Microfluidic Droplet Formation — Capillary Instability

In a microfluidic T-junction or flow-focusing device, competition between interfacial tension and viscous shear determines droplet size via the capillary number Ca = μU/γ. At low Ca, periodic droplets form (squeezing regime); at high Ca, a continuous jet thins and breaks by Plateau-Rayleigh instability.

Flow Parameters

Capillary # Ca: 0.20 Flow rate ratio Q_d/Q_c: 0.30 Viscosity ratio λ: 1.00 Surface tension γ: 1.00

Regime

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Droplet size:

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Break-up frequency:

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Ca < 0.1: squeezing

0.1 < Ca < 1: dripping

Ca > 1: jetting