FIGURE 15 (A) start and (B) end of the trajectory of the bubble
with a diameter greater than 1000 μm; (C) start and (D) end of the
trajectory of the bubble with a diameter less than 1000 μm. Liquid flow
rate: 1.0 ml/min and gas flow rate: 10 ml/min with 10 cm ceramic
membrane
FIGURE 16 The rising velocities of bubbles with 1.3 mm and 0.56
mm diameters. Liquid flow rate: 1.0 ml/min and gas flow rate: 10 ml/min
with 10 cm ceramic membrane
3.5 Intensification of bubble stability by
internals
The control of bubble trajectory contributes to the regulation of bubble
coalescence. After the installation of internals with different numbers
of baffles, the average diameter of the bubbles is effectively
controlled as the rising height increases. The collision frequency
between bubbles is reduced by installing internals inside the ceramic
membrane, thereby inhibiting the coalescence of bubbles. Especially when
three-baffle and four-baffle internals are installed, the bubble sizes
grow slightly during the rising process (Figure 17). The internals
impede the radial migration of the bubbles, reducing the collision
frequency and the possibility of coalescence, allowing for a steady rise
and keeping the size around 350 μm. Subsequently, the trajectory of the
bubble was tracked. The results suggest that the spiral rising
characteristics of large diameter bubbles are weakened (Figure 18). The
velocity of bubbles with a diameter of 1.2-1.4 mm after installing the
internals is analyzed. The velocity varies slightly in the range of
0.12-0.2m/s as shown in Figure 19, which is slower than the bubble
velocity of 1.3 mm diameter without internals. This indicated that the
baffle internals could maintain the stability of bubbles by reducing the
bubble rising velocity.
FIGURE 17 Effect of baffle number of internals on bubble size
at rising distance of 0 cm, 5 cm and10 cm. Liquid flow rate: 1.0 ml/min
and gas flow rate: 5 ml/min with 10 cm ceramic membrane