Design Of Melt Blowing Auxiliary Nozzle Based On Threadline Trajectory

Melt blowing is a method for fabricating ultrafine fiber nonwovens.The polymer melt is drawn into ultrafine fibers by high velocity hot air.The air flow field has an important effect on the final fiber diameter.In order to make the air flow field more favorable for the polymer drawing,our research group installed an auxiliary nozzle below the melt blowing dual slot nozzle.It was found that the auxiliary nozzle did help to reduce the fiber diameter.However,when the polymer threadline enters the auxiliary nozzle,it will vibrate under high velocity air,thus hit the inner wall of the auxiliary nozzle,causing the auxiliary nozzle area to clog rapidly.In this thesis,the polymer threadline trajectories in the melt blow air flow field of the auxiliary nozzle are analyzed.The auxiliary nozzle is reformed while the main nozzle is kept changed to avoid the collision of the polymer threadline with the inner wall of the auxiliary nozzle.After the auxiliary nozzle is adpated,the velocity distribution and temperature distribution of the air flow field will change accordingly,thus affecting the final fiber diameter.Therefore,design of the new auxiliary nozzle has strong practical significance for improving the nonwoven technology and equipment and the product quality of melt blown nonwoven fabrics.In this thesis,the air flow field of the original auxiliary nozzle is simulated numerically.The two-dimensional model of polymer drawing is established.The shape of the new auxiliary nozzle is designed and the inlet width and outlet width of the auxiliary nozzle are optimized.The polymer threadline trajectories in the flow field of the new auxiliary nozzle are obtained by solving the two-dimensional model of polymer drawing which are compared with those of the original auxiliary nozzle.The research content of the thesis is divided into the following three parts:In the first part,the air flow field model of the original auxiliary nozzle is established and simulated numerically.The air velocity distribution and temperature distribution are obtained.The drawing of polymer melt in the melt blowing process is analyzed with Lagrangian method.Based on the analysis of the stress condition and heat transfer of the polymer threadline,the momentum equation and energy equation of the polymer drawing are established,so that a two-dimensional model of melt blowing polymer drawing is constructed.The numerical computation of the polymer stretching model is carried out,and the polymer threadline trajectories are obtained.In the second part,by analyzing the threadline trajectories,it is found that the polymer threadline will hit the inner wall of the auxiliary nozzle and cause clogging during the downward motion.In order to solve this problem,the shape of the auxiliary nozzle is designed.The optimal combination of auxiliary nozzle structure parameters is obtained by combining the numerical simulation of air flow field with the quadratic general rotary unitized design.In the third part,the air flow field model of the new auxiliary nozzle is established.The simulation results of the air flow field are introduced into the polymer drawing model.The polymer drawing model is solved numerically and the fiber diameters under the new and originial auxiliary nozzle air flow field are obtained and compared.The results show that the fiber diameter under the condition of the new auxiliary nozzle air flow field is slightly larger than that of the original auxiliary nozzle air flow field,but the fiber diameter under the condition of the new auxiliary nozzle air flow field still meets the requirements of ultrafine fibers.The results show that with the geometrical structure of the new auxiliary nozzle which ensuring that the fiber diameter is within the required range,the polymer threadline does not hit and stick to the inner wall of the auxiliary nozzle because of the small amplitude of vibration.In summary,in this paper,the optimal parameters of the new auxiliary nozzle are obtained by the combination of the numerical simulation of the air flow field and the quadratic general rotary unitized design.The air flow field model of the new auxiliary nozzle is established,and the air velocity distribution and temperature distribution are obtained.The polymer threadline trajectories are obtained by establishing and solving the two-dimensional model of polymer drawing.The results of this research show that the design of the new auxiliary nozzle can avoid the polymer threadline hit the inner wall of the auxiliary nozzle,which can provide a theoretical reference for the design and reformation of melt blowing nonwoven nozzles.