Abstract
This work presents the splitting dynamics of low-viscous fingers inside the single bifurcating channel through the surface wettability of daughter branches. The propagation of low-viscous fingers inside branching microchannels have importance in many applications, such as microfluidics, biofluid mechanics (pulmonary airway reopening), and biochemical testing. Several numerical simulations are performed where a water finger propagates inside the silicon oil-filled bifurcating channel, and at the bifurcating tip, it splits into two fingers and these fingers propagate into the separate daughter branches. It is noticed that the behaviour of finger splitting at the bifurcating tip depends upon numerous parameters such as surface wettability, capillary number, viscosity ratio, and surface tension. This study aims to trigger the behaviour of finger splitting through the surface wettability of daughter branches θ 1 , θ 2 . Therefore, a series of numerical simulations are performed by considering four different surface wettability configurations of daughter branches, i.e., θ 1 , θ 2 ∈ 78 ° , 78 ° ; 78 ° , 118 ° ; 78 ° , 150 ° ; 150 ° , 150 ° . According to the results obtained from numerical simulations, finger splitting may be categorized into three types based on splitting ratio λ , i.e., symmetrical splitting, nonsymmetrical splitting, and reversal (no) splitting. It is noticed that the surface wettability of both daughter branches is either hydrophilic 78 ° , 78 ° or superhydrophobic 150 ° , 150 ° , providing symmetrical splitting. The surface wettability of one of the daughter branches is hydrophilic and another is hydrophobic 78 ° , 118 ° , providing nonsymmetrical splitting. The surface wettability of one of the daughter branches is hydrophilic and another is superhydrophobic 78 ° , 150 ° , providing reversal splitting. The findings of this investigation may be incorporated in the fields of biochemical testing and occulted pulmonary airways reopening as well as respiratory diseases such as COVID-19.
Highlights
Viscous fingering (VF) is a hydrodynamic interfacial instability that is inherently evolved at the interface of two fluids when a low-viscous fluid displaces another more viscous fluid in the porous medium or Hele-Shaw cell [1,2,3].ese two fluids may be miscible or immiscible. e lowviscous fluid may be invaded radially or linearly in the results; radial or rectilinear linear displacement of more viscous fluid is observed
The entire Y-shaped channel is filled with high viscous fluid-1 after that fluid-2 is invaded through the inlet with the velocity, V. e orientation of the Y-shaped channel is considered as horizontal. erefore, the effect of gravity force due to density difference may be neglected in this investigation. e nature of both fluids is considered immiscible and incompressible. e fluid-2 is injected into the bifurcating channel with a constant velocity of 0.015 m/s
Numerical simulation has been performed by considering the same setups as well as the same working fluids which were used in the experimental investigation
Summary
Viscous fingering (VF) is a hydrodynamic interfacial instability that is inherently evolved at the interface of two fluids when a low-viscous fluid displaces another more viscous fluid in the porous medium or Hele-Shaw cell [1,2,3].ese two fluids may be miscible or immiscible. e lowviscous fluid may be invaded radially or linearly in the results; radial or rectilinear linear displacement of more viscous fluid is observed. E lowviscous fluid may be invaded radially or linearly in the results; radial or rectilinear linear displacement of more viscous fluid is observed According to these displacements, VF is categorized into two groups, radial VF [4,5,6,7] and rectilinear VF[8,9,10,11]. E displacement of more viscous fluid by less viscous fluid leads to be unstable due to viscosity differences (viscous force) and density differences (gravity force) so that finger-shaped instability appears at the interface of two fluids. Saffman and Taylor [17] conducted first experiments in 1958 on viscous fingering instability
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