이중원관내 자성유체의 자연대류에 대한 전열특성

Magnetoreception

A two-dimensional thermal laminar natural convection of molten gallium in square enclosure isothermally heated and cooled from a side vertical wall was numerically computed in both time-periodic magnetic and gravity fields. The magnetic field is described by a sinusoidal time-varying equation. The thermal coefficient heat transfer has been calculated for various magnetic field strengths, but at a certain value of frequency and for different frequencies, but at a certain value of magnetic field strength. The results show that the effect of the time-periodic magnetic field on the flow field and heat transfer is lower than that of steady (DC) magnetic field effect at the same magnetic field strength.

Modeling and optimization of MHD mixed convection in a lid-driven trapezoidal cavity filled with alumina–water nanofluid: Effects of electrical conductivity models

In this study, the behavior of Cu–water nano-fluid in a pipe has been investigated numerically. The pipe is under the external magnetic field, and the magnetic field is applied perpendicularly to the pipe. The temperature of pipe is higher than the temperature of fluid. The study was carried out for three different Reynolds numbers. The magnetic field forces and nano-fluid volume fractions were chosen as Ha = 0, 10, 20 and φ = 0, 0.02, 0.04, respectively. Analysis was carried out with the ANSYS Fluent commercial software. Fluid velocity curves, local Nusselt (NuX) and average Nusselt (Nu) values are presented graphically. In all Re numbers, the fluid velocity decreases with magnetic field strength and nanoparticle effect. Local Nu number has increased with magnetic field, nanoparticle volume fraction (Re = 500) and Re number. However, this increase is less for the nano-fluid volume fraction, and then decreases at Re = 5 and 50. At all magnetic field strengths, the mean Nu number for Re = 5 and 50 is reduced with the addition of nanoparticles, but has increased for Re = 500. At all nano-volume fraction, the average Nu number is increased with the magnetic field for Re = 50 and 500. For Re = 5, the average Nu number increases up to Ha = 10, but it decreases at Ha = 20. As a result, magnetic field strength, nano-fluid volume fraction and Re number have found to be effective on heat transfer, and nano-fluid motion can be controlled by magnetic field.

Magnetic resonance techniques were developed in the mid-1940s to analyze the structures of chemical compounds. In the last 10 years, however, the same principles have been evolved, along with advances in magnet, computer, and display technology into one of the most exciting imaging methods available in the medical field today. Magnetic resonance imaging utilizes the property that certain nuclei when placed in a magnetic field can be stimulated into a resonance condition by external radio-frequency radiation. In recovering from this disturbance, the nuclei in turn emit rf signals (whose frequencies depend on the magnetic field strength in which the nuclei are located). To image the human body, the patient is placed in a large solenoidal magnet (field strength typically 0.5-1.5 T), and the magnetic field Is coded in various ways by the application of gradient fields, causing the protons within the volume to resonate with a range of frequencies. Relating these frequencies to positions within this volume is performed by a Fourier analysis of the signal. Reconstructed images are displayed to the user as slices of the 3-D volume being imaged.

Influence of the shape of the inner boundary on thermomagnetic convection in the annulus between horizontal cylinders: Heat transfer enhancement

This study was conducted to determine the effects of magnetic field (MF) strength on shoot regeneration and Agrobacterium tumefaciens-mediated gene transfer in flax (Linum usitatissimum L.). Seeds of flax cv. Madaras were exposed to different MF strengths (0 – control, 75, 150, and 300 millitesla (mT)) for 24 h by using an electromagnetic generator system fabricated in laboratory conditions. After sterilization, seeds were germinated on MS (Murashige and Skoog) medium in Magenta vessels. Hypocotyl explants excised from 7-days-old seedlings were used for regeneration. GV2260 strain of Agrobacterium tumefaciens was used in transformation studies. Inoculated hypocotyls were cultured on MS medium containing 1 mg/l BAP (6-benzylaminopurine) and 0.02 mg/l NAA (naphthaleneacetic acid) for 2 days by co-cultivation. Then, they were transferred to MS medium containing the same growth regulators, 100 mg/l kanamycin and 500 mg/l Duocid for selection. The presence of the nptII gene was verified by PCR (polymerase chain reaction) analysis in putative transgenic plants. The highest results with respect to shoot regeneration and transformation frequency were obtained from treatments of 75 mT MF strength.

Purpose. Study of the dependence of the thermal modulus of elasticity of a two-component magnetic fluid on the magnitude of the magnetic field strength, the frequency of external disturbance and the volumetric concentration of magnetic particles.Method. The research method is based on the kinetic theory of liquid systems. Based on previously constructed kinetic equations for one-particle and two-particle distribution functions and a microscopic expression for the heat flux vector, an explicit dynamic expression for the thermal modulus of elasticity of magnetic fluids is obtained. In fast processes in liquids, heat transfer occurs in waves and their propagation is similar to the propagation of second sound in helium II. The thermal modulus of elasticity in liquids appears at high frequencies and ensures the propagation of second sound. The expression for the thermal modulus of elasticity consists of potential and kinetic parts, taking into account structural and translational relaxation processes, respectively. To study the thermoelastic properties of magnetic fluids, appropriate expressions of potential interaction energies were selected for each subsystem, allowing for numerical calculations.Results. Numerical calculations of the frequency and concentration dependence of the dynamic thermal modulus of elasticity in the presence of an external magnetic field in a kerosene-based magnetic fluid were carried out. The calculation results show that an increase in the influence of external disturbances leads to a nonlinear increase in the thermal modulus of elasticity in the magnetic fluid. An increase in the volume concentration of magnetic particles and an increase in the magnetic field strength also led to a nonlinear increase in the thermal modulus of elasticity in the magnetic fluid.Conclusion. It has been established that, due to taking into account translational and structural relaxation processes, the region of frequency dispersion of the thermal elastic modulus is wide. Numerical calculations carried out at different values of the external magnetic field and the volume concentration of magnetic particles showed that although an increase in the magnetic field and concentration of magnetic particles leads to an increase in the thermal modulus of elasticity, their increase does not affect the change in the frequency dispersion region.

