液滴滴浸微通道入口段的动力学特性分析
|
摘要
采用流体体积(Volume of Fluid, VOF)函数捕捉气液相界面,研究液滴滴浸微通道入口段的运动,通过改变微通道入口段的截面宽度、润湿特性及液滴雷诺数(Re)和韦伯数(We)研究滴浸过程的动力学特性。结果表明,微通道入口段的截面宽度对液滴浸入微通道时的撞击过程影响最明显,随截面宽度减小,液滴撞击通道入口后通过微通道的难度增加,整个过程液滴所受阻力逐渐增大;当微通道截面宽度减至0.2 mm时,壁面润湿性效应凸显,表现为壁面静态接触角越大,液滴滴浸微通道时所受的阻力也越大。表面接触角较大时,为使液体通过微通道入口段,可适当增大液滴的Re,液体在通道内的浸润长度随Re增加成比例增大,当Re增至4000时,通道内开始出现射流现象。We减小,表面张力效应变得明显,通道内的流动阻力变大,液体流过微通道入口段的难度增大。
Droplet impregnate microchannel was a widely existed phenomenon in microfluidic control, while the mechanism of dynamic motion during impact was not well addressed. A numerical model was developed using volume of fluid(VOF) method and the model was validated by experiments. In this work, the gas-liquid interface was captured using VOF method and the phenomenon of droplet impregnating microchannel was studied. Among the many simulation cases, it was found that the section width, contact angle, Re number and We number had significant influences. In the process, the effects of section width, contact angle, Re number and We number were studied in details. After comparing the results of each cases, it was clear that the cross section's width of the microchannel inlet had the most obvious impact on the process of the droplet impregnating in the microchannel. And it was found that the smaller the width was, the more difficult for the droplet to pass the microchannel after colliding with the entrance of the channel. When the microchannel's cross-sectional width was reduced to 0.2 mm, the effect of the static contact angle of the wall surface would appear. The larger the static contact angle of the wall, the greater the resistance of the droplet to microchannel. Under the condition of large static contact angle, the length of the liquid in the channel can be increased by appropriately increasing the Re number of the droplet so that the liquid passed through the microchannel. However, when the Re number reached 4 000, jet phenomenon would happen. Then the liquid would flow through the microchannel in large quantities, and spread diameter would also increase significantly. As the We number decreased, the surface tension effect became obvious, the flow resistance in the microchannel became larger, and the liquid flowing through the microchannel would be more difficult, meanwhile the length of the infiltration was significantly reduced.
Droplet impregnate microchannel was a widely existed phenomenon in microfluidic control, while the mechanism of dynamic motion during impact was not well addressed. A numerical model was developed using volume of fluid(VOF) method and the model was validated by experiments. In this work, the gas-liquid interface was captured using VOF method and the phenomenon of droplet impregnating microchannel was studied. Among the many simulation cases, it was found that the section width, contact angle, Re number and We number had significant influences. In the process, the effects of section width, contact angle, Re number and We number were studied in details. After comparing the results of each cases, it was clear that the cross section's width of the microchannel inlet had the most obvious impact on the process of the droplet impregnating in the microchannel. And it was found that the smaller the width was, the more difficult for the droplet to pass the microchannel after colliding with the entrance of the channel. When the microchannel's cross-sectional width was reduced to 0.2 mm, the effect of the static contact angle of the wall surface would appear. The larger the static contact angle of the wall, the greater the resistance of the droplet to microchannel. Under the condition of large static contact angle, the length of the liquid in the channel can be increased by appropriately increasing the Re number of the droplet so that the liquid passed through the microchannel. However, when the Re number reached 4 000, jet phenomenon would happen. Then the liquid would flow through the microchannel in large quantities, and spread diameter would also increase significantly. As the We number decreased, the surface tension effect became obvious, the flow resistance in the microchannel became larger, and the liquid flowing through the microchannel would be more difficult, meanwhile the length of the infiltration was significantly reduced.
引文
[1]Abdolali K S,Ali K.Numerical and experimental investigation on the effects of diameter and length on high mass flux subcooled flow boiling in horizontal microtubes[J].International Journal of Heat and Mass Transfer,2016,92:824-837.
[2]胡俊,区卓琨.陶瓷喷墨打印喷头的工作原理、技术指标及其发展趋势[J].佛山陶瓷,2013,23(5):1-5.Hu J,Qu Z K.Ceramic inkjet print head working principle,technical indicators and its development trend[J].Foshan Ceramics,2013,23(5):1-5.
[3]王丽坤.常见喷墨打印头的分类和性能[J].丝网印刷,2015,243(7):39-41.Wang L K.Common inkjet print head?s classification and performance[J].Screen Printing,2015,243(7):39-41.
[4]李宇杰,霍曜,李迪,等.微流控技术及其应用与发展[J].河北科技大学学报,2014,35(1):11-19.Li Y J,Huo Y,Li D,et al.Microfluidics technology and its application and development[J].Journal of Hebei University of Science and Technology,2014,35(1):11-19.
[5]刘婷婷.惯性力作用下金属液滴在变截面微通道内的动态特性研究[D].合肥:中国科学技术大学,2015:40.Liu T T.Dynamic characteristics of metal droplets in a microchannel with variable vross section under inertial force[D].Hefei:University of Science and Technology of China,2015:40.
[6]Sanada T,Watanabe M,Shirota M,et al.Impact of high-speed steamdroplet spray on solid surface[J].Fluid Dynamics Research,2008,40(7):627-636.
