扰流子式空气预热器振动原因分析及解决措施

扰流子式空气预热器试运行时产生强烈振动,文章对扰流子式空气预热器产生震动的原因进行了分析,指出卡门涡流是预热器产生振动的主要原因,因为当气流横向绕流管束时,卡门涡流的交替脱落会引起扰流子式空气预热器中气柱的振动。当漩涡的脱落频率与管箱的声学驻波振动频率接近或一致时,会诱发强烈的管箱声学驻波振动,造成扰流子式空气预热器管箱的共振。卡门涡流所引发的共振,是预热器产生强振的主要原因,要避免预热器产生共振,必须改变传热管的卡门涡流频率,使之与气室固有频率不会重合。     

塔器设计中的横风向振动

塔器振动事故时有发生,从塔器设计者的角度出发,依据标准规范,结合工程实践,对塔器设计中碰到的横风向振动(诱导振动)提出了多种减振和防振措施。     

并排塔器的横风向激振特性与非光滑表面减振

随着化工设备集约化,并排塔器因大幅横风向振动而发生破坏的现象时常发生,然而各塔器间的耦合机制复杂,少有报道。为了解决这一问题,本文应用弹性支撑的刚性截断模型模拟并排塔器的横风向振动,开展了风洞实验,深入分析了并排塔器的横风向激振特性;设计了一种微型翅片,通过调整尺寸参数达到了最佳减振效果。研究结果表明,并排塔器的横风向激振可按照间距比范围分为三种典型振动状态,即单钝体模式、剪切层再附着模式和共同脱涡模式。当间距比S/D<2时,上游塔器在较小的折合流速下即发生驰振,且与下游塔器存在能量转化,在工程中应予以避免。当微型翅片的厚度参数大于0.1D及长度参数大于0.9D时,微型翅片的减振效果最佳,可以防止尾流驰振,使并排塔器的横风向振幅减小78.63%~95.67%。     

粘弹性阻尼器在联合塔器中的减振研究

将土木建筑领域应用广泛的粘弹性阻尼器用于联合塔器,以期减振。设计了联合塔器小试实验模型,得出了附加刚度对联合塔器固有频率和阻尼比的影响规律,与单塔相比,联合塔器固有频率增大70%以上,阻尼比显著增加;同时建立了等效有限元模型,以共振振幅和共振频率为主要判定准则,探究粘弹性阻尼器参数和安装高度对联合塔器减振效果的影响规律,与单塔相比,安装粘弹性阻尼器的联合塔器共振振幅可减小70%以上。     

塔底强制循环泵入口管道防振设计

130kt／a丙烯酸及酯装置分馏塔塔底物料出口至泵入口的管线振动,管内流体的频率和管道结构的固有频率相近是产生振动的原因。提高管道结构的固有频率,使管内流体的频率和管道结构的固有频率错开,可避免管道振动。设计了调整管道元件分布和增加减振系统两种方案,比较确定更加合理的方案。选用增加减振系统方案,方案实施后,管线没有发生振动现象。     

流体流动对筛板稳定性的影响

近年来塔内流致振动诱发的塔板损坏的现象引起了人们的关注,塔板在连接处所发生的螺栓脱落乃至进一步的塔板坍塌对整个生产的效率有很大的影响。采用实验的方法研究了筛孔气速、液体流量、溢流堰高度等参数对塔板振动的影响。实验采用空气-水二相体系,在600 mm有机玻璃塔内水和空气错向流动,接触状态为常压精馏中较为多见的混合泡沫态。实验利用动态应变仪对塔板中心附近径向应变进行测试,然后通过快速傅里叶变换分析其振动特性。结果表明:在混合泡沫态的操作工况下,塔板的振动频率值随筛孔气速的增加而变大,随溢流堰高度的增加而减小,而塔内液体流量对振动频率的影响较小;操作工况偏离正常范围时,可能导致塔板发生较大振动和塑性变形。实验结果为研究流致振动下塔板的破坏提供了一定的依据,为后续工业效率的提高和工作环境的改善奠定了基础。     

连铸结晶器漩涡现象的物理模拟

利用物理模型考察了操作参数对结晶器内漩涡产生频率的影响. 结果表明: 漩涡呈单个或成对形式在水口一侧间歇性出现,是由于两个相向表面流相互剪切而形成的;漩涡的出现频率随拉速的增加而增加,随水口浸入深度的增加而减小,随水口张角的减小而增大;通过改进水口设计可以阻止漩涡的形成.     

