3.3. Boundary conditions and geometry
Taking into account two distinct drag coefficients for each section, the computational domain is divided into two parts. The upper section is initiated from the test tray deck to the outlet zone and the space under the test tray is the lower section where the liquid weeping appears under the special condition. The drag coefficient presented by Krishna et al. [18] independent of bubble diameter is used in the upper space because of its extensive use by several researchers [18, 19, 30, and 33]. Moreover, the heterogeneous and froth bubbly regimes are found in this domain for specific gas velocities. For the lower section, Grace’s drag model is utilized, in which the liquid weeping is subjected to the upward gas stream [28].