涡流空气分级机内流场分析与转笼结构改进

应用F luent软件建立传统涡流空气分级机三维模型并对其内部流场进行数值模拟,同时采用激光多普勒测速仪对分级机内流场进行测量。研究表明:当进口风速一定时,存在一个临界转笼转速使得环形区及转笼叶片间流场分布最均匀,分级性能好。改进转笼结构并进行模拟分析,新结构转笼的叶片设计成流线型,减少了气流与叶片的碰撞。模拟结果表明:与传统涡流空气分级机相比,环形区内速度分布得到了改善,新结构转笼叶片间旋涡趋势减弱,分级机内分级力场优于传统转笼。特别是转笼高速旋转时,结构改进效果更加显著。     

涡流空气分级机内三维流场的数值模拟与测量

为了清楚地认识涡流空气分级机内部流场分布,文中利用Fluent软件建立分级机的三维模型,对其内部三维旋转流场进行了数值模拟计算,得出不同工况下分级机内部流场分布。采用激光多普勒测速仪(LDV)对转笼叶片间流场进行测量,应用测量结果来验证模拟计算结果,模拟结果与测量结果吻合。研究表明,在一定的进口风速下,当环形区靠近叶片处气流切向速度与转笼外缘切向速度相近时,存在一个临界转速使得叶片间流场最稳定,分级机分级效果最好。这为改进涡流空气分级机操作提供了理论指导。     

涡流空气分级机进口风速和转笼转速匹配研究

为寻求涡流空气分级机进口风速和转笼转速的最佳匹配,利用Fluent软件对涡流空气分级机内部流场进行模拟分析,得出:当进口风速与转笼外缘的切向线速度相等或相近时流场最稳定。在流场较稳定的前提下,较高进口风速和转笼转速时,环形区湍流耗散率更大,更有利于物料的分散及分级。碳酸钙物料实验表明:转笼转速分别为800 r/min和1 200 r/min时,取进口风速分别为9 m/s和12 m/s,分级精度和牛顿分级效率都较高。其中进口风速为12 m/s,转笼转速为1 200 r/min时,分级精度和牛顿分级效率最优。该结论为利用涡流空气分级机进行分级合理调节进口风速和转笼转速提供理论依据。     

涡流空气分级机环形区流场的实验研究

为优化涡流空气分级机内的流场,提高分级机性能,研究了涡流空气分级机蜗壳内加水平隔板和不加水平隔板2种结构对分级精度的影响。2种结构分级机环形区流场的激光多普勒测速计测量结果表明:在涡流空气分级机蜗壳内加隔板后,减小了环形区气流的轴向速度,沿转笼轴线方向,切向速度分布趋于均匀一致,流场稳定。重质CaCO3物料实验表明:在所试验的风速和转速范围内,采用较高转速分级,加隔板分级精度降低。环形区内适当的湍流能够提高物料的分散性,对提高分级精度有利。     

导风叶片对涡流空气分级机内流场的影响

利用ANSYS-Fluent 17.0软件对有、无导风叶片两种结构的涡流空气分级机内流场进行数值模拟和对比分析,研究了导风叶片对涡流空气分级机内流场的影响。数值模拟结果表明：导风叶片降低了转笼外缘处气流切向速度,从而影响转笼通道内旋涡的分布情况,使有、无导风叶片两种结构的稳定工况不同;导风叶片减小了转笼外缘处气流径向速度的波动和湍流耗散率,此处流场分布相对均匀,有利于提高分级精度;此外,导风叶片在导流过程中,改变了环形区速度场的分布,气流切向速度减小,径向速度增大,径向速度的增大使其分级粒径增大。碳酸钙物料分级实验结果表明：具有导风叶片结构的涡流空气分级机分级粒径较大,分级精度较高;导风叶片处较大的湍流耗散率有助于粉体分散,明显减弱“鱼钩效应”现象。     

