Computer Automated Radioactive Particle Tracking Research Articles

Development, validation and implementation of multiple radioactive particle tracking technique

Computer Automated Radioactive Particle Tracking (CARPT) technique has been successfully utilized to measure the velocity profiles and mixing parameters in different multiphase flow systems where a single radioactive tracer is used to track the tagged phase. However, many industrial processes use a wide range of particles with different physical properties where solid particles could vary in size, shape and density. For application in such systems, the capability of current single tracer CARPT can be advanced to track more than one particle simultaneously. Tracking multiple particles will thus enable to track the motion of particles of different size shape and density, determine segregation of particles and probing particle interactions. In this work, a newly developed Multiple Radioactive Particle Tracking technique (M-RPT) used to track two different radioactive tracers is demonstrated. The M-RPT electronics was developed that can differentiate between gamma counts obtained from the different radioactive tracers on the basis of their gamma energy peak. The M-RPT technique was validated by tracking two stationary and moving particles (Sc-46 and Co-60) simultaneously. Finally, M-RPT was successfully implemented to track two phases, solid and liquid, simultaneously in three phase slurry bubble column reactors.

Hydrodynamics investigation of laboratory-scale Internal Gas-lift loop anaerobic digester using non-invasive CAPRT technique

Internal gas-lift loop reactor (IGLR) was used as an anaerobic digester and its hydrodynamics were studied using Computer Automated Radioactive Particle Tracking (CARPT) Technique. This paper deals with the experimental study on a laboratory-scale digester. An anaerobic digester is a three-phase system consisting of gas, liquid, and solids; however solid–liquid slurry was treated as a single phase due to smaller size and lower density of solids. The effect of various geometric and operating variables on the hydrodynamics was studied. The superficial gas velocity was maintained at very low values and IGLR was operated in bubbly flow regime, which is suitable for operation of anaerobic digesters. The flow pattern and liquid velocity profile was obtained and effect of gas superficial velocity, draft tube diameter, type of sparger on liquid velocity and dead volume was studied in detail. Mean circulation times were calculated and compared for different digester configurations. Results showed that the increasing gas velocity increases the liquid velocity, decreases circulation time but does not offer any significant advantages in reducing the dead volumes. The configuration with draft tube diameter to tank diameter ratio of 0.5 showed good liquid circulation throughout the digester volume and low mean circulation time implying better mixing.

Effect of Scale on Hydrodynamics of Internal Gas-Lift Loop Reactor-Type Anaerobic Digester Using CFD

Abstract This work evaluates the ability of computational fluid dynamics (CFD) to simulate the flow and predict the hydrodynamics of internal gas-lift loop reactor (IGLR)-type anaerobic digester. In addition, it also analyzes if CFD can account for the effects of operating conditions, geometry as well as scale of the reactor. For this purpose, three-dimensional two-phase CFD simulations were performed using CFX for laboratory-scale and pilot-scale IGLR. The CFD predictions were evaluated against experimental data obtained from computer automated radioactive particle tracking (CARPT). The CFD predictions provided good qualitative but only reasonable quantitative comparison. After validation of CFD model, effect of gas flow rate, draft tube diameter, sparger geometry and reactor scale on flow pattern, liquid velocity and dead volume was investigated. Higher gas flow rates did not offer any significant advantage in increasing liquid circulation in the downcomer or decreasing the dead volume. Configuration with draft tube diameter half of tank diameter, equipped with cross sparger showed comparatively better liquid circulation than other configurations. For same superficial gas velocity, increasing the scale increases the magnitude of liquid velocity but fails to match the mixing intensity observed in laboratory scale. Different interphase forces, turbulence models and closures are also evaluated to improve the predictability of CFD models.

