Experimental study and numerical simulation the air jet flow field of a dual slot sharp blunt die in the melt blowing nonwoven process

In this work, the physical model of a polymer in a melt blowing process is established and solved by introducing the numerical computation results of the air jet flow field of the dual slot sharp inset die. The influence of the melt blowing processing parameters and the die design parameters on the fiber diameter is also studied. A lower polymer throughput rate, higher polymer melt initial temperature, higher air initial temperature, higher air initial velocity, smaller angle between slot and axis of the spinneret, smaller width of the die head, and larger width of the slot can all produce finer fibers. At the same time, the air jet flow field model of the dual slot sharp inset die of polypropylene polymer nonwovens fabrics in melt blowing process was also established. The air jet flow field model was solved by using the finite difference method. The computational simulation results of the distributions of the z‐components of air temperature and air velocity along the spinline during melt blowing process are in accordance with the experimental data. The air drawing model of melt blowing process was simulated by means of the numerical simulation results of the air jet flow field. The predicted fiber diameter agree with the experimental data. The effects of the air initial velocity and air initial temperature on the fiber diameter were studied and discussed. The results demonstrate that a higher air initial velocity and a higher air initial temperature are beneficial to the air drawing of the polymer melt and thus to reduced fiber diameter. The results show the great potential of this research for computer assisted design in melt blowing nonwoven process and technology. POLYM. ENG. SCI., 57:417–423, 2017. © 2016 Society of Plastics Engineers     

熔喷工艺参数和喷嘴设计参数对纤维直径的影响

引　言熔喷法是 2 0世纪 5 0年代发展起来的一种制备超细纤维非织造布的方法 ,其纤维直径仅 1～10 μm.熔喷非织造布是高效精细过滤材料 ,过滤效率可达 99 9%以上 ,广泛用于医疗和环保等领域 .熔喷是依靠高速高温气流喷吹聚合物熔体使其迅速拉伸而形成超细纤维的 .数学模型对于     

Numerical computation of the fiber diameter of melt blown nonwovens produced by the inset die

Melt blowing is used commercially as a one‐step process for converting polymer resin directly into a nonwoven mat of microfibers. The inset die is often used to produce polymeric fibers in the melt blowing process. The air jet flow field model for the dual slot inset die is established. The flow field model is solved by using the finite difference method. The numerical computation results of the air velocity distribution coincide with the experimental data. Then the air drawing model of polymers in the melt blowing process established in our previous research is solved with the aid of simulation results of the air jet flow field. The final fiber diameter of the nonwoven fabrics predicted by the air drawing model of polymers tallies with the experimental data. The results show the great potential of this research for the computer assisted design of melt blowing technology and equipment. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Study on the flow field of the air jet from dual slot die in the melt blowing process

The possibility of describing the jet from the dual slot die in the melt blowing process with a vortex pair was studied according to the nature of the vortex. A model of the synthesis of two jets was developed. The reliability of the model was confirmed by experimental data cited from literature. The prediction of the fiber diameter using this model coincided with that using the fitted equation with the data advanced by Harpham and Shambaugh. The effects of the equipment parameters, such as the angle between the air flow and the axis of the spinneret, the width of the die head and the width of the slot were also discussed.     

Computational fluid dynamics simulation and theoretical study the air jet flow field of a wide slot positive pressure drawing assembly in the spunbonding nonwoven process

The polymer air‐drawing model of polyethylene terephthalate spunbonding nonwovens and the air jet flow field model in wide slot positive pressure spunbonding process have been established. The influence of the density and the specific heat capacity of polymer melt at constant pressure changing with polymer temperature on the fiber diameter have been studied, which is solved by introducing the numerical computation results of the air jet flow field of attenuator. It is simulated by means of the finite difference method. The predicted fiber diameter agrees with the experimental data. The effects of the processing parameters on the fiber diameter with the help of the image analysis method have been investigated. A higher inlet pressure, smaller slot width, and smaller jet angle will all cause higher z‐axis position of air velocity and air pressure, which are beneficial to the air drawing of the polymer melt and thus to reducing the fiber diameter. The experimental results show that the agreement between the results and experimental data is better, which verifies the reliability of these models. The results present great prospects for this research in the field of computer assisted design of spunbonding process, technology, and equipment. POLYM. ENG. SCI., 55:231–242, 2015. © 2014 Society of Plastics Engineers     

