| Due to the arrival of the COVID-19 pandemic,the market demand for melt-blown fabrics is increasing.Melt-blown equipment is an important equipment for the production of melt-blown nonwoven fabrics,its core component is melt-blown die head.The different structure of the nozzle will lead to the change of the airflow field,and the flow field will affect the formation of fibers and thus determine the quality of the meltblown nonwoven fabrics.Velocity,temperature and turbulence intensity are all important parameters in the airflow field,which have an important effect on the diameter of melt-blown fibers.In this paper,a new nozzle structure was designed,a numerical simulation model of the airflow field under the nozzle was built to explore the airflow field characteristics of the new nozzle structure.In addition,orthogonal optimization tests of the related structural parameters of the new nozzle was carried out,and conduct numerical simulation of the polymer/air two-phase flow field,in order to further refine the fiber diameter and improve the filtering efficiency of melt-blown nonwoven fabrics.Firstly,the finite element simulation model of airflow field of common slot die is built based on Fluent module of Ansys to simulate the airflow field and analyze the shortcomings;the new blunt nozzle structure and the new sharp nozzle structure are designed,and the velocity,temperature and turbulence intensity distribution in the airflow field are analyzed and compared with the common slot die.The results show that the new sharp nozzle structure can better optimize the airflow field and refine the fiber diameter;the effect of the outer extension length of the new sharp nozzle structure on the airflow field is investigated,and the study shows that the new sharp nozzle structure with an extension length of 5 mm can better refine the fiber.Next,the new sharp nozzle with better extension length obtained from the above study was selected,and the slot width,slot inclination angle and extension length of the nozzle were changed to conduct orthogonal tests to obtain the velocity and temperature distributions on the centerline of the airflow field below the different nozzles.With the stagnation temperature as the optimization target,the range analysis and variance analysis of stagnation temperature were carried out,and the results show that the extension length has the most significant effect on the stagnation temperature,so as to obtain the optimal combination of higher stagnation temperature of the airflow field.Finally,the new sharp nozzle obtained after the above orthogonal optimization was selected,and the two-phase flow model of polymer and airflow was established based on the VOF method,and the two-phase flow field of polymer/airflow was simulated to obtain the spinning trajectory of polymer in the two-phase flow field,and the two-phase flow field below the original and new nozzle was compared and analyzed.The study showed that although the velocity on the centerline below the new sharp nozzle is slightly lower than that of the original nozzle,the velocity distribution is more stable and the temperature decays more slowly,which enables the fiber to maintain a smooth state for stretching and is more conducive to fiber formation.In addition,the changes of velocity and temperature of the polymer jet in the two-phase flow field under different inlet conditions were also investigated,and the results showed that the high velocity of the airflow would lead to more obvious whipping of the fibers,which is not conducive to fiber stretching.The higher the inlet airflow temperature,the slower the polymer temperature decay. |
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