Effect of Perforated Plate Open Area on Gas Holdup in Rayon Fiber Suspensions

Three different aeration plates are used to study their effect on gas holdup and flow regime transition in fiber suspensions. The aeration plates differ by their open-area ratios (A=0.57%, 0.99%, and 2.14%), where the hole diameter remains the same while the number of holes increase. Experiments are performed using three different Rayon fiber lengths (L=3, 6, and 12mm) over a range of superficial gas velocities (Ug⩽18cm∕s) and fiber mass fractions (0⩽C⩽1.8%) in a 15.24cm dia semi-batch bubble column. Experimental results show that the aeration plate with A=0.99% produces the highest gas holdup in an air-water system and low fiber mass fraction suspensions, and the plate with A=2.14% yields the lowest gas holdup in these systems. In medium fiber mass fraction suspensions, the plate with A=0.57% produces slightly higher gas holdup values, while the other two plates yield similar results. The effect of the aeration plate open area on gas holdup diminishes at high fiber mass fractions (C⩾1.2%). All aeration plates generate homogeneous, transitional, and heterogeneous flow regimes over the range of superficial gas velocities for air-water and low fiber mass fraction suspensions. However, the aeration plate with A=2.14% enhances the flow regime transition, i.e., the superficial gas velocity at which transitional flow appears is lower. Additionally, the fiber mass fraction at which pure heterogeneous flow is observed is lower when A=2.14%.