Magnetic Fluid Temperature Research Articles

Thermal analysis of a miniature magnetic fluid seal installed in an implantable rotary pump

The capacity of a magnetic fluid (MF) seal is decreased by increased MF temperature. A cooling system for MF is limited in a miniature MF seal installed in an implantable rotary pump. MF temperature in an MF seal installed in an implantable rotary pump was studied.The temperature of MF in a rotary pump was measured in vitro. Also, steady-state thermal analyses were conducted for an implantable rotary pump model. The results showed that (1) the decrease in magnetization of an MF due to increased temperature is negligible when the heat transfer coefficient of the seal housing is greater than 500 W/(m2·K) and (2) the increased temperature is mainly due to heat flux from the motor, and the magnitude of temperature increase due to viscous friction in the MF is low.In conclusion, an MF seal can be used in an implantable rotary pump from the standpoint of heat characteristics.

Investigation of structural changes in oil-based magnetic fluids by surface acoustic waves

Surface acoustic waves (SAWs) are used for the first time to investigate structural changes in transformer oil-based magnetic fluids under magnetic field. The measurement of the attenuation of SAW propagating along the interface between magnetic fluid and the piezoelectric substrate is showed as an effective tool to study such processes in the case of magnetic fluids when the obviously utilized longitudinal acoustic waves due to the higher viscosity are not available. The magnetic particles FeO.Fe2O3 in several different volume concentrations, from 0.05% to 3.5%, were added to the transformer oil MOL. Both linear increasing and jumped changed magnetic field were applied to study structural changes. The interaction between the magnetic field and magnetic moments of nanoparticles can lead to the aggregation of magnetic nanoparticles and following chain or cluster formations that have an influence on the SAW attenuation. The concentration of magnetic nanoparticles and temperature of magnetic fluid have a decisive influence on structural changes due to the changes of viscosity and thermal motion with the increasing temperature that both affect the process of cluster formation. The measurement of the acoustic anisotropy and applying the theoretical predictions gives additional useful information about the structure of nanoparticles formations in investigated magnetic fluids. Obtained results are compared and discussed.

Uses and limitation of different thermometers for measuring heating efficiency of magnetic fluids

This paper presents the results of the heating of magnetic fluid (MF) containing magnetite nanoparticles. Volume concentration of magnetite nanoparticles (ϕV = 2.76%) was determined from magnetic experiments. Mean diameter 〈d〉 = 12.7 nm and its standard deviation s = 5.0 nm of the core of magnetic particles were obtained using TEM technique. Magnetic fluid heating experiments were carried out at a frequency of 440 kHz for magnetic field strength up to 3 kA⋅m−1 using lab-made experimental set-up. For temperature measurements, various kinds of devices were used: pyrometer, thermocouple thermometer, optical fiber temperature sensor and thermometer with ultrasonic sensor. Specific absorption rate (SAR) and temperature measurement error were calculated and discussed for all the thermometers used. The influence of eddy currents induced in a thermocouple on the determination of temperature of MF was described. The usefulness of different types of temperature measuring devices and their accuracy in determining the heating rate and the SAR coefficient of the magnetic fluid were analyzed and discussed.

Structure of nanoparticles in transformer oil-based magnetic fluids, anisotropy of acoustic attenuation

The anisotropy of acoustic attenuation in transformer oil-based magnetic fluids upon the external magnetic field was studied to discover the structure of nanoparticles. When a magnetic field is increased, the interaction between the external magnetic field and the magnetic moments of the nanoparticles leads to the aggregation of magnetic nanoparticles and following clusters formation. However, the temperature of magnetic fluids and the concentration of nanoparticles also have very important influence on the structural changes. The measurement of the dependence of the acoustic attenuation on the angle between the magnetic field direction and acoustic wave vector (anisotropy) can give the useful information about the structure of magnetic nanoparticles formations. In the present, the results of anisotropy measurements of the transformer oil-based magnetic fluids are described and using appropriate theory the basic parameters of clusters are calculated. On the basis of the performed calculations, the proportion of the acoustic wave energy used for excitation of the translational and rotational degrees of freedom was also established.

