21 |
Enhancement of mass transfer coefficient in three-phase magnetically stabilized fluidized bedRhee, Brian Kanghee 18 February 1998 (has links)
Graduation date: 1998
|
22 |
The Properties of Polarized Light of Magnetic Fluid with Applied Magnetic FieldLi, Ho-San 12 July 2003 (has links)
Abstract
In this paper, the optical properties of magnetic fluid thin films are studied. We present the experimental observation of optical linear birefringence and dichroism in magnetic fluid thin film induced by crossed magnetic field perpendicular to the direction of light propagation. According to our results, we ascertain that both the magnetic birefringence and dichroism are existed. Besides, we also find that the relations between magnetic field and magneto-optical effects changed with the applied magnetic field intensity.
|
23 |
Quadrupole magnetic field-flow fractionation a novel technique for the characterization of magnetic particles /Carpino, Francesca. January 2008 (has links)
Thesis (Ph.D.)--Cleveland State University, 2008. / Abstract. Title from PDF t.p. (viewed on May 8, 2008). Includes bibliographical references (p. 121-126). Available online via the OhioLINK ETD Center. Also available in print.
|
24 |
Manufacture of ferrofluid : basic aspects and the influence of key parameters on the processVatta, Laura Lisa 18 May 2007 (has links)
Please read he abstract in the section 00front of this document / Dissertation (M Eng (Chemical Engineering))--University of Pretoria, 2007. / Chemical Engineering / unrestricted
|
25 |
Design and testing of a rotating cryogenic check valveHamkins, Christopher P. January 1980 (has links)
Thesis: B.S., Massachusetts Institute of Technology, Department of Mechanical Engineering, 1980 / Includes bibliographical references. / by Christopher P. Hamkins. / B.S. / B.S. Massachusetts Institute of Technology, Department of Mechanical Engineering
|
26 |
Propriedades magneto-ópticas de colóides magnéticos á base de nanopartículas de magnetita recobertas com prata / Magneto-optical properties of magnetic nanoparticles colloids based on magnetite and coated with silverLopes Junior, José Carlos Campello 17 May 2010 (has links)
Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2014-08-19T14:30:36Z
No. of bitstreams: 2
license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5)
Dissertacao_Jose Carlos Campello Lopes Jr.pdf: 3551367 bytes, checksum: fc027437d4c362a01703752003b22515 (MD5) / Made available in DSpace on 2014-08-19T14:30:37Z (GMT). No. of bitstreams: 2
license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5)
Dissertacao_Jose Carlos Campello Lopes Jr.pdf: 3551367 bytes, checksum: fc027437d4c362a01703752003b22515 (MD5)
Previous issue date: 2010-05-17 / In this work we investigated, theoretically and experimentally, the magneto-optical properties
of a magnetic fluid consisting of core-shell nanoparticles, where the core is made of magnetite,
while the shell is silver.
The theoretical model used was based on Mie s theory, under the electrostatic approximation,
i.e. for nanoparticles with diameters much less than the incident wavelength (lambda).
A Clausius-Mosotti for a core-shell system was used to calculate the electrical susceptibility of
the core-shell nanoparticle for equals to 632 nm. The susceptibility was shown to be strongly
dependent on the core diameter and the shell thickness. Nevertheless, a maximum value of
7.20 (greater than isolated nanoparticles of silver, which has 0 = 4.30, or magnetite with
0 = 1.47) was obtained for a fraction f, defined as f = (Dcore/Dcore−shell)3, equal to 0.36. This
result suggest that there exist an ideal fraction f for nanocomposites with enhanced optical
properties.
In order to compare our theoretical results with experimental data a core-shell magnetic
fluid was synthesized on the Institute of Chemistry of UFG by the group of Dr. Em´ılia Celma
de Oliveira Lima. The nanoparticles were suspended in water at fisiological pH and recovered
by a double layer of lauric acid (dodecanoic acid). The nanoparticles were characterized by
X-ray diffraction, high resolution electron transmission, energy dispersive X-ray spectroscopy,
and vibrating sample magnetometer. The Sturges method was used to obtain the nanoparticle
diameter histogram. The data revealed the existence of a bimodal nanoparticle distribution.
Both distributions were curve fitted using a lognormal function. The modal diameter of one of
them was 9.24 ± 0.03 nm with a dispersity of 0.27 ± 0.02, while for the other one we found a modal diameter of 23.0 ± 0.2 nm with disperisty 0.2 ± 0.1. The energy dispersive X-ray
spectroscopy confirmed the existence of magnetite and silver only for larger particle diameters,
while the lower ones only magnetite was found. From the experimental analysis we confirmed
the synthesis of a magnetic fluid containing 10% of core-shell nanoparticles. Magnetization
data was used to estimate the magnetic particle volume fraction.
