This document summarizes a study investigating the effect of varying interaction strength between nanotube atoms and water on water transport through nanotubes. The study finds that there is a narrow transition region, between εNT-OW of 0.05 to 0.075 kcal/mol, where water occupancy and flux through nanotubes increases dramatically with increasing interaction strength. Within this transition region, the change becomes more abrupt with increasing nanotube diameter. Interestingly, this transition region corresponds to water contact angles close to 90 degrees on an unrolled nanotube surface, indicating a link between nanotube wetting and water transport. The observed water flux is proportional to average water occupancy divided by average residence time, with a constant
This document summarizes a computational simulation of inertial effects on low Reynolds number microfluidic flow using COMSOL Multiphysics software. The simulation models two-phase immiscible fluid flow through an S-shaped microchannel. It was found that microfluidic turbulence increased as inlet velocity decreased. Even at very low velocities of 1 micron/second, vortex shedding and interface breaking were observed, demonstrating that inertial effects can induce instability in laminar microscale flows. The computational results provide insight into inertial effects on two-phase microfluidic flows that can be validated through future microchip fabrication and testing.
This document summarizes a study investigating the kinetics of the first hole transfer step in the photocatalytic water oxidation reaction at the interface between n-type strontium titanate (n-SrTiO3) and hydroxyl ions (OH-) in water. Using transient optical spectroscopy of a photoelectrochemical cell, the researchers were able to determine the kinetics as a function of the surface hole potential and separate the first hole transfer step from subsequent steps. They found the kinetics followed a single exponential dependence on surface hole potential, with time constants ranging from 3 ns to 8 ps over a 1 V change in potential. This allowed them to quantify the activation barrier for the first hole transfer step and extrapolate the rate constant when
Penga Ž, Tolj I, Barbir F, Computational fluid dynamics study of PEM fuel cel...Željko Penga
This computational fluid dynamics study examines PEM fuel cell performance under isothermal and non-uniform temperature boundary conditions. The study finds that implementing a non-uniform temperature profile along the cathode channel, as calculated from a Mollier h-u chart, results in close to 100% relative humidity without external humidification and improves fuel cell performance. The model polarization curve and relative humidity distribution agree well with experimental results. Different current collector materials and membrane thickness influence temperature and relative humidity distributions through their effects on thermal conductivity and water transport.
Experimental investigation on thermo physical properties of single walled car...Sabiha Akter Monny
This document experimentally investigates the thermo physical properties of single walled carbon nanotube (SWCNT) nanofluids. Stable SWCNT nanofluids were prepared with concentrations of 0.05-0.25% volume using sodium dodecyl sulfate as a surfactant. Thermal conductivity was measured to increase from 0.615-0.892 W/m K, viscosity increased from 0.67-1.28 mPa s, and specific heat increased from 2.97-3.90 kJ/kg °C as temperature and concentration increased. The maximum 36.39% enhancement in thermal conductivity over water was observed at 0.25% concentration and 60°C. Viscosity exhibited
Experimental Study on the Settling Velocity of
Coastal Mud in Quiescent Water: The Case of
Huangmaohai Estuary, South China Sea by Dong XU in Examines in Marine Biology and Oceanography: Open Access
Molecular Mean-Field Theory of Ionic Solutions: a Poisson-Nernst-Planck-Biker...Bob Eisenberg
We have developed a molecular mean-field theory — fourth-order Poisson-
Nernst-Planck-Bikerman theory — for modeling ionic and water flows in biological ion channels
by treating ions and water molecules of any volume and shape with interstitial voids,
polarization of water, and ion-ion and ion-water correlations. The theory can also be used to
study thermodynamic and electrokinetic properties of electrolyte solutions in batteries, fuel
cells, nanopores, porous media including cement, geothermal brines, the oceanic system, etc.
The theory can compute electric and steric energies from all atoms in a protein and all ions
and water molecules in a channel pore while keeping electrolyte solutions in the extra- and
intracellular baths as a continuum dielectric medium with complex properties that mimic
experimental data. The theory has been verified with experiments and molecular dynamics
data from the gramicidin A channel, L-type calcium channel, potassium channel, and
sodium/calcium exchanger with real structures from the Protein Data Bank. It was also
verified with the experimental or Monte Carlo data of electric double-layer differential capacitance
and ion activities in aqueous electrolyte solutions. We give an in-depth review of
the literature about the most novel properties of the theory, namely, Fermi distributions of
water and ions as classical particles with excluded volumes and dynamic correlations that
depend on salt concentration, composition, temperature, pressure, far-field boundary conditions
etc. in a complex and complicated way as reported in a wide range of experiments.
The dynamic correlations are self-consistent output functions from a fourth-order differential
operator that describes ion-ion and ion-water correlations, the dielectric response (permit2
tivity) of ionic solutions, and the polarization of water molecules with a single correlation
length parameter.
1. INTRODUCTION
Water and ions give life. Their electrostatic and kinetic interactions play essential roles
in biological and chemical systems such as DNA, proteins, ion channels, cell membranes,
Giant convecting mud balls of the early solar systemSérgio Sacani
Carbonaceous asteroids may have been the precursors to the terrestrial planets, yet despite their importance,
numerous attempts to model their early solar system geological history have not converged on a solution. The
assumption has been that hydrothermal alteration was occurring in rocky asteroids with material properties similar
to meteorites. However, these bodies would have accreted as a high-porosity aggregate of igneous clasts
(chondrules) and fine-grained primordial dust, with ice filling much of the pore space. Short-lived radionuclides
melted the ice, and aqueous alteration of anhydrous minerals followed. However, at the moment when the ice
melted, no geological process had acted to lithify this material. It would have been a mud, rather than a rock.
We tested the effect of removing the assumption of lithification. We find that if the body accretes unsorted chondrules,
then large-scale mud convection is capable of producing a size-sorted chondrule population (if the body
accretes an aerodynamically sorted chondrule population, then no further sorting occurs). Mud convection both
moderates internal temperature and reduces variation in temperature throughout the object. As the system is
thoroughly mixed, soluble elements are not fractionated, preserving primitive chemistry. Isotopic and redox heterogeneity
in secondary phases over short length scales is expected, as individual particles experience a range of
temperature and water-rock histories until they are brought together in their final configuration at the end of
convection. These results are consistent with observations from aqueously altered meteorites (CI and CM chondrites)
and spectra of primitive asteroids. The “mudball” model appears to be a general solution: Bodies spanning a
×1000 mass range show similar behavior.
This document summarizes a computational simulation of inertial effects on low Reynolds number microfluidic flow using COMSOL Multiphysics software. The simulation models two-phase immiscible fluid flow through an S-shaped microchannel. It was found that microfluidic turbulence increased as inlet velocity decreased. Even at very low velocities of 1 micron/second, vortex shedding and interface breaking were observed, demonstrating that inertial effects can induce instability in laminar microscale flows. The computational results provide insight into inertial effects on two-phase microfluidic flows that can be validated through future microchip fabrication and testing.
This document summarizes a study investigating the kinetics of the first hole transfer step in the photocatalytic water oxidation reaction at the interface between n-type strontium titanate (n-SrTiO3) and hydroxyl ions (OH-) in water. Using transient optical spectroscopy of a photoelectrochemical cell, the researchers were able to determine the kinetics as a function of the surface hole potential and separate the first hole transfer step from subsequent steps. They found the kinetics followed a single exponential dependence on surface hole potential, with time constants ranging from 3 ns to 8 ps over a 1 V change in potential. This allowed them to quantify the activation barrier for the first hole transfer step and extrapolate the rate constant when
Penga Ž, Tolj I, Barbir F, Computational fluid dynamics study of PEM fuel cel...Željko Penga
This computational fluid dynamics study examines PEM fuel cell performance under isothermal and non-uniform temperature boundary conditions. The study finds that implementing a non-uniform temperature profile along the cathode channel, as calculated from a Mollier h-u chart, results in close to 100% relative humidity without external humidification and improves fuel cell performance. The model polarization curve and relative humidity distribution agree well with experimental results. Different current collector materials and membrane thickness influence temperature and relative humidity distributions through their effects on thermal conductivity and water transport.
Experimental investigation on thermo physical properties of single walled car...Sabiha Akter Monny
This document experimentally investigates the thermo physical properties of single walled carbon nanotube (SWCNT) nanofluids. Stable SWCNT nanofluids were prepared with concentrations of 0.05-0.25% volume using sodium dodecyl sulfate as a surfactant. Thermal conductivity was measured to increase from 0.615-0.892 W/m K, viscosity increased from 0.67-1.28 mPa s, and specific heat increased from 2.97-3.90 kJ/kg °C as temperature and concentration increased. The maximum 36.39% enhancement in thermal conductivity over water was observed at 0.25% concentration and 60°C. Viscosity exhibited
Experimental Study on the Settling Velocity of
Coastal Mud in Quiescent Water: The Case of
Huangmaohai Estuary, South China Sea by Dong XU in Examines in Marine Biology and Oceanography: Open Access
Molecular Mean-Field Theory of Ionic Solutions: a Poisson-Nernst-Planck-Biker...Bob Eisenberg
We have developed a molecular mean-field theory — fourth-order Poisson-
Nernst-Planck-Bikerman theory — for modeling ionic and water flows in biological ion channels
by treating ions and water molecules of any volume and shape with interstitial voids,
polarization of water, and ion-ion and ion-water correlations. The theory can also be used to
study thermodynamic and electrokinetic properties of electrolyte solutions in batteries, fuel
cells, nanopores, porous media including cement, geothermal brines, the oceanic system, etc.
