Enhancement Of Water Flow Research Articles

Experimental Study for Enhancement of Water Flow in Horizontal Pipelines by Using Nanoparticles of Zinc Oxide and Poly Acrylic Acid

Experimental Study for Enhancement of Water Flow in Horizontal Pipelines by Using Nanoparticles of Zinc Oxide and Poly Acrylic Acid

Predicting Quantum-Mechanical Partial Charges in Arbitrarily Long Boron Nitride Nanotubes to Accurately Simulate Nanoscale Water Transport.

Single-walled boron nitride nanotubes (BNNTs) have been explored for various applications, ranging from water desalination to osmotic power harvesting. However, no simulation work so far has modeled the changes in the partial charge distribution when a flat sheet is rolled into a tube, hindering the ability to perform accurate molecular dynamics (MD) simulations of water flow through BNNTs. To address this knowledge gap, we employ electronic density functional theory (DFT) calculations to precisely estimate quantum-mechanically derived partial charges on boron (B) and nitrogen (N) atoms in BNNTs of varying lengths and diameters. We observe a spatially varying charge distribution inside both armchair and zigzag nanotubes of finite lengths. Performing DFT calculations for longer BNNTs is computationally intractable, even with state-of-the-art computing resources. To solve this issue, we devise a charge assignment scheme to predict partial charges for longer BNNTs using DFT data for shorter nanotubes, thus overcoming the need to perform more expensive DFT calculations. We show that these charges reproduce the electrostatic potential predicted from first-principles simulations. Subsequently, we carried out MD simulations to predict the effect of the charge distribution inside BNNTs on water flow enhancement via them. We find that using uniform charges leads to an underprediction in flow enhancement, as compared to using quantum-mechanical charges for both armchair and zigzag BNNTs. We also incorporate atomic vibrations into our simulations and show that these vibrations lead to a reduction in the water flow through aperiodic BNNTs. Our work demonstrates the requirement of a quantum-mechanical charge assignment scheme for BNNTs and evolves a framework to assign charges to nanotubes of arbitrary length, thus allowing realistic MD simulations of long BNNTs using accurate partial charges.

Heat transfer enhancement of water flow over a heating flat plate using 20 kHz ultrasonic waves irradiated from submerged horn-type transducer

The enhancement of heat transfer of water flow over a flat plate under 20 kHz ultrasound irradiated from a submerged horn-type transducer was investigated experimentally in a water tunnel. To examine the ultrasonic effects, the transducer emitted waves perpendicular to the mainstream direction, and the freestream velocity varied between 0.12 and 0.17 m/s. The transducer position was fixed at 0.45 m from the plate leading edge in a streamwise direction. This position was altered in a heightwise direction as dimensionless heightwise distances (Z) that were divided by the diameter of the horn-tip transducer (12 mm) at 1.5, 3.0, and 4.5 from the plate surface. A hot film sensor and thermochromic liquid crystals coated on the test surface were used to demonstrate the hydrodynamic and thermal characteristics, respectively. The maximum temperature reduction of 3.5 °C was observed in the case of Z = 1.5. By employing a horn-type transducer, the acoustic jet and cavitation phenomena played a key role in destabilizing the thermal and velocity boundary layers, which resulted in a decrease in surface temperature. The incident wave shape was triangular, with an enlarging lateral zone along the flow stream. When the waves were released at Z = 1.5, the local Nusselt number was increased up to 2.55 compared to without waves. Under ultrasonic effects, the near-wall flow velocity was detected to be decreasing upstream prior to the incident zone while increasing in the incident region. When waves existed, the highest turbulent intensity was up to 29 times more intense than it was in the absence of waves. Furthermore, a predictive formula for the Nusselt number with ultrasound was established depending on the local Reynolds number and the distance between the ultrasonic source and test surface.

Estimating water transport in carbon nanotubes: a critical review and inclusion of scale effects.

The quasi-frictionless water flow across graphitic surfaces offers vast opportunities for a wide range of applications from biomedical science to energy. However, the conflicting experimental results impede a clear understanding of the transport mechanism and desired flow control. Existing literature proposes numerous modifications and updated boundary conditions to extend classical hydrodynamic theories for nanoflows, yet a consensus or definitive conclusion remains elusive. This study presents a critical review of the proposed modifications of the pressure driven flow or the Hagen-Poiseuille (HP) equations to estimate the flow enhancement through carbon nanotubes (CNTs). For such a case, we performed (semi-)classical molecular dynamics simulations of water flow in various sizes of CNTs, applied the different forms of boundary definitions from the literature, and derived HP equation models by implementing these modifications. By aggregating seven distinct experimental datasets, we tested various flow enhancement models against our measurements. Our findings indicate that including the interfacial layering-based dynamic slip-definition in the proposed HP equations yields accurate estimations. While considering interfacial viscosity predicts the individual CNT experiments well, using the experimental viscosity yields better estimations of measurements for the water flow enhancement through membranes of CNTs. This critical review testing existing literature demonstrates how to refine continuum fluid mechanics to predict water flow enhancement at the nanoscale providing holistic multiscale modeling.