An iterative position reconstruction algorithm for radioactive particle techniques

The Computer Automated Radioactive Particle Tracking (CARPT) technique is widely used to monitor the motion of the flow inside a reactor. Usually a single radioactive particle that is neutrally buoyant with respect to the phase is used as a tracker. The particle moves inside the volume of interest and its positions are determined by an array of scintillation detectors counting incoming photons. Well-known reconstruction algorithms have been traditionally used to map measured counts into the particle position coordinates by solving a minimisation problem between measured events and calibration data. However, these algorithms have serious drawbacks. Their accuracy is determined by resolution of a calibration grid, which results in low accuracy measurements in cases where the measurement interval is short. The article presents an original algorithm for reconstruction of the trace position. The reconstruction procedure calculates iteratively the trace position of the specified calibration data. The results of the simulations based on the MCNP5 package showed that compared with results obtained using the classical approach, the accuracy of the reconstruction position is increased by 46% for low noise counts and 38% for high noise counts. The technique can successfully be applied to monitor the motion of a radioactive tracer in a reactor.

Local characteristics of hydrodynamics in draft tube airlift bioreactor

Airlift column reactors have been widely used in bioprocesses. The design, scale-up, and performance evaluation of such reactors all require extensive and accurate information about the gas–liquid flow dynamics, particularly as computational fluid dynamics (CFD) has become more popular in the last decade. However, due to the limitation of most conventional techniques for gas–liquid flow dynamics measurement, only global hydrodynamic parameters (e.g., cross-sectionally averaged liquid circulation velocity, overall gas holdup, and overall mass transfer rate) have been extensively studied. The local flow characteristics (e.g., the macro-mixing and the turbulence intensity) remain unclear. In this study, we use the computer automated radioactive particle tracking (CARPT) technique to investigate the details of the multiphase flow dynamics in a draft tube airlift bioreactor, such as the liquid velocity field, turbulent kinetic energy field, distributions of shear stresses, etc. The flow structures in the whole reactor, as well as the structure in individual regions, i.e., the top, the bottom, the riser, and the downcorner are also characterized. We found significantly large turbulent kinetic energy in the top and the bottom regions, with spots of very high shear stress, which were also found in the vicinity of the sparger. The results also suggest that the top and bottom clearances have significant effects on the flow structures, which may have substantial effects on the bioreactor performance.

Evaluation of large Eddy simulation and Euler‐Euler CFD models for solids flow dynamics in a stirred tank reactor

AbstractMechanically agitated reactors find wide range of applications for solid suspension and mixing in the chemical, biochemical, and mineral processing industries. Understanding the solids dynamics in these reactors is necessary to improve the design and operation of such reactors. Computational fluid dynamic (CFD) models are often useful in this regard, as it can provide significant insights into the flow and mixing of the phases involved. However, the model predictions need extensive evaluation with experimental results before they can be confidently used for the scale‐up and optimization of large scale reactors. Recently, Guha et al. carried out a systematic experimental investigation of the solids hydrodynamics in dense solid–liquid suspensions (2.5–19% solids loading w/w) in a stirred tank using the Computer Automated Radioactive Particle Tracking (CARPT) technique, which provided extensive information to efficiently assess the ability of the existing CFD models in predicting the solids dynamics in slurry reactors. This work presents such an evaluation by comparing the averaged solids velocities, turbulent kinetic energy, and solids sojourn time distributions predicted by CFD models with those obtained from the CARPT experiment for overall solids holdup of 1% (v/v) (2.5% w/w) at Reynolds number of 74,000. The Large Eddy Simulation (LES) and the Euler‐Euler model are the models chosen for evaluation in the current study. © 2008 American Institute of Chemical Engineers AIChE J, 2008