The theory can compute electric and steric energies from all atoms in a protein and all ions
and water molecules in a channel pore while keeping electrolyte solutions in the extra- and
intracellular baths as a continuum dielectric medium with complex properties that mimic
experimental data. The theory has been verified with experiments and molecular dynamics
data from the gramicidin A channel, L-type calcium channel, potassium channel, and
sodium/calcium exchanger with real structures from the Protein Data Bank. It was also
verified with the experimental or Monte Carlo data of electric double-layer differential capacitance
and ion activities in aqueous electrolyte solutions. We give an in-depth review of
the literature about the most novel properties of the theory, namely, Fermi distributions of
water and ions as classical particles with excluded volumes and dynamic correlations that
depend on salt concentration, composition, temperature, pressure, far-field boundary conditions
etc. in a complex and complicated way as reported in a wide range of experiments.
The dynamic correlations are self-consistent output functions from a fourth-order differential
operator that describes ion-ion and ion-water correlations, the dielectric response (permit2
tivity) of ionic solutions, and the polarization of water molecules with a single correlation
length parameter.
1. INTRODUCTION
Water and ions give life. Their electrostatic and kinetic interactions play essential roles
in biological and chemical systems such as DNA, proteins, ion channels, cell membranes,
Giant convecting mud balls of the early solar systemSérgio Sacani
Carbonaceous asteroids may have been the precursors to the terrestrial planets, yet despite their importance,
numerous attempts to model their early solar system geological history have not converged on a solution. The
assumption has been that hydrothermal alteration was occurring in rocky asteroids with material properties similar
to meteorites. However, these bodies would have accreted as a high-porosity aggregate of igneous clasts
(chondrules) and fine-grained primordial dust, with ice filling much of the pore space. Short-lived radionuclides
melted the ice, and aqueous alteration of anhydrous minerals followed. However, at the moment when the ice
melted, no geological process had acted to lithify this material. It would have been a mud, rather than a rock.
We tested the effect of removing the assumption of lithification. We find that if the body accretes unsorted chondrules,
then large-scale mud convection is capable of producing a size-sorted chondrule population (if the body
accretes an aerodynamically sorted chondrule population, then no further sorting occurs). Mud convection both
moderates internal temperature and reduces variation in temperature throughout the object. As the system is
thoroughly mixed, soluble elements are not fractionated, preserving primitive chemistry. Isotopic and redox heterogeneity
in secondary phases over short length scales is expected, as individual particles experience a range of
temperature and water-rock histories until they are brought together in their final configuration at the end of
convection. These results are consistent with observations from aqueously altered meteorites (CI and CM chondrites)
and spectra of primitive asteroids. The “mudball” model appears to be a general solution: Bodies spanning a
×1000 mass range show similar behavior.
On Similarity of Differential Capacity and Capillary Pressure FractalKhalid Al-Khidir
On Similarity of Differential Capacity and Capillary Pressure Fractal Dimensions for Characterizing Shajara Reservoirs of the Permo-Carboniferous Shajara Formation, Saudi Arabia
This document describes a dissertation on model-data integration for predictive assessment of groundwater reactive transport systems. Specifically, it develops reactive transport models to predict groundwater contamination at a field site where a permeable reactive barrier (PRB) using zero-valent iron is installed. Key challenges addressed include quantifying and reducing conceptual model uncertainty, integrating different types of field data using multivariate methods, and characterizing spatial heterogeneity to estimate model parameters from field measurements.
Applications of colloidal gas aphrons for pollution remediationSoumyadeep Mukherjee
This document discusses the application of colloidal gas aphrons (CGAs) for pollution remediation. CGAs are spherical microbubbles coated with surfactant that can be used to separate contaminants from water and soil. The document reviews techniques for generating CGAs and their uses in pollution removal processes. CGAs function through mechanisms such as bubble-entrained flocculation, electrostatic interactions, gas diffusion from trapped bubbles, and pollutant hydrophobicity. Tables are provided comparing CGA generation technologies and the effectiveness of different pollution remediation applications.
This document summarizes a study that measured the flux of methylmercury (MMHg) across the sediment-water interface at four stations in Boston Harbor. The stations varied in infaunal population densities and bioirrigation intensities. Total MMHg fluxes, measured using sediment core incubations, ranged from -4 to 191 pmol/m2/day and were strongly correlated with burrow densities. Estimated diffusive fluxes, based on porewater MMHg gradients, were lower than total fluxes at three stations, indicating bioirrigation enhances MMHg exchange over molecular diffusion. Porewater exchange of both MMHg and radon, a porewater tracer, increased with burrow density, suggesting burrows enhance both MMHg production
The document summarizes an experiment that measured the advection and dispersion of dye in a simulated river system under room temperature and ice water conditions. Key findings include:
1) Dye dispersed faster and mixed homogenously in room temperature water, but stratified between temperature layers and dispersed more slowly in ice water.
2) Modeling of the data found best fit when the ice water flow rate was decreased to represent stratification, as the model assumed homogeneous mixing.
3) The experiment supported the hypothesis that residence time would be higher and dispersion lower in cold water, though dye stratified rather than mixing as initially predicted.
A Critical Study of Water Loss in Canals and its Reduction MeasuresIJERA Editor
Water is a very precious natural resource. When this precious resource moves through the canals certain part of the water is lost by seepage, evaporation etc. This loss is known as conveyance loss. The conveyance loss was calculated experimentally by different researcher on different canals around the world. In this paper author have tried to review some of the research work and recommend an average water loss from the canal irrespective of the soil and other environmental condition. There are different materials which have been used in canal lining to reduce this water loss. No such material can be said it is the best material for reducing water loss because it depends on the site and its environmental condition. Now a days geosynthetic alone or geosynthetic with concrete or precast concrete is used to for canal lining in this paper they have tried to see the strength, durability etc. of different geosynthetic material and its application in canal lining.
Mesoscopic simulation of incompressible fluid flow in porous mediaeSAT Journals
Abstract
Lattice Boltzmann method is used to simulate cavity driven fluid flow in porous media. A square cavity is considered with the top
lid moving with uniform velocity and other sides kept stationary. Simulation is carried out for values of Darcy number ranging
from 10-6 to10-2 at Reynolds number 10 and 100. Influence of Darcy number and Reynolds number is investigated on velocity
profiles and the streamline plots. Half-way bounce back boundary conditions are employed in the numerical simulation. The
numerical code is first verified with the results available in the literature and then used to simulate the Newtonian fluid flow in
porous media. The Darcy number and the Reynolds number were observed to have great influence on the flow properties and the
location of the primary vortex. Simulation was carried out for a 100100 mesh grid and a fine agreement is established theories
in incompressible fluid flow.
Keywords: Lattice Boltzmann method, incompressible flow, porous media
Measuring Hydrualic Conductivity Using Petro Physical Measurements 2013 compa...Christopher Estevez
This summary provides the key points from the document in 3 sentences:
The document discusses various methods for measuring hydraulic conductivity in soils more accurately in the field, including using gravitational methods for saturated soils and the Proportional Cylinder and Arya-Dierolf models for unsaturated soils. It analyzes modifying Darcy's law to account for centrifugal force when measuring saturated soils and how the Proportional Cylinder and Arya-Dierolf models can help determine unsaturated pore size and estimate hydraulic conductivity. Accurately measuring hydraulic conductivity is important for environmental cleanup efforts to more efficiently remove contaminants from lands.
Number of moles fractal dimensions for characterizing shajara reservoirs of t...Khalid Al-Khidir
This document summarizes a research article that calculates fractal dimensions from the relationship between number of moles, maximum number of moles, and wetting phase saturation in sandstone samples from the Shajara Formation in Saudi Arabia. Porosity was measured on samples and permeability was derived from capillary pressure data. Two equations were used to calculate fractal dimensions from number of moles and from capillary pressure relationships. Results showed similarity between the two fractal dimensions. Samples with a wide range of pore radii had higher fractal dimensions, reflecting greater connectivity and ability to accommodate more moles. The formation was divided into three reservoir units based on fractal dimensions. Higher fractal dimensions indicated higher heterogeneity and permeability, characterizing better reservoirs
This document summarizes a study that used lattice Boltzmann methods to simulate fluid flow through porous media. The study varied the Darcy number from 10-6 to 10-2 and the Reynolds number at 10 and 100 to observe their effects. Velocity profiles and streamline plots were produced from the simulations. Decreasing the Darcy number, which represents permeability, was found to significantly influence the flow properties and location of primary vortices within the porous media. The numerical simulations agreed well with existing theories on incompressible fluid flow.
Unsteady state series CSTR modeling of removal of ammonia nitrogen from domes...IJECEIAES
This document describes modeling the removal of ammonia nitrogen from domestic wastewater treated in an unsaturated vertical flow constructed wetland (VFCW) using an unsteady state series continuous stirred tank reactor (CSTR) model. The model is based on a mass balance for ammonium and nitrate/nitrite concentrations using one to three CSTRs. The model parameters are estimated to minimize errors between model outputs and measured inlet and outlet concentrations. Various model configurations are evaluated based on the coefficient of determination, including the number of CSTRs, whether reactions occur in multiple CSTRs, using equal or different reaction rates, and discretizing reaction rates.
The document presents an analytical solution for modeling groundwater flow in a multi-aquifer system considering vertical flow in the wellbore and well loss due to friction. It extends a previous single aquifer solution to consider two interconnected aquifers separated by an aquiclude. Simultaneous equations are formulated using Bernoulli's theorem under hydrostatic conditions to compute water flow between the two aquifers and well for both steady and unsteady well water level conditions. The solution technique aims to more scientifically and economically characterize parameters in multi-aquifer systems compared to previous approaches that treated interconnected aquifers as isolated.
On Modeling Water Transport in Polymer Electrolyte Membrane Fuel Cell_Crimson...Crimson_Biostatistics
This document discusses modeling water transport in polymer electrolyte membrane fuel cells (PEMFCs). It begins by providing background on fuel cells and their components. It then discusses challenges related to water management and flooding in PEMFCs. Several existing continuum and pore-scale models for predicting water transport are reviewed, noting limitations like computational expense. The document proposes a new approach using a volume averaging technique to develop a two-dimensional macroscale model from three-dimensional microscopic equations. This new model represents an improvement over prior reduced continuum models by developing a more accurate closure model for mass exchange between layers. The goal is to use this new model to better understand water flooding and optimize fuel cell performance and durability.
