Impaction of liquid droplets on perforated plates

This study deals with the problem of a droplet impact on a porous substrate. A numerical calculation is carried out to simulate the droplet impact mechanism on a porous substrate. The results are obtained by solving the governing equations in Eulerian coordinate with definition of volume of fluid (VOF) in each mesh cell. The free surfaces of the liquid are advanced with Young's technique aided with a blocking method that either allows or refuses liquid to pass through. A continuity free surface model (CFS) is utilized to convert the surface tension force to a body force within the free surface mesh.; The geometry of the porous substrate is modelled by two plate model, a perforated plate model and a staggered plate model that collects a staggered array of porous mesh plates. Various of flow conditions are tested. The flow parameters are nondimensionalized to the dimensionless groups, including Re number and We number. Liquid contacts with the solid portion of the porous substrate are generally assumed with a static contact angle, β.; In two plate model, β significantly affects the possibility of capillary spreading. Spreading of a droplet in the capillary gap is possible even for β > 90°. The simulations show that a contact angle up to 93.3° still allows spreading within the capillary gap. Larger β results in the liquid to rebound and finally settle on top of the upper orifice plate. Increasing Re, introduces oscillations into the liquid within the capillary gap while a small We contributes to a large increase in the rate of inner spreading. The perforated plate model and the staggered plate model are both tested and led to similar conclusions. In general, a larger We allows a larger spreading area both inside and outside the porous substrates as Re, enhances the depth of the penetration. However, depth of penetration is hardly influenced as Re is extremely high. On the opposite, if Re is too low, penetration becomes more difficult.; If the capillary gap of the two plate model is allowed to be very large, a droplet-on-orifice impacting droplet generator is proposed to allow the generation of small droplets. By impacting a mother droplet on an orifice plate, small droplets can be generated. The size of the generated droplets weakly decreases with an increase of Re. The size of the daughter droplet is significantly determined by the initial We of the impacting droplet. A high We results in a small daughter droplet. The daughter droplet is allowed to be smaller than 1.677 Do predicted by Rayleigh's theory. In addition, satellite droplets occur at flows with a high We and a high Re and there exists a Re, for each We, below which droplet generation is not possible.