The magneto-optical properties were obtained using a magnetotransmissivity technique,
where the polarizer and analyser axis are positioned on the magnetic field direction.
The sample containing 10% of core-shell nanoparticles, with a total particle volume fraction
of 0.18%, had shown an extinction of light of 100% for a magnetic field of only 500 Oe, while
a magnetic fluid with 100% of core nanoparticles, at a similar particle concentration (0.15%),
had shown a 50% extinction of light at the same field range. The magnetotransmissivity data
were curve fitted with a theoretical model containing only two parameters, one related to the
electrical susceptibility and the other to the formation of self-organized nanostructures in the
colloid. The mean agglomerate size (nanoparticles forming linear chains) had changed from 2.09
to 3.36 for a particle volume fraction increasing from 0.06% to 0.18%. Using the estimative of
the double layer lenght of lauric acid, approximately 2 nm, and analyzing the magnetotransmissivity
data for several particle concentrations, we were able to obtain the fraction f of core-shell
nanoparticles of 0.17. This result, together with TEM data, allowed us to calculate the core
diameter of the core-shell nanoparticle as 13 nm. Indeed such result suggest that in order to be
suscessful in coating the nanoparticle with the shell element one might need monodisperse-like
nanoparticle systems. / Neste trabalho investigamos, teorica e experimentalmente, as propriedades magneto-´opticas de
um fluido magn´etico constitu´ıdo de nanopart´ıculas core-shell (caro¸co-casca), em que o caro¸co
´e feito de magnetita e a casca de prata.
O modelo te´orico utilizado baseou-se no modelo de Mie, dentro da aproxima¸c ao eletrost
´atica, que consiste no caso em que o di ametro das nanopart´ıculas ´e muito menor que o
comprimento de onda da luz incidente ( ). Uma rela¸c ao de Claussius-Mossotti para o sistema
core-shell foi utilizada para o c´alculo da susceptilidade el´etrica da nanopart´ıcula core-shell
para lambda=632 nm. A susceptilidade el´etrica do nanocomposto foi fortemente dependente
do di ametro do caro¸co e da espessura da casca. Entretanto atinge um valor m´aximo de 7,20
(maior que o de uma nanopart´ıcula de prata com 0 = 4, 30 ou de magnetita 0 = 1, 47) para
uma fra¸c ao f, definida como f = (Dcore/Dcore−shell)3, igual a 0,36. Este resultado sugere que
existe uma fra¸c ao ideal entre os materiais que proporciona ao nanocomposto resposta m´axima
`as propriedades ´opticas.
No intuito de comparar nossos resultados te´oricos com dados experimentais, um fluido
magn´etico core-shell foi sintetizado no Instituto de Qu´ımica da UFG pelo grupo da Profa. Dra.
Em´ılia Celma de Oliveira Lima. As nanopart´ıculas foram suspensas em ´agua em pH fisiol´ogico
e recobertas por uma dupla camada de ´acido la´urico (´acido dodecan´oico). As nanopart´ıculas
foram caracterizadas por difra¸c ao de raios-X (DRX), microscopia eletr onica de transmiss ao de
alta resolu¸c ao (HR-TEM), espectrometria de energia dispersiva de raios-X (EDS) e magnetometria
de amostra vibrante (VSM).O m´etodo de Sturges foi utilizado para montar o histograma dos di ametros das nanopart´ıculas. Os dados revelaram a exist encia de uma distribui¸c ao bimodal. Ambas distribui¸c oes foram ajustadas
considerando uma distribui¸c ao do tipo lognormal. O di ametro modal de uma delas foi
de 9.24 ± 0.03 nm com uma dispers ao de 0.27 ± 0.02, enquanto que para a outra distribui¸c ao
foi encontrado um di ametro modal de 23.0 ± 0.2 nm e dispers ao 0.2 ± 0.1. A espectrometria
de energia dispersiva confirmou a presen¸ca de magnetita e prata, em quantidades significativas,
somente nas part´ıculas de maior di ametro, enquanto nas de menor di ametro foi confirmado a
exist encia apenas de magnetita. A partir destas an´alises foi confirmada a s´ıntese de um fluido
magn´etico contendo 10 % das nanopart´ıculas do tipo core-chell . Dados de magnetiza¸c ao
foram obtidos para estimar a fra¸c ao volum´etrica de nanopart´ıculas magn´eticas.
