ABSTRACT
Heat dissipation has become an important issue due to the miniaturization of various electronic devices. Various methods such as spray and nozzle coolers, heat sinks and so on are used for heat dissipation. However, the emergence of ferrofluids drastically improves the operating characteristics of electromagnetic systems and devices. A ferrofluid is a suspension containing 10-nm magnetic particles in a colloidal solution. This material exhibits paramagnetic behavior and is sensitive to magnetic field and temperature. In this study, heat transfer characteristics of ferrofluids in a rotating eccentric cylinder were investigated using the commercial code, COMSOL Multiphysics. Numerical results of the local Nusselt number, magnetophoretic force and velocity distributions were obtained from various eccentricities of the cylinder, and the results were graphically depicted with various flow conditions.
ABSTRACT
This study numerically investigated the flow characteristics in a rectangular enclosure filled with oil-based ferrofluid (EFH-1, Ferrotec.) under the influence of external magnetic fields. The rectangular enclosure contained obstacles with different shapes, such as a rectangle and a triangle mounted on the top and bottom wall surfaces. In order to generate external magnetic fields, a permanent magnet was located in the lower part of the rectangular enclosure, and its direction was selected to be either horizontal or vertical. Our results showed that the ferrofluid flow fields were affected by the applied external magnetic field direction and eddy flow phenomena in the working fluid were generated in the vicinity of high magnetic flux density distributions, such as at the edge of the permanent magnet. It was also confirmed that the magnetophoretic force distributions in the analysis model played a significant role in the development of the ferrofluid flow fields.
ABSTRACT
The characteristics of thermomagnetic convective flow in a rectangular enclosure heated from below and filled with oil-based nanofluid (EFH-1, Ferrotec.), so called ferrofluid, were numerically investigated. The enclosure contained obstacles with rectangular or triangular configurations mounted on the top and bottom walls. To generate homogeneous magnetic fields, a permanent magnet with a uniform magnetic field strength of 600 kA/m was located in the lower part of the rectangular enclosure, and specified the horizontal or vertical direction. Coupling calculations between thermal-flow field and magnetic field in the analysis model were performed using the commercial code, COMSOL Multiphysics. Results showed that the ferrofluid flow fields were affected by the applied external magnetic field directions and that the eddy flow phenomena in the rectangular enclosure were generated in the vicinity of the section of high magnetic flux density fields such as the edge of the permanent magnet. The effect of parameters like temperature distributions and local Nusselt number (Nu) profiles on the thermomagnetic convective flow was graphically depicted with various flow conditions.
ABSTRACT
In previous research, we studied the electrical breakdown characteristics of a transformer oil-based magnetic fluid; mailnly, those were carried out by the experimental measurements. The first study was aimed at enhancing the dielectric breakdown voltage of transformer oil by adding magnetic nanoparticles experimentally under the official testing condition of dielectric liquids. The next study was focused on explaining the reason why the dielectric characterisitics of the fluids were changed through optically visualizing the particles motion in a microchannel using an optical microscopic measurement and numerically calculating the dielectrophoretic force induced in the fluids with considering only the properties of magnetic nanoparticles. In this study, we developed a simplified unified model for calculating further the motion of magnetic nanoparticles suspended in the presence of electrohydrodynamic field using the COMSOL multiphysics finite element simulation suite and investigated the effects of magnetic nanoparticle dielectrophoretic activity aimed at enhancing the electrical breakdown characteristics of transformer oil.
ABSTRACT
Congenital hypertrophic cardiomyopathy (HCMP) is a very rare congenital heart disease. Here, we report a case of neonatal HCMP, which was confirmed by two-dimensional echocardiography and autopsy. The HCMP rapidly progressed and the patient's condition deteriorated, despite the treatment for congestive heart failure.
ABSTRACT
A new type of electrokinetic micromixer with a ring-type channel is introduced for fast mixing. The proposed mixer takes two fluids from different inlets and combines them in a ring-type mixing chamber. The fluids enter two different inlets (inner radius: 25 microm and outer radius: 50 microm), respectively. The total channel length is 500 microm, and four microelectrodes are positioned on the outer wall of the mixing chamber. The electric potentials on the four microelectrodes are sinusoidal with time, having various maximum values of voltage, zeta potential and frequency. Also, in order to compare the mixing performance with different obstacle configurations, we performed a numerical analysis using a commercial code, COMSOL. The concentration of the dissolved substances in the working fluid and the flow and electric fields in the channel were investigated and the results were graphically depicted for various flow and electric conditions.
Subject(s)
Microfluidics/instrumentation , Nanotechnology/instrumentation , Solutions/chemistry , Titanium/chemistry , Equipment Design , Equipment Failure Analysis , Miniaturization , Osmotic PressureABSTRACT
The micromixer that is applied for the electro-osmotic effect in this study, which is a passive type, takes two fluids from different inlets and combines them into a single channel. The fluids then enter the mixing chamber with different inner and outer radii. Four microelectrodes are positioned on the outer wall of the mixing chamber. The electric potentials on the four microelectrodes are sinusoidal for certain values of the time, voltage, zeta potential, and frequency. In order to check the validity of the two-dimensional numerical analysis that already has been performed, we performed a three-dimensional numerical analysis using a commercial code, COMSOL. The incompressible Navier-Stokes equation is solved in this model, with a slip boundary condition on the inner and outer walls of the mixing chamber. The results of two- and three-dimensional models are graphically depicted and compared from the viewpoint of streamlines and concentration.
ABSTRACT
PURPOSE: The aim of this study was to investigate bronchodilator responsiveness (BDR) following methacholine-induced bronchoconstriction and to determine differences in BDR according to clinical parameters in children with asthma. METHODS: The methacholine challenge test was performed in 145 children with mild to moderate asthma, and the provocative concentration causing a 20% decline in FEV1 (PC20) was determined. Immediately after the challenge test, patients were asked to inhale short-acting ß2-agonists (SABAs) to achieve BDR, which was assessed as the change in FEV1% predicted×100/post-methacholine FEV1% predicted. For each subject, the asthma medication, blood eosinophil count, serum total IgE, serum eosinophil cationic protein level, and skin prick test result were assessed. RESULTS: The FEV1 (mean±SD) values of the 145 patients were 90.5±10.9% predicted, 64.2±11.5% predicted, and 86.2±11.2% predicted before and after methacholine inhalation, and following the administration of a SABA, respectively. The BDR did not differ significantly according to asthma medication, age, or gender. However, BDR in the atopy group (37.4±17.7%) was significantly higher than that in the non-atopy group (30.5±10.7%; P=0.037). Patients with blood eosinophilia (38.6±18.1%) displayed increased BDR compared with patients without eosinophilia (32.0±13.8%; P=0.037). CONCLUSIONS: In children with mild to moderate asthma, the responsiveness to short-acting bronchodilators after methacholine-induced bronchoconstriction was not related to asthma medication, but was higher in children with atopy and/or peripheral blood eosinophilia.