Research on temperature and magnetic field sensing characteristics of photonic crystal fiber filled with magnetic fluid

In this study, the photonic crystal fiber (PCF) air holes were filled with a kind of new functional material—magnetic fluid (MF) is presented. According to the sensitive characteristics of MF's refractive index versus temperature and magnetic field, the loss characteristic of the PCF filled with MF caused by temperature/magnetic field were analyzed theoretically by finite element method. It could be concluded that when the surrounding temperature rises from 37.5 to 80°C, the PCF loss sensitivity is about −0.167 dB/°C; when the external magnetic field rises from 20 to 300 Oe, the PCF loss sensitivity is about 0.042 dB/Oe. Besides, experiment was also carried out to verify the aforementioned results. With the same external condition, the loss sensitivity of temperature is about −0.167 dB/°C and loss sensitivity of magnetic field is about 0.046 dB/Oe. The results indicated that theoretical calculation basically agrees with the experimental verification, by which a new method and new thought for temperature and magnetic field measurement is provided. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:831–834, 2014

Acoustic Properties of Magnetic Fluids Based on Transformer Oil Under Magnetic Field

Abstract The structural changes in magnetic fluids based on transformer oil TECHNOL and MOGUL upon the effect of an external magnetic field and temperature were studied by acoustic spectroscopy. When a magnetic field is increased, the interaction between the magnetic field and the magnetic moments of the nanoparticles leads to the aggregation of magnetic nanoparticles and following clusters formation. However, the temperature of magnetic fluids has also very important influence on the structural changes because of the mechanism of thermal motion that acts against the cluster creation. The live time of clusters have relative long time scale for the magnetic fluid based on TECHNOL, while for MOGUL is quite short.

Comparison of Theories of Anisotropy in Transformer Oil-Based Magnetic Fluids

The external magnetic field in transformer oil-based magnetic fluids leads to the aggregation of magnetic nanoparticles and formation of clusters. These aggregations are the result of the interaction between the external magnetic field and the magnetic moments of the nanoparticles occurs. However, the temperature of magnetic fluids has also very important influence on the structural changes because the mechanism of thermal motion acts against the cluster creation. The acoustic spectroscopy was used to study the anisotropy of transformer oil-based magnetic fluids upon the effect of an external magnetic field and temperature. In present the anisotropy of the magnetic fluids can be described by two theories. Taketomi theory assumes the existence of spherical clusters. These clusters form long chains, aligned in a magnetic field direction. Shliomis in his theory supposed that only nanoparticles formed chains. A comparison of the experimental results with the predictions of the Taketomi theory allowed a determination of the cluster radius and the number density of the colloidal particles. The proportions of the acoustic wave energy used for excitation of the translational and rotational motion were determined.

Structure of transformer oil-based magnetic fluids studied using acoustic spectroscopy

The structural changes in transformer oil-based magnetic fluids upon the effect of an external magnetic field and temperature were studied by acoustic spectroscopy. The attenuation of acoustic wave was measured as a function of the magnetic field in the range of 0–300mT and in the temperature range of 15–35°C for various magnetic nanoparticles concentrations. The effect of anisotropy of the acoustic attenuation was determined, too. The both strong influence of the magnetic field on the acoustic attenuation and its hysteresis were observed. When a magnetic field is increased, the interaction between the external magnetic field and the magnetic moments of the nanoparticles occurs, leading to the aggregation of magnetic nanoparticles and following clusters formation. However, the temperature of magnetic fluids also has very important influence on the structural changes because of the mechanism of thermal motion that acts against the cluster creation. The observed influences of both magnetic field and temperature on the investigated magnetic fluid structure are discussed.

Simulating magnetic nanoparticle behavior in low-field MRI under transverse rotating fields and imposed fluid flow

