Experimental Study And CFD Simulation Of The Flow Dynamics And Mass Transfer Behaviors In A Gas-induced Pulsing Bubble Column

It has been thoroughly investigated on the fluid dynamics and mass transfer properties in the gas-liquid two-phase bubble columns in the past few decades. However, as far as we know, no literatures are reported on the study, or at least CFD simulation of the gas-induced pulse in the bubble column. Thus, the purpose of this paper is to study the fluid flow and oxygen mass transfer in a gas-induced pulsing bubble column in both experiment and CFD simulation aspects.The present paper firstly investigates the effects of the pulse parameters, i.e. pulse amplitude and frequency on fluid dynamics, especially the total liquid kinetic energy distribution in the pulsing bubble column. It has been found that the total turbulent kinetic energy radial distribution is parabolic and increases with increasing in pulse amplitude and frequency; it firstly increases with axial position and then decreases, with a maximum value occurs at the height of Z = 0.4 m (Z/D = 2). The gas holdup, gas velocity field and liquid velocity field are greatly influenced by the gas pulse and bubble plume. Furthermore, it is interesting to note that the fluid flow pattern transforms from bubbly flow into churn-turbulent when the frequency is high enough, which would then increase the phase mixing and mass transfer in the column.Then, the relationship between the volumetric mass transfer coefficient kla and the pulse parameters is studied. It has been found that kla under the pulsing condition is smaller than that under the steady state for lower base gas flowrate with the same superficial gas velocity. If the base gas flowrate is equal to the pulse gas flowrate, kla would be higher for the pulsing condition. Moreover, it is shown that the interfacial area density for oxygen mass transfer has a tight relationship with gas holdup and bubble size distribution, and the liquid side mass transfer coefficient shows little dependence on the fluid flow. Furthermore, model prediction has been given on the dissolved oxygen concentration distribution in the bubble column; it is found that the concentration increases with time and the distribution tends to be more homogeneous in the column.