微细气泡生长及生成特性单因素影响规律研究

Abstract

Microbubbles refer to bubbles whose diameter is hundreds of microns.They are small in sizeThey have many characteristics that conventional bubbles do not have,such as small size,slow rise speed,and high mass transfer efficiency.So,microbubbles have considerable potential application value in many fields,such as wastewater treatment, ultrasonic imaging,and skin cleaning.The single-factor inflencing laws of microbubble growth and formation characteristics in the PDMS chip are studied aims to stduy the inflencing laws of microbubble growth and formation characteristics based on the application of microbubbles in sewage treatment and astronauts bathing.

The theory model of microbubble formation surrounded by co-flowing liquid was investigated.The mechanics conditions of the microbubble during its growth process are analyzed in detail based on the ellipsoidal assumptions.The mechanical equation of the surface tension,liquid flow tension,gas power and microbubble inertial force are established.The calculation of above-mentioned model was completed to predict the detachment volume of microbubbles in different environments based on the MATLAB and the fourth-order Runge-Kutta method.

The numerical simulation experiment of microbubble formation surrounded by co-flowing liquid was investigated.The numerical simulation model was established based on the two-phase flow theory and the level set equations in COMSOL Multiphysics.The detachment volume and formation time in different environments were predicted.And the prediction of the change of the volume in the growth process of the microbubble was completed.

The experiments of generation characteristics of the microbubble surrounded by co-flowing liquid was investigated.The PDMS chip based on coaxial flow focusing was processed.A microbubble generation test system was set up to study the generation characteristics of the microbubble surrounded by co-flowing liquid based on the professionally-constucted high-speed microscopic camera system(HSMCS).Image-Pro Plus,Photoshop,and MATLAB are used to process the images in the process of the microbubble generation.The characteristic parameters of the microbubble such as the detachment volume,formation time,and the centroid displacement under different conditions were obtained to investigate the influence of the liquid flow,liquid viscosity, gas pressure and the width of gas channel on generation characteristics of the microbubble.The effect of the prediction of the theoretical model and the simulation model on the detachment volume and the formation time were verified.

The experiments of generation characteristics of the microbubble in microfluidic

-II-

T-junctions was investigated.The PDMS chip based on T-junctions flow focusing was processed.The same experimental system and image processing methods were used to obtain the characteristic parameters of the microbubble such as the detachment volume, formation time,and the process of the change of the volume under different conditions to investigate the influence of the liquid flow,gas pressure and the width of gas channel on the parameters above.The generation frequency of the microbubble and equivalent diameter ratio were set up to compare the effect of the microbubble generation between the coaxial flow focusing and the T-junctions flow focusing environment.

In this paper,basic exploration work about the growth and generation characteristics of microbubbles has been carried out.Theoretical models,simulation models,and single-factor influence laws of bubble growth and generation characteristics have provided theoretical support for the controling of the bubble size and generation frequency.Meanswhile,they also provided theoretical support for the engineering application of microbubbles.

Keywords:microbubble,microfluidics,flow focusing,growth characteristics, formation characteristics

-III-

摘要................................................................................................................................I ABSTRACT......................................................................................................................II 第1章绪论.. (1)

1.1课题来源及研究的目的和意义 (1)

1.1.1课题来源 (1)

1.1.2研究目的和意义 (1)

1.2国内外研究现状 (2)

1.2.1国外研究现状 (2)

1.2.2国内研究现状 (8)

1.2.3研究现状简析 (11)

1.3课题主要研究内容 (12)

第2章同轴流动聚焦式气泡生长及生成特性理论研究 (15)

2.1引言 (15)

2.2气泡生长影响因素理论分析 (15)

2.2.1气泡生长过程中的影响因素分析 (15)

2.2.2气泡生长过程中的受力分析 (16)

2.3基于椭球体假设的气泡生长过程力学分析 (17)

2.3.1椭球体假设 (17)

2.3.2力学建模 (17)

2.3.3数值求解 (19)

2.4气泡生长及生成特性数值模拟 (21)

2.4.1数值模拟控制方程 (22)

2.4.2成泡过程仿真模型的建立 (23)

2.4.3成泡特性数值模拟结果简析 (24)

2.5本章小结 (28)

第3章同轴流动聚焦式气泡生长及生成特性试验研究 (29)

3.1引言 (29)

3.2同轴流动聚焦式PDMS微流控芯片的研制 (29)

3.3试验系统搭建 (30)

3.4试验过程及试验规划 (32)

3.4.1临界成泡气压的确定 (32)

3.4.2试验方法及工艺参数 (33)

3.5气泡图像过程数据处理方法 (33)

-IV-

3.5.1单气泡体积测算方法 (33)

3.5.2单气泡外围轮廓线特征提取方法 (34)

3.6气泡生长特性试验研究 (35)

3.6.1生长脱离过程 (35)

3.6.2体积变化规律 (36)

3.6.3接触角 (37)

3.6.4气泡长宽比及质心位移 (39)

3.7气泡生成特性试验研究 (42)

3.7.1脱离体积 (42)

3.7.2生成时间 (46)

3.8本章小结 (51)

第4章T型流动聚焦式气泡生长及生成特性试验研究 (52)

4.1引言 (52)

4.2T型流动聚焦式PDMS微流控芯片的研制 (52)

4.3试验过程及试验规划 (53)

4.3.1临界成泡气压的确定 (54)

4.3.2试验方法及工艺参数 (55)

4.4气泡生长特性试验研究 (56)

4.4.1生长脱离过程 (56)

4.4.2体积变化规律 (57)

4.4.3长宽比 (59)

4.4.4气泡宽度随时间的变化 (61)

4.5气泡生成特性试验研究 (62)

4.5.1脱离体积 (62)

4.5.2生成时间 (65)

4.6同轴与T型流动聚焦气泡生成效果对比 (68)

4.6.1当量径孔比 (68)

4.6.2气泡生成频率 (70)

4.7本章小结 (71)

结论 (73)

参考文献 (74)

攻读硕士学位期间发表的论文及其它成果 (78)

哈尔滨工业大学学位论文原创性声明及使用权限说明 (79)

致谢 (80)

-V-