Quantum-mechanical water-flow enhancement through a sub-nanometer carbon nanotube.

Experimental observations unambiguously reveal quasi-frictionless water flow through nanometer-scale carbon nanotubes (CNTs). Classical fluid mechanics is deemed unfit to describe this enhanced flow, and recent investigations indicated that quantum mechanics is required to interpret the extremely weak water-CNT friction. In fact, by quantum scattering, water can only release discrete energy upon excitation of electronic and phononic modes in the CNT. Here, we analyze in detail how a traveling water molecule couples to both plasmon and phonon excitations within a sub-nanometer, periodic CNT. We find that the water molecule needs to exceed a minimum speed threshold of ∼50 m/s in order to scatter against CNT electronic and vibrational modes. Below this threshold, scattering is suppressed, as in standard superfluidity mechanisms. The scattering rates, relevant for faster water molecules, are also estimated.

Water flow in a polymeric nanoslit channel with graphene and hexagonal boron nitride wall coatings: An atomistic study

Low flow resistance is essential for the design of nanofluidic platforms. Here, we present a comparative atomic-level study analyzing the fundamentals of water flow enhancement in a polymeric nanochannel due to the implementation of monatomic thick coatings—specifically, graphene and hexagonal boron nitride (hBN). Our results obtained employing large scale non-equilibrium molecular dynamics simulations and continuum models, revealing significant values of slip lengths of ∼29 and ∼6 nm for graphene- and hBN-coated nanochannels, respectively. Equilibrium molecular dynamics simulations, using the Green–Kubo relation, show the significant effect that the partial charges of hBN coating layer have on the water–wall friction. In addition, consistent values of the slip length are obtained from independent sets of equilibrium and non-equilibrium molecular dynamics simulations, confirming that the computed interfacial friction coefficients hold across flow regimes where water molecules no longer occupy the most energetically stable zones at the interface. Hence, the lower interfacial friction observed in the graphene-coated channel leads to a higher water flow enhancement than the one computed in the hBN-coated channel. We also show that the natural undulations of two-dimensional honeycomb-like materials, implemented as wall coatings, remain largely unhindered due to strong interfacial coupling facilitated by π−π stacking between the underlying aromatic polymer substrate and coating monolayers. This is particularly relevant for graphene coatings, which display significant out-of-plane thermal rippling that further enhances water flow. This observation is supported by a stronger atomic-scale vibrational coupling at the water–graphene interface compared to that computed at the water–hBN interface.

Friction versus flow enhancement in nanotube structures with heterojunctions

Water channels have important applications to many problems, including new purification systems, drug delivery, and many others. Depending on the application, such channels must have two key characteristics in order to be effective. One is that their structures must be more complex than straight tubes, while their second characteristic should be preserving enhancement of volume flow rate of water over what the classical hydrodynamics predicts for straight channels, and has been reported for straight nanotubes. We use both equilibrium and non-equilibrium molecular dynamics simulation to explore the effect of nanojunctions on the rate of water transport in a nanostructured system that consists of connected carbon nanotubes (CNTs) with various radii. This type of nanotube has been fabricated in the past and is of practical importance. We show that the wall-water friction coefficient increases dramatically with the roughness, and can be orders of magnitude larger than the corresponding values in smooth CNTs. Despite the increased friction, however, flow of water in such relatively complex nanochannels is still enhanced significantly over what one obtains in ordinary tubes and channels. Our analysis indicates that, similar to straight CNTs, the entrance/exit dissipation in the system suppresses the effect of the wall-water friction in nanotubes connected by nanojunctions, hence allowing enhancement of water flow.

Simulation and analysis of slip flow of water at hydrophobic silica surfaces of nanometer slit pores

Water flow in nanopores is controlled fundamentally by pore wettability and interfacial water features. In the research herein reported, Molecular dynamics (MD) was used to simulate water flow in nanometer slit pores of silica surfaces with variable wetting characteristics. Compared to Couette flow, the simulated slit-pores of the talc (001) and octadecyltrichlorosilane (OTS) monolayer surfaces exhibited water flow enhancement and a positive slip length at the interface, whereas water flow velocity at the quartz (001) and amorphous silica surfaces was zero, adhering to the no slip condition. More intensive interactions between the interfacial water and hydrophilic silica surfaces were confirmed by MD simulation and sum-frequency vibrational spectroscopy (SFVS) results. A water exclusion zone of approximately 3 Å was found at the hydrophobic silica surfaces by quantitative MD interfacial water analysis and validated by SFVS. This exclusion zone dimension was similar in magnitude to the slip length (4–5 Å) as determined from simulated water flow in hydrophobic silica slit pores. The simulated slip lengths at the hydrophobic surfaces (0.2–1 nm) were significantly less than the experimental slip lengths (>40 nm) reported in the literature. In the case of the experimental results, this difference appears to be due to nanobubbles expected to be present at hydrophobic surfaces.

