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针对结晶型聚合物熔体冷却过程的结晶行为,建立了偶合宏观温度场与微观结晶形态的多尺度模型.该模型揭示了宏观温度的变化会引起晶核数、晶体生长速率的改变,从而影响微观结晶形态;而微观结晶释放的潜热也将导致宏观温度的改变.为了求解上述多尺度模型,提出了有限体积/像素法偶合的多尺度算法,即在粗网格上采用有限体积法对宏观温度场进行求解,而在细网格上采用像素法对微观结晶形态进行模拟.基于多尺度模型及多尺度算法,文中对二维聚合物熔体模壁等速降温的冷却问题进行了研究,考察了温度、相对结晶度的变化及结晶形态的演化,并比较了不同冷却速率、初始温度对温度、相对结晶度及结晶形态的影响.数值结果表明,冷却速率是影响结晶行为的关键.高冷却速率下,温度平台出现较早,持续较短;结晶过程对应的温度范围较广;且平均晶体直径较小.而初始温度只影响温度平台及结晶行为出现的早晚,与其持续时间几乎无关。
Aiming at the crystallization behavior of the cooling process of crystalline polymer melt, a multi-scale model of coupling macro-temperature field and microscopic crystal morphology was established. The model reveals that the change of macroscopic temperature leads to the change of crystal nucleus number and crystal growth rate, And the latent heat released by the microcrystal will also lead to the change of macroscopic temperature.In order to solve the above-mentioned multi-scale model, a finite volume / pixel coupled multi-scale algorithm is proposed, which uses the finite volume method on the coarse grid to analyze the macroscopic Temperature field, the microscopic crystal morphology was simulated by the pixel method on the fine grid.According to the multi-scale model and the multi-scale algorithm, the cooling problem of two-dimensional polymer melt wall cooling at constant velocity was studied in this paper, The effects of different cooling rates and initial temperature on temperature, relative crystallinity and crystalline morphology were investigated. The numerical results show that the cooling rate is the key to the crystallization behavior. At the cooling rate, the temperature platform appeared earlier and continued to be shorter; the temperature range corresponding to the crystallization process was broader; and the average crystal straight Small. The initial temperature affects only the morning and evening temperature and crystallization behavior of the platform appeared, almost irrespective of its duration.