文丘里管内空泡云溃灭的压力与边界的数值模拟

The idea that the collapse proceeds from the outer boundary of the cavity cloud towards its center for the ultrasonic cavitation proposed by Hasson and Morch in 1980s is further developed for calculating the collapse pressure and boundaries of cavity cloud at the collapse stage of bubbles for hydraulic cavitation flow in Venturi in present research. The numerical simulation is carried out based on Gilmore’s equations of bubble dynamics, which take account of the compressibility of fluid besides the viscosity and interfacial tension. The collapse of the cavity cloud is considered to proceed layer by layer from the outer cloud towards its inner part. The simulation results indicate that the predicted boundaries of the cavity cloud at the collapse stage agree well with the experimental ones. It is also found that the maximum collapse pressure of the cavity cloud is several times as high as the collapse pressure of out-side boundary, and it is located at a point in the axis, where the cavity cloud disappears completely. This means that a cavity cloud has higher collapse pressure or strength than that of a single bubble due to the interactions of the bubbles. The effects of operation and structural parameters on the collapse pressure are also analyzed in detail.     

基于精细自由基反应机理的丙烷裂解炉炉管CFD模拟(英文)

In the radiant section of cracking furnace, the thermal cracking process is highly coupled with turbulent flow, heat transfer and mass transfer. In this paper, a three-dimensional simulation of propane pyrolysis reactor tube is performed based on a detailed kinetic radical cracking scheme, combined with a comprehensive rigorous computational fluid dynamics（CFD） model. The eddy-dissipation-concept（EDC） model is introduced to deal with turbulence-chemistry interaction of cracking gas, especially for the multi-step radical kinetics. Considering the high aspect ratio and severe gradient phenomenon, numerical strategies such as grid resolution and refinement, stepping method and relaxation technique at different levels are employed to accelerate convergence. Large scale of radial nonuniformity in the vicinity of the tube wall is investigated. Spatial distributions of each radical reaction rate are first studied, and made it possible to identify the dominant elementary reactions. Additionally, a series of operating conditions including the feedstock feed rate, wall temperature profile and heat flux profile towards the reactor tubes are investigated. The obtained results can be used as scientific guide for further technical retrofit and operation optimization aiming at high conversion and selectivity of pyrolysis process.     

齿边浮阀塔内气相流场的数值模拟和分析

A three-dimensional computational fluid dynamics （CFD） model for gas flow through a serrated valve tray was presented. The flow field, as well as the dry-pressure drop of the valve under the full-opening condition was simulated based on the proposed model by using FLUENT 6.0 software. Compared with the values of dry-pressure dro.p in different turbulent models, the.simulated.results using RNG κ-ε model are in reasonable agreement with experimental data, indicating that RNG κ-ε model is suitable in simulating gas flow through the serrated valve tray. Then the CFD model combining RNG κ-ε model was used to study the three-dimensional gas flow through the considered serrated valve tray. The simulated results showed that various eddies existed on the serrated valve tray, and both the eddy and the non-eddy areas were nearly equal. The existence of addendum can decrease the eddy area caused by gas passing through the lateral outlet slots. The size of eddies can be reduced by optimizing the distance between valves.     

用数值模拟方法分析混合和导流筒对搅拌槽中沉淀硫酸钡的影响

1 INTRODUCTION Precipitation of sparingly soluble salts is an im- portant operation widely adopted in the production of functional materials, catalyst, protein, pharmaceutical product and pigment. By precipitation, two aqueous streams containing respective reactants are mixed in a precipitator, and the sparingly soluble salt forms as result of chemical reaction if the concentration of produced salt exceeds its solubility. The quality of the final product obtained by precipitation is strong…     

水力空化强度与空化自由基产量的关系

利用空化释放出的能量对过程进行强化是能量利用的新途径。定量分析空化引发·OH产量与空化强度的关系,对研究空化对过程的强化效应有着十分重要的意义。以亚甲基蓝作为羟自由基捕捉剂,利用紫外-可见分光光度法,间接测定了水力空化产生的·OH产量。分析了管路上游压力、液体温度、空化作用时间等宏观参数对自由基产量的影响,以及自由基产量与空化强度的关系,寻求出有利于空化发生以及提高空化作用强度的适宜操作条件。     

