Abstract

Non-invasive monitoring of multiphase flows is a result of the latest advances realized in non-invasive measurement of multiphase systems by means of various tomographic and velocimetric techniques. The book reviews in 15 chapters the theoretical background and the physics of the measurement process for each of a number of techniques. In addition, the mathematical modeling related to the measured property, such as in the image reconstitution problem for tomography, successful application of the techniques for measurement in various multiphase systems and their advantages and limitations are described.
... Toutes les techniques de mesure de la vitesse des bulles reposent sur la définition de la vitesse : (Chaouki et al., 1997). ...
... Chapitre 3 : Étude hydrodynamique de dégagement des bulles d'oxygène dans une cellule sans écoulement forcé de liquide Pour les particules solides cette technique est limitée à une fraction massique de 15-20 % (Chaouki et al., 1997). La figure 3.9 présente un dispositif dédié à la détermination du champ de vitesse par VIP. ...
... Récemment, certains auteurs ont utilisé des sondes composées de quatre électrodes (figure 3.8) afin de récupérer le maximum d'informations (les trois composantes de la vitesse et le taux vide axial ainsi que le taux de vide radial)(Mishra et al., 2002 ;Zhao et al., 2009, Lucas et Mishra (2005), Fahd, 2011. Il faut noter que les techniques à sondes (optiques ou conductimétriques) ne sont pas applicables dans le cas où les bulles possèdent un mouvement tourbillonnaire(Chaouki et al., 1997) ou lorsque les conditions opératoires sont agressives (de pression, de température ou Chapitre 3 : Étude hydrodynamique de dégagement des bulles d'oxygène dans une cellule sans écoulement forcé de liquide de concentration d'une espèce corrosive). De plus les taux de vide sont sous-estimés en présence de bulles de faible diamètre. ...
Thesis
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Electrogenerated gas in electrochemical reactors is considered as an electrochemical and hydrodynamic phenomenon. The ohmic drop in the electrolyte solution is one of important parameter to evaluate for the optimization design of electrochemical reactors. It is due to the resistance of the solution, therefore, its electrical conductivity and of the distance between the two electrodes. To reduce the energy consumption of the electrolytic reduction cell of hematite particles to metallic iron, we studied the design of anode, the location of oxygen bubbles production, in two equivalent cells for water electrolysis in an alkali media. The results showed that the gas hold up increases along the anode and only 25% of the initial anode height is actually active. Moreover the bubbles reach their terminal velocity after 50% of the initial anode height. This allowed us to formulate recommendations that allow the best conditions of bubbles electrogenerated disengagement and low energy consumption. Keywords : Anode design, current density distribution, ohmic drop, bubble velocity, decoupling electrochemistry/hydrodynamics. Le gaz électrogénéré dans les réacteurs électrochimiques est un phénomène à la fois électrochimique et hydrodynamique. La chute ohmique dans la solution électrolyte est l'un des paramètres importants à évaluer pour l'optimisation des réacteurs électrochimiques. Elle est due à la résistance de la solution, donc, à sa conductivité électrique et la distance entre les deux électrodes. Pour réduire la consommation énergétique de la cellule de réduction électrolytique de particules d'hématite en fer métallique, on a étudié la conception des anodes, sièges de la production des bulles d'oxygène, dans deux cellules équivalentes d'électrolyse d'eau dans un milieu alcalin. Les résultats ont montré que seulement 25% de l'anode est réellement active et que le taux de rétention augmente le long de l'anode et les bulles atteignent leur vitesse terminale dès 50% de la hauteur de l'anode. Ceci nous a permis de formuler des recommandations qui permettent d'avoir les meilleures conditions de désengagement des bulles électrogénérées, pour une consommation énergétique plus faible du procédé électrochimique
... Design, scale up and operation of these contactors highly depend on their complex hydrodynamics and the prevailing flow regime [1]. Advanced techniques employing high energy radioactive sources, such as Radioactive Particle Tracking (RPT) or Positron Emission Particle Tracking (PEPT) and computer tomography have proved to be quite appropriate for capturing the underlying dynamics of these inherently opaque contactors, providing features such as liquid velocities, turbulence parameters and phases holdup profiles, that have been used as the input experimental data required for CFD model verification [2] [3]. However, their implementation in actual industrial installations is rather complicated, preventing their massive use despite their accessible cost and controllable safety issues . ...
... The overall gas holdup was also determined by visual inspection of the disengagement region to get the curve of gas holdup vs gas velocity generally used to identify flow transitions in bubble columns [1] [5]. In addition, the chordal gas holdup determined, at mid-height of the column, by a standard scanning method with an external radioactive source [3] is also measured to have a more quantitative objective way of determining the gas holdup for different experimental conditions. Even if the chordal gas holdup is a local measure, it captures the holdup trend with gas velocity. ...
... On the contrary, Yang et al. [13] found a decrease on both of the transitions velocities (from homogeneous to transition and from transition to heterogeneous) as the liquid viscosity increases. Moreover , some authors [3] [17] reported a complex dependence of the transition with the liquid viscosity, showing a maximum in the transition velocity vs liquid viscosity curve, and an effect of the relaxation time. From the experimental results presented in this work, the gas velocity indicating the end of the homogeneous regime decreases as the liquid viscosity increases, but the start of the completely heterogeneous regime is shifted to higher gas velocities for the higher viscosity non-Newtonian liquids. ...
Article
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The feasibility of extracting relevant dynamic information of a bubble column from the approximate reconstruction of a radioactive tracer axial trajectory using a set of axially aligned detectors (AAD) is explored. The experimental procedure involves scanning simultaneously different column heights with scintillation detectors, located vertically aligned beside the examined vessel, while a neutrally buoyant radioactive tracer particle is freely moving inside. The reconstruction considers that the detectors located closer in axial coordinate to the tracer are the ones which record the largest number of counts. Based on this assumption, time series of the approximate tracer axial coordinate are obtained with a maximum resolution of 2N-1 (N: number of detectors used). Compared to the powerful radioactive particle tracking (RPT) technique, although the information extracted is more limited, the present experimental procedure has the advantage of not requiring a calibration stage, which is rather cumbersome to implement at industrial scale and prevents RPT massive use for troubleshooting. Part of the information extracted from the analysis of tracer axial trajectories in RPT can also be inferred from the discrete tracer axial trajectories obtained with this methodology. Therefore, tracer fast axial velocity distributions, liquid axial mixing time and liquid holdup axial profiles are estimated from the reconstructed axial trajectories and related to the operating conditions, for experiments with water and non-Newtonian aqueous solutions of carboxymethyl cellulose (CMC).
... Many techniques have been developed in recent years to measure fluid flows in different process tanks and devices, including STs (Boyer et al., 2002;Chaouki et al., 1997;Mavros, 2001). Fluid flow measurement techniques can be divided into two general categories: invasive and non-invasive. ...
... A high-speed data acquisition system was used to count the number of γ-rays detected by each detector with a 200-Hz data acquisition frequency. Details on the calibration of the system, the inverse reconstruction strategy for determining the position of the tracer particle, and the errors associated with the measurement technique are provided in previous publications (Chaouki et al., 1997;. ...
... The uncertainty in the reconstruction of tracer particle positions due to the statistical nature of the emission and counting processes has been discussed in detail by Chaouki et al. (1997) and Dubé et al. (2014). Given all the sources of uncertainty of the various methods involved here, it can be concluded from Figs. 2-4 that the RPT technique is indeed adequate for the measurement of turbulent flow fields in STs. ...
Article
Fully turbulent fluid flows in a laboratory-scale stirred tank (ST) equipped with a radial flow impeller (Rushton turbine; RT) or an axial flow impeller (pitched blade turbine; PBT) were analyzed using the radioactive particle tracking (RPT) technique. The present study covered the Eulerian and Lagrangian descriptions of fluid motions. The RPT measurement of the turbulent flow field in a tank agitated by an RT was benchmarked with CFD simulations of RANS-based turbulence models and laser-based measurements. There was good agreement between all the methods for the measured and predicted 3D mean velocity profiles at all locations in the ST. The RPT technique was used to measure the turbulent flow field in a tank agitated by a PBT for the first time. The behavior of the wall jet was investigated. There was close agreement between our results and those of previous studies for both systems. Lagrangian mixing measurements showed that particle trajectories can be used to generate Poincaré maps, which in turn can be used as a tool to visualize the 3D flow structure inside mixing systems. Two mixing indices, one based on the concept of stochastic independence and the other on the statistical concept of memory loss in mixing processes, were used to measure mixing times using RPT results. The present study showed that the RPT technique holds great promise for investigating turbulent flows and the mixing characteristics of STs, and for assessing the adequacy of numerical models.
