Investigation Of Macro-micro Characteristics In Oil And Water Two Phase Flow And Flow Field Processing

Characteristic of oil-water two phase flow is critical for the design and operation managements in the oil gathering and transportation system.Early research generally focus on the macro aspects,including flow patterns,pressure drop and inversion point,while lacking breakthroughs on the clarification of two phase flow flied information,dispersed drop behavior and other micro characteristics.In this paper,based on the previous experimental and theoretical achievements,research including flow pattern identification method,stratified and dispersed flow field information and dispersed drop size distributions was performed by using experimental flow loop and stirred tank.Purpose of this work is to make a deep understanding on the flow mechanisms,further providing theoretical and technical support for the solution of industrial problems.An experimental pilot scale flow loop was designed and constructed for the research of oil-water two phase flow.Measuring methods for flow field information and drop size distribution were introduced in detail.Experimental observation on flow pattern and pressure gradient at different flow conditions were performed.Based on the instability analysis of interface wave,the mechanism of drop entrainment was introduced to establish a new transition principle from stratified to disperse flow regimes.The homogeneity of dispersed flow was discriminated by comparing various drop characteristic sizes.Further,a completed flow pattern identification method was accomplished by coupling the inverse point calculation.Comparing with 8 different experimental data,the high predicted accuracy and wide applicability of the method was proved.Both morphology and flow field information in the process of drop detachment from interface waves to bulk phases were recorded by utilizing high speed camera and particle image velocimetry(PIV).The drop entrainment mechanism was revealed and factors determining the mixing behavior of interface were analyzed.A numerical model for the prediction of drop entrainment volume was proposed by calculating the difference between critical and characterstic amplitudes of interface wave.Further,based on the equilibrium between the drop entrainment and sedimentation,drop entrainment volume fraction was well predicted at 4 different experimental systems.Besides,PIV was employed to investigate the bulk flow field information of the oil-water stratified flow with interface fluctuation.A method calculating the interfacial friction factor was proposed and has been proved to coincide with results from the traditional model.Interfacial configuration of oil-water stratified flow was conducted by resolving Young-Laplace equations.Effect of Bond number and contact angle on the interface shape was analyzed and results between 10 different experimental systems were compared.PIV was used to measure the flow filed information of the dilute dispersion by coupling the angle resolved impeller and refractive index matching technique.Results show that the dispersed phase increment tends to enhance the turbulence kinetic energy and energy dissipation rate,which is attributed to the effect of drop number and size,dispersion viscosity and drop behaviors.Influence of interrogation area and measuring angle on the flow field was analyzed.Further,dispersed phase increment was supposed to homogenize the turbulence.Numerical simulation of disperse flow was carried out by using commercial software of computational fluid dynamics(CFD).Comparison between experimental and simulated results was performed.Systematical research on the oil-water dispersed flow was performed by using focused beam reflectance measurement(FBRM).Effect of mixture velocity and water holdup on the effective viscosity and drop size distribution was investigated.Drop coalescence behavior and its suppressed effect on turbulence intensity were indicated as the major reason of drag reduction caused by addition of dispersed phase.Based on the balance between drop breakage and coalescence,population balance equation(PBE)was established to predict dispersed drop size distribution.For the prediction in pipeline,computational region was divided by referring the measured energy dissipation distribution while the difference of coalescence efficiency between water droplets and oil droplets were also considered.Calculated results were found well predict the experimental data.When applying population balance equation to surfactant dispersions,the combined effect of surfactant molecules,drop size and the number density on the turbulence intensity was coupled into the breakage model.Models of coalescence time that consider partially mobile and immobile interfaces were employed to describe the film drainage at different surfactant concentrations.Both the predicted Sauter mean diameter and cumulative drop size distribution agree well with the experimentally measured values at different surfactant concentrations.