竖直流动沸腾滑移汽泡速度预测及运动机理

为了建立合理的机理模型,需要深入了解滑移汽泡的运动特征。文中通过对竖直流动沸腾下近壁滑移汽泡进行受力分析,建立了滑移汽泡动量守恒方程式,获得了近壁滑移汽泡的速度,并与Maity的实验数据进行了比较分析。模型预测结果表明,随着时间的延长,滑移汽泡的速度逐渐增大,但增大的趋势逐渐变缓慢;汽泡浮升时,滑移汽泡速度高于液相入口主流速度,表明该种情况下,曳力和附加质量力由促使汽泡滑移的动力变为阻力;当滑移汽泡速度大于当地液相速度时,剪切升力使得汽泡靠近壁面,而由于汽泡形状变化所产生的流体惯性力可能是汽泡从壁面浮升的动力。     

Investigation of the relationship between sliding process measurement and induction time test of low rank coal particles in the surfactant solutions

The induction time or sliding time can be used to characterize the hydrophobicity of mineral particles. In order to investigate the relationship between sliding process and induction time, the Induction Timer and high-speed camera technology were adopted in this study. It was found that the flotation recoveries of low rank coal particles increased with the surfactant concentration increase. Howerer, the analysis results of induction time and slip angle velocity indicated that the flotation performances of low rank coal were depressed by anion SDS surfactant. Therefore, the slip angle velocity results can be adopted to support the induction time measurements.     

Effect of insoluble amine on bubble surfaces on particle–bubble attachment in potash flotation

This study shows that in the potash flotation system, in which long‐chain amine collector appears in the form of colloidal particles, the hydrophobicity of sylvite surfaces critically depends on whether the amine is placed onto the solid surface or onto the surface of a bubble. The transportation of amine collector on the surface of bubbles was found to be beneficial for the bubble/KCl particle attachment.     

Hydrogen and Oxygen Bubble Attachment to a Bitumen Drop

Air bubble – bitumen attachment is a critical step in the flotation of bitumen from mined oil sand. In this study, single bubble – bitumen drop attachment was observed directly using a novel experimental technique. Induction time is determined and used as an indication of bubble‐bitumen attachment potency for both hydrogen and oxygen bubbles. The attachment tests were conducted in deaerated municipal water (City of Edmonton tap water) at temperatures ranging from 22–50°C. Induction times measured for hydrogen bubble attachment were shorter than those for oxygen bubbles. Coalescence tests were also conducted in the absence of bitumen, and showed that hydrogen bubbles coalesced more rapidly than oxygen bubbles in both deaerated municipal water and clear (solids‐free) process water.     

单气泡沿倾斜绝热表面运动特性的LBM方法研究

气泡沿斜面运动现象在工业生产中广泛存在,采用格子Boltzmann方法(LBM)研究单个气泡沿倾斜绝热表面的运动过程,考察气泡的初始直径、斜面倾角、Eotvos数(Eo)对气泡的变形和气泡形心与斜面垂直距离的影响,探讨相同初始直径的气泡沿斜面运动的稳定终态速度与倾角和Eo之间的关系。通过模拟得出气泡沿斜面的运动规律:斜面倾角越大,气泡前后端不对称性越大;气泡在上升过程中,形心轨迹与斜面保持平行;当倾角大于45°时,形心与斜面的垂直距离和Eo变化一致,当小于45°时,变化相反;相同初始直径气泡的稳定终态速度随倾角和Eo的增加而增加。     

Investigation of trajectory and rise velocity of loaded and bare single bubbles in flotation process using video processing technique

In flotation, among the key parameters that dictate the hydrodynamic characteristics are bubble rising velocity and trajectory. This study aims to investigate the trajectory and rise velocity of loaded and bare bubbles using an experimental setup and video processing technique. After acquiring the videos of rising bubbles, using the background subtraction algorithm, bubbles were detected and their rise velocity and trajectory were determined with regard to the changes in the coordinates of bubbles’ centers. It was shown that bare bubbles have a zigzag trajectory, while for loaded bubbles the trajectory was close to the straight vertical path. In addition, with increasing bubble size, the rise velocity and the deviation from the straight path increase.     

