Effects Of Magnetic Fields On The Thermocapillary Convection In Two-layer Fluids System

A non-uniform temperature distribution on the fluids'interface induces interfacial tension gradients that, in turn, generates a driving force for thermocapillary convection also known as Marangoni convection. The phenomena can cause adverse effects in many industrial applications, i.e., quality imperfections during crystal growth. At present, the magnetic field application to suppress the fluid convection is considered as an effective method. In this thesis, corresponding the physical model and mathematical model for thermcapillary convection in two-layer fluids system were established, and simulated numerically by finite volume method. Simulation results showed that the magnetic field did reduce the intensity of convection in two-layer fluids system and suppress the hydrothermal wave instability.Numerical studies were conducted to investigate thermocapillary convection characteristics in two-layer fluids system as follows:Firstly, the influence of magnetic fields on the development of thermocapillary convection was investigated numerically. The results showed that, applied the magnetic field in y or z direction could delay the development of the thermocapillary convection in the two layers fluids, and the x direction magnetic field slowed down the development in the upper layer fluid, but the progress was accelerated slightly in the underlayer fluid. Any external magnetic field did suppress the convection and reduced its intensity, and the control capability of z direction magnetic field on the thermocapillary convection was the strongest, that of x direction magnetic field was the second, and that of y direction magnetic field was the weakest. Furthermore, the intensity of z direction magnetic field over 0.15T was sufficient to suppress the convection significantly.Secondly, the magnetic fields impacts on the hydrothermal wave instability were numerical simulated, the results of magnetic field on the oscillatory period and amplitude was obtained. Under the x direction magnetic field, the oscillatory period increased and the oscillatory amplitude increased firstly and then decreased with the increasing of Hartmann number in the two-layer fluids system, while the y direction magnetic field was applied, the oscillatory period decreased firstly and then increased with the Hartmann number increasing, but the change of amplitude was reversed, and under z direction magnetic field, the oscillatory period increased and the amplitude decreased with the Hartmann number increasing. Comparing these results, the function of the z direction magnetic field on the hydrothermal wave instability was the strongest, that of y direction magnetic field was the second and that of x direction magnetic field was the weakest.Lastly, the changes of the free surface in two-layer fluids system under the horizontal and vertical magnetic fields were investigated numerically. The results showed that the ratio of the free surface change decreased with Hartmann number increasing. The effect of vertical magnetic field on the free surface distortion was better when magnetic field intensity was smaller, however, under the stronger magnetic field, the influence of horizontal magnetic field was better.