Liquid Mixing in a Bubble Column

In most of the bubble column designs, it is assumed that the liquid phase is well mixed and spatial distributions of molar concentrations of all components are uniform. However, liquid mixing occurs in actual bubble columns. The performance of a bubble column strongly depends on the liquid mixing induced by bubbles in the column. The above-mensioned assumptions therefore lead to errors in the optimum column design. However, only a few quantitative investigations have been carried out on two-phase turbulence and liquid mixing. In this study, numerical simulations of liquid mixing in a bubble column were carried out and the results obtained were compared with those of experiments. Time-dependent tracer concentrations were measured for test columns 0.3 m in diameter. The height of the columns was 1 m. Bubbles were supplied by using two types of spargers, ring spargers and a perforated plate. A hybrid method, NP2-3D, that is based on a combination of multi-fluid and interface tracking models was used to simulate the flow. In a two-phase turbulence model, the linear superposition of bubble-induced turbulence and shear-induced turbulence was assumed. Numerical were found to be good predictions of the effects of the column diameter and gas inlet on the liquid mixing in the column.