The Experts below are selected from a list of 303 Experts worldwide ranked by ideXlab platform

Rajamani Krishna - One of the best experts on this subject based on the ideXlab platform.

  • Wall effects on the rise of single gas bubbles in liquids
    International Communications in Heat and Mass Transfer, 1999
    Co-Authors: Rajamani Krishna, M.i. Urseanu, J.m. Van Baten, Jürg Ellenberger
    Abstract:

    Abstract We report the results of an extensive experimental investigation on the velocity of rise of air bubbles in the size range db = 3 – 80 mm in water. Measurements were made in Columns with inside Diameters DT = 0.01, 0.02, 0.03, 0.051, 0.1, 0.174 and 0.63 m. The Column Diameter was found to have a significant effect on the rise velocity of the bubbles. When the ratio of the bubble Diameter to the Column Diameter, db/DT, is smaller than 0.125 the influence of the Column Diameter on the rise velocity is negligible and the rise velocity is described quite accurately by the Mendelson equation. With increasing db/DT there is a significant reduction of the rise velocity, i.e. there is a significant “wall effect”. The wall effect for spherical cap bubbles rising in inviscid flow, obtained for bubble Diameters larger than 0.017 m, is described adequately by the Collins relation. The wall effect for bubbles smaller than 0.017 m is described by an empirical relation suggested by Clift, Grace and Weber.

  • Gas Holdup in Slurry Bubble Columns: Effect of Column Diameter and Slurry Concentrations
    AIChE Journal, 1997
    Co-Authors: Rajamani Krishna, Gilbert B. Martina, Jeroen W.a. De Swart, Jürg Ellenberger, Cristina Maretto
    Abstract:

    To study the influence of particle concentration on the hydrodynamics of bubble-Column slurry reactors operating in the heterogeneous flow regime, experiments were carried out in 0.10, 0.19, and 0.38-m-dia. Columns using paraffinic oil as the liquid phase and slurry concentrations of up to 36 vol. %. To interpret experimental results a generalization of the two-phase model for gas-solid fluid beds was used to describe bubble hydrodynamics. The two phases identified are: a dilute phase consisting of fast-rising large bubbles that traverse the Column virtually in plug flow and a dense phase that is identified with the liquid phase along with solid particles and entrained small bubbles. The dense phase suffers backmixing considerably. Dynamic gas disengagement was experimented in the heterogeneous flow regime to determine the gas voidage in dilute and dense phases. Experimental data show that increasing the solid concentration decreases the total gas holdup significantly, but the influence on the dilute-phase gas holdup is small. The dense-phase gas voidage significantly decreases gas holdup due to enhanced coalescence of small bubbles resulting from introduction of particles. The dense-phase gas voidage is practically independent of the Column Diameter. The dilute-phase gas holdup, on the other hand, decreases with increasing Column Diameter, and this dependence could be described adequately with a slight modification of the correlation of Krishna and Ellenberger developed for gas-liquid systems.

Jürg Ellenberger - One of the best experts on this subject based on the ideXlab platform.

  • Wall effects on the rise of single gas bubbles in liquids
    International Communications in Heat and Mass Transfer, 1999
    Co-Authors: Rajamani Krishna, M.i. Urseanu, J.m. Van Baten, Jürg Ellenberger
    Abstract:

    Abstract We report the results of an extensive experimental investigation on the velocity of rise of air bubbles in the size range db = 3 – 80 mm in water. Measurements were made in Columns with inside Diameters DT = 0.01, 0.02, 0.03, 0.051, 0.1, 0.174 and 0.63 m. The Column Diameter was found to have a significant effect on the rise velocity of the bubbles. When the ratio of the bubble Diameter to the Column Diameter, db/DT, is smaller than 0.125 the influence of the Column Diameter on the rise velocity is negligible and the rise velocity is described quite accurately by the Mendelson equation. With increasing db/DT there is a significant reduction of the rise velocity, i.e. there is a significant “wall effect”. The wall effect for spherical cap bubbles rising in inviscid flow, obtained for bubble Diameters larger than 0.017 m, is described adequately by the Collins relation. The wall effect for bubbles smaller than 0.017 m is described by an empirical relation suggested by Clift, Grace and Weber.

  • Gas Holdup in Slurry Bubble Columns: Effect of Column Diameter and Slurry Concentrations
    AIChE Journal, 1997
    Co-Authors: Rajamani Krishna, Gilbert B. Martina, Jeroen W.a. De Swart, Jürg Ellenberger, Cristina Maretto
    Abstract:

    To study the influence of particle concentration on the hydrodynamics of bubble-Column slurry reactors operating in the heterogeneous flow regime, experiments were carried out in 0.10, 0.19, and 0.38-m-dia. Columns using paraffinic oil as the liquid phase and slurry concentrations of up to 36 vol. %. To interpret experimental results a generalization of the two-phase model for gas-solid fluid beds was used to describe bubble hydrodynamics. The two phases identified are: a dilute phase consisting of fast-rising large bubbles that traverse the Column virtually in plug flow and a dense phase that is identified with the liquid phase along with solid particles and entrained small bubbles. The dense phase suffers backmixing considerably. Dynamic gas disengagement was experimented in the heterogeneous flow regime to determine the gas voidage in dilute and dense phases. Experimental data show that increasing the solid concentration decreases the total gas holdup significantly, but the influence on the dilute-phase gas holdup is small. The dense-phase gas voidage significantly decreases gas holdup due to enhanced coalescence of small bubbles resulting from introduction of particles. The dense-phase gas voidage is practically independent of the Column Diameter. The dilute-phase gas holdup, on the other hand, decreases with increasing Column Diameter, and this dependence could be described adequately with a slight modification of the correlation of Krishna and Ellenberger developed for gas-liquid systems.

