| In modern industry,the method to improve the pipeline conveying flow,reduce friction loss,improve the efficiency of pipeline transportation and economic benefits in the process of oil product transportation,is usually adding a small amount of oil-soluble polymer drag reduction agent in the pipeline.Poly alpha olefin(PAO)as one of common oil-soluble polymer drag reduction agent,1ppm of PAO in the oil product turbulent flow can significantly reduce the dissipation of energy in the turbulence.In this paper,PAO's turbulent drag reduction in oil products has been studied,the content is divided to the experimental study and theoretical study:in the experimental part,the influence factors of PAO's turbulent drag reduction characteristic in oil products have been studied by using Anton Paar MCR302 coaxial cylinder rheometer and rheological plate measurement device(RPMD)designed by the author herself;Theoretical part is on the basis of experimental research,using the basic theory of fluid mechanics,rheology,polymer physics and polymer molecular dynamics,through the method combined by experiment,theory and numerical simulation,turbulent drag reduction mechanism of alpha olefin was explored.Finally in poly alpha olefin drag reduction experimental study,mechanism study,shear degradation and damage model study,drag reduction engineering application research many achievements have been obtained,and were validated by the practical engineering application,this provides the theoretical support for later poly alpha olefin's turbulent drag reduction in oil products,which has theoretical significance and practical value.The specific research contents and the main results are as follows:(1)Poly alpha olefin drag reduction experiment researchUsing Anton Paar MCR302 coaxial cylinder rheometer and turbulent drag reduction rheological plate measurement device designed by the author herself,the study of PAO's turbulent drag reduction in diesel has been conducted:(1)The influence rules of turbulent drag reduction in oil product by five types of PAO agent in China and at abroad,viscosity of oil solvent,adding concentration of drag reduction agent and oil flow conditions(eg.temperature)have been obtained,and as well as the influence factors of the polymer additive's shear resistance;(2)Combined with data results of the lab and field experiments,the evaluation of PAO's turbulent drag reduction characteristic in oil products has been conducted,and using shear stress scaling law,nonlinear data fitting,dimensional analysis,theoretical derivation,finally rheological plate device's turbulent drag reduction efficiency prediction model and oil production pipeline drag reduction efficiency prediction model were established,the prediction error is less than 4%.(2)Poly alpha olefin's drag reduction mechanism researchBased on the turbulent coherent structure,the reason and process of turbulence structure changed by polymer molecules were studied:(1)Based on the rheological experiment and LDA experimental data,the standard k-?two-equation model,considering the influence of polymer viscosity on the near wall region the attenuation function f_?was introduced,modifying k and?equations,and the Navier-Stokes equation for the turbulent drag reduction flow with polymer molecules was established;(2)Based on the constitutive equation,distribution of average velocity,turbulent pulsation strength,turbulent kinetic energy and turbulent dissipation rate in drag reduction flow were obtained by FLUENT numerical simulation;(3)According to the simulation results,the mechanism of polymer turbulent drag reduction was described theoretically from rheological,molecular dynamics and energy respectively:1)Polymer drag reduction could make less non-coherent small scale structures in free shear flow,lower bursting frequency of the near wall coherent structure,more large scale coherent structures;2)Polymer molecular and its viscoelasticity can reduce and prevent energy dissipation due to turbulent eddies'damage in the transition layer and logarithmic layer;3)Polymer turbulent drag reduction mainly acts on the transition layer(5?y~+<30)and logarithmic layer(y~+>30)of pipe section;the polymer molecules enhance the axial velocity pulsation,turbulent kinetic energy and turbulent dissipation rate in the turbulent flow,and with the Reynolds number increasing,effect becomes more obvious;the increase of turbulent energy is mainly concentrated in the transition layer and the logarithmic layer,and the corresponding increasement in the turbulent dissipation rate starts from the viscous layer near the wall;4)the polymer molecules will inhibit the kinetic energy in turbulence is transformed into pulsating energy,which reduces the formation and intensity of turbulence,and reduces the turbulent energy dissipation in the form of heat energy;(4)Hydraulic friction coefficient of polymer turbulent drag reduction transportation was corrected,polymer drag reduction efficiency predicting model in pipeline transportation was also established.(3)Poly alpha olefin oil-solution's shear degradation and damage models researchOn the analysis of the affecting factors of polymer shear resistance characteristics,and on the basis of polymer drag reduction agent's effective concentration in the shear degradation process,using the methods of nonlinear data fitting,dimensional analysis and theoretical derivation,finally polymer molecules shear degradation models were established in plate disturbed flow and pipe flow,and were successfully applied in actual business pipeline.The error is less than 5%.(4)Poly alpha olefin drag reduction engineering application researchThrough the established polymer turbulent drag reduction efficiency prediction model and the shear degradation prediction model in plate rheological device and oil product pipeline,model validation researches of polymer turbulent drag reduction efficiency and shear degradation prediction in the 5 field oil product pipelines were conducted.The error is less than5%;predicting problems of drag reduction efficiency and adding dosage have been solved in the process of polymer turbulent drag reduction pipeline transportation eventually,which provided the theory and data support for field application. |
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