偏心双桨搅拌流场及效果分析

生产工艺中需要聚苯乙烯粒子在液相苯乙烯中均匀悬浮与混合,要求底部固相不堆积,固相浓度分布均匀。为了达到理想的搅拌效果,本文研究了双桨的偏心率及转速对搅拌混合效果的影响。以底部椭圆封头,无挡板的反应釜和双层6折叶的开启涡轮式搅拌器为研究对象,用Fluent软件对搅拌器偏心时水的搅拌流场及聚苯乙烯粒子-苯乙烯固液搅拌进行数值模拟。模拟了不同偏心率和转速对搅拌流型、聚苯乙烯粒子浓度分布及能耗的影响,并用粒子图像测速法(PIV)实验验证水的搅拌流场。结果表明,偏心搅拌可使流体速度得到增加,桨叶下方的搅拌死区得到有效抑制;偏心率增大导致两侧的速度偏差越来越大,能量分布不均匀;偏心搅拌的聚苯乙烯粒子浓度分布比对中搅拌的更为均匀,可改善粒子在苯乙烯中的悬浮效果;相同搅拌效果的情况下,偏心率为0.15的功率消耗是对中搅拌的85%;对该固液搅拌时的最佳偏心率和最佳转速分别为0.15和95 r/min,此时固液搅拌混合效果最好,固相浓度分布最为均匀,消耗功率相对较少。     

固-液导流筒搅拌槽内流体流动和颗粒悬浮特性

在直径0.8 m的导流筒搅拌槽内,对单相液体的三维速度分布、固-液两相的固体颗粒浓度分布和离底悬浮特性进行了系统的实验研究. 结果表明,导流筒内外的轴向液相速度远大于径向和切向速度,导流筒外壁附近存在一个与主体轴向流动方向相反的二次流区域;搅拌槽底部结构对固体颗粒的临界离底悬浮转速(NJS)有显著的影响,浅锥底的NJS比平底的低14%以上;NJS随固相浓度的增加而增加,但当浓度超过50%时,NJS略有降低;槽内固相浓度分布的均匀性随固相浓度的增加而得到改善. 本研究结果对导流筒搅拌槽的优化设计具有一定的指导意义.     

高固含搅拌槽内临界离底悬浮转速的数值模拟

使用计算流体软件CFX5.5.1对固液搅拌槽内颗粒的临界离底悬浮转速进行了数值模拟. 搅拌槽直径D=0.476 m,搅拌桨为三叶CBY螺旋桨. 桨叶安装高度h=D/3. 固液两相为玻璃珠-水,固体体积浓度为15%~50%. 对临界离底悬浮的速度判据进行了修正,并利用浓度判据与修正的速度判据得到颗粒临界离底悬浮转速Njs,模拟计算结果与实验数据的误差在工业允许的范围内. 同时,对临界离底悬浮状态槽底部不同浓度下的流体湍流动能的分布情况以及大小进行了预测,并对2种固体临界离底悬浮机理进行了验证.     

烟气脱硫吸收塔底部浆液池内流场特性的数值模拟

为了达到烟气脱硫吸收塔内烟气、吸收液和析出铵盐三相混合的效果,烟气脱硫吸收塔都采用侧入式的推进式搅拌器.运用计算流体力学技术(CFD)对吸收塔底部浆液池内单相和液固两相的侧搅拌流场进行数值模拟.模拟结果表明,液固两相搅拌时,与单相流相比,固相的引入抑制了液体向上的发展,流体循环流动范围变小.径向角作用是产生不对称的循环流,增加流体湍动,但对液固两相的固体悬浮状况没有明显改善.法向角可以改善浆液池底部单相流的湍动和液固两相的固体悬浮,当法向角为7°时,浆液池内固体颗粒的悬浮状态最好.     