Medidas das propriedades magneto-´opticas foram feitas utilizando a t´ecnica de magnetotransmissividade
com polarizador e analisador orientados na dire¸c ao do campo magn´etico
aplicado. Amostra contendo10% de suas nanopart´ıculas do tipo core-shell , com uma fra¸c ao
volum´etrica total de apenas 0,18%, apresentou uma extin¸c ao da luz de 100% a um campo
de apenas 500 Oe, enquanto que uma amostra com 100% de nanopart´ıculas do tipo core ,
em concentra¸c ao semelhante (0,15%), apresentou uma extin¸c ao de 50% na mesma faixa de
campo magn´etico. Os dados de magnetotransmissividade foram ajustados considerando um
modelo contendo apenas 2 par ametros, estando um deles relacionado a susceptibilidade el´etrica
e outro a forma¸c ao de estruturas auto-organizadas no col´oide. O tamanho m´edio de aglomerados
(nanopart´ıculas formando uma cadeia linear) variou de 2.09 para 3.36 para uma fra¸c ao
volum´etrica crescendo de 0,06% para 0,18%. Usando dados da literatura acerca da estimativa
do comprimento da dupla camada de ´acido la´urico, como sendo de aproximadamente 2 nm, e
analisando os dados de magnetotransmissividade para diversas concentra¸c oes de nanopart´ıculas,
foi poss´ıvel obter a fra¸c ao f das nanopart´ıculas core-shell como sendo de 0,17. Este resultado,
conjuntamente com os dados de TEM, permitiu concluir que o di ametro do caro¸co na
nanopart´ıcula core-shell ´e de 13 nm. Este resultado ´e interessante tecnologicamente, pois
sugere que, para se obter sucesso no recobrimento de nanopart´ıculas, seja necess´ario, ou ao
menos importante, utilizar amostras com baixa dispers ao de di ametros.
|
27 |
Coupled momentum and heat transport in laminar axisymmetric pipe flow of ferrofluids in non-uniform magnetic fields : theory and simulationCruz-Fierro, Carlos Francisco 02 April 2003 (has links)
The effect of a non-uniform magnetic field on the coupled transport of
momentum and heat is studied for the case of laminar pipe flow of a
magnetically susceptible ferrofluid. The momentum and heat transport
equations are complemented with the necessary electromagnetic terms and
used to develop a computer simulation of the velocity profile and temperature
distribution in the fluid.
Two magnetic field configurations are studied. The first configuration is
produced by a single short solenoid, located around the pipe. The magnetic
field produced has both radial and axial components. For the second
configuration, the electric current is inverted in one half of the solenoid,
creating much stronger field gradients in both directions.
The flow is laminar, driven by a constant pressure difference between
the ends of the pipe. The apparent viscosity of the ferrofluid is modeled as
dependent on temperature and magnetic field. In simulations involving heat
transfer, a section of the pipe is maintained at higher constant temperature.
The rest of the wall is adiabatic.
A Visual-Basic code, FiRMa (Flow in Response to Magnetic field), was
developed to perform the numerical simulations.
For the water-based ferrofluid, results show reduction of average
velocity and small deviations from the parabolic velocity profile as the result of
vortex viscosity. Heat transfer calculations show a decrease in the heat
transfer coefficient and an increase in the fluid exit temperature. These effects
are due to the change in flow pattern and average velocity.
Current research aims for the development of a stable liquid-metal
based ferrofluid, because of the high electric and thermal conductivities. The
FiRMa code is used to examine the expected response of a mercury-based
ferrofluid to the magnetic fields under study. Results show that the
electromagnetic effects on the liquid metal-based ferrofluid are much stronger,
due to induced electric currents and the Lorentz force acting on them. / Graduation date: 2003
|
28 |
Magneto-optical Effects of Magnetic FluidsLin, Man-chien 08 July 2001 (has links)
In this thesis, the study of optical properties of magnetic fluid thin films is the main purpose.
We measured the intensity of linear polarized laser beam, which passed through our sample, magnetic fluid thin film with external magnetism, to analyze the relationships between magnetic field intensity and magneto-birefringence and magneto-dichroism. According to our experimental results, we ascertain that both the magneto-birefringence and magneto-dichroism are existed. Besides, we found that the difference of index at magnetic fluid thin film changed with magnetic field intensity also. The phenomenon let us believe that magnetic fluid thin film is anisotropy.