... These number of counts were used later to calculate the coordinates of the tracer. Details of the system calibration and the inverse reconstruction strategy for tracer position rendition are described by Larachi et al. [6,7]. Fig. 1 shows a schematic presentation of reactor and detectors around the bed. ...
... Such wall effects can be expected to diminish with increasing column diameter. The influence of the column diameter on the rise velocity of bubble in liquid has been taken into account by introducing a scale factor correction into the Davies-Taylor relation [7]: ...
... where the superscript 0 is used to emphasize that the rise velocity refers to that of a single, isolated bubble. Collins [7] determined the scale correction factor: ...
Article
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Effect of scale on the hydrodynamics of gas-solid fluidized beds was investigated in two fluidized beds of 152 mm and 78 mm in diameter. Air at room temperature was used as the fluidizing gas in the bed of sand particles. The Radioactive Particle Tracking (RPT) technique was employed to obtain the instantaneous positions of the particles at every 20 ms of the experiments. These data were used to calculate hydrodynamic parameters, such as mean velocity of upward and downward-moving particles, jump frequency, cycle frequency and axial and radial diffusivities, which are representative of solid mixing and diffusion of particles in the bed. These hydrodynamic parameters were compared in both scales in order to determine the scale effect on the hydrodynamics of the gas-solid fluidized bed. In all cases, it was shown that solid mixing and diffusivity of particles increase by increasing column diameter. The results of this study would help to understand solid mixing which might be critical in industrial fluidized bed reactors.
... Various techniques can be used to track the motion of agglomerates in a fluidized bed. Tomography using γ-rays or X-rays [2,27], Positron Emission Particle Tracking (PET) [2,20] and Radioactive Particle Tracking (RPT) [2,5,6,7,9,16,21,22,23,24,25,30]. RPT was selected for our application because of the accessibility of the hardware. ...
... Various techniques can be used to track the motion of agglomerates in a fluidized bed. Tomography using γ-rays or X-rays [2,27], Positron Emission Particle Tracking (PET) [2,20] and Radioactive Particle Tracking (RPT) [2,5,6,7,9,16,21,22,23,24,25,30]. RPT was selected for our application because of the accessibility of the hardware. ...
... Various techniques can be used to track the motion of agglomerates in a fluidized bed. Tomography using γ-rays or X-rays [2,27], Positron Emission Particle Tracking (PET) [2,20] and Radioactive Particle Tracking (RPT) [2,5,6,7,9,16,21,22,23,24,25,30]. RPT was selected for our application because of the accessibility of the hardware. ...
Article
The Radioactive Particle Tracking (RPT) technique was used to study agglomerates behavior inside a cold flow recirculating fluidized bed with internals (known as sheds), mimicking the stripper baffles of a Fluid CokerTM. A higher fluidization gas velocity increases the time that agglomerates spend above the sheds and reduces the time spent in the shed zone and below the sheds, which is highly desirable. The residence time of the agglomerate in the stripper zone quadruples when the solid recirculation rate is cut by half. The release of vapors from agglomerates can be estimated by combining the RPT results with a coking reaction model. As the concentration of agglomerates inside the fluidized increases from 0 to 10 wt%, this study predicts wet agglomerates entering the stripper section with 30 wt% liquid would release 17% more hydrocarbon vapors below the top stripper shed.
... Measuring the velocity or the flow rate of these components is difficult and usually requires the use of non-invasive methods. One of these techniques, which have been employed for many years in measurements of two-phase flows in pipelines and open channels, is a method using sealed radioactive sources emitting gamma ray and the application of its absorption (Arvoh et al., 2012;Chaouki et al., 1997;Hanus et al., 2014a;Johansen and Jackson, 2004;Jung et al., 2009;Maad et al., 2010;Kumara et al., 2010;Petryka et al., 2005Petryka et al., , 2010Petryka et al., , 2012Salgado et al., 2010;Zhao et al., 2013;Zych et al., 2014aZych et al., , 2014b. This method is relatively simple in principle, but there is an associated requirement to meet strict safety requirements for personnel and the environment to protect both from the effects of ionizing radiation and radioactive pollution. ...
... Beams of gamma rays emitted by the sources and formed by collimators are partially absorbed by the flowing medium (Chaouki et al., 1997;Johansen and Jackson, 2004;Jung et al., 2009;Kumara et al., 2010;Petryka et al., 2012;Zhao et al., 2013). Voltage pulses I x (t) and I y (t), received on the output of scintillation detectors, situated at the L distance on the opposite side of the pipeline, are counted down within Dt sampling intervals, giving the mutually delayed discrete stochastic signals x(n) and y(n). ...
Article
Full-text available
Measuring parameters of two-phase flows usually requires contactless measuring techniques to be used together alongside advanced methods of signal processing. One of these techniques, which has been employed for many years in measurements of liquid-gas, liquid-solids and gas-solid flows is a method of gamma-ray densitometry. Frequently in such measurements mutually delayed stochastic signals are received from the scintillation detectors. For the analysis of such signals a well-known cross-correlation function (CCF) is used due to the random nature of the signals and the presence of disturbances. This paper applies the Hilbert Transform to the time delay estimation in measurements of two-phase flow performed by using gamma-ray absorption. It presents the selected results of study of the modified CCFHT cross-correlation method, in which a Hilbert Transform of one measured signal is used. The experiments have been carried out for two-phase water-air flow through a horizontal pipeline of 30 mm inner diameter. A sealed 241Am gamma ray source of 59.5 keV energy has been used in the experiments mentioned above, together with scintillation detectors based on NaI(Tl) crystals. Based on obtained values of time delay the mean velocity of gaseous phase transported by liquid was calculated. It is stated, that the CCFHT method provides better metrological properties than the classical CCF. In the presented experiments combined uncertainties of the gas phase average velocity did not exceed 3.1% for CCF and 0.05% for CCFHT. (http://www.sciencedirect.com/science/article/pii/S0301932215000233)
... However, the application of tomography to engineering issues is relatively new (mid-1980's). In recent years, the X-ray CT has become a useful tool for studies of flows in porous media , Chaouki et al. (1997)). The method can ...
... When an object such as a porous medium is imaged, the attenuation coefficient or CT number varies from location to location. CT numbers may be used to calculate porosity and fluid saturation (Chaouki et al. (1997), Cai and Hicks (1999)). The images from the CT scanner are transferred to a personal computer and afterwards analyzed by the special graphical software FPImage (Wahlberg W.M., http://www.fpimage.com). ...
Article
The present work describes a new experimental method that makes it possible to investigate diffusion coefficients in a porous medium. The method is based on application of X-ray computed tomography (CT). The general applicability of this method for the determination of diffusion coefficients is demonstrated. A series of such experiments was carried out. Several samples of carbonaceous and sandstone rock were investigated. The diffusion coefficients in porous media were determined by measuring the concentration of salt in different slices of a sample as a function of time. In cases where stable values of diffusion coefficients were obtained (all samples except for one highly heterogeneous sample), these values served for the determination of the tortuosity-porosity factors for a given type of porous medium.
... Where T is the dwell time, τ is the dead-time of the detectors, A is the source activity, ν is the number of photons emitted by disintegration, ϕ is the photopeak-to-total ratio and ε i ( , t) is the efficiency of ith detector with respect to a position p in a time t. Besides the distance to the particle, the number of photons recorded depends on the attenuation properties of the materials disposed between the particle and the detector, and on the properties of the detector [16]. For a greater accuracy in particle location, a high number of detected photons is required and this occurs because the number of photons detected is subject to statistical fluctuations during the detection process. ...
... The detection system employed depends on some aspects that affect the interaction of the gammarays with the detectors materials [16]. The most important aspects are the characteristics of the radioactive particle such as gamma-ray energy and activity; the types of gamma-rays interaction with matter (in this work: photoelectric effect and Compton scattering); the solid angle at which the irradiated surface of the detector is subjected, as seen by the particle; the detection efficiency; the photopeak fraction; and the dead-time of the acquisition system. ...
