垂直磁场条件下锗熔体粘度的测量

设计制作了由永磁材料构成的,能提供均匀磁场的环形磁场.在锗熔体范围内引入此磁场提供的垂直磁场.采用旋转转子法,测定了不同温度不同磁场强度条件下锗熔体的粘度.结果表明,不同的条件下,锗熔体的粘度有不同程度的降低.粘度降低的原因,可以用磁场对运动带电粒子的作用来解释.     

纳米磁性液体薄膜磁光特性研究

制备出了纳米磁性液体薄膜，研究了纳米磁性液体薄膜在不同外加磁场（垂直和平行）下，其透射光学特性随着磁场变化的规律，对纳米磁性液体薄膜磁光现象产生的原因进行了解释。研究发现：（1）薄膜外加垂直磁场时，光透射强度随着磁场强度的增加而减小；（2）薄膜外加平行磁场时，垂直偏振光和平行偏振光的透射强度随着磁场强度的增加而变化规律不同；（3）存在一个临界磁场，其值约为4776A/m，当外加磁场（垂直和平行）强度＞4776A/m后，薄膜透射光强的变化规律有明显不同，这种现象是由于外加磁场使纳米磁性液体微粒产生聚集，磁场〉4776A/m后，形成有规则的排列结构所造成；（4）纳米磁性液体外加垂直磁场下透射强度的响应时间随磁场强度的变化情况。     

在磁场作用下Al-Pb合金连续凝固组织的形成过程

在恒定磁场作用下对Al-Pb合金进行连续凝固实验,研究了磁场对Al-Pb偏晶合金凝固特性的影响。结果表明,在恒定磁场作用下得到了弥散相均匀分布于基体的凝固试样。随着磁场强度的提高试样中富Pb相粒子的弥散度增加。恒定磁场能增加合金熔体的有效粘度,减小弥散相液滴相对于基体熔体的运动速度,抑制基体熔体对流,促进偏晶合金形成弥散型复合凝固组织。     

磁场对KNbO3熔体中温度分布影响的实验研究

研究了磁场对ＫＮｂＯ_３熔体中的温度分布的影响．利用加磁场的休仑微分干涉显微实时观察装置及一种近似的间接测温方法,对在不同磁场强度０、７０、１１７、１３５ｍＴ下,ＫＮｂＯ_３熔体中的径向温度分布进行测量．发现随着磁场强度的增大,熔体中的径向温度梯度减小,尤其在坩埚－熔体界面附近,浮力驱动对流占主要作用的区域,温度梯度的减小更加明显．这可能是由于磁场对熔体中浮力驱动对流抑制的结果．     

磁场对KNbO3熔体中温度分布影响的实验研究

研究了磁场对ＫＮｂＯ３熔体中的温度分布的影响,利用加磁场的休仑微分干涉显微实时观察装置及一种近似的间接测量方法。对在不同磁场强度０、７０、１１７、１３５ｍＴ下,ＫＮｂＯ３Ｏ熔体中的径向温分布进行测量。     

磁场中浆料粘度与内部结构的关系研究

当外磁场施加在由铁磁性Ni和非磁性ZrO₂粒子组成的浆料时, 浆料的粘度会明显增大. 实验采用磁场线圈、旋转粘度计和金相显微镜对磁场中Ni/ZrO₂复合浆料的粘度与内部结构的关系进行了系统研究. 结果表明, 浆料粘度随着磁场强度和Ni含量的增加而增大. 当外磁场作用于浆料时, 浆料中会形成链状Ni团簇. 随着磁场强度的增加, Ni团簇尺寸变大, 阻碍了粒子的自由运动, 因此粘度增加. 同样, 随着Ni含量的增大, 浆料中Ni团簇增多, 因此粘度增大.     

铝熔体中磁性杂质颗粒的电磁分离

分析了磁性杂质颗粒在电磁场中的受力情况,采用磁平衡法测量了铝熔体中两种典型富铁相杂质颗粒的磁化率,指出铝熔体中的富铁相杂质是顺磁性物质,在电磁场中受到电磁力和磁场力的驱动作用,确定其在分离器上的聚集方式．静态电磁分离试验结果表明,当磁场强度大于145mT时,电磁力起主要作用;当磁场强度小于120mT时,磁场力起主要作用．     

勾形磁场作用下分离结晶中熔体热毛细对流的数值模拟

为了更好地了解勾形磁场对分离结晶法制备CdZnTe晶体过程中熔体热毛细对流的影响,采用有限差分法对熔体内的热量和动量传递进行数值模拟。假定熔体为不可压缩牛顿流体,熔体的高径比为1,狭缝自由表面无因次宽度为0.1,研究了不同Ma数下,Ha数分别为0、45、90、135时的CdZnTe晶体生长过程。结果表明,勾形磁场能够有效地抑制熔体内部的对流,并且随着磁场强度的增加,抑制作用增强,熔体内部流动减弱。     

