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鱼尾型片材机头内熔体流动的三维有限元模拟 总被引:1,自引:0,他引:1
利用ANSYS和MATLAB软件,对鱼尾型片材机头流道内熔体的速度、压力和剪切应力的分布进行三维有限元模拟和分析。通过对机头流道不同截面处熔体场量分布的模拟,探知了熔体在流道内的运动规律及特点,对口模设计具有一定的指导作用。 相似文献
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为提高管材挤出机头的加工性能,加强机头流道的塑化作用,以挤出机头中直通式管材挤出机头作为研究对象,建立其挤出加工过程的数学模型,利用ANSYS Fluent软件对管材挤出机头流道的流动过程进行模拟研究,用CFD-post对模拟结果进行分析,并根据模拟结果对管材挤出机头流道的结构进行优化设计。模拟结果表明:优化后的管材挤出机头流道增加了熔体的流动速度,减少了熔体在机头流道内的停留时间,提高了流动性能;并降低了压缩段末端的压力降,提高了成型段上的压力降,增强了熔体的塑化性能,使制品变得更加紧密。 相似文献
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利用有限元软件包Polyflow模拟不同条件下发泡机头流道内PS/CO2熔体的流动,获得了压力,计算出压降速率,并分析熔体温度、CO2含量、机头模口流道直径和质量流率对流道内压力和压降速率的影响。结果表明,在加工条件允许的范围内,降低熔体温度,可以显著提高机头流道中的压力和机头模口流道中的压降速率;当熔体温度一定时,机头流道中的压力和机头模口流道中的压降速率随着CO2含量的增加而降低。尤其当熔体温度为150℃,CO2质量含量由1%增加到2%时,机头模口流道中的压降速率急剧降低;减小机头模口流道直径可有效地提高机头流道内的压力和压降速率。熔体温度175℃,CO2质量含量5%、质量流率1kg/h时,模口直径由1mm减小到0.5mm,机头入口段压力由5.9MPa增大到近30MPa。 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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提出了一种新型的全部流道由平直板条组成的片材机头结构。全部流道中在熔体特征黏度相等的假定条件下,给出了确定构成流道的栅条尺寸的算法及相关计算公式。在幅宽为0.87m、口模间隙为1mm的实验机头上进行了PP片材的挤出实验以证实机头结构的可行性和设计方法的正确性。结果表明,用这种形式的机头可以获得厚度均匀的挤出片材(沿幅宽最小厚度与最大厚度的比值为0.97)。熔体沿幅宽的平均停留时间分布分析结果表明,平均停留时间分布在幅宽上是不均匀的,但其不均匀性远低于T形机头。 相似文献
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目的研究大肠埃希菌、肺炎克雷伯菌、阴沟肠杆菌的耐药性变迁。方法对2007~2009年临床分离的大肠埃希菌(645株)、肺炎克雷伯菌(260株)和阴沟肠杆菌(150株),采用纸片扩散法进行体外药敏测定,并依据美国临床实验室标准化协会(Clinical and Laboratory Standards Institute,CLSI)规定的标准,分析3种肠杆菌科细菌的耐药性变迁。结果大肠埃希菌、肺炎克雷伯菌、阴沟肠杆菌对氨苄西林的耐药率均较高;对头孢他啶的耐药率低于头孢噻肟;与2007年比较,2008年和2009年对头孢吡肟的耐药率明显增长;未发现对亚胺培南耐药菌株的产生。结论细菌耐药性不断增强已成为临床治疗面临的重要难题,应从耐药监测、医院感染控制、合理使用抗生素等多方面努力,减少细菌耐药性的产生。 相似文献
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A. A. Konnov 《Combustion, Explosion, and Shock Waves》2005,41(5):496-503
A simple phenomenological diffusive-thermal model of cellular instability of premixed flames of ternary mixtures is developed
and presented. The model shows that preferential diffusion can alter stoichiometry of the mixture, i.e., the ratio of the
fuel and oxidizer concentrations, and also its effective dilution by an inert. Key parameters of the model are estimated using
numerical modeling of burning velocities. Laminar burning velocities are calculated for hydrogen-oxygen-nitrogen, methane-oxygen-nitrogen,
and propane-oxygen-nitrogen mixtures. Conditions for the appearance of cellular instability in ternary mixtures are determined
and compared with experiments. In good agreement with experimental observations, the diffusive-thermal instability is predicted
in hydrogen flames with equivalence ratios φ ≲ 1.45, in lean methane flames with φ ≲ 1.02, and in rich propane flames with
φ ≳ 1.03. The magnitude of the change in the local flame velocity due to preferential diffusion is evaluated. It is demonstrated
that nitrogen diffuses faster than oxygen in hydrogen-air and methane-air flames, while oxygen diffuses faster than nitrogen
in flames of propane and other heavier hydrocarbons. In mixtures of air with propane or heavier hydrocarbons, the transition
between stable and unstable regimes is predicted in mixtures that are leaner than the mixture corresponding to the peak of
the burning velocity curve, in agreement with experimental observations.
