Steady-State Systems Bubbles and Droplets

Steady-State Systems Bubbles and Droplets Bubbles are made by injecting vapor below the liquid surface. In contrast, droplets are commonly made by atomizing nozzles that inject liquid into a vapor. Bubble and droplet systems are fundamentally different, mainly because of the enormous difference in density of the injected phase. There are situations where each is preferred. Bubble systems tend to have much higher interfacial area as shown by Example 16 contrasted with Examples 14 and 15. Because of their higher area, bubble systems will usually give a closer approach to equilibrium. 

Unstable Systems Froths and Hollow Cone Atomizing Nozzles We usually think of interfacial contact as a steady-state system of raining droplets or rising bubbles, but some of the most efficient interfacial contactors take advantage of unstable interfacial geometry. The most common is the distillation tray which operates with a wild mix of bubbles, jets, films, and droplets. The mix is often described as froth. Gas pressure drop provides the energy to create the froth. 

The term coalescence generally describes the prcxiess in which the primary produced, mostly very small gas bubbles or drops merge together into larger, stable ones. In fact, in fluid G/1 and L/L material systems, dispersion and merging together (coalescence) of the dispersed phase takes place constantly and the so-called stable bubble (droplet) size, under turbulent flow conditions, merely represents the the steady-state situation. 

---