Flow of long chain hydrocarbons through carbon nanotubes (CNTs)

The pressure-driven flow of long-chain hydrocarbons in nanosized pores is important in energy, environmental, biological, and pharmaceutical applications. This paper examines the flow of hexane, heptane, and decane in carbon nanotubes (CNTs) of pore diameters 1–8 nm using molecular dynamic simulations. Enhancement of water flow in CNTs in comparison to rates predicted by continuum models has been well established in the literature. Our work was intended to observe if molecular dynamic simulations of hydrocarbon flow in CNTs produced similar enhancements. We used the OPLS-AA force field to simulate the hydrocarbons and the CNTs. Our simulations predicted the bulk densities of the hydrocarbons to be within 3% of the literature values. Molecular sizes and shapes of the hydrocarbon molecules compared to the pore size create interesting density patterns for smaller sized CNTs. We observed moderate flow enhancements for all the hydrocarbons (1–100) flowing through small-sized CNTs. For very small CNTs the larger hydrocarbons were forced to flow in a cork-screw fashion. As a result of this flow orientation, the larger molecules flowed as effectively (similar enhancements) as the smaller hydrocarbons.

Water flow enhancement in amorphous silica nanochannels coated with monolayer graphene

Inspired by the recently reported translucency of monolayer graphene (GE) to wetting, atomistic simulations are employed to evaluate water flow enhancement induced by GE deposited on the inner surfaces of hydrophilic nanochannels. The flow in the coated channels exhibits a slip length of approximately 3.0 nm. Moreover, by contrasting the flow rates in channels with coated walls against flow rates in the corresponding uncoated channels, an “effective” flow enhancement from 3.2 to 3.7 is computed. The probability density function of the water dipole orientation indicates that the flow enhancement is related to a thinner structured water layer at the solid–liquid interface. This study provides quantitative evidence that GE employed as coating reduces substantially hydraulic losses in hydrophilic nanoconfinement.

Strong Electroosmotic Coupling Dominates Ion Conductance of 1.5 nm Diameter Carbon Nanotube Porins.

Extreme confinement in nanometer-sized channels can alter fluid and ion transport in significant ways, leading to significant water flow enhancement and unusual ion correlation effects. These effects are especially pronounced in carbon nanotube porins (CNTPs) that combine strong confinement in the inner lumen of carbon nanotubes with the high slip flow enhancement due to smooth hydrophobic pore walls. We have studied ion transport and ion selectivity in 1.5 nm diameter CNTPs embedded in lipid membranes using a single nanopore measurement setup. Our data show that CNTPs are weakly cation selective at pH 7.5 and become nonselective at pH 3.0. Ion conductance of CNTPs exhibits an unusual 2/3 power law scaling with the ion concentration at both neutral and acidic pH values. Coupled Navier-Stokes and Poisson-Nernst-Planck simulations and atomistic molecular dynamics simulations reveal that this scaling originates from strong coupling between water and ion transport in these channels. These effects could result in development of a next generation of biomimetic membranes and carbon nanotube-based electroosmotic pumps.

Ultrahigh Water Flow Enhancement by Optimizing Nanopore Chemistry and Geometry.

The high permeability of nanoporous membranes is crucial for separation processes and energy conversions, especially for the world today that is facing growing water scarcity and energy demands. Unfortunately, further improving permeability, without sacrificing the required selectivity for specific applications, is still extremely challenging. Here, we shed light on the mechanisms of extremely high water permeability of artificial nanopores with the aquaporin-inspired pore geometry and propose a simple yet practical optimization strategy by using computational research to relate nanopore chemistry and geometry to permeability performance. We demonstrated that an ultrahigh water flow enhancement, up to 7 orders of magnitude, can be achieved by optimizing the combination of chemical and geometrical parameters of bioinspired artificial nanopores. Moreover, we addressed an existing debate over the water flow enhancement spanning over 10-1 to 105, attributed to the huge differences in chemical and geometrical properties. Our work provides a guideline to the design and optimization of nanofluidic devices with excellent performance.

Reply to 'On phonons and water flow enhancement in carbon nanotubes'.

Reply to 'On phonons and water flow enhancement in carbon nanotubes'.

On phonons and water flow enhancement in carbon nanotubes.

On phonons and water flow enhancement in carbon nanotubes.

