【作者】 陈廷；

【导师】 黄秀宝；

【作者基本信息】 东华大学 ， 纺织工程， 2003， 博士

【摘要】 本文研究工作覆盖两大部分：一是高温喷射流场理论建模与数值模拟；二是在对前人聚合物拉伸模型进行改进的基础上，建立基于喷射流场理论模型的完整的聚合物拉伸模型。 论文第一章论述了选题背景，介绍了国外聚合物熔体在喷射流场中拉伸机理研究的现状，由于美国俄克拉何马大学Shambaugh研究组的工作代表了上述领域国际上最先进的水平，因而重点介绍了该研究组的工作成果。 论文第二章应用经典的解析方法求解了熔喷双槽形喷嘴喷射流场。以势流(涡偶)代替射流进行合成，推导出双股射流合成后喷丝孔轴线方向的气流速度沿该轴线的分布，理论计算结果与激光多普勒实验测试结果吻合较好。将气流速度分布的理论公式代入熔喷聚合物拉伸理论模型，计算得到的纤维直径预测结果与实测结果吻合较好。还讨论了喷嘴设计参数对气流速度分布的影响，发现气流流道与喷丝孔轴线夹角的减小、槽口宽度的增大和头端宽度的减小，均使同一轴向位置上的气流速度增大。经典的解析方法从理论角度证实了流场预测的潜在效益及喷嘴设计对流场分布的重要影响，可用于简捷地预测一定工艺条件下成型的纤维最终直径以及分析不同工艺参数和不同喷嘴设计参数对最终纤维直径的影响。但这种方法只能给出沿喷丝孔轴线方向的速度分布，因而有一定的局限性。 为了对喷射流场有更加全面、深入的认识，论文第三、四、五、六章对双槽形喷嘴喷射流场进行了数值模拟研究，并进行了实验验证。 论文第三章简单介绍了有限差分方法，论文述及建立有限差分方程的两种方法，即泰勒级数展开法和控制容积法，给出了偏微分方程离散化必须遵循的四条基本规则，介绍了控制微分方程离散成代数方程后，求解代数方程组的常用方法。 论文第四章建立了熔喷双槽形喷嘴喷射流场理论模型。双槽形喷嘴喷射流场理论模型实质上是两股平面射流碰撞混合的流场模型。喷射流场理论模型由连续方程、动量方程、能量方程、紊流动能方程和紊流动能耗散率方程及边界条件组成。由于该流场存在回流区，且必须考虑对流和扩散作用的影响，所以紊流模型采用k—ε双方程模型。采用有限差分方法中的控制容积法对喷射流场理论模型进行离散化，从而建立了相应的有限差分方程。过对几种差分格式进行比较，决定采用乘方定律格式。通过分析“流函数一涡量法”的优缺点，决定采用“原始变量法”进行求解。为避免计算时出现锯齿状的压力场和速度场，在控制方程的离散化过程中引入了交错网格和SIMPLE算法，并给出了SIMPLE算法的计算步骤。还讨论了应用TDMA法结合松弛法求解代数方程。通过用模块化方法对PHOENICS软件的计算设置及运行进行剖析，列出了计算程序的总体结构，并对各模块的功能进行了说明。还对数值模拟实践中的经验体会进行了总结。 论文第五章对七种熔喷双槽形喷嘴的喷射流场进行了数值模拟，给出了相应的流场矢量图。通过对矢量图进行分析，发现:减小气流流道与喷丝孔轴线的夹角，增加槽口宽度，减小头端宽度，都能使气流速度得到提高，从而有利于对聚合物熔体进行气流拉伸。流场矢量图还证实了论文第二章采用势流合成方法对熔喷双槽形喷嘴喷射流场进行近似模拟的合理性。 论文第六章利用激光多普勒测速仪和热线风速仪对具有不同设计参数的七个熔喷双槽形喷嘴喷射流场的气流速度分布和温度分布进行了实验测试，文中同时给出了测试结果及相应的第五章求解结果，二者吻合较好，从而在多个层面上显示了本文所建立的一整套数值模拟算法完全可用于预测双槽形喷嘴的喷射流场及喷嘴参数的优化设计。 测试和模拟结果表示:(l)气流流道与喷丝孔轴线的夹角越小，喷丝孔轴线方向的气流速度越大，气流温度越高，但受结构设计的限制。(2)槽口宽度越大，喷丝孔轴线方向的气流速度越大，气流温度越高。但增加槽口宽度，意味着在恒定的气流初始速度条件下，会增加空气流量和能源消耗。(3)头端宽度越小，喷丝孔轴线方向的气流速度越大，气流温度越高，但是头端宽度受喷头加工的限制。因此，要提高流场的速度和温度，比较可行的办法是，在不降低气流初始速度的前提下，尽量增大槽口宽度。 通过以上四章的工作，最终得到了喷射流场的气流速度分布和气流温度分布，从而为聚合物拉伸模型的建立奠定了坚实的基础。 论文第七章着重讨论了熔喷聚合物拉伸理论模型的建立和求解以及有关工艺参数对最终纤维直径的影响。首先分析了熔喷气流拉伸过程的基本规律，讨论了溶喷气流拉伸过程中纺丝线上的动力学和传热，比较详细地分析了纺丝线上的受力情况和气流拉伸力系数q及传热系数h的表达式。在此基础上，对前人的聚合物拉伸理论模型进行了改进，以幂律模型作为描述聚合物熔体流变行为的本构方程，并考虑了聚合物熔体密度和定压比热随聚合物熔体温度变化而变化这个因素，从而建立了尽完整的熔喷聚合物拉伸理论模型。采用四阶Runge一一Kutta法求解该理论模型，数值求解结果与实验测定结果吻合较好。 利用该理论模型讨论了有关工艺参数对纤维直径?更多还原

