熔喷过程中纤维直径再次变大的模拟与验证

为直观表达熔喷过程中气流对纤维的拉伸作用,对熔喷过程中的纤维运动进行了数值模拟。首先将熔喷过程中的纤维看作是由麦克斯韦(Maxwell)元件连接的珠子;之后将已知的纤维速度、纤维温度数据加载到纤维模型上,通过拉格朗日法数值模拟预测纤维在熔喷过程中的运动速度、纤维直径等信息。模拟结果表明,纤维在远离喷丝孔的过程中,由于气流速度、气流温度逐渐衰减,致使纤维受到气流力的作用逐渐减弱,若气流力小于纤维自身的黏弹力,纤维会在黏弹力的作用下回缩,在宏观上表现为纤维直径的再次增大。最后在一定实验条件下,利用线下方法测量了熔喷纤维的直径,实验结果也验证了熔喷过程中纤维直径会有再次变大的现象。     

熔喷气流场中的纤维运动模拟与分析

为探究纤维在熔喷气流场中的牵伸运动过程,对熔喷气流场和纤维牵伸过程进行数值模拟。分析了熔喷气流场的分布特点,采用欧拉-拉格朗日法建立了熔喷纤维牵伸力学模型,获得熔喷纤维在气流场中的运动轨迹、牵伸倍数等信息;利用高速摄影机捕获了纤维在熔喷气流场中的运动轨迹并验证了模拟结果。结果表明：熔喷喷嘴下方存在气流回旋区,气流场分为射流单独流动区、射流汇合融合区和射流合并区;熔喷纤维的牵伸倍数先增加后减小,纤维运动在射流单独流动区出现鞭动,在射流合并区中存在纤维折叠成圈现象;射流汇合融合区是纤维细化的主要区域,该区域内纤维鞭动增加,牵伸倍数最大;验证实验中纤维运动中的鞭动、折叠成圈和运动轨迹与模拟结果一致。     

纺制超细和纳米纤维的Nanoval分裂纺技术

Nanoval分裂纺是一项纺制超细和纳米纤维的新技术。介绍了熔体裂变原理以及分裂纺的工艺与设备。在一般纤维平均直径范围内,Nanoval工艺的产量可与熔喷法相竞争,而能耗占有优势;在超细和纳米纤维生产中能耗可以降低一个数量级。Nanoval技术在操作条件、纤维直径和适用原料方面非常灵活,最适合生产极细纤维的熔纺材料。     

熔喷气流场与纤维运动及纤维直径的数学计算

对狭槽模头下熔喷气流场进行了数值模拟,得到气流的流线以及速度矢量分布,采用高速摄像技术捕捉狭槽喷嘴下的纤维运动轨迹,并对纤维运动的特征及其与气流场特征之间关系进行探讨,结果显示纤维的二维运动特征是由气流场的二维特征决定的。因为熔喷过程中纤维运动速度很高,测量设备很难在线测量熔喷过程中的纤维直径的变化规律,本文建立了一种可以计算纤维直径的数学方法,该方法只凭借纤维轨迹信息就能在线计算纤维直径的变化规律。首先对这种数学方法做统一的理论推导,之后在理论推导基础上对纤维模型进行离散处理,经过离散处理后可得到更精确的数学解,将数学预测的结论与实验获得的纤维直径进行对比,结果表明数学预测与实验结论较为吻合。     

静电纺丝拉伸模型与实验

利用珠链纤维模型对静电场作用下聚合物溶液的纺丝拉伸过程进行模拟,通过计算纺丝过程中聚合物射流细度随时间的动态变化,可得到不同工艺条件下所纺纤维的直径。为了验证模型的可行性,采用聚乙烯醇溶液进行静电纺丝实验,初步探讨纤维细度与接收距离之间的关系。实验结果表明,当接收距离在14~40 cm范围内,纤维直径随接收距离的增加有逐渐变细的趋势。通过与模拟结果的对比可以看出,在接收距离小于30 cm时,实验数据和模拟结果吻合较好。     

聚丙烯/聚酯双组分微纳米纤维熔喷非织造材料制备及其性能

针对聚丙烯(PP)超细纤维材料韧性不足的问题,以聚酯(PET)和PP为原料,采用共混熔喷法制备了PP/PET双组分微纳米纤维熔喷非织造材料,研究了PP/PET双组分聚合物熔体的流动指数和热性能,并对制备样品的形貌特征和柔韧性进行分析。结果表明:样品形貌为典型的熔喷非织造材料结构特征,细纤维与粗纤维在水平方向上交错排列形成叠合形态;且随PET质量分数从8% 增大到15%,纤维的平均直径从5.52 μm逐渐降低到3.61 μm;在双组分纤维内,PET与PP之间有清晰相界面,且PET以直径为10~100 nm的微纤形式存在;样品的韧性得分随着PET质量分数的提高从29.91增到35.20。     