Article
Agitators or mixers are highly used in the chemical, food, pharmaceutical and cosmetic industries. During the fabrication process, the equipment may fail and compromise the appropriate stirring or mixing procedure. Besides that, it is also important to determine the right point of homogeneity of the mixture. Thus, it is very important to have a diagnosis tool for these industrial units to assure the quality of the product and to keep the market competitiveness. The radioactive particle tracking (RPT) technique is widely used in the nuclear field. In this paper, a method based on the principles of RPT is presented. Counts obtained by an array of detectors properly positioned around the unit will be correlated to predict the instantaneous positions occupied by the radioactive particle by means of an appropriate mathematical search location algorithm. Detection geometry developed employs eight NaI(Tl) scintillator detectors and a Cs-137 (662 keV) source with isotropic emission of gamma-rays. The modeling of the detection system is performed using the Monte Carlo Method, by means of the MCNP-X code. In this work, a methodology is presented to predict the position of a radioactive particle to evaluate the performance of agitators in industrial units by means of an Artificial Neural Network.
... RPT systems allow the study of fluidized beds [14 -17], bubble columns reactors [18 -22], conical spouted bed [23], concrete mixers [24,25], among others. The RPT detection system depends on some factors, in which it is possible to highlight: gamma ray and source activity; interaction of gamma ray with matter (Compton scattering, photoelectric absorption); solid angle of the detector; detection efficiency; photopeak fraction and dead time [26]. In addition, the performance of a RPT system is directly related to the characteristics of the radionuclide chosen as a radioactive particle, such as: purity; activity; half-life; and gamma ray energy [26]. ...
... The RPT detection system depends on some factors, in which it is possible to highlight: gamma ray and source activity; interaction of gamma ray with matter (Compton scattering, photoelectric absorption); solid angle of the detector; detection efficiency; photopeak fraction and dead time [26]. In addition, the performance of a RPT system is directly related to the characteristics of the radionuclide chosen as a radioactive particle, such as: purity; activity; half-life; and gamma ray energy [26]. Therefore, the choice of the radionuclide is of great importance. ...
Article
Full-text available
Radioactive particle tracking (RPT) is a minimally invasive nuclear technique that tracks a radioactive particle inside a volume of interest by means of a mathematical location algorithm. During the past decades, many algorithms have been developed including ones based on artificial intelligence techniques. In this study, RPT technique is applied in a simulated test section that employs a simplified mixer filled with concrete, six scintillator detectors and a ¹³⁷Cs radioactive particle emitting gamma rays of 662 keV. The test section was developed using MCNPX code, which is a mathematical code based on Monte Carlo simulation, and 3516 different radioactive particle positions (x,y,z) were simulated. Novelty of this paper is the use of a location algorithm based on a deep learning model, more specifically a 6-layers deep rectifier neural network (DRNN), in which hyperparameters were defined using a Bayesian optimization method. DRNN is a type of deep feedforward neural network that substitutes the usual sigmoid based activation functions, traditionally used in vanilla Multilayer Perceptron Networks, for rectified activation functions. Results show the great accuracy of the DRNN in a RPT tracking system. Root mean squared error for x, y and coordinates of the radioactive particle is, respectively, 0.03064, 0.02523 and 0.07653.
... The use of non-invasive techniques for monitoring multiphase flows has increased in the last decades (Chaouki et al., 1997;Bhusarapu et al., 2005). One such technique is the Computer Automated Radioactive Particle Tracking (CARPT) which uses the high penetration capability of gamma rays to visualise the flow inside a reactor (Lin et al., 1985;Devanathan et al., 1990;Roy et al., 2002). ...
... Currently three different classes of this method for identification of particle position are available (Chaouki et al., 1997): (a) data reduction scheme; (b) neural network based model; and (c) the Monte Carlo based model. The last method (Larachi et al., 1994;Gupta, 2002) needs calibration data (a calibration map) which represents intensity of radiation for each detector at the specified tracker positions. ...
... From the experimental work point of view, it should be noted that the results may come with some uncertainties. It has been reported that the different sources of noise such as Poisson statsitcs of the γ-ray counts, density fluctuations in the flow and propagation error through algorithmic computation cause a discrepancy between the true tracer location and the tracer position obtained by RPT (Chaouki et al., 1997). In order to assess the extent of error in locating the tracer in this study some tests were performed for each experiment by placing the tracer in several known locations in the bed and measuring the γ-ray counts for twelve hundred times. ...
... Improvement in design methodology demands that we develop reliable experimental techniques for studying the microstructure of such opaque flows, and be able to quantify both the mean flow patterns as well as their turbulent and dynamic behavior. In recent years, several novel methods for non-invasive probing of multiphase flows have been developed: such as Particle Image Velocitmetry (PIV), Laser Doppler Anemometry (LDA), Hot Wire Anemometry, Nuclear Magnetic Resonance Imaging (NMRI) etc. for phase velocity measurement, and various kinds of densitometry and tomography techniques (such as gamma ray tomography, and electric impedance tomography) for measuring phase volume fractions (Chaouki et al., 1997a). In addition to providing guidelines for better design and equipment scale-up, experimental findings from these novel techniques are also useful to benchmark fundamental models of complex multiphase flow systems; those based on computational fluid dynamics (CFD) in particular. ...
Conference Paper
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Reliable experimental data for flow characterization in multiphase reactors is of great interest to the process industry. In this paper, we summarize the principles of two non-invasive flow measurement techniques that are being researched and applied to study multiphase reactors in our laboratory, viz., Computer Automated Radioactive Particle Tracking (CARPT) and gamma ray Computer Assisted Tomography (CAT). Versatility of these methods in studying flow patterns in diverse reactor configurations is presented. Future directions in development of these methods are discussed.
... The recent development of electrical tomographic techniques, as applied to the process industries, can be judged by recent textbooks (Williams and Beck, 1995; Chaouki et al., 1997). Electrical techniques developed and applied at UMIST (now The University of Manchester), UK, include electromagnetic (Yu et al., 1993), capacitance (Dyakowski et al., 1999) and resistance (Mann et al., 1997) tomography. ...
Conference Paper
Electrical resistance tomography (ERT) provides a non-invasive and non-intrusive technique for the full 3D interrogation of a typical stirred vessel reactor up to a spatial discrimination of approximately 2,500 derived data points. Some recent ERT results are presented for a 4 ring 16-sensor 6.6 litre vessel detecting the conductivity changes throughout the whole volume of the vessel providing an augmented-reality visualisation during the precipitation reactions. A variety of reactant concentrations, agitation rates and feed modes were investigated. The time evolving conductivity profiles during each experiment provides information on the complex reaction kinetics present in such systems. These conductivity profiles consist of three distinct regions which highlights the systems dependence upon mixing intensity. Also presented are a number of sliced images which clearly indicate the extent of the systems departure from a perfectly mixed state. As expected lower agitation rates produce a less homogeneous conductivity distribution. ERT offers new possibilities for control action linked to spatiotemporal distributions of phases and components for industrial applications. © 2014 International Society for Industrial Process Tomography.
... Several invasive and non-invasive methods have been developed in recent years to measure local gas hold-up. These methods all have inherent advantages and disadvantages that have been reviewed by [92]. ...
Article
A multiscale gas/liquid flow model was developed as a tool for the design and scale-up of stirred tank reactors (STRs). The model is based on the compartmentalization of the STR into zones and the use of simplified less computationally intensive gas/liquid flow simulations. It predicts the mean value of the local volumetric mass transfer coefficient ( ) in each compartment based on the local hydrodynamic parameters therein (i.e., gas hold-up and liquid turbulent energy dissipation rate). The adequacy of the model at each step was carefully assessed using experimental data drawn from the literature. The proposed model was able to predict the overall volumetric mass transfer coefficient in STRs agitated with a Rushton turbine with good adequacy. The effects of operating conditions and scale-up on the distribution of were also studied. The contributions of each compartment to the overall mass transfer inside the STR could be changed considerably by altering the operating conditions and scale-up. It was estimated that by increasing the STR size, the overall volumetric mass transfer coefficient decreased by at least 20% following a conventional scale-up rule. This was explored by combining the concepts of the local residence time distribution (RTD) of the liquid phase and the local values inside the STR. These findings revealed the challenges involved in scaling up multiphase stirred tanks. Lastly, some alternative approaches are suggested for the design and scale-up of multiphase reactors that may mitigate the inherent limitations of conventional rules.
... An Epoxy/Gold tracer-particle prepared as suggested by Godfroy (4), was selected as the radioactive source. When gold is radiated in a nuclear reactor (for this research, the Material Test Reactor at McMaster University in Canada), some of it transforms into Au 198 isotope with a half-life of 2.69 days (2). For this study, the tracer-particle radiation decreased gradually from 166 to 70 µCi. ...
