New Methodology For Benchmarking Hydrodynamics In Bubble Columns With Intense Internals Using The Radioactive Particle Tracking (RPT) Technique

A new methodology for implementing radioactive particle tracking (RPT) in bubble columns with intense vertical rod internals was developed and implemented to investigate the effect of dense internals on hydrodynamics. The methodology utilizes a hybrid of Monte Carlo N-Particle (MCNP) simulation and an automated RPT calibration device to generate a large number of calibration points for accurate reconstruction of the instantaneous positions of radioactive particles using a similarity algorithm. Measurements were conducted in a 6-inch (15.24 cm) Plexiglas column using an air–water system at a superficial gas velocity of 40 cm/s. Vertical Plexiglas rods 0.5 in (1.27 cm) in diameter were used to cover ~25% of the total cross-sectional area of the column to represent the effect of a heat-exchanging tube in industrial Fisher–Tropsch synthesis. The results showed that the internals increased liquid velocity near the center of the column by more than 30%, resulting in enhanced liquid circulation and frequency of liquid eddy movement. In addition, turbulence parameters decreased noticeably when using vertical internals in the bubble column due to a reduction in velocity fluctuations. Reliable data can help validate computational fluid dynamics (CFD) models to predict hydrodynamic parameters at other various conditions

A Comparison of Alternating Minimization and Expectation Maximization Algorithms for Single Source Gamma Ray Tomography

Lange and Carson (1984 J. Comput. Assist. Tomogr. 8 306-16) Defined Image Reconstruction for Transmission Tomography as a Maximum Likelihood Estimation Problem and Derived an Expectation Maximization (EM) Algorithm to Obtain the Maximum Likelihood Image Estimate. However, in the Maximization Step or M-Step of the EM Algorithm, an Approximation is Made in the Solution Which Can Affect the Image Quality, particularly in the Case of Domains with High Attenuating Material. O\u27Sullivan and Benac (2007 IEEE Trans. Med. Imaging 26 283-97) Reformulated the Maximum Likelihood Problem as a Double Minimization of an I-Divergence to Obtain a Family of Image Reconstruction Algorithms, Called the Alternating Minimization (AM) Algorithm. the AM Algorithm Increases the Log-Likelihood Function While Minimizing the I-Divergence. in This Work, We Implement the AM Algorithm for Image Reconstruction in Gamma Ray Tomography for Industrial Applications. Experimental Gamma Ray Transmission Data Obtained with a Fan Beam Geometry Gamma Ray Scanner, and Simulated Transmission Data based on a Synthetic Phantom, with Two Phases (Water and Air) Were Considered in This Study. Image Reconstruction Was Carried Out with These Data using the AM and the EM Algorithms to Determine and Quantitatively Compare the Holdup Distribution Images of the Two Phases in the Phantoms. When Compared to the EM Algorithm, the AM Algorithm Shows Qualitative and Quantitative Improvement in the Holdup Distribution Images of the Two Phases for Both the Experimental and the Simulated Gamma Ray Transmission Data. © 2008 IOP Publishing Ltd

Experimental Study of the Solids Velocity Field in Gas-Solid Risers

Solids Flow Dynamics in Gas-Solid Risers is Inherently Complex. Model Refinement through Experimental Validation Requires the Acquisition of Detailed Nonintrusive Measurements. in This Study, Noninvasive Computer-Automated Radioactive Particle Tracking (CARPT) is Employed to Visualize and Quantify in a Three-Dimensional Domain the Solids Dynamics and Mixing in Gas-Solid Risers. This Technique Has the Added Advantage that, along with the Derived Eulerian Solids Flow Field (Time-Average Velocity Map and Various Turbulence Parameters Such as the Reynolds Stresses, Turbulent Kinetic Energy), It Also Provides Directly the Lagrangian Description of the Solids Motion. the Solids Velocity Field Data Are Obtained in Two Different Risers at Low and High Solids Fluxes at Varying Superficial Gas Velocity to Span Both the Fast-Fluidized (FF) and Dilute Phase Transport (DPT) Regimes. the Effect of Operating Conditions on Solids Flow and Mixing is Studied. Comparative Analysis of the Results is Presented to Provide Insights into the Complex Solids Flow Patterns Characteristic of Gas-Solid Risers. © 2005 American Chemical Society

