Flow Regime Identification in a Bubble Column Via Nuclear Gauge Densitometry and Chaos Analysis

The Bubble Column Performance Can Change Significantly as a Result of Flow Regime Change. Since Reactor Volume Productivity, Mass and Heat Transfer as Well as Mixing Are Affected by the Prevailing Flow Regime, It is Very Important to Know How to Identify It. in This Work, Flow Regime Identification Was Performed on the Basis of the Kolmogorov Entropy (KE) Algorithm Applied to Nuclear Gauge Densitometry Data. in Addition, the Average Cycle Time Was Used for Validation of the Results. Three Transition Velocities Were Identified that Delineated the Boundaries of the Three Main Hydrodynamic Regimes. the First Two Transition Points Were Also Confirmed by the Information Entropy Concept. the Increasing KE Trend in the Bubbly Flow Regime and the Decreasing KE Trend in the Churn-Turbulent Regime Were Predicted Successfully by Means of New Semi-Theoretical Models. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Phase Distribution in an Upflow Monolith Reactor using Computed Tomography

Computed Tomography (CT) is Known to Be a Viable Technique for Determining Flow Maldistribution in Two-Phase Flow through Packed Beds. in This Study, Gamma Ray Computed Tomography Has Been Used to Quantify the Flow Distribution in a Monolith Catalytic Bed, with Water as the Liquid Phase and Air as the Gas Phase, Flowing Co-Currently Upward. the Flow Conditions Were Selected to Bracket Some Commercially Viable Operating Conditions for Such Reactors. in the Monolith Core Region, Fairly Uniform Flow Distribution Has Been Obtained for All the Flow Conditions Used. This Distribution is Quantified using the Standard Deviation of the Holdup Distribution. However, Maldistribution of Air and Water in the Monolith Bed Wall Region Due to Wall Effects at the Monolith Entrance Has Been Observed and Quantified by CT. the Obtained Results Confirm that the Entrance and Exit Regions of the Monolith Bed Need to Be Carefully Designed and to Be Free of Obstacles and Vortex Creating Devices. © 2005 American Institute of Chemical Engineers

Comparison of Single- and Two-Bubble Class Gas-Liquid Recirculation Models - Application to Pilot-Plant Radioactive Tracer Studies during Methanol Synthesis

Radioactive Gas Tracer Measurements Conducted during Liquid-Phase Methanol Synthesis from Syngas in a Pilot-Scale Slurry Bubble Column at the Alternate Fuels Development Unit (AFDU), La Porte Have Been Compared with Simulations from Two Mechanistic Reactor Models - Single-Bubble Class Model (SBCM) and Two-Bubble Class Model (TBCM). the Model Parameters Are Estimated from an Independent Sub-Model Gas and Liquid Recirculation, and the Long-Time-Averaged Slip Velocity between the Gas and Liquid/slurry in the Column Center Can Be as High as 50-60 Cm/s Depending on the Operating Conditions. Comparison of Experimental Data with Simulation Results from the Two Models Indicates that Accurate Description of Interphase Gas-Liquid Mass Transfer is Crucial to the Reliable Prediction of Tracer Responses. Coupled with a Correct Description of Gas and Liquid Recirculation, the Models Presented Here Provides a Simple and Fundamentally based Methodology for Design and Scale-Up of Bubble Column Reactors. © 2001 Published by Elsevier Science Ltd

Experimental Investigation on Heat Transfer in a Prismatic Modular Reactor under Cosine Heat Flux

The current study has investigated natural convection heat during pressurized conduction cooldown (PCC) accident scenario to understand the passive safety features of prismatic modular reactors (PMR) under different intensities of nonuniform center peaking step heat flux distributions (approximating cosine shape) using an advanced fast-response heat transfer technique. A scaled-down PMR module was designed and developed at Missouri S&T by the research team of the Multiphase Reactors Engineering and Applications Laboratory (mReal). The module consists of upper and lower plena connected by heated and cooled channels. Nonuniform heat flux distribution was applied to the heated channel under nonuniform heating center peaking step (approximating cosine shape), simulating nonuniform heat distribution within the core of PMR. Air was used as the coolant to study the effect of nonuniform heating under a range of heat flux intensity (four sets of nonuniform heat flux and one set of uniform heat flux were tested) at 413.7 kPa (60 psi). At an axial position of Z/L = 0.409 along the heated channel, the heat transfer coefficient is increased by 35% for nonunifor libJo2O18*m heat flux distributions of set 1 (0.25*2.579 kW.m-2+0.50*3.152 kW.m-2+0.25*2.579 kW.m-2) and set 2 (0.25*2.292 kW.m-2+0.50*2.865 kW.m-2+0.25*2.292 kW.m-2) with respect to the the uniform heat flux set 5(2.865 kW.m-2), and it is decreased by 56% for nonuniform heat flux distributions of set 3 (0.25*2.006 kW.m-2+0.50*2.579 kW.m-2+0.25*2.006 kW.m-2) and set 4 (0.25*1.719 kW.m-2+0.50*2.292 kW.m-2+0.25*1.719 kW.m-2) with respect to the uniform heat flux set (set 5). There is a significant reorder in the heat transfer coefficients distribution curves in descending order along the heated channel after the inflection point (after Z/L =0.773)