The document discusses assessing relative permeabilities in geothermal reservoirs through analyzing the effect of gravity on relative permeabilities, performing laboratory measurements using real geothermal fluids, and calculating relative permeabilities from field data at several geothermal fields in Iceland. The results showed differences in relative permeabilities with flow direction and magnitude, and that wells within the same field can follow different relative permeability curves. Comparisons were made between laboratory and field measurements.
Effect of Height and Surface Roughness of a Broad Crested Weir on the Dischar...RafidAlboresha
Weir is usually incorporated as control or regulation devices in hydraulic systems,
with flow measurement as their secondary. It is normally intended for use in the field and thus
to regulate broad discharges. Broad-Crested weir is among the oldest common weir types. In this
paper, the effect of height and surface roughness for different Board Crested weirs models were
studied on discharge coefficient (Cd) in a horizontal open channel. In the crest of the weir,
certain materials may be combined with concrete (e.g., boulders) or may be used as cladding to
minimize the effect of water overflow (e.g. stone). The weir surface should not be considered
smooth in this case, and the discharge coefficient (Cd) must be re-estimated. For these purposes, laboratory flume was used to study the effect of height and surface roughness on the discharge coefficients with four of the different weir models dimensions of the concrete blocks. In this study, the flow conditions were considered to be free water flow and the viscosity effect was neglected. In all cases, the weir height effect was directly proportional to the discharge coefficient while the surface roughness effect was found to be inversely proportional to the coefficient Cd of the case study.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
1) The document analytically solves the nonisothermal Buckley-Leverett problem for two-phase immiscible flow in porous media including a tracer component and temperature effects.
2) Mass balances for the fluids and tracer and a convective heat balance equation are formulated and solved using the method of characteristics.
3) The solutions can be used to analyze pressure transients, interpret formation testing, calculate temperature front propagation during waterflooding, and benchmark simulators.
Modelling study of jet metal interaction in ld processeSAT Journals
Abstract Water model experiments have been carried out in a 1/30th scaled down model of the 100 ton LD converter in order to investigate the effect of changing the lance height and the gas flow rate on the penetration depth of liquid with different exit diameters. It is found the penetration depth increases with decreasing nozzle diameter, decreasing the lance height and with increase the gas flow rate. Gas jets impinging onto a gas–liquid interface of a liquid pool are also studied using computational fluid dynamics modeling, which aims to obtain a better understanding of the behavior of the gas jets. The gas and liquid flows are modeled using the volume of fluid technique. The governing equations in the axisymmetric cylindrical coordinates are solved by the CFD simulation using FLUENT. The computed results are compared with experimental result and it isfound a good match with all the data. Keywords: LD process, Water Modeling, Penetration Depth, Volume of Fluid, CFD.
This computational fluid dynamics study used simulations to analyze the effect of bend radius on erosion magnitude and location in an S-bend pipe carrying gas-solid or liquid-solid flows. Simulations were run for air velocities of 15.24-45.72 m/s and water velocities of 0.1-10 m/s, with particle sizes of 50-300 microns and bend radius to pipe diameter ratios (r/D) of 1.5, 2.5, and 3.5. Maximum erosion was found at certain velocity-particle size combinations and occurred at specific angle locations within each bend. The simulations aim to provide insight on erosion behavior to inform pipe design and operating conditions.
Hydrate Formation During Transport of Natural Gas Containing Water And Impuri...IJERDJOURNAL
ABSTRACT: The upper limit of water content permitted in a natural gas stream during its pipeline transport without a risk of hydrate formation is a complex issue. We propose a novel thermodynamic scheme for investigation of different routes to hydrate formation, with ideal gas used as reference state for all components in all phases including hydrate phase. This makes comparison between different hydrate formation routes transparent and consistent in free energy changes and associated enthalpy change. From a thermodynamic point of view natural gas hydrate can form directly from water dissolved in natural gas but quite unlikely due to limitations in mass and. The typical industrial way to evaluate risk of hydrate formation involves calculation of water condensation from gas and subsequent evaluation of hydrate from condensed water and hydrate formers in the natural gas. Transport pipes are rusty even before they are mounted together to transport pipelines. This opens up for even other routes to hydrate formation which starts with water adsorbing to rust and then leads to hydrate formation with surrounding gas. Rust consist on several iron oxide forms but Hematite is one of the most stable form and is used as a model in this study, in which we focus on maximum limits of water content in various natural gas mixtures that can be tolerated in order to avoid water dropping out as liquid or adsorbed and subsequently forming hydrate. Calculations for representative gas mixtures forming structure I and II hydrates are discussed for ranges of conditions typical for North Sea. The typical trend is that the estimated tolerance for water content is in the order of 20 times higher if these numbers are based on water dew-point rather than water dropping out as adsorbed on Hematite. For pure methane the maximum limits of water to be tolerated decrease with increasing pressures from 50 to 250 bars at temperatures above zero Celsius and up to six Celsius. Pure ethane and pure propane show the opposite trend due to the high density non-polar phase at the high pressures. Typical natural gas mixtures is, however, dominated by the methane so for systems of 80 per cent methane or more the trend is similar to that of pure methane with some expected shifts in absolute values of water drop-out mole-fractions.
Dokumen tersebut membahas tentang kanker prostat, termasuk definisi, etiologi, gejala, dan epidemiologi penyakit kanker prostat. Kanker prostat adalah bentuk kanker yang berkembang di kelenjar prostat dan dapat menyebabkan berbagai gejala seperti sulit dan sering buang air kecil. Penyebab pastinya belum diketahui namun beberapa faktor seperti usia, genetik, dan gaya hidup dapat meningkatkan risiko terken
Being a Christian is challenging! We are challenged to imitate Christ! We are challenged to make our conduct consistent with our calling! We are challenged to remember where we were and where Jesus brought us. Yes, Christianity is challenging!
On Similarity of Differential Capacity and Capillary Pressure FractalKhalid Al-Khidir
On Similarity of Differential Capacity and Capillary Pressure Fractal Dimensions for Characterizing Shajara Reservoirs of the Permo-Carboniferous Shajara Formation, Saudi Arabia
This document describes a dissertation on model-data integration for predictive assessment of groundwater reactive transport systems. Specifically, it develops reactive transport models to predict groundwater contamination at a field site where a permeable reactive barrier (PRB) using zero-valent iron is installed. Key challenges addressed include quantifying and reducing conceptual model uncertainty, integrating different types of field data using multivariate methods, and characterizing spatial heterogeneity to estimate model parameters from field measurements.
Applications of colloidal gas aphrons for pollution remediationSoumyadeep Mukherjee
This document discusses the application of colloidal gas aphrons (CGAs) for pollution remediation. CGAs are spherical microbubbles coated with surfactant that can be used to separate contaminants from water and soil. The document reviews techniques for generating CGAs and their uses in pollution removal processes. CGAs function through mechanisms such as bubble-entrained flocculation, electrostatic interactions, gas diffusion from trapped bubbles, and pollutant hydrophobicity. Tables are provided comparing CGA generation technologies and the effectiveness of different pollution remediation applications.
This document summarizes a study that measured the flux of methylmercury (MMHg) across the sediment-water interface at four stations in Boston Harbor. The stations varied in infaunal population densities and bioirrigation intensities. Total MMHg fluxes, measured using sediment core incubations, ranged from -4 to 191 pmol/m2/day and were strongly correlated with burrow densities. Estimated diffusive fluxes, based on porewater MMHg gradients, were lower than total fluxes at three stations, indicating bioirrigation enhances MMHg exchange over molecular diffusion. Porewater exchange of both MMHg and radon, a porewater tracer, increased with burrow density, suggesting burrows enhance both MMHg production
The document summarizes an experiment that measured the advection and dispersion of dye in a simulated river system under room temperature and ice water conditions. Key findings include:
1) Dye dispersed faster and mixed homogenously in room temperature water, but stratified between temperature layers and dispersed more slowly in ice water.
2) Modeling of the data found best fit when the ice water flow rate was decreased to represent stratification, as the model assumed homogeneous mixing.
3) The experiment supported the hypothesis that residence time would be higher and dispersion lower in cold water, though dye stratified rather than mixing as initially predicted.
A Critical Study of Water Loss in Canals and its Reduction MeasuresIJERA Editor
Water is a very precious natural resource. When this precious resource moves through the canals certain part of the water is lost by seepage, evaporation etc. This loss is known as conveyance loss. The conveyance loss was calculated experimentally by different researcher on different canals around the world. In this paper author have tried to review some of the research work and recommend an average water loss from the canal irrespective of the soil and other environmental condition. There are different materials which have been used in canal lining to reduce this water loss. No such material can be said it is the best material for reducing water loss because it depends on the site and its environmental condition. Now a days geosynthetic alone or geosynthetic with concrete or precast concrete is used to for canal lining in this paper they have tried to see the strength, durability etc. of different geosynthetic material and its application in canal lining.
Mesoscopic simulation of incompressible fluid flow in porous mediaeSAT Journals
Abstract
Lattice Boltzmann method is used to simulate cavity driven fluid flow in porous media. A square cavity is considered with the top
lid moving with uniform velocity and other sides kept stationary. Simulation is carried out for values of Darcy number ranging
from 10-6 to10-2 at Reynolds number 10 and 100. Influence of Darcy number and Reynolds number is investigated on velocity
profiles and the streamline plots. Half-way bounce back boundary conditions are employed in the numerical simulation. The
numerical code is first verified with the results available in the literature and then used to simulate the Newtonian fluid flow in
porous media. The Darcy number and the Reynolds number were observed to have great influence on the flow properties and the
location of the primary vortex. Simulation was carried out for a 100100 mesh grid and a fine agreement is established theories
in incompressible fluid flow.
