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arXiv · 2206.05742

CFD analysis of effects of surface wettability and flow rates on the interface evolution and droplet pinch-off mechanism in the cross-flow microfluidic systems

Akepogu Venkateshwarlu·Ram Prakash Bharti
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Abstract

This study has numerically investigated the effect of surface wettability on two-phase immiscible flow and dynamics of droplet pinch-off in a T-junction microchannel using finite element method. A conservative level set method (CLSM) has been adopted to capture the interface topology in squeezing regime ($Ca_c <10^{-2}$) for wide flow rate ratio ($1/10 \leq Q_r \leq 10$) and contact angle ($120^{\circ} \leq θ\leq 180^{\circ}$). Based on the instantaneous phase profiles, droplet formation stages are classified as initial, filling, squeezing, pinch-off and stable droplet. Wettability effects are insignificant in filling stage. However, hydrophobic effects are more visible in squeezing and pinch-off stages. Engineering parameters have generally shown complex dependence on dimensionless parameters ($Ca_c$, $Q_r$, $θ$). Capturing the instantaneous interface evolution has revealed droplet shape senstivity with the contact angle. Interface profiles transform from convex into concave immediately for hydrophobic ($120^{\circ} \leq θ\leq 135^{\circ}$) whereas slowly for super hydrophobic ($150^{\circ} \leq θ\leq 180^{\circ}$) conditions. In contrast to the literature, pressure in dispersed phase is not constant, but it is an anti-phase with pressure in continuous phase. Comparing the filling and pinch-off time based on the pressure and phase profiles has brought new insights that the droplet pinch-off mechanism can be elucidated by installing the pressure sensors even without the flow visualization and phase profiles. The interface curvature adopts a flattened to a more concave shape when the Laplace pressure varies from a smaller to a higher value. The interface neck width (2r) shows an increasing trend up to a threshold value and then decreases linearly with the contact angle.

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Akepogu Venkateshwarlu, Ram Prakash Bharti. 2022-10-10. CFD analysis of effects of surface wettability and flow rates on the interface evolution and droplet pinch-off mechanism in the cross-flow microfluidic systems. https://doi.org/10.1016/j.ces.2022.118279

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