磁性液体在均匀磁场中的瞬态双热线导热系数的测试

将封有聚α-烯烃合成油基磁性液体的两玻璃管放置于磁场中,为消除磁场力、重力所引起的磁性液体自然对流的影响,消除端部效应,研制了磁性液体在均匀磁场中瞬态双热线导热系数的实验测量系统,经与蒸馏水、乙醇标准样品的导热系数测量比较,实验装置有较高的测量精度。实验测量了不同方向的均匀磁场对不同体积浓度的磁性液体导热系数的影响。结果显示,当磁场方向与热通量方向一致时,磁场显著强化磁性液体的导热系数,其导热系数随磁场强度的增加而近似线性增加,且体积浓度越大增加量越大;当磁场方向与热通量方向垂直时,磁性液体的导热系数随磁场强度的变化不明显。     

磁场作用下对血浆速冻品质的实验研究

本文以更高效保存新鲜冰冻血浆为研究重点,在现有速冻工艺基础上,通过添加磁场辅助冻结以进一步提高血浆品质。分析0~100 Gs磁场强度下速冻实验中血浆冰晶结构尺寸变化,由于磁场辅助速冻加速传质传热速度,冰晶生长的速度快于水分迁移的速度,导致冰晶在形态及分布上发生变化,在血浆中形成了细小、圆整、均匀的冰晶,减少冰晶对血浆完整结构的损伤,从而达到提高血浆品质的目的。对比0~100 Gs磁场强度下速冻实验中血浆凝血因子Ⅷ含量与新鲜冰冻血浆凝血因子Ⅷ含量可知：辅助磁场下各磁场强度凝血因子Ⅷ含量均出现了不同程度的降低,最大降低发生在20 Gs磁场强度作用下,下降3.56%。相对于其他磁场强度,在60、80 Gs磁场作用下的活性浓度数值更高,速冻保存后的血浆品质更好。     

磁场力对磁性杂质颗粒的作用的研究

磁场对处于其中的磁性颗粒有力的作用,通过对交流磁场和稳恒磁场的磁场力的比较分析,证明这2种磁场力可以统一,与磁性颗粒的作用规律相似.采用磁平衡法测量了MnFeAl36和MnFeSiAl42种金属间化合物的磁化率,证明它们是顺磁性的物质,利用磁场力可以将其分离.利用自制的交变磁场和稳恒磁场装置对铝熔体进行分离试验,结果表明磁场力可以将铝熔体中的磁性杂质颗粒分离出来.     

Physical Simulation of Mold-Filling Processing of Thin-Walled Castings under Traveling Magnetic Field

Mold-filling process of thin-walled castings under the condition of traveling magnetic field has been studied by physical simulation method using gallium melt and fast speed photography. Flow morphology and its formation mechanism were obtained and discussed for thin-walled casting. The influences of magnetic field density on the filling ability, filling velocity and mold filling time have been studied. The differences in filling capability between gravity casting and casting under the traveling magnetic field have been compared. The results indicate that the mold filling ability of the gallium melt increases greatly under the condition of traveling magnetic field; the filling time is shortened from 18 s under gravity field to 3 s under the traveling magnetic field and average flow rate of the melt increases from 1.6 to 8.68 cm3/s; the change law of the cross-section morphology of the gallium melt during the mold filling is that at first, the cross-section area does not change, then it decreases gradual     

用PMCZ法生长的单晶硅中氧和电阻率的均匀性

用永磁体环形磁场直拉（PMCZ）炉代替普通的MCZ炉生长了质量较高的单晶硅。在PMCZ炉中水平辐射状磁力线均匀分布，可有效地抑制熔体中不规则的对流和固液界面处的温度波动，降低以至消除微观生长速率的起伏。在用PCMCZ法生长的硅晶体中氧浓度较低，杂质的径向分布均匀性好。简单地讨论了PMCZ法控氧优于普通MCZ法的机理。     

Effect of Traveling Magnetic Field on Mould-Filling Length of the A357 Melt during Casting THin Walled Plate

In order to improver the mould filling ability ,the method for production of thin-walled castings in the traveling magnetic field was applied,The relationship between magnetic field density and input voltage as well as distance was investigated,and the mould filling length of A357 melt has been studied,The electromagnetic forces applied on the melt were also analyzed,The result shows that the mould-filling length of the melt increase rapidly with the increase of magnetic flux density,The mould filling lengths in gypsum upper mould and magnetic material upper mould were compared from the standpoint of application,It demonstrated that the steel upper mould is superior to gypsum mould.     

