Fluid Transport Behavior Research Articles

Numerical analysis of thermal fluid transport behavior during electron beam welding of 2219 aluminum alloy plate

A two-dimensional mathematical model based on volume-of-fluid method is proposed to investigate the heat transfer, fluid flow and keyhole dynamics during electron beam welding (EBW) on 20 mm-thick 2219 aluminum alloy plate. In the model, an adaptive heat source model tracking keyhole depth is employed to simulate the heating process of electron beam. Heat and mass transport of different vortexes induced by surface tension, thermo-capillary force, recoil pressure, hydrostatic pressure and thermal buoyancy is coupled with keyhole evolution. A series of physical phenomena involving keyhole drilling, collapse, reopening, quasi-stability, backfilling and the coupled thermal field are analyzed systematically. The results indicate that the decreased heat flux of beam in depth can decelerate the keyholing velocity of recoil pressure and promote the quasi-steady state. Before and close to this state, the keyhole collapses and complicates the fluid transport of vortexes. Finally, all simulation results are validated against experiments.

Effects of elastic anisotropy on primary petroleum migration through buoyancy-driven crack propagation

Material anisotropy may significantly influence the behavior of fluid transport in sedimentary basins and other environments with laminated or foliated rocks. In this paper, we present a fracture mechanics model to investigate primary migration of petroleum (oil and gas) through propagation of a vertical, buoyancy-driven blade crack in a transversely isotropic source rock. The source rock is assumed to have very low permeability and hence can be modeled as a linear elastic medium. Fracture parameters (stress intensity factor and crack opening displacement) are derived using an equivalent set of anisotropic elastic properties. The crack propagation velocity (i.e., petroleum migration velocity) and crack opening (fracture aperture) are determined using a fracture mechanics criterion together with the first order approximation of plane Poiseuille flow equations of fluid mechanics. For subhorizontal layering, we find that the fluid migration velocity and fracture aperture are significantly increased if the elastic modulus in the vertical direction is smaller than that in the horizontal direction. Finally, we discuss the applicability of the formula for isotropic materials along with the equivalent anisotropic elastic parameters introduced in this paper to evaluate fracture aperture for cracks in anisotropic rocks.

Electrochemical Impedance Spectroscopy study on the absorption and evaporation processes in natural stones

Efforts have been made to create new procedures based on Electrochemical Impedance Spectroscopy (EIS) to study several characteristics of cementitious materials with practical interest. Similar approaches can be followed to study other materials, in which the comprehension of their physical, transport-related and durability properties are also needful. Natural stones are one of these materials, wherein such properties play a fundamental role on their performance when in service, in both monumental and non-monumental constructions.This work aims at presenting a first approach on the application of EIS to study electrolyte absorption and evaporation processes in stones. Stones with different porosities and different fluid-transport behaviors were monitored by EIS using a setup of 4 or 2 electrodes assemblies.During absorption, EIS spectra presented two distinct responses according to the frequency, a resistive behaviour and a capacitive slope. The evolution of the spectra showed that the absorption process can be accurately monitored in less porous stones, whereas in more porous stones the procedure still requires some improvements.In what concerns evaporation tests, EIS spectra were more complex, especially for longer periods. At early stages two time constants were poorly detectable, but the evolution of evaporation produced progressive modifications on the spectra and a second time constant became well-resolved, as result of two effects: a gradual loss of contact efficiency and a decrease of moisture within the pores.In both cases EIS enabled to distinguish between different fluid-transport behaviors and showed to be dependent upon the moisture content within the pores and open porosity of each stone variety.

