Numerical Simulation And Experimental Study Of Polymer Flow Behavior In Microfluidics Fields

With the unremitting efforts of scientific research and the strong promotion of engineering applications,the development of microfluidic technology has been extremely rapid,and it has been widely used in most fields of industury and life.With the rapid development of computer technology,numerical simulation has become a great method matching with theoretical analysis and experimental research.In this thesis,the complex viscoelastic rheological behavior of polyethylene oxide(PEO)aqueous solution in contraction microchannels was investigated by numerical simulation and experiment.The rheological behaviors of commercial low-density polyethylene melts(LDPE,DSM,Stamylan LD 2008 XC43)in microchannels with cylindrical contraction and cross-slot microchannels were numerically simulated by two differential viscoelastic constitutive models,DCPP and S-MDCPP,respectively.The calculation of the DCPP constitutive model is based on Polyflow software where the quadratic interpolation is adopted for velocity,and the linear interpolation for pressure and stress are.The calculation of the S-MDCPP constitutive model achieved by the code in house.The numerical computation method used the pressure-stability iterative fractional step scheme based on the finite increment calculus(FIC),which realizes the low-order linear interpolations for velocity,pressure and stress.Firstly,the rheological behavior of polyethylene oxide(PEO)aqueous solution in the 4:1 contraction microchannel was studied experimentally and numerically with the help of the microfluidic experimental platform and the PTT constitutive model.The numerical calculation results are in good agreement with the experimental results,which verifies the accuracy and reliability of the numerical method.In addition,the effects of Weissenberg(Wi)number,solution concentration,microchannel constriction ratio and contraction geometry upon the flow behavior of PEO aqueous solution are discussed.In the study of viscoelastic rheology,the flow problems of around a cylinder and plane contraction flow are bench examinations.In this thesis,we combined the 4:1plane contraction microchannel with a cylindrical,and the DCPP model and the S-MDCPP model to describe the flow behavior of LDPE melt in this complex microchannel are simulated.Results show that the constitutive model and numerical algorithm in our code can give a good prediction for the flow behavior of polymer fluids in the microfluidic field.Furthermore,the effects of cylinder radius,cylinder position and the constitutive parameters of the S-MDCPP model upon the flow behavior of LDPE melt in the contraction microchannel with a cylinder are discussed.Finally,the flow behavior of LDPE melt in cross-slot microchannel are simulated by using the DCPP and S-MDCPP models,respectively.The convergence of mesh is verfied,and the results of the two constitutive models are compared,which further verifies the stability of the pressure-stability iterative fractional step scheme based on the FIC procedure.The influences of the flow velocity ratio at the runner inlet and the constitutive parameters of the S-MDCPP model on the flow behavior of LDPE melt in the cross-slot microchannel is investigated.