Interfacial Transport Phenomena Research Articles

Dislocation-driven surface dynamics on solids.

Dislocations are line defects that bound plastically deformed regions in crystalline solids. Dislocations terminating on the surface of materials can strongly influence nanostructural and interfacial stability, mechanical properties, chemical reactions, transport phenomena, and other surface processes. While most theoretical and experimental studies have focused on dislocation motion in bulk solids under applied stress and step formation due to dislocations at surfaces during crystal growth, very little is known about the effects of dislocations on surface dynamics and morphological evolution. Here we investigate the near-equilibrium dynamics of surface-terminated dislocations using low-energy electron microscopy. We observe, in real time, the thermally driven nucleation and shape-preserving growth of spiral steps rotating at constant temperature-dependent angular velocities around cores of dislocations terminating on the (111) surface of TiN in the absence of applied external stress or net mass change. We attribute this phenomenon to point-defect migration from the bulk to the surface along dislocation lines. Our results demonstrate that dislocation-mediated surface roughening can occur even in the absence of deposition or evaporation, and provide fundamental insights into mechanisms controlling nanostructural stability.

Transient Mass Transfer and Vortex Bifurcation of an Aerosol Droplet in Motion

An investigation of transient mass transfer in an aerosol droplet is performed in this study. The droplet is suddenly exposed to a polluted flow. Particular emphasis is focused on interfacial momentum and mass transport phenomena. When the aerosol droplet is under a specific Reynolds number (viz., Re g = 120), it is discovered that there is a drastic interaction on the flow field between the gas phase and the liquid phase. Specifically, with increasing time the flow structure in the droplet proceeds from a single vortex to a double vortex and finally back to a single vortex. For the double vortex it is constructed by a primary and a secondary vortex. During the appearance of the secondary vortex, it is called a transient vortex bifurcation. Because of the variation of the flow field described above, the entire solute uptake process is divided into three subperiods, consisting of the initial period (or time lag period), the vortex bifurcation period, and the single vortex period. Furthermore, it is found t...

Dynamic behavior of bubble interface during boiling

A brief review with discussions is conducted for some pertinent works, done and ongoing in the Laboratory of Phase-Change and Interfacial Phenomena at Tsinghua University, on interfacial behavior of vapor bubbles and interfacial transport phenomena during liquid nucleation boiling. From a sequence of experimental investigations, some new phenomena, particularly, the visually observed interfacial transport phenomena or processes including jet-like flows, bubble interaction and spatial scale effect, were described in this article. The interfacial effects and transport phenomena associated with surface tension gradients caused by temperature and concentration variations were theoretically analyzed to reveal the marked influence on bubble interfacial shape and dynamic behavior, the bubble dynamics including nucleation, bubble motion and coalescence. Several theoretical models and methods were proposed to describe the dynamic characteristics and explain the physics of interfacial phenomena/processes. The special emphases were addressed on the mass and heat transfer occurring at the interface of bubbles.

Flow and heat transfer characteristics in the porous wick condenser of CPL

An analytical investigation has been conducted to understand the internal fluid flow and heat transfer in the condenser with porous wick of an innovative capillary pumping loop (CPL) system. A mathematical model is proposed and used to describe the flow and heat transfer, especially interfacial transport phenomena. The liquid-vapor interface of the condensed liquid film was numerically determined. Some factors, such as vapor pressure, wall subcooling, wall heat load and thermofluid properties, have significant influence on the heat transfer process and the shape of liquid-vapor interface. Meanwhile, an experimental facility was setup and an experimental investigation was completed. Theoretical prediction and experimental results show quite good consistence.

A FULL 3-DIMENSIONAL ADAPTIVE FINITE VOLUME SCHEME FOR TRANSPORT AND PHASE-CHANGE PROCESSES, PART I: FORMULATION AND VALIDATION

A full three-dimensional (3-D) numerical formulation for accurate simulation of transport and phase-change processes is presented. These processes are characterized by a variety of flow and heat transfer mechanisms in irregular domains with or without the movement of phase-change interfaces and free surfaces. A generalized 3-D nonorthogonal curvilinear finite volume formulation is developed in conjunction with a robust mesh generation scheme known as multizone adaptive grid generation (MAGG) to tackle such problems. The coupling between the interfacial dynamics and transport phenomena in the bulk of the phases is inherent in this formulation. A 3-D k-epsilon model is also incorporated to tackle the turbulent flows in these applications. The unified numerical model is validated against classical 3-D problems such as turbulent natural convection in a differentially heated cube, solidification in a cavity, and so on. In a companion paper, Part II (see this issue), application of this formulation to 3-D simulation of hydrothermal crystal growth and low and high pressure Czochralski (Cz) crystal growth is presented.

