A. Kemoun - Academia.edu (original) (raw)

Papers by A. Kemoun

The overall objective of this collaborative project between Washington University, Ohio State Uni... more The overall objective of this collaborative project between Washington University, Ohio State University and Air Products and Chemicals is to advance the knowledge and understanding of the hydrodynamics of Fischer-Tropsch (FT) slurry bubble column reactors at FT synthesis conditions.

Powder Technology, 2001

We propose a simple method for accurately estimating the solids circulation rate in a closed-loop... more We propose a simple method for accurately estimating the solids circulation rate in a closed-loop liquid–solid circulating fluidized bed. The technique is based on the use of radioactive isotopes for estimating the solids velocity and volume fraction distribution in a chosen section of the circulating fluidized bed loop. The method is demonstrated for a liquid–solid circulating fluidized bed, and is

Indoor Air, 2001

Many ice rink arenas have ice resurfacing equipment that uses fossil fuel as power. The combustio... more Many ice rink arenas have ice resurfacing equipment that uses fossil fuel as power. The combustion byproducts are a major source of contamination. Ventilation along with other pollution source control measures is the most widely applied strategy to lower the contaminant level below the threshold limit and maintain acceptable indoor air quality (IAQ). A computational fluid dynamics (CFD) model has been developed and used to predict the contaminant concentrations, air velocity, and air temperature distributions in ice rinks. The numerical results agree reasonably with the corresponding experimental data for both steady-state and transient conditions. The CFD model is a useful and inexpensive tool to investigate ventilation parameters, such as air distribution methods, ventilation effectiveness, air exchange rates, and various ventilation control strategies.

Chemical Engineering Science, 2001

Experiments carried out to study the liquid displacements in bubble columns via the computer auto... more Experiments carried out to study the liquid displacements in bubble columns via the computer automated radioactive particle tracking technique are analyzed by means of Lagrangian and qualitative dynamics tools. The Lagrangian approach yields the detailed motion sequences of the tracer as entrained by the fast ascending bubbles or by the liquid ow alongside the column walls. The qualitative dynamics tools, on the other hand, provide prima facie corroboration of chaos in liquid motion based on an analysis of the volume-averaged Kolmogorov entropy and the mutual information function. Other features of the chaotic motion, the reconstructed attractors and the radial and axial distributions of Lyapunov exponents, are noted. Variations in the liquid hydrodynamics due to changes in column diameter and operating pressure are inspected. By increasing pressure the attractor's correlation dimension and the information loss rate decrease, whereas the liquid ow path is dramatically a ected. ? 2001 Published by Elsevier Science Ltd.

Chemical Engineering Science, 2001

In this study, computer-automated radioactive particle tracking (CARPT) is implemented for the fi... more In this study, computer-automated radioactive particle tracking (CARPT) is implemented for the first time in the characterization of flows in stirred tanks. Both the experimental technique and the experimental set-up are discussed. The CARPT technique is seen to capture qualitatively most of the important flow phenomena observed in stirred tank flows, like the two recirculating loops above and below the