Macro-mixing in a draft-tube airlift bioreactor

Airlift reactors are pneumatically agitated reactors that have been widely used in industries, particularly in bioprocesses. Extensive studies about the flow dynamics in airlift column reactors exist; however, most of these studies have focused on global hydrodynamic parameters using conventional techniques. The local flow characteristics, such as the macro-mixing and the turbulence intensity, are crucial for reliable design and scale-up, and they remain unclear. This work focuses on studying the macro-mixing in a draft-tube airlift bioreactor utilizing an advanced flow dynamic measurement technique, computer automated radioactive particle tracking (CARPT). True residence time distribution analyses for the overall column as well as individual regions, i.e., the riser, the downcomer, the top, and the bottom regions, are conducted for the first time based on CARPT measured particle trajectories. The effects of the superficial gas velocity and the top/bottom clearances on the macro-mixing are also discussed. The results suggest that although the flow structures in the overall draft-tube column reactor, as well as in the riser and in the downcomer, are close to plug flows, bypassing and stagnancy exist in the top and the bottom regions.

Numerical Simulation of Gas−Solid Dynamics in a Circulating Fluidized-Bed Riser with Geldart Group B Particles

Circulating fluidized-bed (CFB) risers with Geldart group B particles have found significant application in combustion reactions. The present work attempts to study the solids flow dynamics in a CFB riser that is operated with group B particles, using computational fluid dynamics (CFD) techniques. The key feature in the present study is that the various closure schemes in the CFD model have been evaluated against data from non-invasive experimental techniques: computer automated radioactive particle tracking (CARPT) for solids velocity field and computed tomography (CT) for solids holdup. Since solids flow in a riser is multiscale in character, in addition to the measured averaged solids velocity profiles and solids fraction profiles in the experimental section, mean granular temperature profiles have also been compared. Two flow regimes (viz., fast fluidization and dilute phase transport) have been considered in this study.

Flow field of suspended solids in a stirred tank reactor by Lagrangian tracking

Solid–liquid stirred tank reactors are widely used in the chemical, biochemical and mineral processing industries. Characterization of solid hydrodynamics in these reactors is essential to optimize the design and operation of such reactors. Although few studies exist of the solid hydrodynamics in dilute suspensions, a systematic investigation with relatively dense systems is still lacking in the open literature. The non-invasive computer automated radioactive particle tracking (CARPT) technique is used in the current work to study the solids flow field in dense solid–liquid suspensions (2.5–19% solids loading) in a stirred tank. CARPT provides Lagrangian description of the solids flow field which is used to obtain the time-averaged velocity fields and the turbulent quantities. The Lagrangian information has also been used to calculate the solid sojourn time distribution at different axial regions in the reactor, which clearly show that the Zwietering's correlation over-predicts the “just-suspension” speed at which incipient suspension of solids is achieved.

Effect of sparger design on hydrodynamics of a gas recirculation anaerobic bioreactor

The effects of sparger design and gas flow rate on, gas holdup distribution and liquid (slurry) recirculation velocity have been studied in a surrogate anaerobic bioreactor used for treating bovine waste with a conical bottom mixed by gas recirculation. A single orifice sparger (SOS) and a multi-orifice ring sparger (MORS) with the same orifice open area and gas flow rates (hence the same process power input) are compared in this study. The advanced non-invasive techniques of computer automated tomography (CT) and computer automated radioactive particle tracking (CARPT) were employed to determine gas holdup, liquid recirculation velocity, and the poorly mixed zones. Gas flows (Q(g)) ranging of 0.017 x 10(-3) m(3)/s to 0.083 x 10(-3) m(3)/s were used which correspond to draft tube superficial gas velocities ranging from 1.46 x 10(-2) m/s to 7.35 x 10(-2) m/s (based on draft tube diameter). Air was used for the gas, as the molecular weights of air and biogas (consisting mainly of CH(4) and CO(2)) are in the same range (biogas: 28.32-26.08 kg/kmol and air: 28.58 kg/kmol). When compared to the SOS for a given gas flow rate, the MORS gave better gas holdup distribution in the draft tube, enhanced the liquid (slurry) recirculation, and reduced the fraction of the poorly mixed zones. The improved gas holdup distribution in the draft tube was found to have increased the overall liquid velocity. Hence, for the same process power input the MORS system performed better by enhancing the liquid recirculation and reducing the poorly mixed zones.

