均一粒径を持つ極微細気泡生成技術の開発

使用高速摄像机通过显微镜以每秒500,000帧的帧速率获得超声场中毛细管波破碎的连续图像。实验结果表明，在运动粘度为5~100mm2/S的高粘度液体中，加入少量气体，以恒定的周期速率产生直径为4~15 mm的微气泡.结果表明：(1)稳定产生微气泡的条件受激发频率、液体表面张力和粘度以及针头尺寸的影响；(2)稳定产生微气泡的两个控制参数是Weber数(We=ρf^2d&lt；In&GT；In&GT；^3/σ，其中ρ是液体的密度，f是激发频率，dm是针的内径，a-是表面张力)和Wo+=d_&lt；in&gt；(Flv)^&lt；1/2&gt；，其中ν是液体的运动粘度)，(3)当Wo&lt；300时和2&lt；wo&lt；5.用边界元方法，我们也模拟了这种气液界面行为。虽然模拟模型很简单，因为针头周围的流场假设是轴对称的无旋转的，但对周期性界面行为以及针头内液体粘度和气体压力的影响的模拟结果与实验结果定性地吻合。模拟和实验结果表明，微气泡是通过表面波从针外向内传播而产生的投影的顶部脱离而产生的。表面波是由针壁附近的速度差产生的，然后通过表面张力传播。由于液体粘度的影响，气液界面呈周期性收敛，所产生的微气泡的尺寸变得均匀。

Consecutive images of the fragmentation of capillary waves in an ultrasonic field were obtained using a high-speed video camera through a microscope at a frame rate of 500,000 frames per second. The images showed that micro bubbles of uniform diameter from 4 to 15 μm were generated at a constant periodic rate when a small amount of gas was introduced into a highly viscous liquid whose kinematic viscosity was between 5 and 100 mm^2/s. Results revealed that (1) conditions for stable generation of micro bubbles are affected by excitation frequency, surface tension and viscosity of the liquid, and dimensions of the needle, (2) two controlling parameters for stable generation are the Weber number ( We = ρf^2d_<in>^3/σ, where ρ is density of the liquid, fis excitation frequency, dm is inner diameter of the needle, and a-is surface tension) and Womersley number (Wo+= d_<in>(flv)^<1/2>, where ν is the kinematic viscosity of liquid), and (3) uniform-diameter micro bubbles are generated stably when We < 300 and 2 < Wo < 5. Using a boundary element method, we also simulated this gas-liquid interface behaviour. Although the simulation model is simple because the flow field around the needle is assumed axisymmetrical and irrotational, the simulation results of the periodic interface behaviour and of the effects of liquid viscosity and gas pressure inside the needle qualitatively agreed with experimental results. Simulation and experimental results revealed that a micro gas bubble is generated by detachment of the top of a projection produced by propagation of a surface wave travelling from the outside to inside of the needle. The surface wave is produced by the difference in velocity near the needle wall, and is then propagated by surface tension. The size of the generated micro gas bubbles becomes uniform because the gas-liquid interface converges on periodic behaviour due to the influence of liquid viscosity.