... Positron emission particle tracking (PEPT) is an experimental technique allowing one to follow the movements of a radioactive tracer particle [30]. This method has been adapted from Positron Emission Tomography (PET) and it is used in particle technology for studying the dynamic behaviour of dry particulate systems such as gas-fluidised beds, tumbling mills, pneumatic conveying etc. used in various industrial processes [31][32][33][34]. PEPT allows for non-invasive particle imaging and tracking deep within the particulate system for an extended period of time, thus enabling the analysis of the insitu kinematics and dynamics of the particle flow [35,36]. ...
Article
The behaviour of a traced alumina particle lying on limestone powders with similar features has been studied in a test tube agitated by a vortex shaker aiming at studying dust emissions from powders. PEPT (Positron Emission Particle Tracking) was used for measuring the particle's position. Population densities were computed as the frequency of the particle's presence in different regions dividing the two horizontal axes and the vertical axis, respectively. The velocities of the particle were calculated by filtering out all displacements inferior to a critical distance dcrit so as not to consider spurious movements caused by experimental noise. After its validation, the methodology was applied to the standard condition of a vortex shaker experiment (ω = 1500 rpm, 2 g of powder and open test tube). While the horizontal coordinates and velocity components follow a symmetric distribution, the vertical coordinate is characterised by a large asymmetrical plateau. The heights reached by the particle (up to 24.3 mm) are small in comparison to that of the test tube (150 mm). The greatest velocities are found near the inner wall of the test tube and at the highest heights where the population densities are the lowest. The median velocity of the particle is 0.0613 m.s −1 whereas its median kinetic energy is 8.4E-12 J. The method explicated in the present study is directly applicable to any other sets of data obtained through PEPT, especially if the system is of small dimension.
... Non-invasive techniques (e.g. dynamic gas disengagement, photography, radiography, NMR, particle image velocimetry, laser Doppler anemometry) have also been used to measure bubble size distributions or phase velocities (Chaouki et al., 1997). As discussed by Boyer et al. (2002) however, these techniques are limited by the operating conditions, low gas holdup requirements, and/or relative costs. ...
Thesis
Full-text available
Commercial ebullated bed hydroprocessors, such as the LC-Finer, are used for the production of synthetic crude oil by upgrading bitumen extracted from the Alberta oil sands. The objective of this thesis was to investigate the impact of an increased vacuum distillation tower bottoms feed fraction on the reactor fluid dynamics (e.g., bed and freeboard phase holdups, bubble characteristics and local fluidization behaviour). Industrial conditions were simulated in a high pressure gas-liquid-solid fluidization system based on dimensional and geometric similitude. Considering important geometric characteristics and matching dimensionless groups, base-case conditions resulted in an ebullated bed of nitrogen, 0.5 wt.% aqueous ethanol, and aluminum cylinders (average lengths and diameters of 7.5 and 3.2 mm, respectively) operating at 6.5 MPa and a gas-to-liquid superficial velocity ratio of 0.78. The proposed scale-down method resulted in high gas holdup conditions similar to industrial measurements. The use of the Sauter mean diameter to account for particle size and shape at the simulation conditions was investigated by comparing glass spheres with diameters of 4 and 1.5 mm to aluminum cylinders with equivalent volume-to-surface area ratios. Local bubble characteristics, including gas holdups, bubble rise velocities, and chord lengths, were then investigated under various operating conditions using a monofibre optical probe. Overall fluid dynamics were studied when increasing the liquid viscosity and varying the gas and liquid superficial velocities due to their relevance for industrial ebullated bed hydroprocessors. Freeboard and bed region gas holdup relations were studied and correlations were developed for gas and solid holdups at the simulation conditions based on the dimensionless groups. Mesophase generation in hydroprocessors due to undesired secondary reactions was also considered for an increased vacuum residue feed fraction. Adding a dispersed immiscible liquid phase which preferentially wetted the particles was therefore experimentally studied at non-simulating conditions using nitrogen, biodiesel, glycerol and various particles, where fluidization behaviour and phase holdups were considerably affected due to particle clustering. A study on the impacts of particle size, shape and material demonstrated the influences of fluid and particle properties, specifically the relative surface energies and viscous forces, on agglomeration due to interparticle liquid bridging.
... 3,5 RPT on the other hand does not suffer from these limitations and has emerged as the non-invasive technique appropriate for these measurements in dense multiphase systems. 5,[11][12][13] RPT is based on the idea of tracking the motion of single, γ-ray-emitting radioactive tracer particle, acting as the marker of the phase being tracked. 5,12,14 Typically, RPT is implemented in two phases: calibration run and experimental run. ...
Article
Radioactive particle tracking (RPT) is one of the most widely used non‐intrusive velocimetry technique for multiphase reactors. The large volume of interrogation and the presence of internals limit the application of RPT in large‐scale real‐world systems. The main challenge lies in having fast reconstruction algorithms applicable to conventional (i.e., bubble columns, fluidized beds, etc.) as well as new vessels. In this contribution, a reconstruction methodology is proposed based on machine learning. Three machine‐learning algorithms, namely, artificial neural network (ANN), support vector regression (SVR), and relevance vector regression (RVR), have been employed for RPT reconstruction. The results show that the position reconstruction accuracy of SVR was best for all cases and that the accuracy of RVR was comparable to SVR for large training datasets. Whereas, in terms of reconstruction speed, RVR outperforms SVR significantly, owing to sparser RVR model. SVR and RVR based reconstruction algorithms expedite the position reconstruction.
... By comparing the combined detector response for a several locations in the column with the actual values measured when the tracer is moving, the tracer position while freely moving in the column is calculated. Further details of the reconstruction procedure can be found in Chaouki, Larachi, and Dudukovic (1997). ...
Article
Liquid–solid fluidized beds (LSFB) modeling validation is crucial for establishing design rules and monitoring tools. However, it generally relies on comparing global variables, which overlook dynamic features that influence reaction outputs. This work aims to implement time series analysis tools to compare Radioactive Particle Tracking data with a simulation consisting of Computational Fluid Dynamics coupled with Discrete-Element Method. Experiments have been performed in a pilot-scale LSFB of calcium alginate spheres fluidized with a calcium chloride solution. The Diks’ test indicates that the simulation can capture the LSFB behavior. It also allows diagnosing flow regime transitions from the simulation. Trends of solid dispersion coefficients and mixing times predicted by the simulation are in good agreement with the experiments.
... Performance of any multiphase system critically relies on the underpinning hydrodynamics. Consequently, a number of non-intrusive (Chen and Fan, 1992;Wolf et al., 1993;Dyakowski, 1996;Elkow and Rezkallah, 1996;Chaouki et al., 1997;Prasser et al., 1998;McGuinn et al., 2002;Dong et al., 2005;Ismail et al., 2005;Rahim et al., 2007) and intrusive (Andreussi et al., 1988;Cartellier, 1992;Fossa, 1998;Lucas and Mishra, 2005;Da Silva et al., 2007;Lee and Dudukovic, 2014;Mota et al., 2015;Zhai et al., 2016;Chugh et al., 2017;Tyagi and Buwa, 2017) techniques have been developed to measure one or more of the following parameters: velocity, holdup, pressure drop, and size distribution in a multiphase system. Examples of non-intrusive techniques are particle image velocimetry (PIV), laser Doppler anemometry, radioactive particle tracking, positron emission particle tracking, X-ray tomography, γ-ray tomography, and electrical capacitance tomography. ...
Article
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For a detailed characterisation of multiphase flows, a local measurement technique that is capable of quantifying both continuous and dispersed phases has to be employed. In the present study, a new optical probe was tested for its ability to provide simultaneous local measurements of gas and liquid/solid in a three-phase system. The new probe can measure the intensity of light reflection due to the presence of gas or liquid medium surrounding the probe tip in conjunction with the Doppler frequency caused by the approach of a solid particle. The experiments were carried out in a pseudo-2D rectangular column by passing gas bubbles through a stationary liquid with suspended seeding particles. In these experiments, measurements were carried out by using three techniques namely optical probe, particle image velocimetry (PIV), and high-speed imaging (HSI). PIV measurements were used to validate seeding particle velocity obtained using the optical probe, whereas HSI technique was used to validate bubble chord length data from optical probe. The difference between the particle velocity from the probe and PIV was in a range of 13%–20%, w hile the difference between chord length measured by the probe and HSI was within ±8%.
... Unlike the standard aspect of the computed tomography (CT) for medical application, industrial tomography systems applications should be adapted to the different size and geometry objects, usually placed in an aggressive environment, which contains flammable superheated or corrosive materials, and, eventually, subject to high internal pressure, all these factors bring in many difficulties for setting CT devices [1,2]. In addition, the industrial systems involve multiphase dynamic processes containing solids, liquids and gases mixtures [3][4][5][6][7]. ...
