
Interfacial Area ◽  
Time Dependent ◽  
Internal Stresses ◽  
Order Tensor ◽  
Structural Variables ◽  
Interfacial Area Density ◽  
Isothermal Mass

We propose a model for isothermal mass transport into immiscible complex fluids. The interface is described by two, space and time dependent, structural variables: a scalar Q(r,t) denoting the interfacial area density and a traceless symmetric second order tensor q(r,t) accounting for the shape anisotropy. The mass flux expression includes new contributions attributed to the dynamical changes of the interface. The diffusion-morphology coupling is found to influence both the mass transfer and the dynamics of the interface. The former exhibits non-Fickian behavior while the latter undergoes interfacial deformations that affect both its size and shape, creating internal stresses at the same time.

scholarly journals Effect of Pressure With Wall Heating in Annular Two-Phase Flow

2003 ◽  
Vol 125 (1) ◽  
pp. 84-96 ◽  
Author(s):  
Ranganathan Kumar ◽  
Thomas A. Trabold
Keyword(s):  
Aspect Ratio ◽  
Void Fraction ◽  
High Aspect Ratio ◽  
Test Section ◽  
Full Range ◽  
Interfacial Area ◽  
Two Phase ◽  
Local Flow ◽  
Area Density ◽  
Interfacial Area Density

The local distributions of void fraction, interfacial frequency, and velocity have been measured in annular flow of R-134a through a wall-heated, high aspect ratio duct. High aspect ratio ducts provide superior optical access to tubes or irregular geometries. This work expands upon earlier experiments conducted with adiabatic flows in the same test section. Use of thin, transparent heater films on quartz windows provided sufficient electrical power capacity to produce the full range of two-phase conditions of interest. With wall vapor generation, the system pressure was varied from 0.9 to 2.4 MPa, thus allowing the investigation of flows with liquid-to-vapor density ratios covering the range of about 7 to 27, far less than studied in air-water and similar systems. There is evidence that for a given cross-sectional average void fraction, the local phase distributions can be different depending on whether the vapor phase is generated at the wall, or upstream of the test section inlet. In wall-heated flows, local void fraction profiles measured across both the wide and narrow test section dimensions illustrate the profound effect that pressure has on the local flow structure; notably, increasing pressure appears to thin the wall-bounded liquid films and redistribute liquid toward the edges of the test section. This general trend is also manifested in the distributions of mean droplet diameter and interfacial area density, which are inferred from local measurements of void fraction, droplet frequency and velocity. At high pressure, the interfacial area density is increased due to the significant enhancement in droplet concentration.

scholarly journals A Nonequilibrium Vapor Generation Model for Flashing Flows

1984 ◽  
Vol 106 (1) ◽  
pp. 198-203 ◽  
Author(s):  
P. Saha ◽  
N. Abuaf ◽  
B. J. C. Wu
Keyword(s):  
Flow Regime ◽  
Bubbly Flow ◽  
Interfacial Area ◽  
Superheated Liquid ◽  
Generation Model ◽  
Vapor Generation ◽  
Area Density ◽  
Interfacial Area Density ◽  
Inception Point ◽  
Liquid Superheat

A nonequilibrium vapor generation model for flashing flows is presented. The model consists of a flashing inception point, a bubbly flow regime followed by a bubbly-slug regime, an annular or annular-mist regime, and finally a dispersed-droplet regime. Existence of superheated liquid at the inception point and beyond is recognized. The vapor generation rate is calculated from the flow-regime dependent interfacial area density and net interfacial heat flux. However, the bubble number density at the flashing inception point was varied to obtain optimum fits with the void fraction data taken in a vertical converging-diverging nozzle. The interfacial area density at the inception point, thus determined, showed a rapid increase with the decrease in the liquid superheat at that point. This trend is plausible, since in the limit of thermal equilibrium flow where the liquid superheat approaches zero, the interfacial area for heat and mass transfer should be very large.

A Numerical Study of the Influence of Pouring Technique on the As-Cast Structure of Al-Cu Ingots

2014 ◽  
Vol 790-791 ◽  
pp. 67-72
Author(s):  
Mahmoud Ahmadein ◽  
Meng Huai Wu ◽  
Peter Schumacher ◽  
Andreas Ludwig
Keyword(s):  
Volume Fraction ◽  
Numerical Study ◽  
Initial Growth ◽  
Multiple Streams ◽  
Cast Structure ◽  
Solidification Model ◽  
Columnar Grains ◽  
Columnar To Equiaxed Transition ◽  
Five Phases ◽  
Equiaxed Grains

Experimental evidence [Ohno 1987] revealed the influence of some pouring techniques on the as-cast structure. In the current work the process of pouring of the molten Al-4.0 wt.%Cu via one or multiple streams into a graphite mold is studied using a 3-phase model by considering the nucleation, the initial growth and transport of globular equiaxed crystals. The three phases are the melt, air and globular equiaxed crystals. Results showed that pouring via multiple streams increases the volume fraction and number density of crystals in the as-filled state. The subsequent solidification is calculated using a 5-phase mixed columnar-equiaxed solidification model. The five phases are the extradendritic melt, the solid dendrite and interdendritic melt inside the equiaxed grains, the solid dendrite and interdendritic melt inside the columnar grains. As final result the as-cast structure including the distinct columnar and equiaxed zones, columnar-to-equiaxed transition (CET), grain size, macrosegregation, and rest eutectic is predicted. Effect of melt convection and crystal sedimentation during the pouring and solidification is taken into account. The predicted as-cast structure, under the influence of single/multiple jet pouring, is evaluated bycomparison with the available experiments of Ohno.

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