CFD Study On Magnetic Fluid In High Gradient Magnetic Field

HGMS is widely used in magnetic drug targeting (MDT) and industrial fields.Incorporating magnetic particles into drug carriers and using an externally appliedmagnetic field is one way to physically direct these magnetic drug carrier particles(MDCP) to a human vivo. So the particle moving behaviors and the magnetic fluid flowbehaviors are to be investigated.We used Cluster-moving Metropolis Monte Carlo method to simulate the magnetic particles (or magnetic carried particles) aggregation in uniform magnetic field, and once particles aggregate together then permanently attach to each other. The dynamics of aggregation is characterized in terms of particle mean size, fractal dimension, distribution of orientations and radial distribution function on different sized particles. From small to large diameters, the distribution of orientations approach the orientation of magnetic field direction step by step, the larger one forms chain-like clusters, smaller size forms clusters with branched and looped shapes.The fractal dimensions of each diameter indicate fluctuation for 20, 40, 100nm during the process. For the polydisperse system, the radial distribution function shows the peaks shift from the integer multiples of average diameter. It indicates that particles larger than those of average diameter are the most common to be found forming clusters, the behavior of the small particles is not the main factor in the cluster formation.We simulated the capture behavior and the advection-diffusion behavior of magnetic particles in the cross-section of different curvature magnetic sources which bring the high gradient magnetic field with the time evolution. The results show that the capture behavior is affected not only by the fluid velocities, dynamic viscosity, particle size, and susceptibility, but also by the shape of magnetic sources. Although the curvature of magnetic source dominates the gradient of the magnetic field, enough large area facing the incoming fluid is still the main factor which affects the capture efficiency. The distribution of concentration in the cross section area and source surface are both affected by the surface curvature, especially under the relatively stronger interaction of magnetic source, the influence by surface curvature becomes much more evident, larger curvature costs shorter time for particles accumulation than the smaller one, the magnetic force competing with the fluid drag force could decides the concentration situation. We also simulated the separation behaviors in the branch vessel, different direction of magnets and inlet velocity would decide the separation efficiency.The convection and diffusion behaviors of the moving magnetic fluid or ferrofluid in the vessel in the high gradient magnetic field were simulated using incompressible Navier-Stokes equations. The particles accumulation behavior and the streamlines and the contour of concentration are both affected by the susceptibility, intensity of magnetic field and its gradient, and the flow velocity and also by the different size vessels. The accumulation behaves as a solid obstacle in the flow as result of the competing between magnetic and fluid drag forces and gives rise to a rigidly bound core region followed by a wash away region near the vessel boundary under the condition of 10mm vessel in width. While the vessel is near 1mm in width, the magnetic force exerts almost on the whole vessel area, the vortex is not seen, the wash away area disappears and the concentration changes in the whole vessel. The results of the analysis provide meaningful information on ferrofluid transport and stabilization for various magnetic drug targeting and the magnetic fluid sealing, and other using in industrial and medical circumstance. We also described a theoretical analysis of advection and diffusion behavior of magnetic drug targeting particles moving in the blood vessel especially considering adhesion and detachment behaviors which cause the diffusion to the vessel wall in the high gradient magnetic field located on the boundary of the vessel. The numerical results show that the concentration distribution and other parameters are mainly affected by the magnetic force parameters, adhesion and detachment rate coefficients on the vessel wall, and the diffusion coefficient of the particles in the fluid. The effect of adhesion rate coefficient is especially important in this magnetic targeting model, the peak of concentraion appears while the adhesion rate effect can dominate the magnetic interaction effect. Magnetic fluid flows around magnet in a channel under the influence of high gradient magnetic field and the difference of temperature between upper and lower boundaries of the channel,it is considered that its magnetization of the fluid varies linearly with temperature and magnetic field intensity. The numerical solution of above model is described by a coupled and non-linear system of PDEs. Results indicate that the presence of magnetic field and temperature field appreciable influence the flow field, vortexes are arose almost around the magnetic source, and also appear near the left upper and right lower boundaries, temperature, local skin friction coefficient and the rate of heat transfer fluctuate evidently near the high gradient magnetic field area and are all affected by the magnitude and the position of the magnetic source, velocity, difference of temperature between upper and lower boundaries, the changing of the local skin friction coefficient and rate of heat transfer with above parameters is contrary on the upper and lower boundaries. The orientation of magnetic can also affect the flow and temperature fields.We introduced some simulation methods of two phases fluid, then we mainly investigated the numerical simulation of two phases fluid behavior of ferrofluid and blood using level set method in the channel in the HGMF, results show that the difference and the magnitude of inlet velocities of these fluids both make different situations of fluid interface and ferrofluid region distribution with the time evolution. When the velocity of blood is larger or smaller than it of ferrofluid, the interface is not flat and the controlled area is small, when the velocity of blood is nearly equal to the velocity of ferrofluid, the interface is relatively flat. When ferrofluid is strongly controlled by the magnet the controlled area is larger and the interface is not flat. So the choosing suitable inlet velocities would optimize the MDT efficiency. Although here we simulated the two phases in vivo, the behavior is also helpful in other industrial fields such as in MEMs and so on.