The effect of gas‐liquid counter‐current operation on gas hold‐up in bubble columns using electrical resistance tomography

BACKGROUND: In order to improve the performance of a counter‐current bubble column, radial variations of the gas hold‐ups and mean hold‐ups were investigated in a 0.160 m i.d. bubble column using electrical resistance tomography with two axial locations (Plane 1 and Plane 2). In all experiments the liquid phase was tap water and the gas phase air. The superficial gas velocity was varied from 0.02 to 0.25 m s^?1, and the liquid velocity varied from 0 to 0.01 m s^?1. The effect of liquid velocity on the distribution of mean hold‐ups and radial gas hold‐ups is discussed. RESULTS: The gas hold‐up profile in a gas–liquid counter‐current bubble column was determined by electrical resistance tomography. The liquid velocity slightly influences the mean hold‐up and radial hold‐up distribution under the selected operating conditions and the liquid flow improves the transition gas velocity from a homogeneous regime to a heterogeneous regime. Meanwhile, the radial gas hold‐up profiles are steeper at the central region of the column with increasing gas velocity. Moreover, the gas hold‐up in the centre of the column becomes steeper with increasing liquid velocity. CONCLUSIONS: The value of mean gas hold‐ups slightly increases with increasing downward liquid velocity, and more than mean gas hold‐ups in batch and co‐current operation. According to the experimental results, an empirical correlation for the centreline gas hold‐up is obtained based on the effects of gas velocity, liquid velocity, and ratio of axial height to column diameter. The values calculated in this way are in close agreement with experimental data, and compare with literature data on gas hold‐ups at the centre of the column. Copyright © 2010 Society of Chemical Industry     

Experimental Study of Oxygen Mass Transfer Coefficient in Bubble Column with High Temperature and High Pressure

The volumetric gas‐liquid mass transfer coefficient, k_Lα, for oxygen was studied by using the dynamic method in slurry bubble column reactors with high temperature and high pressure. The effects of temperature, pressure, superficial gas velocity and solids concentration on the mass transfer coefficient are systemically discussed. Experimental results show that the gas‐liquid mass transfer coefficient increases with the increase in pressure, temperature, and superficial gas velocity, and decreases with the increase in solids concentration. Moreover, k_Lα values in a large bubble column are slightly higher than those in a small one at certain operating conditions. According to the analysis of experimental data, an empirical correlation is obtained to calculate the values of the oxygen volumetric mass transfer coefficient for a water‐quartz sand system in two bubble columns with different diameter at high temperature and high pressure.     

The effect of system pressure on gas‐liquid slug flow in a microchannel

Characteristics of gas‐liquid two‐phase flow under elevated pressures up to 3.0 MPa in a microchannel are investigated to provide the guidance for microreactor designs relevant to industrial application. The results indicate that a strong leakage flow through the channel corners occurs although the gas bubbles block the channel. With a simplified estimation, the leakage flow is shown to increase with an increase in pressure, leading to a bubble formation shifting from transition regime to squeezing regime. During the formation process, the two‐phase dynamic interaction at the T‐junction entrance would have a significant influence on the flow in the main channel as the moving velocity of generated bubbles varies periodically with the formation cycle. Other characteristics such as bubble formation frequency, bubble and slug lengths, bubble velocities, gas hold‐up, and the specific surface area are also discussed under different system pressures. © 2013 American Institute of Chemical Engineers AIChE J, 60: 1132–1142, 2014     

On the Hydrodynamic Theory of Detonation

When the enthalpy of the unreacted explosive is correctly taken into account, the detonation rate D depends to some extent on the explosive's sound speed a₀. With a perfect or Abel gas equation, correction terms of the order $ 1 - \frac{{{\rm a}_{\rm 0}^{\rm 2} }}{{{\rm D}^{\rm 2} }} $ with respect to the classical theory are obtained. They increase D, but lower density and pressure in thc C-J plane. This agrees with the finding that data derived from experiments on the basis of the classical theory correspond better to a weak Than to a C-J detonation. The observed difference in density coefficients, dD/dϱ₀, of liquid and solid TNT as well as the anisotropy of D of elastically stretched rubberized high explosives are quantitatively understood. It is shown that the extended equations, though based on a gas equation of state, hold approximately for condensed explosives too, provided their compressibility is not too low.     

