The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
Akio Tomiyama - One of the best experts on this subject based on the ideXlab platform.
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Terminal Velocity of Single Drops in Stagnant Liquids
Journal of Fluid Science and Technology, 2020Co-Authors: Win Myint, Shigeo Hosokawa, Akio TomiyamaAbstract:Terminal velocities of single drops rising through infinite stagnant liquids under wide ranges of fluid properties were measured to examine the effects of initial shape deformation, surfactants and the viscosity ratio. As a result, the following conclusions were obtained: (1) the Terminal Velocity VT of a drop is not affected by initial shape deformation due to strong viscous damping of shape oscillation, (2) the drop drag coefficient CD is a function of the drop Reynolds number Re, the viscosity ratio κ and surfactant concentration, (3) surfactants increase CD and the influence of surfactants on CD becomes weaker as κ increases, which is consistent with the Levich's drag model, (4) the effect of κ on CD can be evaluated by the factor in the Levich's model, [(2+3κ)/(1+κ)], even at intermediate drop Re numbers, and (5) the combination of the Levich's model and Schiller & Nauman's correlation gives good estimation of CD of single drops in clean and fully contaminated systems under the conditions of -11.6
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effects of surfactant on Terminal Velocity of a taylor bubble in a vertical pipe
International Journal of Multiphase Flow, 2012Co-Authors: Kosuke Hayashi, Akio TomiyamaAbstract:Abstract Effects of soluble surfactant on the Terminal Velocity of a Taylor bubble rising through a vertical pipe are investigated using an interface tracking method. A level set method is utilized to track the interface. Transport of surfactant in the bulk liquid and at the interface is taken into account. The amount of adsorption and desorption is evaluated using the Frumkin and Levich model. The normal component of surface tension force is computed using a ghost fluid method, whereas the tangential component, i.e., the Marangoni force, is evaluated by making use of the continuum surface force model. Simulations of small air bubbles contaminated with soluble surfactant are carried out for validation. The Marangoni effects on the bubbles, i.e., the surface immobilization and the increase in drag coefficient, are well predicted. Then Taylor bubbles rising through vertical pipes filled with contaminated water at a low Morton number are simulated for various Eotvos numbers, various bulk surfactant concentrations and two different surfactants, i.e., 1-pentanol and Triton X-100. As a result, the following conclusions are obtained: (1) the reduction of surface tension near the bubble nose is the cause of the increase in Terminal Velocity, (2) the surfactant does not affect the Terminal velocities of high Eotvos number bubbles since the bubbles at high Eotvos numbers are independent of surface tension, (3) the Terminal Velocity of a low Morton number Taylor bubble can be evaluated by making use of available correlations for clean Taylor bubbles, provided that the degree of contamination near the bubble nose is known and the Marangoni effect in the nose region is negligible, and (4) the Hatta number, which is the ratio of the adsorption Velocity to the bubble Velocity, is a primary factor governing the degree of contamination in the bubble nose region.
