Model for Plateau border drainage of power-law fluid with mobile interface and its application to foam drainage

A model for drainage of a power-law fluid through a Plateau border is proposed which accounts for the actual Plateau border geometry and interfacial mobility. The non-dimensionalized Navier-Stokes equations have been solved using finite element method to obtain the contours of velocity within the Plateau border cross section and average Plateau border velocity in terms of dimensionless inverse surface viscosity and power-law rheological parameters. The velocity coefficient, the correction for the average velocity through a Plateau border of actual geometry compared to that for a simplified circular geometry of the same area of cross section, was expressed as a function of dimensionless inverse surface viscosity and flow behavior index of the power-law fluid. The results of this improved model for Plateau border drainage were then incorporated in a previously developed foam drainage model [G. Narsimhan, J. Food Eng. 14 (1991) 139] to predict the evolution of liquid holdup profiles in a standing foam. Foam drainage was found to be slower for actual Plateau border cross section compared to circular geometry and faster for higher interfacial mobility and larger bubble size. Evolution of liquid holdup profiles in a standing foam formed by whipping and stabilized by 0.1% beta-lactoglobulin in the presence of xanthan gum when subjected to 16g and 45g centrifugal force fields was measured using magnetic resonance imaging for different xanthan gum concentrations. Drainage resulted in the formation of a separate liquid layer at the bottom at longer times. Measured bubble size, surface shear viscosity of beta-lactoglobulin solutions and literature values of power-law parameters of xanthan gum solution were employed in the current model to predict the evolution of liquid holdup profile which compared well with the experimental data. Newtonian model for foam drainage for zero shear viscosity underpredicted drainage rates and did not agree with the experimental data.     

Determining Solubility and Diffusivity by Using a Flow Cell Coupled to a Mass Spectrometer

One of the main challenges in metal–air batteries is the selection of a suitable electrolyte that is characterized by high oxygen solubility, low viscosity, a liquid state and low vapor pressure across a wide temperature range, and stability across a wide potential window. Herein, a new method based on a thin layer flow through cell coupled to a mass spectrometer through a porous Teflon membrane is described that allows the determination of the solubility of volatile species and their diffusion coefficients in aqueous and nonaqueous solutions. The method makes use of the fact that at low flow rates the rate of species entering the vacuum system, and thus the ion current, is proportional to the concentration times the flow rate (c?u) and independent of the diffusion coefficient. The limit at high flow rates is proportional to . Oxygen concentrations and diffusion coefficients in aqueous electrolytes that contain Li⁺ and K⁺ and organic solvents that contain Li⁺, K⁺, and Mg²⁺, such as propylene carbonate, dimethyl sulfoxide tetraglyme, and N‐methyl‐2‐pyrrolidone, have been determined by using different flow rates in the range of 0.1 to 80 μL s^?1. This method appears to be quite reliable, as can be seen by a comparison of the results obtained herein with available literature data. The solubility and diffusion coefficient values of O₂ decrease as the concentration of salt in the electrolyte was increased due to a “salting out” effect.     

Modern methods and devices for associated petroleum gas metering

Main terms and definitions relevant to associated petroleum gas metering were presented along with the classifications, components, and metrological assurance requirements for metering systems. Particular attention was given to the operation conditions and requirements, as well as to special selection criteria for associated petroleum gas flow meters intended for low-pressure flare lines. Flow measurement methods were reviewed, and the results of a comparative study of flow meters were presented.     

