Horizontal
falling film absorber has been widely applied in petroleum,
chemical industry, and toxic gas disposal due to its advantages of
large fluctuation of gas–liquid interface, accurately controlled
interface, easy separation of gas–liquid interface, and low-pressure
drop. The study of the velocity evolution of the liquid film at low-spray
density is essential to understand the micro-mass transfer mechanism
of the reactor and strengthen the absorption. The present study first
deciphered the subregion features of the falling film motion over
a horizontal tube with varied flow patterns and the parameters, such
as spray density, spray height, and salinity that affects the velocity
distribution of the falling film at low-spray density for the superhydrophilic
surface, were also investigated using the modified PIV method. The
result indicated that the velocity distribution of the film renders
a typical subregion effect, i.e., nonimpact zone and impact zone for
droplet mode, while, for jet mode, the film between the adjacent columns
exists in the form of mutual repetition, and the velocity of the film
will be slightly higher than that of the body motion region at the
interaction ring. It was also found that the spray density and spray
height had a positive effect on the average velocity of falling film
over the horizontal tube for droplet mode and jet mode. However, for
the droplet mode, the spray density increases the velocity of the
film by increasing the frequency of the droplet impact. In addition,
the average velocity of the film decreases with the increase in the
salinity (viscosity).