Moreover, we also applied the statement, which agreed by most physicists to explain what we found from our real measurements.
|
29 |
Efeito magnetoforético aplicado à separação de nanopartículas magnéticas biocompatíveis / Efeito magnetoforético aplicado à separação de nanopartículas magnéticas biocompatíveis / Magnetoforetic effect applied to biocompatible magnetic Nanoparticle segregation / Magnetoforetic effect applied to biocompatible magnetic Nanoparticle segregationSANTOS, Marcus Carrião dos 13 April 2011 (has links)
Made available in DSpace on 2014-07-29T15:07:08Z (GMT). No. of bitstreams: 1
Marcus Carriao dos Santos Dissertacao.pdf: 903168 bytes, checksum: 91f54bc8f60266322bb1f15c18b8d279 (MD5)
Previous issue date: 2011-04-13 / In this work a magnetophoretic experiment (MPE) was developed to study the effect of a gradient of magnetic field in the diameter and size dispersivity of nanoparticles in a magnetic fluid (MF). In this experiment, the mass of a permanent magnet is measured by a balance which data varied due to the interaction with the magnetic fluid, which is placed a few centimeters above. Curves of variation of apparent mass of the magnet were obtained as function of time and related to the characteristics of fractions taken from the surface of the MF at different times. The MF consisted of magnetite nanoparticles surface-coated with phosphate. Samples were synthesized by the coprecipitation method and characterization was performed using x-ray diffraction, high resolution transmission electron microscopy (HR-TEM) and vibrating sample magnetometry (VSM). Fractions of the MF were taken during the MPE at five different times. Those fractions were characterized by VSM, from which magnetic diameters were estimated. The magnetic diameters showed a decrease of nanoparticle size in the surface of the MF sample submitted to MPE for longer times of exposure to the field gradient. These same fractions were characterized by HR-TEM and histograms of nanoparticles size distribution were made. Studies of mean and modal (obtained by lognormal fit) diameters had confirmed the behavior indicated by the magnetic diameters showing a decrease of size as function of time. Studies of standard deviation and full width at half maximum (obtained by lognormal fit) had shown a decrease in dispersivity. However, studies of the σ factor were inconclusive, since no significant variations were found for nanoparticles at the experimental size range. Indeed, the MPE results had shown a variation of 16.02% in modal diameter (Dmodal), 14.63% in mean diameter, 30.90% in standard deviation e 33.33% in full width at half maximum between the original sample and the part which was exposed to gradient magnetic field by 60 hours, of fluid with largest initial diameter (Dmodal = 9.24±0.08 nm and σ=0.238±0.009). In addition magnetohyperthemia experiments at 300 kHz were obtained for each sample. Higher specific absorption rates were found for larger particle sizes, which have important applications for cancer treatment. Therefore, we concluded that the magnetophoretic experiment can be used to select the magnetic fluids properties, due to diameter and size standard deviation control, for several technological, environmental and biomedical applications. / Neste trabalho foi desenvolvido um experimento magnetoforético (EMF) para estudar o efeito de um gradiente de campo magnético sobre o diâmetro e dispersão de tamanhos de nanopartículas em fluidos magnéticos (FM). Neste experimento, a massa de um imã permanente é medida por uma balança enquanto varia graças à interação com o FM, colocado alguns centímetros acima. Curvas de variação da massa aparente do imã foram obtidas em função do tempo e relacionadas às características de alíquotas retiradas da superfície do FM em tempos distintos. Os fluidos eram constituídos de nanopartículas de magnetita recobertas com fosfato. As amostras foram sintetizadas pelo método de coprecipitação e caracterizadas por difratometria de raios-x, microscopia eletrônica de transmissão de alta resolução (HR-TEM) e magnetometria de amostra vibrante (VSM). Foram retiradas alíquotas do EMF em cinco intervalos de tempo distintos. Essas alíquotas também foram caracterizadas por VSM e foram estimados diâmetros magnéticos a partir delas. Os diâmetros magnéticos mostraram uma diminuição do tamanho das nanopartículas na superfície da amostra submetida ao EMF para tempos maiores de exposição ao gradiente de campo. Essas mesmas alíquotas foram ainda caracterizadas por HR-TEM e foram construídos histogramas com os tamanhos das nanopartículas. Estudos dos diâmetros médios e modais (obtido pelo ajuste lognormal) confirmaram o comportamento estimado pelos diâmetros magnéticos e mostraram a diminuição do tamanho das nanopartículas em função do tempo. O estudo dos desvios padrão e da largura a meia altura (obtido pelo ajuste lognormal) indicaram uma diminuição da dispersão. O estudo do fator σ (parâmetro do ajuste lognormal) foi inconclusivo, não apresentando variações significativas na faixa de tamanhos estudada. Os resultados mostraram que o EMF produziu uma variação de 16,02% no diâmetro modal (Dmodal), 14,63% no diâmetro médio, 30,90% no desvio padrão e 33,33% na largura a meia altura entre a amostra original e a alíquota exposta ao gradiente de campo por 60 horas, para o fluido de maior diâmetro inicial (Dmodal = 9,24±0,08 nm e σ=0,238±0,009). Estudos de magnetohipertermia foram realizados a 300kHz para as alíquotas estudadas. Foram encontradas taxa de absorção específicas (SAR) maiores para sistemas com nanopartículas maiores, propriedade muito importante nas aplicações relacionadas ao tratamento de câncer. Portanto, conclui-se que o experimento magnetoforético pode ser utilizado para selecionar propriedades de fluidos magnéticos, por meio do controle do diâmetro e desvio padrão de tamanhos, para diversas aplicações tecnológicas, ambientais e biomédicas.