Article
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The greatest impact of the tomography technology currently occurs in medicine. The success is due to the fact that human body presents standardized dimensions with well-established composition. These conditions are not found in industrial objects. In industry, there is a great deal of interest in using the tomography in order to know the inner part of (i) manufactured industrial objects or (ii) the machines and their means of production. In these cases, the purpose of the tomography is: (a) to control the quality of the final product and (b) to optimize the production, contributing to the pilot phase of the projects and analyzing the quality of the means of production. This scan system is a non-destructive, efficient and fast method for providing sectional images of industrial objects and it is able to show the dynamic processes and the dispersion of the materials structures within these objects. In this context, it is important that the reconstructed image may present a great spatial resolution with a satisfactory temporal resolution. Thus, the algorithm to reconstruct the images has to meet these requirements. This work consists in the analysis of three different iterative algorithm methods, namely the Maximum Likelihood Estimation Method (MLEM), the Maximum Likelihood Transmitted Method (MLTR) and the Simultaneous Iterative Reconstruction Method (SIRT. The analyses involved the measurement of the contrast to noise ratio (CNR), the root mean square error (RMSE) and the Modulation Transfer Function (MTF),in order to know which algorithm fits the conditions to optimize the system better. The algorithms and the image quality analyses were performed by Matlab® 2013b.
... Apart from different methods discussed in previous sections for the preparation of microparticles, other methods can also be adopted depending upon the experimental requirement (Chaouki et al., 1997). Various other methods for the preparation of the microparticle are discussed in this section. ...
Article
Radioactive particle tracking (RPT) technique is a relatively newer technique for the characterization of flow of process materials (liquids, solids) in laboratory- and pilot-scale industrial systems. The technique uses a single particle labelled with a suitable radioisotope having similar physical properties to that of the bulk of the process material. The preparation of a representative radioactive microparticle is a challenging task in the implementation of the technique. There are no standard methods available for the preparation of radioactive microparticles. This paper discusses some of the methods of preparation of radioactive microparticles for RPT studies. A few examples of RPT applications using the prepared microparticles are also discussed.
... Therefore, these techniques are mainly used for statistical analysis of flow fields based on representative tracer particles. Computed tomography (CT) can provide more direct information from transient cross-sectional particle concentration profiles on the continuum level (Seville et al., 1986;Banholzer et al., 1987;Dudukovic et al., 1997;Bieberle et al., 2012;Mathews et al., 2017). Limited by the number of transmitters and receivers, the sampling frame rate has to be compromised with the spatial resolution in terms of the voxel number. ...
Article
This article reviews the general features of the multiscale structures in particle–fluid systems and the characterization, modeling, and simulation methods for these systems. The discussion focuses on the effects of mesoscale behavior, especially those present in process industries for materials and energy transformation and utilization. When there is substantial multiscale heterogeneity in these systems, local non-equilibrium and anisotropy generally lead to a lack of scale separation. Accurate and efficient simulation methods based on first principles and applied across different scales are highly desirable to reveal and quantify the complexities of these systems. Meanwhile, precisely designed experiments and exhaustive nonintrusive measurements are necessary to validate and expand the numerical findings. With this knowledge, rational mesoscale models can be established to provide multiscale simulation methods that do not need to fully reproduce the micro- and mesoscale details of the systems but can still take into account their effects on macroscales. Such multiscale methods are attractive for industrial applications but substantial effort in physical modeling and numerical implementation is still required before their widespread implementation.
Thesis
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The stripper section of a Fluid CokerTM consists of a system of baffles (sheds) that enhances the removal of interstitial and adsorbed hydrocarbon vapors from the fluidized coke-particles. Most of the hydrocarbon-vapors released below a stripper shed flow up to the stripper shed, where they may crack and form coke deposits that foul the shed. Extensive fouling changes the shapes of the sheds, makes them thicker and reduces the free-space between the adjacent sheds until downward solids flow is so impaired that the Coker has to be shut down. The Radioactive Particle Tracking (RPT) technique allows the determination of a radioactive tracer-particle location within a certain space inside a fluidized bed and has been the main tool used to study the motion of agglomerates and their interactions with internals. The research presents an innovative use of the RPT system, as a tool to measure the growth of internals fouling in time without the need of stopping the process. Moreover, the technique was able to characterize the type of interactions the agglomerate has with the sheds. In conjunction with a mathematical drying model, it was possible to predict the flow of organic vapors reaching each shed, thus estimating the risk of shed fouling, as well as the amount of liquid lost with the agglomerate as it leaves the stripper section. The investigation found that small agglomerates lose very quickly their liquid and therefore its ability to cause fouling. Moreover, experimental work showed that the solid recirculation rate is a very important parameter, e.g., decreasing it by half, quadruples the residence-time in all zones. The comparison of different types of sheds and configurations concluded that the Mesh-Shed type of internals performs the best. With regular sheds, the best configuration reduces the total open area by only 30%, instead of 50% as with the current sheds. A study of a ring-baffle that is inserted above the stripper section showed that its main advantage is that it increases the residence time of the agglomerates above the baffle, providing them with more time to dry. Adding flux-tubes to the baffle is detrimental to their performance.
Thesis
Handling and processing of granular material release fine solid dust particles, which in an occupational setting, can severely affect worker health & safety and the overall plant operation. Dustiness or the ability of a material to release dust particles depends on several material and process parameters and is usually measured by lab-scale dustiness testers. Dustiness tests remain mostly experimental studies and lack reliable predictive ability due to limited understanding of the dust generation mechanisms and the complex interactions between the particles, wall and fluid, occurring simultaneously during dust generation. In the framework of EU ITN project T-MAPPP, this thesis uses an experimental approach to understand the dust generation mechanisms by studying: a) the effects of key bulk and particle properties on powder dustiness; b) the nature and magnitude of inter-particle, particle-wall and particle-fluid interactions; c) the evolution of dustiness and generation mechanisms for long duration powder applications. The results indicate that the dust generation mechanisms differ based on particle size and size distribution of the powder. For the given test samples and experimental conditions, the differences in powder dustiness and dust emission patterns can be characterized by three different groups of powders; powders containing fine cohesive particles, bi-modal (consisting of fine and large particles) powders and lastly, powders consisting of only large particles. While bulk cohesion, especially that stemming from van der Waals forces (measured using shear testers) determines the level of dustiness for the fine powders (in such a way that higher bulk cohesion leads to lower dustiness), both the fraction of fine particles and cohesion determine the dustiness of bi-modal powders. The large particles can emit dust only through attrition of the primary particles into smaller aerosolizable fine particles. Analysis of a traced particle motion inside a cylindrical tube agitated by a vortex shaker dustiness tester shows the cyclic nature of the particle motion. The motion (position and velocity) is symmetric and isotropic in the horizontal plane with lowest radial velocities close to the tube centre and highest at the boundary wall of the test tube. The particles tend to rise up slowly in the middle of the tube while descending rapidly close to the wall. The highest values of the velocity are found at the highest heights and close to the wall of the test tube, where the population densities are lowest. Increasing particle size and vortex rotation speeds tends to increase particle velocity whereas increase in powder mass leads to a decrease in particle velocity for rotation speeds up to 1500 rpm. For the given samples (silicon carbide, alumina and acetylene coke) and the experimental conditions, the initial dustiness is determined by the fraction of fine respirable particles present in the powder but the long-term dust generation patterns and levels are influenced by the material attrition behaviour. Dust is generated by the fragmentation and/or abrasion of primary particles, which may lead to the production and emission of fine daughter particles as dust. The samples with large irregularly shaped particles are likely to show high dustiness by shedding angular corners through inter-particle and particle-wall collisions, thus becoming more spherical in shape. On the contrary, the smaller particles are more resistant to abrasion and generate relatively less dust. While the vortex shaker dustiness tests show similar trends as an attrition tester, our study using alumina and acetylene coke indicate that the results are not interchangeable. Results from this thesis help understand the influence of powder and process parameters which may be manipulated to reduce dust generation. Furthermore, experimental results can be used to develop and validate numerical models to predict dustiness.