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Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 5, pp. 14–22, September–October, 2005. 相似文献
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Alexander M. Mearns Kingsley Ofosu-Asiedu 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1984,34(6):341-349
The kinetics of reaction between oxides of nitrogen, ammonia, water vapour and oxygen in ppm quantities in nitrogen were studied. The kinetics of the nitrogen dioxide-ammonia reaction and of the nitrogen dioxide-water reaction were investigated separately, and a reaction model was developed to predict the rate of disappearance of nitrogen dioxide in the overall reaction system based on the reaction rate expressions deduced for the separate reactions. There was satisfactory agreement between measured and predicted dioxide concentrations as a function of time. The results have relevance to consideration of clean-up processes of tail gases in nitric acid plants and to studies of reactions in polluted atmospheres. 相似文献
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目的对本地区142名新生儿溶血病患者进行血清学检测,评价直接抗人球蛋白试验、游离抗体试验和抗体释放试验在该病诊断中的价值。方法对2005年1月~2007年6月各医院送检的高胆红素血症新生儿血液标本进行"三项试验"。结果142名新生儿溶血病患者中,血型分布规律为:B>A>AB>O,54.22%为B型,43.66%为A型,二者差异有显著意义。直抗试验阳性率为76.76%,释放试验阳性率为100%,游离试验阳性率为50.70%。释放试验阳性的A型患者中,抗-AB检出率为47.17%,B型患者中的检出率为53.03%,二者差异无显著意义。结论释放试验敏感度最高,是判定新生儿溶血病最有力的证据,在本地区,B型新生儿可能更易患新生儿溶血病。 相似文献
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Application of shear was found to have considerable effect on the radical polymerization of styrene initiated by benzoyl peroxide. The initial rate of polymerization decreases by as much as 30% for low shear rates (γ), but on further increasing γ it increases slightly, levelling ultimately at the 10% reduction level. The effect of solvent was shown to have negligible effect, in direct contrast to that observed by Kumar et al.1–3 for methyl methacrylate and acrylonitrile. Experiments confirm that the reduction in the rate of initial polymerization can be attributed largely to the change in initiator efficiency on the application of shear rate. As a further test, the decomposition rate of benzoyl peroxide in nitrobenzene at 80°C was measured and was found to increase significantly on application of shear. This confirms the importance of mass transfer resistance in removal of CO2. The reduction in the rate of polymerization of styrene can now be explained as follows. In the reaction mass, there are benzoyloxy as well as phenyl radicals and styrene molecules have been shown by Bevington4 to react preferentially with the former. The fall in the rate of polymerization of styrene occurs because, on the application of shear, decomposition of benzoyloxy radicals is favoured in the forward direction and its concentration in the reaction mass falls. As a result the initiation of polymer radicals reduces, which in turn gives a lower rate of polymerization. 相似文献
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将以往实验教学中分散的、孤立的关于阿司匹林方面的实验加以总结和进一步延伸,使其系列实验内容涉及知识面较广、较深,涵盖的基本技能操作较全面,使之达到培养学生的综合能力、创新能力及提高综合素质的一项综合性实验。 相似文献
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随着纳米材料科学的迅速发展,越来越多的研究表明纳米颗粒不仅能强化传热,同时也能强化吸收。本文提出了在氨水溶液中添加碳纳米颗粒和表面活性剂辛基苯酚聚氧乙烯醚(OP-10)的配制纳米流体的方法,并对其稳定性进行了一定的实验研究。根据吸附理论讨论了活性剂对纳米炭黑颗粒在氨水溶液中的分散机理,在此基础上,探讨了一定纳米颗粒浓度所对应的最小的活性剂浓度,以及表面活性剂浓度对纳米颗粒悬浮液稳定性的影响。以便为氨水纳米流体的强化吸收研究作基础。 相似文献
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Nan Li Toshiaki Ohshima Kei-ichi Shozen Hideki Ushio Chiaki Koizumi 《Journal of the American Oil Chemists' Society》1994,71(6):623-627
In order to evaluate the effects of the degree of unsaturation of triacylglycerols on cholesterol oxidation, mixtures of purified
sardine oil triacylglycerols (iodine value, IV=182.6) and cholesterol; of partially hydrogenated sardine oil triacylglycerols
(IV=174.5) and cholesterol; and of fully hydrogenated sardine oil triacylglycerols (IV=92.0) and cholesterol were incubated
at 25°C in the dark. The oxidative stability of the samples decreased with increasing degree of unsaturation of the triacylglycerols
in the sample mixtures; the induction period for peroxide values (PV) of the sardine oil triacylglycerols and cholesterol
was shorter than that of the partially hydrogenated sardine oil triacylglycerols and cholesterol. Certain polyunsaturated
fatty acids (PUFAs) in the constituent fatty acids of sardine oil triacylglycerols started to decrease after a shorter induction
period compared with that of the partially hydrogenated triacylglycerols. The prominent cholesterol oxides accumulated in
the samples were 7β-hydroxycholesterol, 7-ketocholesterol, β-epoxide and cholestane triol. The tendency for accumulation of
cholesterol oxides in the time course coincided with the changes in PV as well as the decrease in PUFAs. Cholesterol was oxidized
in conjunction with autoxidation of coexisting fish oil triacylglycerols. Although lowering the degree of unsaturation of
fish oil triacylglycerols was effective in prolonging the induction period of cholesterol oxidation, the rate of cholesterol
oxidation in the cholesterol oxides' formation phase after the induction period was not affected by the difference in the
proportion of highly unsaturated fatty acids in the natural and partially hydrogenated triacylglycerols of fish oils. 相似文献