Recurrence quantification analysis of MHD turbulent channel flow

We present Recurrence Plots (RPs) and Recurrence Quantification Analysis (RQA) of time series of velocities in a low-Reynolds-number magnetohydrodynamic turbulent channel flow. The flow was simulated using a fully spectral code with Fourier and Chebyshev decomposition in the periodic and wall bounded directions, respectively. Direct numerical simulations of the flow were performed for Reτ=180, based on the friction velocity and the channel half-height, for the hydrodynamic flow and in the case of a streamwise magnetic field with magnetic interaction number 0.1. The turbulent velocity time series of both cases of the flow were recorded at several positions in the wall-normal direction at fixed spanwise and streamwise positions and analyzed along all directions using RPs and RQA. Using this approach, a number of different flow regions were identified depending on the distance from the channel walls in accordance to the turbulent boundary-layer theory. Different characteristic times were extracted for the various velocity components and related to the dynamics of the flow. Moreover, with the use of Recurrence Plots several distinct system regimes were identified and the effect of the magnetic field was localized. © 201

Effects of channel size, wall wettability, and electric field strength on ion removal from water in nanochannels

Molecular dynamics simulations are employed to estimate the effect of nanopore size, wall wettability, and the external field strength on successful ion removal from water solutions. It is demonstrated that the presence of ions, along with the additive effect of an external electric field, constitute a multivariate environment that affect fluidic interactions and facilitate, or block, ion drift to the walls. The potential energy is calculated across every channel case investigated, indicating possible ion localization, while electric field lines are presented, to reveal ion routing throughout the channel. The electric field strength is the dominant ion separation factor, while wall wettability strength, which characterizes if the walls are hydrophobic or hydrophilic has not been found to affect ion movement significantly at the scale studied here. Moreover, the diffusion coefficient values along the three dimensions are reported. Diffusion coefficients have shown a decreasing tendency as the external electric field increases, and do not seem to be affected by the degree of wall wettability at the scale investigated here. © 2022, The Author(s)

Computational analysis of paramagnetic spherical Fe3O4 nanoparticles under permanent magnetic fields

The influence of permanent constant magnetic fields on the paramagnetic nanoparticles motion is analyzed in this study. The numerical model is developed in the OpenFOAM® platform and includes all major forces acting on particles. The model combines Navier Stokes equations for a liquid and Lagrangian kinematics for the nanoparticles and can predict the aggregation of nanoparticles. Several series of simulations are performed under different intensities of the magnetic field and the nanoparticles aggregation formation and motion is analysed for concentrations of 1.125mg/ml,2.25mg/ml and 4.5mg/ml. Furthermore, two different diameter distributions of the particles with μ=0,σ2=0.2 and μ=0,σ2=1 are simulated for the concentration of 1.125mg/ml in order to determined this effect on the aggregations mean length. Results show that both the increase of the magnetic field intensity and the concentration of nanoparticles in the water solution lead to the increase of the mean length of the aggregations. Finally, different distributions of nanoparticles leads to differences of the mean length of aggregations. © 2018 Elsevier B.V

A computational tool for the estimation of the optimum gradient magnetic field for the magnetic driving of the spherical particles in the process of cleaning water

The use of magnetic nanoparticles for cleaning potable water from heavy metals is a novel technique. Suitable magnetic fields are imposed in order to separate magnetic nanoparticles from the water main stream. A numerical methodology that combines computational fluid dynamics and evolution strategy techniques for the optimum magnetic navigation of particles in water is presented here. The method is based on an iterative algorithm that aims to minimize the deviation of particles from a desired trajectory by continuously adjusting a gradient magnetic field in an appropriate way. For the evaluation of the performance of this computational method, several series of simulations are performed with different number of adjustments of the magnetic field gradient. Using the above-mentioned method, it is found that the increase of the number of adjustments of the magnetic field gradient results in the decrease of the particles’ deviation from the desired trajectory. Finally, the percentage of particles that are following the desired trajectory increases as the concentration of the simulated particles increases. © 2017 Desalination Publications. All rights reserved

Computational Study of the Optimum Gradient Magnetic Field for the Navigation of the Spherical Particles in the Process of Cleaning the Water from Heavy Metals

The usage of magnetic spherical nanoparticles, coated with substances and driven to targeted areas in tanks, is proposed for cleaning the water from heavy metals. In the present paper, a computational study for the estimation of the optimum gradient magnetic field is presented in order to ensure the optimum driving of the particles into the targeted area. The optimization of the gradient magnetic field rates' is verified with the particles' deviation from a desired trajectory. Using the above mentioned method, it was depicted that with the increase of the optimization parameters number, the particles' deviation from the desired trajectory is decreased. © 2016 The Authors

Spatiotemporal Time Series Analysis Methods for the Study of Turbulent Magnetohydrodynamic Channel Flows