Effects of surfactants on hydrodynamics and mass transfer in a split‐cylinder airlift reactor

Effects of various concentrations (0–5 ppm) of anionic (sodium dodecyl sulfate, SDS) and non‐ionic (Tween‐80 and Triton X‐405) surfactants on gas hold‐up and gas–liquid mass transfer in a split‐cylinder airlift reactor are reported for air–water. Surfactants were found to strongly enhance gas hold‐up. Non‐ionic surfactants were more effective in enhancing gas hold‐up compared to the anionic surfactant SDS. An enhanced gas hold‐up and a visually reduced bubble size in the presence of surfactants implied an enhanced gas–liquid interfacial area for mass transfer. Nevertheless, the overall gas–liquid volumetric mass transfer coefficient was reduced in the presence of surfactants, suggesting that surfactants greatly reduced the true liquid film mass transfer coefficient and this reduction outweighed the interfacial area enhancing effect. Presence of surfactants did not substantially affect the induced liquid circulation rate in the airlift vessel.     

Mass transfer and hydrodynamic characteristics in a co‐current downflow contacting column

Hydrodynamic and mass transfer characteristics of water–air system in a co‐current downflow contacting column (CDCC) were studied for various nozzle diameters at different superficial gas velocities and liquid re‐circulation rates. Gas hold‐up and liquid‐side mass transfer coefficient increased with increasing superficial gas velocity and liquid flow rate but decreased with increasing nozzle diameter. It is shown that correlations developed, which are based on liquid kinetic power per liquid volume present in the column, and superficial gas velocity explains gas hold‐up and the mass transfer coefficient within an error 20% for all gas and liquid flow rates and nozzle diameters used. The constants of correlations for gas hold‐up and mass transfer coefficient were found to be considerably different from other gas–liquid contacting systems. © 2003 Society of Chemical Industry     

A dimensionless model for predicting the mass‐transfer area of structured packing

The mass‐transfer area of nine structured packings was measured in a 0.427 m ID column via absorption of CO₂ from air into 0.1 kmol/m³ NaOH. The mass‐transfer area was most strongly related to the specific area (125–500 m²/m³), and liquid load (2.5–75 m³/m²·h). Surface tension (30–72 mN/m) had a weaker but significant effect. Gas velocity (0.6–2.3 m/s), liquid viscosity (1–15 mPa·s), and flow channel configuration had essentially no impact on the mass‐transfer area. Surface texture (embossing) increased the effective area by 10% at most. The ratio of mass‐transfer area to specific area (a_e/a_p) was correlated within the limits of ±13% for the entire experimental database ${{a_{\rm{e}} } \over {a_{\rm{p}} }}= 1.34 \left[ {\left( {{{\rho _{\rm{L}} } \over \sigma }} \right)g^{1/3} \left( {{Q \over {L_{\rm{p}} }}} \right)^{4/3}} \right]^{\,0.116}$ . © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Relation between polymer surface tension and orientation of thermotropic liquid crystals

The orientation (tilt angle φ) of thermotropic liquid crystals (LC) on the interface to a polymer-coated surface is not only determined by the numerical value ${\rm \gamma }_{\rm S} {\rm }\left( {{\rm \gamma }_{\rm S} {\rm = \gamma }_{\rm S}^{\rm d} {\rm + \gamma }_{\rm S}^{\rm p} } \right)$ of the substrate surface tension. However, the ratio between the dispersive and the polar part of ${\rm \gamma }_{\rm S} {\rm }\left( {{\rm\gamma }_{\rm S}^{\rm d} {\rm : \gamma }_{\rm S}^{\rm p} } \right)$ also influences the LC orientation on the substrate surface. A polyimide and an amide-modified styrene/maleic anhydride copolymer were used as polymers.     