Gas holdup in three-phase immobilized-cell bioreactors

A number of studies in the published literature deal with gas holdup in three-phase reactors. However, very few address the cases in which the solid density approaches that of the liquid phases and in which low gas velocities are involved. These conditions are commonly encountered in immobilized-cell bubble columns and in fluidized-bed bioreactors. This paper reports the effect of gas and liquid velocity upon gas holdup and bed expansion in fluidized-bed bioreactors. For liquid-fluidization of low-density alginate beads in the absence of gas, the terminal sedimentation velocity (vT) of the particles is a constant, and expansion of the bed follows Richardson and Zaki’s correlation. In the presence of gas, however, the apparent terminal sedimentation velocity value is affected by the velocity of the gas and liquid phases. For gas velocities above a minimum value, the calculated value of vT depends on liquid velocity only, and a constant bed expansion was observed for a range of gas and liquid flow rates. For the gas-liquid interactions, a modified drift-flux model was found to be valid. For superficial gas velocities between 5 and 17 cm/min, the modified drift-flux velocity was observed to be a function of gas velocity, suggesting the prevalence of a coalescence regime.     

The titration of clay minerals I. Discontinuous backtitration technique combined with CEC measurements

Evolution of liquid holdup profile in a standing foam formed by whipping and stabilized by sodium caseinate in the presence of xanthan gum when subjected to 16 and 29g centrifugal force fields was measured using magnetic resonance imaging for different pH, ionic strength, protein and xanthan gum concentrations. Drainage resulted in the formation of a separate liquid layer at the bottom at longer times. Foam drainage was slowest at pH 7, lower ionic strength, higher protein and gum concentrations. Foam was found to be most stable at pH 5.1 near the isoelectric point of protein, lower ionic strength and higher protein and xanthan gum concentrations. A predicted equilibrium liquid holdup profile based on a previous model (G. Narsimhan, J. Food Eng. 14 (1991) 139) agreed well with experimental values at sufficiently long times. A proposed model for velocity of drainage of a power law fluid in a Plateau border for two different simplified geometries was incorporated in a previously developed model for foam drainage (G. Narsimhan, J. Food Eng. 14 (1991) 139) to predict the evolution of liquid holdup profiles. The model predictions for simplified circular geometry of Plateau border compared well with the experimental data of liquid holdup profiles at small times. At longer times, however, the predicted liquid holdup profile was larger than the observed, this discrepancy being due to coarsening of bubble size and decrease in foam height not accounted for in the model. A Newtonian model for foam drainage under predicted drainage rates did not agree with the experimental data.     

Investigation of liquid–solids fluidized bed of different particle size through radioactive particle tracking techniques

Radioactive particle tracking technique (RPT) has proven to be a powerful and versatile technique both in terms of the richness of information it provides as well as the variety of multiphase flow situations it has been successfully employed. This work reports the execution of RPT technique for investigation of liquid–solids fluidized bed of different particle sizes (1.2 and 0.6 mm). Experiments are performed in a 10 cm ID cylindrical column for different liquid velocities. Further, RPT experiments are performed for both the solids and effect of liquid velocity and particle size on flow behaviour of liquid–solid fluidized bed is quantified.     

Increased Sensitivity Spectrophotometric Flow Analysis Method for Copper Determination in Water Samples

A reverse configured flow injection system was developed for the determination of copper in water samples. In this study, a bathocuproine disulfonic acid copper complexing reagent was used. In the presence of a reducing agent (hydroxylamine), the formation of complex was monitored at 484 nm. The determination range extended from 1 to 40 µg L^?1, with an applicable determination rate of 40 h^?1. The developed method was applied to the determination of copper in water samples (estuarine, river, and drinking water) and showed good accuracy (z-score below 2). The detection limit of 0.7 µg L^?1 copper is consistent with the requirement of the target water samples. The developed method was also used for the comparison of different spectrophotometric flow cells. Alternative flow cells (U, Z shaped, and the liquid waveguide capillary cell) were compared in terms of their sensitivity and response to refractive index changes.     

