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气泡的破裂行为能够直接改变相界面积与流场分布,进而对于多相反应器中的传递与反应过程产生重要影响。由于在湍流与气泡破裂机理以及数值模拟方法上仍存在诸多不足,目前针对湍流环境中自由运动的气泡破裂过程研究仍非常欠缺。作者分别在二维与三维数值模拟条件下,利用VOF模型研究了单气泡在典型射流场中的运动、形变与破裂过程,并通过高速摄像与PIV方法同步开展了实验研究。该研究对气泡破裂过程特别是破裂前后的形态、周围流场以及与气泡间的相互作用进行了分析。结果表明,该流场条件下液相的剪切作用是气泡破裂的主要影响因素;由于二维模拟可以使用精度更高的网格,对于气泡形变与破裂过程中的界面变化模拟相对精确,而三维模拟对于流场整体结构的模拟更接近PIV实验结果,而在气泡的扭曲变形还原方面误差相对较大。该研究对于实际破裂过程具有较好的参考价值,有助于加深多相流体力学认识,为相关多相反应器的设计与优化提供理论支撑。 相似文献
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对三种管口浸没方式下气泡生成行为过程进行可视化实验和三维数值模拟。对比分析了管口浸没方式、管口直径、气体流量等因素对气泡生成形态、气泡脱离直径、气泡膨胀脱离时间以及气液流场速度的影响。实验与数值模拟取得较为一致的结果。研究发现,气泡生成过程可分为单气泡生成和双气泡生成聚并两种模式,两者之间存在明显的气泡脱离形态转折点;三种管口浸没方式下,气泡脱离直径均随着管径和气体流量的增大而增大;气泡膨胀脱离时间随管径的增大而增加,而随气体流量的增加先急剧下降然后趋于平缓;在底吹和侧吹方式下,气泡长短轴比C值分别在0.75和1.1附近波动,其最终脱离形式均接近于球形;而顶吹方式下,C值在1.5附近波动,气泡脱离形态为椭球形。关键词:气液两相流;气泡;数值模拟;浸没方式;脱离直径 相似文献
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对三种管口浸没方式下气泡生成行为过程进行可视化实验和三维数值模拟。对比分析了管口浸没方式、管口直径、气体流量等因素对气泡生成形态、气泡脱离直径、气泡膨胀脱离时间以及气液流场速度的影响。实验与数值模拟取得较为一致的结果。研究发现,气泡生成过程可分为单气泡生成和双气泡生成聚并两种模式,两者之间存在明显的气泡脱离形态转折点;三种管口浸没方式下,气泡脱离直径均随着管径和气体流量的增大而增大;气泡膨胀脱离时间随管径的增大而增加,而随气体流量的增加先急剧下降然后趋于平缓;在底吹和侧吹方式下,气泡长短轴比C值分别在0.75和1.1附近波动,其最终脱离形式均接近于球形;而顶吹方式下,C值在1.5附近波动,气泡脱离形态为椭球形。 相似文献
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底吹气连铸中间包内气液两相流的数值模拟 总被引:5,自引:0,他引:5
以宝钢集团梅山钢厂1台连铸中间包为原型,进行底吹气中间包水模型研究. 实测结果表明,底吹气在中间包内形成"鼓泡流"形式的流动结构;"鼓泡流"的形成一方面能够破坏中间包内"层流"形式的短路流动,增强混合,另一方面能在中间包内形成"气幕挡墙",有利于夹杂物去除. 针对中间包内气-液两相"鼓泡流"特征,建立了底吹气中间包内气-液两相欧拉多流体模型,模型中考虑了气泡的存在对湍流增强的影响,考虑了相间滑移、气泡浮力及湍流分散力. 采用所建立的模型对底吹气中间包内气液两相流动和混合特性进行了模拟和分析,结果与水模型实测结果一致. 相似文献
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鼓泡塔气液两相流不同曳力模型的数值模拟 总被引:2,自引:0,他引:2
采用欧拉-欧拉双流体模型对圆柱形鼓泡塔内气液两相流动进行了三维数值模拟. 通过UDF自定义程序对气相出口边界进行了速度修正,解决了模拟中自由区域内有漩涡的问题;分别使用单一气泡尺寸模型和群体平衡模型(PBM)计算气泡尺寸,并比较其对气含率分布的预测结果,分别采用Schiller-Naumann, Grace和Tomiyama曳力系数模型进行模拟. 结果表明,在全塔径均匀进气的简化条件下,单一气泡尺寸模型不适用,在合适的Hamaker数下,PBM模型中原用于颗粒计算的Abrahamson模型可计算气泡聚并速率;Tomiyama曳力模型耦合PBM模型可更好地描述塔内流动情况,并与文献值吻合良好. Schiller-Naumann模型所得平均气含率与实验值相差约40%,而Grace模型所得湍动耗散比Tomiyama的结果高14.5%,气含率分布与文献值相差16.3%. 相似文献
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超临界CO2/PS微孔塑料挤出成型中成核数对气泡核自由长大的影响 总被引:5,自引:0,他引:5
以超临界CO2为发泡剂,研究了PS微孔塑料挤出成型中气泡核自由长大的机理,选用球形模型为表征气泡长大的物理模型,利用Dewitt本构方程、守恒定律和理想气体状态方程导出了气泡核自由长大阶段的数学模型。通过此数学模型着重对气泡成核数与气泡核自由长大平均半径之间的关系进行了数值模拟预测,并以实验验证了其正确性,结果表明:当其他加工条件不变时,增加气泡的成核数,气泡长大的平均半径将变小。因此,在制备微孔塑料时,我们可以通过增加气泡的成核数来改善制品的泡孔结构。 相似文献
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M. S. J. Simmonds W. M. Blaney F. Delle Monache M. Marquina Mac-Quhae G. B. Marini Bettolo 《Journal of chemical ecology》1985,11(12):1593-1599
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. 相似文献
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Cheng-Le Zhao Shane Porzio Alan Smith Haiyan Ge H. T. Davis L. E. Scriven 《Journal of Coatings Technology and Research》2006,3(2):109-115
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. 相似文献
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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. 相似文献
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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. 相似文献
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Peter A. Edwards Grant Striemer Dean C. Webster 《Journal of Coatings Technology and Research》2005,2(7):517-527
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. 相似文献