共查询到20条相似文献,搜索用时 31 毫秒
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运用有限元分析软件Polyflow对不同结构和不同螺杆转速下的修正Maddock混炼元件流场进行三维非等温数值模拟,得到了流场的压力、速度、温度和剪切速率的分布;利用粒子示踪法(PTA)对不同结构和不同螺杆转速的修正Maddock混炼元件流场内聚合物熔体所经历的混合过程进行模拟,并对结果进行了统计学分析;通过比较平均解聚功等参数对不同结构和不同螺杆转速下修正Maddock混炼元件的分散混合效果进行分析研究,并借助实验进行验证。结果表明,等腰反向型修正Maddock混炼元件对聚合物熔体的剪切作用和分散混合性能最好;适当提高螺杆转速可以有效地促进物料的分散混合。 相似文献
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《塑料》2017,(1)
在普通单螺杆的计量段插入周期性间断多副螺棱以触发混沌混合,对其加工聚合物的分布混合与分散混合特征进行模拟,同时与普通单螺杆比较,并进行不相容体系共混实验。结果表明:周期性间断多副螺棱螺杆使物料在流道内的停留时间增长,停留时间概率密度曲线峰增宽,使得粒子承受的扰动频率增大,有效地降低了粒子的分离尺度;周期性间断多副螺棱螺杆的最大剪切速率均值高于普通单螺杆,在聚合物加工过程中产生混沌混合,增强了聚合物的拉伸折叠作用;采用扫描电镜观察PC/HDPE不相容共混物的脆断面形貌,分散相PC颗粒经历被拉伸成片状结构、破碎成更小的纤维状结构、进一步破碎成球状形态的演变过程,分散相破碎演变得早,分散相粒径细小,周期性间断多副螺棱螺杆挤出机就具有很好的混沌混合特征。 相似文献
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为解决普通螺杆单元对聚合物粒子混合效果较差的问题,提出了三螺棱孔型拉伸单元,并且,利用流体仿真软件Polyflow与普通螺杆单元加工聚合物进行了模拟对比。结果表明,孔型拉伸单元的聚合物粒子的混合指数分布区间更高,以大于0.5区域为主,最大混合指数达0.778 9;孔型拉伸单元的最大剪切应力集中分布在0.06~0.08 MPa之间,与普通螺杆单元的0.04~0.06 MPa相比较高;孔型拉伸单元的聚合物粒子经历的累积停留时间更长,集中分布在6 s以上,普通螺杆单元的集中分布在4~6 s;孔型拉伸单元的分离尺度曲线下降更迅速,当在轴向长度为20 mm时,迅速下降至最低点;当轴向长度为20~70 mm时,曲线平缓无波动,聚合物粒子无团聚现象。因此,孔型拉伸单元对聚合物粒子的分散混合和分布混合的能力大于普通螺杆单元,孔型拉伸单元能够提高聚合物粒子的混合效果。 相似文献
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《现代塑料加工应用》2019,(5)
通过在螺杆螺槽内插入周期性间断结构副螺棱,建立新型螺杆计量段螺槽展开简化模型。借助动力学软件Ployflow,对聚合物在新型螺杆及普通螺杆螺槽内的流动情况进行模拟仿真,对比分析其流动混合效果,同时进行低密度聚乙烯(LDPE)/nano-CaCO_3的共混挤出试验验证。结果表明,副螺棱周期性的扰动可触发混沌混合,提高聚合物流体的分散准数,延长粒子在螺槽中的停留时间分布,同时试验挤出物脆断面的微观结构也显示新型螺杆具有更好的混合效果。 相似文献
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《塑料》2016,(1)
针对叶片式挤出和注射成型加工设备中的屏障混炼塑化单元,应用流体动力学软件Polyflow对其加工聚合物的塑化混合特征进行模拟并与螺纹单元比较。结果表明:屏障混炼塑化单元熔体黏度沿单元周向转动方向逐渐降低,最大剪切速率曲线在螺纹单元的右方,混合指数以大于0.5的区域为主,分离尺度曲线与螺纹单元的相近,拉伸长度对数、拉伸速率和时均混合效率的曲线均在螺纹单元的上方。因此,屏障混炼塑化单元实现了对聚合物熔体的正位移输送,有利于聚合物塑化能力和混合效果的提高;屏障混炼塑化单元流场内物料以拉伸作用为主,对聚合物的拉伸作用要强于螺纹单元,有利于对物料分散混合效率的提高;屏障混炼塑化单元对聚合物的分布混合能力与螺纹单元相当,对聚合物的分散混合能力大于螺纹杆单元,采用屏障混炼塑化单元加工聚合物具有很好的混合质量和节能效果。 相似文献
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啮合同向双螺杆挤出机新型混炼元件性能及应用 总被引:6,自引:3,他引:3
就全啮合同双向螺杆挤出机中的混合过程进行了分析讨论,分析了普通螺纹元件和捏合盘元件的混合特性和泵送特性,针对这些元件存在的问题讨论了新型混炼元件的特点(包括典型分散性混炼元件和典型分布性混炼元元件),并作了深入的对比讨论,就上述元件在聚合物改性加工,共混和填充过程中典型的应用示例进行了分析讨论。 相似文献
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建立了带有间断副螺棱的新型单螺杆计量段螺槽展开物理模型及数学模型。借助流体动力学软件Ployflow,采用网格叠加技术,对熔体在新型单螺杆及普通单螺杆挤出机计量段展开螺槽内的流动情况分别进行了数值模拟。运用粒子示踪技术及统计学方法以停留时间分布、分离尺度及累计混合指数为指标来表征螺杆的混合性能。结果表明,相比于普通单螺杆,新型单螺杆不仅可以减小熔体物料分离尺度,提高混合指数,还可以加宽停留时间分布概率密度曲线,获得更好的混合分散效果。 相似文献
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Joëlle Aubin 《化学工程与技术》2019,42(8):1544-1544