Keywords: Lattice Boltzmann method, incompressible flow, porous media
Measuring Hydrualic Conductivity Using Petro Physical Measurements 2013 compa...Christopher Estevez
This summary provides the key points from the document in 3 sentences:
The document discusses various methods for measuring hydraulic conductivity in soils more accurately in the field, including using gravitational methods for saturated soils and the Proportional Cylinder and Arya-Dierolf models for unsaturated soils. It analyzes modifying Darcy's law to account for centrifugal force when measuring saturated soils and how the Proportional Cylinder and Arya-Dierolf models can help determine unsaturated pore size and estimate hydraulic conductivity. Accurately measuring hydraulic conductivity is important for environmental cleanup efforts to more efficiently remove contaminants from lands.
Number of moles fractal dimensions for characterizing shajara reservoirs of t...Khalid Al-Khidir
This document summarizes a research article that calculates fractal dimensions from the relationship between number of moles, maximum number of moles, and wetting phase saturation in sandstone samples from the Shajara Formation in Saudi Arabia. Porosity was measured on samples and permeability was derived from capillary pressure data. Two equations were used to calculate fractal dimensions from number of moles and from capillary pressure relationships. Results showed similarity between the two fractal dimensions. Samples with a wide range of pore radii had higher fractal dimensions, reflecting greater connectivity and ability to accommodate more moles. The formation was divided into three reservoir units based on fractal dimensions. Higher fractal dimensions indicated higher heterogeneity and permeability, characterizing better reservoirs
This document summarizes a study that used lattice Boltzmann methods to simulate fluid flow through porous media. The study varied the Darcy number from 10-6 to 10-2 and the Reynolds number at 10 and 100 to observe their effects. Velocity profiles and streamline plots were produced from the simulations. Decreasing the Darcy number, which represents permeability, was found to significantly influence the flow properties and location of primary vortices within the porous media. The numerical simulations agreed well with existing theories on incompressible fluid flow.
Unsteady state series CSTR modeling of removal of ammonia nitrogen from domes...IJECEIAES
This document describes modeling the removal of ammonia nitrogen from domestic wastewater treated in an unsaturated vertical flow constructed wetland (VFCW) using an unsteady state series continuous stirred tank reactor (CSTR) model. The model is based on a mass balance for ammonium and nitrate/nitrite concentrations using one to three CSTRs. The model parameters are estimated to minimize errors between model outputs and measured inlet and outlet concentrations. Various model configurations are evaluated based on the coefficient of determination, including the number of CSTRs, whether reactions occur in multiple CSTRs, using equal or different reaction rates, and discretizing reaction rates.
The document presents an analytical solution for modeling groundwater flow in a multi-aquifer system considering vertical flow in the wellbore and well loss due to friction. It extends a previous single aquifer solution to consider two interconnected aquifers separated by an aquiclude. Simultaneous equations are formulated using Bernoulli's theorem under hydrostatic conditions to compute water flow between the two aquifers and well for both steady and unsteady well water level conditions. The solution technique aims to more scientifically and economically characterize parameters in multi-aquifer systems compared to previous approaches that treated interconnected aquifers as isolated.
On Modeling Water Transport in Polymer Electrolyte Membrane Fuel Cell_Crimson...Crimson_Biostatistics
This document discusses modeling water transport in polymer electrolyte membrane fuel cells (PEMFCs). It begins by providing background on fuel cells and their components. It then discusses challenges related to water management and flooding in PEMFCs. Several existing continuum and pore-scale models for predicting water transport are reviewed, noting limitations like computational expense. The document proposes a new approach using a volume averaging technique to develop a two-dimensional macroscale model from three-dimensional microscopic equations. This new model represents an improvement over prior reduced continuum models by developing a more accurate closure model for mass exchange between layers. The goal is to use this new model to better understand water flooding and optimize fuel cell performance and durability.
The document discusses assessing relative permeabilities in geothermal reservoirs through analyzing the effect of gravity on relative permeabilities, performing laboratory measurements using real geothermal fluids, and calculating relative permeabilities from field data at several geothermal fields in Iceland. The results showed differences in relative permeabilities with flow direction and magnitude, and that wells within the same field can follow different relative permeability curves. Comparisons were made between laboratory and field measurements.
Effect of Height and Surface Roughness of a Broad Crested Weir on the Dischar...RafidAlboresha
Weir is usually incorporated as control or regulation devices in hydraulic systems,
with flow measurement as their secondary. It is normally intended for use in the field and thus
to regulate broad discharges. Broad-Crested weir is among the oldest common weir types. In this
paper, the effect of height and surface roughness for different Board Crested weirs models were
studied on discharge coefficient (Cd) in a horizontal open channel. In the crest of the weir,
certain materials may be combined with concrete (e.g., boulders) or may be used as cladding to
minimize the effect of water overflow (e.g. stone). The weir surface should not be considered
smooth in this case, and the discharge coefficient (Cd) must be re-estimated. For these purposes, laboratory flume was used to study the effect of height and surface roughness on the discharge coefficients with four of the different weir models dimensions of the concrete blocks. In this study, the flow conditions were considered to be free water flow and the viscosity effect was neglected. In all cases, the weir height effect was directly proportional to the discharge coefficient while the surface roughness effect was found to be inversely proportional to the coefficient Cd of the case study.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
1) The document analytically solves the nonisothermal Buckley-Leverett problem for two-phase immiscible flow in porous media including a tracer component and temperature effects.
2) Mass balances for the fluids and tracer and a convective heat balance equation are formulated and solved using the method of characteristics.
3) The solutions can be used to analyze pressure transients, interpret formation testing, calculate temperature front propagation during waterflooding, and benchmark simulators.
Modelling study of jet metal interaction in ld processeSAT Journals
Abstract Water model experiments have been carried out in a 1/30th scaled down model of the 100 ton LD converter in order to investigate the effect of changing the lance height and the gas flow rate on the penetration depth of liquid with different exit diameters. It is found the penetration depth increases with decreasing nozzle diameter, decreasing the lance height and with increase the gas flow rate. Gas jets impinging onto a gas–liquid interface of a liquid pool are also studied using computational fluid dynamics modeling, which aims to obtain a better understanding of the behavior of the gas jets. The gas and liquid flows are modeled using the volume of fluid technique. The governing equations in the axisymmetric cylindrical coordinates are solved by the CFD simulation using FLUENT. The computed results are compared with experimental result and it isfound a good match with all the data. Keywords: LD process, Water Modeling, Penetration Depth, Volume of Fluid, CFD.
This computational fluid dynamics study used simulations to analyze the effect of bend radius on erosion magnitude and location in an S-bend pipe carrying gas-solid or liquid-solid flows. Simulations were run for air velocities of 15.24-45.72 m/s and water velocities of 0.1-10 m/s, with particle sizes of 50-300 microns and bend radius to pipe diameter ratios (r/D) of 1.5, 2.5, and 3.5. Maximum erosion was found at certain velocity-particle size combinations and occurred at specific angle locations within each bend. The simulations aim to provide insight on erosion behavior to inform pipe design and operating conditions.
Hydrate Formation During Transport of Natural Gas Containing Water And Impuri...IJERDJOURNAL
ABSTRACT: The upper limit of water content permitted in a natural gas stream during its pipeline transport without a risk of hydrate formation is a complex issue. We propose a novel thermodynamic scheme for investigation of different routes to hydrate formation, with ideal gas used as reference state for all components in all phases including hydrate phase. This makes comparison between different hydrate formation routes transparent and consistent in free energy changes and associated enthalpy change. From a thermodynamic point of view natural gas hydrate can form directly from water dissolved in natural gas but quite unlikely due to limitations in mass and. The typical industrial way to evaluate risk of hydrate formation involves calculation of water condensation from gas and subsequent evaluation of hydrate from condensed water and hydrate formers in the natural gas. Transport pipes are rusty even before they are mounted together to transport pipelines. This opens up for even other routes to hydrate formation which starts with water adsorbing to rust and then leads to hydrate formation with surrounding gas. Rust consist on several iron oxide forms but Hematite is one of the most stable form and is used as a model in this study, in which we focus on maximum limits of water content in various natural gas mixtures that can be tolerated in order to avoid water dropping out as liquid or adsorbed and subsequently forming hydrate. Calculations for representative gas mixtures forming structure I and II hydrates are discussed for ranges of conditions typical for North Sea. The typical trend is that the estimated tolerance for water content is in the order of 20 times higher if these numbers are based on water dew-point rather than water dropping out as adsorbed on Hematite. For pure methane the maximum limits of water to be tolerated decrease with increasing pressures from 50 to 250 bars at temperatures above zero Celsius and up to six Celsius. Pure ethane and pure propane show the opposite trend due to the high density non-polar phase at the high pressures. Typical natural gas mixtures is, however, dominated by the methane so for systems of 80 per cent methane or more the trend is similar to that of pure methane with some expected shifts in absolute values of water drop-out mole-fractions.
Dokumen tersebut membahas tentang kanker prostat, termasuk definisi, etiologi, gejala, dan epidemiologi penyakit kanker prostat. Kanker prostat adalah bentuk kanker yang berkembang di kelenjar prostat dan dapat menyebabkan berbagai gejala seperti sulit dan sering buang air kecil. Penyebab pastinya belum diketahui namun beberapa faktor seperti usia, genetik, dan gaya hidup dapat meningkatkan risiko terken
Being a Christian is challenging! We are challenged to imitate Christ! We are challenged to make our conduct consistent with our calling! We are challenged to remember where we were and where Jesus brought us. Yes, Christianity is challenging!