Chemical effect of hydrodynamic cavitation: Simulation and experimental comparison

The chemical effect of hydrodynamic cavitation (HC) in a Venturi reactor from both the theoretical and the experimental point of view is dealt. A mathematical model is presented to simulate the global production of hydroxyl radicals; it is based on a set of ordinary differential equations that account for the hydrodynamics, mass diffusion, heat exchange, and chemical reactions inside the bubbles. Experimentally, the degradation of p‐nitrophenol (initial concentration 0.15 g dm^?3) has been conducted in a lab scale Venturi reactor at inlet pressure ranging from 0.2 to 0.6 MPa and has been used to estimate the hydroxyl radical production. The optimum configuration, suggested by numerical simulations, has been experimentally confirmed. Thanks to the empirical validation, this novel modeling approach can be considered as a theoretical tool to identify the best configuration of HC operating parameters. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2566–2572, 2014     

空化射流流场数值模拟的研究进展

空化射流因具有高效能、无污染等优点而被广泛应用,但是由于其流场结构和水动力学性能过于复杂,使得对其的应用受到限制,为进一步认识和研究空化射流流场特性,对空化射流数值模拟过程中的空化模型、数值计算方法和流场特性影响因素的研究进行了综合论述.阐述了数值模型中不同的空化模型、湍流模型和多相流模型各自的特点、适用条件及存在的问题;对比分析了拉格朗日和欧拉数值计算方法在空化射流模拟中的应用,以及空化射流自身特点对计算方法的要求;对空化射流流场特性的影响因素研究情况进行了综合概述,使复杂的空化射流流场结构有更加清晰的表现,为以后的研究与应用提供了依据.通过以上论述,对目前空化射流数值模拟研究进展中存在的问题进行了分析,并根据所提出的问题,对以后的研究方向提出展望,有助于以后在空化射流流场的数值模拟研究中取得进展.     

CFD simulation of acoustic cavitation in a crude oil upgrading sonoreactor and prediction of collapse temperature and pressure of a cavitation bubble

In acoustic cavitation, high pressure and temperature are generated due to cavitation bubble collapse in the liquid bulk around the bubble which causes physical and chemical changes in the liquid. In this study, pressure distribution in water caused by ultrasonic wave propagation in a sonoreactor was investigated. Active cavitation zones were determined by calculating acoustic pressure threshold for cavitation inception and compared with experimental results. Collapse pressure and temperature were predicted 3000 atm and 3200 K, respectively, for crude oil at temperature of 25 °C by evaluating cavitation bubble dynamics in the exerted acoustic field. As a consequence, the huge amounts of energy generated by this phenomenon can be applied for changes in oil properties and crude oil upgrading.     

对《茜素紫光度法检测H2O2/Co2+产生的羟自由基》一文中自由基清除率计算公式的刍议

提出对《茜素紫光度法检测H2O2／Co^2 产生的羟自由基》一文中自由基清除率计算公式的修改,并探讨公式适应范围。实验发现该文中的公式有疏忽,按原公式计算结果和其他文献对相同物质维生素C清除羟自由基的结果有差异。故对原公式提出修改,并提出有颜色的抗氧化剂适用公式。     

羟基自由基对全钒液流电池石墨毡电极的性能影响

采用H2SO4和H2O2的分解产物羟基自由基,对石墨毡电极进行表面处理。循环伏安法和交流阻抗测试显示,处理后石墨毡的阴阳极峰电流分别提高160.96%和120.24%,极化反应电阻从74.95 Ω·cm2显著降低至18.92 Ω·cm2。红外光谱测试表明石墨毡处理后表面含有大量含氧亲水基团,拉曼光谱测试结果显示处理后石墨毡的石墨化度降低,进一步证明了石墨毡电极表面受到了不同程度的氧化。X射线光电子能谱测试显示石墨毡处理后的含氧量提高0.58%,定量地证明了红外光谱和拉曼光谱的测试结果。采用自制静态单电池对石墨毡电极进行测试,处理后石墨毡的充放电容量分别提高37.04%和22.22%,表明该方法处理石墨毡电极能够显著提高全钒液流电池性能。     

