The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform
Mohammad Jamialahmadi - One of the best experts on this subject based on the ideXlab platform.
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effect of superficial gas Velocity on bubble size terminal bubble Rise Velocity and gas hold up in bubble columns
Developments in Chemical Engineering and Mineral Processing, 2008Co-Authors: Mohammad Jamialahmadi, H MuullersteinhagenAbstract:It is important to have a reliable estimate of bubble size, terminal bubble Rise Velocity and gas hold-up in bubble columns, since these parameters are directly related to the transfer coefficients and the transfer area. Mean bubble diameters have been measured as a function of the superficial gas Velocity in air-water systems. In the bubbly flow regime, the bubble size is a strong function of the orifice diameter and the wettability of the gas distributor and a weak function of superficial gas Velocity. In the turbulent churn flow regime this functionality is reversed and the bubble diameter becomes a strong function of the superficial gas Velocity. A correlation is presented which covers both regimes. The terminal bubble Rise Velocity was measured as a function of the bubble size and the results were compared with correlations recommended in the literature. Finally, the gas hold-up was measured over a wide range of superficial gas velocities. The results were compared with a variety of empirical and theoretical correlations. New equations are presented which predict gas hold-up of the air-water system with good accuracy.
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Effect of Superficial Gas Velocity on Bubble Size, Terminal Bubble Rise Velocity and Gas Hold‐up in Bubble Columns
Developments in Chemical Engineering and Mineral Processing, 2008Co-Authors: Mohammad Jamialahmadi, H. Müuller-steinhagenAbstract:It is important to have a reliable estimate of bubble size, terminal bubble Rise Velocity and gas hold-up in bubble columns, since these parameters are directly related to the transfer coefficients and the transfer area. Mean bubble diameters have been measured as a function of the superficial gas Velocity in air-water systems. In the bubbly flow regime, the bubble size is a strong function of the orifice diameter and the wettability of the gas distributor and a weak function of superficial gas Velocity. In the turbulent churn flow regime this functionality is reversed and the bubble diameter becomes a strong function of the superficial gas Velocity. A correlation is presented which covers both regimes. The terminal bubble Rise Velocity was measured as a function of the bubble size and the results were compared with correlations recommended in the literature. Finally, the gas hold-up was measured over a wide range of superficial gas velocities. The results were compared with a variety of empirical and theoretical correlations. New equations are presented which predict gas hold-up of the air-water system with good accuracy.
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terminal bubble Rise Velocity in liquids
Chemical Engineering Research & Design, 1994Co-Authors: Mohammad Jamialahmadi, C A Branch, Hans MullersteinhagenAbstract:We present new experimental results of terminal bubble Rise Velocity for a variety of fluids and a model which accurately predicts the bubble Rise Velocity over a wide range of bubble sizes. A comparison is made between experimental results obtained in the investigation as well as by other authors and the predictions of the correlations of Clift et al. (1978), Wallis (1974) and the present authors
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Effect of alcohol, organic acid and potassium chloride concentration on bubble size, bubble Rise Velocity and gas hold-up in bubble columns
The Chemical Engineering Journal, 1992Co-Authors: Mohammad Jamialahmadi, H. Müller-steinhagenAbstract:Abstract The effect of alcohol, organic acid and potassium chloride concentration on bubble size, bubble stability, terminal bubble Rise Velocity and gas hold-up in bubble columns was investigated. The addition of alcohols and organic acids to the water reduced the bubble size and the bubble Rise Velocity significantly. These organic solutes also changed the coalescence behaviour of aqueous solutions drastically, from high coalescence behaviour of pure water to coalescence restrain of the various solutions. The mechanism of the coalescence suppression behaviour of electrolytic solutions of potassium chloride is discussed on the basis of ionic forces between ions and water molecules. The gas hold-up for low potassium chloride concentration increased owing to the ions reinforcing the liquid film between bubbles against bubble coalescence. For high potassium chloride concentration and low superficial gas Velocity, large but unstable bubbles formed at the gas distributor plate. Increasing the gas Velocity causes these bubbles to break into many smaller bubbles, thus increasing the gas hold-up.
Liang-shih Fan - One of the best experts on this subject based on the ideXlab platform.