In the present study, the direct numerical simulation of the turbulent flow of an electrically conductive fluid in a channel is performed and time series are recorded at a range of locations along the y-direction between the parallel plates of the channel. An external streamwise magnetic field is applied and the correlations between pairs of time series of the fluctuating velocities from the magnetohydrodynamic and the hydrodynamic cases measured at the same probing location of the channel are analyzed. We compare the situation with and without magnetic field using the nonlinear method of Cross Recurrence Plots and Cross Recurrence Quantification Analysis (CRQA). The results of CRQA indicate very well the spatiotemporal extension of the effect of the applied magnetic field on the flow and are in very good agreement with the detailed analysis obtained with other methods. © 2015 Springer International Publishing Switzerland

Blood flow and diameter effect in the navigation process of magnetic nanocarriers inside the carotid artery

Background and objective: Serious side effects are occurred during the cancer therapy. Magnetic driving of nanoparticles is a novel method for the elimination of these effects by supplying with anticancer drug or increase the temperature of the infected area. For this reason, a numerical model for optimal guidance of nanoparticles, through the gradient magnetic field, inside the human artery system is presented in this study. Methods: The present method couples Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM) techniques. In addition, the optimum magnetic intensity each time is evaluated by using the covariance matrix adaptation evolution strategy (CMA-ES). Under five feature blood flow velocities in cardiac cycle, the developed method evaluate and select the optimum gradient magnetic field in order to eliminate the deviation of the guided nanoparticles from a pre-described trajectory. Results: Results of the simulations indicate both the influence of the blood flow and the volume of nanocarriers in the magnetic driving process in real conditions. Specifically, the blood flow and the volume of particles are inversely proportional parameters in the magnetic navigation process. As the blood flow is decreased, the deviation of nanoparticles compared to the desired path is minimized. On the contrary, the decrease of the volume of nanocarriers increase the distance of particles from the described trajectory. However, greater magnetic gradient values are needed as the blood flow is increased. Furthermore, the imposed gradient magnetic values are strongly connected with the position of the nanoparticles and the blood blow velocity. Conclusions: Based on the results of the present study, the most important parameter in the navigation process is the magnetic volume of particles. Under real conditions, the effect of the blood flow is insignificant compared to the volume of particles in the navigation process. In addition, great differences in the optimized magnetic sequence are presented both among the different blood flows and the volume of particles. © 2022 Elsevier B.V

Computational study of the effect of gradient magnetic field in navigation of spherical particles

The use of spherical magnetic nanoparticles that are coated with drugs and can be navigated in arteries to attack tumors is proposed as an alternative to chemotherapy. Navigation of particles is due to magnetic field gradients that may be produced in an MRI device. In the present work, a computational study for the evaluation of the magnitude of the gradient magnetic field for particles navigation in Y bifurcations is presented. For this purpose, the presented method solves for the fluid flow and includes all the important forces that act on the particles in their discrete motion. The method is based on an iteration algorithm that adjusts the gradient magnetic field to minimize the particles' deviation from a desired trajectory. Using the above mentioned method, the appropriate range of the gradient magnetic field for optimum navigation of nanoparticles's aggregation is found. © Published under licence by IOP Publishing Ltd

Heavy metal adsorption using magnetic nanoparticles for water purification: A critical review

Research on contamination of groundwater and drinking water is of major importance. Due to the rapid and significant progress in the last decade in nanotechnology and its potential applications to water purification, such as adsorption of heavy metal ion from contaminated water, a wide number of articles have been published. An evaluating frame of the main findings of recent research on heavy metal removal using magnetic nanoparticles, with emphasis on water quality and method applicability, is presented. A large number of articles have been studied with a focus on the synthesis and characterization procedures for bare and modified magnetic nanoparticles as well as on their adsorption capacity and the corresponding desorption process of the methods are presented. The present review analysis shows that the experimental procedures demonstrate high adsorption capacity for pollutants from aquatic solutions. Moreover, reuse of the employed nanoparticles up to five times leads to an efficiency up to 90%. We must mention also that in some rare occasions, nanoparticles have been reused up to 22 times. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

An Effect of Radiation and MHD Newtonian Fluid over a Stretching/Shrinking Sheet with CNTs and Mass Transpiration

The invention of carbon nanotubes (CNT) has a wide range of industrial and medical applications. The notion of boundary layer flow is used in medicine, particularly in nanomedicine, and the use of magnetic fields is used to treat cancer tumour growth. The governing PDEs are altered into ODEs with the help of suitable transformations. The mass transfer of a chemically reactive species and the flow of MHD over a stretching plate subjected to an inclined magnetic field are investigated, and analytical solutions for velocity in terms of exponential function and temperature field in terms of incomplete Gamma function are obtained using the Laplace transformation. We investigate the variation of physically important parameters with varying suction, magnetic field, and slip using the analytical results. The differences in velocity and temperature profiles are explored in relation to a number of physical parameters. MWCNT nanofluids have higher effective velocities than the SWCNT deferred nanofluids, and this might assist in industrial applications and medical benefits. Earlier research tells us that carbon nanotubes are likely quicker than nanoparticles at achieving the same tumour instance. As a result, in the presence of CNTs or nanoparticles, the magnetic field can also act as a source. We found that SWCNTs nanofluids are better nanofluids than MWCNTs nanofluids. © 2022 by the authors. Licensee MDPI, Basel, Switzerland