In the presence of alternating-sinusoidal or rotating magnetic fields, magnetic nanoparticles will act to realign their magnetic moment with the applied magnetic field. The realignment is characterized by the nanoparticle's time constant, τ . As the magnetic field frequency is increased, the nanoparticle's magnetic moment lags the applied magnetic field at a constant angle for a given frequency, Ω , in rad s −1. Associated with this misalignment is a power dissipation that increases the bulk magnetic fluid's temperature which has been utilized as a method of magnetic nanoparticle hyperthermia, particularly suited for cancer in low-perfusion tissue (e.g., breast) where temperature increases of between 4 and 7 °C above the ambient in vivo temperature cause tumor hyperthermia. This work examines the rise in the magnetic fluid's temperature in the MRI environment which is characterized by a large DC field, B 0. Theoretical analysis and simulation is used to predict the effect of both alternating-sinusoidal and rotating magnetic fields transverse to B 0. Results are presented for the expected temperature increase in small tumors ( ∼ 1 cm radius) over an appropriate range of magnetic fluid concentrations (0.002–0.01 solid volume fraction) and nanoparticle radii (1–10 nm). The results indicate that significant heating can take place, even in low-field MRI systems where magnetic fluid saturation is not significant, with careful the goal of this work is to examine, by means of analysis and simulation, the concept of interactive fluid magnetization using the dynamic behavior of superparamagnetic iron oxide nanoparticle suspensions in the MRI environment. In addition to the usual magnetic fields associated with MRI, a rotating magnetic field is applied transverse to the main B 0 field of the MRI. Additional or modified magnetic fields have been previously proposed for hyperthermia and targeted drug delivery within MRI. Analytical predictions and numerical simulations of the transverse rotating magnetic field in the presence of B 0 are investigated to demonstrate the effect of Ω , the rotating field frequency, and the magnetic field amplitude on the fluid suspension magnetization. The transverse magnetization due to the rotating transverse field shows strong dependence on the characteristic time constant of the fluid suspension, τ . The analysis shows that as the rotating field frequency increases so that Ω τ approaches unity, the transverse fluid magnetization vector is significantly non-aligned with the applied rotating field and the magnetization's magnitude is a strong function of the field frequency. In this frequency range, the fluid's transverse magnetization is controlled by the applied field which is determined by the operator. The phenomenon, which is due to the physical rotation of the magnetic nanoparticles in the suspension, is demonstrated analytically when the nanoparticles are present in high concentrations (1–3% solid volume fractions) more typical of hyperthermia rather than in clinical imaging applications, and in low MRI field strengths (such as open MRI systems), where the magnetic nanoparticles are not magnetically saturated. The effect of imposed Poiseuille flow in a planar channel geometry and changing nanoparticle concentration is examined. The work represents the first known attempt to analyze the dynamic behavior of magnetic nanoparticles in the MRI environment including the effects of the magnetic nanoparticle spin-velocity. It is shown that the magnitude of the transverse magnetization is a strong function of the rotating transverse field frequency. Interactive fluid magnetization effects are predicted due to non-uniform fluid magnetization in planar Poiseuille flow with high nanoparticle concentrations.

Heating in the MRI environment due to superparamagnetic fluid suspensions in a rotating magnetic field

In the presence of alternating-sinusoidal or rotating magnetic fields, magnetic nanoparticles will act to realign their magnetic moment with the applied magnetic field. The realignment is characterized by the nanoparticle's time constant, τ. As the magnetic field frequency is increased, the nanoparticle's magnetic moment lags the applied magnetic field at a constant angle for a given frequency, Ω, in rad/s. Associated with this misalignment is a power dissipation that increases the bulk magnetic fluid's temperature which has been utilized as a method of magnetic nanoparticle hyperthermia, particularly suited for cancer in low-perfusion tissue (e.g., breast) where temperature increases of between 4°C and 7°C above the ambient in vivo temperature cause tumor hyperthermia. This work examines the rise in the magnetic fluid's temperature in the MRI environment which is characterized by a large DC field, B(0). Theoretical analysis and simulation is used to predict the effect of both alternating-sinusoidal and rotating magnetic fields transverse to B(0). Results are presented for the expected temperature increase in small tumors (~1 cm radius) over an appropriate range of magnetic fluid concentrations (0.002 to 0.01 solid volume fraction) and nanoparticle radii (1 to 10 nm). The results indicate that significant heating can take place, even in low-field MRI systems where magnetic fluid saturation is not significant, with careful selection of the rotating or sinusoidal field parameters (field frequency and amplitude). The work indicates that it may be feasible to combine low-field MRI with a magnetic hyperthermia system using superparamagnetic iron oxide nanoparticles.

Effects of the sweep rate of the magnetic field on the changes of ultrasonic wave velocity in magnetic fluid

An external magnetic field applied to a homogeneous magnetic fluid induces a change in its structure manifested as the appearance of chains of magnetic particles arranged along the direction of the field. This change implies changes in the acoustic and magnetic properties of the magnetic fluid such as the acoustic wave propagation velocity and coefficient of ultrasonic wave absorption, and in magnetisation. The paper reports results of a study on the influence of the magnetic field sweep rate and the magnetic fluid temperature on the value of ultrasonic wave velocity, proving that the degree of the aggregation of the magnetic particles (chain formation process) depends on the above-mentioned parameters.