Thesis
In bubbling fluidized beds, bubble characteristics such as size, shape and velocity have a vital influence on the hydrodynamics of the bed and hence on its performance as a chemical reactor and/or a heat exchange unit. In many industrial applications such as lignite dryer heat transfer tubes are usually inserted to enhance the rate of heat and mass transfer and chemical conversion. However, their presence strongly influences the bubbling behavior of the beds. Therefore, reliable design and scale-up of these systems come only after fundamental understanding of the bubbling behavior is achieved. Therefore, in this research work the influences of tube bank geometries and particle size on bubble characteristics were thoroughly investigated. In this research work, both numerical and experimental studies were employed. For the experimental measurements, a new nonintrusive digital image analysis technique was developed. The technique allowed for the simultaneous measurements of bed expansion and various bubble properties. An in-house software was developed to fully automate the image acquisition and data processing procedure. For the numerical studies, the Eulerian-Eulerian two-fluid model based on the kinetic theory of granular flow was used. Though, this CFD model has been considered as a fundamental tool for modeling gas-solid fluidized beds, its quantitative validation remains insufficient for a wide range of reactor geometries and operating conditions. Therefore, in this work validation of the model using experimental measurements of bed expansion and bubble properties obtained from a pseudo-two-dimensional fluidized bed was performed. The influence of two-dimensional simulations and different modeling parameters such as the friction packing limit, drag model and solid-wall boundary conditions were investigated. The two-fluid model generally showed reasonable agreement with the experimental measurements of pressure drop, bed expansion and bubble properties in bubbling regime. However, as the gas superficial velocity is increased and the bed moved towards slugging and turbulent regimes a big deviation arose and the two-fluid model failed to predict reasonably the fluidized bed hydrodynamics for the freely bubbling bed. The mean bubble properties predicted by two-dimensional simulations were in reasonable agreement with experiments at lower superficial velocities. They deviated at higher bed height and this was more pronounced at higher gas superficial velocities. The results from three-dimensional simulations were in better agreement with the experimental measurements; however, the computational effort need was very high making them impractical for parametric studies and sensitivity analyses. It was also showed that the choice of friction packing limits, drag laws and specularity coefficients have little influence on the bubble properties. For a bubbling bed, both experimental measurements and numerical simulations showed that inserting horizontal tube banks had either no or marginal influence on the static bed pressure drop and bed expansion. On the other hand, bubble hydrodynamics were strongly influenced and controlled by the geometry of the immersed tubes. In freely bubbling fluidized beds bubble size as well as rise velocity increased with bed height and superficial velocity. In beds with immersed tubes, such general trends were completely disturbed. Tubes appeared to restrict rapidly growing bubbles. As a result the mean bubble diameter and rise velocity were lower in the vicinity of the tube banks than in the freely bubbling bed. Results from different particle sizes showed that in a freely bubbling bed increasing the mean particle size increased the bubble diameter and rise velocity as well as bed expansion. In fluidized beds with dense horizontal tubes on the other hand, the mean bubble properties were almost independent of the particle sizes.
Article
This paper presents an extensive review of the kinetics, hydrodynamics, mass transfer, heat transfer and mathematical as well as computational fluid dynamics (CFD) modeling of Low-Temperature Tropsch Synthesis (LTFT) synthesis in Slurry Bubble Column Reactors (SBCRs), with the aim of identifying potential research and development areas in this particular field. The kinetic expressions developed for F-T synthesis over iron and cobalt catalysts along with the water gas shift (WGS) reactions are summarized and compared. The experimental data and empirical correlations to predict the hydrodynamics (gas holdup, Sauter mean bubble diameter, and bubble rise velocity), mass transfer coefficients and heat transfer coefficients are presented. The effects of various operating variables, including pressure, temperature, gas velocity, catalyst concentration, reactor geometry, and reactor internals on the hydrodynamic and transport parameters as well as the performance of SBCRs are discussed. Additionally, modeling efforts of SBCRs, using axial dispersion models (ADM), multiple cell recirculation models (MCCM) and computational fluid dynamics (CFD), are addressed. This review revealed the following: (1) Numerous F-T and WGS kinetic rate expressions are available for cobalt and iron catalysts and one must be careful in selecting the appropriate expressions for LTFT. Iron catalyst suffers from severe attrition and subsequent deactivation in SBCRs and accordingly building a costly catalyst manufacturing facility onsite is required to maintain a steady operation of the F-T reactor; (2) Experimental data on the hydrodynamic and transport parameters at high pressures and temperatures, typical to those of actual F-T synthesis, remain scanty when compared with the plethora of studies conducted using air–water systems in small reactors at ambient conditions; (3) Several empirical correlations for predicting the hydrodynamic and mass as well heat transfer parameters are available and one should select those which consider the reactor diameter, gas mixtures and the potential foamability of the F-T liquids; (4) The effect of cooling internals configuration and sparger design on the hydrodynamic and transport parameters, local turbulence, mixing and catalyst attrition are yet to be seriously addressed; (5) The impact of operating variables on the hydrodynamic and transport parameters as well as the overall performance of the SBCRs should be investigated using actual F-T fluid–solid systems under typical pressures and temperatures using a large-scale reactor (>0.15 m ID) in the presence of gas spargers and cooling internals; (6) Significant efforts are still required in order to advance CFD modeling of SBCRs, particularly those pertaining to the relevant closure models, such as drag, lift and turbulence. Also, cooling internals configuration and the design as well as orientation of gas spargers should be accounted for in the CFD modeling; and (7) Proper validations of the CFD formulations using actual systems for F-T SBCR are needed.
Article
Two-phase gas-liquid flows, the simultaneous flow of a gas and liquid in a pipe, are commonly found in several industrial activities, among them during the extraction and processing of crude oil. Wire-mesh sensors are flow imaging devices which are able to generate images of phase distribution of two-phase flows within a pipe cross section at high spatial and temporal resolutions. Appropriated image processing algorithms are however necessary in order to extract important flow parameter from raw data. In this paper, we describe a bubble identification algorithm based on three-dimensional image segmentation. Results of bubbles velocity and flow rate measurement based on the development algorithm are validated against reference models showing good agreement.
Article
Shadow imaging is used for the investigation of bubbly gas–liquid two-phase flow in a porous structure. The porous structure is made of Somos WaterShed XC 11122, a clear epoxy resin used in rapid prototyping. Optical access is provided by using an aqueous solution of sodium iodide and zinc iodide having the same refractive index as the structure material (n = 1.515). Nitrogen is injected into the continuous phase at volumetric transport fractions in the range of (\dot{\varepsilon } = 2.4-4.1%) resulting in a hold-up of (\varepsilon = 0.94-2.17%). The obtained images of overlapping bubble shadows are processed to measure the bubble dimensions. Therefore, a new processing sequence is developed to determine bubble dimensions from overlapping bubble shadows by ellipse fitting. The accuracy of the bubble detection and sizing routine is assessed processing synthetic images. It is shown that the developed technique is suitable for volumetric two-phase flow measurements. Important global quantities such as gas hold-up and total interfacial area can be measured with only one camera. Operation parameters for gas–liquid two-phase flows are determined to improve mass and heat transfer between the phases.
Article
Gamma densitometry is a widespread nonintrusive method for measuring the void fraction among all the methods. Void fraction is a fundamental parameter and generally obtained by the logarithmic and linear equations by means of single-beam gamma-densitometry. However, using these two equations in large diameter pipeline is a hard goal to reach because of the limitation of the radioactive source. In this paper, we proposed a formula for the void fraction measurements in large diameter pipeline and this formula can be also utilized in small diameter pipeline. Deviations between the calculated and actual void fraction of the methods in this paper are demonstrated. The theoretical errors of the new formulae are relatively insignificant in comparison to the logarithmic and linear equations. The method for large diameter pipe has even a smaller theoretical error than multi-beam gamma-densitometry. Disadvantages of the logarithmic equation are analyzed and the modification of the void fraction measurement formulae is proved to be progressive in mathematics. We discussed the simplifications in the novel methods and they have negligible effect on the measurements. Measurement positions and areas are optimized based on the theoretical deduction. In addition, we formulated the experimental requirements of different void fraction expressions.
Chapter
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The article deals with approaches to the rational and complex development of titanium deposits of different genetic types: primary, residual and placers. The task was to select the most rational way of working out prospective fields for which the modeling of deposits using GIS was made. For the primary deposits, the geological section was detailed by geochemical methods, with allocation within each unitthe layers with different mineralization; the distribution of minerals was studied, and the existence of latent layering was proved. These researches improve the ore enrichment schemes. An open cast-underground mining method has been proposed for the Stremyhorod deposit, which allows reducing by 15-18 hectares the area of the extracted lands and by 25-28 million m3 of the amount of overburden. For the residual Torchyn deposit it is proposed to use a vertical reserve index to construct the geological-technological model, which allowed the selecting the most profitable blocks for mining. On the example of the Tarasovka placer it is shown a model where an integral indicator is applied, which includes the sale value of all useful components in two productive horizons and the cost of their extraction. Such approaches allow the development of a rational scheme for field exploration, providing complex extraction of useful components.