Este documento proporciona una guía para formular un Proyecto Educativo TIC en la Institución Educativa Enrique Pupo Martínez. La guía incluye pasos para definir la pregunta del proyecto, establecer objetivos generales y específicos, y seleccionar estándares de competencia. El proyecto propuesto busca minimizar el uso de papel a través de la utilización de medios tecnológicos como estrategia didáctica.
This document outlines Josh Huisgenga's process for projects which includes discovery, idea generation, refinement, and production. It emphasizes including the client throughout and taking a minimalist approach to remove unnecessary elements. It also references providing services for clients like milestone hitters and funded start-ups through warm introductions over email without pressure.
many times the Bible uses the phrase "That Day." What does it mean, what is its purpose, what need will I have on "that day" and what was the Apostle Paul's attitude towards it?
Este documento presenta una guía para diseñar secuencias didácticas utilizando Recursos Educativos Digitales Abiertos. Propone que los docentes trabajen en grupos para definir el área, tema, objetivos y actividades de la secuencia didáctica. Además, incluye un formato estándar para el diseño de la secuencia didáctica con secciones como datos generales, objetivos, contenidos, metodología, recursos y evaluación. Finalmente, pide a los docentes aplicar la secuencia diseñada con sus estudiantes y subir
What causes martyrs to be willing to give their lives and yet most Christians today won't give an extra hour or two of their lives? Let's examine the apostles and why they left everything and gave their lives for Jesus.
Heading into Thanksgiving, I am glad to be a part. I'm glad to be a part of God's family, my congregational family and a part of our Highland Annual Family Thanksgiving Meal and Fellowship.
We have all failed. As a matter of fact, we fail often in all areas of life. Why do we fail? Is it because we are ignorant of what to do? Do we lack ability? Is it because of laziness? Or could it be a matter of getting our priorities straight?
Gambaran histopatologik lambung tikus wistar yang diberikan buahNovida situmorang
Dokumen ini membahas hasil penelitian histopatologi lambung tikus yang diberi jus pepaya sebelum induksi aspirin. Terdapat 5 kelompok tikus yang diberi perlakuan berbeda selama 10 hari, yaitu diberi pakan standar, jus pepaya 0,8 cc/hari, aspirin 30 mg/hari, jus pepaya 0,8 cc lalu aspirin, dan jus pepaya 2,4 cc lalu aspirin. Hasilnya menunjukkan bahwa pemberian jus pepaya sebelum aspirin
El documento describe los huesos que forman la cara anterior del cráneo, incluyendo los huesos frontales, cigomáticos, maxilares y la mandíbula. Explica que el viscerocráneo, que alberga las estructuras faciales como los ojos, nariz y boca, domina la vista frontal del cráneo. Además, señala que la mandíbula se articula con el resto del cráneo a través de la articulación temporomandibular y que sus músculos generan fuerza para morder y masticar.
El nervio troclear es el más pequeño de los nervios craneales. Inerva solo el músculo oblicuo superior en la órbita. Tiene su origen en el mesencéfalo y emerge de la cara dorsal del mesencéfalo, cruza al lado opuesto, y discurre alrededor del pedúnculo cerebral hasta la órbita donde inerva el músculo oblicuo superior. La parálisis del nervio troclear causa diplopía debido a la desviación del ojo por el músculo antagonista no afectado.
This document discusses how time has no meaning in three situations: 1) When one has nothing to live for and their work seems meaningless, as described in Ecclesiastes, 2) When the task at hand is of great importance, such as Anna's service at the temple or Paul's warnings, and 3) In consideration of eternity, whether eternal punishment or eternal life, as eternity exists outside of time and a thousand years is like a day.
Sneaker culture marketing e vendas - jéssica telesJéssica Teles
O documento descreve a história das marcas esportivas Adidas e Puma, que tiveram origem na mesma família na Alemanha no século XX. Com o tempo, desavenças entre os irmãos fundadores levaram à separação das empresas e uma longa rivalidade. Outras marcas como Nike também são descritas.
This document presents the results of a neutron reflectometry study investigating the hydration of ultrathin antifouling organosilane adlayers on oxidized silicon wafers. The study finds that for a monoethylene glycol silane adlayer, there exists a relatively thick, continuous transition zone of water stemming from within the adlayer. In contrast, for a less effective adlayer lacking internal ether oxygen atoms, this physically distinct interfacial water phase is much thinner and confined to the adlayer-bulk water interface. These results provide further insight into the link between surface hydration and antifouling properties of organosilane adlayers.
This document summarizes research on condensation in an oblique microchannel using lattice Boltzmann modeling. Key points:
1) Condensation in oblique microchannels provides advantages for cooling applications due to increased surface area and secondary flows enhancing heat transfer.
2) The study models droplet formation, hydrodynamics during condensation, and liquid evacuation in an oblique channel.
3) Results show the channel slope angle affects droplet nucleation rate and evacuation time, with little effect on liquid profile above 45 degrees. Slope angle can control droplet coalescence time and liquid evacuation time from the channel.
Thermal Energy on Water and Oil placed Squeezed Carreau Nanofluids FlowMOHAMMED FAYYADH
this research work is focused on the numerical study regarding Carreau nanofluids’ squeezed flow via a permeable sensor surface. The nanofluids’ thermal conductivity is considered to be dependent on temperature. A convenient transformation is employed to reorganize governing equations into ordinary differential equations. The Runge–Kutta method and shooting technique are employed to accurately solve the boundary layer momentum as well as heat equations. Graphical and tabular aids are used to evaluate the solutions of applicable parameter with regards to temperature as well as the rate of heat transfer. In this work, a comparison is done from three nanofluids, i.e. copper, oxide aluminum and SWCNTs (nanoparticles) based fluids (water, crude oil and ethylene glycol) to improve heat transfer. It is found that the temperature dimensionless was dropped and dominated with the squeezed flow parameter and nanoparticle volume fraction parameter. That is for all nanomaterials. When compared with water and ethylene glycol, crude oil is cooler and a thinner thermal boundary layer is presented. For the rate of heat transfer (Nusselt number) was higher in: Ethylene glycol- SWCNT with high permeable velocity parameter 0.2, Ethylene glycol- SWCNT with low squeeze flow parameter 0.1 and Ethylene glycol- oxide aluminum with low nanoparticle volume fraction 0.05
Functionalization of carbon nanotubes and its application in nanomedicine: A ...Nanomedicine Journal (NMJ)
Abstract
This review focuses on the latest developments in applications of carbon nanotubes (CNTs) in medicine. A brief history of CNTs and a general introduction to the field are presented.
Then, surface modification of CNTs that makes them ideal for use in medical applications is highlighted. Examples of common applications, including cell penetration, drug delivery, gene delivery and imaging, are given. At the same time, there are concerns about their possible adverse effects on human health, since there is evidence that exposure to CNTs induces toxic effects in experimental models. However, CNTs are not a single substance but a growing family of different materials possibly eliciting different biological responses. As a consequence, the hazards associated with the exposure of humans to the different forms of CNTs may be different. Understanding the structure–toxicity relationships would help towards the assessment of the risk related to these materials. Finally, toxicity of CNTs, are discussed. This review article overviews the most recent applications of CNTs in Nanomedicine, covering the period from 1991 to early 2015.
Solar Radiation Energy Issues on Nanoparticle Shapes in the Potentiality of W...MOHAMMED FAYYADH
Energy is an extensive view for industrial advancement. Solar thermal energy is designed by light and heat which is radiated
by the sun, in the form of electromagnetic radiation. Solar energy is the highest promptly and sufficiently applicable authority of
green energy. Impact of nanoparticle shapes on the Hiemenz nano fluid (water based Cu, Al2O3 and SWCNTs) flow over a porous
wedge surface in view of solar radiation energy has been analyzed. The three classical form of nanoparticle shapes are registered
into report, i.e. sphere , cylinder and laminar . Nanoparticles in the water based Cu, Al2O3 and SWCNTs have been advanced as a
means to boost solar collector energy through explicit absorption of the entering solar energy. The controlling partial differential
equations (PDEs) are remodeled into ordinary differential equations (ODEs) by applying dependable accordance alteration and it is
determined numerically by executing Runge Kutta Fehlberg method with shooting technique. It is anticipated that the lamina shape
SWCNTs have dynamic heat transfer attainments in the flow improvement over a porous wedge surface as compared with the other nanoparticle shapes in different nano fluid flow regime.
Carbon nanotubes for adsorption of organic contaminantsUCLM
This document summarizes research on using carbon nanotubes (CNTs) for adsorbing organic contaminants from water. It discusses how CNTs have a very large surface area and strong affinity for organic chemicals due to hydrophobicity and pi-pi interactions. The document covers how surface functionalization and different CNT structures (single-walled vs multi-walled) can influence adsorption properties. It also discusses how CNTs can be used as scaffolds to enhance the adsorption of other materials. The document concludes that CNTs show potential as adsorbents in water treatment, but further research is needed to evaluate their real-world application.
Infrared radiation associated with vapor-liquid phase transition of water is investigated
using a suspension of cloud droplets and mid-infrared (IR) (3–5 lm) radiation absorption
measurements. Recent measurements and Monte Carlo (MC) modeling performed at
60 C and 1 atm resulted in an interfacial radiative phase-transition probability of
5108 and a corresponding surface absorption efficiency of 3–4%, depending on
wavelength. In this paper, the measurements and modeling have been extended to 75 C
in order to examine the effect of temperature on water’s liquid-vapor phase-change radiation.
It was found that the temperature dependence of the previously proposed phasechange
absorption theoretical framework by itself was insufficient to account for
observed changes in radiation absorption without a change in cloud droplet number density.