时空调控微柱表面浸润性强化单气泡沸腾换热

微结构耦合浸润性调控是目前强化核态沸腾换热的主要手段,针对水工质在单晶硅微柱表面的核态沸腾过程,采用CFD-VOF三维数值模拟方法,对比研究时间及空间分别调控表面浸润性对沸腾气泡动力学、相界面形变及传热性能的影响。结果表明：亲水性增强使得气泡界面曲率增大、合力增强,促使气泡的脱离;空间调控主要表现为增大气泡体积,时间调控则主要表现为优化气泡动力学过程,提高热流较大的生长阶段在整个气泡周期内的占比,从而强化换热;本实验工况下,空间梯度浸润表面以及在生长阶段提高壁面亲水性,均可大幅度提高单气泡沸腾换热性能,平均热流最大可提高42.7%;考虑微尺度下梯度浸润性加工难度,时间调控浸润性强化沸腾换热具有更好的发展前景。     

Experimental rapid surface heating by induction for micro‐injection molding of light‐guided plates

This work experimentally investigates the use of induction‐heating to heat mold surfaces rapidly, and thus enhance the replication effect of the microstructure of light‐guided plates (LGP) in the injection molding process. This investigation employs a 2‐inch LGP injection mold as the experimental carrier, and compares the replication effect on the microstructure of induction heating with that of conventional oil‐heating. Temperature increases on the mold plate are examined using a thermal video system. The experimental results show that (1) the flat induction coil design promotes rapid surface heating. (2) Induction‐heating the mold surface to 110°C improves the replication rate of the height of the micro‐structure by up to 95%. (3) The LGP produced by induction heating has no significant residual stress. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of immersion time and cationic latex nanoparticles concentration on flotation recovery

The influences of different concentrations of Polystyrene/Dodecyltrimethylammonium bromide latex nanoparticles and immersion times of mineral surfaces on flotation recovery have been investigated. Advancing water contact angle (θ_a) on the glass slides surfaces measured after conditioning them in different concentrations of diluted latex (0.028, 0.28, 0.56 g/L) at different immersion times (1, 10, 20, 30 min). Under these conditions, θ_a was changed between 29 and 105 degrees. The results showed that the concentrations of diluted latex as well as immersion time have important roles on the hydrophobic property of surfaces that covered with cationic latex nanoparticles.     

Mass‐transfer enhancement by a reversible chemical reaction across the interface of a bubble rising under Stokes flow

Mass transfer around a bubble rising in a liquid under Stokes regime is investigated when a reversible chemical reaction, , is taken into account. Four dimensionless parameters control the interfacial transfer rate: the Péclet and Damköhler numbers, the ratio of the diffusion coefficient of both species, and the reaction equilibrium constant. The mass‐transfer equations are solved numerically with a finite element technique. A boundary layer approach is also proposed and solved with a coupled technique of finite difference and Chebyshev‐spectral method. The equilibrium constant and the ratio of diffusion coefficients have a strong influence on the coupling between the chemical reaction and mass transfer leading to an increase of the Sherwood number. The interaction between the chemical reaction and advection is clearly established by the simulations. Conditions corresponding to Péclet number larger than the Damköhler number reduces the effect of the chemical reaction. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3376–3388, 2014     

Studies of dielectric characteristics and surface energies of spin‐coated polyimide films

A two‐step method, that is, polyamic acid formation with subsequent curing, was used to synthesize six kinds of polyimides. Dielectric constants and surface energies were investigated to determine the nature of the fluorinated and nonfluorinated polyimides. The dielectric constant decreased from 3.3 (at 100 kHz) for PMDA/ODA to 2.6 (at 100 kHz) for 6FDA/4,4′‐6F when the fluorine content increased from 0 to 30.7 wt %. Simultaneously, the water contact angle increased from 65° for PMDA/ODA to 78° for 6FDA/4,4′‐6F. Experimental results indicated that fluorinated polyimides contained a lower dielectric constant with improved water resistance. The surface energy values obtained from experiments agreed well with Holmes' correlation between surface energy and dielectric constant. The surface energies and dielectric constants were significantly affected by the polymer backbone structures, especially by the fluorination effect. Therefore, by choosing the appropriate monomers, polyimides of low dielectric constants with hydrophobic surfaces could be obtained. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1642–1652, 2001     

Formation of needle‐like lepidocrocite fine particles by oxidation of an aqueous suspension of ferrous hydroxide in a bubble column

Fine particles of needle‐like lepidocrocite (γ‐FeOOH) were synthesized by the oxidation of aqueous suspensions of ferrous hydroxide using a bubble column with draft tube at a constant temperature ranging from 20°C to 30°C. The oxidation steps leading to green rust (an intermediate) and lepidocrocite (final product), termed Step I and II, respectively, could be described apparently as first order, with respect to oxygen, and zero order, with respect to total ferrous species. When the concentration of oxygen in the feed stream was varied under a constant gas velocity, the mean size based on the major axis of needle‐like particle decreased from 0.60 to 0.35 μm with increasing oxidation rate. When the gas velocity was varied under a constant oxygen concentration, the particle size was almost independent of the oxidation rate and was equal to ca. 0.6 μm. By the addition of a small amount of sodium dihydrogenphosphate (NaH₂PO₄), the major axis could be reduced to 0.2 μm with the minor axis and the oxidation rate almost unchanged.     