Electric Field Poling Induces Ordered Membrane Morphology Giving Exceedingly High Proton Conductivity

Enhancing ion conductivity is the primary goal in membrane development in fuel cell, lithium battery, vanadium redox flow battery, or energy storage devices involving ion exchange. The challenge grows when requirements are also given to preserve high mechanical strength while improving ion transport property. A common approach proposed to make the break through is by forming inorganic–organic hybrid. Composite with inorganic nanoparticles is found to retain water/moisture through inorganic surface such that it maintains high conductivity and conserved high energy out-put at elevated temperature and at low environment humidity. Though highly important, the issue of membrane morphology has not been addressed sufficiently in order to improve ion conductivity. Membrane morphology is known to be a primary structure factor responsible for fluid transport in semi-permeable membrane. Since ion transportation relies heavily on fluid transport behavior; charge conduction would be also deeply dependant on channel morphology. In present study, a novel approach is proposed to prepare ion conducting membrane by applying electric field poling on Nafion ionomer where one dimension metal oxide (ZrO2, MnO2, TiO2) nanorods and nanotubes are impregnate first. The field induced dipole oriented the low dimensional nanotube/nanorod thus created aligned hydrophilic morphological texture that is fixed after membrane formation. The ordered and oriented nano-structures formed in the direction of the applied electric field, provided a direct and continuous ion path. Proton conductivity has reached 7.5x10-2 S/cm in 100% RH condition when 5 wt% of sulfonated group surface functionalized ZrO2 and TiO2 nanotube is composited with Nafion. Upon applying a DC voltage over 1000V, the conductivity is raised to 8.35x10-2 S/cm. With continue increasing of the electric field to 7000 V/cm, the conductivity in the composite film raised further to a record value of 11.6x10-2S/cm. This is substantially improved over that of commercially available Nafion membrane N117 (5.84x10-2S/cm) or the locally recast Nafion(5.2x10-2S/cm) membrane.Diffusion tensor mapping derived from NMR micro-imagine of these membrane confirmed (1) faster water diffusion as reflected in the stronger diffusion tensor, (2) more ordered tensor orientation (narrowing of Euler angle distribution) along the Z-direction (cross-channel director) , and (3) more homogeneously distributed diffusion tensor in the electric field poled membrane. These results confirmed ordered diffusion in the e-field poled ionomer membranes is indeed responsible for the high proton conductivity. Due to the more ordered morphology originated from the e-field poling, membrane mechanical property is also enhanced. Most interestingly, water uptake is gradually reduced from 24% (without poling) to 21% (with poling at 7000 V/cm). Small angle x-ray diffraction shows the tubular flow channel dimension shrinks after electric field poling. This corroborates with the fact that water swelling ratio is reduced from 30% (without poling) to 11% (with poling at 7000 V/cm). The fact that electric field poling produces membrane with lower water uptake and smaller swelling ratio but displayed high proton conductivity is a surprising find. The results asserted that high proton conductivity can be achieved by effective use of water through synergistic cooperation of direct water permeation channel and well distributed and connected sulfonate groups. The amount of water required to conduct proton can actaully be reduced with membrane morphology optimized. Enhanced fuel cell performance is realized by employing the e-poled membrane with superbly high ion conductivity.

A hollow osteon model for examining its poroelastic behaviors: Mathematically modeling an osteon with different boundary cases

Abstract A single osteon is modeled as a hollow poroelastic annular cylinder to examine its fluid pressure distribution and transport behavior. We propose an extension of the osteon model by considering four types of different boundary conditions that might be encountered in physiological environments or yet-to-be-developed laboratory testing procedures. This model links the external loads to the osteonal fluid pressure and velocity, which may have a significant stimulus to the mechanotransduction of bone remodeling signals. This model can also be used for analyzing other experiments performed on similarly shaped poroelastic specimens. The obtained analytical pressure and velocity solutions demonstrate the effects of the loading conditions and the material parameters. The results show the pore pressure and fluid velocity are both proportionate to the strain amplitude and the frequency. Nevertheless, the key loading role governing the poroelastic response of the osteon is strain rate. At the osteon scale, the pressure is also strongly affected by the material parameter of permeability variations whereas fluid velocity is not.