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on the Rise Velocity of an interactive bubble in liquids
Chemical Engineering Journal, 2003Co-Authors: Jian Zhang, Liang-shih FanAbstract:Abstract Bubble Rise Velocity is one of the important parameters characterizing bubble column systems. Mathematical models for predicting the Velocity of an interactive spherical bubble rising in-line in liquids for intermediate Reynolds number range [Re ∼O(100)] are developed in the present study. The equation for the balance of forces on a bubble rising in-line is formulated. The models are derived based on this equation and different assumptions for the forces on the bubble. The ratios of the Rise Velocity of the trailing bubble to that of an isolated bubble, varying with the separation distance between the leading and trailing bubbles, are predicted by these models at Re of 35.4, 21.5 and 3.06. Comparisons between the predictions and the measurements show that the model incorporating both the wake effect and the bubble acceleration effect which includes the added mass and Basset forces can well predict the Rise Velocity of the trailing bubble in the far wake region of the leading bubble. The commonly used model which accounts for only the wake effect is found to lead to an overestimation of the Rise Velocity of the trailing bubble.
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On the Rise Velocity of bubbles in liquid-solid suspensions at elevated pressure and temperature
Chemical Engineering Science, 1997Co-Authors: Xukun Luo, Katsumi Tsuchiya, Jian Zhang, Liang-shih FanAbstract:Experiments are conducted to measure the Rise Velocity of single bubbles in liquid-solid suspensions at pressures up to 17 MPa and temperatures up to 88°C over the bubble size range from 1 to 20 mm. It is found that the bubble Rise Velocity decreases with increasing pressure and with decreasing temperature. The decrease of bubble Rise Velocity is due mainly to the variations of gas density and liquid viscosity with pressure and temperature. The presence of solid particles also reduces the Rise Velocity; the extent of reduction can be examined in terms of an increase in the apparent suspension viscosity by applying the homogeneous, Newtonian analogy. A mechanistic model is developed which considers a balance of forces acting on a single bubble, including the impact force due to solid particles, as well as buoyancy, gravity and liquid drag forces. Comparisons between the model predictions and the experimental data on the bubble Rise Velocity in liquid-solid fluidized beds are shown to be satisfactory.
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Suspension viscosity and bubble Rise Velocity in liquid-solid fluidized beds
Chemical Engineering Science, 1997Co-Authors: Katsumi Tsuchiya, Liang-shih Fan, Akihiko Furumoto, Jianping ZhangAbstract:The effective viscosity which characterizes the pseudo-homogeneous property of the liquid-solid suspension in gas-liquid-solid fluidization is examined in light of the Velocity of single bubbles rising through the suspension. Experiments conducted in this study cover a wide range of bubble diameters (2–23 mm) under high solids holdup (0.48 – 0.57) conditions. The study reveals that the liquid-solid medium exhibits a homogeneous, Newtonian property at any given solids holdup when the bubble diameters are greater than 12–17 mm. The effective viscosities obtained in this study based on equivalency of the single bubble Rise Velocity in Newtonian media as well as those reported in the literature are found to follow the Mooney-type relationship for solids holdup dependence. The two parameters underlying this relationship can be correlated as a function of the particle terminal Velocity, particle shape and packed solids holdup. When the bubble diameters are smaller than 12–17 mm, the effective viscosity of the liquid-solid medium deviates from the viscosity of the corresponding Newtonian liquid. The deviation which marks the reduction in the bubble Rise Velocity reflects a significant close-range interaction between particles. In this bubble size range, the liquid-solid medium exhibits a non-Newtonian property characterized by shear-thinning behavior with flow index ≈ 12.
Daniel D. Joseph - One of the best experts on this subject based on the ideXlab platform.
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Ellipsoidal model of the Rise of a Taylor bubble in a round tube
International Journal of Multiphase Flow, 2005Co-Authors: Toshio Funada, Daniel D. Joseph, Takanori Maehara, S. YamashitaAbstract:Abstract The Rise Velocity of long gas bubbles (Taylor bubbles) in round tubes is modeled by an ovary ellipsoidal cap bubble rising in an irrotational flow of a viscous liquid. The analysis leads to an expression for the Rise Velocity which depends on the aspect ratio of the model ellipsoid and the Reynolds and Eotvos numbers. The aspect ratio of the best ellipsoid is selected to give the same Rise Velocity as the Taylor bubble at given values of the Eotvos and Reynolds numbers. The analysis leads to a prediction of the shape of the ovary ellipsoid which Rises with same Velocity as the Taylor bubble.
