Numerical Research On Phase Separation And Pressure Drop Of Mist Flow In T Junctions

With the T junction in parallel piping structure as the research object,the present investigation generated phase separation and pressure drop data of steam-water mist flow by numerical simulation.This article studied the influence of different inlet parameters on the phase separation,as well as pressure variation.Through summarizing the phase separation regularity and the pressure drop trend,comparing the consistency of results between pressure drop prediction model and numerical simulation,,numerical simulation software FLUENT and Mixture two-phase flow model were verified to be effective for mist flow research in T junctions.What's more,effective reference was provided in order to optimize two phase flow distribution in T junctions and piping system design.Main conclusions are as follows:Mixture model for mist flow with low liquid content and droplet form was selected for the simulation according to the two phase flow pattern and flow conditions.This article did some simulation for two phase flow and phase separation in horizontal T junctions.Two phase flow distribution and pressure variation were explored under different gas and liquid flow rate,droplet diameter,entry average flow velocity and fluid content.Reasons of phase separation for two phase flow in the diversion structures were analyzed without considering gravity and neglecting heat and mass transfer between gas and liquid.The vortex "suction" could affect gas and liquid for different levels because the inertial force of liquid was much bigger than that of gas.The sliding between two phases which leads to the gas not capable to carry droplets was also an important reason for phase separation.The research results showed a preference for the gas phase to exit through the branch tube.Liquid split ratio could be more easily affected by flow conditions changes compared with gas.Mist flow phase separation in T junctions kept basically constant with the change of tube diameters.However,it might be affected obviously by phase velocity,liquid hold up and droplet diameter changes.With the increase of phase velocity and droplet diameters,more liquid exited through branch tube.Phase separation might be weakened with the increase of liquid holdup.Reasons of phase separation for two phase flow in the T junction diversion structures were analyzed.Without considering gravity,heat and mass transfer between two phases,inertial force difference between gas and liquid lead to that they were affected by branch vortex "suction" in different degree.Two phase obvious sliding was found on the diversion structure,fluid turbulence and viscosity change lead to a change in ability for gas carrying liquid.Comprehensive analysis showed that inertial force,two phase interaction force and fluid disturbance were the important causes for mist flow phase separation in T junctions.The local resistance pressure drop caused in T junctions varied remarkably with the change of two phase flow conditions.Compared with the run tube,the irreversible pressure drop in the branch could be affected more obviously by the change of branch tube diameter and it would increase quickly when the branch tube diameter decrease.For most inlet conditions,with increasing W3/W1,the magnitude of ?P12 would increase to a maximum before decreasing.Increasing the inlet mass flow rate,inlet velocity and liquid hold up generally had the effect of increasing the absolute values of ?P12 or ?P13.The pressure drop predicting models for run and branch tube were compared against simulated results respectively,which contained ZT,CF models for run tube and HM,CM,QLM,PHM models for branch tube.It was found that ZT model performed better than CF model when predicting ?P12,?P13 predicted by HM,CM,QLM model was basically identical with simulated results.The consistency between PHM model and simulation was little worse than that of other three model.Factors such as two phase flow rate,inlet velocity,liquid hold up and tube diameter have an effect on the consistency of pressure drop predicting model and simulated results for different levels.The best consistency of predicting model and simulated results could be got for larger tube diameter,lower W3/W1 and lesser inlet flow rate.