A Detailed Hydrodynamic Study of the Split-Plate Airlift Reactor by using Non-Invasive Gamma-Ray Techniques

This study focused on detailed investigations of selected local hydrodynamics in split airlift reactor by using an unconventional measurements facility: computed tomography (CT) and radioactive particle tracking (RPT). The local distribution in a cross-sectional manner with its radial\u27s profiles for gas holdup, liquid velocity flow field, shear stresses, and turbulent kinetic energy were studied under various gas velocity 1, 2 and 3 cm/s with various six axial level z = 12, 20, 40, 60, 90 and 112 cm. The distribution in gas–liquid phases in the whole split reactor column, the riser and downcomer sides, including their behavior at the top and bottom sections of the split plate was also described. The outcomes of this study displayed an exemplary gas–liquid phases dispersion approximately in all reactor\u27s zones and had large magnitude over the ring of the sparger as well as upper the split plate. Furthermore, the outcomes pointed out that the distribution of this flow may significantly impacts the performance of the split reactor, which may have essential influence on its performance particularly for microorganisms culturing applications. These outcomes are dependable as benchmark information to validate computational fluid dynamics (CFD) simulations and other models

Measuring Gas-Liquid Distribution in a Pilot Scale Monolith Reactor Via an Industrial Tomography Scanner (ITS)

An Industrial Tomography Scanner (ITS) Was Designed and Developed to Study and Quantify the Phase Distribution in a Two-Phase Flow Pilot Scale Monolith Reactor that Was 24 In. (0.60 M) in Diameter and 192 In. (4.9 M) in Height. the Monolith Reactor Was Operated Co-Current Up-Flow in the Taylor Flow Regime with Water as the Liquid Phase and Air as the Gas Phase. the Cross-Sectional Holdup Distributions Were Measured at Three Axial Elevations. the Operating Conditions Were Selected to Bracket Commercial Operating Conditions for Fixed Bed Monolithic Reactor Systems. the Results Show that its Can Capture the Flow Features in a Large Diameter Column. Also, the Findings Suggest the Need for Careful Design of the Internals of the Reactor. Spatial Resolution Down to 1.5 Cm Was Obtained So that Gross Phase Maldistribution Could Be Reliably Observed. However, Improvement is Needed for the its to Be Effectively Utilized in Industry. © 2006 Elsevier B.V. All Rights Reserved

A Detailed Hydrodynamic Study of the Split-Plate Airlift Reactor by using Non-Invasive Gamma-Ray Techniques

This study focused on detailed investigations of selected local hydrodynamics in split airlift reactor by using an unconventional measurements facility: computed tomography (CT) and radioactive particle tracking (RPT). The local distribution in a cross-sectional manner with its radial\u27s profiles for gas holdup, liquid velocity flow field, shear stresses, and turbulent kinetic energy were studied under various gas velocity 1, 2 and 3 cm/s with various six axial level z = 12, 20, 40, 60, 90 and 112 cm. The distribution in gas-liquid phases in the whole split reactor column, the riser and downcomer sides, including their behavior at the top and bottom sections of the split plate was also described. The outcomes of this study displayed an exemplary gas-liquid phases dispersion approximately in all reactor\u27s zones and had large magnitude over the ring of the sparger as well as upper the split plate. Furthermore, the outcomes pointed out that the distribution of this flow may significantly impacts the performance of the split reactor, which may have essential influence on its performance particularly for microorganisms culturing applications. These outcomes are dependable as benchmark information to validate computational fluid dynamics (CFD) simulations and other models

Enhancing Heat Transfer Performance In Simulated Fischer–Tropsch Fluidized Bed Reactor Through Tubes Ends Modifications

Fluidized bed reactors are essential in a wide range of industrial applications, encompassing processes such as Fischer–Tropsch synthesis and catalytic cracking. The optimization of performance and reduction in energy consumption in these reactors necessitate the use of efficient heat transfer mechanisms. The present work examines the considerable impact of tube end geometries, superficial gas velocity, and radial position on heat transfer coefficients within fluidized bed reactors. It was found that the tapered tube end configurations have been empirically proven to improve energy efficiency in fluidized bed reactors significantly. For example, at a superficial gas velocity of 0.4 m/s, the tapered end form\u27s local heat transfer coefficient (LHTC) demonstrated a significant 20% enhancement compared to the flat end shape. The results and findings of this work make a valuable contribution to the advancement of complex models, enhance the efficiency of fluidized bed reactor processes, and encourage further investigation into novel tube geometries

