CFD Simulation Of Flow Characteristics Of Liquid Phase In The Packing Zone In A Rotating Packed Bed

Rotating packed bed(RPB)is a typical equipment for process intensification,which possesses excellent mass transfer and micro mixing performance.Due to the complexity of the rotor and packing structure,basic research about the liquid flow in the packing zone in RPB is rarely reported.At present,visualization experiment is the main method to explore the flow characteristics of the liquid phase in RPB.Developing a simple and accurate way to obtain the accurate flow state of the liquid in the packing zone by a more simply and accurately way is still the focus and challenge of RPB research.In this paper,CFD simulation is employed to study the flow characteristics of liquid phase in RPB's packing zone based on the two-dimensional geometric model of wire mesh packing.Three different turbulence models of SST,RKE and RSM were used to obtain the flow state of the liquid in the packing zone and measure the liquid holdup of RPB.A quantitative basis for the thickness of the entrance region is put forward for the first time.The thickness of the entrance region and the end region were measured in simulation by monitoring the vaiation of the cell Reynolds number and liquid tangential angle with the radial distance of the packing.The effects of operating conditions(such as rotating speed,liquid initial velocity and liquid viscosity)on the flow characteristics of liquid phase were investigated.The main research conclusions are as follows:(1)Simulation results based on the three turbulence models of SST,RKE and RSM show that the liquid flow state will change from liquid film-dominated flow pattern to liquid droplet-dominated flow pattern and the liquid holdup will decrease with increasing the rotating speed.The flow state of the liquid will change from liquid droplet-dominated flow pattern to liquid film-dominated flow pattern and the liquid holdup will increase with increasing the liquid initial velocity.The flow state of the liquid will change from liquid droplet-dominated flow pattern to liquid line-dominated flow pattern and the liquid holdup will increase with increasing the liquid viscosity.A new RPB liquid holdup correlation based on the simulation results of the liquid holdup was obtained.The obtained correlation exhibit more accurate results than Burns' correlation when predicting the liquid holdup.(2)When SST,RKE and RSM are used to simulate the liquid flow in RPB,the simulation results of the liquid holdup showed obvious differences,but the simulation results of the liquid flow pattern are approximately the same.Our results show that SST turbulence model performes better at low liquid initial speed;RKE turbulence model performes better at high liquid initial speed;RSM turbulence model performes better at high liquid viscosity.Those results provide a basis to select appropriate turbulence models for RPB's liquid flow CFD simulation under specific operating conditions.(3)In this paper,measuring the thickness of the entrance region and the end region by CFD simulation is firstly proposed.The results of the study show that:the thickness of the entrance region and the end region decreases with the increase of rotating speed and viscosity and the decrease of the liquid velocity.Based on the simulation data,a new accurate correlation is established.The predicted liquid holdup value that calculated by the new correlations matches well with the simulated value and the average relative error is with in ±20%.For the correlation of the end region,the deviation between values calculated by this correlation and values calculated by the probability method is within ±15%.The thickness of the turbulence developing region can be predicted by calculating the difference between the thickness of the entrance region and the end region under the same opearting condition,and the reasons for mass transfer efficiency changes for different operating conditions is explained from the perspective of liquid flow.