微通道中空泡动力学特性及壁面润湿性调控技术研究
发布时间：2019-03-25 14:57
【摘要】：随着微纳米技术的发展,空泡技术在生物医学、化学工程和国防军事等领域发挥着巨大的作用。空泡技术的关键是如何实现对空泡动力学特性的有效控制,本文针对微通道构型对空泡动力学特性的影响以及壁面润湿性的调控技术进行了系统研究,对微流控系统的设计具有重要意义。利用高速摄像技术对通气空泡在T型微通道处的产生过程进行了研究,重点分析了流速、气液流速比以及通道尺寸对空泡动力学特性的影响。结果表明,空泡的产生方式包括四种,其对应的生成机制分别为挤压、剪切、挤压和剪切共同作用以及壁面阻力。空泡大小随着流速、气液流速比以及通道宽度的增大而增大。借助高速摄像技术并结合计算流体动力学方法研究了通气空泡在T型、Y型和文丘里管型微通道中发生形变或分裂的动力学特性。研究发现,T型和Y型通道中空泡的分裂机理主要包含通道结构和流场两种,文丘里管型通道中空泡的分裂机理为流场作用。空泡发生形变或分裂的强度随着流速的增大而增强,随着空泡体积和通道尺寸的增大而减弱。采用激光加工和自组装技术制备了具有不同润湿性的微通道壁面,借助高速摄像系统着重分析了流速和壁面疏水性对空泡动态接触角的影响。试验结果表明,随着流速的增大,空泡在壁面处的动态接触角和两侧壁面处的动态接触角比值均减小。空泡在通道两侧壁面处的动态接触角比值与通道左侧壁面润湿性之间存在着对应关系,此对应关系可用于微通道壁面润湿性的表征。利用薄片组装结合自组装分子膜沉积的方法设计并制作了一种表面润湿性可调控的疏水／超疏水表面,借助接触角测量仪对表面具有不同肋板高度时对应的静态接触角进行测量。测量结果表明,通过精确控制表面微肋板高度,可快速实现表面润湿性在弱疏水和强疏水甚至超疏水之间的可逆调控,且调控效果具有连续性。将设计的润湿性可调控表面进行改进并集成到微通道中作为通道一侧壁面,研究了流速和壁面疏水性对空泡动态接触角的影响。研究发现,通过控制微肋板结构可改变气液固三相的接触状态,从而实现壁面实际润湿性在强疏水和亲水之间的可逆调控。另外,壁面润湿性的调控效果和壁面处的空泡动态接触角均受薄片厚度和流速二者的影响。
[Abstract]:With the development of micro / nano technology, cavitation technology plays an important role in biomedicine, chemical engineering and national defense. The key of cavitation technology is how to effectively control the dynamic characteristics of cavitation. In this paper, the influence of micro-channel configuration on the dynamic characteristics of cavitation and the control technology of wall wettability are systematically studied. It is of great significance to the design of microfluidic system. The formation process of aerated vacuoles at T-type microchannels was studied by using high-speed camera technology. The effects of velocity of flow, gas-liquid velocity ratio and channel size on the dynamic characteristics of the vacuoles were analyzed with emphasis on the flow rate, gas-liquid velocity ratio and channel size. The results show that there are four types of cavitation formation, and the corresponding mechanisms are extrusion, shear, extrusion and shear together, and wall resistance. The bubble size increases with the increase of flow velocity, gas-liquid velocity ratio and channel width. The dynamic characteristics of deformation or splitting of aerated vacuoles in T-type Y-type and Venturi-type microchannels were studied by means of high-speed camera technique and computational fluid dynamics (CFD) method. It is found that the splitting mechanism of vacuoles in T-type and Y-type channels mainly consists of two kinds of channel structure and flow field, and the splitting mechanism of vacuoles in Venturi-type channel is flow field. The strength of void deformation or splitting increases with the increase of flow velocity and decreases with the increase of bubble volume and channel size. The micro-channel walls with different wettability were fabricated by laser processing and self-assembly technology. The effects of velocity and wall hydrophobicity on the dynamic contact angle of cavitation were analyzed by means of high-speed camera system. The experimental results show that the dynamic contact angle at the wall surface and the dynamic contact angle ratio at both sides of the cavity decrease with the increase of the velocity of flow. There is a corresponding relationship between the dynamic contact angle ratio at both sides of the channel and the wettability of the left side of the channel, which can be used to characterize the wettability of the micro-channel wall. A hydrophobic / superhydrophobic surface with adjustable wettability was designed and fabricated by using the method of thin film assembly and self-assembled molecular film deposition. By means of contact angle measuring instrument, the static contact angle of the surface with different height of rib plate is measured. The measurement results show that the reversible regulation of surface wettability between weak hydrophobic and strong hydrophobic or even superhydrophobic can be realized quickly by accurately controlling the height of the surface micro-rib, and the control effect is continuous. The designed wettability adjustable surface was improved and integrated into the micro-channel as one side of the channel. The effects of flow velocity and wall hydrophobicity on the dynamic contact angle of the cavitation were studied. It is found that the contact state of gas-liquid-solid three-phase can be changed by controlling the structure of micro-ribbed plate, so that the reversible regulation of the actual wettability of the wall between strong hydrophobic and hydrophilic can be realized. In addition, the governing effect of wall wettability and the dynamic contact angle of vacuoles on the wall surface are affected by the thickness and velocity of the film.