Therefore, the results suggest a strong temperature dependence of cloud condensation
nuclei (CCN) concentration, i.e., CCN increasing approximately a factor of two from
60 C to 75C at near saturation conditions. The new radiative phase-transition probability
is decreased slightly to 3108. Theoretical results were also calculated at 50 C
in an effort to understand behavior at conditions closer to atmospheric. The results suggest
that accounting for multiple interface interactions within a single droplet at wavelengths
in atmospheric windows (where anomalous IR radiation is often reported) will be
important. Modeling also suggests that phase-change radiation will be most important at
wavelengths of low volumetric absorption, i.e., atmospheric windows such as 3–5 lm and
8–10 lm, and for water droplets smaller than stable cloud droplet sizes (<20 lm diameter),
where surface effects become relatively more important. This could include unactivated,
hygroscopic aerosol particles (not CCN) that have absorbed water and are
undergoing dynamic evaporation and condensation. This mechanism may be partly responsible
for water vapor’s IR continuum absorption in these atmospheric windows.
1) Carbon nanotubes are cylindrical tubes composed of rolled graphene sheets and can have unique electronic and mechanical properties depending on their structure and chirality.
2) They are synthesized through arc discharge or chemical vapor deposition and contain a mixture of single-walled and multi-walled nanotubes that require purification methods like heating or acid treatment.
3) Nanotubes can be filled with other materials by soaking in salt solutions, melt filling, or using them as templates for nanorods, and have potential applications in electronics, sensors, and composite materials due to their remarkable strength and conductivity.
Lattice boltzmann simulation of non newtonian fluid flow in a lid driven cavitIAEME Publication
This document summarizes a study that uses Lattice Boltzmann Method (LBM) to simulate non-Newtonian fluid flow in a lid driven cavity. The study explores the mechanism of non-Newtonian fluid flow using the power law model to represent shear-thinning and shear-thickening fluids. It investigates the influence of power law index and Reynolds number on velocity profiles and streamlines. The LBM code is validated against published results and shows agreement with established theory and fluid rheological behavior.
Computer simulations of realistic ion channel structures have always been challenging and
a subject of rigorous study. Simulations based on continuum electrostatics have proven to
be computationally cheap and reasonably accurate in predicting a channel’s behavior. In
this paper we discuss the use of a device simulator, SILVACO, to build a solid-state model for
KcsA channel and study its steady-state response. SILVACO is a well-established program,
typically used by electrical engineers to simulate the process flow and electrical characteristics
of solid-state devices. By employing this simulation program, we have presented an
alternative computing platform for performing ion channel simulations, besides the known
methods of writing codes in programming languages. With the ease of varying the different
parameters in the channel’s vestibule and the ability of incorporating surface charges,
we have shown the wide-ranging possibilities of using a device simulator for ion channel
simulations. Our simulated results closely agree with the experimental data, validating our
model.
New Technique for Measuring and Controlling the Permeability of Polymeric Mem...Editor IJCATR
Membranes have wide uses in industry and medicine applications. Polymer membranes are important materials
because of their high chemical resistance, but they are of weak mechanical resistance against high pressures. Therefore, it was
essential to modify a permeability measuring technique free from high pressure application. The current work represented a
modification for the permeability measuring technique of membranes, where ionic salt was added with known concentration
to water as common solvent and the electrolyte current was measured behind the membrane. The electrolysis current was
correlated to the flow rate of water across a polyvinyl alcohol (PVA) membrane. Some other problems were raised such that
polarization on electrodes and changes in electrolyte contents during the long time of the slow process. Pulsed potential on
electrodes resolved these problems and other associated problems like rush in current and the double layer capacitance effect.
An empirical equation was suggested to evaluate the permeability of polymer membranes by this modified method. Easy and
accurate measurement of permeability helped authors to change the permeability of PVA membranes by adding copper nano
particles in membrane to reduce its permeability, and adding silicone dioxide micro particles to the PVA membranes to
increase its permeability. Authors suggested a mechanism for these permeability changes. Scanning electron microscope
images for the filled PVA membranes supported the suggested mechanism
New Technique for Measuring and Controlling the Permeability of Polymeric Mem...Editor IJCATR
Membranes have wide uses in industry and medicine applications. Polymer membranes are important materials because of their high chemical resistance, but they are of weak mechanical resistance against high pressures. Therefore, it was essential to modify a permeability measuring technique free from high pressure application. The current work represented a modification for the permeability measuring technique of membranes, where ionic salt was added with known concentration to water as common solvent and the electrolyte current was measured behind the membrane. The electrolysis current was correlated to the flow rate of water across a polyvinyl alcohol (PVA) membrane. Some other problems were raised such that polarization on electrodes and changes in electrolyte contents during the long time of the slow process. Pulsed potential on electrodes resolved these problems and other associated problems like rush in current and the double layer capacitance effect. An empirical equation was suggested to evaluate the permeability of polymer membranes by this modified method. Easy and accurate measurement of permeability helped authors to change the permeability of PVA membranes by adding copper nano particles in membrane to reduce its permeability, and adding silicone dioxide micro particles to the PVA membranes to increase its permeability. Authors suggested a mechanism for these permeability changes. Scanning electron microscope images for the filled PVA membranes supported the suggested mechanism.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Review on Molecular Dynamics Simulations of Effects of Carbon Nanotubes (CNTs...LidaN16
The document summarizes research on molecular dynamics (MD) simulations that analyze the effects of various factors on the thermal and electrical conductivity of carbon nanotube (CNT)-modified polymer composites. Specifically, it discusses how MD simulations have shown that CNT chirality, length, hydrogen bonding, and overlap length can impact conductivity. For CNT chirality, the simulations demonstrated that zigzag CNTs have lower conductivity than armchair CNTs, and the effect of chirality decreases with increasing length. Hydrogen bonding was also found to affect composite conductivity by allowing better electron/phonon transport along CNTs.
This document discusses high density hydrogen storage in nanocavities using porous solids. It presents hydrogen adsorption isotherm data for a series of cubic nitroprussides with varying nickel and cobalt content. The highest hydrogen storage density was found for the nickel-containing material, with up to 10.4 hydrogen molecules stored in a 448.5 angstrom cubed cavity, yielding a local density of 77.6 g/L, which is above the density of liquid hydrogen. This high density is attributed to the electrostatic contribution of the adsorption potential within the cavity for the hydrogen molecule.
This article presents a numerical investigation of heat transfer performance and pressure drop of nanofluids flowing under laminar flow conditions. Various nanoparticles including Al2O3, CuO, carbon nanotube and titanate nanotube dispersed in water and ethylene glycol/water were simulated. A single-phase model was used to predict the effects of parameters such as particle concentration, diameter, Brownian motion, Reynolds number, nanoparticle type and base fluid on heat transfer coefficient and pressure drop. The results indicated that particle concentration, Brownian motion and aspect ratio increased heat transfer, while particle diameter decreased it. The study provides considerations for choosing appropriate nanofluids for applications.
This document summarizes key concepts from Chapter 2 of Edward J. Hickin's book "River Hydraulics and Channel Form". It discusses why rigid-boundary models are useful for understanding river behavior, even though real rivers erode and deposit sediment. It also introduces concepts like the energy equation, specific energy, critical flow, the Froude number, subcritical and supercritical flow, and energy losses. Key properties of water like viscosity and its temperature dependence are reviewed. Streamlines, streamtubes, steady and unsteady flow are defined.
This document summarizes a research article that analyzes the stability of a horizontal porous layer saturated with a viscoelastic nanofluid when the boundaries are subjected to periodic temperature modulation. The analysis uses the Darcy-Brinkman-Oldroyd-B fluid model and considers infinitesimal disturbances. Three cases of oscillatory temperature fields are examined: symmetric modulation, asymmetric modulation, and modulation of only the bottom wall. A perturbation solution is obtained and the effect of modulation frequency on stability is shown. The stability is characterized by a correction Rayleigh number calculated as a function of various parameters representing viscoelasticity, concentration, porosity, heat capacity, and modulation frequency. Modulation is found to generally have a destabilizing
This document discusses a molecular dynamics simulation of nanochannel flows that explores the effects of wall lattice-fluid interactions. The simulation models Couette and Poiseuille flows of liquid argon confined between face-centered cubic crystal walls. It examines how varying parameters like wall density, lattice plane orientation, flow orientation angle, and Lennard-Jones interaction energy impact the nanochannel flow characteristics. The results provide insight into nanoscale hydrodynamics and flow rate control applications.
1. Published: October 28, 2011
r 2011 American Chemical Society 2978 dx.doi.org/10.1021/jz2012319 |J. Phys. Chem. Lett. 2011, 2, 2978–2983
LETTER
pubs.acs.org/JPCL
Water Transport through Nanotubes with Varying Interaction
Strength between Tube Wall and Water
Matthew Melillo,†
Fangqiang Zhu,‡
Mark A. Snyder,†
and Jeetain Mittal*,†
†
Lehigh University, Department of Chemical Engineering, Bethlehem, Pennsylvania 18015, United States
‡
Laboratory of Chemical Physics, NIDDK, National Institutes of Health, Bethesda, Maryland, United States
bS Supporting Information
Fluid transport through carbon nanotubes (CNTs) has been
the topic of much interest recently as a greater understanding
of the flow phenomenon has emerged.1À3
CNTs have many
potential applications that cover a broad range from drug delivery
and cancer therapy to nanoelectronics, gas storage, and mem-
brane separation devices.4
The applications utilizing water trans-
port through CNTs such as design of CNT-based desalination
membranes5À8
are of particular interest due to the fast water
transport predicted by molecular dynamics (MD) simulations9
and later observed in experiments.10,11
Specifically, Majumder et al.
have shown experimentally that water flows through multiwalled
CNTs at a rate that is four to five orders of magnitude faster than
predicted by macroscopic hydrodynamics.10
These flow enhance-
ments are believed to be due to the more ordered and stronger
hydrogen bonds between water molecules confined inside a nano-
tube than in bulk water that leads to concerted and rapid motion
along the tube axis.9
Additionally, the weak interaction between
water and hydrophobic walls of CNTs results in a smooth nanotube
surfacewithminimaltozerofriction.12
Thenatureandmagnitudeof
flow through small diameter CNTs is also comparable to that found
in naturally occurring biological channels.13
Therefore, gaining a
more fundamental understanding of the flow mechanism through
CNTs can also lead to deeper insight into the function of biological
water channels.