A population balance-Monte Carlo method for particle coagulation in spatially inhomogeneous systems

Insight into the spatiotemporal evolution of particle size distribution (PSD) is very useful in many natural and engineering systems in which the multiphase fields are spatially inhomogeneous and complicated dynamic processes of particle population, e.g., coagulation between particles, occur with field-dependent rates. Traditional population balance modeling (PBM) is usually used to simulate spatially homogeneous dynamic processes, only obtaining the time evolution of PSD. In this paper, we presented an algorithm to predict the spatiotemporal evolution of PSD accounting for mutual coupling of particle population and hydrodynamics. The differentially-weighted Monte Carlo method for PBM is used to simulate coagulation behavior of particles in each grid that is considered to be spatially homogeneous, and the transport behavior of fluid and particles towards neighbor grids that are spatially inhomogeneous are described by general conservation equations of multiphase flows. The simulation strategy is based on the selection of a time step within which the fluid transport, the particle transport and the particle dynamics are uncoupled and then separately simulated. A limiting case of the coarse high-inertia particles whose motion is independent of surrounding fluid is chosen to validate the population balance-Monte Carlo (PBMC) method for the spatiotemporal evolution of PSD. The computational time is found to be less by a factor of 10 compared to the direct numerical simulation (DNS), yielding reasonably closer predictions of spatiotemporal particle size distributions.

A test of systematic coarse-graining of molecular dynamics simulations: Thermodynamic properties

Coarse-graining (CG) techniques have recently attracted great interest for providing descriptions at a mesoscopic level of resolution that preserve fluid thermodynamic and transport behaviors with a reduced number of degrees of freedom and hence less computational effort. One fundamental question arises: how well and to what extent can a "bottom-up" developed mesoscale model recover the physical properties of a molecular scale system? To answer this question, we explore systematically the properties of a CG model that is developed to represent an intermediate mesoscale model between the atomistic and continuum scales. This CG model aims to reduce the computational cost relative to a full atomistic simulation, and we assess to what extent it is possible to preserve both the thermodynamic and transport properties of an underlying reference all-atom Lennard-Jones (LJ) system. In this paper, only the thermodynamic properties are considered in detail. The transport properties will be examined in subsequent work. To coarse-grain, we first use the iterative Boltzmann inversion (IBI) to determine a CG potential for a (1-φ)N mesoscale particle system, where φ is the degree of coarse-graining, so as to reproduce the radial distribution function (RDF) of an N atomic particle system. Even though the uniqueness theorem guarantees a one to one relationship between the RDF and an effective pairwise potential, we find that RDFs are insensitive to the long-range part of the IBI-determined potentials, which provides some significant flexibility in further matching other properties. We then propose a reformulation of IBI as a robust minimization procedure that enables simultaneous matching of the RDF and the fluid pressure. We find that this new method mainly changes the attractive tail region of the CG potentials, and it improves the isothermal compressibility relative to pure IBI. We also find that there are optimal interaction cutoff lengths for the CG system, as a function of φ, that are required to attain an adequate potential while maintaining computational speedup. To demonstrate the universality of the method, we test a range of state points for the LJ liquid as well as several LJ chain fluids.

The effects of Haversian fluid pressure and harmonic axial loading on the poroelastic behaviors of a single osteon

In order to well understand the mechanism of the mechanotransduction in bone, we propose a new model of transverse isotropic and poroelastic osteon cylinder considering Haversian fluid pressure. The analytical pore pressure and velocity solutions are obtained to examine the fluid transport behavior and pressure distribution in a loaded osteon on two different exterior surface cases. Case I is stress free and fully permeable and case II is impermeable. The following are the results obtained. (i) The Haversian fluid may not be ignored because it can enlarge the whole osteonal fluid pressure field, and it bears the external loads together with the solid skeleton. (ii) The increase of both axial strain amplitude and frequency can result in the increase of fluid pressure and velocity amplitudes, while in case II, the frequency has little effect on the fluid pressure amplitude. (iii) Under the same loading conditions, the pressure amplitude in case II is larger than that in case I, while the velocity amplitude is smaller than that in case I. This model permits the linking of the external loads to the osteonal fluid pressure and velocity, which may be a stimulus to the mechanotransduction of bone remodeling signals.

