Decai Li

Compact magnetic-field sensor based on optical microfiber Michelson interferometer and Fe3O4 nanofluid.

We report a magnetic-field sensor by merging the advantages of optical fiber Michelson interferometers with that of magnetic fluid. Compact and low-cost optical fiber Michelson interferometers were first fabricated by a high-frequency CO(2) laser, and then they were inserted into glass capillaries with water-based Fe(3)O(4) magnetic fluid as sensing elements. The sensing characteristics have been investigated and the experimental results show that the reflective spectrum of the fiber-magnetic sensor linearly shifted with the change of the magnetic-field strength that is perpendicular to the axial of the devices. The fiber-magnetic sensor with interference arms diameter of 50 μm is most sensitive to the external magnetic field, and the sensitivity is up to 64.9 pm/mT, which is 20 times higher than that of 125 μm diameter.

Full Eulerian lattice Boltzmann model for conjugate heat transfer.

In this paper a full Eulerian lattice Boltzmann model is proposed for conjugate heat transfer. A unified governing equation with a source term for the temperature field is derived. By introducing the source term, we prove that the continuity of temperature and its normal flux at the interface is satisfied automatically. The curved interface is assumed to be zigzag lines. All physical quantities are recorded and updated on a Cartesian grid. As a result, any complicated treatment near the interface is avoided, which makes the proposed model suitable to simulate the conjugate heat transfer with complex interfaces efficiently. The present conjugate interface treatment is validated by several steady and unsteady numerical tests, including pure heat conduction, forced convection, and natural convection problems. Both flat and curved interfaces are also involved. The obtained results show good agreement with the analytical and/or finite volume results.

Simulation of steady fluid-solid conjugate heat transfer problems via immersed boundary-lattice Boltzmann method

In this paper, we extend the lattice Boltzmann method (LBM) in combination with the immersed boundary method (IBM) to simulate the steady-state fluid-solid conjugate heat transfer problems in complex geometries. The no-slip boundary condition is handled by the immersed boundary method. The pseudo-solid-specific-heat technique is used to ensure the continuity of heat flux at the fluid-solid interface. The present LB thermal field solver retains the simple structure of standards thermal LB model. The performance of the present method is validated by several heat conduction/convection problems. The numerical results agree well with exact solutions or published results.

Calculation of magnetic levitation force exerted on the cylindrical magnets immersed in ferrofluid

The magnetic levitation force exerted on the magnets immersed in ferrofluid is the theoretical basis of various application of ferrofluid. In this paper, based on the equivalent magnetic charge models and the equivalent current models of cylindrical magnets, magnetic charge image method and current image method are used to calculate the magnetic levitation force exerted on the cylindrical magnets immersed in ferrofluid respectively. The magnetic levitation force under the same conditions is calculated by the Comsol Multiphysics software according to the mechanical formula after the distribution of the magnetic field is obtained using finite element method. The magnetic levitation force is also measured experimentally, whose results are compared with the theoretical results obtained by the three methods. The analysis shows that the variation law of the magnetic levitation force and the influence by various parameters can be evaluated by the calculation with magnetic charge image method and current image method, but there is great difference between the theoretical results and the experimental results, and the greatest difference are 46% and 62% respectively. The agreement between the theoretical and the experimental results is quite good when the finite element method is used, whose greatest difference is 9%.

Finite-volume method with lattice Boltzmann flux scheme for incompressible porous media flow at the representative-elementary-volume scale.

Based on the Darcy-Brinkman-Forchheimer equation, a finite-volume computational model with lattice Boltzmann flux scheme is proposed for incompressible porous media flow in this paper. The fluxes across the cell interface are calculated by reconstructing the local solution of the generalized lattice Boltzmann equation for porous media flow. The time-scaled midpoint integration rule is adopted to discretize the governing equation, which makes the time step become limited by the Courant-Friedricks-Lewy condition. The force term which evaluates the effect of the porous medium is added to the discretized governing equation directly. The numerical simulations of the steady Poiseuille flow, the unsteady Womersley flow, the circular Couette flow, and the lid-driven flow are carried out to verify the present computational model. The obtained results show good agreement with the analytical, finite-difference, and/or previously published solutions.

