非均匀电场下乳化油中液滴变形动力学行为

外加电场下液滴的变形动力学行为是乳化液电脱水机理研究的重要内容。基于Cahn-Hilliard方程的相场方法,建立了液滴在非均匀电场下的仿真模型,研究了电场作用下乳化液中液滴在形变、移动和聚结过程中电荷密度和电场力的分布规律,以及流场和电场的耦合作用。仿真分析了液滴粒径、电场强度以及电场非均匀系数对液滴运动行为的影响。利用实验室小型脱水系统开展了乳化液脱水实验,并通过高速摄像机对乳化液中液滴的运动行为进行了观测与分析。研究结果表明,在非均匀电场中液滴表面的极化电荷分布不均,由液滴中部向两端逐渐增大,在靠近电场集中方向处的电荷密度和Maxwell应力值最大;在一定范围内增大电场强度、电场非均匀系数或液滴粒径,可使液滴形变量增大,液滴向电场集中区域的移动速度以及液滴间的聚结速度增加。

Kinetics behavior of water droplet deformation in emulsified oil subjected to non-uniform electric field

Kinetics behavior of droplet deformation under electric field is important in the research on emulsion electric dehydration mechanism. In order to study the dynamic behavior of water droplets under non-uniform electric field, a simulation model of droplet under non-uniform electric field was established through the phase field method based on Cahn-Hilliard formulation. The distributions of charge density and electric field force on the droplet surface as well as the coupling effect of flow field and electric field were investigated during the process of droplet deformation, moving and coalescence. The influences of droplet size, electric field strength and non-uniform coefficient on droplet behavior were simulated and analyzed. The experimental study on the emulsion dehydration under non-uniform electric field was conducted by using the small dehydration test system in laboratory, and the droplets motion in the emulsion under different conditions was observed and analyzed by high-speed camera. The distribution of polarization charges was different on the droplet surface under non-uniform electric field, increasing from the center to both ends of the droplet. The values of polarization charge and Maxwell stress at droplet's one end surface closed to electric field concentrated area were the largest. The increase of electric field strength, electric field non-uniformity coefficient or droplet diameter could lead to larger droplet deformation, faster moving of droplet to concentrated electric field area, and higher coalescence rate.