Froth characteristics of shallow bubble columns with sieve plates

Radial profiles of gas holdup, liquid circulation and equivalent clear liquid height in the froth regime were measured in a shallow bubble column withCorrelations for radial profiles of gas holdup in the middle region, which is one of three axial regions in the froth, and for mean values of equivalen     

气流床煤气化炉内流动、混合与反应过程的研究进展

气流床气化过程涉及高温高压下湍流多相流动与复杂化学反应过程的相互作用,涵盖喷嘴雾化与弥散、复杂多相射流流动、炉内湍流混合、复杂气化反应、火焰结构及温度分布等诸多方面,是世界各国研究的热点.对近年来世界各国在气流床气化过程研究上取得的进展进行了综述,包括喷嘴雾化与颗粒弥散机理与雾化过程的影响因素、撞击流驻点偏移规律和撞击面振荡规律、撞击火焰结构与炉内三维温度场、典型煤种气化反应特性与石油焦气化特性以及气流床气化过程模拟.对气流床气化过程未来的研究重点进行了展望.     

Open-tubular liquid chromatography under turbulent and secondary flow conditions

Summary Liquid chromatography in open tubes at flow rates around 0.1 cm · s^–1 and less can generate an enormous number of theoretical plates but suffers from long analysis times. The Golay and van Deemter equations are also obeyed with high accuracy.If straight tubes of circular cross section and very smooth inner surface are used, secondary flow effects can be neglected. Thus the plate height should depend only on the flow velocity and the number of theoretical plates should decrease with increase in linear flow, whereas the number of plates per unit time should be constant.Under turbulent conditions, however, the plate height seems to be more or less independent of linear flow over a wide range. Increasing the flow to several hundred cm · s^–1 causes, for example, 0.2 mm ID capillaries to show the reverse effect and a slight decrease in plate height is found. Alkali treated and silanized capillaries below 100 m i. d. deviate from the Golay prediction before turbulence occurs and a relative decrease in the plate height and thus higher efficiency is found possibly caused be secondary flow effects in the coiled tube or the roughness of the inner walls. These effects allow an increase in the efficiency of given open-tubular systems simply by increasing the solvent velocity drastically. Although plate heights are in the range mm to cm, efficiencies, in theoretical plates per second, similar to classic HPLC, are found. Therefore the quite interesting possibility of overcoming the well-known restrictions of classical HPLC to achieve high efficiency liquid chromatograms exists.Presented at the 17th International Symposium on Chromatography, September 25–30, 1988, Vienna, Austria.     

Flow field in a downward diverging channel and its application

The flow in a downward divergent channel turns out to be an interesting experimental setup for the observation of upward floating bubbles that appear to be levitating in view of the observer. A more detailed analysis of this flow and its characteristic parameters is necessary for better understanding of this phenomenon. The boundary layer theory was used to derive the velocity field for the experimental setup. The actual flow of a liquid in the presence of a bubble was studied experimentally by measuring the position of the bubble; the data were then statistically processed by an image analysis. Observation of the bubble positions distribution showed that it is reasonable to assume a flat velocity profile of the liquid in the channel and that the bubbles do not tend to move into the boundary layer. In our experiments, volume of the air bubbles floating in water was 200 mm and of that of bubbles floating in aqueous glycerin was 300 mm³. Thus, the experiment used in this work is suitable for reliable determination of instantaneous and average bubble rising velocities as well as of those of horizontal and vertical oscillations.     

Hydrodynamic Behavior in a Tapered Bubble Column

IntroductionBubble column( BC) and slurry bubble column( SBC) reactors have emerged as one of the mostpromising devices in chemical,biochemical and en-vironmental engineering operations because of theirsimple construction,isothermal conditions,highheat and mass transfer rates,and on- line catalystaddition and withdrawal[1_ 4] .The utilization of ta-pered slurry bubble column( TSBC) reactorshas re-cently received much attention ofsome scholars andscientists who are engaged in biochemical rea…     

Gas Holdups of Small and Large Bubbles in a Large-scale Bubble Column with Elevated Pressure

Gas holdups of large bubbles and small bubbles were measured by means of dynamic gas disengagement approach in the pressured bubble column with a diameter of 0. 3 m and a height of 6.6 m. The effects of su-perficial gas velocity, liquid surface tension, liquid viscosity and system pressure on gas holdups of small bub-bles and large bubbles were investigated. The holdup of large bubbles increases and the holdup of small bub-bles decreases with an increase of liquid viscosity. Meanwhile, the holdup of large bubbles decreases with in-creasing the system pressure. A correlation for the holdup of small bubbles was obtained from the experimen-tal data.     