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The stretching and folding of fluid element during chaotic mixing field is studied using numerical method. The chaotic mixing process is caused by periodic secondary flow in a twisted curved pipe. Using the nonlinear discrete velocity field as the dynamical system, the present study connects the fluid particle‘s stretching along its trajectory in one period to a linearized time-varying variational equation. After numerical approximation of the variational equation, fluid stretching is calculated on the whole cross section. The stretching distribution shows an exponential fluid stretching and folding, which indicates an excellent mixing performance. 相似文献
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Y. Kawase M. Moo-Young 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1989,44(1):63-75
The mixing time in bioreactors is discussed. Theoretical correlations for the mixing time in stirred tank and bubble column reactors respectively, are derived. They are based on Kolmogoroff's theory of isotropic turbulence and the relationships between the mixing time and the axial dispersion coefficient in the turbulent flow regime. The predictions of the proposed correlations are in reasonable agreement with several available data and correlations. A wide divergence among the data for the mixing time reported in the literature is also discussed. 相似文献
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Mixing in curved tubes 总被引:1,自引:0,他引:1
Vimal Kumar 《Chemical engineering science》2006,61(17):5742-5753
The mixing efficiency in a curved tube is a complex function of the Reynolds number, Schmidt number, curvature ratio and tube pitch, therefore, the relative effectiveness of a helical tube is quite complicated and challenging over a straight tube. A state of art review on mixing of two miscible liquids in curved tubes revealed that the mixing in coils of circular cross section has not been reported in the literature. In the present work a computational fluid dynamics study is performed in curved tubes of circular cross-section of finite pitch under laminar flow conditions to examine the scalar mixing of two miscible fluids using scalar transport technique. In the present study the phenomenon of mixing by convection and diffusion of two flow streams with inlet scalar concentrations of zero and unity in the two halves of a tube perpendicular to the plane of curvature has been reported. The mixing efficiency has been quantified with concentration distributions and unmixedness coefficient at different cross-sections and process conditions (Reynolds number, Schmidt number and curvature ratio) in the straight and curved tube of circular cross-section. The result shows that, in curved tube, for higher Schmidt number fluids, mixing is considerably improved at moderately low Reynolds numbers (Re∼10), but is not affected for Reynolds number of the order of 0.1. It is also reported that mixing in the curved tube is higher at low values of curvature ratio as compared to the higher curvature ratio. 相似文献