Hydrodynamic Model for Horizontal Two‐phase Flow Through Porous Media

A unidirectional, two‐fluid model based on the volume‐average mass and momentum balance equations was developed for the prediction of two‐phase pressure drop and external liquid hold‐up in horizontally positioned packed beds experiencing stratified, annular and dispersed bubble flow regimes. The so‐called slit model drag force closures were used for the stratified and annular flow regimes. In the case of dispersed bubble flow regime, the liquid‐solid interaction force was formulated on the basis of the Kozeny‐Carman equation by taking into account the presence of bubbles in reducing the available volume for the flowing liquid. The gas‐liquid interaction force was evaluated by using the respective solutions of drag coefficient for an isolated bubble in viscous and turbulent flows. The proposed drag force expressions for the different flow patterns occurring in the bed associated with the two‐fluid model resulted in a predictive method requiring no adjustable parameter to describe the hydrodynamics for horizontal two‐phase flow in packed beds.     

Kinetic study of the hydrolysis of cellulose acetate in the pH range of 2–10

A kinetic study of the hydrolysis of 39.8 wt.-% acetyl cellulose acetate has been made as a function of pH and temperature over the pH range of 2.2–10 and temperature range of 23–95°C. The hydrolysis reaction was carried out on highly porous membranes under quasihomogeneous conditions and the data have been treated as a pseudo-first-order reaction in acetyl concentration. The reaction can be represented by the equation \documentclass{article}\pagestyle{empty}\begin{document}$k_1 {\rm = }\;k_{\rm H ^ +} \left[ {{\rm H^+}} \right]{\rm +}k_{\rm OH^-}\left[ {{\rm OH}^ - } \right] + k_{\rm H_2O} $\end{document}, and where \documentclass{article}\pagestyle{empty}\begin{document}$k_{\rm H} ^ + {\rm = 5}{\rm .24}\;{\rm x 10}^{\rm 5} {\rm exp }\left\{ {{\rm ‐ 16}{\rm .4 x 10}^{\rm 3} /RT} \right\},{\rm }k_{{\rm OH}} ^ ‐ {\rm = 1}{\rm .55}\;{\rm x 10}^{\rm 4} {\rm exp }\left\{ {{\rm ‐ 8}{\rm .1 x 10}^{\rm 3} /RT} \right\}$\end{document}, and \documentclass{article}\pagestyle{empty}\begin{document}$k_{\rm H_2O} {= 4.25\;\times 10}^{- 2} {\rm exp }\left\{ {{- 11.5 \times 10^3 /RT}} \right\}$\end{document} (where the quantities in brackets are activities of the ions shown).     

鼓泡床反应器内流动与传质行为的研究进展

总结了有关浆态鼓泡床反应器内流动、混合用气液传质特性的研究成果,详细地介绍了鼓泡床反应器内气含率、液速、液体轴向扩散系数、传质系数的测量方法,阐述了鼓泡床反应器性能的主要影响因素,如系统压力、温度、气体表观气速、液体性质及固含率等对流动、液相混合和传质特性的影响,并对鼓泡床反应器的应用前景进行了详述.     

Effect of Surface Tension on Hydrodynamics and Mass Transfer Coefficient in Airlift Reactors

The hydrodynamics and volumetric mass transfer coefficient play important roles in the design and scale-up of airlift reactors. The effect of surface tension on hydrodynamics and volumetric mass transfer coefficient in internal loop airlift reactors was investigated. With reduction of the surface tension of the fluid, the hydrodynamic parameters raised, namely, gas phase holdup, flow regime transition point, and interfacial area, whereas the bubble diameter as well as the liquid velocity decreased and the volumetric mass transfer coefficient increased. Empirical correlations are proposed for gas-phase holdup and volumetric mass transfer coefficient in terms of dimensionless numbers and can be applied in the design of airlift reactors.     

Gas hold‐up in bubble columns: Operation with concentrated slurries versus high viscosity liquid