The synthesis of individual or membrane-incorporated CNTs
of a specific diameter and chirality is challenging because of the lack
of control over nanotube growth.14
Also, CNT functionalization is
largely limited to only the tube ends due to sp2
hybridization of
carbon along the inert tube surface, although novel ways have been
proposed toovercome thislimitation.15,16
Inscalingup technologies
utilizing nanotubes (NTs) for specific purposes, the discovery of
other materials with which NTs are easier to synthesize than carbon
but possess a greater capacity for functionalization than carbon is
desirable.17,18
However, it is not clear how water transport proper-
ties will be affected. Synthesis of boron nitride nanotubes (BNNTs)
provides some insight in this regard and has been found to have
similar or better water conduction properties than CNTs.19,20
MD
simulations have shown that BNNTs of the (5,5) armchair arrange-
ment can conduct water, whereas CNTs of the same size do not,19
indicating that a difference in physical characteristics between
carbon and the boron-nitride material, in this case favorable
interactions with water, can be the key factor permitting water flux
to occur.
In MD simulations, the difference in physical properties is
usually accounted for by changing the Lennard-Jones (LJ)
potential parameters: the well-depth ε and the characteristic
distance σ. Boron, nitrogen, and carbon all have different LJ
parameters that will dictate their interaction with water. Of
course, in several cases such as BNNTs there will be additional
contribution from partial charges, but in the present study we
Received: September 9, 2011
Accepted: October 28, 2011
ABSTRACT: We present the results from extensive molecular dynamics simulations to
study the effect of varying interaction strength, εNTÀOW, between the nanotube atoms
and water’s oxygen atom. We find the existence of a narrow transition region (εNTÀOW
≈ 0.05 to 0.075 kcal/mol) in which water occupancy within a nanotube and flux through
it increases dramatically with increasing εNTÀOW, with the exact location defined by
nanotube diameter and length. This transition region narrows with increasing nanotube
diameter to nearly a step-change in water transport from no flow to high water flux
between εNTÀOW = 0.05 and 0.055 kcal/mol for tube diameter 1.6 nm. Interestingly, this
transition region (εNTÀOW = 0.05 to 0.075 kcal/mol) also coincides with water contact
angles close to 90° on an unrolled nanotube surface hinting at a fundamental link
between nanotube wetting characteristics and water transport through it. Finally, we
find that the observed water flux is proportional to the average water occupancy divided
by the average residence time within the nanotube, with a proportionality constant
found to be 0.36, independent of the nanotube diameter and length.
SECTION: Macromolecules, Soft Matter
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solely focus on the effect of LJ interactions between NT atoms
and water. In one previous study, the effect of varying partial
charges on water flow through peptide backbone-based nano-
scopic channels was studied.21
As we discuss later, the results
found in our study are quite comparable to these findings. These
parameter values for a given element are also not precisely
determined and vary based on which force field is utilized in
MD simulations.22
It has been shown previously that a small
variation in these parameters can cause dramatic shifts in the
behavior of water in CNTs. Hummer et al. observed two distinct
states in which a CNT was either completely empty or com-
pletely filled with water for εNTÀOW = 0.065 kcal/mol but only a
single state with a completely filled CNT existed for εNTÀOW =
0.114 kcal/mol.9
This intriguing behavior motivates this current
study aimed at determining how critical a role the LJ potential
well depth, εNTÀOW, between the NT atoms (carbon, boron-
nitride, or any other element) and water’s oxygen plays in
influencing the flux of water through NTs. Previous work by
Hummer and coworkers focused on occupancy levels and filling/
emptying kinetics as a function of εNTÀOW for a small diameter
(6,6) NT but did not directly calculate water flux or study larger
diameter tubes.23
In this Letter, we study water transport through cylindrical
NTs (atoms arranged in a honeycomb lattice in an armchair
arrangement) made up of different materials by systematically
varying εNTÀOW over a wide range. The first question that we
want to address is if increasing the hydrophilicity of a NT surface
will always result in increased water transport through the NT.
One can imagine that a continued increase in NTÀwater
interaction strength will also increase residence time of mol-
ecules in addition to increasing water occupancy. This can
conceivably result in decreased water transport through hydro-
philic NTs. Second, we want to elucidate possible analogies
between transport behavior within NTs and macroscopic wetting
of the NT wall. In the end, we would like to identify simple design
parameters linking flow properties within specific nanotubes with
water occupancy and residence time.
Through these investigations, we hope to identify a range of
εNTÀOW values that provide the optimum water occupancy and
flux and thereby provide design insight to guide future material
selection for specific applications such as drug delivery.24,25
Our study focuses on understanding the sensitivity of water
flow to changes in physical properties of the NT material, and
thus we use the NT atoms to represent a range of materials
having different interaction strengths with water. Specifically, we
simulate εNTÀOW for a range of values from 0.02 kcal/mol, highly
hydrophobic NTs, up to 0.20 kcal/mol, strongly hydrophilic
NTs. The standard LJ potential form is used, and the resulting
potential functions are shown in the Supporting Information
(Figure S1). We use the TIP3P model of water for which cross-
interactions between water’s hydrogen atom and NT atoms are
zero. For simplicity, all of the NT atoms are arranged in a
honeycomb lattice, as found in the case of CNTs. We arrange 12
hexagonally packed CNTs in a 3 Â 4 membrane that allows us to
accumulate 12 times more data than a single NT simulation. (See
Figure 1A.) The nanotubes are allowed to move during the
simulation, and we find that the membrane structure is main-
tained during the whole simulation. Here we consider NTs of
armchair types (6,6), (7,7), (8,8), (9,9), and (12,12), all of length
1.34 nm, to study diameter dependence of our results. We also
consider 5.6 nm long (6,6) armchair NTs to study possible
effects of NT length on the observed behavior. All of the
simulations are performed using the molecular simulation pack-
age NAMD.26
Shorter NTs are simulated for 15.2 ns and longer
NTs are simulated for 30.4 ns with the first 200 and 400 ps,
respectively, discarded as equilibration and the remaining trajec-
tory used for all subsequent analysis. In addition, we simulate low
εNTÀOW values (0.04 to 0.06 kcal/mol) for (12,12) tubes for 100
ns to accommodate relatively slow filling kinetics. We also study
the wetting behavior of a water droplet on a flat unrolled
nanotube surface, as shown in Figure 1B.
All simulations utilize periodic boundary conditions in all
directions. For NT simulations, temperature and pressure are
maintained at 300 K and 1 atm, respectively. The water droplet
simulations are performed in an NVT ensemble at 300 K. We use
PME method for electrostatic interactions. We have used
Langevin thermostat with a damping coefficient of 0.5 psÀ1
to
maintain constant temperature and Langevin piston NoseÀ
Hoover method that allows all dimensions of the periodic cell
to fluctuate independently to control pressure.27
We use 12 Å
cutoff distance for pair interactions with a smoothing function
applied at 9 Å distance and neighbor list radii 14 Å with a
rebuilding frequency of 10 steps.
In an effort to elucidate the relation between water flow and
nanotube properties, we first study how changes in εNTÀOW
affect the water occupancy levels (number of water molecules
contained in the nanotube) in different diameter NTs. Pre-
viously, Hummer et al. showed for a small diameter (0.8 nm)
NT, capable of only accommodating a single-file chain of water,
that an increase in εNTÀOW increases the probability of observing
the filled state.9
The filled state in that case, however, was
identified by a narrow occupancy level (N = 5 or 6). In
Figure 2AÀC, we show the probability P(N) of finding N
number of water molecules inside a nanotube for several
εNTÀOW values. The panels A, B, and C correspond to
1.34 nm long (6,6), (9,9), and (12,12) NTs, respectively. It is
clear from these plots that as the interaction strength εNTÀOW
increases for wider tubes (panels B and C), significantly more
water molecules occupy the NTs. Because of this increase in
water occupancy with increasing εNTÀOW, a significant change in
water structuring within the NT can also be expected.
Figure 2D shows the 2D density profiles in radial-axial
directions for (6,6), (9,9), and (12,12) NTs for εNTÀOW values
corresponding to panels AÀC, with corresponding snapshots of
water structure at higher occupancy shown in panel F. Only in
the (6,6) NTs does there seem to be favorable axial locations
(clearly seen for εNTÀOW = 0.07 kcal/mol) for water molecules
inside the NTs as previously observed,9
but this preference
Figure 1. System setup. (A) Side-view of nanotube membraneÀwater
system used for most of the data presented in this Letter. (B) Water
droplet resting on an infinite unrolled nanotube sheet used for contact
angle measurements.
3. 2980 dx.doi.org/10.1021/jz2012319 |J. Phys. Chem. Lett. 2011, 2, 2978–2983
The Journal of Physical Chemistry Letters LETTER
diminishes as εNTÀOW or nanotube diameter increases. As
expected, when the tubes are very hydrophilic (higher εNTÀOW),
the water molecules are pulled closer to the NT walls. In large-
diameter NTs, this effect is strong enough such that a second
layer of water molecules is formed near the center of the NT (i.e.,
εNTÀOW = 0.20 for (9,9) and (12,12) NTs).
