Three Dimensional Poymer Drawing Model Of Melt Blowing Process Based On Numerical Simulations Of The Air Jet Flow Field

In this thesis,by considering the transverse motion of the polymer and the effects of the polymer temperature on the density and specific heat capacity of the polymer and by introducing the constitutive equation of non-Newtonian fluid,the macroscopic three dimensional polymer drawing model of the melt blowing process is established.The model is solved with numerical simulations.The numerical results are compared with the experimental data.Effects of the processing parameters on the polymer drawing are also studied.In chapter one,the current status of researches on both the mechanism of polymer drawing and air jet flow field of the melt blowing process is introduced.The importance and content of this thesis are also put forward.In chapter two,the general equations of the air jet flow field are given. The air jet flow field of the annular die is simulated numerically.The distributions of air velocity and air temperature are obtained.The good coincidence of the numerical results and experiment data verifies the numerical simulation of the air jet flow field,which is an important foundation to the establishment of the three dimensional polymer drawing model.In chapter three,the establishment of the three dimensional polymer drawing model of the melt blowing process is described.The model is combined with the numerical simulations of the air jet flow field. Effects of the polymer temperature on the density and specific heat capacity of the polymer and the constitutive equation of non-Newtonian fluid are also considered.In chapter four,the method and results of the polymer drawing model are given.The fiber diameter,polymer vibration frequency and amplitude are computed.The computing results tally well with the experimental data,which confirms the validity of the polymer drawing model.The comparison of the high speed photography of the polymer drawing process with the computing results of the polymer vibration amplitude also verifies the polymer drawing model to a certain extent. Using this model,effects of the initial air velocity and initial air temperature on the fiber diameter,polymer vibration frequency and amplitude are investigated.The results show that higher initial air velocity will produce finer fibers and larger vibration amplitude.But its effect on the polymer vibration frequency is first increase then decrease. However,effects of the air initial temperature on the fiber diameter, vibration amplitude and vibration frequency are not significant.To sum up,the three dimensional polymer drawing model of the melt blowing process based on numerical simulations of the air jet flow field is established which is verified by the experiments.This thesis lays a solid foundation for the deepgoing research of the polymer drawing mechanism in the melt blowing nonwoven process.