Experimental System
Experiments were performed in a water tank with a size of 100 mm ×150 mm
×400 mm as shown in Figure 1. The air supplied from two micro-syringe
pumps was injected into water through a bent capillary nozzle. The
nozzle orifice faced downward and its injection part was inclined at
3±1o from vertical direction. The mass flow rate was
monitored by two gas mass flow meters (FMA-A2302 and FMA-A2303; Omega
Engineering Inc., USA). The gas injection experiments were repeated for
different
gas
flow rate Q (40-5400 mL/h) and inner nozzle radiusR 0 (0.030, 0.065, 0.085, 0.130, 0.155, 0.205,
0.255 mm). The processes of bubble behaviors were recorded on a
high-speed video camera (Mini UX100; Photron, Japan) under illumination
by either a LED light (capturing structure of bubble surface) or a
mental-halide light (capturing very high-speed coalescence behaviors).
The captured high-speed videos were processed with an image processing
procedure programmed by MATLAB. The uncertainty of bubble radius is 3%
approximately. The detailed information on image processing procedure
and uncertainty analysis of bubble parameters has been introduced in our
previous work25.