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universal correlation for the Rise Velocity of long gas bubbles in round pipes
Journal of Fluid Mechanics, 2003Co-Authors: Flavia Viana, Raimundo Pardo, Rodolfo Yanez, Jose L Trallero, Daniel D. JosephAbstract:We collected all of the published data we could find on the Rise Velocity of long gas bubbles in stagnant fluids contained in circular tubes. Data from 255 experiments from the literature and seven new experiments at PDVSA Intevep for fluids with viscosities ranging from 1 mPa s up to 3900 mPa s were assembled on spread sheets and processed in log–log plots of the normalized Rise Velocity, $\hbox{\it Fr} \,{=}\,U/(gD)^{1/2}$ Froude Velocity vs. buoyancy Reynolds number, $R\,{=}\,(D^{3}g (\rho_{l}-\rho_{g}) \rho_{l})^{1/2}/\mu $ for fixed ranges of the Eotvos number, $\hbox{\it Eo}\,{=}\,g\rho_{l}D^{2}/\sigma $ where $D$ is the pipe diameter, $\rho_{l}$ , $\rho_{g}$ and $\sigma$ are densities and surface tension. The plots give Rise to power laws in $Eo$ ; the composition of these separate power laws emerge as bi-power laws for two separate flow regions for large and small buoyancy Reynolds. For large $R$ ( $>200$ ) we find \[\hbox{\it Fr} = {0.34}/(1+3805/\hbox{\it Eo}^{3.06})^{0.58}.\] For small $R$ ( $ ) we find \[ \hbox{\it Fr} = \frac{9.494\times 10^{-3}}{({1+{6197}/\hbox{\it Eo}^{2.561}})^{0.5793}}R^{1.026}.\] The flat region for high buoyancy Reynolds number and sloped region for low buoyancy Reynolds number is separated by a transition region ( $10\,{ ) which we describe by fitting the data to a logistic dose curve. Repeated application of logistic dose curves leads to a composition of rational fractions of rational fractions of power laws. This leads to the following universal correlation: \[ \hbox{\it Fr} = L[{R;A,B,C,G}] \equiv \frac{A}{({1+({{R}/{B}})^C})^G} \] where \[ A = L[\hbox{\it Eo};a,b,c,d],\quad B = L[\hbox{\it Eo};e,f,g,h],\quad C = L[\hbox{\it Eo};i,j,k,l],\quad G = m/C \] and the parameters ( $a, b,\ldots,l$ ) are \begin{eqnarray*} &&\hspace*{-5pt}a \hspace*{-0.8pt}\,{=}\,\hspace*{-0.8pt} 0.34;\quad b\hspace*{-0.8pt} \,{=}\,\hspace*{-0.8pt} 14.793;\quad c\hspace*{-0.8pt} \,{=}\,\hspace*{-0.6pt}{-}3.06;\quad d\hspace*{-0.6pt} \,{=}\, \hspace*{-0.6pt}0.58;\quad e\hspace*{-0.6pt} \,{=}\,\hspace*{-0.6pt} 31.08;\quad f\hspace*{-0.6pt} \,{=}\, \hspace*{-0.6pt}29.868;\quad g\hspace*{-0.6pt}\,{ =}\,\hspace*{-0.6pt}{ -}1.96;\\ &&\hspace*{-5pt}h = -0.49;\quad i = -1.45;\quad j = 24.867;\quad k = -9.93;\quad l = -0.094;\quad m = -1.0295.\end{eqnarray*} The literature on this subject is reviewed together with a summary of previous methods of prediction. New data and photographs collected at PDVSA-Intevep on the Rise of Taylor bubbles is presented.