【学位授予单位】：大连海事大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O359.1;O352
本文编号：2447074
[Abstract]:With the development of micro / nano technology, cavitation technology plays an important role in biomedicine, chemical engineering and national defense. The key of cavitation technology is how to effectively control the dynamic characteristics of cavitation. In this paper, the influence of micro-channel configuration on the dynamic characteristics of cavitation and the control technology of wall wettability are systematically studied. It is of great significance to the design of microfluidic system. The formation process of aerated vacuoles at T-type microchannels was studied by using high-speed camera technology. The effects of velocity of flow, gas-liquid velocity ratio and channel size on the dynamic characteristics of the vacuoles were analyzed with emphasis on the flow rate, gas-liquid velocity ratio and channel size. The results show that there are four types of cavitation formation, and the corresponding mechanisms are extrusion, shear, extrusion and shear together, and wall resistance. The bubble size increases with the increase of flow velocity, gas-liquid velocity ratio and channel width. The dynamic characteristics of deformation or splitting of aerated vacuoles in T-type Y-type and Venturi-type microchannels were studied by means of high-speed camera technique and computational fluid dynamics (CFD) method. It is found that the splitting mechanism of vacuoles in T-type and Y-type channels mainly consists of two kinds of channel structure and flow field, and the splitting mechanism of vacuoles in Venturi-type channel is flow field. The strength of void deformation or splitting increases with the increase of flow velocity and decreases with the increase of bubble volume and channel size. The micro-channel walls with different wettability were fabricated by laser processing and self-assembly technology. The effects of velocity and wall hydrophobicity on the dynamic contact angle of cavitation were analyzed by means of high-speed camera system. The experimental results show that the dynamic contact angle at the wall surface and the dynamic contact angle ratio at both sides of the cavity decrease with the increase of the velocity of flow. There is a corresponding relationship between the dynamic contact angle ratio at both sides of the channel and the wettability of the left side of the channel, which can be used to characterize the wettability of the micro-channel wall. A hydrophobic / superhydrophobic surface with adjustable wettability was designed and fabricated by using the method of thin film assembly and self-assembled molecular film deposition. By means of contact angle measuring instrument, the static contact angle of the surface with different height of rib plate is measured. The measurement results show that the reversible regulation of surface wettability between weak hydrophobic and strong hydrophobic or even superhydrophobic can be realized quickly by accurately controlling the height of the surface micro-rib, and the control effect is continuous. The designed wettability adjustable surface was improved and integrated into the micro-channel as one side of the channel. The effects of flow velocity and wall hydrophobicity on the dynamic contact angle of the cavitation were studied. It is found that the contact state of gas-liquid-solid three-phase can be changed by controlling the structure of micro-ribbed plate, so that the reversible regulation of the actual wettability of the wall between strong hydrophobic and hydrophilic can be realized. In addition, the governing effect of wall wettability and the dynamic contact angle of vacuoles on the wall surface are affected by the thickness and velocity of the film.
【学位授予单位】：大连海事大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O359.1;O352
【引证文献】
相关硕士学位论文 前1条
1 石栋栋;Y型微通道中空泡动力学特性研究[D];大连海事大学;2017年
，本文编号：2447074
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