羟基自由基活性氧用于中水处理

羟基自由基在液相中的氧化电势为2.8 V,能够破坏微生物通透性屏障,破坏病原微生物的蛋白质、酶和核酸,导致病原微生物的死亡.在现场进行的中水灭菌实验中,当药剂质量浓度为38.2 g/L,投加量为O.14 kg/t时,大肠杆菌杀灭率可达到99.9%以上.同时,水体中的COD降低50%、NH3-N降低35%.羟基自由基制备原料为空气、水和电解质溶液,在常温常压条件下进行,无三废排放,兼具安全性和环境友好性.实践证明:它是替代氯气消毒的优选消毒品种.     

Peroxyl and hydroxyl radical scavenging activity of some natural phenolic antioxidants

The autoxidation of linoleic acid dispersed in an aqueous media and the antioxidant effect of hydroxytyrosol, oleuropein, caffeic acid and tyrosol were studied. Linoleic acid autoxidation rate was estimated by the increase of conjugated diene level and by the decrease of linoleic acid content in the samples. The phenolic compounds exhibited an antioxidant activity which increased in the order: tyrosol < caffeic acid < oleuropein < hydroxytyrosol. The analysis of the hydroperoxide isomers pointed out that hydroxytyrosol, oleuropein and caffeic acid at a concentration of 10⁻⁴M inhibited the formation oftrans- trans isomers in the increasing order: caffeic acid < oleuropein < hydroxytyrosol. This inhibition could be related to the ability of phenolic compounds to scavenge peroxyl radical. Tyrosol did not inhibit the formation oftranstrans isomers. Phenolic compounds were degraded as a consequence of their antioxidant activity and their degradation rate was positively correlated to their antioxidant efficacy. These phenolic compounds, at a concentration of 6 × 10⁻³M, also scavenged hydroxyl radical, with an efficiency which increased in the order: tyrosol < hydroxytyrosol < oleuropein < caffeic acid. Polar substituents at the para position, such as in caffeic acid and oleuropein, were correlated with higher hydroxyl radical quenching ability.     

电化学诱发羟基自由基降解水中酚类污染物

DMPO（5,5-dimethyl-1-pyrroline-N-oxide）为自旋捕集剂,采用电子自旋共振技术（electron spin resonance spectroscopy,ESR）直接证实了经氟树脂改性的β PbO₂阳极和不锈钢网阴极构成的电化学体系中产生的羟基自由基（·OH）。通过电化学氧化水中含酚类及其前驱体污染物,发现环状结构化合物受电化学产生的羟基自由基攻击而发生开环反应产生易生物降解的有机酸,如反丁烯二酸和草酸,直至完全矿化为CO₂和水分子,苯醌是酚类污染物开环前产生的共同稳态中间体。该类污染物的电化学降解共性规律为电化学氧化技术的工业化应用和提高其处理工艺的经济性提供了理论依据。     

三维液氮空化的大涡模拟和机理

以三维扭曲翼型（Twist-11N）为研究对象,基于大涡（LES）湍流模型开展了三维液氮空化的数值模拟。通过压力波动曲线得到了液氮空化的空泡脱落周期,观察周期内空泡脱落的过程,与常温空化的数值模拟结果对比,得出了低温空化具有脱落更彻底、过程更复杂的特性。从压力分布和气相云图观察到了三维模拟特有的尾部回射流和侧面射流,分析了三维空化不同于二维的独特性。从涡旋角度分析了空泡脱落与流场的关系,认为空化的发生首先导致了流场的不稳定和涡旋的产生,而涡旋的发展造成了流场边界层分离和空泡的脱落。