Multiscale method for characterization of porous microstructures and their impact on macroscopic effective permeability

AbstractRecent technology advancements on X‐ray computed tomography (X‐ray CT) offer a nondestructive approach to extract complex three‐dimensional geometries with details as small as a few microns in size. This new technology opens the door to study the interplay between microscopic properties (e.g. porosity) and macroscopic fluid transport properties (e.g. permeability). To take full advantage of X‐ray CT, we introduce a multiscale framework that relates macroscopic fluid transport behavior not only to porosity but also to other important microstructural attributes, such as occluded/connected porosity and geometrical tortuosity, which are extracted using new computational techniques from digital images of porous materials. In particular, we introduce level set methods, and concepts from graph theory, to determine the geometrical tortuosity and connected porosity, while using a lattice Boltzmann/finite element scheme to obtain homogenized effective permeability at specimen‐scale. We showcase the applicability and efficiency of this multiscale framework by two examples, one using a synthetic array and another using a sample of natural sandstone with complex pore structure. Copyright © 2011 John Wiley & Sons, Ltd.

Prediction of the viscosity of water confined in carbon nanotubes

In this paper, the viscosity of water confined in single-walled carbon nanotubes (SWCNTs) with the diameter ranging from 8 to 54 A is evaluated, which is crucial for the research on the nanoflow but difficult to be obtained. An “Eyring-MD” (molecular dynamics) method combining the Eyring theory of viscosity with the MD simulations is proposed to tackle the particular problems. For the critical energy which is a parameter in the “Eyring-MD” method, the numerical experiment is adopted to explore its dependence on the temperature and the potential energy. To demonstrate the feasibility of the proposed method, the viscosity of water at high pressure is computed and the results are in reasonable agreement with the experimental results. The computational results indicate that the viscosity of water inside SWCNTs increases nonlinearly with enlarging diameter of SWCNTs, which can reflect the size effect on the transports capability of the SWCNTs. The trend of the viscosity is well explained by the variation of the hydrogen bond of the water inside SWCNTs. A fitting equation of the viscosity of the confined water is given, which should be significant for recognizing and studying the transport behavior of fluid through the nanochannels.

Limitation of Finite Element Analysis of Poroelastic Behavior of Biological Tissues Undergoing Rapid Loading

The finite element method is used in biomechanics to provide numerical solutions to simulations of structures having complex geometry and spatially differing material properties. Time-varying load deformation behaviors can result from solid viscoelasticity as well as viscous fluid flow through porous materials. Finite element poroelastic analysis of rapidly loaded slow-draining materials may be ill-conditioned, but this problem is not widely known in the biomechanics field. It appears as instabilities in the calculation of interstitial fluid pressures, especially near boundaries and between different materials. Accurate solutions can require impractical compromises between mesh size and time steps. This article investigates the constraints imposed by this problem on tissues representative of the intervertebral disc, subjected to moderate physiological rates of deformation. Two test cylindrical structures were found to require over 10(4) linear displacement-constant pressure elements to avoid serious oscillations in calculated fluid pressure. Fewer Taylor-Hood (quadratic displacement-linear pressure elements) were required, but with complementary increases in computational costs. The Vermeer-Verruijt criterion for 1D mesh size provided guidelines for 3D mesh sizes for given time steps. Pressure instabilities may impose limitations on the use of the finite element method for simulating fluid transport behaviors of biological soft tissues at moderately rapid physiological loading rates.