振动特性对中空纤维膜组件管外传质的影响

为提高中空纤维膜组件的传质效率,减轻浓差极化,运用计算流体力学软件Fluent动网格技术,以含氧水的除氧过程为研究对象,研究了振动特性对中空纤维膜组件管外传质的影响。研究结果表明:与静止的工况相比,振动能够使流体产生二次流,使得流动从层流转化为紊流,增强流体与膜组件以及中空纤维管壁面的碰撞,极大程度地减轻浓差极化现象,进而强化传质;随着振动频率和振幅的增大,膜组件出口处氧质量浓度降低,水中氧的清除率增大,传质效果变好;一定条件下振动工况比静止工况氧的清除率最高可以提高144%,固定振幅为6 mm振动频率从2.5 Hz增加到10 Hz时清除率提高76%;固定频率为2.5 Hz振幅由2 mm增加到6 mm时清除率提高10%,增大振动频率对于强化传质的效果要好于增大振幅。研究结果可以为实际的工程应用提供理论指导。     

流速对圆柱绕流旋涡脱落的分析

本论文应用CFD方法数值模拟了绕流中最为经典的绕流问题即圆柱绕流问题。在不同雷诺数下的,卡门涡街的变化情况。研究了不同振幅和振动频率下的流场结构、涡脱落模态和一些重要流动参数的关系并通过速度参数图、压力等值线图展示。本文计算分析流向振荡圆柱绕流中涡脱落方式,结果表明:随着雷诺数Re的增加,相对圆柱绕流脱落增大。     

气量无级调节系统在运行中的问题分析及改进

往复式压缩机上增加了气量无级调节系统后,先后出现压缩机进气管道最远端和进口处管道振动,通过对现场振动现象和对气量无级调节系统工作原理的分析,采取了一些减振措施,最终解决振动问题。     

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.     

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.     

Many Drugs of Abuse May Be Acutely Transformed to Dopamine,Norepinephrine and Epinephrine In Vivo

It is well established that a wide range of drugs of abuse acutely boost the signaling of the sympathetic nervous system and the hypothalamic–pituitary–adrenal (HPA) axis, where norepinephrine and epinephrine are major output molecules. This stimulatory effect is accompanied by such symptoms as elevated heart rate and blood pressure, more rapid breathing, increased body temperature and sweating, and pupillary dilation, as well as the intoxicating or euphoric subjective properties of the drug. While many drugs of abuse are thought to achieve their intoxicating effects by modulating the monoaminergic neurotransmitter systems (i.e., serotonin, norepinephrine, dopamine) by binding to these receptors or otherwise affecting their synaptic signaling, this paper puts forth the hypothesis that many of these drugs are actually acutely converted to catecholamines (dopamine, norepinephrine, epinephrine) in vivo, in addition to transformation to their known metabolites. In this manner, a range of stimulants, opioids, and psychedelics (as well as alcohol) may partially achieve their intoxicating properties, as well as side effects, due to this putative transformation to catecholamines. If this hypothesis is correct, it would alter our understanding of the basic biosynthetic pathways for generating these important signaling molecules, while also modifying our view of the neural substrates underlying substance abuse and dependence, including psychological stress-induced relapse. Importantly, there is a direct way to test the overarching hypothesis: administer (either centrally or peripherally) stable isotope versions of these drugs to model organisms such as rodents (or even to humans) and then use liquid chromatography-mass spectrometry to determine if the labeled drug is converted to labeled catecholamines in brain, blood plasma, or urine samples.     

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.     

Novel polyurethane coating technology through glycidyl carbamate chemistry

Glycidyl carbamate chemistry combines the excellent properties of polyurethanes with the crosslinking chemistry of epoxy resins. Glycidyl carbamate functional oligomers were synthesized by the reaction of polyfunctional isocyanate oligomers and glycidol. The oligomers were formulated into coatings with several amine functional crosslinkers at varying stoichiometric ratios and cured at different temperatures. Properties such as solvent resistance, hardness, and impact resistance were dependent on the composition and cure conditions. Most coatings had an excellent combination of properties. Studies were carried out to determine the kinetics of the curing reaction of the glycidyl carbamate functional oligomers with multifunctional and model amines. Detailed kinetic analysis of the curing reactions was also undertaken. The results indicated that the glycidyl carbamate functional group is more reactive than a glycidyl ether group. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, on October 27–29, 2004, in Chicago, IL.