A Lagrangian Description of Flows in Stirred Tanks Via Computer-Automated Radioactive Particle Tracking (CARPT)

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 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 Impeller and the Dead Zones at the Bottom of the Tank. the CARPT Data is Also Used to Extract \u27\u27Sojourn\u27\u27 Time Distributions in Different Zones of the Reactor. These Distributions Are Used to Partially Quantify the Observed Dead and Active Zones in the Tank. © 2001 Elsevier Science Ltd. All Rights Reserved

Computation of Effectiveness Factors for Partially Wetted Catalyst Pellets using the Method of Fundamental Solution

Trickle Bed Reactors Are Widely Used in Many Process Industries. the Catalyst Particles Are Often Incompletely Wetted Especially in the Trickling Flow Regime and Hence to Design These Reactors, the Effectiveness Factor of Partially Wetted Catalyst Needs to Be Calculated Accurately. Numerical Solutions by Traditional Methods Are Time Consuming and Not Very Accurate, Especially for Some Commonly Used Complex Catalyst Shapes Such as Trilobes, Quadrilobes Etc. the Paper Presents a Novel Numerical Solution for These Problems based on the Method of Fundamental Solutions. the Advantage of the Method is that It Involves Only Boundary Collocation and Can Be Applied to Catalysts of Any Shape. Further the Method Provides an Accurate Estimate of the Gradient of the Concentration Profiles and This Information Can Be Related Directly to the Effectiveness Factor. This Accuracy of the Method is Demonstrated for Two Dimensional (2-D) and Axisymmetric Problems for a Linear Kinetics. Illustrative Results Are Presented for Some Complex Shapes under Partial Wetting Conditions. © 2003 Elsevier Science Ltd. All Rights Reserved

GEANT4 Simulation for Radioactive Particle Tracking (RPT) Technique

In the past two decades, the radioactive particle tracking (RPT) measurement technique has been proven to visualize flow fields of most multiphase flow systems of industrial interest. The accuracy of RPT, and hence the data obtained, depend largely on the calibration process, which stands here as a basis for two subsequent processes: tracking and reconstruction. However, limitations in the RPT calibration process can be found in different experimental constrains and in assumptions made in the classical Monte Carlo approach used to simulate number of counts received by the detectors. Therefore, in this work, we applied a GEANT4-based Monte Carlo code to simulate the RPT calibration process for an investigated multiphase flow system (i.e., gas–liquid bubble column). The GEANT4 code was performed to simulate the number of counts received by 28 scintillation detectors for 931 known tracer positions while capturing all the types of photon interaction and overcoming solids\u27 angle limitations in classical approaches. The results of the simulation were validated against experimental data obtained using an automated RPT calibration device. The results showed a good agreement between the simulated and experimental counts, where the maximum absolute average relative deviation detected was about 5%. The GEANT4 model typically predicted the number of counts received by all the detectors; however, it over-estimated the counts when the number of primary events applied in the model was not the optimal

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

X-Ray Digital Industrial Radiography (DIR) for Local Liquid Velocity (VLL) Measurement in Trickle Bed Reactors (TBRs): Validation of the Technique

Local liquid velocity measurements in Trickle Bed Reactors (TBRs) are one of the essential components in its hydrodynamic studies. These measurements are used to effectively determine a reactor\u27s operating condition. This study was conducted to validate a newly developed technique that combines Digital Industrial Radiography (DIR) with Particle Tracking Velocimetry (PTV) to measure the Local Liquid Velocity (VLL) inside TBRs. Three millimeter-sized Expanded Polystyrene (EPS) beads were used as packing material. Three validation procedures were designed to test the newly developed technique. All procedures and statistical approaches provided strong evidence that the technique can be used to measure the VLL within TBRs

Inferring Liquid Chaotic Dynamics in Bubble Columns

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 Flow 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\u27s Correlation Dimension and the Information Loss Rate Decrease, Whereas the Liquid Flow Path is Dramatically Affected. © 2001 Published by Elsevier Science Ltd