Chemical Engineering Research and Design, 2001

ABSTRACT Single phase flows in stirred tanks have been extensively characterized using different ... more ABSTRACT Single phase flows in stirred tanks have been extensively characterized using different experimental techniques like Hot Wire Anemometry1, Laser Doppler Anemometry2, and Digital Particle Imaging Velocimetry3. None of these techniques however, show much promise for the interrogation of opaque multiphase flows. Hence, little or no information of the local fluid dynamics of multiphase flows in stirred tanks is available. Non-optical techniques like Computer Automated Radioactive Particle Tracking (CARPT) and Computed Tomography (CT) have been successfully applied to probe a variety of multiphase reactors4–5 such as bubble columns6–7, risers8 etc., over a range of dispersed phase holdups. CARPT provides the local fluid dynamic information such as velocities and the turbulence parameters throughout the system that is investigated. CT provides time averaged local dispersed phase holdup profiles in various planes of the entire reactor. In this study, it is proposed to extend these techniques to characterize gas-liquid flows in stirred tank reactors. As a first step, CARPT is implemented in characterization of single phase flows in stirred tanks. CARPT experiments have been performed with water at 150 rpm in a 0.20m cylindrical tank quipped with a six bladed Rushton turbine (0.067m dia) conforming to the standard Holland and Chapman9 configuration. The CARPT technique is shown to capture some of the important flow phenomena observed in such flows, like the two recirculating loops above and below the impeller and the dead zones at the bottom of the tank. Radial pumping numbers determined by CARPT (0.67 near the impeller tip) compare reasonably well with data reported in the literature. Comparison of the complete three dimensional mean velocity profiles from CARPT with similar PIV, LDA and other data reported in the literature reveals that CARPT captures the right order of magnitude of the radial and the tangential velocities. Comparisons of the fluctuating velocity components, like the root mean squared (rms) velocity and the turbulent kinetic energy, suggest that the CARPT experiments were limited by large tracer particle size (dp = 2.3 mm) from sampling the high frequency fluctuations of the fluid. In addition, the three dimensional profiles of the components of the Reynolds stress tensor are measured. The detailed comparisons, even with the large tracer particle, indicate that CARPT measurements capture all the important qualitative features of the flow and quantitatively capture the right order of magnitude of the mean flow parameters. The quantitative comparisons suggest that the current size of the tracer particle restricts it from responding completely to the fluid phase fluctuations. Some Lagrangian measures of the fluid dynamics like the ‘Sojourn’ time distributions (STDs) in different zones of the reactor, Circulation Time Distributions (CTDs), Particle Return Maps to specific planes, Poincarre sections and Hurst exponents are evaluated from the collected CARPT data.

AIChE Journal, 2005

ABSTRACT Liquid–solid fluid dynamics has been investigated in a 6-in. (0.15 m) “cold-flow” circul... more ABSTRACT Liquid–solid fluid dynamics has been investigated in a 6-in. (0.15 m) “cold-flow” circulating fluidized bed riser using non-invasive flow monitoring methods. Gamma-ray computed tomography (CT) was used to measure the time-averaged cross-sectional solids volume fraction distributions at several elevations. The time-averaged mean and “fluctuating” solids velocity fields were quantified using the computer-automated radioactive particle tracking (CARPT) technique. The experimental equipment, protocol of implementation, and data analysis have been discussed briefly, with particular emphasis on the specific features in the use of these techniques for studying high-density turbulent flows as in a liquid–solid riser. The experimental study examines nine operating conditions, that is, three liquid superficial velocities and three solids flow rates. The solids holdup profile is found to be relatively uniform across the cross section of the riser, with marginal segregation near the walls. The time-averaged solids velocity profiles are found to have a negative component at the walls, indicating significant solids backmixing. Detailed characterization of the solids velocity fields in terms of RMS velocities, kinetic energies, Hurst exponents, residence time distributions, trajectory length distributions, dispersion coefficients, and so forth are presented. Comparative and symbiotic analyses of the results were used to develop a coherent picture of the solids flow field. In addition, the work also serves to demonstrate the power and versatility of these flow-imaging techniques in studying highly turbulent and opaque multiphase systems. © 2005 American Institute of Chemical Engineers AIChE J, 51: 802–835, 2005

International Journal of …, 2001

Gas holdup in a pressurized bubble column (pressures from 0.1 to 0.7 MPa) was studied in a labora... more Gas holdup in a pressurized bubble column (pressures from 0.1 to 0.7 MPa) was studied in a laboratory scale vessel (diameter 0.162 m) with air–water system over a range of superficial gas velocities (0.02–0.18 m/s) using non-invasive γ-ray based Computed Tomography ...

Chemical Engineering and Processing: Process Intensification, 2005

A newly developed γ-ray computed tomography scanner was implemented to study liquid flow distribu... more A newly developed γ-ray computed tomography scanner was implemented to study liquid flow distribution in a 30.48-cm-diameter column packed with corrugated structure using countercurrent air–water flow. Validation experiments confirm that spatial resolution of ∼2.5mm can be achieved by the new CT unit.Within the gas (0–10cm/s superficial velocity) and liquid (0.6–2.5cm/s superficial velocity) flow ranges investigated, a good liquid distribution was observed at all conditions, as manifested by uniformity factor in excess of 70%. The liquid saturation increases with increasing superficial liquid velocity as well as down the column height. Within the conditions studied, the effect of gas velocity was, in general, found to be minimal.