Dynamical features of the solid motion in gas–solid risers

The trajectories of a solid tracer with the same characteristics as the circulating solids in the risers of two pilot-scale circulating fluidized beds (CFBs), obtained by the computer automated radioactive particle tracking (CARPT) technique, are examined in detail to get further insights into the complex solids dynamics of these systems. The analysis uses tools from the theory of non-linear dynamics and symbolic dynamics. Distinct features of the solids dynamics within the fast fluidization and the dilute phase transport flow regimes are highlighted and related to the operating conditions. The possibility of downflow cluster existence within the central region of the riser is particularly examined.

Solids flow mapping in a gas–solid riser: Mean holdup and velocity fields

In this study, solids flow dynamics has been investigated in a 6 in. “cold-flow” circulating fluidized bed riser using non-invasive flow techniques. Gamma ray Computed Tomography (CT) has been used to measure the time-averaged cross-sectional solids holdup distribution. The time-averaged mean and fluctuating solids velocity fields have been quantified using the Computer Automated Radioactive Particle Tracking (CARPT) technique. Details of the experimental techniques, protocol of implementation and data analysis are discussed. The experimental studies examine operating conditions in fast fluidization and dilute phase transport regimes. Comparative and symbiotic analyses of the results obtained from CARPT and CT have been used to develop a coherent picture of the solids flow field. In addition, this work also demonstrates the power of CARPT and CT as flow mapping techniques in studying highly turbulent and opaque multiphase systems.

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 insi...

Experimental investigation of the hydrodynamics in a liquid–solid riser

AbstractLiquid–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

Gas–liquid flow generated by a Rushton turbine in stirred vessel: CARPT/CT measurements and CFD simulations

In this work, computer-automated radioactive particle tracking (CARPT), computed tomography (CT) and computational fluid dynamic (CFD) based models were used to investigate gas–liquid flow generated by a Rushton turbine. CARPT and CT measurements were carried out in a gas–liquid stirred vessel operating in two different flow regimes and captured the quantitative Eulerian information of gas–liquid flow. The CARPT data was then used to extract the circulation time distribution in a vessel. A two-fluid model along with the standard k – ε turbulence model was used to simulate the dispersed gas–liquid flow in a stirred vessel. Appropriate drag corrections to account for bulk turbulence (along the lines proposed by Brucato et al. (Chem. Eng. Sci. 45(1998) 3295)) were developed to correctly simulate different flow regimes. The computational snapshot approach was used to simulate impeller rotation and was implemented in the commercial CFD code, FLUENT4.5 (of Fluent. Inc., USA). Most model predictions compared favourably with CARPT and CT measurements. Validated CFD models as attempted in this paper are promising to simulation of industrial stirred vessels.

Flow pattern visualization in a mimic anaerobic digester using CFD

Three-dimensional steady-state computational fluid dynamics (CFD) simulations were performed in mimic anaerobic digesters to visualize their flow pattern and obtain hydrodynamic parameters. The mixing in the digester was provided by sparging gas at three different flow rates. The gas phase was simulated with air and the liquid phase with water. The CFD results were first evaluated using experimental data obtained by computer automated radioactive particle tracking (CARPT). The simulation results in terms of overall flow pattern, location of circulation cells and stagnant regions, trends of liquid velocity profiles, and volume of dead zones agree reasonably well with the experimental data. CFD simulations were also performed on different digester configurations. The effects of changing draft tube size, clearance, and shape of the tank bottoms were calculated to evaluate the effect of digester design on its flow pattern. Changing the draft tube clearance and height had no influence on the flow pattern or dead regions volume. However, increasing the draft tube diameter or incorporating a conical bottom design helped in reducing the volume of the dead zones as compared to a flat-bottom digester. The simulations showed that the gas flow rate sparged by a single point (0.5 cm diameter) sparger does not have an appreciable effect on the flow pattern of the digesters at the range of gas flow rates used.