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Terminal Velocity of a taylor drop in a vertical pipe
International Journal of Multiphase Flow, 2011Co-Authors: Kosuke Hayashi, Ryo Kurimoto, Akio TomiyamaAbstract:Abstract A scaling analysis based on the field equations for two phases and the jump conditions at the interface is carried out to deduce a balance of forces acting on a Taylor drop rising through stagnant liquid in a vertical pipe. The force balance is utilized to deduce a functional form of an empirical correlation of Terminal Velocity of the Taylor drop. Undetermined coefficients in the correlation are evaluated by making use of available correlations for two limiting cases, i.e. extremely high and low Reynolds number Taylor bubbles in large pipes. Terminal Velocity data obtained by interface tracking simulations are also used to determine the coefficients. The proposed correlation expresses the Froude number Fr as a function of the drop Reynolds number ReD, the Eotvos number EoD and the viscosity ratio μ*. Comparisons between the correlation, simulations and experimental data confirm that the proposed correlation is applicable to Taylor drops under various conditions, i.e., 0.002
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Terminal Velocity of single drops in stagnant liquids
Journal of Fluid Science and Technology, 2006Co-Authors: Win Myint, Shigeo Hosokawa, Akio TomiyamaAbstract:Terminal velocities of single drops rising through infinite stagnant liquids under wide ranges of fluid properties were measured to examine the effects of initial shape deformation, surfactants and the viscosity ratio. As a result, the following conclusions were obtained: (1) the Terminal Velocity VT of a drop is not affected by initial shape deformation due to strong viscous damping of shape oscillation, (2) the drop drag coefficient CD is a function of the drop Reynolds number Re, the viscosity ratio κ and surfactant concentration, (3) surfactants increase CD and the influence of surfactants on CD becomes weaker as κ increases, which is consistent with the Levich's drag model, (4) the effect of κ on CD can be evaluated by the factor in the Levich's model, [(2+3κ)/(1+κ)], even at intermediate drop Re numbers, and (5) the combination of the Levich's model and Schiller & Nauman's correlation gives good estimation of CD of single drops in clean and fully contaminated systems under the conditions of -11.6
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Terminal Velocity of single bubbles in surface tension force dominant regime
International Journal of Multiphase Flow, 2002Co-Authors: Akio Tomiyama, Shigeo Hosokawa, Gian Piero Celata, S YoshidaAbstract:Abstract Terminal Velocity V T of a single bubble rising through an infinite stagnant liquid in surface tension force dominant regime was investigated theoretically and experimentally. A theoretical V T model, which is applicable to a distorted spheroidal bubble with a high bubble Reynolds number, was deduced from a jump condition and a potential flow theory for a flow about an oblate spheroid. Experiments were conducted using air and water to measure bubble trajectories, shapes and velocities. As a result, it was confirmed that (1) the primal cause of widely scattered V T in this regime is not surfactant concentration but initial shape deformation, (2) small initial shape deformation results in a low V T and a high aspect ratio, whereas large initial shape deformation results in a high V T and a low aspect ratio, (3) the primal role of surfactants in this regime is to cause the damping of shape oscillation, by which a contaminated bubble behaves as if it were a clean bubble with low initial shape deformation, and (4) the proposed model gives good predictions of V T for single distorted bubbles.
Vassilios C Kelessidis - One of the best experts on this subject based on the ideXlab platform.
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prediction of Terminal Velocity of solid spheres falling through newtonian and non newtonian pseudoplastic power law fluid using artificial neural network
International Journal of Mineral Processing, 2012Co-Authors: Reza Rooki, Vassilios C Kelessidis, Doulati F Ardejani, Ali Moradzadeh, M NouroziAbstract:Abstract Prediction of the Terminal Velocity of solid spheres falling through Newtonian and non-Newtonian fluids is required in several applications like mineral processing, oil well drilling, geothermal drilling and transportation of non-Newtonian slurries. An artificial neural network (ANN) is proposed which predicts directly the Terminal Velocity of solid spheres falling through Newtonian and non-Newtonian power law liquids from the knowledge of the properties of the spherical particle (density and diameter) and of the surrounding liquid (density and rheological parameters). With a combination of non-Newtonian data with Newtonian data taken from published data giving a database of 88 sets, an artificial neural network is designed. Analysis of the predictions shows that the artificial neural network could be used with good engineering accuracy to directly predict the Terminal Velocity of solid spheres falling through Newtonian and non-Newtonian power law liquids covering an extended range of power law values from 1.0 down to 0.06.
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an explicit equation for the Terminal Velocity of solid spheres falling in pseudoplastic liquids
Chemical Engineering Science, 2004Co-Authors: Vassilios C KelessidisAbstract:Abstract An explicit equation is proposed which predicts directly the Terminal Velocity of solid spheres falling through stagnant pseudoplastic liquids from the knowledge of the physical properties of the spheres and of the surrounding liquid. The equation is a generalization of the equation proposed for Newtonian liquids. By properly defining the dimensionless diameter, d * , a function of the Archimedes number, Ar , and the dimensionless Velocity, U * , a function of the generalized Reynolds number, Re , to account for the non-Newtonian characteristics of the liquid, the final equation relating these two variables has similar form to the Newtonian equation. The predictions are very good when they are compared to 55 pairs of Re— C D for non-Newtonian data and 37 pairs for Newtonian data published previously. The root mean square error on the dimensionless Velocity is 0.081 and much better than the only other equation previously proposed.
