介电液体电羽流流动特性实验研究

Experimental study on the flow characteristics of electro-hydrodynamic plumes of dielectric liquid

利用静电场可以实现不同流体介质内部输运过程的有效控制,这为基于电场的主动流动和传热控制技术、电场驱动泵、电雾化等一系列创新应用提供了基础.这些应用依赖于电场、电荷和流场间相互耦合关系的深入理解.本文对针-板电极结构介电液体在高压直流电场作用下的流动和电压-电流特性进行了实验研究.实验结果表明,对曲率0.1 mm的针电极,当针-板间距为30 mm而施加的电压的绝对值在5~6 kV时,液体处于稳定对流状态,流动方向为从针电极指向板电极,流动形态与浸没射流有一定的相似性.该流动是由电场作用在从针电极表面注入流体内部的自由电荷上的库仑力驱动产生的.通过对轴向速度、纵向速度和羽流宽度分析发现,流场中最大流动速度位于水平对称轴上.在稳态流动区间,随电压增强,流型基本保持不变,但流动强度增大.另外,实验结果表明同样幅值下施加负电压时电流值和流动强度均更大,羽流核心区位置也离针电极更远.

Electrostatic field can be effectively used to control the transport process in different types of fluids, which provides the foundation for various innovative applications, such as the active control of heat and fluid flow based on the electric field(EF),electrohydrodynamic pumping, and electro-spraying. These applications depend on a deep understanding of the mutual coupling between EFs, charges, and flow fields(FFs). In this study, we experimentally investigated the flow and voltage–current characteristics of a dielectric liquid subjected to high voltage DC field in a needle–plate configuration. The experimental results show that for the needle electrode with a curvature around 0.1 mm, when the needle–plate distance is 30 mm and the absolute value of the applied voltage is 5–6 kV, liquid is in a stable state of convection, flow direction originates from the needle electrode toward the plate electrode, and flow pattern is similar to the typical submerged jet. The flow is driven by the Coulomb force due to the EF acting on the injected ions from the needle–liquid interface. Through the analysis of axial velocity, longitudinal velocity, and plume width, we observed that the maximum velocity in the FF is located on the horizontal axis. In the steady-state flow range, the flow pattern remains unchanged, but the flow intensity increases along the voltage. In addition, experimental comparison revealed that the current value and flow intensity are larger when we applied the negative voltage under the same amplitude, and the core position of the plume was farther away from the needle electrode.