【Abstract】 The content of the thesis covers two parts. One is the theoretical modeling and numerical simulation of the air jet flow field with high temperature. The other is the foundation of the air drawing model of polymer in which the theoretical model of the air jet flow field is integrated.In foreword the background of topic selection of this thesis is described.In chapter 1 the recent progress in the world of studies on the mechanism of air drawing of polymer melts in the air jet flow field with high temperature is introduced. As the research work done by Shambaugh’s group at the University of Oklahoma in the United States represents the most advanced level in the above field, their research works are, therefore, majorly mentioned.In chapter 2 a solution of the air jet flow field of dual slot die in melt blowing process by using classical analytic method is proposed. By substituting vortex pairs for the synthesis of jet flows, the distribution of air velocity along the spinneret axis is deduced, and its computed results are confirmed by the experimental data measured by Laser Doppler Velocimeter. By introducing the theoretical formula of the air velocity distribution into the air drawing model of the polymer for the prediction of fiber diameter, the results also coincide with the measured diameter. The effects of the die design parameters on the air velocity distribution are also discussed. It is found that the air velocity in the direction of the spinneret axis can be increased by decreasing the angle between the air slot and the spinneret axis, increasing the slot width and decreasing the head width, which shows that the modeling of the flow field is of benefit to improving the melt blowing process. This method can be used for quickly predicting the final fiber diameter under certain processing conditions and analyzing the effects of both different processing and die design parameters on the final fiber diameter. However, the method is limited because it can only determine the air velocity distribution along the spinneret axis.The numerical simulation method and experimental verifications are further employed in studying the air jet flow field of dual slot die in chapter 3, 4, 5 and 6 for a comprehensive understanding of it.In chapter 3 some basic knowledge are briefly introduced, including the finite difference methods, i.e. the control volume method, the regulations of the discretization of the partial differential equations, and the methods common used for solving the algebraic equations which is the sequent of the governing differential equations discretization.In chapter 4 the theoretical model of the air jet flow field of dual slot die in melt blowing is founded. It is actually the model of two plane jets flow field developed by jet collision and mixing. The model consists of the continuity equation, momentum equations, energy equation, turbulent kinetic energy equation, equation of dissipation rate of turbulent kinetic energy and boundary conditions. The k- s model is adopted as the turbulence model because there are recirculation flows in the flow field and the convective and diffused effects must be taken into account. The governing equations are discretized by the control volume method and the corresponding finite difference equations are obtained.In chapter 5 the numerical simulation procedure of the theoretical model is described in detail. The power-law scheme is chosen as the preferred difference scheme at first. The "Primitive Variables Method" is then used for solving the pressure linked equations. To avoid the tooth-like distribution of pressure and velocity, the staggered grid and SIMPLE algorithm are introduced, and also the computation procedure of SIMPLE algorithm is given. The use of TDMA method in combination with relaxation method to solve the algebraic equations is discussed. Based on the above study, the computation setup and running procedure of PHOENICS software are analyzed with the aid of modular construction. The integrated structure of the computation program is更多还原