Comparative Hydrodynamics Study in a Bubble Column using Computer-Automated Radioactive Particle Tracking (CARPT)/computed Tomography (CT) and Particle Image Velocimetry (PIV)

The Hydrodynamics of a 10-Cm-Diameter Cylindrical Bubble Column at the Superficial Gas Velocity of 2, 4, and 8 Cm/s Are Investigated by Computer-Automated Radioactive Particle Tracking (CARPT), Particle Image Velocimetry (PIV), and Computed Tomography (CT). These Experimental Techniques Are Capable of Providing the Knowledge of Velocity and Holdup Fields in a Bubble Column System, Which Are Essential as the Experimental Benchmark for Modeling of Such Systems. the Flow Field of Liquid Phase, as Well as the Reynolds Stresses, Obtained by CARPT and PIV in an Air-Water System Are Compared in Detail. the Results Indicate that CARPT and PIV Complement Each Other Well. Further, the Profile of Gas Holdup Obtained by Gamma Ray based on CT Compares Favorably to the Independently Determined Holdup

Analysis of Photobioreactors for Culturing High-Value Microalgae and Cyanobacteria Via an Advanced Diagnostic Technique: CARPT

Photosynthetic Algal Cultures Are a Potential Source of Many High-Value Products. in Photobioreactors (PBR), the Availability and the Intensity of the Light, Which Are Affected by the Cells\u27 Movement, Are the Major Factors Controlling the Biomass Productivity. Hydrodynamics, Hence, Play a Significant Role in the Reactor\u27s Performance, as They Determine Not Only the Flow Field, I.e. Liquid Flow and Mixing, Shear Stresses, Etc., But Also the Movements of the Cells. in This Work, Computer-Automated Radioactive Particle Tracking (CARPT) Technique Was Employed to Evaluate its Feasibility for Characterizing PBRs. Liquid Velocity Profiles, Cells\u27 Movement, and the Temporal Irradiance Patterns Obtained by Coupling the Cells\u27 Trajectories and the Irradiance Distribution Model Have Been Determined. the Effects of the Biomass Concentration, Reactor Geometry, and the Aeration Rate on the Irradiance Patterns Are Discussed. the Results Demonstrate that the CARPT Technique is Promising for PBR Analysis. It Provides Fundamental Information Needed to Advance the Cells\u27 Growth Prediction and Modeling, and the Design, Scale-Up and Operation of PBRs. © 2003 Elsevier Science Ltd. All Rights Reserved

Gas Holdup in a Trayed Cold-Flow Bubble Column

An Experimental Study Was Performed to Investigate the Effect of Sieve Trays on the Time-Averaged Gas Holdup Profiles and the overall Gas Holdup in a Cold-Flow Bubble Column that Was Scaled-Down from a Commercial Unit. Γ-Ray Computed Tomography (CT) Was Used to Scan the Column at Several Axial Locations in the Presence and Absence of Trays from Which the Local Variation of the Gas Holdup Was Extracted. the overall Gas Holdup Was Also Determined using the Same Configuration by Comparing the Expanded and Static Liquid Heights. Air and Water Were Used as the Gas-Liquid System. the Superficial Gas and Liquid Velocities Were Selected to Span the Range of the Commercial System using Gas Spargers Having Multiple Lateral Distributors that Were Also Scaled-Down from the Commercial Design. to Investigate the Impact of Sparger Hole Density on the Local and overall Gas Holdup, Two Difference Sparger Designs Were Used in Which the Hole Density Per Lateral Was Varied. the Gas Hole Velocity Was Maintained Constant at Ca. 245 M/s, Which Approached that Used in the Commercial Reactor. It is Shown that the Local Gas Holdup Determined by CT is Generally Higher in the Tray Down Comer Region and Exhibits an Asymmetric Pattern When Trays Are Present. the Use of Increased Sparger Hole Density at a Constant Gas Superficial Velocity Leads to Steeper Gradient in the Gas Holdup Near the Column Centerline and a Higher overall Gas Holdup. These Findings Suggest that the Performance of Bubble Column Reactors for Various Applications is Sensitive to Both Sparger and Tray Design. © 2001 Elsevier Science Ltd. All Rights Reserved