涡流分级机蜗壳内水平隔板对其流场的影响

为了探究蜗壳结构对涡流空气分级机流场特性的影响,文中利用Fluent软件对蜗壳内增加不同数目水平隔板的涡流空气分级机流场进行数值模拟。研究表明:蜗壳内水平隔板数目对流场速度以及环形区湍流耗散率有不同影响,存在临界隔板数使流场轴向速度分布均匀,在本文条件下的临界隔板数为3;在蜗壳中增加水平隔板可以对转笼外柱面处切向速度产生不同影响,在文中条件下增加1—3层水平隔板可以在一定程度上减小转笼切向速度与气流切向速度的差值,从而改善转笼叶片间的惯性反漩涡;随着隔板数的增加,湍流耗散率得到显著提高,物料分散性变好;涡流空气分级机的结构设计中应当考虑水平隔板对分级流场的影响。     

涡流空气分级机转笼结构对其分级性能的影响

摘要：研究了涡流空气分级机底盘开口与封闭两种型式的转笼对分级指标的影响。重质CaCO₃物料试验表明：采用底盘开口转笼时,切割粒径小,分级精度低;随着分级转速增加,切割粒径对风速的敏感性下降。另外,用激光多普勒测速计测量了上述两种转笼结构的分级机环形区的流场特性,结果表明：转笼底盘开口,环形区气流出现旁路,进入转笼径向风速减小,造成分级物料切割粒径减小;底盘封闭的分级机环形区内靠近转笼处,切向风速突变增大,特别是轴向上湍流度的增大,有利于团聚物料的分散和分级精度的提高。     

涡流分级机环形区流场的激光多普勒测速研究

采用激光多普勒测速计研究了涡流分级机环形区气流的切向速度分布。测量了蜗壳进口风速18 m/s时,从330 r/min到1800 r/min之间6个不同转笼转速条件下的环形区气流切向速度。结果表明:当转笼转速小于1 200 r/min时,转笼转速的变化对环形区气流平均切向速度的数值影响很小;转笼高速旋转,环形区气流切向速度数值大小与转速有关。用系数F表示转笼附近环形区气流切向速度波动程度与转笼转速之间的关系,当转笼低速旋转时F大,极小值点出现在转笼旋转速度与当地气流速度一致时,随着转速的增加,趋于平稳。     

几何相似涡流空气分级机环形区流场变化规律研究及预测

为探究几何相似涡流空气分级机环形区流场的分布特性,建立不同尺寸的涡流空气分级机模型,提取关键结构的几何参数,通过数值模拟分析尺寸比例因数对分级机环形区流场分布的影响。模拟结果表明,在相同进口风速下,几何相似分级机模型环形区内切向速度呈准自由涡的分布。模型尺寸增大,环形区内柱面面积加权平均切向速度增大,环形区切向速度分布不均匀。转笼内外缘切向速度越接近,环形区内近转笼外缘处切向速度产生的波动越小。几何相似分级机模型环形区内径向速度分布符合点汇流动的规律,除了在靠近转笼外缘处径向速度数值有较大差异外,环形区其余位置柱面面积加权平均径向速度不随比例因数变化而变化。以几何相似分级机模型数值模拟数据作为训练样本拟合分级机环形区内柱面面积加权平均切向速度和径向速度预测公式,并建立测试样本分级机模型对预测公式进行验证。柱面面积加权平均切向速度和径向速度预测值与模拟值的最大误差分别为3.5%和1.8%。此外,通过对几何相似涡流空气分级机模型环形区流场运动相似和动力相似分析,得出几何相似分级机模型流场具有相似性。     

