正向螺纹元件组合对反向螺纹元件熔体输送特性的影响

目的：探究熔体输送段正向螺纹元件间的不同组合对反向螺纹元件的熔体输送特性的影响。方法：通过改变导程构建两种不同模型,使用SolidWorks软件建立三维模型,使用Polyflow软件对两种模型在熔体输送段的挤出过程进行数值模拟,分析不同导程下螺纹元件的螺槽宽度及螺棱厚度对流场的影响及不同转速下流场的变化,通过实验验证转速对物料混合效果的影响。结果：所构建的模型均可使熔体通过反向螺纹元件;在相同螺杆转速下,由大导程螺纹元件构建的模型一建压能力和输送能力强于由小导程构建的模型二;模型一在分散混合能力上优于模型二,在分布混合能力上弱于模型二;在两端压差相同的情况下,增加转速可以提高物料的分散混合效果。结论：在聚乳酸改进加工过程中采用模型一且提高螺杆转速可进一步破碎物料,提高挤出物的质量。     

双圆弧齿轮泵流量特性影响因素数值模拟

目的：分析新型双圆弧齿轮泵内部流场脉动特性的影响因素，采用合理参数以提高齿轮泵输出效率。方法：建立齿轮泵的二维流场仿真模型，采用计算流体力学软件Fluent进行仿真分析，研究不同齿顶间隙、不同齿轮偏心距、负载及转速对齿轮泵出油口瞬时流量、流量脉动、流场特性的影响。结果：随着齿顶间隙增大，齿轮泵出口流量逐渐减小，当齿顶间隙为0.09 mm时，出口流量脉动系数最小为0.135，为该结构参数下齿轮泵最佳齿顶间隙；受负载压力和转速的影响，齿轮泵中心轴线产生偏差，随着齿轮泵转子中心轴线偏心距增加，齿轮泵出口流量逐渐增大，当偏心距为0.05 mm时，齿轮泵出口流量比无中心偏差时增加了5.09%，提高了流量输出。结论：齿轮泵流量特性主要影响因素为转子转速和齿顶间隙，中心偏差的影响较小。     

磨粉机粉碎流场数值模拟及参数优化

采用Fluent软件对"粉碎—盘磨"两级磨粉机的粉碎流场进行数值模拟研究,对比分析刀片分布方案对循环流场的影响及规律;运用正交试验设计方法对粉碎刀片进行参数优化,分析刀片偏转角、刀片长度及刀片间距对粉碎效果的影响规律,并进一步探讨刀片转速对粉碎效果的影响;为获得磨粉最佳的性能参数,对物料粉碎进行试验,以粉碎转速、粉碎时间、磨盘间隙为影响因素,以粒度合格率和耗电量为目标函数,进行三因素三水平回归试验,利用Design-Expert软件对该模型优化求解得到最佳参数组合。结果表明:刀片呈上下螺旋状分布,刀片偏转角为60°、刀片长度为120 mm、刀片间距为等距30mm时,有着良好的粉碎效果;刀片转速对物料最大剪切应变率、动压力、湍流动能的影响呈线性关系;当粉碎转速为1 500r/min,粉碎时间为20s,磨盘间隙为0.045mm时,粒度合格率(80目以上为合格)达90.4%,耗电量为118.3kJ。     

带捏合块的渐加速型单螺杆三维流场分析

目的:提高单螺杆挤出机的混合性能和工作效率.方法:设计了一种利用行星轮组件和混合元件的同轴渐加速单螺杆,利用Ansys/cfx对其流道进行了三维流场分析,得到了宏观压力场、速度矢量图、速度流线图以及轴向速度变化曲线并与传统单螺杆进行了对比,结果:随着螺杆转速的不断变大,物料在机筒内停留时间变短,渐加速螺杆的挤出效率得以提高20%～25%,使得耗能大大减少,由于捏合块的存在,物料在捏合块处被反复挤压,使得渐加速型单螺杆在增加产能的同时混合性能又可以得到保证.结论:同轴渐加速单螺杆高速旋转的捏合块可使物料混合更充分,且能缩短物料在螺杆中的停留时间,提高产量.     

双螺杆挤压过程中物料成分对其停留时间分布影响的研究

为研究双螺杆挤压机生产挤压食品过程中物料成分对停留时间分布的影响,以碳粉为示踪剂,用台式分光测色仪测定添加不同物料成分后各段挤出物的总色差,并对各组样品的停留时间分布进行分析。结果表明:物料成分会影响到原料在挤压机内的停留时间及混合程度,初始MRT为182 s,初始Pe值为19,玉米淀粉添加量为25%时MRT降为173 s,Pe值降为10,大米蛋白、膳食纤维、大豆油添加量分别为15%、10%、6%时,MRT分别延长到214、229、212 s,Pe值分别上升到31、66和29;20组回归正交试验的扩散数模式属于混合流中的中间量扩散模式;各变量对初始物料MRT影响的顺序依次为:大豆油添加量膳食纤维添加量大米蛋白添加量玉米淀粉添加量。     