The hydrodynamics of bubble columns with concentrated slurries of paraffin oil (density, ρ_L = 790 kg/m³; viscosity, μ_L = 0.0029 Pa·s; surface tension, σ = 0.028 N·m¹) containing silica particles (mean particle diameter d_p = 38 μm) has been studied in columns of three different diameters, 0.1, 0.19 and 0.38 m. With increasing particle concentration, the total gas hold‐up decreases significantly. This decrease is primarily caused by the destruction of the small bubble population. The hold‐up of large bubbles is practically independent of the slurry concentration. The measured gas hold‐up with the 36% v paraffin oil slurry shows remarkable agreement with the corresponding data obtained with Tellus oil (ρ_L = 862 kg/m³; μ_L = 0.075 Pa·s; σ = 0.028 N·m^?1) as the liquid phase. Dynamic gas disengagement experiments confirm that the gas dispersion in Tellus oil also consists predominantly of large bubbles. The large bubble hold‐up is found to decrease significantly with increasing column diameter. A model is developed for estimation of the large bubble gas hold‐up by introduction of an wake‐acceleration factor into the Davies‐Taylor‐Collins relation (Collins, 1967), describing the influence of the column diameter on the rise velocity of an isolated spherical cap bubble.     

Gas-Liquid Mass Transfer Characteristics in a Gas-Liquid-Solid Bubble Column under Elevated Pressure and Temperature

abstract The volumetric mass transfer coefficient kLa of gases (H2, CO, CO2) and mass transfer coefficient kL on liquid par-affin side were studied using the dynamic absorption method in slurry bubble ...     

A Study on Hydrodynamics and Heat Transfer in a Bubble Column Reactor with Yeast and Bacterial Cell Suspensions

Hydrodynamics and heat transfer experiments were carried out in a slurry bubble column with air‐water‐yeast cells and air‐water‐bacteria cells systems to investigate gas hold‐up, bubble characteristics and heat transfer coefficients with cell concentrations of 0.1% w/w and 0.4% w/w and superficial gas velocity up to 0.20 m/s. The gas hold‐ups and heat transfer coefficients were found to increase with increasing gas velocity and cell concentration. The heat transfer coefficients were higher at the centre of the column as compared to the near wall region. The development of empirical correlations to predict the heat transfer coefficient in two‐ and three‐phase systems was carried out with ±15% confidence interval at most.     

The Radiation Chemistry of Cytochrome c

The literature on the reaction of cytochrome c with the radiolytically generated radicals \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm e}_{{\rm eq}}^ -,^. {\rm OH,}^{\rm .} {\rm H,CO}_2^ -,{\rm O}_{\rm 2}^ -,{\rm Br}_{\rm 2}^ - $\end{document} and various organic radicals is reviewed. It would appear that negatively charged radicals, aided by the electric field of cytochrome c, react at the exposed haem edge. Uncharged organic radicals also react at this site. \documentclass{article}\pagestyle{empty}\begin{document}$ ^. {\rm H} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ ^. {\rm OH} $\end{document} are likely to reduce the prosthetic group indirectly by a tunnelling mechanism.     

Adsorptive removal of nitrate and phosphate anions from aqueous solutions using functionalised SBA‐15: Effects of the organic functional group

Adsorption of nitrate and monovalent phosphate anions from aqueous solutions on mono, di‐ and tri‐ammonium‐functionalised mesoporous SBA‐15 silica was investigated. The adsorbents were prepared via a post‐synthesis grafting method, using either 3‐aminopropyltrimethoxysilane (N‐silane) or [1‐(2‐aminoethyl)‐3‐aminopropyl]trimethoxysilane (NN‐silane) or 1‐[3‐(trimethoxysilyl)‐propyl]‐diethylenetriamine (NNN‐silane), followed by acidification in HCl solution to convert the attached surface amino groups to positively charged ammonium moieties. The nominal loading of amino moieties on the SBA‐15 surface was varied from 5% to 20% as organoalkoxysilane/silica molar ratio. The adsorption experiments were conducted batchwise at room temperature. Results showed that adsorption capacity increased with increasing the concentration of monoammonium groups on the SBA‐15 adsorbent. Nitrate adsorption capacity increased from 0.34 to 0.66 mmol ${\rm NO}_{3}^{{-} } /{\rm g}$ adsorbent while phosphate adsorption capacity increased from 0.34 to 0.63 mmol ${\rm H}_{2} {\rm PO}_{4}^{{-} } /{\rm g}$ adsorbent when the molar ratio organoalkoxysilane/silica was varied from 5% to 20%, respectively. Also, for the same organoalkoxysilane/silica molar ratio of 10%, the adsorption capacity increased with the increase of the number of protonated amines in the functional groups. Therefore, maximum adsorption capacities of 0.80, 1.16 and 1.38 mmol ${\rm NO}_{3}^{{-} } /{\rm g}$ adsorbent and 0.72, 0.82 and 1.17 mmol ${\rm H}_{2} {\rm PO}_{4}^{{-} } /{\rm g}$ adsorbent were obtained using mono‐, di‐ and triammonium functionalised SBA‐15 adsorbents, respectively. © 2011 Canadian Society for Chemical Engineering     

