镁熔液中氢气泡析出动力学模型

Kinetic model of hydrogen gas bubble evolution in magnesium melt

针对镁熔液中氢气泡的析出过程,分析氢气泡析出的动力学特性。考虑多种因素对氢气泡析出影响,对镁熔液中氢气泡上浮运动进行受力分析,利用牛顿第二定律得出氢气泡上浮运动过程中的瞬时加速度方程,并结合气体状态方程、传质边界层方程及流函数等相关性质,推导出镁熔液中氢气泡在析出过程中气泡速度、气泡半径、气泡上浮高度与时间变化关系的动力学模型。采用龙格库塔算法将模型方程在MATLAB中进行编程计算,得到气泡传质速率与时间及气泡半径与时间的关系曲线。研究结果表明:氢气泡形核后析出,随着上浮高度的增加,气泡速度与半径都随之变大,加速度先增大后减小;临近界面处,气泡趋于某一速度值析出并破裂。此模型为镁熔液中氢气泡的形成机理提供了一定的理论基础,对镁合金液态质量控制具有重要意义。

The kinetic property of hydrogen was analyzed in the process of hydrogen gas bubble evolution. According to the force analysis, a transient acceleration equation of hydrogen gas bubble in magnesium melt was established by the Newton＇s Second Law considering influential factors. Simultaneously, a kinetic model that described the changing relation of hydrogen gas bubble velocity, radius, rising height and time was obtained by in combination with three other equations and theoretical deduction. These equations were the boundary layer mass transfer equation, the gas state equation and the nature of stream function. Simplified model was verified by programming on MATLAB with Runge-Kutta. A relation graph of bubble transfer speed and time was obtained. Meanwhile, the relation graph of bubble radius change rate and time was also got. The results show that the bubble speed and radius grow with the rising height increasing in the hydrogen gas bubble evolution. And the acceleration increases firstly, and then decreases. While it rises to the surface, the bubble precipitates at a certain velocity and breaks. The model offers theoretical basis to the formation mechanism of hydrogen gas bubble in magnesium melt, which has great significance for controlling process of production in molten magnesium.