Effects of partial and full pipe flow on hydrochemographs of Logsdon river, Mammoth Cave Kentucky USA

Summary Logsdon River, within Kentucky’s Mammoth Cave System, drains the 25 km2 Cave City groundwater basin. Temperature, specific conductance, stage, and velocity were measured at the river’s downstream end within the cave with 2-min resolution for one year beginning on May 5, 1995. New interpretation of these data show relationships to the conduit’s geometry and fluid transport behavior. The 37 observed storm hydrographs/chemographs are classified into two groups: open channel flow and pipe flow (conduit filled). In the 16 pipe flow events Logsdon River exceeded the capacity of its conduit, raising the water table above the conduit ceiling with some storm water thus temporarily stored within the aquifer adjacent to the conduit. Pipe flow events were characterized by depression of specific conductance (spC) before peak discharge, a peak in spC at peak discharge, and a second depression in spC after peak discharge. The first spC minimum represents the maximum concentration of passing storm water and the second is interpreted as the result of recent storm water draining back into the conduit, having been temporarily stored in the aquifer adjacent to the conduit. Mean velocity decreases in the transition from partial to full pipe flow due to increased head loss at full pipe flow compared to nearly full pipe flow. Each of the open channel flow cases shows a depression in spC either coincident with, or after, peak discharge. While the hydrochemographs of pipe flow are mainly controlled by the aquifer conduit network geometry, in open channel cases they are mainly controlled by external recharge conditions, including behavior of sinking streams.

Coupled Heat and Moisture Transport in Concrete at Elevated Temperatures—Effects of Capillary Pressure and Adsorbed Water

ABSTRACT The importance of capillary pressure and adsorbed water in the behavior of heat and moisture transport in concrete exposed to high temperatures is explored by incorporating their behavior explicitly into a computational model. The inclusion of these two phenomena is realized with a formulation of a modified model, which represents an extension to the significant work of Tenchev et al. Comparative studies were carried out, using a benchmark problem, and it was determined that while the Tenchev formulation underestimated the capacity for fluid transport in the concrete, resulting in an overprediction of pore pressures (which may affect the prediction of mechanical damage and spalling), the inclusion of capillary pressure had little effect on the results. More important was the accurate representation of the free water flux, which has a significant effect on the prediction of vapor content and subsequently pore pressure. It was furthermore found that, while the adsorbed water flux may be minimal when concrete is exposed to high temperature, its presence has a significant effect on the fluid transport behavior and the prediction of pore pressures.

Large limits of electrical efficiency in hydrocarbon fueled SOFCs

This paper develops a model for the study of solid oxide fuel cell (SOFC) electrical efficiency. The chemically reacting flow model considers the coupled behavior of fluid mechanics, thermodynamic equilibrium, and transport of electroactive species through the electrolyte. Fuel cells are treated as plug flow tubular reactors with no upstream diffusion. Minimization of free energy is used to calculate gas composition along the length of the fuel channel without specifying a set of reactions. The model serves to place an upper bound on electrical efficiencies. The usefulness of the model is demonstrated by simulating SOFC electrical efficiency as a function of operating voltage for in situ reforming of four different fuel mixtures, including steam reforming and partial oxidation of CH 4, syngas, and pure CH 4.