竖直涡旋向对卧轮式分级机流场及性能影响

采用数值模拟方法对卧轮式分级机内气相流动特性进行了研究,重点考察了竖直涡旋向对分级机内全流场的影响。模拟结果表明,分级机锥体段以旋转上升的竖直涡为主流型,竖直涡旋向对分级室内流型有重要影响。根据右手定则,竖直涡旋向与转笼旋向满足象限Ⅰ和Ⅲ时,分级室内形成两股旋向相反的水平涡,局部出现二次涡流,转笼外缘气流切向速度接近为0;竖直涡旋向与转笼旋向满足象限Ⅱ或Ⅳ时,分级室内流场分布一致性较好,转笼外缘及叶片间速度分布比较均匀且波动较小。以流化催化裂化(FCC)催化剂为分级物料,处于象限Ⅳ的分级机其分级粒径平均减少5.3?m,分级精度平均提高7.5%;以粉煤灰为物料,分级粒径平均减少2.2?m,分级精度平均提高8.4%,粉料分级试验结果与数值模拟结果吻合。研究结果对卧轮式分级机的结构设计有一定指导作用。     

Insect antifeedant properties of anthranoids from the genusVismia

Vismiones and ferruginins, representatives of a new class of lypophilic anthranoids from the genusVismia were found to inhibit feeding in larvae of species ofSpodoptera, Heliothis, and inLocusta migratoria.     

Direct observation of freeze-thaw instability of latex coatings via high pressure freezing and cryogenic SEM

Despite its industrial importance, the subject of freeze-thaw (F/T) stability of latex coatings has not been studied extensively. There is also a lack of fundamental understanding about the process and the mechanisms through which a coating becomes destabilized. High pressure (2100 bar) freezing fixes the state of water-suspended particles of polymer binder and inorganic pigments without the growth of ice crystals during freezing that produce artifacts in direct imaging scanning electron microscopy (SEM) of fracture surfaces of frozen coatings. We show that by incorporating copolymerizable functional monomers, it is possible to achieve F/T stability in polymer latexes and in low-VOC paints, as judged by the microstructures revealed by the cryogenic SEM technique. Particle coalescence as well as pigment segregation in F/T unstable systems are visualized. In order to achieve F/T stability in paints, latex particles must not flocculate and should provide protection to inorganic pigment and extender particles. Because of the unique capabilities of the cryogenic SEM, we are able to separate the effects of freezing and thawing, and study the influence of the rate of freezing and thawing on F/T stability. Destabilization can be caused by either freezing or thawing. A slow freezing process is more detrimental to F/T stability than a fast freezing process; the latter actually preserves suspension stability during freezing. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27–29, 2004 in Chicago, IL. Tied for first place in The John A. Gordon Best Paper Competition.     

Ethanol and (−)-α-Pinene: Attractant Kairomones for Bark and Ambrosia Beetles in the Southeastern US

In 2002–2004, we examined the flight responses of 49 species of native and exotic bark and ambrosia beetles (Coleoptera: Scolytidae and Platypodidae) to traps baited with ethanol and/or (−)-α-pinene in the southeastern US. Eight field trials were conducted in mature pine stands in Alabama, Florida, Georgia, North Carolina, and South Carolina. Funnel traps baited with ethanol lures (release rate, about 0.6 g/day at 25–28°C) were attractive to ten species of ambrosia beetles (Ambrosiodmus tachygraphus, Anisandrus sayi, Dryoxylon onoharaensum, Monarthrum mali, Xyleborinus saxesenii, Xyleborus affinis, Xyleborus ferrugineus, Xylosandrus compactus, Xylosandrus crassiusculus, and Xylosandrus germanus) and two species of bark beetles (Cryptocarenus heveae and Hypothenemus sp.). Traps baited with (−)-α-pinene lures (release rate, 2–6 g/day at 25–28°C) were attractive to five bark beetle species (Dendroctonus terebrans, Hylastes porculus, Hylastes salebrosus, Hylastes tenuis, and Ips grandicollis) and one platypodid ambrosia beetle species (Myoplatypus flavicornis). Ethanol enhanced responses of some species (Xyleborus pubescens, H. porculus, H. salebrosus, H. tenuis, and Pityophthorus cariniceps) to traps baited with (−)-α-pinene in some locations. (−)-α-Pinene interrupted the response of some ambrosia beetle species to traps baited with ethanol, but only the response of D. onoharaensum was interrupted consistently at most locations. Of 23 species of ambrosia beetles captured in our field trials, nine were exotic and accounted for 70–97% of total catches of ambrosia beetles. Our results provide support for the continued use of separate traps baited with ethanol alone and ethanol with (−)-α-pinene to detect and monitor common bark and ambrosia beetles from the southeastern region of the US.     