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measurements and prediction of Terminal Velocity of solid spheres falling through stagnant pseudoplastic liquids
Powder Technology, 2004Co-Authors: Vassilios C Kelessidis, G MpandelisAbstract:Abstract Prediction of the Terminal Velocity of solid spheres falling through stagnant pseudoplastic fluids is required in several applications like oil well drilling, geothermal drilling, transportation of non-Newtonian slurries and mineral processing. Prior attempts utilized various Newtonian correlations to predict the drag coefficient and from this the Terminal Velocity with varying degrees of success. We report here carefully derived experimental data for solid spheres falling through non-Newtonian liquids and present them together with measurements reported in the literature, for a total of 80 pairs of Re–CD, and show that the data fall along the same curve. Through nonlinear regression, an equation is derived, similar to the most accurate, simple, five-constant equation proposed for Newtonian liquids, which has not yet been tested for non-Newtonian liquids. The predictions compare favorably with the measurements both for the proposed equation and for the Newtonian equation. With a combination of non-Newtonian data with Newtonian data, from this work and work from other investigators, giving a database of 148 pairs, an improved equation is derived. Analysis of the predictions shows that the Newtonian equation describes extremely well the Newtonian data and furthermore it could be used with good engineering accuracy to predict the Terminal Velocity of solid spheres falling through stagnant non-Newtonian liquids.
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Terminal Velocity of solid spheres falling in newtonian and non newtonian liquids
2003Co-Authors: Vassilios C KelessidisAbstract:The prediction of the Terminal Velocity of solid spheres falling in non-Newtonian shear thinning stagnant liquids is required in many industrial applications. Various correlations have been proposed but an accurate and comprehensive equation covering the whole range of Reynolds numbers is not yet available. Furthermore, there is scarcity of much needed experimental data to aid in the derivation of the optimal correlation. Many investigators opt for using correlations derived for Newtonian liquids. However, there is a great variety of such correlations and not much is known about the optimal one or about the differences among them. The scope of this work was to propose an equation for predicting the Terminal Velocity of solid spheres falling in non-Newtonian shear thinning stagnant liquids. The equation is firstly chosen by comparing the various proposed correlations using three indicators. It is then compared to experimental data taken using solid spheres falling through water solutions of Carboxylmethylcellulose of various concentrations and Newtonian fluids. The equation proposed compares favorably both to the experimental data presented and to experimental data reported by other investigators.
Laura Danly - One of the best experts on this subject based on the ideXlab platform.
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high Velocity rain the Terminal Velocity model of galactic infall
The Astrophysical Journal, 1997Co-Authors: Robert A. Benjamin, Laura DanlyAbstract:A model is proposed for determining the distances to falling interstellar clouds in the galactic halo by measuring the cloud Velocity and column density and assuming a model for the vertical density distribution of the Galactic interstellar medium. It is shown that falling clouds with N(H I) 1019 cm-2 may be decelerated to a Terminal Velocity which increases with increasing height above the Galactic plane. This Terminal Velocity model correctly predicts the distance to high-Velocity cloud Complex M and several other interstellar structures of previously determined distance. It is demonstrated how interstellar absorption spectra alone may be used to predict the distances of the clouds producing the absorption. If the distance, velocities, and column densities of enough interstellar clouds are known independently, the procedure can be reversed, and the Terminal Velocity model can be used to estimate the vertical density structure (both the mean density and the porosity) of the interstellar medium. Using the data of Danly and assuming a drag coefficient of CD 1, the derived density distribution is consistent with the expected density distribution of the warm ionized medium, characterized by Reynolds. There is also evidence that for z 0.4 kpc one or more of the following occurs: (1) the neutral fraction of the cloud decreases to ~31 ? 14%, (2) the density drops off faster than characterized by Reynolds, or (3) there is a systematic decrease in CD with increasing z. Current data do not place strong constraints on the porosity of the interstellar medium.
Kosuke Hayashi - One of the best experts on this subject based on the ideXlab platform.