Article
A rotating packed bed (RPB) has received considerable attention of many researchers due to its high mass transfer rate and mixing efficiency. In order to effectively promote and employ RPB in the chemical industry, it is necessary to have a better understanding of its flow characteristics. In this study, a noninvasive X-ray technique was employed for the first time to examine the hydrodynamics of RPB. Time-average tomographic cross sectional images showing the distribution of liquid in the packing zone under various operating conditions were captured. It was observed that high rotational speed improves the distribution of liquid in the packing. Additionally, quantitative analysis based on liquid holdup was made, and the effects of rotational speed, liquid flow rate, fluid viscosity, surfactant and two different kinds of packings on liquid holdup were evaluated. Results indicate that liquid holdup decreases with an increase in rotational speed and a reduction in both liquid flow rate and liquid viscosity. However, it was observed that surfactant has no significant effect on liquid holdup. Correlations to predict liquid holdup were developed, and the calculated values are in agreement with the experimental values with deviations within ±22%. Furthermore, the mean residence time in various conditions is calculated based on liquid holdup.
Thesis
In dieser Arbeit wird der Weg zu einem ab-initio Modell für gasdurchströmte Schüttschichtreaktoren dargestellt. Diese Reaktoren zeichnen sich durch eine komplexe Struktur ihres Festbetts aus. Diese Struktur bestimmt die Durchströmung sowie das Vermischungsverhalten dieses Reaktortyps und beeinflußt so auch die chemische Reaktion. Um die Wechselwirkung auf das radiale Vermischungsverhalten von Reaktoren und deren Schüttung zu untersuchen, wurde ein Gesamtmodell geschaffen, daß ausgehend von einer Simulation der Schüttung die Durchströmung beschreibt. Aufbauend auf der Schüttungssimulation wird die Strömung in einem zweidimensionalen Kontinnuumsmodell und einem diskreten Modell beschrieben und mit Messungen verglichen. Dem Autor ist es gelungen, mit dem in dieser Arbeit dargestellten Gesamtmodell, das radiale Dispersionsverhalten eines Festbettreaktors nachzuvollziehen, ohne effektive Parameter dafür zu nutzen. Dieser Vorteil gegenüber den bestehenden Ansätzen entsteht aus der Kopplung der Schüttungsmodelle mit den Strömungsmodellen zu einem Gesamtmodell. Bedingt durch den dreidimensionalen Ansatz liefert das diskrete Modell eine realitätsnähere Beschreibung der radialen Dispersion, während das zweidimensionale Kontinuumsmodell einen größeren Detailreichtum bei der Beschreibung der radialen Strömungsprofile zuläßt. Ein wesentliches Element des Gesamtmodells ist das Schüttungsmodell, ohne dessen gute Übereinstimmung mit lockeren Kugelschüttungen die darauf aufbauenden Simulationsschritte nicht möglich wären. Diese gute Kongruenz konnte gegenüber anderen in der Literatur dargestellen Schüttungsmodellen gerade im Randbereich erreicht werden. Eine richtige Beschreibung dieses Bereichs ist notwendig, um Effekte wie Bypassing zu erfassen. Auch bewirkt eine nicht-realitätsnahe Beschreibung dieses Bereichs eine zu geringe Strömung im Kern der Schüttung. Beide Strömungsmodelle des Gesamtmodells zeigen, daß der in dieser Arbeit verwendete Ansatz der Kopplung von Schüttungs- und Strömungsmodell ein Schritt auf dem Weg zu einem ab-initio Modell sein kann. So gelingt es durch die detaillierte Schüttungsstruktur, den effektiven Parameter der radialen Dispersion zu eliminieren, so daß entsprechende Messungen bzw. Abschätzungen für die Simulation eines Reaktors nicht mehr notwendig sind. Dies gilt insbesondere für den Bereich großer Durchmesserverhältnisse von Kugel- zu Reaktordurchmesser, in dem die Abschätzungen, wie sie in der Literatur genutzt werden, nicht mehr validiert sind.
Article
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Fluid flow through packed porous media and fluid–particle interactions are of importance in various industrial and natural processes. However, the lack of knowledge about the velocity field in the pore space and distribution of drag force on individual particles has been a source of uncertainties in modeling these processes. Therefore, an improved understanding of the velocity field and fluid–particle interactions is a fundamental step for better understanding of these systems. In this article, the pore-scale velocity field and fluid–solid interaction from a single particle to randomly-packed mono-sized porous media are investigated using a 3D GPU-based parallel Lattice Boltzmann model. The packed porous media are generated by means of discrete element method and have a wide range of porosity values. The developed model is first validated by experimental results of fluid flow around single and two interactive particles; the validated model is then used to conduct statistical analysis of velocity in the pore space and drag force on individual particles. The results suggest that the velocity field in porous media can be divided into four zones, namely: zero-velocity zone, low-velocity zone, high-velocity zone, and recirculation zone. Moreover, the probability density distribution of velocity is highly dependent on Reynolds number and porosity and can be bi-modal, depending on a combination of Reynolds number and porosity. The probability density distribution of the drag force always shows a single peak at the mean value with a skewness to the right. Finally, a simpler and more accurate correlation for the mean drag force over a wide range of Reynolds number and porosity is proposed based on the numerical results. The accuracy and reliability of several empirical equations, including the one proposed in this study, for the mean drag force are compared through a statistical analysis.
Thesis
Handling and processing of granular material release fine solid dust particles, which in an occupational setting, can severely affect worker health & safety and the overall plant operation. Dustiness or the ability of a material to release dust particles depends on several material and process parameters and is usually measured by lab-scale dustiness testers. Dustiness tests remain mostly experimental studies and lack reliable predictive ability due to limited understanding of the dust generation mechanisms and the complex interactions between the particles, wall and fluid, occurring simultaneously during dust generation. In the framework of EU ITN project T-MAPPP, this thesis uses an experimental approach to understand the dust generation mechanisms by studying: a) the effects of key bulk and particle properties on powder dustiness; b) the nature and magnitude of inter-particle, particle-wall and particle-fluid interactions; c) the evolution of dustiness and generation mechanisms for long duration powder applications. The results indicate that the dust generation mechanisms differ based on particle size and size distribution of the powder. For the given test samples and experimental conditions, the differences in powder dustiness and dust emission patterns can be characterized by three different groups of powders; powders containing fine cohesive particles, bi-modal (consisting of fine and large particles) powders and lastly, powders consisting of only large particles. While bulk cohesion, especially that stemming from van der Waals forces (measured using shear testers) determines the level of dustiness for the fine powders (in such a way that higher bulk cohesion leads to lower dustiness), both the fraction of fine particles and cohesion determine the dustiness of bi-modal powders. The large particles can emit dust only through attrition of the primary particles into smaller aerosolizable fine particles. Analysis of a traced particle motion inside a cylindrical tube agitated by a vortex shaker dustiness tester shows the cyclic nature of the particle motion. The motion (position and velocity) is symmetric and isotropic in the horizontal plane with lowest radial velocities close to the tube centre and highest at the boundary wall of the test tube. The particles tend to rise up slowly in the middle of the tube while descending rapidly close to the wall. The highest values of the velocity are found at the highest heights and close to the wall of the test tube, where the population densities are lowest. Increasing particle size and vortex rotation speeds tends to increase particle velocity whereas increase in powder mass leads to a decrease in particle velocity for rotation speeds up to 1500 rpm. For the given samples (silicon carbide, alumina and acetylene coke) and the experimental conditions, the initial dustiness is determined by the fraction of fine respirable particles present in the powder but the long-term dust generation patterns and levels are influenced by the material attrition behaviour. Dust is generated by the fragmentation and/or abrasion of primary particles, which may lead to the production and emission of fine daughter particles as dust. The samples with large irregularly shaped particles are likely to show high dustiness by shedding angular corners through inter-particle and particle-wall collisions, thus becoming more spherical in shape. On the contrary, the smaller particles are more resistant to abrasion and generate relatively less dust. While the vortex shaker dustiness tests show similar trends as an attrition tester, our study using alumina and acetylene coke indicate that the results are not interchangeable. Results from this thesis help understand the influence of powder and process parameters which may be manipulated to reduce dust generation. Furthermore, experimental results can be used to develop and validate numerical models to predict dustiness.