国外双螺杆挤压膨化机的研究现状

为适应纤维食品加工技术的需要,本文从挤出理论,物料流型及混合效果,停留时间分布等方面介绍了国外８０年代以来双螺杆挤压膨化机的研究动向。     

三螺棱周期性扰动混炼单元混炼性能模拟

通过Solidworks软件建立三螺棱周期性扰动混炼单元模型,利于Polyflow的流体分析功能对新型混炼单元与普通螺杆单元进行模拟分析。通过统计停留时间、分离尺度、最大剪切应力三个参数来表征混炼单元的混炼性能,模拟表明:新型混炼单元使物料的分布混合性能和分散混合性能均优于普通螺杆单元;新型混炼单元的流道内物料粒子受到小于2500Pa最大剪切应力的粒子数多于普通螺杆单元的,降低了物料因摩擦过热而导致降解的风险;新型混炼单元的混炼性能优于普通螺杆单元,主要是使物料受到的拉伸作用强于普通螺杆单元。     

平均停留时间与热敏性物料的蒸发

在浓缩热敏性物料时,为了保证产品质量,应尽可能缩短物料的停留时间。可是对判断物料在各类蒸发器中的停留时间,却缺乏实际观测资料。为此,本文从讨论物料的停留时间对产品质量的影响以及停留时间与蒸发器生产强度和蒸发器结构的关系入手,对五种典型的蒸发器内的停留时间进行了分析和比较。作者认为,对热敏性物料的蒸发,用平均停留时间比用蒸发强度能更好地表征蒸发器的性能。     

同向全啮合双螺杆植物蛋白挤出机不同螺杆元件的仿真分析

为了明确和量化同向全啮合双螺杆挤出机各螺杆元件的功能,增加配置用于生产植物基肉双螺杆挤出机螺杆的合理性,以低温脱脂花生蛋白粉的物性参数为条件,对SLZ36型挤出机的3种元件长度为32 mm的螺杆元件双头螺旋元件、5啮合盘啮合元件及3齿形盘齿形元件的剪切速率、混合指数、物料停留时间、最大剪切应力分布进行仿真分析。采用Solidworks软件建立元件的几何模型,应用Gambit软件进行模型的网格划分及网格质量分析,在Polyflow软件中进行数值模拟,通过Fieldview软件对仿真结果进行后处理分析。结果表明：通过混合指数分析得到3种螺杆元件对物料的混合性能大小为齿形元件>啮合元件>螺旋元件;通过物料停留时间分析得到3种螺杆元件的轴向混合性能大小为齿形元件>螺旋元件>啮合元件;通过剪切速率及平均最大剪切应力分析得到对物料的剪切性能大小为啮合元件>螺旋元件>齿形元件。进行植物基肉双螺杆挤出机螺杆组合时,针对目前整个螺杆配置螺旋元件最多的情况,在进行物料更换时可以合理地配置啮合元件以增加螺杆剪切能力,配置齿形元件以增加螺杆的混合能力。     

脉冲示踪法测定烟丝在滚筒加工设备中的停留时间分布

为了能够使滚筒加工设备中烟丝停留时间分布测定真实准确,选用CO2膨胀烟丝作为示踪物,通过示踪物添加量及方法重复性研究,建立了采用脉冲示踪法研究滚筒加工设备中烟丝停留时间分布的测定方法,利用CO2膨胀烟丝回收率验证了方法的准确度,并分析了滚筒转速和介质流向对烟丝停留时间分布的影响。结果表明:1该方法具有测试方法重复性好、准确度高、应用范围广的特点;2物料在滚筒中的平均停留时间随转速的增加而减少,无因次方差随着滚筒转速的增加而增大;3物料在滚筒中的平均停留时间与介质流向有关,介质顺流时物料停留时间与逆流时相比有所减少。     

Distribution of the residence time in a single-screw extruder with differing numbers of mixing elements

Starch was extruded with sodium trimetaphosphate and sodium hydroxide in a single‐screw extruder at 40% moisture content and screw speeds of 90 and 140 r.p.m. The effect of screw configurations, which included one and two mixing elements, on mean residence time, spread of residence time distribution (RTD), and flow pattern were determined. Increasing the screw speed and reducing the number of mixing elements reduced mean residence time. Higher RTD spread values were obtained at a screw speed of 90 r.p.m. when compared with 140 r.p.m. and increasing the number of mixing elements in the screw increased the RTD spread. The flow pattern was between plug and mixed flow, and increasing the number of a mixing element in the screw did not significantly affect the flow pattern in the single‐screw extruder.     

