Research on demulsification of O/W emulsion by spiral plate microchannel with ultra-large aspect ratio

doi:10.11949/0438-1157.20200862

Abstract

Abstract:

A three-dimensional spiral plate-type microchannel (3D-SPM) with high separation flux was designed and processed. The coupling effect between the unique oleophilic and hydrophobic surface in the microchannel and the 3D-SPM microstructure was utilized to strengthen the demulsification process of the O/W emulsion. Combined with computer simulation methods, the effects of the number of microchannels, emulsion volume flow rate, and residence time on the demulsification rate were studied. The results showed that the demulsification efficiency increased with the increased plate number of the microchannel, and the size of liquid droplets decreased gradually after the demulsification. With the increase of the volume flow rate of emulsion, the demulsification efficiency firstly increases to a maximum and then decreases, which reflects the coupling effect of the surface effect and the Dean vortex. The maximum single demulsification efficiency was 25%. With the increase of residence time, the demulsification efficiency increased. After 8 cycles of demulsification, the maximum demulsification efficiency reached 85.9%. The numerical simulation by computer simulation revealed that as the flow rate increases, both of the number and intensity of Dean vortex inside the rectangular cross-section increase, and the vortex region expands to the outer walls continuously. When the volume flow rate was 8 ml/min, the number of Dean vortex reached a maximum of 2 pairs, the maximum shear rate inside the microchannel was 5527 s^-1 and the demulsification efficiency reached the maximum. Further increase the flow rate, the demulsification rate decreases due to the excessive disturbance of the shear rate at the wall and the Dean vortex.

Key words: microchannels, emulsions, demulsification, computer simulation, Dean vortex

摘要：

设计加工出一种高分离通量的三维螺旋板式微通道（three-dimensional spiral plate-type microchannel，3D-SPM），利用该微通道内的亲油疏水表面与三维螺旋微结构之间的耦合作用，强化了对水包油（O/W）型乳状液的破乳过程。结合计算机模拟方法，研究了微通道片数、乳状液体积流速、停留时间对破乳率的影响。实验结果表明：随着微通道片数的增加，破乳率增加，破乳后的液滴粒径逐渐减小；随着乳状液体积流速的增加，破乳率呈先上升后下降的趋势，体现出通道的表面作用和Dean涡流作用的耦合效果，最大单次破乳率为25%；随着停留时间的增加，破乳率增加，8次循环破乳后，最大破乳率为85.9%。通过计算机模拟发现：随着流速增加，微通道矩形截面中Dean涡流的个数及强度随之增加，涡流区域不断向上下壁面拓展，当体积流速为8 ml/min时Dean涡流的个数达到最大为2对，此时壁面剪切速率为5527 s^-1，达到最大破乳率，进一步提升流速，由于壁面处剪切速率和Dean涡流扰动过大，导致破乳率降低。

关键词: 微通道, 乳液, 破乳, 计算机模拟, Dean涡流

CLC Number:

MA Zhengdong, WEI Meixiu, LU Qilin, DILIYAER?Hamiti , CHEN Xiao. Research on demulsification of O/W emulsion by spiral plate microchannel with ultra-large aspect ratio[J]. CIESC Journal, 2021, 72(3): 1392-1399.

马正东, 韦梅秀, 卢琪霖, 地力亚尔·哈米提null, 陈晓. 超大宽高比螺旋板式微通道对O/W乳状液的破乳研究[J]. 化工学报, 2021, 72(3): 1392-1399.

Figures/Tables 6

Fig.1 Three-dimensional spiral plate-type microchannel

Fig.2 Stability of the emulsion(a); Contact angle on the surface of PTFE(b)

Fig.3 Effect of plate number on demulsification efficiency(a); Effect of cycle times on demulsification efficiency (b); Effect of cyclic demulsification on droplet size(c)

Fig.4 Arc section of microchannel(a); Force analysis of droplets in the cross section (b); Shear rate inside the cross section(c); Dean vortex inside the cross section(d)

Fig.5 Shear rate inside the cross section(a); Velocity in z direction and Dean vortex inside the cross section(b)（The size and direction of the arrows represent the intensity and the flow direction of Dean vortex, and the color legend represents the velocity in z direction）

Fig.6 Effect of residence time on demulsification efficiency

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