Natural Convection of a Magnetic Fluid under the Magnetic Field

对立方空腔、水平圆柱体的立方体空腔和同轴圆柱体三种模型的磁流体自然对流进行了实验和数值研究。永磁体向不同方向施加磁场。利用热敏液晶片来显示壁面温度分布。为了弄清磁场方向和强度对自然对流的影响，进行了几种实验。采用有限元方法进行了数值模拟，得到了磁流体内部的速度场和温度场。计算中采用了Boussininesq近似，忽略了磁性粒子运动产生的感应磁场。根据计算结果，详细观察了磁性液体内的温度分布和速度场。由于这些结果，人们知道磁性液体的自然对流是受…控制的为了研究磁性流体的热性质，我们引入了一种确定磁性流体本构方程的新方法。这就是在热力学讨论的基础上，将完整性基理论和最大耗散率原理相结合的方法。用该方法得到的基本方程满足材料框架无差异原理。利用该方法，给出了非导电非极性磁性流体和导电非极性磁性流体的基本方程，并通过实验研究了容器中磁性液体的一些动力学行为。分别对矩形、圆柱形和球形容器进行了实验研究。这些容器是横向摆动的。垂直不均匀磁场由安装在集装箱下方的永磁体施加。结果表明，磁场对表面波的简谐运动、旋波和流型均有影响。随着磁场强度的增大，流体-容器系统的共振频率向高频区移动。用线性近似理论对这一行为进行了研究。理论计算结果与实验结果定性吻合较好。较少

Natural convection of a magnetic fluid was studied experimentally and numerically for three models which was a cubic cavity, a cubic cavity which had a horizontal cylinder and the coaxial cylinders. Magnetic fields were applied in various directions by permanent magnets. The thermosensitive liquid crystal sheet was utilized in order to visualize wall-temperature distributions. Several kinds of experiment were carried out in order to clarify the influence of direction and strength of magnetic fields on the natural convection. Numerical Simulations by finite element method were used to show velocity and temperature fields in the magnetic fluid. Boussininesq approximation was used and the induced magnetic field caused by a motion of magnetic particle was ignored in the calculation. Temperature distributions and velocity field in magnetic fluid were observed in detail by the calculation results. As these results it became known that the natural convection of a magnetic fluid was controlled … More by the intensity and direction of the magnetic fields.To investigate the thermal properties of magnetic fluids, we introduced a new way of determining constitutive equations of magnetic fluids. That is the method which is a combination of the theory of integrity bases and the principle of maximal dissipation rate based on the thermodynamical discussions. The basic equations, which derived by this method, satisfy the principle of material frame indifference. Furthermore, they express viscoelastic effect internal freedom, conducting effect, and nonlinear effect simultaneously Using this method, the basic equations of both nonconducting and conducting nonpolar magnetic fluids were given.Some dynamic behavior of a magnetic fluid in a container were experimentally examined. Experiments were carried out for rectangular, cylindrical and spherical containers respectively. These containers were laterally oscillated. The vertical non-uniform magnetic field was applied by permanent magnets which were fitted underneath the container. It was found that harmonic wave motion, swirling waves and flow pattern of surface waves were influenced by the magnetic fields. The resonant frequency of the fluid-container system moved toward high frequency region with the magnetic field intensity. This behavior was also studied by the linear approximate theory. Theoretical results were qualitatively in good agreement with experimental results. Less