Fluid Particle Coalescence Process

Studies on coalescence between fluid particles have been paid much attention to for many years, since the coalescence plays an important role in many industrial processes such as absorption, extraction, emulsification, polymer blending and so on. The coalescence involves interactions between fluid particles and drainage of intervening film, so it is intrinsically more complex than breakup and more difficult to study either theoretically or experimentally.Coalescence is usually modeled and described as taking place in three consecutive stages. Firstly, fluid particles collide, trapping a small amount of liquid between them. The second stage is the film drainage. As the film thins, the distance between the two surfaces may become small enough for non-hydrodynamic attractive forces to trigger an instability leading to film rupture. When it occurs, the third stage leads rapidly to coalescence. Since the duration of the third stage is virtually instantaneous compared with the two previous stages, it is generally assumed that the drop collision and film drainage stages essentially dictate the outcome of the interaction and these two processes are the focus of most studies, especially for the film drainage.However, the previous research methods usually decompose coalescence process into the approach process of fluid particles and the drainage process of intervening film between them, and then study these two processes separately. When the approach process is studied, the relative velocity and distance of fluid particles have been studied from the view of force, and the interaction time (from contacting to separating) has been estimated without considering the change of liquid film thickness. When the film drainage process is studied, the variation of liquid film thickness and interface shape has been obtained according to momentum transport equation within the liquid film, and the coalescence time, required for drainage of the liquid film between fluid particles has been calculated. Then, coalescence efficiency for fluid particles can be estimated from the interaction time and coalescence time.Coalescence process can't be cut apart. During the approach of fluid particles, the intervening liquid film thins when the relative velocity, distance and nterface shape change. According to previous result, the intervening liquid film has a critical thickness. When the liquid film thickness is equal to or less than this critical thickness, liquid film will rupture. During the approach of fluid particles, when the rebounding force caused by interface distortion is big enough to counteract the external force and...