Dispersion of bubbles and gas-liquid mass transfer in a gas-stirred system.

Abstract

SynopsisBubble dispersion and mass transfer between gas and liquid in a gasstirred 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 C02-water system was measured. Experimental conditions were as follows: gas-flow rate (qG) =(16.7-167) X 10-6 m3/s, radius of vessel (r1)=O.055-.'0.50m, height of water (z1) = 0.1-0.4 m and diameter of nozzle = 6 mm.A mathematical model based on the boundary-layer theory is proposed. The model consists of equation of flow with uniform effective kinematic viscosity ve and equations of bubble and solute diffusion with uniform effective d fusivities, De ,B and Dens, respectively. Equations were solved numerically assuming ve=De ,B=Dens, 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 ye could be obtained for various qG, rl and z1. The values of ve were correlated with qG 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.

Empirical Equations for Bubble Formation Frequency from Downward-Facing Nozzle with and without Rotating Flow Effects

“…Previous investigators, however, mentioned mainly about the bubble formation from an upward-facing nozzle and the subsequent rising behavior of the bubbles. [4][5][6][7][8] Information on the behavior of bubbles generated from a downward-facing nozzle attached to a top lance is rather limited.…”

Gas-Liquid Reaction Model in Gas-Stirred Systems: Part 1. Numerical Model

“…Following the surface-renewal model (Danckwerts, 1951), Kataoka and Miyauchi proposed the following correlation to calculate the mass-transfer coefficient in open channels: [29] k ' ¼ 0:5 eq ' l '…”

“…(2) The resistance of the gas-phase mass transfer can be disregarded in front of the liquid mass-transfer resistance. (3) The effective diffusivity of both phases, D k j , is assumed to be equal to the liquid effective kinematic viscosity, m eff : [1,29] …”

Numerical analysis of fluid flow in continuous casting mold by bubble dispersion model.

“…The density of liquid is constant in the bubble dispersion zone, although the liquid is subject to a buoyant force proportional to gas holdup. (3) The diameter and slip velocity of the gas bubbles are constant in the system. (4) Turbulent kinematic viscosity, ,Jt, is estimated by the k-e two-equation turbulent model.…”