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Rise Velocity of a spherical cap bubble
Journal of Fluid Mechanics, 2003Co-Authors: Daniel D. JosephAbstract:The theory of viscous potential flow is applied to the problem of finding the Rise Velocity $U$ of a spherical cap bubble (see Davies & Taylor 1950; Batchelor 1967). The Rise Velocity is given by \frac{U}{\sqrt{gD}}=-\frac{8}{3}\frac{\nu(1+8s)}{\sqrt{gD^3}}+ \frac{\sqrt{2}}{3}\left[ 1-2s-\frac{16s\sigma}{\rho gD^2}+ \frac{32v^2}{gD^3}(1+8s)^2\right]^{1/2}, \nonumber where $R = D/2$ is the radius of the cap, $\rho$ and $\nu$ are the density and kinematic viscosity of the liquid, $\sigma$ is surface tension, $r(\theta) = R(1 + s\theta^2)$ and $s = r''(0)/D$ is the deviation of the free surface from perfect sphericity $r(\theta)=R$ near the stagnation point $\theta = 0$ . The bubble nose is more pointed when $s and blunted when $s > 0.$ A more pointed bubble increases the Rise Velocity; the blunter bubble Rises slower. The Davies & Taylor (1950) result aRises when $s$ and $\nu$ vanish; if $s$ alone is zero, \[\frac{U}{\sqrt{gD}}= -\frac{8}{3}\frac{\nu}{\sqrt{gD^3}}+\frac{\sqrt{2}}{3} \left[ 1+\frac{32\nu^2}{gD^3}\right]^{1/2},\] showing that viscosity slows the Rise Velocity. This equation gives Rise to a hyperbolic drag law \[C_D =6+32/R_e,\] which agrees with data on the Rise Velocity of spherical cap bubbles given by Bhaga & Weber (1981).
J. Ellenberger - One of the best experts on this subject based on the ideXlab platform.
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Rise Velocity of single circular-cap bubbles in two-dimensional beds of powders and liquids
Chemical Engineering and Processing: Process Intensification, 2000Co-Authors: Rajamani Krishna, J.m. Van Baten, M.i. Urseanu, J. EllenbergerAbstract:Abstract An expression for the Rise Velocity of single circular-cap gas bubbles in two-dimensional (2D) beds consisting of powders or liquids is developed with the aid of experimental data and computational fluid dynamics. Experiments were performed in a two-dimensional rectangular column of width D T =0.3 m by injecting air bubbles in fluidised beds of silica (mean particle size, d p =38 μm) and polystyrene (mean particle size, d p =570 μm) and in water. The Rise Velocity of single gas bubbles in the size range d b =0.015–0.12 m were found to decrease significantly with increasing ratio of bubble diameter to bed width, d b / D T . Computational fluid dynamics simulations of single gas bubbles rising in water, carried out using the volume-of-fluid (VOF) method, showed good agreement with experiment and were used to develop a common expression for the Rise Velocity of single gas bubbles in gas–solid fluidised beds and bubble columns. The 2D circular-cap bubble Rise Velocity is found to ∼10–30% lower than that of a 3D spherical-cap bubble having the same equivalent diameter.
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Rise Velocity of a swarm of large gas bubbles in liquids
Chemical Engineering Science, 1999Co-Authors: Rajamani Krishna, J.m. Van Baten, M.i. Urseanu, J. EllenbergerAbstract:This paper develops a procedure for estimation of the Rise Velocity of a swarm of large gas bubbles in a bubble column operating in the churn-turbulent flow regime. The large bubble swarm Velocity is estimated by introducing two correction factors into the classical Davies–Taylor (1950) relation for Rise of a single spherical cap bubble in a liquid Vb=0.71gdb(SF)(AF). The scale correction factor (SF) accounts for the influence of the column diameter. This correction is given by the Collins relation (J. Fluid Mech., 28, 97–112, 1967) and is a function of the ratio of the bubble diameter db to the column diameter DT. Volume-of-fluid simulations confirm the validity of the Davies–Taylor–Collins relations for a variety of liquid properties. The acceleration factor (AF) accounts for the increase in the Rise Velocity of a bubble because of its interaction with the wake of a bubble preceding it. By analysis of video recordings of the interactions between two bubbles, both in-line and off-line, it is found that the acceleration factor AF increases linearly as the vertical distance of separation between the two bubbles decreases. Increasing liquid viscosity reduces this wake acceleration effect. With the aid of an extensive data set on the large bubble swarm Velocity in columns of 0.051, 0.1, 0.174, 0.19, 0.38 and 0.63 m in diameter a correlation is developed for the acceleration factor. The large bubble swarm Velocity is found to be three to six times higher than that of a single isolated bubble.
Hans Mullersteinhagen - One of the best experts on this subject based on the ideXlab platform.
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terminal bubble Rise Velocity in liquids
Chemical Engineering Research & Design, 1994Co-Authors: Mohammad Jamialahmadi, C A Branch, Hans MullersteinhagenAbstract:We present new experimental results of terminal bubble Rise Velocity for a variety of fluids and a model which accurately predicts the bubble Rise Velocity over a wide range of bubble sizes. A comparison is made between experimental results obtained in the investigation as well as by other authors and the predictions of the correlations of Clift et al. (1978), Wallis (1974) and the present authors
