垂直振动颗粒系统气液相变的临界特征

Critical characteristics of gas-liquid phase transition in vertical vibrating particle systems

为了研究颗粒系统在外界能量驱动下体系内部的运动与结构变化,采用局部密度判断法和粒子图像测速法,测量垂直振动二维圆盘内均值粒径为2 mm的球型颗粒的局部概率密度分布和速度分布,探究气液相变过程中离散颗粒的空间分布特征和动力学特征;通过增加圆盘颗粒的填充密度和振动台的加速度,建立局部概率密度分布的特征参数K值、均值密度φ和加速度Γ的关系模型。结果表明:当垂直振动颗粒系统处于气态时,颗粒系统中颗粒的速度分布满足指数分布,颗粒速度分布指数等于1.52。在改变φ和Γ的过程中,颗粒系统发生气液相变,气液相变过程中颗粒速度速度分布的临界条件是一致的,即当颗粒速度分布指数等于1.40时,垂直振动颗粒系统开始从气态向液态转变。

In order to study the internal motion and structural changes of the particle system driven by external energy,the local probability density distribution and velocity distribution of spherical particles with an average diameter of 2 mm in the vertical vibrating two-dimensional disk were measured by local density judgment method and particle image velocimetry method,and the spatial distribution characteristics and kinetic characteristics of discrete particles during gas-liquid phase transition were explored.By increasing the filling density of particles in the disk and the acceleration of the shaker,the relationship model of the characteristic parameters K,mean densityφand accelerationΓof the local probability density distribution was established.The results show that when the vertical vibrating particle system is in the gas state,the velocity distribution of particles in the particle system satisfies the exponential distribution,and the particle velocity distribution index is equal to 1.52.In the process ofφandΓof the particle system,the critical condition of the gas-liquid phase transition of the particle system and the velocity distribution of the particle velocity during the gas-liquid phase transition is consistent,that is,when the particle velocity distribution index is equal to 1.40,the vertical vibrating particle system begins to transform from the gaseous state to the liquid state.