Non-contact manipulation of nonmagnetic materials by using a uniform magnetic field: Experiment and simulation

Different volume concentrations (1.2, 0.6, 0.3 wt%) of Fe 3 O 4 /water nanofluids and for different Reynolds number (Re) varying from 2180 to 9160 were used experimentally. The aim of work is to study the effect of applying various magnetic field intensity 15.1, 30.3, 45.5 mT on heat transfer enhancement in a horizontal pipe heated with constant heating flux of 420 W. Results showed that Nusselt number (Nu) increases with increasing Re for the nanofluids and water regardless the presence or absence of the magnetic field. Also, higher values were obtained than water. The average increase in Nu for Fe 3 O 4 -nanofluids is 16.7% relative to water when the magnetic field is not applied. However, the average increase in heat transfer coefficient and Nusselt number are 9.4%, 26.1%, 31.3% and 8.8%, 13.1%, and 23.9% in the presence of magnetic field [Formula: see text] compared to the absence of magnetic field and base fluid water, respectively. Furthermore, pressure drop increases with the increase of Reynolds number and magnetic field strength. It can be concluded that the magnetic field has a big effect on the thermal transfer performance of Fe 3 O 4 /water nanofluid when compared with the thermal motion of magnetic nanoparticles. Finally, it is found that the performance factor is above unity in the presence and absence of magnetic field strength. This means that Nusselt number enhancement is higher than friction changes, which indicates the applicability of the heated pipe in the improvement of heat transfer. These results can be useful for enhancing heat transfer in many engineering applications such as heat exchangers, medical devices, and electronic devices.

The dispersed particles of magnetic fluid form stable chain-like clusters under the magnetic field, and shows “the flowing is controllable and the shape is controllable” effect. Based on this characteristic, using migration magnetic acted on the magnetic fluid, the object directional migration can be realize, then the magnetic fluid form ribbon at the same time, has the similar fluctuation behavior. The magnetic fluid aerosol migration principle, the aerosol magnetic circuit design, the magnetic field strength and the magnetic force were separately discussed in this paper. The magnetic fluid hover height using the MSL micrometer dial has determined and aerosol migration feasibility has confirmed using the experiment.

Static weak magnetic field measurements based on low-field nuclear magnetic resonance.

The potential of colloidal subdomain ferrite particle suspensions (SDP) (‘magnetic fluids’), exposed to an alternating magnetic field, is evaluated for hyperthermia. Power absorption measurements of different magnetic fluids are presented in comparison to multidomain ferrite particles (MDP). Variations with frequency as well as magnetic field strength have been investigated. The experimental results clearly indicate a definite superiority of even non-optimized magnetic fluids over MDP ferrites regarding their specific absorption rate (SAR). Based on the work of [Shliomis, Pshenichnikov, Morozov, Shurubor. Magnetic properties of ferrocolloids. J Magn Magn Mater 1990;85:40–46 and [Hanson The frequency dependence of the complex susceptibility of magnetic fluids. J Magn Magn Mater, 1991;96 (In press).], a solid-state physical model is applied to explain the specific properties of magnetic fluids with respect to a possible use in hyperthermia. The experimentally determined SAR data on magnetic fluids are used to estimate the heating capabilities of a magnetic induction heating technique assuming typical human dimensions and tissue parameters. It is considered that for a moderate concentration of 5 mg ferrite per gram tumour (i.e. 0.5% w/w) and clinically acceptable magnetic fields, intratumoral power absorption is comparable to RF heating with local applicators and superior to regional RF heating (by comparison with clinical SAR measurements from regional and local hyperthermia treatments). Owing to the high particle density per volume, inductive heating by magnetic fluids can improve temperature distributions in critical regions. Furthermore, localized application of magnetic fluids in a tumour might be easier and less traumatic than interstitial implantation techniques.

Heat transfer coefficient is a key parameter for efficiency evaluation of heat exchangers. Good stability and high heat transfer coefficient are essential for the application of nanofluids in heat exchangers and solar systems. In this work, nanofluids with good stability were prepared, and the influence of vertical magnetic field on flow and heat exchange of magnetic nanofluids under laminar and turbulent conditions was mainly studied. The flow and heat transfer rules of Fe3O4 nanofluids with or without magnetic field conditions, magnetic field strength, magnetic field distribution, the nanoparticle concentration and nanofluids temperature were systematically studied by setting up an experimental platform. The results show that the intensity and distribution of magnetic field had a significant influence on the heat transfer of magnetic nanofluids, whether in laminar or turbulent flow. When the magnetic field strength is 800G and 1000G, the convective heat transfer coefficient increases by an average of 23.89% and 26.12%. However, the influence of magnetic field on its flow characteristics is not obvious, and the effect on resistance coefficient increases by only 2.01%. In addition, the characteristics of magnetic nanofluids also have a certain influence on its flow and heat transfer. When the temperature of magnetic nanofluids is increased, the convective heat transfer coefficient will increase. When the concentration of magnetic nanofluids is increased, the pressure drop will also increase, but it has little effect on the drag coefficient.

Magnetic field induced acceleration or deceleration of bubble rising inside ferrofluids: A fractional step lattice Boltzmann investigation