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effects of surfactant on Terminal Velocity of a taylor bubble in a vertical pipe
International Journal of Multiphase Flow, 2012Co-Authors: Kosuke Hayashi, Akio TomiyamaAbstract:Abstract Effects of soluble surfactant on the Terminal Velocity of a Taylor bubble rising through a vertical pipe are investigated using an interface tracking method. A level set method is utilized to track the interface. Transport of surfactant in the bulk liquid and at the interface is taken into account. The amount of adsorption and desorption is evaluated using the Frumkin and Levich model. The normal component of surface tension force is computed using a ghost fluid method, whereas the tangential component, i.e., the Marangoni force, is evaluated by making use of the continuum surface force model. Simulations of small air bubbles contaminated with soluble surfactant are carried out for validation. The Marangoni effects on the bubbles, i.e., the surface immobilization and the increase in drag coefficient, are well predicted. Then Taylor bubbles rising through vertical pipes filled with contaminated water at a low Morton number are simulated for various Eotvos numbers, various bulk surfactant concentrations and two different surfactants, i.e., 1-pentanol and Triton X-100. As a result, the following conclusions are obtained: (1) the reduction of surface tension near the bubble nose is the cause of the increase in Terminal Velocity, (2) the surfactant does not affect the Terminal velocities of high Eotvos number bubbles since the bubbles at high Eotvos numbers are independent of surface tension, (3) the Terminal Velocity of a low Morton number Taylor bubble can be evaluated by making use of available correlations for clean Taylor bubbles, provided that the degree of contamination near the bubble nose is known and the Marangoni effect in the nose region is negligible, and (4) the Hatta number, which is the ratio of the adsorption Velocity to the bubble Velocity, is a primary factor governing the degree of contamination in the bubble nose region.
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Terminal Velocity of a taylor drop in a vertical pipe
International Journal of Multiphase Flow, 2011Co-Authors: Kosuke Hayashi, Ryo Kurimoto, Akio TomiyamaAbstract:Abstract A scaling analysis based on the field equations for two phases and the jump conditions at the interface is carried out to deduce a balance of forces acting on a Taylor drop rising through stagnant liquid in a vertical pipe. The force balance is utilized to deduce a functional form of an empirical correlation of Terminal Velocity of the Taylor drop. Undetermined coefficients in the correlation are evaluated by making use of available correlations for two limiting cases, i.e. extremely high and low Reynolds number Taylor bubbles in large pipes. Terminal Velocity data obtained by interface tracking simulations are also used to determine the coefficients. The proposed correlation expresses the Froude number Fr as a function of the drop Reynolds number ReD, the Eotvos number EoD and the viscosity ratio μ*. Comparisons between the correlation, simulations and experimental data confirm that the proposed correlation is applicable to Taylor drops under various conditions, i.e., 0.002
G Mpandelis - One of the best experts on this subject based on the ideXlab platform.
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measurements and prediction of Terminal Velocity of solid spheres falling through stagnant pseudoplastic liquids
Powder Technology, 2004Co-Authors: Vassilios C Kelessidis, G MpandelisAbstract:Abstract Prediction of the Terminal Velocity of solid spheres falling through stagnant pseudoplastic fluids is required in several applications like oil well drilling, geothermal drilling, transportation of non-Newtonian slurries and mineral processing. Prior attempts utilized various Newtonian correlations to predict the drag coefficient and from this the Terminal Velocity with varying degrees of success. We report here carefully derived experimental data for solid spheres falling through non-Newtonian liquids and present them together with measurements reported in the literature, for a total of 80 pairs of Re–CD, and show that the data fall along the same curve. Through nonlinear regression, an equation is derived, similar to the most accurate, simple, five-constant equation proposed for Newtonian liquids, which has not yet been tested for non-Newtonian liquids. The predictions compare favorably with the measurements both for the proposed equation and for the Newtonian equation. With a combination of non-Newtonian data with Newtonian data, from this work and work from other investigators, giving a database of 148 pairs, an improved equation is derived. Analysis of the predictions shows that the Newtonian equation describes extremely well the Newtonian data and furthermore it could be used with good engineering accuracy to predict the Terminal Velocity of solid spheres falling through stagnant non-Newtonian liquids.
