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Experimentally Investigate the Vortex Ferro-Viscosity under Directional Field

In this study, apparent ferro-viscosity on applied directional field, through the evaluation of mean piping flow velocity, is examined. Here viscosity in magnetized ferro-flow is found to be closely dependent on the field intensity as well as direction, which is quite different from the constant thermal property usually used in traditional fluid dynamics problem. To predict ferro-magnetization and ferro-viscosity induced under horizontal and vertical field imposed , an auxiliary electromagnetic mechanism is then designed and set up ,As a result, the apparent viscosity ,for ferro-concentration ψ0.4 and 0.04 exposed to field in different direction, will initiate a faster growth within field strength of 6~12 mT where the quick magnetization of ferro-particles starts working, and magnetic field along with flow direction is found to have more potential to induce viscous drag. While compared with theoretic results on Brownian relaxation theory in Langevin function, experimental vortex viscosity behave a good agreement within the working magnetic intensity 0~36 mT and their maximum relative errors will be less than 10% and 50% for ferro-concentration ψ0.4 and 0.04 at working temperature at 25 o c.

Using Rayleigh-Taylor Model to Predict Surfacial Tension of Static Ferro-Fluid

Rayleigh-Taylor model, an important theory dealing with ferro-hydrodynamic ( FHD ) instability, is utilized to predict the ferro-surface tension in this study. Before hexagonal peaking patterns induced by critical magnetization of ferro-solution, the simplification from proposed theory could be further made under the consideration of normal field imposed, i.e., linear relation of free surface tension proportional to apparent ferro-weight might be successfully predicted. That offers a simple semi-formula easier to study the static ferro-surface tension. To validate above results, a self-designed ring-pull device is set up as auxiliary experimental mechanism. Here relevant test of ferro-sample in various volumetric concentration as well as field intensity will be performed. Consequently, both results accessed from ferro-experiment and theoretic analysis delivers an agreement within the working magnetic intensity 0~40 mT, where a remarkable increase of surface tension coefficient occurs at higher magnetic field for ferro-solution with denser volumetric concentration considered.

Study the Ferro-Surface Tension on Magnetization Degree of Ferrofluid

Surface tension of ferrofluid, an important parameter enclosing the boundary condition of ferro-hydrodynamic ( FHD ) problem, is investigated in this study. Referred to modified Langevin function and apparent weight loss theory, an auxiliary experimental mechanism of ring-pull method is then designed and set up, which will be used to determine the surface tension of testing sample through various magnetization degree induced by field intensity. While compared with the results predicted from Rayleigh theory using commercial product of Matsumoto Co., an excellent agreement is delivered within the working magnetic intensity 0~40 mT. Here dimensionless parameter α is found to dorminate the prompt increase of surface tension coefficient as the ferro-magnetization ratio reaches at 70 % saturation magnetization. .

Analytically Study the Ferrohydrostatic Pressure with FHD Bernoulli Theory

The ferrohydrostatic pressure is an important magnetization characteristic for the ferro-fluid used as the working medium of shock absorber or as a leak-proof dynamics seal of rotating shaft. To generalize and analyze the experimental results, an analytic formulation of magnetic pressure derived from the Ferrohydrodynamics (FHD) Bernoulli theory is constituted. Meantime, an auxiliary testing mechanism on the magnetic levitation, features as an easy, economical and efficient utility, is then set up in this study and which is quit different from the expensive cost required in precise VSM measurement system. While compared with above results, a good agreement will be accessed within the working interval of magnetic flux 0 ~ 60 mT.

Study the Relative Permeability of Ferrofluid with the Mean Value Analysis of Experimental Apparent Gravity

Relative permeability is an important magnetic characteristic for ferrofluid to exhibit its magnetized potential during the magnetization process. To understand above physical property varying with field intensity, a popular analytic model, based on Langevin theory, has been usually considered and widely used. Unfortunately, an implicit model, derived from above hypothesis, for solving the instantaneous magnetization of ferro-particle will be carried out unless the determination of saturated magnetization should be conducted in advance. Just for the study dealing with magnetic property of testing ferro-sample is concerned, the previous acquisition of magnetization curve is impossible and unpractical without the precise measurement of magnetization-degree. On the other hand, required experimental expense is still so costly that it seems to be unaffordable for general laboratory. Thus a self-designed electromagnetic mechanism with special facility of smaller size, economical cost and efficient operation to quantify the reduced gravity of ferro-sample attracts our interest and is set up in this study. Meantime, an auxiliary numerical method, Newton interpolatory divided-difference formulas in trapezoidal rule, involved in this study successfully avoids the essentiality of saturated magnetization determined previously, and which also provides a numerical approximation through the weight loss of ferrofluid experienced by the designed experimental system. As compared with the result measured by VSM (vibration sample magnetometer) method, the estimated profile shows an excellent agreement except the extraordinary outcome occurring at B=6 mT, where a drastic increase of relative permeability will be evaluated due to the faster magnetization starts.