微纳米纤维的熔喷制作工艺

通过数值计算方法和熔喷实验方法,探索微纳米纤维的熔喷制作工艺。选用 Shambaugh 一维数学模型,运用数值计算方法,得出空气速度、熔体流量和喷丝孔直径对纤维直径的影响关系。通过分析比较得到这 3 个参数对纤维直径减小程度的影响顺序：熔体流量影响最大,空气速度次之,喷丝孔直径影响最小。根据熔喷实际情况,得出喷丝孔直径不能够太大。设计微纳米纤维的熔喷实验工艺,进行熔喷工艺实验和纤维直径测定实验,得到了纳米级纤维。证明了工艺参数对纤维直径影响关系和影响顺序规律的正确性,也证实了微纳米纤维制作工艺的有效性。     

采用脉冲气流的熔喷工艺

采用脉冲气流的熔喷工艺在常规的熔喷工艺中，对挤压长丝的拉伸采用的是一束热空气。在适当条件下，纤维拉的最细可足以生产出直径在几分之一微米的微纤维。在喷吹阶段中，应用的空气受到高温、高压的处理，形成超声气流，实现了对纤维极高的拉伸。由于在喷吹阶段中使用的...     

确定熔喷理论模型流变力初值的新方法

以Uyttendaele Shambaugh一维熔喷理论模型为基础,提出一种新的确定流变力初值的方法。采用该方法求解熔喷理论模型预测最终纤维直径时,预测效果较好,特别对于某些熔喷实验,预测准确度相比于其它方法可提高30%以上。     

芳纶纤维束力学性能的统计本构方程

用MTS和旋转盘式杆—杆型冲击拉伸试验装置，获得0．01—1000s^-1应变率范围内芳纶纤维束的应力应变曲线。并根据纤维束统计本构模型，获得不同变率下芳纶纤维束力学性能的统计本构方程。     

Numerical modelling of microfibers formation and motion during melt blowing

Melt blowing (MB) is a widely used one-step process to manufacture products comprising microfibers in large quantities. However, fiber formation and motion are complicated and difficult to modeling in MB. In this study, a comprehensive MB model from orifice exit to collection screen is developed. Fiber is described as a model of a series of beads connected by polymer element. Fiber formation and motion are simulated by predicting beads deformation and speed. Compared with our previous work, the improved model introduces Giesekus constitutive equation, adds fiber crystal energy term and fiber thermal radiation term in the energy equation and considers fiber crystallization during fiber formation. The model can be used for predicting fiber spatial position, velocity, temperature, diameter, and crystallinity. This study provides precisely predicted results and a better understanding on the fiber formation process.     

亚麻纤维线密度与直径回归相关模型的构建及验证

为建立一个快速有效的亚麻纤维细度的测试方法,采用传统的中段称重法获得纤维细度（Nm）,用直径显微图像仪测试出亚麻纤维直径（d）。统计软件SPSS 3.0拟合分析纤维直径和纤维细度的相关性,获得6个回归模型。优化后的回归方程为Nm=159＋2.505×105/d2,相关系数 r=0.801**,表明亚麻纤维直径和纤维细度间存在着比较好的相关性。F-检验和t-检验证明该方法与传统中段称重法差异不显著。实验室间验证结果表明该方法具有比较好的精密度、重现性和再现性。因此通过显微图像仪测试纤维直径,再经过存储在主机上回归方程的换算,同步实现亚麻纤维细度的自动化快速检测。     

Modeling Flow and Heat Transfer During Freezing of Foods in Forced Airstreams

ABSTRACT: Mathematical modeling of food freezing has been limited to the modeling of the internal heat transfer where the external convective heat-transfer coefficients are assumed or empirically estimated. Previous procedures followed to solve the external boundary layer in tandem with the internal heat transfer were constrained by numerical complexities due to the transient nature of the heat transfer, requiring unsteady formulation for the flow. In this article, attempts have been made to decouple the flow and heat transfer equations for the external boundary layer flow over a food product being frozen. The flow equations have been solved as a steady-state problem using Falker-Skan transformations of the boundary layer equation. The heat-transfer equation for fluid flow is solved as an unsteady-state problem in conjunction with the internal heat transfer and phase change inside the product undergoing freezing. The model is validated for a case of air-impingement freezing.     

