Razeghiyadaki Amin, Wei Dongming, Perveen Asma, Zhang Dichuan, Wang Yanwei
Department of Mathematics, School of Sciences and Humanities, Nazarbayev University, Nur-Sultan 010000, Kazakhstan.
Department of Mechanical & Aerospace Engineering, School of Engineering and Digital Sciences, Nazarbayev University, Nur-Sultan 010000, Kazakhstan.
Polymers (Basel). 2022 Aug 3;14(15):3161. doi: 10.3390/polym14153161.
In the design of coat hanger extrusion dies, the main objective is to provide a uniform flow rate at the die exit. Previously, a multi-rheology isothermal method model for coat hanger extrusion dies was developed to reach this objective. Polymer melts in extrusion dies commonly experience high shear rates. Viscous dissipation rooted by high shear rate may lead to significant temperature differences across the die. Due to temperature-dependency of viscosity, temperature differences may lead to nonuniform flow rates, which may significantly affect the flow rate at the die exit. As a result, a new design method is proposed to take into account the effects of temperature and viscous dissipation in the design of coat hanger dies. Although more non-Newtonian fluid rheology models can be adapted in the proposed study, as demonstration, temperature-dependent power-law and Carreau-Yasuda models are adapted in this study. Performances are compared with our isothermal method published earlier. In addition, the novel nonisothermal method is comprehensively examined where the effect of viscous dissipation is studied through Brinkman number of extrusion die. It is demonstrated that, for a low Brinkman number, both isothermal and nonisothermal design give similar flow uniformity level. However, for higher Brinkman numbers, the proposed nonisothermal method produces a design with more desirable velocity uniformity level along with a maximum improvement of 5.24% over the isothermal method. In addition, dependency of flow field on temperature, due to temperature-dependent viscosity, is studied, and it is demonstrated that fully-developed velocity profile changes as temperature increases along the flow channel. Moreover, the effect of the temperature sensitivity parameter in temperature-dependent non-Newtonian models is considered. It is demonstrated that the temperature boundary condition with the Biot number of 1.0 gives adequate results for lower values of the temperature sensitivity parameter.
在衣架式挤出模头的设计中，主要目标是在模头出口处提供均匀的流速。此前，已开发出一种用于衣架式挤出模头的多流变等温方法模型来实现这一目标。挤出模头中的聚合物熔体通常会经历高剪切速率。高剪切速率引起的粘性耗散可能导致模头内出现显著的温度差异。由于粘度与温度相关，温度差异可能导致流速不均匀，这可能会显著影响模头出口处的流速。因此，提出了一种新的设计方法，在衣架式模头的设计中考虑温度和粘性耗散的影响。尽管在所提出的研究中可以采用更多的非牛顿流体流变模型，但作为示例，本研究采用了与温度相关的幂律模型和卡雷奥 - 亚苏达模型。将性能与我们之前发表的等温方法进行了比较。此外，对这种新颖的非等温方法进行了全面研究，通过挤出模头的布林克曼数来研究粘性耗散的影响。结果表明，对于低布林克曼数，等温设计和非等温设计给出的流动均匀性水平相似。然而，对于较高的布林克曼数，所提出的非等温方法产生的设计具有更理想的速度均匀性水平，比等温方法最大提高了5.24%。此外，研究了由于粘度与温度相关而导致的流场对温度的依赖性，结果表明，随着温度沿流动通道升高，充分发展的速度剖面会发生变化。此外，考虑了与温度相关的非牛顿模型中温度敏感性参数的影响。结果表明，对于较低的温度敏感性参数值，比奥数为1.0的温度边界条件能给出足够的结果。
