Study On Liquid Circulation In Gas-liquid Bubble Columns

Bubble Column Reactor is widely used as gas-liquid and gas-liquid-solid multiphase reactor because of its simple structure, no mechanical transmission, high interfacial area, high efficient heat and mass transfer. How to describe and predict the radial liquid velocity distribution in bubble column is related to the design, scaling up and optimization of bubble column reactor. However, since the behavior in multiphase reactor is influenced by the system property and reactor structure, it lacks of enough theoretical guide in commercial application, especially in reactor structure design, plant scale-up, optimization and property prediction. It is necessary to seek for new study method and idea for pushing forward the commercial application of bubble column.This paper proposes a modified model of eddy-viscosity distribution for liquid flows in bubble columns based on a relationship from single-phase flows and then develops a liquid circulation model for bubble columns. The comparison between the liquid circulation model and the reported experimental data shows that the model based on modified model of eddy viscosity distribution not only agrees with the data very well but also has a wide application range, it also explains that the varying rule of eddy viscosity distribution model derived from single phase flow. In addition, the determining rules for the model parameters are discussed according to the simulations for the reported data by this model, it shows that the value of model parameter k_R influencing calculated results very much. It should be 0.189 for low viscosity system and 0.3 for high viscosity system. Parameter m, which depends on the viscosity and flow state in system, should be 2, 4, 6, 8 for sorts of turbulent system. Parameter k_L, which depends on the diameter of bubble column, should be 2-2.2 for large diameter and 1-1.2 for small diameter.Mixing length theory is one of the simplest modeling means for turbulent flow. This paper proposes two models for turbulent flow in circular tubes, by modifying the mixing length through introducing a damping function for the viscous sublayer and using the second-order derivative to approximate eddy viscosity. The calculated results show that the models are able to be in good agreement with the reported empirical relationships of the time-smoothed velocity, eddy viscosity and friction factor and that effect of the viscous sublayer on profiles of the velocity and friction factor. It shows that this model is stronger theoretic and lager application range than the empirical equations, it is propitious to realize and study for the turbulent flow phenomena. Based on the verify check of the method and the research results above, this paper proposes the method of the modeling of liquid circulation in bubble column based on modified mixing length theory, and expects the development and improvement of this problem.