Adrian Neculae

Numerical analysis of nanoparticle behavior in a microfluidic channel under dielectrophoresis

This article analyzes the behavior of a nanoparticle suspension in a dense and viscous fluid under dielectrophoresis (DEP), a phenomenon which induces spatial movement, depending on the dielectric properties of the particles and the surrounding medium. The dielectrophoretic forces and the nanoparticle concentration profile in a DEP-based separation micro system, consisting of a microchannel, were numerically investigated using a finite element code. In particular, the trajectories described by the particle movement for a planar electrode array configuration were simulated, and the vertical variation of the dielectrophoretic force, as a function of the rectangular electrodes’ height, was analyzed. This article shows how, by carefully selecting the design parameters of several microchannel devices, one can extend the applications of DEP phenomena to the nanoscale.

Passive dispersion in dendritic structures

In order to improve mass transport description in solidification modeling, this study deals with the determination of the solute dispersion tensor in columnar dendritic mushy zone. The closure problem associated with the derivation of the macroscopic species conservation equation, using the volume averaging method, is solved numerically. Using schematic structures and digitized images of real dendritic structures observed experimentally during solidification of succinonitrile-4 wt.% acetone, the influence of tortuosity and microscopic dispersion on the determination of the effective solute dispersion coefficients is represented in terms of the Peclet number.

Nanoparticles' Promises and Risks

This introductory chapter gives relevant historical information about nanoparticles and the attempts to define the nanoparticle size (1–1,000 nm), as well as their most important general properties, which vary with size: surface area, optical properties, uniformity, fictionalisation, quantum confinement and other fractal-type characteristics. 1.1 General Overview Nanoparticles are considered a discovery of the twentieth century, but a brief overview of the field reveals that artisans in Mesopotamia used finely divided materials of this type as early as the ninth century BC, to obtain a glittering effect on the surface of ceramic vessels. In the Middle Ages and the Renaissance, the production of glittering metallic films led to methods of covering glassy surfaces developed in various Far Eastern or European centres which became famous thanks to these methods that are largely employed even today. During the Renaissance and in later times, the development of visual arts (painting in particular) and printing and engraving methods contributed to the technique of producing fine inorganic and organic dust particles, close to nanoparticles in size, and dispersions that were stable in different solvents and used as dyes or ink [1]. N. Strambeanu (*) Pro Air Clean Ecologic, 37, Vadul Crisului Street, Timisoara 300613, Romania e-mail: ns_arana@yahoo.com L. Demetrovici Pro Air Clean Ecologic, Timisoara, Romania D. Dragos Department of Pharmacy, “Victor Babes” University of Medicine and Pharmacy, Timisoara, Romania M. Lungu Department of Physics, West University of Timisoara, Blv. V. Parvan No. 4, 300223 Timisoara, Romania

Nanoparticle Characterization Using Nanoparticle Tracking Analysis

Characterization of nanoparticles in environmental samples involves determining their size, their chemical composition, and their concentrations in the bulk matrix. Environmental changes in their environment metallic nanoparticles as colloidal aggregates tend to be stable or dispersions. Filter size differential is most commonly used method to isolate nanoparticles in aqueous solutions. Micro-filtration, nanofiltration, cross-flow filtration, and ultracentrifugation are commonly used to achieve the highest degree of separation. Chemical characterization of the nanoparticles has traditionally been performed using a transmission microscope/scanning electron (TEM/SEM), followed by spectroscopy, energy dispersive X-ray (EDS), and X-ray diffraction (XRD). Due to the inherent limitations these methods were combined. This review describes the current status and challenges of isolation, separation, and detection of nanoparticles in samples. Nanoparticle Tracking Analysis (NTA) is a common procedure for the analysis of nanoparticles in complex aqueous matrices.

The dopant fields in “uniform-diffusion-layer”, “global-thermal-convection” and “precrystallization-zone” models

Abstract In the case of vertically stabilized Bridgman–Stockbarger semiconductor, crystal growth system, this study compares the computed dopant fields in the neighborhood of the melt/solid interface in “uniform-diffusion-layer”, “global-thermal-convection” and “precrystallization-zone” models. Using quasi-steady state approximation, this comparison is made for crystal and melt with thermophysical properties similar to those of gallium-doped germanium, for different Rayleigh numbers and different Schmidt numbers related to the melt/solid interface. Numerical simulations put in evidence the differences between the computed dopant fields in the above three models. For example, the dopant concentration computed in the “precrystallization-zone” model for a volumic concentration ϕ=0.055 of “solid inclusions” at the interface on the axis of the cylinder is five times bigger than the dopant concentration computed in the “global-thermal-convection” model. At the same time, the percent radial segregation computed in the “precrystallization-zone” model for ϕ=0.055 is considerably larger than in the “global-thermal-convection” model. Therefore, the influence of the microstructures from the precrystallization-zone on the dopant dispersion in the neighborhood of the melt/solid interface is relevant and there is no reason to ignore it in general.

