EXPERIMENTAL INVESTIGATION ON RISING BEHAVIOR OF SINGLE BUBBLE UNDER THE EFFECT OF UNIFORM DC ELECTRIC FIELD
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摘要: 电场中的气泡对于强化传热有显著的作用, 对于电场中气泡动力学特性的研究对增强换热器效率, 提高能源利用率有重要意义. 为了获得外加电场作用下气泡的动力学特性, 设计与搭建了可视化实验平台. 采用50 kV高压直流电源构建均匀电场, 高清摄像机拍摄实验图像. 引入电场强度、气泡体积与溶液介电常数作为变量, 探究其对于气泡动力学特性的影响. 观测了竖直与水平均匀电场中气泡的上升过程, 分析了不同变量下气泡变形状况与上升速度的变化. 引入气泡长宽比L/D用于表示气泡拉伸变形程度, 截取单个气泡上升过程分时段图像展示形态变化过程. 研究结果表明, 气泡沿电场方向伸长, 且电场强度越大, 变形越明显; 竖直电场中气泡伸长导致上升速度增大, 而水平电场中气泡上升速度减小. 气泡尺寸增大, 浮升力作用增强, 气泡上升速度增大. 溶液介电常数增加, 电场力作用明显增加, 气泡变形更加明显.Abstract: Bubbles in an electric field have a significant effect on enhancing heat transfer. The study of the dynamic characteristics of bubbles in an electric field is important for enhancing the efficiency of heat exchangers and improving energy efficiency. In order to obtain the dynamics of bubbles under an applied electric field, a visualization experiment was designed and built. A 50 kV high voltage direct current power supply was used to construct a uniform electric field and a high-definition camera was used to capture the experimental images. The electric field strength, bubble volume and dielectric constant of the solution were introduced as variables to investigate their effects on the dynamic properties of the bubbles. The rise of the bubble in a vertical and horizontal uniform electric field was observed and the variation of the bubble deformation and rise velocity for different variables was analyzed. The bubble aspect ratio L/D was used to represent the degree of bubble stretching and deformation, and the individual bubble rising process was captured in separate time periods to show the shape change process. The results show that the bubble elongates in the direction of the electric field, and the larger the electric field strength, the more obvious the deformation is; in the vertical electric field, the elongation of the bubble causes the rising speed to increase, while in the horizontal electric field, the rising speed decreases. As the size of the bubble increases, the buoyancy force on the bubble increases and the rate of rising bubbles increases. As the dielectric constant of the solution increases, the electric field force on the bubble increases significantly and the bubble deformation becomes more pronounced.
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Key words:
- bubble /
- fluid mechanics /
- interfacial tension /
- electric field /
- experiment
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图 3 U = 0 kV与30 kV时气泡长宽比L/D随时间的变化
Figure 3. Variation of bubble aspect ratio L/D with time at U = 0 kV and U = 30 kV
图 4 不同电场作用下气泡稳定上升阶段的形状与长宽比
Figure 4. Shape and aspect ratio of bubbles in the steady rise phase under the effect of different electric fields
图 5 不同电场作用下上升气泡的速率与阻力系数变化
Figure 5. Variation of the velocity and drag coefficient of rising bubbles under different electric fields
图 6 50 kV时不同尺寸气泡的变形情况及长宽比变化
Figure 6. Deformation and aspect ratio variation of different bubble sizes at 50 kV
图 7 不同电场作用下溶液介电常数对气泡变形的影响
Figure 7. Effect of solution dielectric constant on bubble deformation under different electric fields
图 8 不同溶液中气泡长宽比L/D随电压的变化
Figure 8. Variation of bubble aspect ratio L/D with voltage in different solutions
图 9 水平电场中不同电压强度下气泡的上升过程
Figure 9. Rising bubbles in a horizontal electric field at different voltage intensities
图 10 水平电场中气泡长宽比L/D随电压的变化
Figure 10. Variation of bubble aspect ratio L/D with voltage in a horizontal electric field
图 11 水平电场中不同电压下上升气泡的速率变化
Figure 11. Variation in the rate of rising bubbles at different voltages in a horizontal electric field
图 13 水平电场蓖麻油溶液中气泡上升过程
Figure 13. Rising of bubbles in castor oil solution in a horizontal electric field
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