As shown in Figure 2E, the number of water molecules inside a
nanotube, ÆNæ, increases with increasing εNTÀOW over the entire
range of values studied, with a precipitous change occurring only
over a narrow range of interaction strengths (εNTÀOW = 0.05 to
0.075 kcal/mol). Moreover, the change in ÆNæ with εNTÀOW
becomes sharper with increasing NT diameter. Waghe et al.
observed a similar behavior in their study of the effect of different
Lennard-Jones parameters on filling kinetics of different length
(6,6) armchair CNTs. In that work, for longer tubes, in which
100 water molecules could occupy the CNT, the transition from
empty to filled was much sharper than that for shorter tubes in
which only five water molecules could fit inside.23
Here we show
that this observation is not limited to the length of a narrow (6,6)
CNT in which single-file water flow occurs. Rather, it also holds
true for larger diameter tubes. Therefore, with increasing NT
volume, due to either NT diameter or length, one can expect to
see a sharpened sensitivity of nanotube filling/emptying to subtle
changes in εNTÀOW.
To identify if this transition region in εNTÀOW for water
occupancy may be related to NT surface wetting characteristics,
we next investigate the behavior of a water droplet on an infinite
unrolled NT surface, as shown in Figure 1B. We calculate the
Figure 2. Water occupancy. (AÀC) Probability of a nanotube containing N water molecules inside it at any given time. Panels AÀC are for (6,6), (9,9),
and (12,12) NTs (1.34 nm long), respectively. (D) Water number density profiles as a function of radial distance away from the nanotube center and
axial distance along the nanotube are shown corresponding to εNTÀOW anddiameters inpanels AÀC. (E) Average numberofwater molecules occupying a
nanotube ÆNæ as a function of εNTÀOW is shown for different diameter nanotubes. The curves from bottom to top correspond to (6,6), (7,7), (8,8), (9,9),
and (12,12) nanotubes, respectively. (F) Representative snapshots of water molecules confined in a filled nanotube for different diameter tubes.
Figure 3. Wettability of a flat surface. (A) Cosine of the contact angle of
a water droplet on a graphene surface versus the nanotube materialÀ
water interaction potential strength. (B) Two-dimensional contour
density plots for water droplet resting on a graphene surface with cosine
of the contact angles 1 (θ = 0°; top), 0 (θ = 90°; middle), and À0.87
(θ = 150°; bottom).
4. 2981 dx.doi.org/10.1021/jz2012319 |J. Phys. Chem. Lett. 2011, 2, 2978–2983
The Journal of Physical Chemistry Letters LETTER
contact angle θ of the water droplet on the surface by using a
method proposed by Giovambattista et al.28
A surface with Cos θ
greater than 0 is usually interpreted as hydrophilic, whereas Cos
θ 0 indicates a hydrophobic surface. Figure 3A shows the
Cosine of the contact angle θ as a function of εNTÀOW. This data
shows that the surface changes from highly hydrophobic, yielding
a very high contact angle of 150° (Cos θ = À0.87) for an
εNTÀOW value of 0.02 kcal/mol (Figure 3B, bottom panel), to
partially wetting at an εNTÀOW value of ∼0.1 kcal/mol. For
εNTÀOW values of 0.14 kcal/mol and higher, the water droplet
completely spreads out on the surface (Figure 3B top panel);
therefore, the surface is completely wetted. Most importantly, we
find that εNTÀOW values in the transition region of Figure 2E
correspond to contact angles near 90°, the contact angle at which
the surface transitions from wetting to nonwetting, thus revealing
a fundamental connection between water occupancy inside NTs
and wettability of an NT surface.
The primary focus of this study, which has not been addressed
in any previous study to our knowledge, is to understand how a
change in εNTÀOW will affect water transport through an NT
membrane for NTs with different diameters and lengths. Here
we define water flux to be the total permeations of water
molecules per nanosecond, where a permeation is defined as a
water molecule entering either end of the NT and leaving from
the opposite end. The water molecules that enter and leave the
same side of the nanotube are not counted in total permeation.
Again, the diameter of armchair NTs is changed by adjusting the
chirality vector (n,n) and increases with n. We observe burst-like
flow due to either liquidÀvapor oscillations29
through an empty-
ing-filling nanotube or pulse-like conduction through a water-
filled nanotube.9
In Figure 4, we plot water flux as a function of interaction
strength between an NT atom and water’s oxygen for NTs of
length 1.34 nm (filled points) and NTs of length 5.60 nm (empty
circles). Similar to water occupancy variations, these data show
that variations in εNTÀOW have a dramatic effect on water flux
over a very narrow range, from roughly 0.05 to 0.075 kcal/mol,
leading to an off-on transition in water flow through the NTs. As
discussed above, this transition region for εNTÀOW values is the
range in which NTs change from hydrophobic to hydrophilic, as
shown by contact angle measurements in Figure 3.
Upon closer inspection of Figure 4, we find that the change
from no water transport to significant water flux becomes sharper
with increasing NT diameter, a sharpening of the transition
consistent with that which was observed for water occupancy
(Figure 2E). As the tube diameter increases, water occupancy
also increases. The concomitant increase in the number of water
molecules that are able to interact with the NT surface leads to an
enhanced response to the changes in interaction strength, and
thus the flux increases more sharply than in smaller diameter
NTs. Quite remarkably, inside the transition region extremely
small increases in εNTÀOW, on the order of 0.0025 kcal/mol,
result in drastic increases in the water flux through an NT. This
observation should impact future design strategies aimed at
controlling water flow through nanotube based membranes by
tuning simple properties such as temperature,30
a topic that we
are currently investigating. We find that any further increase in
εNTÀOW beyond ∼0.075 kcal/mol (boundary of the transition
region) actually decreases the water flux, presumably due to
longer residence times of water molecules within the hydrophilic
environment of the nanotube. A similar change in water perme-
ability with changing channel polarity was observed by Portella
et al.21
In that case the channel polarity was controlled by varying
partial charges on channel atoms; therefore, significantly reduced
waterpermeabilitywasobservedforhighchannelpolaritypresumably
due to hydrogen bonding between water and channel atoms.
So far, we have shown that flux increases drastically for εNTÀ
OW values in the transition region and subsequently decreases as
interaction strength increases. In addition, the number of mol-
ecules occupying the NT continuously increases with increasing
εNTÀOW over the range of values we have tested. Such an inverse
relation between water permeation and water occupancy sug-
gests that one needs to consider additional factors that can
account for the observed behavior. An obvious parameter to
consider is the residence time of a water molecule within the
nanotube. We calculate average residence time τ based on all of
the water molecules that transmit through an NT averaged over
time and plot it in Figure 5 as a function of εNTÀOW. The
measured τ values cover a range from 10 to 200 ps and in-
crease with increasing εNTÀOW, as expected due to enhanced
Figure 4. Effect of nanotubeÀwater interaction strength on water
permeability. Number of water permeation events are shown as a
function of nanotubeÀwater interaction strength εNTÀOW for nano-
tubes of different diameter and length. Diameters (from center of
nanotube atoms) range from 0.82 nm in the (6,6) arrangement to
1.66 nm in the (12,12) arrangement. The filled data points represent
NTs 1.34 nm in length, and the empty data points represent NTs
5.60 nm in length.
Figure 5. Average residence time measured for water molecules that
enter the nanotube from one side and leave from the other side is plotted
as a function of nanotubeÀwater interaction strength εNTÀOW for
different nanotube diameters, as shown in the legend.
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waterÀnanotube interactions. Also, we notice that τ is only
weakly dependent on nanotube diameter, an observation that
may be very useful in developing theories of water flow through
nanoscopic channels.
Since an increase in εNTÀOW past the transition region leads to
a decline in flux (Figure 4), an increase in occupancy (Figure 2E),
and an increase in residence time (Figure 5), we anticipate that
both ÆNæ and τ will be the relevant parameters for defining water
transport through nanotube-based membranes, and a combina-
tion of the two may be able to explain the observed flow with
changing NT diameter and length. The simplest possible func-
tional form that one may be able to use is, flux µ ÆNæ/τ with a
proportionality constant that may or may not depend on tube
diameter and εNTÀOW. To test this, we plot observed permeation
events per unit time versus ÆNæ/τ in Figure 6 for all NT diameters
and lengths studied. Incredibly, regardless of diameter or length,
a linear relationship exists yielding a slope of 0.36.
We have shown that the interaction strength between water
molecules and the wall material of a nanotube, characterized by
the Lennard-Jones potential well depth, has a significant impact
on the ability for water molecules to enter a nanotube and reside
there for a given amount of time only for a narrow range of
εNTÀOW values. By varying interaction strength as a design
parameter representative of various materials, we have discov-
ered a narrow transition region of values from 0.05 to 0.075 kcal/
mol in which the nanotube abruptly changes from exhibiting
strongly hydrophobic characteristics with zero water flux and low
water occupancy, to hydrophilic behavior with extremely high
water flux and relatively high occupancy. This transition region
corresponds to a near 90° contact angle of a water droplet
measured on a flat unrolled nanotube surface. At εNTÀOW values
higher than 0.075, the nanotube becomes strongly hydrophilic
resulting in gradually declining flux due to even greater occu-
pancy and higher water residence times. Larger diameter nano-
tubes exhibit sharper transition regions and more abrupt changes
in water flux and occupancy due to the larger number of
interactions between water molecules and the NT wall. Finally,
regardless of length, diameter, or Lennard-Jones parameters, the
observed water flux is proportional to average occupancy divided
by average residence time.
’ ASSOCIATED CONTENT
bS Supporting Information. Lennard-Jones potential between
nanotube atoms and water, comparison of permeation events
between our membrane system (3 Â 4 nanotubes) and a single
nanotube system, effect of changing σNT‑OW for a given interaction
strength εNT‑OW, and simulation setup details. This material is
available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: jeetain@lehigh.edu.
’ ACKNOWLEDGMENT
We acknowledge useful discussions with Profs. Manoj
Chaudhury, Anand Jagota, Tony McHugh, and Kemal Tuzla.
M.M. is thankful to Apratim Bhattacharya for providing a code
for contact angle calculations. This study utilized the high-
performance computational capabilities of the Biowulf PC/Linux
cluster at the National Institutes of Health, Bethesda, MD
(http://biowulf.nih.gov).
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