Numerical modeling,simulation, and experimental validation of predicting fiber diameter in wide‐slot positive‐pressure spunbonding process

An air‐drawing model of polypropylene (PP) polymer and an air jet flow field model in wide‐slot positive‐pressure spunbonding process are established. The influences of the density and the specific heat capacity of polymer melt at constant pressure changing with polymer temperature on the fiber diameter have been studied. The predicted fiber diameter agrees with the experimental data as well. The effects of the processing parameters on the fiber diameter have been investigated. The air jet flow field model is solved by means of the finite difference method. The numerical simulation computation results of distribution of the fiber diameter match quite well with the experimental data. The air‐drawing model of polymers is solved with the help of the distributions of the air velocity. It can be concluded that the higher air velocity and air temperature can yield the finer fibers diameter. The higher inlet pressure, longer drawing segment length, smaller air knife edge, longer exit length, smaller slot width, and smaller jet angle can all cause higher air velocity and air pressure along z‐axis position, which are beneficial to the air drawing of the polymer melt and thus to reduce the fiber diameter. The experimental results show that the agreement between the predicted results and the experimental measured data is very better, which verifies the reliability of these models. Also, they reveal great prospects for this work in the field of computer‐assisted design (CAD) of spunbonding process. POLYM. ENG. SCI., 58:1371–1380, 2018. © 2017 Society of Plastics Engineers     

Empirical formulas for distributions of air velocity/temperature along the spinline of a dual slot die

Empirical formulas, which describe the air velocity and air temperature decays along the spinline of a dual slot die, are improved by introducing the influence of the ratio of die end width to air slot width. The thus‐improved empirical formulas include more die geometry parameters and are more accurate than the existing ones. The fiber diameters of nonwoven web are predicted by incorporating these new empirical formulas into a one‐dimensional theoretical model for melt‐blowing process. The agreement between the predicted results and the experimental data cited from literature is very good, which confirms the reliability and the accuracy of these new formulas. POLYM. ENG. SCI., 45:1092–1097, 2005. © 2005 Society of Plastics Engineers     

Study on airflow field and fiber motion with new melt blowing die

In this study, a new melt‐blowing die was studied with the computational fluid dynamic approach. A bead‐viscoelastic element fiber model was established to model three‐dimensional paths of the fiber motion with the standard linear solid (SLS) constitutive equation in different airflow fields. The effects of this newly designed die on the velocity field, temperature field, and turbulence fluctuation field at the centerline were studied and compared with the traditional melt blowing die. The fiber motion was simulated and compared with the airflow field of different dies. The simulations results demonstrated that the new die was able to reduce the velocity fluctuations of the air flow near the outlet of the polymer capillary and generate the higher centerline air velocity and temperature. The fiber attenuation and motion were related to the centerline air velocity, temperature, and turbulent fluctuation in the melt blowing process. POLYM. ENG. SCI., 59:1182–1189 2019. © 2019 Society of Plastics Engineers     

纺粘法扁平狭缝牵伸器喷射流场的数值模拟

采用标准K-ε模型描述了纺粘法扁平狭缝流道牵伸器喷射流场的湍流运动,利用有限差分法对该模型求解。通过对6种纺粘法牵伸器喷嘴的喷射流场进行数值模拟,得到了相应的流场矢量图。分析流场矢量图发现,适当减小拉伸段宽度,增加喷射喷口长度,适当选择牵伸器喷口宽度和牵伸器的拉伸段长度,有利于提高气流速度,从而有利于对聚合物熔体进行气流拉伸,使纤维直径变细,提高纺粘法成网的质量。     

