Study On The Air Flow Field And Polymer Drawing Of The Melt Blowing Process With An Auxiliary Nozzle

Melt blowing is a polymer laid nonwoven technology for producing superfine fibers. Inthis process, the polymer melt is attenuated into superfine fibers by high velocity hot air.Therefore, distributions of air velocity and air temperature have great effect on the finalfiber diameter. In this thesis, an converging-diverging nozzle is installed below the meltblowing main nozzle in order to change the distributions of air velocity and air temperature,which has practical values on improving the melt blowing technology and product quality.In this thesis, the air flow field with the auxiliary nozzle is simulated. The distributionsof air velocity and air temperature are obtained. The polymer drawing in the air flow fieldwith the auxiliary nozzle is simulated numerically. The structural parameters of theauxiliary nozzle are designed optimally. This thesis consists of three parts:In Part one, the air flow field model with the auxiliary die in the melt blowing processis established and simulated numerically. The distributions of the air velocity distributionand air temperature are obtained. An IFA300hot wire anemometer is employed to measurethe distributions of the air velocity and air temperature. The simulated results are comparedwith the measured results and they have a good agreement, which indicates that the airflow field model is correct. It lays a foundation for the optimal design of the auxiliarynozzle.In Part two, the polymer drawing model with an auxiliary nozzle is established. Thesimulated air velocity and air temperature are introduced into the polymer drawing model.The model is solved numerically using the fourth order Runge-Kutta method. The changetrend of the fiber diameter is simulated and compared with the fiber diameter without theauxiliary nozzle. It is found that the fiber diameter with the auxiliary nozzle is muchsmaller than that without the auxiliary nozzle.In the last part, based on the air flow field model, the optimal design for the auxiliarynozzle is carried out using quadratic general rotary unitized design method. The auxiliarynozzle structural parameters include the throat width, the converging-diverging ratio, inletwidth and outlet width. It is found that the inlet width and outlet width have little effect on the average velocity in the main drawing zone while the throat width andconverging-diverging ratio have quite significant influence. The optimal structuralparameters of the auxiliary nozzle are obtained and verified.To sum up, the air flow field model with the auxiliary nozzle in the melt blowingprocess is established and simulated numerically. The polymer drawing with the auxiliarynozzle is simulated numerically. The structure of the auxiliary nozzle has been designedoptimally. This research lays a foundation for further researches on the air flow field andpolymer drawing in the melt blowing process with the auxiliary nozzle.