Flow characteristics and circulatory motion in wavy falling films with and without counter-current gas flow

A laser-induced photochromic tracer technique was used to investigate the flow structure in a thin, wavy falling liquid film in a vertical tube both with and without interfacial shear induced by a counter-current flow of gas. Instantaneous velocity profile and film thickness were measured simultaneously to better understand the turbulence characteristics and the enhancement effect of interfacial waves and shear on the heat and mass transfer rates. While surface ripples were found to exert almost no influence on the near-wall hydrodynamics, the large wave effects could easily be sensed close to the solid wall, altering the turbulence intensity profiles. Flow visualization experiments revealed the occurrence of circulatory motions with significant velocities normal to the tube wall under the large waves, which may be the dominant mechanism for wall-to-liquid and interfacial transport phenomena for wavy films.

Glycine and Leucine Transport through a Cation Exchange Membrane in their Mixed Solution: Effects of HCl Concentration on Interfacial Transport.

The glycine and leucine permeability coefficients, Pgly and Pleu, in their mixed solutions through a cation exchange membrane were measured as a function of HCl concentration, CHCl, from 0 to 10-1 mol/l for three different interfacial conditions and were compared with the results for Pgly and Pleu, in their single solutions. Generally Pgly increases with an increase in HCl concentration. However, Pgly decreased between CHCl=10-2mol/l and CHCl=10-1 mol/l for only the case when HCl was added to the amino acid feed side. Compared with Pgly in a single glycine solution, Pgly in a mixed solution was smaller than that in the single solution. However, their profile outlines are similar. Pleu, also increased with an increase in HCl concentration. Pleu, is smaller than that of Pgly, which corresponds with the result in a single solution. Pleu decreased between CHCl=10-2 mol/l and CHCl =10-1 mol/l for only the case when HCl is added to the amino acid feed side. Compared with the Pleu in the single leucine solution, Pleu in mixed solution is not very different. The transport mechanism was determined to be an interfacial transport phenomenon. However, the effect of the interfacial transport in mixed solution appears to be decreased if compared with the case in a single solution. The reduced results for glycine in mixed solutions imply that the glycine transport is affected by that of leucine. As the solutions are not idealistic, which means that there exists an interaction between glycine and leucine, the permeability coefficient ratios of glycine to leucine, Pgly /Pleu, in the mixed solution did not correspond with that of the single solution. The highest Pgly /Pleu was 6.7 at CHCl=10-4mol/l for the case when HCl was added to the amino acid-permeated side and the next one was 6.1 at CHCl=10-4 mol/l for the case when HCl was added to both sides of the membrane.

Analysis of damage formation and propagation in metallic thin films under the action of thermal stresses and electric fields

A quantitative analysis is presented of void formation, morphological stability, and evolution in metallic thin films, which are problems that underlie serious reliability issues in interconnections used in integrated circuits. The analysis is based on the coupling of bulk and interfacial mass transport phenomena with elastic deformations and current stressing. The formation and growth of intergranular voids in bamboo-structure conductor lines due to stresses that develop during processing is investigated. The investigation is aided by self-consistent simulation of bulk and grain-boundary diffusional processes using bicrystal models with elastic grains. A systematic analysis is presented of the morphological evolution of transgranular voids in passivated and unpassivated aluminum lines under current densities that are typical of electromigration testing. The effects of the electric field and surface properties on the morphological stability of voids are examined and morphologies that bifurcate from rounded or wedge-like void shapes are predicted. The theoretical results are discussed in the context of experimental data of void propagation under electromigration conditions.

Use of the electrically driven emulsion-phase contactor for a biphasic liquid-liquid enzyme system

An alternative approach to the operation of bioprocessing systems within non-aqueous environments would require the development of reaction systems that would provide effective interfacial contact between the biocatalyst, contained within an aqueous phase, and the organic phase containing the substrate. A biphasic liquid-liquid (BLL) reactor that provides for intimate liquid-liquid contact would be the most probable approach for this application. For the BLL reactions considered in this work, the overall effectiveness of the system will depend on both compatibility of the biocatalyst with the chemical species present and intrinsic reaction and interfacial transport phenomena typically involved with liquid-liquid operations. The focus of this article is to investigate the removal and oxidation of p-cresol dissolved in toluene by aqueous-phase horseradish peroxidase. Contacting of the liquid-liquid biphasic enzyme system is carried out in an advanced solvent extraction contacting device, the electrically driven emulsion-phase contactor (EPC).