气流辅助聚合物熔体微分电纺流道优化设计

为进一步降低熔体微分电纺的纤维直径,使其达到纳米尺度,在现有直线狭缝电纺喷头的基础上设计了可以使高速气流汇聚的“V”形风道,通过高速气流对熔体微分射流进行二次牵伸细化。采用实验研究和数值模拟相结合的方法,以射流间距和喷头端电场强度为指标,研究了“V”形风道结构、材质对电纺微分射流的影响。研究结果表明,风道结构会不可避免地削弱喷头端的电场强度、降低射流的效率。增加风刀与喷头尖端的头端凸出量以及采用不导电的聚醚醚酮作为风刀材质都可以有效地降低风刀对射流效率的影响,而风道的宽度对喷头端电场强度影响不大。在优化的风刀结构和材质的基础上,成功制备了平均直径为825 nm的熔体电纺超细纤维。研究证实在气流辅助牵伸的作用下,直线狭缝电纺能够实现熔体电纺超细纤维的批量制备。     

Numerical analysis of the stagnation phenomenon in the coat‐hanger die of melt blowing process

In this paper the stagnation phenomenon occurred in the coat‐hanger die is investigated using a three‐dimensional finite element method to simulate the polymer fluid flow in the die. The stagnation zone is defined to evaluate the degree of the stagnation. The effects of the inlet flow rate, the slot gap, the manifold angle, and the power‐law index on the stagnation are then analyzed numerically. It is found that the manifold angle and the geometric abrupt change between the manifold and the slot have significant influence on the stagnation, and a coat‐hanger die with tear‐dropped manifolds to be capable of diminishing the stagnation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

熔喷法气流拉伸机理与喷射流场的研究进展

介绍了熔喷法非织造布的气流拉伸机理和空气喷射流场的研究进展,评价了聚合物熔喷气流拉伸的数学模型和空气喷射流场等对纤维直径的影响。指出今后的研究应探索建立熔喷法的三维拉伸模型和喷嘴气流喷射流场理论。     

Polymer melt differential electrospinning from a linear slot spinneret

Preparation of melt electrospun fibers with high efficiency and high productivity remains a big challenge. A polymer melt differential electrospinning system with linear slot spinneret (LSSP) was proposed in this work. Under a high electric field, multiple jets distributed at the tip of LSSP were self-organized from the polymer melt film with controlled thickness. The spinning parameters were investigated, and the electric filed between spinneret and collector was analyzed. The results showed that the interjet distance decreased significantly with the decrease of the thickness of polymer melt film and the Tayler cone size. The smallest average interjet distance of 1.9 mm with deviation of 0.5 mm was obtained under the condition of applied voltage of 45 kV, collecting distance of 9 cm, temperature of 250 °C, and slot thickness of 0.2 mm. The high output of 75.6 g/h was achieved and could be increased just by increasing the slot width. It was demonstrated that the proposed technology was a promising way to fabricate melt electrospun fibers with high efficiency. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48922.     

螺杆计量段参数对导光板注射成型中PC熔体温度均匀性的影响

使用CFD软件Polyflow对导光板注射成型中螺杆计量段的流场进行了三维非等温数值模拟,讨论分析了不同计量段参数对流道内聚碳酸酯熔体温度的影响。研究发现,计量段参数对轴向温差的影响从大到小依次为螺棱间隙、推力面倾斜角、螺槽深度、导程和螺棱宽度,而对径向温差的影响从大到小依次为螺槽深度、推力面倾斜角、螺棱间隙、导程和螺棱宽度。     

Studies on structural foam processing I. The rheology of foam extrusion

An experimental study was carried out to investigate the flow behavior of gas-charged molten polymers in foam extrusion. For the study, a rectangular slit die with glass windows was constructed to permit visual observations, from the direction perpendicular to flow, of the dynamic behavior of gas bubbles when a gas-charged molten polymer flows between two parallel planes. Pictures were taken of gas bubbles in the flow channel with the aid of a camera attached to a microscope, and these were later used to determine the position at which gas bubbles start to grow. Using three melt pressure transducers mounted on the short side of the rectangular slot, pressure distributions were measured along the longitudinal centerline of the die. The polymeric materials used were high-density polyethylene and polystyrene, and the chemical blowing agents used were a proprietary hydrazide which generates nitrogen, and sodium bicarbonate which generates carbon dioxide. It was observed that the gas-charged molten polymer shows a curved pressure profile as the melt approaches the die exit, whereas the polymer without a blowing agent shows a linear pressure profile. The visual observations of the bubble growth in the flow channel, together with the pressure measurements, permitted us to determine the bubble inflation pressure, often referred to as the critical pressure for bubble inflation. It was found that the critical pressure decreases with increasing melt extrusion temperature, and increases with increasing blowing agent concentration. It was also found that the bulk viscosity of gas-charged molten polymers decreases with increasing blowing agent concentration and with increasing melt temperature. A general remark is made concerning the precaution one should take when an Instron rheometer is used for determining the bulk viscosity of gas-charged molten polymers.     

