Study On Flow Characteristics Of Liquid In Countercurrent Rotating Packed Bed

As a chemical process strengthening equipment,the rotating packed bed the liquid into tiny droplet units by means of high-speed rotating packing,which increases the liquid of specific area,greatly improves the gas-liquid mass transfer efficiency and improves the micro-mixing performance.However,due to the complicated structure and high liquid velocity in the rotating packed bed,it is difficult to qualitatively and quantitatively analyze it by means of the prior art,so that the current research on the rotating packed bed mostly focuses on the influence of fluid properties and operating parameters on the fluid flow law.On the one hand,there is a lack of in-depth exploration of the internal fluid mechanics of the packing structure,and the completion of this part of the work is of great significance for the optimization of the internal structure of the rotating packed bed and further industrial application.Therefore,on the basis of previous studies,this paper uses CFD and PIV techniques to explore the influence of liquid flow characteristics in countercurrent rotating packed bed by rational design and change of packing property.In this paper,the PIV technique is first used to visually observe the liquid motion behavior of the countercurrent rotating packed bed of the sieve plate packing.Using water-air as the research system,the effects of sieve packing characteristic sizes(radial thickness: 0.067~0.118 m),rotational speeds(400~1200 rpm)and liquid initial velocities(0.5~2.5 m/s)on hydrodynamic characteristics were investigated.Simultaneous,using Fluent 15.0 of CFD technology as the calculation platform,the two-dimensional numerical simulation calculation of the countercurrent rotating packed bed of the sieve plate packing was carried out by using VOF multiphase flow model,RSM model and SM model by reasonable simplification of the packing geometry.The system and conditions used in the simulation and experiment are the same.Through the comparison and analysis of the two research results,the influence of operating parameters and packing characteristic sizes on liquid morphology,average diameter of droplet,droplet size distribution and droplet velocity was obtained.Results show that: There are mainly ligament flow and liquid film flow in the packing zone,and the cavity zone is mainly droplets.When the radial thickness of the sieve plate packing is less than 0.101 m,liquid flow and droplets of various shapes appear in the cavity zone.When the rotational speed and the radial thickness of packing increase,the average droplet diameter gradually becomes smaller and the droplet size distribution tends to be more uniform.As the liquid initial velocity increases,the average droplet diameter increases and the particle size distribution becomes worse.The correlation between the average droplet diameter and the parameters is obtained by linear fitting,in which the radial thickness of packing has the most significant effect.The relative errors between simulated and predicted results are within ±15%.The cumulative volume distribution curve of the droplets obtained by experiment and simulation accords with the R-R distribution.The droplet velocity increases as the radial thickness of packing increases,and gradually decreases as it reaches the cavity zone.Based on the above research,the liquid flow under the wire mesh packing is visualized by PIV technology.The variation of the hydrodynamic characteristics in the wire mesh packing with the rotation speeds(400~1200 rpm)and the liquid initial velocities(0.5~2.5 m/s)was investigated and compared with the flow field characteristics in the sieve plate packing.Analysis of the results of the two found: In the cavity zone,the droplet size and uniformity under the wire mesh packing are better than the sieve plate packing.The type of packing does not restrict the influence of the rotational speed and liquid initial velocity on the average droplet diameter.Under the wire mesh packing,the effect of the rotational speed on the droplet size is most significant,and the correlation between the experimental and the predicted results is within ±15% through the correlation and fitting error figure.The droplet size distribution under the experimental wire mesh packing is consistent with the R-R distribution,and the droplet distribution range is smaller than the sieve plate packing.The droplet velocity increases only with increasing rotational speed and is not affected by the type of packing and the liquid initial velocity.This paper provides a method for studying the hydrodynamic characteristics of countercurrent rotating packed bed by using PIV technology to investigate the structural parameters of the packing.And compared with the CFD simulation method,this will provide some theoretical guidance and basis for the amplification optimization and structural design of the rotating packed bed.