Measurement of the Viscosity of Dilute Magnetic Fluids

The capillary tube viscometer is used to measure the viscosity of aqueous magnetic fluids under the influence of parallel and perpendicular magnetic fields. The effects of the volume fraction of the suspended magnetic particles, the concentration of surfactants, and the external magnetic field strength, as well as the orientation, on the viscosity of the magnetic fluid are analyzed. The experimental results show that the viscosity of the sample magnetic fluids increases with increases in the concentrations of suspended magnetic particles and surfactants. The external magnetic field is also an important factor that affects the viscosity of the magnetic fluid. The viscosity first increases with the magnetic field and finally approaches a constant as the magnetization attains a saturation state. For the same magnetic fluid, the viscosity in a perpendicular magnetic field is larger than that in a parallel magnetic field for the same magnetic field.Paper presented at the Seventh Asian Thermophysical Properties Conference, August 23–28, 2004, Hefei and Huangshan, Anhui, P. R. China     

Two Dimension Finite Element Simulations on the Electromagnetic Containment in Twin-Roll Strip Casting

Distribution of magnetic field and electromagnetic force in twin-roll casting of steels was studied by the metod of numerical simulation in this paper,Two-dimension finite element model ,which includes the regions of melt ,stainless collar ,coil and magnetic core ,has been constructed,By solving magnetic vector potential formulations of quasi-static electromagnetic field,distribution of magnetic flux density and magnetic force at different molten heigh is determined,Calculated results showed that intensity of the distribution of magnetic flux density increased linearly with the increased coil current ;and the magnetic force in the melt increased as a quadratic cure with creased coil current ,More attention was given to the distribution of eddy current and magnetic force in the melt ,the confine effect at different molten height was also discussed.     

Variable viscosity effect on hydromagnetic flow and heat transfer about a fluid underlying the axisymmetric spreading surface

Summary. The effect of variable viscosity on the flow and heat transfer about a fluid underlying the axisymmetric spreading surface in the presence of an axial magnetic field has been investigated. The viscosity of the fluid is assumed to vary as an inverse linear function of temperature and the magnetic field strength is inversely proportional to the radial coordinate. The partial differential equations, governing the present problem, have been transformed, by suitable similarity variables, into a system of ordinary differential equations. This system is solved numerically by the shooting technique. Numerical results are introduced in graphical form for different values of viscosity parameter, _r, and magnetic field parameter. In the presence of variable viscosity, an increase in Prandtl number leads to a rise in the velocity field. Generally, it leads to a fall in the temperature field. Both magnetic field and variable viscosity raise the heat transfer and suppress the fluid flow.     

Magnetic-field effect on the rheological properties of strontium ferrite suspensions

The effect of a magnetic field and surfactants on the rheological properties of strontium ferrite suspensions has been studied. An applied magnetic field is shown to raise the suspension viscosity, which is attributable to the formation of three-dimensional chain structures made up of ferrite particles. After the magnetic field is removed, these structures do not fully break down, which leads to hysteretic behavior of the suspension viscosity. The introduction of polyelectrolytes reduces the viscosity of the suspension both in a magnetic field and after the field is removed. This is due to the formation of an electrical double layer on the particle surface, which reduces interparticle friction and the strength of the three-dimensional structures. The results of this study may be useful in devising processes for enhancing the texture and density of highly anisotropic strontium ferrite materials produced by wet pressing.     

Inverse design of directional solidification processes in the presence of a strong external magnetic field

A computational method for the design of directional alloy solidification processes is addressed such that a desired growth velocity ν_f under stable growth conditions is achieved. An externally imposed magnetic field is introduced to facilitate the design process and to reduce macrosegregation by the damping of melt flow. The design problem is posed as a functional optimization problem. The unknowns of the design problem are the thermal boundary conditions. The cost functional is taken as the square of the L₂ norm of an expression representing the deviation of the freezing interface thermal conditions from the conditions corresponding to local thermodynamic equilibrium. The adjoint method for the inverse design of continuum processes is adopted in this work. A continuum adjoint system is derived to calculate the adjoint temperature, concentration, velocity and electric potential fields such that the gradient of the L₂ cost functional can be expressed analytically. The cost functional minimization process is realized by the conjugate gradient method via the FE solutions of the continuum direct, sensitivity and adjoint problems. The developed formulation is demonstrated with an example of designing the boundary thermal fluxes for the directional growth of a germanium melt with dopant impurities in the presence of an externally applied magnetic field. The design is shown to achieve a stable interface growth at a prescribed desired growth rate. Copyright © 2001 John Wiley & Sons, Ltd.     

The Effect of Constant Magnetic Fields on the Dynamics of Molten Zones in the Field of Structural Inhomogeneity of Silicon

The effect of constant magnetic fields on the formation and dynamics of molten Al–Si inclusions in silicon in the field of structural inhomogeneity of a crystal (the dislocation density-gradient field) is considered. The migration rates of liquid inclusions in crystals have been found experimentally under conditions of prevailing melting–crystallization mechanisms at the phase interfaces between the melt and matrix before and after magnetic exposure. It has been found that a preliminarily exposure of dislocation silicon samples in a constant magnetic field leads to an increase in the displacement speed of molten zones in the density-gradient field.