搅拌槽内固液悬浮和气液分散的实验研究

在实验室提出的新型三相搅拌槽——自吸式龙卷流型搅拌槽中,采用六直叶圆盘涡轮桨进行三相混合性能的实验。从固液悬浮、气液分散和传质性能等方面对搅拌槽进行了研究,探讨了固相颗粒对气含率和传质性能的影响,得到了搅拌槽中不同性能参数的变化规律。结果表明:自吸式龙卷流型搅拌槽作为一种新型的三相搅拌槽,能够获得良好的固液悬浮和气液分散效果;当搅拌槽内固相体积分率较低(φ<20%)时,可采用颗粒的壁面堆积高度作为完全悬浮状态的判定标准;固相颗粒的存在会使气含率明显降低,但对传质性能的影响较为复杂,φ<5%时的体积传氧系数K L a高于纯溶液,φ>5%时的K L a低于纯溶液,但都随固相体积分率的增加而降低。     

搅拌槽内固液悬浮和气液分散的实验研究

在实验室提出的新型三相搅拌槽——自吸式龙卷流型搅拌槽中,采用六直叶圆盘涡轮桨进行三相混合性能的实验。从固液悬浮、气液分散和传质性能等方面对搅拌槽进行了研究,探讨了固相颗粒对气含率和传质性能的影响,得到了搅拌槽中不同性能参数的变化规律。结果表明:自吸式龙卷流型搅拌槽作为一种新型的三相搅拌槽,能够获得良好的固液悬浮和气液分散效果;当搅拌槽内固相体积分率较低(φ20%)时,可采用颗粒的壁面堆积高度作为完全悬浮状态的判定标准;固相颗粒的存在会使气含率明显降低,但对传质性能的影响较为复杂,φ5%时的体积传氧系数K L a高于纯溶液,φ5%时的K L a低于纯溶液,但都随固相体积分率的增加而降低。     

偏心搅拌反应器内的液相混合行为

利用先进的无干扰流场测试手段——平面激光诱导荧光技术(PLIF),对斜叶桨搅拌反应器内的液相混合过程进行高精度定量可视化。对比了中心搅拌和3种不同偏心率下的偏心搅拌混合行为,引入参数混合均匀度和均匀混合时间定量描述测量平面的示踪剂浓度分布。研究发现,偏心搅拌过程由于破坏了流场的对称性,比中心搅拌能更快达到均匀混合。反应器内局部混合存在差异,偏心搅拌中不同监测点达到均匀混合时间差异较小,体现了偏心搅拌在液相混合中的优势。     

无挡板搅拌槽中液－固体系的分散特性

在内径0.3 m、高0.45 m的无挡板搅拌槽内,采用直径0.15 m的三叶70o下推斜叶透平桨(PBTD, Pitched Blade Turbine Downflow)进行水-二氧化硅两相体系液固分散特性的研究. 应用PC-6A粉体浓度测量仪对体系中颗粒局部浓度进行测定. 考察了颗粒平均相含率为0.005的条件下,不同搅拌转速、搅拌桨离底高度对颗粒局部浓度分布的影响. 结果表明,采用较高搅拌转速、较低的搅拌桨离底高度有利于固体颗粒的悬浮. 本实验中,在搅拌转速为173 r/min、搅拌桨离底高度为0.08 m的操作条件下,颗粒悬浮效果最好.     

偏心搅拌槽内宏观不稳定性的分离涡模拟

为研究偏心搅拌槽内的宏观不稳定性,基于分离涡模型建立了偏心搅拌数值模拟方法。采用滑移网格法模拟搅拌桨的旋转,实现了偏心搅拌流场的非稳态模拟。对不同工况时的宏观不稳定性进行了频谱分析,讨论了偏心率、雷诺数和桨径比对宏观不稳定频率的影响,并进行了PIV实验验证。研究表明,偏心搅拌槽内存在明显的宏观不稳定现象,其变化周期约为桨叶通过周期的10倍;PIV实验结果与分离涡模拟结果吻合较好,都表明偏心搅拌槽内的宏观不稳定频率随雷诺数的升高而增大,随偏心率的增大而减小,随桨径比的增大而增大。     

搅拌釜内液固悬浮体系的浓度分布

在120°锥底、内径为φ700mm、φ250mm 的有机玻璃釜中,采用直接取样称重法研究了液固系搅拌釜内桨的结构、桨的位置及转速、固含量、物系性质等因素对釜内固相浓度分布的影响,同时用两区沉降扩散模型对实验数据进行分析,得到了固相悬浮质量与操作条件的关系,并提出了均匀悬浮的判据,为放大设计搅拌反应器提供了可行的理论依据。     

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。