|
30 |
EQUAÇÕES DE LORENZ-CROSS NA FERROHIDRODINÂMICA / Equations LORENZ IN CROSS-FERROHIDRODINÂMICASASAKI, Nélio Martins da Silva Azevedo 05 April 2008 (has links)
Made available in DSpace on 2014-07-29T15:07:10Z (GMT). No. of bitstreams: 1
Dissertacao nelio.pdf: 402379 bytes, checksum: 978793fda386f5ccef16f94380d52b6f (MD5)
Previous issue date: 2008-04-05 / In this work we investigated the problem of Rayleigh-Bénard for a magnetic binary fluid,
i.e., a magnetic fluid, which consist of magnetic nanopartilces stably dispersed in a liquid
carrier. The theoretical calculations were performed based on a Lorenz-like model, which
transforms a system of partial differential equations into ordinary differential ones. The
analysis of the magnetic binary fluid problem used the Navier-Stokes, thermal conduction
and mass diffusion equations. The magnetic body force was obtained using the Cowley-
Rosensweig tensor as well as the Maxwell equations. The mass flux had included the
difusive contribution, associated to Fick s law, and also the thermal diffusion term, due to
the Soret effect. Our model consist of a system of eight ordinary differential equations,
which were shown to mantain the same mathematical form as the ones obtained earlier by
Cross for a non-magnetic binary fluid. However, as expected, our coefficients depend on
the magnetic field. According to our investigation on the site www.isiknowledge.com this
is the first time in the literature that those equations are obtained, which we named the
Lorenz-Cross equations on Ferrohydrodynamics. The validity of our system of equations
were, also, checked in the limit of a simple fluid, where our model returns to the
Lorenz equations. The only difference is the existence of an effective Rayleigh number,
represented by the sum of the Rayleigh number and the magnetic Rayleigh one. Finally,
the efect of magnetophoresis in the system of equations had also been discussed. / Neste trabalho investigamos o problema de Rayleigh-Bénard para um fluido binário
magnético, ou seja, um fluido magnético, que consiste de nanopartículas magnéticas
dispersas em um líqüido carreador.Os cálculos teóricos foram baseados na construção
de um modelo tipo Lorenz, pelo qual transformamos um sistema de equações diferenciais
parciais em equações diferenciais ordinárias. O sistema de equações para o fluido binário
utilizou as equações de Navier-Stokes, condução de calor e difusão de massa.A força
magnética foi obtida, usando o tensor eletromagnético de Cowley-Rosensweig, levando
em conta as equações de Maxwell. O fluxo de massa considerou o termo difusivo,
associado a Lei de Fick, e a contribuição termodifusiva, devido ao efeito de Soret.Nosso
modelo consiste de um sistema de 8 equações diferenciais ordinárias, e manteve a mesma
forma matemática daquelas obtidas anteriormente por Cross para um sistema binário
não-magnético. Entretanto, possui contribuições dependentes do campo magnético. De
acordo com nosso levantamento bibliográfico essa é a primeira vez na literatura que
essas equações são obtidas, as quais denominamos de equações de Lorenz-Cross na
Ferrohidrodinâmica.A validade do nosso sistema de equações foi verificada, também,
no limite de um fluido simples, no qual nosso sistema retorna ao modelo tradicional de
Lorenz com a diferença da contribuição de um número de Rayleigh efetivo, que representa
a soma do número de Rayleigh tradicional com um Rayleigh magnético. A contribuição
do efeito magnetoforético para o sistema de equações também foi discutida.
|
Page generated in 0.0799 seconds