啮合同向双螺杆挤出机不同螺杆构型对其流场的影响

目的：探究啮合同向双螺杆挤出机不同螺杆构型对流场的影响,改善聚乳酸的材料性能。方法：应用Solidworks软件建立双头螺纹元件的几何模型,在Polyflow中进行数值模拟,借助Fieldview软件对仿真结果进行后处理分析,并对比剪切速率场、压力场、速度场、黏度场以及停留时间分布曲线RTD,得出螺槽深度对流场的影响。结果：在中心距相同的情况下,通过改变螺纹元件的外径和内径之比改变螺槽深度,在相同的工艺条件下,同向双螺杆流道内各物理场以及混合性能均存在较大差异;与构型二相比,构型一的剪切作用更强,但构型二的建压能力更好;挤出过程中,构型二轴向混合能力较好但自清洁能力较差,而构型一轴向混合能力较差、自清洁能力较好。结论：螺槽深度的改变对流道混合性能有着一定影响且存在规律性,可有效指导双螺杆挤出机螺纹元件的设计。     

EFFECT of SCREW CONFIGURATION and SPEED ON RTD and EXPANSION of RICE EXTRUDATE

The influence of screw configuration and screw speed on the residence time distribution and product expansion was determined for rice meal processed in a corotating twin screw extruder. Screw speed had strong effect on the E(t)- and F(t)-diagrams, with the mean residence time varying inversely with screw speed from 206 s to 256 s. the F-diagram was modeled by the combination of perfect mixing and plug flow. the P estimates, which express the fraction of material in plug flow, varied inversely with screw speed from 0.41 to 0.55 for the operating conditions in this study. Both screw configuration and screw speed were statistically significant to the expansion ratios of rice extrudate, with the expansion in the height ranging from 2.98 to 4.13.     

Numerical simulation of the extrusion process for food materials in a single-screw extruder

A numerical study of extrusion cooking of starch based materials in a single-screw extruder is carried out. The low moisture levels and high temperatures typically encountered in practical circumstances are considered. The starch conversion process is studied in the rheological region of the extruder which is often the last few turns of the screw, where the material is treated as a non-Newtonian fluid. A numerical method based on finite-difference approximation is employed to solve the governing non-linear equations for momentum, energy and mass conservation for a non-Newtonian fluid undergoing physicochemical changes. The initial conditions for the problem are taken from experimental observations. The screw configuration and the operating parameters, such as barrel temperature, screw speed and throughput, are varied to study their influence on the conversion of starch. It is found that 28% conversion is obtained due to viscous dissipation alone, whereas 61% conversion occurs by raising the barrel temperature by about 25 °C above the inlet. It is also observed that, at any screw speed, a smaller flow rate caused by a smaller die diameter leads to a higher degree of conversion. Furthermore, it is found that the compression ratio of the screw has a significant influence on pressure rise, bulk temperature and average residence time. As the compression ratio increases the temperature increases but the residence time decreases. The former effect increases the degree of conversion where as the latter decreases the degree of conversion. Therefore there exists a compression ratio at which a minimum degree of conversion at the die is obtained.     

基于ANSYS/CFX渐加速双螺杆设计及三维流场分析

目的:提高双螺杆挤出机的混合效率和工作性能。方法:设计了一种内嵌行星轮系和安装捏合块的新型双螺杆挤出机，并用SolidWorks建立三维模型，以有限体积法为基础，用ANSYS/CFS有限元分析软件对其流道进行分析。获得其宏观压力图、速度矢量图、速度流线图并与传统双螺杆挤出机三维流场进行对比。结果:在行星轮系和捏合块的渐加速作用下，渐加速双螺杆挤出机的混合性能和工作效率要明显优于传统双螺杆，经计算渐加速型双螺杆比普通双螺杆提高20%～25%。结论:渐加速双螺杆在不断加速的过程中使得物料在机筒内停留的时间变短，从而提高产量且减少耗能，捏合块的加入更使得物料可以得到更好的剪切。     

PROPERTIES of CROSS-LINKED STARCH PRODUCED IN A SINGLE SCREW EXTRUDER WITH and WITHOUT A MIXING ELEMENT

Starch was extruded with sodium hydroxide and sodium trimetaphosphate in order to cross‐link it in a single‐screw extruder with and without a mixing element at constant screw speed of 90 rpm in the first set of experiments and at similar mean residence time controlled by screw speed in the second set of experiments. For the screw without mixing element in the second set of experiments, screw speed was adjusted to give the similar residence time as the single‐screw extruder with mixing element at 220 rpm. Phosphorus content and pasting curves of extrudates showed that starch was cross‐linked during extrusion. Replacing the screw without mixing element by the screw with mixing     

基于ANSYS的带行星轮同轴变速单螺杆挤出机三维流场分析

运用ANSYS/CFX软件对带行星轮同轴变速单螺杆挤出机流道进行分析,并与普通单螺杆进行对比。结果表明：相较于普通单螺杆,新型同轴变速单螺杆挤出机的建压能力更好,物料在螺杆中的停留时间更长,有利于物料更好地混合,表明带行星轮同轴变速单螺杆可局部降低物料运输速度,增加物料混合能力以及螺杆建压能力。     

Particle Residence Time Distributions in Two-phase Flow in Straight Round Conduit

Residence times were studied for single particles (polystyrene spheres 19.1 mm diam) in the straight portion of the holding section of a continuous flow system. Particle residence times were all less than the mean residence time of fluid; their ranges were within particle-to-fluid residence time ratios of 0.8 to 1.0. The velocities of the fastest moving particles were all about 1.25 times the mean fluid velocity in the turbulent flow regime. Particle density was important in the flow patterns of two-phase flow. The effect of particle-to-fluid density ratios on the particle residence time followed a quadratic function where particles with density ratio of 1.01 had the least residence time.