Compositional Dependence of Wetting and Contact Angles in Solid‐Liquid‐Liquid Systems under Realistic Environments

The Dual Drop Dual Crystal (DDDC) contact angle measurement technique has been used in this study with a high‐pressure high‐temperature optical cell apparatus to measure dynamic contact angles in rock‐oil‐brine systems at realistic reservoir conditions of temperature and pressure. The experimental observations with live, stocktank, de‐asphalted and de‐resined crude oils indicate that the stability of oil, which determines the precipitation of asphaltenes for wettability alteration, is controlled by the entire oil composition. The ionic interactions caused by the brine composition and surface charged behaviour of rock substrates have been identified as another main mechanism that can affect wetting and contact angles in solid‐liquid‐liquid systems.     

Comparison of the performance of a direct-contact bubble reactor and an indirectly heated tubular reactor for solar-aided methane dry reforming employing molten salt

A theoretical approach is presented for the comparison of two different atmospheric pressure reactors—a direct-contact bubble reactor (DCBR) and an indirectly heated tubular reactor (IHTR)—to evaluate the reactor performance in terms of heat transfer and available catalytic active surface area. The model considers the catalytic endothermic reactions of methane dry reforming that proceeds in both reactors by employing molten salts at elevated temperatures (700–900 °C) in the absence of catalyst deactivation effects. The methane conversion process is simulated for a single reactor using both a reaction kinetics model and a heat transfer model. A well-tested reaction kinetics model, which showed an acceptable agreement with the empirical observations, was implemented to describe the methane dry reforming. In DCBR, the heat is internally transferred by direct contact with the three phases of the system: the reactant gas bubbles, the heat carrier molten salts and the solid catalyst (Ni-Al₂O₃). In contrast, the supplied heat in the conventional shell-and-tube heat exchanger of the IHTR is transferred across an intervening wall. The results suggest a combination system of DCBR and IHTR would be a suitable configuration for process intensification associated with higher thermal efficiency and cost reduction.     

Effects of environment and heat treatment on an oxygen plasma-treated polyimide surface and its adhesion to a chromium overcoat

—The effects of oxygen plasma treatment time, duration of storage, and heat treatment on the surface chemistry of and Cr adhesion to Dupont RC5878 and Kapton polyimides were investigated using X-ray photoelectron spectroscopy (XPS), and contact angle and peel strength measurements. The XPS results indicate that the initial stage of plasma treatment involves oxygen adsorption with insignificant modification of the surface chemistry. After 5 s of plasma treatment the surface chemistry is modified, as suggested by the changes in the carbonyl and partially oxidized carbon functional groups' contributions to the C(1s) line shape. These modifications resulted in an increase in the peel strength and a decrease in the contact angle of water. Over the first month of storage, the intensity of the carbonyl functional group peak decreased, while the contact angle increased and reached a steady-state value of 30° after 20 days of storage. These changes are mainly attributed to moisture absorption. Importantly, the metal adhesion to polyimide remained fairly constant over the storage period. The aged plasma-treated surface experienced loss of moisture when baked at 150°C for less than 5 min. This was followed by an increase of the partially oxidized carbon at the expense of the plasma-induced carbon-oxygen bonds at higher baking temperatures or longer times.     

Prediction of gas hold‐up in a bubble column filled with pure and binary liquids

A dimensionless correlation for gas hold‐up in a bubble column filled with pure liquids and binary mixtures has been developed. The criteria of bubble coalescence in pure liquids and foamability of binary mixtures have been included successfully in the proposed correlation. For the first time, comprehensive data of gas hold‐up with respect to concentration in four binary systems are presented. The often‐reported enhancement of gas hold‐up in aqueous alcohol mixtures has been observed experimentally. The proposed correlation is able to predict successfully the trend of gas hold‐up enhancement with respect to concentration. The estimated values are found to be within 7% of the measured values.     

Preparation of composite‐crosslinked poly(N‐isopropylacrylamide) gel layer and characteristics of reverse hydrophilic–hydrophobic surface

The composite‐crosslinked poly(N‐isopropylacrylamide) (PNIPAAm) gels were prepared by grafting N‐isopropylacrylamide on the surface of glass plates modified by organosilanes. The glass plates as the substrate increase the mechanical strength of composite PNIPAAm gel layers. We investigated the effects of a series of organosilanes and the reaction time of organosilanes on surface characteristics, such as the static contact angle and the layer thickness. We discuss the equilibrium swelling ratio and the water release behavior of the gel layers in terms of the crosslinking density of the composite gels. The composite gels exhibit not only the characteristics of remarkable water release but also the reversed hydrophilic–hydrophobic surface properties. The gel layers are hydrophilic under 25°C and change to hydrophobic above 40°C. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1–11, 1999