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1. Acoustic Microstreaming for Droplet Breakup in a Micro Flow-Focusing
Device
Figure 1: (a) Flow-focusing device geometry. LW = LO = L
≈ 150 µm, Lr ≈ 40 µm (b) Piezoelectric actuator attached onto the top of the
flow-focusing device
Figure 2: Phase diagram of the actuated
droplet production process. Voltage applied is a continuous sine wave with
peak-to-peak value as indicated. The flow-rate of mineral oil (QO) is in µl/hr
and that of D.I. water (QW) is in µl/min
Figure 3: Variation of droplet size with frequency of acoustic
actuation. QO is in µl/hr and QW is in µl/min, the voltage applied is a
continuous sine wave with peak-to-peak value as indicated
Figure 4: Droplets produced after acoustic actuation. Voltage
applied is continuous sine wave with 300V P-P and at frequencies of (a, f) 0
Hz; (b, g) 250 Hz; (c, h) 500 Hz; (d, i) 750 Hz and
(e, j) 1000Hz. Flow-rate combination for (a) to (e) is of QO : QW = 100 µl/hr :
0.33 µl/min and that for (f) to (j) is of QO : QW = 100 µl/hr : 2.33 µl/min
Figure 5: (a) Vibrating motion of the fluid-fluid interface
at the cross-junction with acoustic actuation. (b) Fluid-fluid interface at the
cross-junction without acoustic actuation. Velocity vector fields (c) with (300
V P-P, 300 Hz) and (d) without acoustic actuation, cases (c) and (d) are of the
flow-rate combination of QO : QW = 100 µl/hr : 0.5
µl/min
Figure 6: Phase-averaged velocity vector fields for
acoustic actuation at 300 V P-P, 300 Hz and the flow-rate combination is QO : QW = 100 µl/hr : 0.5 µl/min