The overall objective of this collaborative project between Washington University, Ohio State Uni... more The overall objective of this collaborative project between Washington University, Ohio State University and Air Products and Chemicals is to advance the knowledge and understanding of the hydrodynamics of Fischer-Tropsch (FT) slurry bubble column reactors at FT synthesis conditions.

Powder Technology, 2001

We propose a simple method for accurately estimating the solids circulation rate in a closed-loop... more We propose a simple method for accurately estimating the solids circulation rate in a closed-loop liquid–solid circulating fluidized bed. The technique is based on the use of radioactive isotopes for estimating the solids velocity and volume fraction distribution in a chosen section of the circulating fluidized bed loop. The method is demonstrated for a liquid–solid circulating fluidized bed, and is

Indoor Air, 2001

Many ice rink arenas have ice resurfacing equipment that uses fossil fuel as power. The combustio... more Many ice rink arenas have ice resurfacing equipment that uses fossil fuel as power. The combustion byproducts are a major source of contamination. Ventilation along with other pollution source control measures is the most widely applied strategy to lower the contaminant level below the threshold limit and maintain acceptable indoor air quality (IAQ). A computational fluid dynamics (CFD) model has been developed and used to predict the contaminant concentrations, air velocity, and air temperature distributions in ice rinks. The numerical results agree reasonably with the corresponding experimental data for both steady-state and transient conditions. The CFD model is a useful and inexpensive tool to investigate ventilation parameters, such as air distribution methods, ventilation effectiveness, air exchange rates, and various ventilation control strategies.

Chemical Engineering Science, 2001

Experiments carried out to study the liquid displacements in bubble columns via the computer auto... more Experiments carried out to study the liquid displacements in bubble columns via the computer automated radioactive particle tracking technique are analyzed by means of Lagrangian and qualitative dynamics tools. The Lagrangian approach yields the detailed motion sequences of the tracer as entrained by the fast ascending bubbles or by the liquid ow alongside the column walls. The qualitative dynamics tools, on the other hand, provide prima facie corroboration of chaos in liquid motion based on an analysis of the volume-averaged Kolmogorov entropy and the mutual information function. Other features of the chaotic motion, the reconstructed attractors and the radial and axial distributions of Lyapunov exponents, are noted. Variations in the liquid hydrodynamics due to changes in column diameter and operating pressure are inspected. By increasing pressure the attractor's correlation dimension and the information loss rate decrease, whereas the liquid ow path is dramatically a ected. ? 2001 Published by Elsevier Science Ltd.

Chemical Engineering Science, 2001

In this study, computer-automated radioactive particle tracking (CARPT) is implemented for the fi... more In this study, computer-automated radioactive particle tracking (CARPT) is implemented for the first time in the characterization of flows in stirred tanks. Both the experimental technique and the experimental set-up are discussed. The CARPT technique is seen to capture qualitatively most of the important flow phenomena observed in stirred tank flows, like the two recirculating loops above and below the

