Abstract:

Investigations on the bubble dynamics under the influence of electric fields are beneficial to have a deeper understanding of the mechanism of electrohydrodynamics (EHD) enhancing boiling heat transfer. In view of this, the dynamic behavior of single bubble attached to the solid upper-wall under the effect of uniform AC (Alternating Current) electric field was simulated by the VOSET (Volume-of-Fluid and Level Set) method coupled with electric field force model. And, the effect of voltage frequency, electric field intensity and liquid permittivity was investigated. The numerical results showed that the electric field force acted on the gas-liquid interface and points to the interior of the bubble. The periodical variation of the voltage U led to the periodical variation of the electric field force. Under the extrusion action of electric field force, the bubble had the periodical deformation. The frequency of bubble deformation had a close relationship with voltage frequency. When the voltage frequency was small, bubble deformation had good following with the voltage. But the following performance gradually became weak as the increasing of the voltage frequency. Electric field intensity and liquid permittivity were important factors affecting electric field force. With the increasing in electric field intensity and liquid permittivity, the effect of the extrusion action of electric field force was obviously enhanced, which resulted in larger bubble deformation. But the changes of the electric field intensity and liquid permittivity had no obvious influence on the frequency of bubble deformation. It can also be found that the distortion degree of the electric potential and electric field line was more obvious with the increasing in liquid permittivity, which led to the decrease in the density of electric field line inside the bubble.

Key words: bubble, AC electric field, electric field force, interfacial tension, numerical simulation

摘要：

深入研究外加电场作用下气泡的动力学特性，有助于了解电场强化沸腾换热的机理。鉴于此，采用VOSET界面追踪技术并耦合电场力模型数值模拟研究了交流电场中贴壁气泡的动态变形过程，分析了电压变化频率、电场强度、液体介电常数的影响机理。研究结果表明，电场力作用于气液界面，且指向气泡内部，通过挤压作用促使气泡变形；电压周期性变化导致电场力随之改变，促使气泡沿竖直方向的变形具有周期性，且气泡变形周期与电压变化频率紧密相关。电压变化频率较小时，气泡形变能够跟随电压变化，随着电压变化频率逐渐增大，气泡形变的跟随性逐渐减弱。电场强度与液体介电常数是影响电场力的重要因素，随着电场强度与液体介电常数的增加，电场力的挤压作用明显增强，气泡变形程度明显增加，峰值高度也随之增加，但是气泡变形周期无明显变化。同时，随着液体介电常数增大，气液界面周围电势与电场线的扭曲程度明显增加，气泡内部电场线密度也随之降低。

关键词: 气泡, 交流电场, 电场力, 界面张力, 数值模拟