Research on a Novel Ferrofluid Inertial Sensor With Levitating Nonmagnetic Rod

This paper presents a novel inertial sensor with a movable nonmagnetic rod immersed in the ferrofluid, which can be used as a low band accelerometer. Movement of the nonmagnetic rod inside a container under the influence of external inertial forces will lead to the change of the ferrofluidic volume distribution. A couple of sensing coils detect the change and a corresponding signal occurs. The nonmagnetic rod with a dumbbell-shaped structure improves the linearity and stability of the sensor. The specially arranged permanent magnets create a non-uniform magnetic field, which generate a powerful restoring force determining the position of the nonmagnetic rod. The restoring force is performed by means of the comparison between experimental measurements and theoretical calculation. Compared with the conventional ferrofluid inertial sensors, one of the most significant advantage of the proposed device is that it can be applied in the magnetic environment.

Hydrodynamics and energy dissipation in a ferrofluid damper

A ferrofluid damper with a simple structure is proposed. Hydrodynamics and energy dissipation in the damper are studied theoretically and experimentally. This is applied to the study of damping of a cantilever whose free extremity is installed with the ferrofluid damper. The dependences of the decrement of the oscillations on the geometrical characteristics of the damper are described by a theoretical model and are shown to predict the experimental result well under some conditions.

Research on a novel magnetic fluid micro-pressure sensor

The article presents a novel micro-pressure sensor based on magnetic fluid. Some characteristics of the sensor are determined by theoretical predictions based on the state equation of ideal gas. The variation of external pressure will lead to the compression of a chamber between the body and mobile part, and a corresponding signal occurs. A comparison between inductance detection mode and magnetic field detection mode is performed by means of the transfer characteristics. The proposed device might be used as a micro-pressure sensing device with the advantages of low cost, simple structure, and convenient replacement.

Investigation into loss in ferrofluid magnetization

Ferrofluids containing γ-Fe2O3/Ni2O3 nanoparticles (not chemically treated) were synthesized using water and mixed water–glycerol as carrier liquid and the ferrofluid viscosity was modified by varying the glycerol content in the carrier liquid. The apparent magnetization of the ferrofluids decreased with increasing glycerol content. The loss in magnetization is described by the ratio of effective magnetic volume fraction to physical volume fraction of nanoparticles in the ferrofluids as a characteristic parameter. We ascribe the loss to the formation of “dead aggregates” having a ring-like structure of closed magnetic flux rather than to any chemical reaction. Such dead aggregates exist in zero magnetic field and do not contribute to the magnetization in the low or high field regime, so that the effective magnetic volume fraction in the ferrofluids decrease. An increase in carrier liquid viscosity is similar to a weakening of the thermal effect, so the number of dead aggregates increases and the magnetiza...

Preparation of γ-Fe2O3/ZnFe2O4 nanoparticles by enhancement of surface modification with NaOH

BackgroundDuring liquid-phase synthesis of γ-Fe2O3 nanoparticles by chemically induced transition in FeCl2 solution, enhancement of surface modification by adding ZnCl2 was attempted by using NaOH. By using transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectrometry, and vibrating sample magnetometry, the dependence of the synthesis on the amount of additional NaOH was studied.ResultsThe experimental results show that the surface of the γ-Fe2O3 nanoparticles could be modified by adding ZnCl2 to form composite nanoparticles with γ-Fe2O3/ZnFe2O4 ferrite core coated with Zn(OH)2 and adsorbed FeCl3, and that modification could be enhanced by adding NaOH.ConclusionsIn the experimental conditions, when the concentration of additional NaOH was below 0.70xa0M, the amounts of ZnFe2O4 and Zn(OH)2 phases increased slightly and that of adsorbed FeCl3 was unchanged. When the concentration of NaOH exceeded 0.70xa0M, the amount of FeCl3, ZnFe2O4, and Zn(OH)2 increased.