Critical behavior of transport in sea ice

Geophysical materials such as sea ice, rocks, soils, snow, and glacial ice are composite media with complex, random microstructures. The effective fluid, gas, thermal, and electromagnetic transport properties of these materials play an important role in the large-scale dynamics and behavior of many geophysical systems. A striking feature of such media is that subtle changes in microstructural characteristics can induce changes over many orders of magnitude in the transport properties of the materials, which in turn can have significant large-scale geophysical effects. For example, sea ice, which mediates energy transfer between the ocean and atmosphere, plays a key role in global climate, and serves as an indicator of climatic change, is a porous composite of ice, brine and gases. Relevant length scales range from microns and millimeters for individual brine structures, to centimeters and meters for connected brine channels across floes, to hundreds of kilometers across an ice pack. Sea ice is distinguished from many other porous composites, such as sandstones or bone, in that its microstructure and bulk material properties can vary dramatically over a relatively small temperature range. The fluid permeability of sea ice ranges over six orders of magnitude for temperatures between 0°C and −25°C. Moreover, small changes in brine volume fraction around a threshold value of about 5%, corresponding to variations in temperature around a critical point of about −5°C, control an important transition between low and high fluid permeability regimes. Below this critical temperature, the sea ice is effectively impermeable, while for higher temperatures the brine phase becomes connected over macroscopic scales, allowing fluid transport through the ice. This transition has been observed to impact a wide range of phenomena such as surface flooding and snow–ice formation, enhancement of heat transfer due to fluid motion, mixing in the upper ocean, melt pool persistence, surface albedo (ratio of reflected to incident radiation) and other optical properties, growth and nutrient replenishment of algal and bacterial communities living in sea ice, and remote sensing of the sea ice pack from space. Recently, we have shown how continuum percolation theory can be used to understand the critical behavior of fluid transport in sea ice. Here we review this application of percolation theory to sea ice, and briefly discuss electromagnetic transport in sea ice, in particular how the geometry and connectivity of the brine microstructure determine its effective complex permittivity.

Brine percolation and the transport properties of sea ice

AbstractSea ice is distinguished from many other porous composites, such as sandstones or bone, in that its microstructure and bulk material properties can vary dramatically over a small temperature range. For brine-volume fractions below a critical value of about 5%, which corresponds to a critical temperature of about −5°C for salinity of 5 ppt, columnar sea ice is effectively impermeable to fluid transport. For higher brine volumes, the brine phase becomes connected and the sea ice is permeable, allowing transport of brine, sea water, nutrients, biomass and heat through the ice. Over the past several years it has been found that brine transport is fundamental to such processes as sea-ice production through freezing of flooded ice surfaces, the enhancement of thermal and salt fluxes through sea ice, nutrient replenishment for sea-ice algal communities, and to sea-ice remote sensing. Motivated by these observations, recently we have shown how percolation theory can be used to understand the critical behavior of fluid transport in sea ice. We applied a percolation model developed for compressed powders of large polymer particles with much smaller metal particles, which explains the observed behavior of the fluid permeability in the critical temperature regime, as well as Antarctic data on surface flooding and algal growth rates. Moreover, the connectedness properties of the brine phase play a significant role in the microwave signature of sea ice through its effective complex permittivity and surface flooding. Here we review our recent results on brine percolation and its role in understanding the fluid and electromagnetic transport properties of sea ice. We also briefly report on measurements of percolation we made on first-year sea ice during the winter 1999 Mertz Glacier Polynya Experiment.

Laboratory investigation of matrix imbibition from a flowing fracture

Predicting fluid flow and transport behavior in unsaturated, fractured rock is greatly simplified where matrix imbibition can be modeled as a linear function of the square root of time (t1/2); however, such treatment implicitly assumes homogenous matrix properties. To investigate matrix heterogeneity effects, we perform a simple experiment in which x‐ray imaging is used to measure the imbibition of water from a flowing fracture into a slab of volcanic tuff. Experimental results show matrix imbibition to follow a linear t1/2 relationship even though the saturated hydraulic conductivity of the tuff varies by over four orders of magnitude.

A continuum model for momentum, heat and species transport in binary solid-liquid phase change systems—II. Application to solidification in a rectangular cavity

A newly developed continuum model has been used with a well-established control-volume-based, finite-difference scheme to investigate solidification of a binary, aqueous ammonium chloride solution in a rectangular cavity. Advective transport of water enriched interdendritic fluids across the permeable liquidus interface has been identified as the primary mechanism for macroscopic species redistribution. The extent of this penetration is governed by the relative strengths of solutally driven mushy region flows and thermally driven flows in the bulk liquid. Unstable and double-diffusive conditions which accompany the discharge of interdendritic fluids into the liquid core have been shown to result in localized growth rate variations, remelting, and fluctuating bulk fluid transport behavior.