Figure 2. Number density of the droplets for different height.
According to Eq. 1, the droplet number density function should be
obtained before determining the DBFF. The droplet number density
function at different height is shown in Figure 2. It can be seen that
the droplet size shows a positive skewed distribution at different
column height. This is different from the results in our previous report36, 37 where the droplet size showed a normal
distribution. The reason is probably the introduced mass transfer
changed the behaviors of droplets. It is also found that the droplet
diameter mainly distributes between 0.3 mm and 1.8 mm. The number
density of droplets smaller than 0.3 mm is small because it is difficult
for large droplets to produce such small daughter droplets
(heterogeneous breakup) in the process of breaking up. The surface
energy of small droplets is large, the energy consumed in the process of
droplet breaking is insufficient to support the formation of such small
droplets under the energy inputting condition in our experiments. The
number density of droplets lager than 1.8 mm is small because the
breakup of large droplets is easier. The breakup frequency for droplet
larger than 1.8 mm is much larger in this work, which will be shown in
the next section. It can be further seen that the number density of
small droplets (around 0.75 mm) increases with the increasing of column
height. The reason is that the droplets from upstream are further broken
up when they go downstream and therefore the number of small droplets
increases.
Experimental result on drop breakup
frequency
function