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两端进料式宽幅片材挤出机头流道流场分析 总被引:1,自引:0,他引:1
建立两端进料式宽幅片材挤出机头流道三维几何模型,并对物料在流道内的流动进行数值模拟.模拟结果表明,流道内部压力在沿挤出方向递减的同时逐渐趋于横向均匀.高度分别为5和8 mm的阻尼部分对比分析表明,适当调整阻尼部分高度,可影响出口区域挤出速度横向分布,使横向挤出压力和速度更均匀. 相似文献
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在分析了塑料熔体经过机头流道的流动过程与流变学特性基础上,将机头流道压缩段的过渡形状设计为直线型和圆弧型。利用Ployfow软件对直线型和圆弧型过渡压缩段的机头流道进行数值模拟,分析不同压缩段过渡形状对流道压力场、速度场和剪切速率场的影响。结果表明,流道压缩段过渡形状设计为圆弧型后,增大了熔体在成型段内的压力降、流动速度几流道出口速度均匀性,提高了管材的密实度、壁厚均匀性和力学强度,减少了熔体在流道内的停留时间。改进后的流道成型段最大壁面剪切速率从99.6 s-1降低至76.3 s-1,远低于硬质聚氯乙烯(PVC-U)管材表面出现鲨鱼皮现象的临界剪切速率,流道出口壁面剪切速率均匀性与管材表面质量均得到显著提高。 相似文献
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为了研究螺杆剪切性能对3D打印成型过程中物料熔融效果的影响,设计了一种螺杆挤出式3D打印机及不同的剪切段螺杆结构,分别建立螺杆的模型并对螺杆和流体域进行网格划分。以聚丙烯为打印材料结合流体仿真软件进行了剪切性能的数值模拟实验,对仿真实验结果的压力场和剪切速率场以及螺杆流道内粒子的停留时间进行分析。结果表明,棱柱型螺杆的最大压力与无剪切结构相比提高了0.13%左右,圆环型螺杆所形成的最大剪切速率相较于无剪切结构提升了约22.56%,圆柱型螺杆流道内粒子的停留时间最长。说明该结构可以增强物料的塑化熔融以及混合效果,在一定程度上还可以使材料内部无序的分子链重新分布,增强材料自身的性能。 相似文献
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为探究层叠流道中天然高分子材料挤压流动过程与混合特性,建立层叠流道的三维物理模型和有限元网格模型,利用POLYFLOW软件计算了食品熔体在不同的入口流量,挤压过程中的压力、速度、剪切速率分布。结果表明,压力沿着挤出方向呈梯度递减,随着入口流量增大中间位置压力差增大;剪切速率在流道中变化明显,剪切速率从流道中间位置向四周递减,从壁面到流道内部递减;速度在流道内沿着挤出方向先增大后减小,靠近壁面速度小;层叠扭转流道的结构和尺寸设计,有助于提高天然高分子物料的混合效果,并且第1、4层流道混合效果优于第2、3层流道,提高入口流量也有利于提高物料的混合效果。 相似文献
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This is the first time an extensive investigation has been carried out regarding the effects of riser exit geometry on pressure drop and solid behaviour inside the Internal Circulating Fluidized Bed (ICFB) riser, using different riser exit geometries at several operating conditions.The Radioactive Particle-Tracking (RPT) technique was used for solid concentration measurements and solid residence time distribution at the exit zone. Experiments were conducted using Geldart B particles, in the gas superficial velocity range of 4 to 10 m/s. Axial solid hold-up, solid residence time distribution in the exit zone, and the reflux ratio factor km, (defined earlier by [E.H. Van der Meer, R.B. Thorpe, J.F. Davidson, Flow patterns in the square cross-section riser of a circulating fluidized bed and the effect of riser exit design, Chem. Eng. Sc. 55 (19) (2000) 4079-4099]), were the main criteria used to investigate the impact of gas-solid separator devices implemented at the ICFB riser exit.Solid residence time distribution results and axial solid hold-up profiles provided clear evidence that the separator device at the riser exit strongly influences the hydrodynamic structure of the ICFB riser. The V-shaped riser exit geometry was found to be the optimum of all the configurations studied. 相似文献
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微型流化床反应器液相冷态进样停留时间分布模拟与实验 总被引:1,自引:0,他引:1
为了得出气、液相流量变化对微型流化床反应器液相停留时间的影响规律,借助Fluent软件对反应器内部流场进行数值模拟,得到其速度、压力分布特性和反应器出口液相浓度的变化曲线。采用示踪剂侧面脉冲进样法,实验测定了反应器中液相的停留时间分布。结果表明,气相流量和液相流量均对液相停留时间有明显的影响,气、液相流量为410L/h时,液相平均停留时间可以控制在1.1110L/h时,液相平均停留时间可以控制在1.111.89s;气、液相流量的增加均会导致液相停留时间的减少,但气相流量对停留时间的影响要大于液相流量对液相停留时间的影响。数值模拟与实验数据对比分析发现二者结果吻合良好,模型可用。 相似文献
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利用大型有限元软件ANSYS对聚乙烯熔体在四螺杆挤出机常规螺纹元件中的流动情况进行了分析,求出了速度场、压力场、黏度场,对流道的中心区进行了重点分析。计算结果表明:四螺杆的四个啮合区具有较大的压力梯度、速度梯度,其混合性能明显好于双螺杆挤出机。中心区有明显的环流现象,物料在中心区的停留时间较长,中心区物料没有滞留现象。 相似文献
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On the basis of the theory of relative motions, a novel nested screw extruder was invented in which one rotating outer screw acted as the barrel for an inner screw; the combination of the outer screw and outer barrel was the other extrusion system. It was realized that centrifugal force resulted in the difference between the forces acting on the solids by the screw and by the barrel, which further compacted the solid pellet or powder. These factors benefited the frictional drag of solids and the early melting. This was consistent with the fact that the solids conveying flow rate increased greatly when the barrel and screw rotated oppositely at the same time. Thus, centrifugal force and material compressibility were significant in the feeding zone. A mathematical model was developed to calculate the output, pressure, and velocity of the solids in the screw down‐channel with consideration of the centrifugal force and material compressibility. The predicted pressure distribution and output were better than those by previous models in fitting the experimental data. The simulations revealed that the maximum traction angle was close to 90° ? the helix angle for maximum output in contrast to the maximum traction angle of 90° predicted by the Darnell–Mol theory. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