基于ANSYS CFX的棉纤维马克隆值的建模与仿真

为探究棉纤维马克隆值与棉纤维质量关系紊乱的原因,取棉纤维的平均直径和成熟度为自变量,推导棉纤维气流仪工作的原理方程。选择6种棉样进行实验,通过测量棉纤维在等压差、等密度情况下的入口流量和马克隆值,采用中段称重法和显微镜法分别测量棉纤维的线密度和成熟度,将该值与利用公式计算的流量值进行比较分析。结果表明,等压差下通过气流入口的流量值与棉纤维成熟度和直径乘积的平方大致成正比。仿照棉纤维的结构,根据直径和成熟度构造棉纤维透气性模型,利用ANSYS CFX仿真软件进行仿真。仿真结果与实验值的最大相对误差为7.92%,证明了该模型的有效性,为修正棉纤维的Kozeny-Carman常数,进一步提高计算准确率提供参考。     

纤维束本构方程的研究

应用弹性力学方法,根据各向异性弹性理论,导出非加捻纤维束线性和非线性本构方程。通过对纤维束的纵向拉伸和羊毛纤维束的横向压缩实验,绘出了其拉伸性能曲线和压缩性能曲线。分析了加捻纤维束的变形几何关系,利用能量法揭示了加捻对纤维束性能参数的影响。指出了纤维束本构方程的研究对预测纺织复合材料力学性能的重要作用。     

Stress and crack prediction during drying of Japanese noodle (udon)

The distribution of stress during drying of fresh Japanese noodle (udon) was investigated by mathematically modelling the changes in shrinkage and other mechanical properties, this allowed crack formation to be predicted. It was observed that the shrinkage coefficients were nearly the same in all three directions with changing moisture content, and the degree of shrinkage was independent of the temperature. The Young's modulus, yield stress and fracture stress could be expressed as exponential functions of moisture content. Changes in stress distribution during drying were calculated by coupling the moisture transfer equation with the constitutive equation using a finite element method. The calculated stress distribution indicated that a rapid drying rate causes extensive internal tensile stress in udon. The scheme used in the present study was found to effectively represent the potential for crack formation along the central axis, this was shown to be consistent with the actual cracking pattern.     

Analysis of flow behavior of non-Newtonian fluids based on a concept of traveling force

The non-Newtonian flow behavior of a culture fluid with suspended adhesive particles of microbes and polysaccharides is analyzed in this study based on a new concept. The concept assumes that the force generated by the contact between particles under shearing flow due to mixing is decreasingly transmitted through the fluid in radial directions. A viscosity equation that includes the degree of force transmisson is derived by considering the shear stress to the force. On the other hand, the shear stress dependence on the concentration of bound particles is expressed in an equation by introducing an effective shear stress that works on the contact sites of the bindings and varies the concentration. Relating the degree of force transmission to the concentration derives a non-Newtonian viscosity equation in terms of shear stress (or shear rate), in which zero-shear viscosity is correlated with both the particle concentration and molecular weight of polymers. It is confirmed that calculations based on the equation are in good agreement with experimental results previously reported for aqueous solutions of several polysaccharides.     

凝固点降低法计算溶剂活度的关系式

根据热力学原理，不忽略溶剂液态和固态的热容受温度的影响，推导出凝固点降低法精确计算溶液中溶剂活度的方程式．最后用不同的方程计算了水溶液中水的活度，且对其进行了比较．     

Thermodynamic Analysis of the Freezing and Thawing of Foods: Ice Content and Mollier Diagram

On the basis of the freezing point depression equation, an ice content equation was derived. The required parameters are similar to equations for enthalpy and apparent specific heat previously developed. Validity and accuracy of the equation are demonstrated with experimental data for meat, fish and fruit juices. Cohesive data for enthalpy, apparent specific heat and ice content are calculated for a wide range of temperatures between 20 and -40°C. The calculated results are consistent with values obtainable through enthalpy-moisture content-temperature (Mollier) diagrams developed by Riedel.     

Research of foreign fibers in cotton yarn defect model based on regression analysis

The detecting of foreign fiber may not be very effective, particularly around the detection zone where many types of foreign fibers may coexist. In order to eliminate the fibers more effectively, a model has been established to detect foreign fiber faults in yarn. Relevant data were collected through investigation of a number of standard samples, with the length and area of foreign fibers as the independent variables, and the number of defects as the dependent variable, which were combined using linear regression theory to establish a regression equation for different fiber defects. The equations to find the regression coefficients, which include the model fitting degree, the Durbin–Watson value, the standard error, and the Cook distance, were rigorously tested, and the regression equation was eventually compiled to produce the yarn faults model. When the fiber detection equipment recognizes fibers with a foreign profile, the calculated profile fiber size is used in a corresponding regression equation which obtains the defect points and compares them with each other, so that foreign fibers which are potentially more dangerous can be identified and preferentially eliminated. In order to verify the model, spinning experiments are performed. The actual defects from the experiment are compared with the predicted theoretical defects from the equation, and the prediction accuracy was found to reach more than 95%, showing that the foreign fiber yarn faults model, which lays a theoretical foundation for foreign fiber detection, is accurate and effective.