RESULTS AND DISCUSSION
3.1 Effect of ceramic membrane length and gas pressure on
bubbles size
Figure 4 shows typical images of bubbles generated by ceramic membranes
with different lengths at a liquid flow rate of 1.0 ml/min and a gas
flow rate of 10 ml/min. It can be seen that the distribution of bubbles
generated by the ceramic membrane with 10 cm length is the most uniform,
and the quantity of bubbles is larger than other length’s membranes.
Bubbles generated from a ceramic membrane with a length of 5 cm are also
well distributed, while the small effective membrane pore area which is
proportional to the length, leading to less quantity of bubbles than
10cm ceramic membrane. As the length of the ceramic membrane increased,
the possibility of bubble coalescence increased during the rising
process, resulting in larger size and less quantity of
bubbles.16 Figure 5 indicates that the average
diameter of bubbles decreases first and then increases with the increase
of the length of ceramic membrane. Under conditions that the length of
the ceramic membrane was 10 cm, the average diameter of the bubbles was
the smallest, only 320 μm, which was smaller than other ceramic
membranes. Figures 6 and 7 are performed to demonstrate that the changes
of gas pressure in the range of 0.2-0.6 MPa have few effects on the flow
pattern, distribution, and size of bubbles. In other words, when the gas
feed at low pressure (no more than 0.6 MPa), the increase of gas
pressure has no effect on the average diameter of bubbles. Results also
illustrate that the CMGD does not require extra energy consumption as a
green and high-performance gas distributor.