The Numerical Simulation Study About The Two Phase Flow Dynamics And Mass Transfer In The Packed Column

The early study of multiphase flow in packed tower was achieved through theexperiment. As the lab scale was small, there was obvious amplification effect when thestudy results were applied in the practical engineering. Compared with experimentalmethod, computational fluid dynamics(CFD) approach has great advantages of low costand precisely reproduce the real physical model in various working conditions. So thestudy of two-phase flow characteristic in the structured packed columns with the CFDmethod has become the emerging trends.The movement of two phase fluid in large scale was simulated based on two-phaseflow module in COMSOL Multiphysics4.1. By using the phase field method，the flowcharacteristics of and the interaction between the gas-liquid in the unit packing withperiodic boundary conditions were studied. The flow mechanics of two phase wasillustrated. Due to the gas-liquid phase interacting and influencing each other, theinterface is dynamically changing with time, which is a very complicated process.Through the analysis of simulation results, liquid flowed along the packing fromtop to bottom under its own gravity. The gas phase flowed from bottom to top in thetower under pressure drop of P. There was an obvious gas-liquid interface, and theinterface varied with time. Firstly, the fluid velocity changed with P, air velocityincreased with the increasing of P; The velocity of liquid phase decreased with theincreasing of P; Secondly, the volume distribution of two phase fluid in the packingwas changed with the P. When the pressure difference P of the unit packing wasbetween1Pa~10Pa, liquid volume remained stable, which belonged to the constantliquid area; When P was between10Pa~20Pa, liquid volume decreased with the Pincreasing, which belonged to carry liquid area; When P exceeded30Pa, the volume fraction of the liquid phase in the unit packing increased rapidly, almost occupying thewhole packing channel,meanwhile，the gas and liquid were mixed and the interface wasnot obvious.The study was based on the principle of the dissolution in the similar materialstructure, as long as the two phases were contacted，the mass transfer could berealized, and the influence of two phase absorption equilibrium could be ignored. Theresistance force in the mass transfer was mainly focused on the interface, so the flowcharacteristics was an important factor affecting mass transfer process. Concentratedspecies transfer model was coupled with the original laminar flow field model. Theresult showed，a certain concentration of species flowed into the packed tower with gas,part of the species in gas phase transfer to the liquid phase and flowed out of the towertogether with the liquid, finally the separation was achieved. At last, the pressure dropof the whole tower under different gas velocity were simulated, and obtained therelationship between the gas velocity and the pressure drop. This research can provide atheoretical basis for the design of the absorption tower.