Theory and Computer Simulation of Grain-Boundary and Void Dynamics in Polycrystalline Conductors

AbstractMicrostructure evolution in polycrystalline metallic thin films under stress and electric current underlies many reliability issues in microelectronics. This paper presents a quantitative analysis of grain-boundary and void dynamics based on the coupling between bulk and interfacial mass transport phenomena with elastic deformations and current stressing. The formation and growth of intergranular voids in bamboo-structure conductor lines due to stresses that develop during processing is analyzed. The analysis is aided by self-consistent simulation of bulk and grain-boundary diffusional processes using bicrystal models with elastic grains. A systematic analysis is presented of the morphological evolution of transgranular voids in aluminum lines under current densities that are typical of electromigration testing. The effects of the electric field and surface properties on the morphological stability of voids are examined and morphologies that bifurcate from rounded or wedge-like void shapes are predicted. The theoretical results are discussed in the context of experimental data for void propagation under electromigration conditions.

Investigation of an Evaporating Extended Meniscus Based on the Augmented Young–Laplace Equation

The microscopic details of fluid flow and heat transfer near the contact line of an evaporating extended meniscus of heptane formed between a horizontal substrate and a “washer” were studied at low heat fluxes. The film profile in the contact line region was measured using ellipsometry and microcomputer-enhanced video microscopy, which demonstrated the details of the transition between a nonevaporating superheated flat thin film and an evaporating curved film. Using the augmented Young-Laplace equation, the interfacial properties of the system were initially evaluated in situ and then used to describe the transport processes. New analytical procedures demonstrated the importance of two dimensionless parameters. Both fluid flow and evaporation depend on the intermolecular force field, which is a function of the film profile. The thickness and curvature profiles agreed with the predictions based on interfacial transport phenomena models. The heat flux distribution and the pressure field were obtained. Since there are significant resistances to heat transfer in this small system due to interfacial forces, viscous stresses, and thermal conduction, the “ideal constant heat flux” cannot be attained. The description of the pressure field gives the details of the coupling between the disjoining and capillary pressures.

Boundary layers in crystal growth -Facts and fancy

The term “boundary layer” has become a catch-all expression in discussions of interfacial transport phenomena in crystal growth. It is shown that during the solidification or crystallization of many materials from their melt or solutions, gradients in velocity or concentration, even when locally steep at the respective interface, do not necessarily possess the features of a fluid dynamically well defined boundary layer. In crystal growth from vapors, on the other hand, such gradients often extend essentially over the whole bulk nutrient, i.e. spatial changes are gradual and no narrow layers are formed. Consequently, predictions of crystal growth transport phenomena based on boundary layer models cannot be expected to be accurate. In order for this review to benefit an interdisciplinary readership, the presentation is mostly phenomenological. For further studies of this complex topic, more rigorous and specialized treatments are referenced.

Separated flow modelling and interfacial transport phenomena

Separated flow modelling and interfacial transport phenomena

INTERFACIAL TRANSPORT PHENOMENA INVITED REVIEW

Abstract Interfacial transport phenomena include all effects associated with momentum, energy, and mass transfer at phase interfaces. I shall begin by examining the nature of the phase interface and associated common lines. I then will develop the general balance equations at each point within a phase, at each point on a dividing surface, and at each point on a common line. Mass conservation, momentum transfer, energy transfer, and mass transfer are treated as special cases.

A Surface Renewal Model for Unsteady-State Transfer Processes

A surface renewal model is proposed for the analysis of free or fixed interfacial transport phenomena occurring in transient processes. These processes begin at a certain instant in a turbulent system in hydrodynamic equilibrium. For such a treatment a transient form of the generalized gamma residence time distribution function has been derived, from which the more relevant internal age distribution function has been obtained. Published data on four different systems, three of which pertain to entrance region transfer to fluids in turbulent flow and the fourth to transient heat transfer rates in gas fluidized beds, have been used to confirm the applicability of the dynamic model. The predictive expression relates the ratio of the transient Nusselt or Sherwood number to its respective steady-state value to the product of the ratio of the incomplete to complete gamma functions and a known function of the model parameters. The expression takes the form ▪ where ξ is given by ▪ In the limit of t tending to infinity, ψ becomes unity.

Phosphorus Diffusion in Silicon from a Spin‐on P‐Doped Silicon Oxide Film

A liquid P doping source was prepared by adding P compounds to tetraethylorthosilicate in organic solvent solution. The thicknesses of the spin‐on applied silica films are observed to be linearly proportional to the P concentration in the solution in the range of 1.6–25.0 g/l. In the same range, the plot of vs. P concentration in the solution shows two distinct linear regions. After 40 min of isochronal diffusion under in the temperature range of 850°–1115°C, the plots of vs. change from linear to nonlinear dependence, in the direction approaching independence, as increases. The current diffusion models for a doped oxide source are shown to predict the Si‐silicon oxide interfacial mass transport phenomena only at weight percent and at . The calculated 's, from the Arrhenius plots of and , are in the range of values that have been reported in the literature. Besides showing a dependence, the 's also show a definite data, i.e., and , dependence and a possible temperature dependence.