Numerical simulation of bioparticle separation by dielectrophoretic field-flow-fractionation (DEP-FFF)

The separation systems based on dielectrophoretic field-flow-fractionation (DEP-FFF) are used for a wide range of bioparticle types, including cells, bacteria, viruses, proteins, etc. An array of interdigitated microelectrodes lining the bottom surface of a thin chamber is used to generate dielectrophoretic forces that levitate the bioparticle mixture. The balance between DEP levitation and gravitational forces determines the bioparticles position at equilibrium heights within a fluid-flow profile, and consequently determines their velocities and the corresponding elution times. The elution time depends on the voltage applied on the microelectrodes, geometry of the device, bioparticle dielectric properties and density. This paper analyses numerically the behavior of a bioparticle mixture suspended in a dense and viscous fluid under dielectrophoresis. The controlled spatial separation of bioparticle mixture is performed by a combination of dielectrophoretic and hydrodynamic forces. The theoretical backgrou...

Numerical Study on Radiative Heat Transfer and Boundary Control of Glass Fibers Cooling Process

In this paper we present a set of numerical simulations for the cooling of a cylindrical glass fiber after the splicing process. Due to the glass high melting point, the radiative term must be taken into account. The nonstationary heat transfer equation is solved using code based on the finite element method under different boundary conditions. The effect of the outer temperature field on the temperature gradients inside the fiber (which causes the thermal stress) is analyzed. Based on this type of study, an optimal control of the temperature inside the fiber can be prescribed.

Temperature measurement using optical fiber with applications to automobiles considering a highly accurate numerical solution for the conductive heat transport in a circular cylinder

The computation of the heat transfer equations solution generally implies the use of commercial codes, often expensive. An important goal of solving heat transfer problem in a given context is to obtain an accurate solution using accessible tools at a low computational time cost. Because of complexity of the problem, a variety of different approximations are used and their validity limit must be tested in each case performing comparisons with experimental results. In this paper we present a simple, rapid and accurate method to compute the temperature evolution during the heating or cooling of a metal circular cylinder. For moderate temperature values only the conductive transfer can be considered and the resulted heat transport equation is solved. The initial temperature distribution is described by Dirichlet type boundary conditions. Taking into account a sufficiently large number of terms in the analytical solution expression so that the initial boundary condition is fulfilled (in our case N = 500), we obtain a simple yet accurate approximation of the full transport solutions. The results are consistent with experimental data and in excellent agreement with simulations performed with much more complex codes for the investigated temperature domain. The method can be adapted to the temperature measurement inside the engine. Using the specific advantages of the optical fibers might be a reliable tool for improving the temperature control in the engine and consequently the performances of the automobile.

Eddy current separation of small nonferrous particles using a complementary air-water method

ABSTRACT The paper describes a new eddy-currents separation technique, based on a complementary air-water method, designed for the recovery of nonferrous particles, smaller than 5 mm, from heterogeneous mixtures. The main part of the equipment is a horizontal magnetized rotary cylinder with four poles of NdFeB permanent magnets, alternately oriented. This separation method consists of initial electromagnetic actions upon strongly conducting particles in air, followed by the combined electromagnetic actions and Magnus forces upon tailing particles in water. The dependencies of the separation parameters Grade, Yield and Separation Efficiency versus rotation speed for an Al-Cu waste are presented and discussed.

Analysis of airborne particulate matter pollution in Timisoara city urban area and correlations between measurements and meteorological data

Air pollution is known to have many adverse effects, among which those on human health are considered the most important. Healthy people of all ages can be adversely affected by high levels of air pollutants. Nanoparticles can be considered among the most harmful of all pollutants as they can penetrate straight into the lungs and blood stream. Their role in the aging process has also recently been revealed. In Romania, practically in all important urban areas (Bucuresti, Iasi, Timisoara, Brasov, Baia Mare, etc.) the daily limit values for airborne particulate matter are exceeded, so more efforts in controlling air quality are required, along with more research and policies with positive impact on reducing the pollutants concentration in air. The approaches that have been developed to assess the air quality and health impacts of pollution sources are based on analytical methods such as source apportionment, factor analyses, and the measurement of source-relevant indicator compounds. The goal of the present...