Bubble dispersion and mass transfer between gas and liquid in a gas-stirred system have been studied experimentally and theoretically.
Nitrogen gas was injected into water through a nozzle located at the bottom center of a cylindrical vessel. Local gas-holdup distributions were measured by an electrical resistivity probe. The volumetric coefficient in the bubble-dispersion zone for the absorption of CO₂-water system was measured. Experimental conditions were as follows: gas-flow rate (q_G) =(16.7-167)×10^-6m³/s, radius of vessel (r₁)=O.055-0.50m, height of water (z₁)=0.1-0.4m and diameter of nozzle =6mm.
A mathematical model based on the boundary-layer theory is proposed. The model consists of equation of flow with uniform effective kinematic viscosity υ_e and equations of bubble and solute diffusion with uniform effective diffusivities, D_{e, B} and D_{e, S}, respectively. Equations were solved numerically assuming υ_e=D_{e, B}=D_{e, S}, and the theoretical distribution of local gas holdup, axial velocity, and solute concentration were obtained. By comparing the theoretical distributions of local gas holdup with the measured ones, values of υ_e could be obtained for various q_G, r₁ and z₁. The values of υ_e were correlated with q_G on the basis of dimensional analysis. This correlation was consistent with related data available in the literature. Volumetric coefficients, calculated by the present model, were in agreement with the observed ones.