Oblate Electrohydrodynamic droplet formation in a microfluidic T-junction
ORAL
Abstract
External-field-driven interfacial instabilities have demonstrated considerable potential for miniaturizing flow patterns within microfluidic devices. The effect of externally applied electric field on the droplet formation mechanism in a microfluidic T-junction is presented. The electrical properties considered for the two fluids result in a system that exhibits oblate droplet deformation. Leaky dielectric theory is considered to model the electrical response of the droplets formed in the surrounding medium. We present the results of three-dimensional simulations for a range of Capillary number (Ca) values that is broad enough to investigate the effect of oblate Electrohydrodynamic (EHD) on different breakup mechanisms in confined microfluidic T-junction. We have used the electric Capillary number (CaE) to quantity the magnitude of the applied electric field in a dimensionless framework.
We observe that, at CaE=0, the breakup dynamics is predominantly governed by the squeezing and dripping mechanisms at low (5x10-3) and high Ca (5x10-2) respectively. However, at CaE =1, we find that the fluid-fluid interface is acted upon by strong compressive forces causing it to flatten perpendicular to the direction of electric field. The oblate EHD resists the droplet formation mechanism by delaying the necking of the fluid-fluid interface (the time required for neck formation increases) at the T-junction. Therefore, the droplet breakup time has been found to increase with an increase in CaE for both high and low Ca. This is quite astonishing since, the literature (R. Singh, S. S. Bahga, and A. Gupta, J. Fluid Mech. 905,A29 (2020)) reported a decrease in the droplet filing time leading to the formation of smaller sized droplets owing to prolate EHD. We have revealed that the application of electric field, coupled with oblate EHD, shifts the droplet breakup mechanism from droplets at T-junction (DTJ, CaE=0) to droplets in channel (DC, CaE=1) at high Ca. The findings reported here shed light over the oblate EHD droplet formation mechanism that is in complete contrast with the prolate EHD induced droplet formation mechanism.
We observe that, at CaE=0, the breakup dynamics is predominantly governed by the squeezing and dripping mechanisms at low (5x10-3) and high Ca (5x10-2) respectively. However, at CaE =1, we find that the fluid-fluid interface is acted upon by strong compressive forces causing it to flatten perpendicular to the direction of electric field. The oblate EHD resists the droplet formation mechanism by delaying the necking of the fluid-fluid interface (the time required for neck formation increases) at the T-junction. Therefore, the droplet breakup time has been found to increase with an increase in CaE for both high and low Ca. This is quite astonishing since, the literature (R. Singh, S. S. Bahga, and A. Gupta, J. Fluid Mech. 905,A29 (2020)) reported a decrease in the droplet filing time leading to the formation of smaller sized droplets owing to prolate EHD. We have revealed that the application of electric field, coupled with oblate EHD, shifts the droplet breakup mechanism from droplets at T-junction (DTJ, CaE=0) to droplets in channel (DC, CaE=1) at high Ca. The findings reported here shed light over the oblate EHD droplet formation mechanism that is in complete contrast with the prolate EHD induced droplet formation mechanism.
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Presenters
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Joy Mandal
Jadavpur University
Authors
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Joy Mandal
Jadavpur University
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Sandip Sarkar
Professor, Department of Mechanical Engineering, Jadavpur University, Kol-700032, India.