Gas and Liquid Phase Imaging of Foam Flow Using Pure Phase Encode Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is a non-invasive and non-optical measurement technique, which makes it a promising method for studying delicate and opaque samples, such as foam. Another key benefit of MRI is its sensitivity to different nuclei in a sample. The research presented in this article focuses on the use of MRI to measure density and velocity of foam as it passes through a pipe constriction. The foam was created by bubbling fluorinated gas through an aqueous solution. This allowed for the liquid and gas phases to be measured separately by probing the ¹H and ¹⁹F behavior of the same foam. Density images and velocity maps of the gas and liquid phases of foam flowing through a pipe constriction are presented. In addition, results of computational fluid dynamics simulations of foam flow in the pipe constriction are compared with experimental results.     

Non-invasive imaging of shallow bubble columns using electrical capacitance tomography

This paper deals with application of non-invasive electrical capacitance tomography to study the hydrodynamics of shallow bed bubble columns. Two bubble columns with different height to diameter ratio were used. Air–kerosene system that represents dielectric two-phase mixture was investigated. The ECT provided good measurement of the gas holdup at different gas velocities compared to the classical pressure measurements. The ECT was able to provide the gas hold up and the bubble velocities distribution across the column diameter at different gas velocities. The study revealed that spatial gas holdup and bubble velocity distributions are sharp with parabolic shape in the small bubble column (H_D/D_C = 5). However, in the large bubble column (H_D/D_C = 4) the gas holdup and bubble velocity profiles were flatter indicating improvement in the mixing homogeneity and leading to well-mixed reactor. 3D graphical visualization of the flow regimes and transition points were also examined using the ECT. In the small bubble column flow regimes were heterogeneous to slugs flow especially at high flow rate, resulted in downward flow near the walls and imperfect mixing.     

Sound dispersion and attenuation in concentrated H2SO4 by visible and ultraviolet Brillouin spectroscopy

The acoustic properties of highly concentrated H(2)SO(4) are investigated performing visible and ultraviolet Brillouin scattering measurements. We analyzed the isotropic and anisotropic spectra of this molecular liquid in a wide temperature and exchanged wavector range in order to study the evolution of its sound velocity and viscosity. This allows us to extract the parameters required to describe its viscoelastic relaxation behavior. We found that the behavior of the hydrodynamic parameters of this molecular liquid shares some similarities with that of water indicating a rather high increase of sound velocity if compared to that measured by ultrasonics.     

Flow birefringence of concentrated polymer solutions in two-dimensional flows

The results of flow birefringence measurements are reported for polymer solutions of moderate concentration subjected to a wide range of two-dimensional flows. These flows were generated in a four-roll mill which enables one to systematically vary the ratio of the vorticity to the rate of strain in the flow while holding the velocity gradient constant. It is shown that steady-state birefringence data collected over a wide range of flow types can be correlated against the eigenvalue of the velocity gradient tensor, in agreement with criterion for strong and weak flows from model calculations. Transient birefringence measurements in which purely extensional flows were started from rest are also reported. It was observed that the birefringence went through a pronounced overshoot in time for two different polymer/solvent systems. Flow induced increases in the solution turbidity were also observed and the increased turbidity remained constant over a period of many hours after extensional flows were arrested. The birefringence, on the other hand, decayed to zero almost immediately after the flows were stopped. These changes in the turbidity suggest that crystallization of the polymer was occurring. The qualitative results of experiments are compared to recent network model calculations using the theory of Yamamoto for concentrated polymer systems. It is found that this model can predict qualitatively many of the experimental observations if the function describing the breakage of polymer chain entanglements is allowed to depend on the conformation of the polymer segments bridging the entanglements. In particular, this dependency of the entanglement breakage on the conformation of the network segments leads to a predicted overshoot of birefringence when purely extensional flows are started from rest. It is also demonstrated through this model that birefringence data taken over a wide range of flow types can be used to estimate the degree to which the network deforms affinely with the flow field.     