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This paper reports measurements of the influence of riser exit geometry upon the particle residence time distribution in the riser of a square cross section, cold model, circulating fluidised bed. The bed is operated within the fast fluidisation regime. The fast response particle RTD technique developed by Harris et al. (Chem. Eng. J. 89 (2002) 127-142) was used to measure the residence time distribution.The geometry of the riser exit is shown to have a modest but consistent influence upon the particle RTD; the influence of operating conditions, i.e. superficial gas velocity and solids flux is more significant.Increasing the refluxing effect of the riser exit increases the mean, variance and breakthrough time and decreases the coefficient of variation of the residence time distribution. Changes in reflux do not have a systematic effect upon the skewness of the RTD. 相似文献
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In a spouted bed of 80mm in ID and 1700mm in height, the gas residence time distributions at different radial positions in both spout and annular area were measured with five different kinds of particles as spouting material, air as spouting gas, and hydrogen as tracer. The effects of superficial gas velocity, operating pressure, particle size and its category on gas residence time distribution were discussed. It was found that the gas velocity profile in spout was more uniform than that in annulus. It could be concluded that the gas flow in the spout could be treated as a plug-flow, while that in the annulus inhibited a strong non-ideal flow behavior. Increasing the superficial gas velocity and decreasing the operating pressure, the particle density and its size gave rise to spouting disturbance, thus the measured tracer concentrations vs. time curves fluctuated. The variances of residence time distribution curves could be taken as a measure of the gas fluctuation degree. 相似文献
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采用高速摄影的方式,对矩形通道内过冷沸腾时的汽泡在倾斜状态下的行为进行了可视化研究,分析了加热面倾斜角度对汽泡生长-冷凝速率以及平均汽泡最大直径与对应生长时间的影响。结果表明:在同一入口工况参数下,汽泡的最大直径与寿期均随角度的增加而上升,且与倾斜角度近似呈正比;不同倾斜条件下的汽泡最大直径与对应生长时间基本满足0.5次幂的函数关系,其系数与倾斜角度呈正比;采用Zuber量纲1形式表示后,不同倾角时的平均汽泡生长-冷凝曲线在生长阶段随倾角增加而增加,而在冷凝阶段则与角度无明显关联。 相似文献
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Modelling the solids inflow and solids conveying of single-screw extruders using the discrete element method 总被引:7,自引:0,他引:7
P.A. Moysey 《Powder Technology》2005,153(2):95-107
A new solids-conveying model for the single-screw extruder based on the Discrete Element Method (DEM) is proposed in this work. The polymer solids are treated as spherical particles moving in a 3-D environment which includes the feed hopper, the solids-inflow zone, and the solids-conveying region of an extruder, without inclusion of the plug flow assumption common to continuum models. Normal and tangential forces resulting from inelastic collisions with neighboring particles and surfaces dictate how each polymer pellet is conveyed through the model extruder. The DEM technique was implemented in this work to allow fundamental study of the local transport phenomena within the screw channel. Reported in this paper are results examining the cross- and down-channel velocity profile of solids in the screw; the residence time distribution; the cross-channel temperature profile; and the coordination number distribution. Two exit conditions were evaluated by the model: i) the open-discharge case where no compaction of the solids occurred; and ii) the restricted case where the axial pressure increased as the solids flowed towards the barrel exit. The predictions of the DEM simulations allowed for detailed observations of the solids movement in the screw, providing insight into the inherent flow fluctuations of extrusion systems. 相似文献