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