Chemical Engineering Research and Design, 2001

ABSTRACT Single phase flows in stirred tanks have been extensively characterized using different ... more ABSTRACT Single phase flows in stirred tanks have been extensively characterized using different experimental techniques like Hot Wire Anemometry1, Laser Doppler Anemometry2, and Digital Particle Imaging Velocimetry3. None of these techniques however, show much promise for the interrogation of opaque multiphase flows. Hence, little or no information of the local fluid dynamics of multiphase flows in stirred tanks is available. Non-optical techniques like Computer Automated Radioactive Particle Tracking (CARPT) and Computed Tomography (CT) have been successfully applied to probe a variety of multiphase reactors4–5 such as bubble columns6–7, risers8 etc., over a range of dispersed phase holdups. CARPT provides the local fluid dynamic information such as velocities and the turbulence parameters throughout the system that is investigated. CT provides time averaged local dispersed phase holdup profiles in various planes of the entire reactor. In this study, it is proposed to extend these techniques to characterize gas-liquid flows in stirred tank reactors. As a first step, CARPT is implemented in characterization of single phase flows in stirred tanks. CARPT experiments have been performed with water at 150 rpm in a 0.20m cylindrical tank quipped with a six bladed Rushton turbine (0.067m dia) conforming to the standard Holland and Chapman9 configuration. The CARPT technique is shown to capture some of the important flow phenomena observed in such flows, like the two recirculating loops above and below the impeller and the dead zones at the bottom of the tank. Radial pumping numbers determined by CARPT (0.67 near the impeller tip) compare reasonably well with data reported in the literature. Comparison of the complete three dimensional mean velocity profiles from CARPT with similar PIV, LDA and other data reported in the literature reveals that CARPT captures the right order of magnitude of the radial and the tangential velocities. Comparisons of the fluctuating velocity components, like the root mean squared (rms) velocity and the turbulent kinetic energy, suggest that the CARPT experiments were limited by large tracer particle size (dp = 2.3 mm) from sampling the high frequency fluctuations of the fluid. In addition, the three dimensional profiles of the components of the Reynolds stress tensor are measured. The detailed comparisons, even with the large tracer particle, indicate that CARPT measurements capture all the important qualitative features of the flow and quantitatively capture the right order of magnitude of the mean flow parameters. The quantitative comparisons suggest that the current size of the tracer particle restricts it from responding completely to the fluid phase fluctuations. Some Lagrangian measures of the fluid dynamics like the ‘Sojourn’ time distributions (STDs) in different zones of the reactor, Circulation Time Distributions (CTDs), Particle Return Maps to specific planes, Poincarre sections and Hurst exponents are evaluated from the collected CARPT data.

AIChE Journal, 2005

ABSTRACT Liquid–solid fluid dynamics has been investigated in a 6-in. (0.15 m) “cold-flow” circul... more ABSTRACT Liquid–solid fluid dynamics has been investigated in a 6-in. (0.15 m) “cold-flow” circulating fluidized bed riser using non-invasive flow monitoring methods. Gamma-ray computed tomography (CT) was used to measure the time-averaged cross-sectional solids volume fraction distributions at several elevations. The time-averaged mean and “fluctuating” solids velocity fields were quantified using the computer-automated radioactive particle tracking (CARPT) technique. The experimental equipment, protocol of implementation, and data analysis have been discussed briefly, with particular emphasis on the specific features in the use of these techniques for studying high-density turbulent flows as in a liquid–solid riser. The experimental study examines nine operating conditions, that is, three liquid superficial velocities and three solids flow rates. The solids holdup profile is found to be relatively uniform across the cross section of the riser, with marginal segregation near the walls. The time-averaged solids velocity profiles are found to have a negative component at the walls, indicating significant solids backmixing. Detailed characterization of the solids velocity fields in terms of RMS velocities, kinetic energies, Hurst exponents, residence time distributions, trajectory length distributions, dispersion coefficients, and so forth are presented. Comparative and symbiotic analyses of the results were used to develop a coherent picture of the solids flow field. In addition, the work also serves to demonstrate the power and versatility of these flow-imaging techniques in studying highly turbulent and opaque multiphase systems. © 2005 American Institute of Chemical Engineers AIChE J, 51: 802–835, 2005

International Journal of …, 2001

Gas holdup in a pressurized bubble column (pressures from 0.1 to 0.7 MPa) was studied in a labora... more Gas holdup in a pressurized bubble column (pressures from 0.1 to 0.7 MPa) was studied in a laboratory scale vessel (diameter 0.162 m) with air–water system over a range of superficial gas velocities (0.02–0.18 m/s) using non-invasive γ-ray based Computed Tomography ...

Chemical Engineering and Processing: Process Intensification, 2005

A newly developed γ-ray computed tomography scanner was implemented to study liquid flow distribu... more A newly developed γ-ray computed tomography scanner was implemented to study liquid flow distribution in a 30.48-cm-diameter column packed with corrugated structure using countercurrent air–water flow. Validation experiments confirm that spatial resolution of ∼2.5mm can be achieved by the new CT unit.Within the gas (0–10cm/s superficial velocity) and liquid (0.6–2.5cm/s superficial velocity) flow ranges investigated, a good liquid distribution was observed at all conditions, as manifested by uniformity factor in excess of 70%. The liquid saturation increases with increasing superficial liquid velocity as well as down the column height. Within the conditions studied, the effect of gas velocity was, in general, found to be minimal.