Cristina Maretto - One of the best experts on this subject based on the ideXlab platform.

  • Gas Holdup in Slurry Bubble Columns: Effect of Column Diameter and Slurry Concentrations
    AIChE Journal, 1997
    Co-Authors: Rajamani Krishna, Gilbert B. Martina, Jeroen W.a. De Swart, Jürg Ellenberger, Cristina Maretto
    Abstract:

    To study the influence of particle concentration on the hydrodynamics of bubble-Column slurry reactors operating in the heterogeneous flow regime, experiments were carried out in 0.10, 0.19, and 0.38-m-dia. Columns using paraffinic oil as the liquid phase and slurry concentrations of up to 36 vol. %. To interpret experimental results a generalization of the two-phase model for gas-solid fluid beds was used to describe bubble hydrodynamics. The two phases identified are: a dilute phase consisting of fast-rising large bubbles that traverse the Column virtually in plug flow and a dense phase that is identified with the liquid phase along with solid particles and entrained small bubbles. The dense phase suffers backmixing considerably. Dynamic gas disengagement was experimented in the heterogeneous flow regime to determine the gas voidage in dilute and dense phases. Experimental data show that increasing the solid concentration decreases the total gas holdup significantly, but the influence on the dilute-phase gas holdup is small. The dense-phase gas voidage significantly decreases gas holdup due to enhanced coalescence of small bubbles resulting from introduction of particles. The dense-phase gas voidage is practically independent of the Column Diameter. The dilute-phase gas holdup, on the other hand, decreases with increasing Column Diameter, and this dependence could be described adequately with a slight modification of the correlation of Krishna and Ellenberger developed for gas-liquid systems.

Robert Franke - One of the best experts on this subject based on the ideXlab platform.

  • experimental investigation of the influence of Column scale gas density and liquid properties on gas holdup in bubble Columns
    International Journal of Multiphase Flow, 2015
    Co-Authors: Philipp Rollbusch, Marc Becker, Martina Ludwig, Andre Bieberle, Marcus Grunewald, Uwe Hampel, Robert Franke
    Abstract:

    Abstract Measurements of gas holdups in bubble Columns of 0.16, 0.30 and 0.33 m Diameter were carried out. These Columns were operated in co-current flow of gas and liquid phases and in semibatch mode. The Column of 0.33 m Diameter was operated at elevated pressures of up to 3.6 MPa. Nitrogen was employed as the gas phase and deionized water, aqueous solutions of ethanol and acetone and pure acetone and cumene as the liquid phase. The effects of differing liquid properties, gas density (due to elevated pressure), temperature, Column Diameter and superficial liquid velocity on gas holdup were studied. The gas holdup measurements were utilized by differential pressure measurements at different positions along the height of the bubble Columns which allowed for the identification of axial gas holdup profiles. A decrease of gas holdup with increasing Column Diameter and an increase of gas holdup with increasing pressure was observed. The effect of a slightly decreasing gas holdup with increasing liquid velocity was found to exist at smaller Column Diameters. The use of organic solvents as the liquid phase resulted in a significant increase in gas holdup compared to deionized water. It is found that published gas holdup models are mostly unable to predict the results obtained in this study.

Kaveh Ahangari - One of the best experts on this subject based on the ideXlab platform.

  • Jet grouting: mathematical model to predict soilcrete Column Diameter - part I
    International Journal of Mining and Mineral Engineering, 2015
    Co-Authors: Babak Nikbakhtan, Derek B. Apel, Kaveh Ahangari
    Abstract:

    Predicting soilcrete Column Diameter in jet grouting operations is one of the challenging tasks of engineers. By being able to determine the Diameters, number of required Columns and their spacing needed for activities such as cut off walls, soil improvement and slope stability activities can be calculated. However, there is no precise method to calculate and design the Diameter before the operations. Therefore authors attempt to present a mathematical model using sum of squared–deviations (SSDs) method to estimate the Diameter of soilcrete created by triple fluid jet grouting system. To do so, the actual data where soilcrete Diameters have been measured, is used to prove and test the mathematical model. The effective jet grouting operational parameters that impact the Diameter have been determined according to literature review of previous studies. On the basis of the results of modelling, the presented equation can predict soilcrete Diameters with error range of 3–20%.

  • Jet grouting: using artificial neural networks to predict soilcrete Column Diameter - part II
    International Journal of Mining and Mineral Engineering, 2015
    Co-Authors: Babak Nikbakhtan, Derek B. Apel, Kaveh Ahangari
    Abstract:

    Previously authors attempted to predict soilcrete Diameter using Sum of Squared–Deviations mathematical model (Part I). It has been shown that the mathematical model cannot relate all impacting parameters with the Diameter where the relation between soil conductivity and grout density did not match with literature and field observations. Therefore, in this paper an approach based on artificial neural network (ANN) with a wider range of data are used to calculate the Diameter. ANN is a useful predictive method because it utilises both extensive computerised database and existing knowledge of what influences the Diameter. This paper attempts to evaluate potential as well as limitations of ANN for predicting the Diameter and to develop optimal neural network models to reduce the need for trial jet grouting as much as possible. One of the most significant results of this study is the optimisation of the costs and time needed for mining and civil projects.