Article
Since years conventional x-ray tomography has been successfully used to study the flow structures of vertical gas-solids flows. Now, the additional implementation of a dual-energy technique makes it possible to investigate multiphase flows like an injection of liquid educts in a gas-solids fluidized bed or a reaction progress in a three-phase bubble column. The x-ray tomography system mainly consists of an 160 kV/640W x-ray source, which can be operated at different energy levels, and an x-ray linear detector with 1024 sensitive elements. With a dual-energy technique the dependence of the materials absorption coefficients on the x-ray energy is used. A number of static test objects composed of two different materials have been investigated to simulate technical applications like mixing or drying processes of granulated material. Additionally, the dual-energy x-ray tomography system has been applied to determine the solids, liquid and gas distribution in a three-phase bubble column in order to show the possibilities of this measuring technique. © 2014 International Society for Industrial Process Tomography.
Article
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The intermittent flow (slug and plug type) of liquid–gas mixtures in a horizontal pipeline measured by the specific radiometric apparatus is presented. The measurement system consists of two sources of Am-241 gamma radiation and two scintillation probes. An analysis of the signals measured by the radiometric equipment is performed in the domain of time and of frequency. Recognised signal parameters are directly referred to physical quantities associated with a liquid–gas flow. The employed methodology enables determination of gas-phase flow velocity and estimation of the average depth and length of bubble gas structures. In the paper, the processing and interpretation results of the selected experiment are presented to show the in-depth description of gas structures and the type of flows recognition.
Conference Paper
Effectively measure wet gas phase fractions and flow rate has always been a challenge to the multiphase flow measurement community. While measurements using gamma ray approach has so far proven to be the most accurate, it also requires good "line of sight" phase fraction representation in the flow line. Such requirement often leads to increased complexity and cost in equipment configuration (i.e. vertical Venturi, or additional gamma ray detectors). Venturi placed horizontally reduces configuration complexity however the "line of sight" phase fraction would not be representative if a single gamma source/detector is used, due to gravitational separation of phases in horizontal flow. A model of two eccentric circles of the same diameter was developed to use the horizontal configuration, yet not sacrifice accuracy of phase fraction measurement. The model has been validated with previous experiment data and the results were well matched. Additional verification at a third party facility (National Engineering Laboratory of UK) was also conducted and RMS error in flow rate of each phase were well below 6%. The model and associated equipment configuration form a simple and effective system for wet gas flow measurements, reduce system cost, complexity in installation and associated safety risk, and have a great value for marginal oil and gas fields as well as production optimization management.
Conference Paper
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Void fraction measuring techniques are reviewed with emphasis on applications to multiphase flow. The presentation is divided into two main sections; intrusive where the probe penetrates into the flow field, and non-intrusive where the detection is done remotely. The latter is more preferrable than the former. We subdivided the non-intrusive techniques into into two main categories; nuclear and non-nuclear. In the nuclear section, we discussed the utilization of almost all types of radiations, namely; beta, neutrons, gamma, X-ray, near infrared, in addition to the nuclear magnetic resonance. In the non-nuclear techniques, we presented the following methods; fluorescence, optical sensors, laser, autotransformer winding, ultrasonic, and photgraphy. Some other non nuclear miscellaneous techniques were discussed.
Article
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Radioisotope techniques are constantly and extensively used all over the world as a method to identify process systems malfunctions in various industries without requiring the shut down of the processing plant thus leading to high economical benefits to the plant owner. Different aspects of industrial radiotracer technology for troubleshooting, process control and optimization are evaluated through an exhaustive literature survey. The review covers the advantages of radiotracers, most commonly used radiotracers in industry for specific studies, applications of radiotracer techniques in various chemical industries, the design of radiotracer technology experiments, radiation detection and data acquisition in radiotracer technology as well as radiological safety aspects. Two industrial radiotracer techniques of residence time distribution (RTD) measurements and radioactive particle tracking (RPT) are discussed. The design of radiotracer technology experiments are also divided into two categories - radioactive particle tracking applications and residence time distribution applications.
Chapter
There are three types of Fischer-Tropsch (FT) reactors in commercial use at present: fixed bed reactor, fluidized bed reactor, and slurry phase reactor. Fixed bed reactors are very heavy and this limits the size to which they can be scaled up as transportation can become the limiting factor. To resolve the problem in the fixed bed reactors, the slurry bubble column reactor (SBCR) is developed. This chapter describes the transport phenomena in SBCRs including the hydrodynamics characteristics, heat transfer, and mass transfer. It emphasizes the importance of studying the instantaneous heat transfer in bubble columns under wide range of conditions for a comprehensive understanding of the heat transfer mechanism and reliable modeling to improve design and operation. The chapter discusses the computational fluid dynamics (CFD) model, where how to close the interaction force and efficient viscosity is very important.
Chapter
Multiphase flow processes involving gas‐liquid (and solid) are of great interest to the chemical process industry due to their wide range of applications. Therefore, the main purpose of this chapter is to discuss process innovations being made with the help of multiphase flow measurements & simulations techniques. The first section provides a brief introduction to conventional GL/GLS systems, describing their applications and comparing their performance with respect to different process parameters. The second section briefly discusses the advanced experimental techniques & modeling tools that can offer enormous possibilities to achieve performance optimization and process innovations in GL/GLS systems. In the third & fourth sections, the recent developments on process intensification carried out by manipulating the multiphase flows in the conventional GL/GLS systems are reviewed. In addition, the progress on novel and intensified gas‐liquid contactors/reactors, made by leveraging the knowledge on multiphase flows, is discussed.
Article
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In granular flow operations often particles are non-spherical. This has inspired a vast amount of research in understanding the behaviour of these particles. Various models are being developed to study the hydrodynamics involving non-spherical particles. Experiments however are often limited to obtain data on the translational motion only. This paper focusses on the unique capability of Magnetic Particle Tracking to track the orientation of a marker in a full 3D cylindrical fluidized bed. Stainless steel particles with the same volume and different aspect ratios are fluidized at a range of superficial gas velocities. Spherical and rod-like particles show distinctly different fluidization behaviour. Also the distribution of angles for rod-like particles changes with position in the fluidized bed as well as with the superficial velocity. Magnetic Particle Tracking shows its unique capability to study both spatial distribution and orientation of the particles allowing more in depth validation of Discrete Particle Models. This article is protected by copyright. All rights reserved.
Article
An ERT linear probe was used to measure gas hold‐up in a two‐phase (gas‐liquid) and three phase (gas‐solid‐liquid) stirred tank system equipped with a Rushton turbine. The ERT linear probe was chosen rather than the more commonly used ring cage geometry to achieve higher resolution in the axial direction as well as its potential for use on manufacturing plant. Gas phase distribution was measured as a function of flow regime by varying both impeller speed and gas flow rate. Global and local gas hold‐up values were calculated using ERT data by applying Maxwell's equation for conduction through heterogeneous media. The results were compared with correlations, hard‐field tomography data and CFD simulations available in the literature, showing good agreement. This study thus demonstrates the capability of ERT using a linear probe to offer, besides qualitative tomographic images, reliable quantitative data regarding phase distribution in gas‐liquid systems. This article is protected by copyright. All rights reserved.
Presentation
Test the Radioactive Particle Tracking (RPT) technique to detect the thickness of the shed [Simulation of Fouling] within a conical section of a cold fluidized bed containing one single shed. Obtain the radioactive source strength range in which RPT provides reliable data.
Presentation
Study new shed configurations to mitigate the fouling problem inside the stripper section without affecting stripping efficiency. Construct a new cold flow fluidized bed unit to test different sheds configurations. Use the radioactive particle tracking technique to characterize hydrodynamics in the stripper section and evaluate the contacts frequency between solid particles and shed surfaces. But first, how precisely is the radioactive particle tracking technique?
Chapter
Multiphase flows are frequently encountered in both nature and large‐scale industrial processes. The inherent multiscale nature of multiphase flows and associated scientific challenges, makes numerical modelling of multiphase flows very complex. In this chapter we will focus on the modelling of gas–liquid, liquid–solid and gas–liquid–solid flows. The different simulation techniques are grouped in terms of Euler–Euler, Euler–Lagrange and fully resolved or Direct Numerical Simulation techniques. Both the governing equations and numerical implementation will be presented, as well as different methods to describe the interfaces between phases. Special attention will be given to the exchange of Momentum, Heat and Mass between the phases. Each subsection will contain a short discussion on the application of the different methods presented.
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