Bubble flow is defined as a Two-Phase Flow where small bubbles are dispersed or suspended as discrete substances in a liquid continuum. Typical features of this flow are moving and deformable interfaces of bubbles in time and space domains and complex interactions between the interfaces, and also between the bubbles and the liquid flow. According to the magnitude of these interactions, bubble flow is classified into four different flow regimes: i.e., ideally-separated bubble flow;interacting bubble flow; churn turbulent bubble flow; and clustered bubble flow, as shown in Figure 1.