超声空化及絮体破碎过程的模拟与试验分析

为探究利于空化效应的超声条件及超声波破碎絮体机理,基于Matlab平台建立空化气泡模型及2种简化的有限扩散聚集(DLA)絮体破碎模型,进行计算机仿真,并通过试验分析得到实际絮体破碎模式.结果表明:随着超声频率的增加,空化效应减弱;声能密度的增加导致空化气泡振幅增大,声能密度为7W/mL时气泡振幅可达初始半径的200倍,空化效果较好.低声能密(0.03~3W/mL)和低超声频率(25~40kHz)处理絮体时,剥蚀作用为主导作用,超声后絮体粒径减小,分形维数增大;声能密度超过3W/mL或频率大于40kHz,大规模破碎占主导作用,实际絮体粒径减幅小且结构散.40kHz的超声频率更利于絮体的破碎,作用10min后,絮体粒径减幅达9.8%,分形维数为1.394,结构更加密实.

Simulation of ultrasound cavitation bubble and numerical/experimental analysis of flocs breakage process

In order to explore the sonication condition for the ideal cavitation effect and to find out the breakage mechanism of flocs exposed to ultrasound, a model of cavitational bubble and two sorts of simplified models of diffusion-limited aggregation (DLA) floc breakage were established and simulated based on Matlab. The practical flocs breakage patterns were verified through experimental analysis. The results indicated that the cavitation effect decreased as the ultrasonic frequency increased. The increase of ultrasonic density led to the increscent amplitude of cavitation bubble, when the sonication density was 7W/mL, the radius of cavitation bubbles can be enlarged to 200 times longer and the cavitation effect was fairly good. When the flocs were treated at low energy density (0.03~3W/mL) and low frequency (25~40kHz) ultrasonication, surface erosion dominated the breakage effect, which was reflected by decreased radius and increased fractal dimension of flocs. When the energy density exceeds 3W/mL or the frequency surpasses 40kHz, the large scale fragmentation was the main mechanism, leading to the smaller flocs size and looser structures. The sonication of the frequency of 40kHz is more beneficial to flocs breakage, with the experimental result that 10minutes’ ultrasonication can lead to a dinimutioin rate of 9.8% of the radius and a fractal dimension of 1.394, and the structure of the flocs were more compact.