湿颗粒分离中的液桥力作用及临界分离初速度

Effect of liquid bridge force and critical velocity for the separation of wet granule

利用液桥理论研究了湿颗粒分离过程中在液桥力作用下颗粒速度的变化规律,运用组合的4/5阶龙格-库塔-芬尔格算法求解了液桥拉伸过程颗粒的运动方程,计算了分离100种等径湿颗粒以及从平面上分离湿颗粒所需的临界分离初速度.研究表明:湿颗粒的分离引起粒间液桥的拉伸,使颗粒分离速度随着颗粒表面间距的增加而迅速衰减,在液桥断裂前若颗粒速度衰减为零,则湿颗粒不能实现分离.湿颗粒的分离需要一临界分离初速度,在工业上可通过碰撞、振动、气力等方式施加.水分的增加使得湿颗粒难分的主要原因是液桥的断裂变难,并非增大的液桥力.

Applying the liquid bridge theory,the physical law and variation of velocity with granule＇s distance in the separation process of wet granules are investigated. Velocity condition for the separation of wet granules has been presented from the view of dynamics. It has been found that separation movement of wet granules causes the stretch of liquid bridge and separation velocity decreased rapidly with the enlargement of granule surface distance. If the separation velocity of granule decays to zero before the rupture of liquid bridge,separation can not happen. Separation needs a critical normal initial velocity. Employing 4 /5 order of Runge- Kutta- Fehlberg arithmetic,initial velocities of 100 types of wet granules needed in the separation are calculated and listed,which can be loaded to wet granules by collision,vibration or pneumatic components in industry. The major reason why the separation of wet granule gets difficult with increasing moisture lies in the hard rupture of liquid bridge,not in increasing liquid force as widely believed.