重力驱动多相层流分离离子选择性电极检测集成化微流控芯片系统

将微流控芯片多相层流分离技术与离子选择性电极检测技术联用,利用重力驱动的芯片多相层流分离系统,在线净化生物(血液)试样.同时,在芯片上加工微离子选择性电极进行待测物的在线检测,实现整体分析系统的芯片集成化,并将其用于血样中K⁺的测定.对5.5×10^-3mol/L钾溶液5次平行测定的相对标准偏差(RSD)为5.6%,检出限为6.8×10^-5mol/L,线性范围10^-4～10^-1mol/L.     

连续流动分析技术测定水中阴离子合成洗涤剂方法优化

阴离子合成洗涤剂是洗涤用品的主要成分,属于生物难降解的物质,是当前环境水污染的重要指标,具有较好的去污能力且价格低,广泛应用于餐饮界和工业的消毒,该类物质虽毒性低但降解缓慢,同时还抑制其它有毒物质的降解。为了建立基于连续流动分析检测技术的阴离子合成洗涤剂检测方法,对GB/T5750.4-2023中的连续流动法中仪器流路进行调整,将酸性亚甲基蓝流路变为碱性亚甲基蓝流路直接进样,优化亚甲基蓝体系配比,蠕动泵方向为反转且泵的转速为12 r/min,注射时间为40 s,管路清洗时间为300 s,积分时间设置为30 ms,于650 nm波长下进行测量,实验参比波长为490 nm,以阴离子合成洗涤剂浓度值为横坐标,峰高信号值为纵坐标,制作标准曲线,并对该方法的线性范围、检出限、精密度、准确度进行验证。该方法在0~0.35 mg/L浓度范围内,阴离子合成洗涤剂的标准曲线方程为y = 0.1243x - 0.0012,且相关系数r值为0.9995,检出限为0.0027 mg/L,添加回收率98.4%~103.2%之间,精密度在0.74%~1.82%之间。结果表明：该方法线性关系良好,精密度和准确度高,操作简单,污染少,适用于生活饮用水中阴离子合成洗涤剂的大批量分析检测。     

Characterization of Simultaneous Heat and Mass Transfer Phenomena for Water Vapour Condensation on a Solid Surface in an Abiotic Environment—Application to Bioprocesses

The phenomenon of heat and mass transfer by condensation of water vapour from humid air involves several key concepts in aerobic bioreactors. The high performance of bioreactors results from optimised interactions between biological processes and multiphase heat and mass transfer. Indeed in various processes such as submerged fermenters and solid-state fermenters, gas/liquid transfer need to be well controlled, as it is involved at the microorganism interface and for the control of the global process. For the theoretical prediction of such phenomena, mathematical models require heat and mass transfer coefficients. To date, very few data have been validated concerning mass transfer coefficients from humid air inflows relevant to those bioprocesses. Our study focussed on the condensation process of water vapour and developed an experimental set-up and protocol to study the velocity profiles and the mass flux on a small size horizontal flat plate in controlled environmental conditions. A closed circuit wind tunnel facility was used to control the temperature, hygrometry and hydrodynamics of the flow. The temperature of the active surface was controlled and kept isothermal below the dew point to induce condensation, by the use of thermoelectricity. The experiments were performed at ambient temperature for a relative humidity between 35?C65% and for a velocity of 1.0?ms^?1. The obtained data are analysed and compared to available theoretical calculations on condensation mass flux.