Flow pattern visualization of a simulated digester

Mixing patterns inside a simulated flat bottom digester were imaged using the non-invasive techniques of computer automated radioactive particle tracking (CARPT) and computed tomography (CT). Mixing/agitation was provided using gas (air) recirculation at three different flow rates (Qg) of 28.32, 56.64 and 84.96l/h, corresponding to superficial gas velocities of 0.025, 0.05 and 0.075cm/s, respectively. Better mixing was observed in the upper zone near the top of the draft tube. However, at the bottom of the digester there was a total stagnancy at all the three gas flow rates. The maximum value of the time-averaged axial velocity inside the draft tube, at a gas flow rate of 84.96l/h, was observed as 34.4cm/s. The turbulent kinetic energy was observed to be maximum (724dyn/cm2) inside the draft tube, and decreases radially toward the wall of the digester. The present study showed that the CARPT and CT techniques could be successfully used to identify the flow pattern in the digester and to calculate velocity and turbulence parameters quantitatively. On the other hand, the increase in gas circulation rate from 28.32 to 84.96l/h did not significantly reduce the dead zones inside the flat bottom digester. To achieve the desired mixing and reactor performance, the operating conditions and reactor configuration need to be optimized.

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’ movement, are the major factors controlling the biomass productivity. Hydrodynamics, hence, play a significant role in the reactor's 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’ movement, and the temporal irradiance patterns obtained by coupling the cells’ 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’ growth prediction and modeling, and the design, scale-up and operation of PBRs.

Eulerian Flow Field Estimation from Particle Trajectories: Numerical Experiments for Stirred Tank Type Flows

The computer automated radioactive particle tracking (CARPT) and positron emission particle tracking (PEPT) techniques have been developed to characterize opaque multiphase flows. In CARPT and PEPT, the Eulerian flow field is inferred from the knowledge of reconstructed tracer particle trajectories. The present study was undertaken to assess the strengths and limitations of the process of estimating the Eulerian flow field from particle trajectories. A two-dimensional problem, which mimics the characteristics of flow in a stirred tank reactor equipped with a standard Rushton turbine, was considered. The Eulerian flow field was numerically simulated. Care was taken to minimize effects of numerical issues on the computed flow field, which was then used to calculate particle trajectories. Standard CARPT data processing was carried out on the simulated particle trajectories to estimate the Eulerian flow field. This estimated flow field was compared with the original flow field used for trajectory simulations ...

Opaque multiphase flows: experiments and modeling

This brief review deals with the characterization of multiphase flows needed in reaction engineering and describes the techniques and methods available to accomplish it. It emphasizes the fact that most multiphase systems of industrial interest (e.g. stirred tanks, slurry bubble columns, gas–solid or liquid–solid risers and fluidized beds, pneumatic transport reactors, etc.) operate in churn turbulent flow at large volume fraction of the dispersed phase and are opaque. This inevitably leads to the use of the Euler–Euler, interpenetrating fluid model in describing their fluid dynamics, which raises issues of closure for the interfacial momentum terms and turbulence. Hence, computational fluid dynamic (CFD) models based on the Euler–Euler approach with selected closures require experimental validation. Due to the non-transparency of the systems involved, non-conventional experimental techniques are required. The paper briefly describes two such techniques which have been successfully implemented at the Chemical Reaction Engineering Laboratory for characterization of opaque, multiphase flows. One is the gamma ray computed tomography (CT), the other is the computer automated radioactive particle tracking (CARPT). Their use in characterizing diverse systems such as liquid–solid risers and bubble columns is illustrated as well as the utility of CARPT-CT data in validation of the Euler–Euler CFD models. The goal is to enable the reader to grasp the advantages and limitations of the described experimental techniques and computational fluid dynamic models.