Flow regime transition identification in three phase co‐current bubble columns

Bubble columns have wide applications in absorption, bio‐reactions, catalytic slurry reactions, coal liquefaction; and are simple to operate, have less operating costs; provide good heat and mass transfer. Experiments have been performed for identifying transition regime in a 15 cm diameter bubble column with liquid phase as water and air as the gas phase. Glass beads of mean diameter 35 µm have been used as solid phase. The superficial gas velocity is in the range 0 ≤ U_g ≤ 16.3 cm/s and superficial liquid velocity in the range of 0 ≤ U_l ≤ 12.26 cm/s. Solid loading up to 9% (w/v) has been used. Pressure signals have been measured using differential pressure transducers (DPTs) at four different axial locations. Classical analysis (Wallis approach and Zuber–Findlay approach), Statistical analysis and Fractal analysis have been used for regime transition identification. Statistical analysis and Fractal analysis have shown almost the same transition points for all the liquid and gas velocities. Effect of solid concentration, liquid velocity and gas velocity over transition regime has also been studied. As the solid concentration is increased it has insignificant effect over transition regime for lower values (<1%), while transition values decrease for higher solid concentration (>1%). © 2012 Canadian Society for Chemical Engineering     

Comprehensive models for predicting aromaticity of coals

The principal objective of the present study is to develop suitable models to predict aromaticity of coals on the basis of atomic ratios of the H/C, O/C, O/H, and weight percentage volatile matter (V.M.) in coals. Based on dry mineral matter free (dmmf) basis, aromaticity (fa) of coal is computed through the following expressions: \eqalignno{{\rm fa}_1&= 1.202913 - 0.0126^{\ast} {\rm V.M}.,&(2)\cr{\rm fa}_2&= 1.36396 - 0.53715^{\ast} {\rm O}/{\rm C} - 0.7846^{\ast} {\rm H}/{\rm C},&(3)\cr{\rm fa}_3&= 1.365615 - 0.51187^{\ast} {\rm O}/{\rm C} - 0.02108^{\ast} {\rm O}/{\rm H} - 0.78645^{\ast} {\rm H}/{\rm C},&(4)\cr{\rm fa}_4&= 174.4405 + 621.6823^{\ast} {\rm O}/{\rm C} - 856.495^{\ast} {\rm O}/{\rm H} - 629.617^{\ast} {\rm H}/{\rm C}&(5) \cr& \quad+ 9.133897^{\ast} {\rm V.M}.} The absolute average % error of estimate and correlation coefficients of the developed models (Equations (2), (3), (4), and (5)) were found to be 7.48,0.91; 6.23, 0.92; 6.24, 0.92; and 6.23, 0.92 on (dmmf) basis, respectively.     

Computational Fluid Dynamics Modeling of Gas‐Liquid Two‐Phase Flow around a Spherical Particle

Microscale studies, which can provide basic information for meso‐ and macroscale studies, are essential for the realization of flow characteristics of a packed bed. In the present study, the effects of gas velocity, liquid velocity, liquid‐solid contact angle, and liquid viscosity on the flow behavior were parametrically investigated for gas‐liquid two‐phase flow around a spherical particle, using computational fluid dynamics (CFD) methodology in combination with the volume‐of‐fluid (VOF) model. The VOF model was first validated and proved to be in good agreement with the experimental data. The simulation results show that the film thickness decreases with increasing gas velocity. This trend is more obvious with increasing operating pressure. With increasing liquid velocity, the film thickness tends to be uniform on the particle surface. The flow regime can change from film flow to transition flow to bubble flow with increasing contact angle. In addition, only at relatively high values does the liquid viscosity affect the residence time of the liquid on the particle surface.