Negative effect of nanoconfinement on water transport across nanotube membranes.

Nanoconfinement environments are commonly considered advantageous for ultrafast water flow across nanotube membranes. This study illustrates that nanoconfinement has a negative effect on water transport across nanotube membranes based on molecular dynamics simulations. Although water viscosity and the friction coefficient evidently decrease because of nanoconfinement, water molecular flux and flow velocity across carbon nanotubes decrease sharply with the pore size of nanotubes. The enhancement of water flow across nanotubes induced by the decreased friction coefficient and water viscosity is markedly less prominent than the negative effect induced by the increased flow barrier as the nanotube size decreases. The decrease in water flow velocity with the pore size of nanotubes indicates that nanoconfinement is not essential for the ultrafast flow phenomenon. In addition, the relationship between flow velocity and water viscosity at different temperatures is investigated at different temperatures. The results indicate that flow velocity is inversely proportional to viscosity for nanotubes with a pore diameter above 1 nm, thereby indicating that viscosity is still an effective parameter for describing the effect of temperature on the fluid transport at the nanoscale.

Molecular dynamics simulations of water flow enhancement in carbon nanochannels

Fluidic flow in carbon nanochannels or nanopores has shown great application prospects in nanofiltration. Therefore, enhancing water flux while maintaining their filtration property is crucial to further extend their applications. In this work, inspired by the hourglass-shaped aquaporin water channel, we proposed a method to optimize water flux in carbon nanochannels using conical carbon nanochannels. Adopting nonequilibrium molecular dynamics simulations, water flow in a series of conical carbon nanochannels was simulated. The results showed that the conical channel with apex angle of 19.2° (38.9°) had the optimum water flux when water flowed from the base (tip) side to the tip (base) side of the conical channel, and the water flux was nearly twice as the recently developed MoS2 desalination membrane. Then, the physical mechanism for the conical channel optimizing water permeation was revealed through detailed analyses of potential of mean forces, average number of hydrogen bonds and pressure distributions of the simulation systems. Finally, the microscopic water structures in these channels were also analyzed to further rationalize the optimizing mechanism. This work indicates that other than decreasing the membrane thickness, regulating the channel configuration is a more effective method to enhance water permeation rate in channels with limited channel sizes.

Modeling the effects of material chemistry on water flow enhancement in nanotube membranes

Abstract

Ultrafast diffusion of Ionic Liquids Confined in Carbon Nanotubes.

Over the past decade many works have focused on various aspects of the dynamics of liquids confined at the nanoscale such as e.g. water flow enhancement through carbon nanotubes (CNTs). Transport of room temperature ionic liquids (RTILs) through various nanochannels has also been explored and some conflicting findings about their translational dynamics have been reported. In this work, we focus on translational dynamics of RTILs confined in various CNTs. By means of molecular dynamics simulations we highlight a substantially enhanced diffusion of confined RTILs with an increase up to two orders of magnitude with respect to bulk-phase properties. This ultrafast diffusion of RTILs inside CNTs is shown to result from the combination of various factors such as low friction, molecular stacking, size, helicity, curvature and cooperative dynamics effects.

Pressure-driven molecular dynamics simulations of water transport through a hydrophilic nanochannel

ABSTRACTTransport of fluids inside porous materials is relevant to many fields of application. Non-equilibrium molecular dynamics simulation is a powerful technique to explore fluid transport through porous media at the molecular scale. In this work, we compared two commonly used methods for studying pressure-driven transport. The first method was based on the application of an external force field on each fluid particle. The second method made use of two movable walls, acting as pistons, so as to generate transport. These two methods were used to study water transport inside a cylindrical hydrophilic silica nanopore. Several pressure differences were considered from 20 bar to 1000 bar. The results were compared to the theoretical Poiseuille fluid flow. No significant difference was found between the two methods. However, a substantial water flow enhancement was observed compared with the theoretical flow. Both the structural and dynamical properties of water remained unaffected by the applied pressure difference.

Enhancement of water flow across a carbon nanotube

It is important to investigate how to enhance the flow rate of single-file water molecules across nanochannels. To our knowledge, all the existing methods are based on pressure gradients, external point charges or uniform/graded electric fields. Accordingly, these methods are all based on exogenous tools, and thus bring challenges for both energy-saving and miniaturisation. In contrast, here we manage to reveal an endogenously determined mechanism of flow enhancement. On the basis of molecular dynamics simulations, we investigate water permeation across a single-walled carbon nanotube (SWCNT A) in the presence of another SWCNT (SWCNT B). We find that the flow rate of the single-file water molecules across SWCNT A is enhanced for the case of unblocked SWCNT B compared with the rate for the case of blocked SWCNT B, and that this flow rate is determined by the separation between the two SWCNTs and the diameter of SWCNT B.