[7]梁超,王宏,朱恂,等.液滴撞击不同浸润性壁面动态过程的数值模拟[J].化工学报,2013,64(8):2745-2751.Liang C,Wang H,Zhu X,et al.Numerical simulation of the dynamic process of droplet impacting on different wetting walls[J].CIESCJournal,2013,64(8):2745-2751.
[8]Tang C L,Qin M X,Weng X Y,et al.Dynamics of droplet impact on solid surface with different roughness[J].International Journal of Multiphase Flow,2017,96:56-69.
[9]Zhao J N,Li X P,Cheng P.Lattice Boltzmann simulation of a droplet impact and freezing on cold surfaces[J].International Communications in Heat and Mass Transfer,2017,87:175-182.
[10]Siddhartha F L,Vivek V B,Nigam K D P.Numerical simulations of drop impact and spreading on horizontal and inclined surfaces[J].Chemical Engineering Science,2007,62(24):7214-7224.
[11]Guo Y L,Wei L,Liang G T,et al.Simulation of droplet impact on liquid film with CLSVOF[J].International Communications in Heat and Mass Transfer,2014,53:26-33.
[12]Xu M J,Wang C J,Lu S X.Water droplet impacting on burning or unburned liquid pool[J].Experimental Thermal and Fluid Science,2017,85:313-321.
[13]Li X L,Zhang L,Ma X W,et al.Dynamic characteristics of droplet impacting on prepared hydrophobic/superhydrophobic silicon surfaces[J].Surface and Coatings Technology,2016,307:243-253.
[14]Ashgriz N,Poo J Y.FLAIR:flux line-segment model for advection and interface reconstruction[J].Journal of Computational Physics,1991,93(2):449-468.
[15]Rudman M.Volume-tracking methods for interfacial flow calculations[J].International Journal for Numerical Methods in Fluids,2015,24(7):671-691.
[16]尹东霞,马沛生,夏淑倩.液体表面张力测定方法的研究进展[J].科技通报,2007,23(3):424-429.Yin D X,Ma P S,Xia S Q.Research progress of measurement methods of liquid surface tension[J].Technology Bulletin,2007,23(3):424-429.
[2]胡俊,区卓琨.陶瓷喷墨打印喷头的工作原理、技术指标及其发展趋势[J].佛山陶瓷,2013,23(5):1-5.Hu J,Qu Z K.Ceramic inkjet print head working principle,technical indicators and its development trend[J].Foshan Ceramics,2013,23(5):1-5.
[3]王丽坤.常见喷墨打印头的分类和性能[J].丝网印刷,2015,243(7):39-41.Wang L K.Common inkjet print head?s classification and performance[J].Screen Printing,2015,243(7):39-41.
[4]李宇杰,霍曜,李迪,等.微流控技术及其应用与发展[J].河北科技大学学报,2014,35(1):11-19.Li Y J,Huo Y,Li D,et al.Microfluidics technology and its application and development[J].Journal of Hebei University of Science and Technology,2014,35(1):11-19.
[5]刘婷婷.惯性力作用下金属液滴在变截面微通道内的动态特性研究[D].合肥:中国科学技术大学,2015:40.Liu T T.Dynamic characteristics of metal droplets in a microchannel with variable vross section under inertial force[D].Hefei:University of Science and Technology of China,2015:40.
[6]Sanada T,Watanabe M,Shirota M,et al.Impact of high-speed steamdroplet spray on solid surface[J].Fluid Dynamics Research,2008,40(7):627-636.
[7]梁超,王宏,朱恂,等.液滴撞击不同浸润性壁面动态过程的数值模拟[J].化工学报,2013,64(8):2745-2751.Liang C,Wang H,Zhu X,et al.Numerical simulation of the dynamic process of droplet impacting on different wetting walls[J].CIESCJournal,2013,64(8):2745-2751.
[8]Tang C L,Qin M X,Weng X Y,et al.Dynamics of droplet impact on solid surface with different roughness[J].International Journal of Multiphase Flow,2017,96:56-69.
[9]Zhao J N,Li X P,Cheng P.Lattice Boltzmann simulation of a droplet impact and freezing on cold surfaces[J].International Communications in Heat and Mass Transfer,2017,87:175-182.
[10]Siddhartha F L,Vivek V B,Nigam K D P.Numerical simulations of drop impact and spreading on horizontal and inclined surfaces[J].Chemical Engineering Science,2007,62(24):7214-7224.
[11]Guo Y L,Wei L,Liang G T,et al.Simulation of droplet impact on liquid film with CLSVOF[J].International Communications in Heat and Mass Transfer,2014,53:26-33.
[12]Xu M J,Wang C J,Lu S X.Water droplet impacting on burning or unburned liquid pool[J].Experimental Thermal and Fluid Science,2017,85:313-321.
[13]Li X L,Zhang L,Ma X W,et al.Dynamic characteristics of droplet impacting on prepared hydrophobic/superhydrophobic silicon surfaces[J].Surface and Coatings Technology,2016,307:243-253.
[14]Ashgriz N,Poo J Y.FLAIR:flux line-segment model for advection and interface reconstruction[J].Journal of Computational Physics,1991,93(2):449-468.
[15]Rudman M.Volume-tracking methods for interfacial flow calculations[J].International Journal for Numerical Methods in Fluids,2015,24(7):671-691.
[16]尹东霞,马沛生,夏淑倩.液体表面张力测定方法的研究进展[J].科技通报,2007,23(3):424-429.Yin D X,Ma P S,Xia S Q.Research progress of measurement methods of liquid surface tension[J].Technology Bulletin,2007,23(3):424-429.