Numerical approach to modeling fiber motion during melt blowing

Melt blowing involves applying a jet of hot air to an extruding polymer melt and drawing the polymer stream into microfibers. This study deals with the dynamic modeling of the instabilities and related processes during melt blowing. A bead‐viscoelastic element model for fiber formation simulation in the melt blowing process was proposed. Mixed Euler‐Lagrange approach was adopted to derive the governing equations for modeling the fiber motion as it is being formed below a melt‐blowing die. The three‐dimensional paths of the fiber whipping in the melt blowing process were calculated. Predicted parameters include fiber diameter, fiber temperature, fiber stress, fiber velocity, and the amplitude of fiber whipping. The mathematical model provides a clear understanding on the mechanism of the formation of microfibers during melt blowing. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

熔喷技术

介绍了熔喷生产工艺及熔喷技术的关键部件——熔喷模头的设计。指出:模头顶点 E 的宽度小于0.508mm,毛细孔直径范围为0.076—0.56mm,气槽 G 的尺寸范围是0.203—0.381mm,阐述了熔喷生产过程中气流速度、气流温度和树脂的流动速度的相互关系,及对熔喷产品质量的影响,并对熔喷技术所用的原料及最终产品的性能和用途作了简要介绍。     

Numerical analysis of new modified melt‐blowing dies for dual rectangular jets

According to the aerothermodynamic analysis and turbulence characteristic analysis, there might be two main kinds of kinetic energy loss of the jets from rectangular nozzles for the blunt melt‐blowing die. To reduce the energy loss, the new modified dies with stabilizing pieces are designed and compared with the blunt die. The air flow fields for the new dies are simulated using computational fluid dynamic technology, whereby the shear stress transport model is used for turbulence simulation. Three parameters (i.e., the velocity along the y‐direction, the static temperature, and the turbulence intensity) are vitally important for producing fibers and thus are used to evaluate the performances of the slot dies. The simulation results reveal that the inner stabilizing pieces is helpful to decrease the negative velocity in the recirculation zone, enhance the downward centerline mean velocity, slow the centerline temperature decay, and make the air flow near the nose piece smoother. However, the external stabilizing pieces conduce only to increase the centerline velocity in the local area. POLYM. ENG. SCI., 54:110–116, 2014. © 2013 Society of Plastics Engineers     

Shear flow of molten polymer in melt blowing

Besides the air flow field, the flow field of molten polymer plays a key role in fiber formation in the melt‐blowing (MB) process. In this article, the flow field of molten polymer was discussed, and its effects on the fiber microstructures were studied through theory and experiments. First, this field was supposed to be a kind of shear flow field. Two equations were introduced and solved. Then, analyzing the solutions combining with the actual melt‐blown practice, we concluded that the distribution profile of this flow field was a series of inverse parabolic in the course of the polymer stream attenuating. Further inferring from this flow pattern, we could also assume that there could have been a novel cross‐sectional microstructures in the melt‐blown fibers. Finally, the comparison experiments concerning the MB and its fibers were designed and carried out. The results indicated that the shear flow field could be qualitatively described by the equations, and the assumptions about the microstructures are basically in agreement with the experimental results. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

聚酯熔体直纺长丝环吹技术及应用

聚酯熔体纺丝采用环吹风装置,有压缩空间位置、节省吹风成本等诸多优点,而环吹风风量、风温等条件对纤维的结构与性能有非常重要的影响。通过对涤纶长丝环吹风工艺条件进行摸索,并与侧吹风工艺进行了比较,得到了环吹风风量、风压、无风区高度与纤维品质指标、品种之间的关系,验证了涤纶长丝环吹风技术及成本优势。