Numerical Simulation Of Transient Characteristics In Bubble Column Reactors

Bubble column reactors (BCRs) are widely used in the industrial applications. However, it is very difficult to design and scale up this kind of reactor, in that the present study has focused on the transient characteristics of the inherent gas-liquid flow increasingly. Following the development of the computer technology, Computational Fluid Dynamics (CFD) has become a useful and strong method to study the multiphase flow. Moreover, as a kind of turbulent model, Large Eddy Simulation (LES) can capture the transient flow information of every phase, which has attracted more attention.On the basis of multiphase flow dynamics theory, the paper selected the BCRs as the study objects, which have two kinds of gas distributor, central air aerated and partial air aerated. Using the LES model, the hydrodynamics parameters and the transient flow pattern in the gas-liquid BCRs were investigated in the Euler-Euler coordinate.The simulation results indicated that using LES model could obtain the fluctuation of the velocity at any position and any time, which made us obtain more high frequency pulsing details of the fluid velocity. No matter the central air aerated or the partial air aerated, the gas hold-up distribution and the transient flow pattern were all in agree with the experimental results of Buwa, Sokolichin and Becker. That proved the LES model had high reliability to study the gas-liquid transient flow in BCRs. In addition, the velocity vector distribution reflected the dynamic flow structure. The development of the vortex structure and the vorticity magnitude distribution indicated that the whole flow structure was affected by large eddy.The simulation results of central air aerated BCRs suggested that using time-averaged turbulent model could not reflect the real transient flow structure in BCRs; higher liquid viscosity had limitation to the development of the vortex scale; increasing the gas-in velocity made the vorticity magnitude distribution tend to be more disequilibrium; decreasing the bubble scale made the energy distribution more uniform, which could enhance the efficiency of heat and mass transfer in BCRs.Using LES model to simulate the partial air aerated BCRs also could get the following results: increasing the gas-in velocity made the distribution of the hydrodynamics parameters more uniform in a rather short time; while, higher liquid viscosity were against the energy distribution in the flow field and small aspect ratio would made the vorticity magnitude be more concentrated.