Methyl 2,4,6-decatrienoates Attract Stink Bugs and Tachinid Parasitoids

Halyomorpha halys (Stål) (Pentatomidae), called the brown marmorated stink bug (BMSB), is a newly invasive species in the eastern USA that is rapidly spreading from the original point of establishment in Allentown, PA. In its native range, the BMSB is reportedly attracted to methyl (E,E,Z)-2,4,6-decatrienoate, the male-produced pheromone of another pentatomid common in eastern Asia, Plautia stali Scott. In North America, Thyanta spp. are the only pentatomids known to produce methyl 2,4,6-decatrienoate [the (E,Z,Z)-isomer] as part of their pheromones. Methyl 2,4,6-decatrienoates were field-tested in Maryland to monitor the spread of the BMSB and to explore the possibility that Thyanta spp. are an alternate host for parasitic tachinid flies that use stink bug pheromones as host-finding kairomones. Here we report the first captures of adult and nymph BMSBs in traps baited with methyl (E,E,Z)-2,4,6-decatrienoate in central Maryland and present data verifying that the tachinid, Euclytia flava (Townsend), exploits methyl (E,Z,Z)-2,4,6-decatrienoate as a kairomone. We also report the unexpected finding that various isomers of methyl 2,4,6-decatrienoate attract Acrosternum hilare (Say), although this bug apparently does not produce methyl decatrienoates. Other stink bugs and tachinids native to North America were also attracted to methyl 2,4,6-decatrienoates. These data indicate there are Heteroptera in North America in addition to Thyanta spp. that probably use methyl 2,4,6-decatrienoates as pheromones. The evidence that some pentatomids exploit the pheromones of other true bugs as kairomones to find food or to congregate as a passive defense against tachinid parasitism is discussed.     

2007～2008年世界塑料工业进展

收集了2007年7月～2008年6月世界塑料工业的相关资料,介绍了2007～2008年国外塑料工业的发展情况,提供了世界塑料产量、消费量及全球各类树脂的需求量及产能情况.按通用热塑性树脂(聚乙烯、聚丙烯、聚苯乙烯、聚氯乙烯、ABS树脂)、工程塑料(尼龙、聚碳酸酯、聚甲醛、热塑性聚酯、聚苯醚)、特种工程塑料(聚苯·硫醚、液晶聚合物、聚醚醚酮)、通用热固性树脂(酚醛、聚氨酯、不饱和聚酯树脂、环氧树脂)不同品种的顺序,对树脂的产量、消费量、供需状况及合成工艺、产品应用开发、树脂品种的延伸及应用的进一步扩展等技术作了详细介绍.     

2005～2006年国外塑料工业进展

收集了2005年7月～2006年6月国外塑料工业的相关资料,介绍了2005—2006年国外塑料工业的发展情况。提供了世界塑料产量、消费量及全球各类树脂生产量以及各国塑料制品的进出口情况。作为对比,介绍了中国塑料的生产情况。按通用热塑性树脂（聚乙烯、聚丙烯、聚苯乙烯、聚氯乙烯、ABS树脂）、工程塑料（聚酰胺、聚碳酸酯、聚甲醛、热塑性聚酯、聚苯醚）、通用热固性树脂（酚醛、聚氨酯、不饱和树脂、环氧树脂）、特种工程塑料（聚苯硫醚、液晶聚合物、聚醚醚酮）的品种顺序,对树脂的产量、消费量、供需状况及合成工艺、产品开发、树脂品种的延伸及应用的扩展作了详细的介绍。