Critical Flow Theory on Nonlinear Penetrating Mechanism of High Energy Beam Drilling

For most of previous study on electron beam drilling (E.B) or laser beam drilling (L.B), the evaporating phenomena was assumed to be a minor parameter and could be neglected. In fact, the assumption usually leads to the overestimation of drilling efficiency and causes a significant deviation from experiment result. To improve this defect, a critical flow theory, based on the reacting pressure downward into the melting layer, is first introduced in this study; which not only successfully separates the evaporating model to convective model, but the critical transition of drilling characteristic will be also accessed. Examine the melting cavity of copper drilling conducted in E.B process, the evaporating phenomena responsible for drilled cavity had been verified to be as a prior parameter as the incident energy density is below 6×1010 w/m2. When compared with the experiment data made by Allmen [1], proposed theory shows an excellent agreement for copper drilling and their relative errors are no more than 30%.

Measuring Apparent Gravity Effect to Characterize the Magnetization of Ferro-Fluid

Due to the reversible transformation of physical property is strongly induced for ferro-fluid, so called intelligent working medium, subjected to the magnetic flux, its effective viscosity, especially, is closely dependent on the magnetization of ferro-particle and shows a special advantage in reducing the damping effect without magnetization hysteresis. Therefore magnetized fluid as a new engineering material, used for the shock absorber of building structure, has gradually attract scientist’s interest and engineer’s attention. Instead of previous experimental measuring the magnetized degree of ferro-fluid by costly Vibration Sample Magnetometer (VSM), a designed testing mechanism, based on modified Langevin function in apparent weight loss to characterize the magnetic behavior, is introduced in this study. It not only features as an stable, economical and affordable utility for local researchers, but a safe, easy operation with fast data acquisition would be also accessed. While compared with the experimental result conducted by VSM for ferro-sample provided by Matsumoto Co., the significant deviation using classic Langevin function in saturated magnetization Md ,within the magnetic field, 0 ~ 6 mT, can be effectively lessened to 50 % as the calculation undergone by modified model proposed.

The Determination of Key Material Property in High Energy Beam Drilling

In this study, a 2-D model with dimensionless analysis was proposed by discussing the roles of the active material properties in high energy beam drilling. With the assumption of small Pelect number, quasi-steady transformation and scalar analysis in this model, several dimensionless parameters had been generalized. Among these parameters, the dimensionless material property , defined as evaporation latent heat to internal energy at melting point, was proven to be the key member; which not only significantly influenced the nonlinear variation inside the work piece, but also directly determined the penetration results whose behavior showed a resemblance to the distribution of exponential function in . Further more, the maximum efficiency had been successfully estimated, and the dramatic change of drilling characteristic during the transitional energy region was also reasonably simulated. When compared with the experimental results from Allmen [1], the present model with given copper properties showed an excellent agreement on material removal rate (their relative errors were not more than 15 ％.)

Evaluating the Micromachining Rate of Nanosecond Laser with Thermal Analysis

For optical micro- machinery processing, nanosecond laser possess a special advantage in using it as a fabrication method of smaller hole subjected to the minimum thermal distortion. Thus it has become an effective and powerful tool widely used in drilling, cutting and welding process for micro-manufacturing field. To estimate the working performance of pulsed laser, an auxiliary method in numerical skill or semi-empirical technology is usually utilized, where the important parameters including energy intensity, duration and wavelength of laser beam will be taken into account. Nevertheless, several troubles, the unstable numerical iteration for phase change and precise calibration of sensor required in the measuring process, seem to be still inevitable, and which easily makes the numerical calculation become more complicated, even the global ablating behavior will be lost. To compensate the inadequacy mentioned above, an analytic model of optical ablation for pulsed laser, based on the evaporation effect responsible for penetration mechanism, is then derived in this study. Here the penetrating behavior, during the micro-machining process, can be clearly examined with the consideration of plasma absorption. After compared with experimental results made by Chen and Schmidt for copper drilling and steel ablation for Tim, a better agreement of analytic results identifies the accessibility of proposed model which also contributes to the future investigation on pico-or femto- laser material processing.

Nonlinear Penetrating Behavior in High Energy Beam Drilling

The geometrical keyhole scale produced in high energy beam drilling is approximately several hundred micrometers in size. Detecting its physical transport in such a narrow cavity is extremely difficult, let alone understanding the associated energy distribution in the workpiece. To describe nonlinear behavior in the penetration process, this study develops a 2D quasi-steady velocity model based on the enthaply theory. In the application of separation method, the penetration velocity can be expressed as an exponential function of liquidthickness and thermal properties. Setting up non-uniform grids in the calculating domain enables successful prediction of nonlinear penetration behaviors such as efficiency, mass flow rate, liquid film, and energy transport versus incident energy density. Even the continous formation of the drilling cavity can also be reasonably simulated. Compared with the experimental data of Allmen, the present model shows a good agreement for copper drilling, where the relative errors between the calculated and experimental data are no more than 20%.