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