Countercurrent Flow Of Liquid Research Articles

Measurement of air-water counter-current flow rates in vertical annulus using multiple differential pressure signals and machine learning

Abstract Gas–liquid counter-current flow in vertical annulus is involved in several industrial fields such as petroleum engineering. For example, in coalbed methane wells with liquid pump drainage, obtaining the real-time flow rate of gas–liquid two-phase in the annulus is crucial for the development management of coalbed methane wells. However, due to complex flow conditions, this demand is difficult to achieve through traditional flow metering means. Therefore, this paper proposes a flow prediction method based on multi-group differential pressure signals and machine learning technology. Air-water two-phase flow experiments were carried out on a vertical annulus pipeline with inner and outer diameters of 75 mm/125 mm and adjustable eccentricity. The probability density function and power spectrum density of 3 groups of differential pressure signals collected at different height intervals in the annulus were used as model inputs. A gas–liquid two-phase flow prediction model was constructed based on the artificial neural network model, and the model hyper-parameters were optimized using Bayesian optimization. The results show that on the 440-group test dataset under the combined conditions of air superficial velocity of 0.06–5.04 m s−1, water superficial velocity of 0.03–0.25 m s−1, and pipeline eccentricity of 0, 0.25, 0.5, 0.75, 1, etc. This model can achieve average prediction errors of 9.12% and 29.34% for gas and water flow rates respectively. This method can be applied to the non-throttling, non-invasive measurement of phase flow rate under the condition of annulus air-liquid counter-current flow.

Operation of iron-based monolithic catalyst packing ozonation for industry wastewater advanced treatment: The importance of gas–liquid flow patterns and wastewater flow regimes

In this study, from the feasibility verification of the lab-scale test to the working condition study of the pilot-scale test the large-scale engineering application of the display manufacturing industry wastewater advanced treatment by ozonation with iron (Fe)-based monolithic catalyst packing was finally realized. Different from chemical packings, the catalyst packing has large porosity and specific surface area, while the pore size is small, which meets the requirements of •OH reaction, and these characteristics are necessary for engineering applications. Under the three scales, the reaction procedure and the corresponding reactor structure were introduced in detail. The importance of gas–liquid flow patterns and gas distribution device on treatment effect were proved in pilot-scale test. The treatment effect under gas–liquid counter-current flow was better than that of co-current flow. Through the analysis of the working conditions, the working parameters for high wastewater quantity and high organic loading were obtained. The large-scale test achieved the same excellent treatment effect as the lab/pilot-scale test, after 5 years of operation, the average chemical oxygen demand (COD) removal was about 72.0 %, and the COD concentrations after treatment were all lower than 30 mg/L. The biochemical oxygen demand (BOD5) decreased from 10.22 to 2.50 mg/L on average. Under the short-circuiting phenomenon, the wastewater through the catalyst area unevenly and the organic pollutants were not effectively oxidized and decomposed. This also proved the importance of Fe-based monolithic catalyst packing in advanced treatment. This work proved the importance of gas–liquid flow patterns and wastewater flow regimes in the reactor, which can provide reference for other catalytic ozonation technology in large-scale engineering applications.

Flow regimes identification of air water counter current flow in vertical annulus using differential pressure signals and machine learning

This study investigates the gas–liquid two-phase counter-current flow through a vertical annulus, a phenomenon prevalent across numerous industrial fields. The presence of an inner pipe and varying degrees of eccentricity between the inner and outer pipes often blur the clear demarcation of flow regime boundaries. To address this, we designed a vertical annulus with adjustable eccentricity (outer and inner diameters of 125 mm and 75 mm, respectively). We conducted gas–liquid counter-current flow experiments under specific conditions: gas superficial velocity ranging from 0.06 to 5.04 m/s, liquid superficial velocity from 0.01 to 0.25 m/s, and five levels of eccentricity (e = 0, 0.25, 0.5, 0.75, 1). We collected differential pressure data at two distinct height distances (DP1: 50 mm and DP2: 1000 mm). We used vectors, composed of both the probability density functions (PDFs) of the differential pressure signals and the power spectral density (PSD) reduced via Principal Component Analysis, as features. Using the CFDP clustering algorithm—based on local density—we clustered the flow regimes of the experimental data, thereby achieving an objective and consistent identification of the flow regime of gas–liquid two-phase counter-current flow in a vertical annulus. Our analysis reveals that for DP1, the main differences in the PSD of various flow regimes occur within the 0.5–1 Hz range. Among the three flow regimes involved, the slug flow exhibits the highest power intensity, followed by the bubbly flow, with the churn flow having the least. In terms of differential pressure distribution, the bubbly and churn flows have a concentrated distribution, while the slug flow is more dispersed. For DP2, the PSD differences primarily exist within the 0.5–2 Hz range. The churn flow has the highest power intensity, followed by the slug flow, with the bubbly flow being the weakest. Here, the bubbly flow's differential pressure distribution is concentrated, while the slug and churn flows are more dispersed. Based on the results of the flow regime classification, we generated a flow regime map and analyzed the influence of annulus eccentricity on the flow regime. We found that in most cases, pipe eccentricity does not significantly affect the flow regime. However, in the transition region—such as the bubbly to slug flow transition zone—flows with medium eccentricity values (e = 0.5, 0.75) are more likely to transition to slug flow. We compared the visual recognition results of flow regimes with the clustering results. 4.04% of the total samples showed different results from visual recognition and clustering, primarily located in the flow regime transition area. Since visually distinguishing flow regimes in these areas is typically challenging, our methodology offers an objective classification approach for gas–liquid two-phase counter-current flow in a vertical annulus.

Statistical Analysis of Bubble Parameters from a Model Bubble Column with and without Counter-Current Flow

Bubble columns are widely used in numerous industrial processes because of their advantages in operation, design, and maintenance compared to other multiphase reactor types. In contrast to their simple design, the generated flow conditions inside a bubble column reactor are quite complex, especially in continuous mode with counter-current liquid flow. For the design and optimization of such reactors, precise numerical simulations and modelling are needed. These simulations and models have to be validated with experimental data. For this reason, experiments were carried out in a laboratory-scale bubble column using shadow imaging and particle image velocimetry (PIV) techniques with and without counter-current liquid flow. In the experiments, two types of gases—relatively poorly soluble air and well-soluble CO2—were used and the bubbles were generated with three different capillary diameters. With changing gas and liquid flow rates, overall, 108 different flow conditions were investigated. In addition to the liquid flow fields captured by PIV, shadow imaging data were also statistically evaluated in the measurement volume and bubble parameters such as bubble diameter, velocity, aspect ratio, bubble motion direction, and inclination. The bubble slip velocity was calculated from the measured liquid and bubble velocities. The analysis of these parameters shows that the counter-current liquid flow has a noticeable influence on the bubble parameters, especially on the bubble velocity and motion direction. In the case of CO2 bubbles, remarkable bubble shrinkage was observed with counter-current liquid flow due to the enhanced mass transfer. The results obtained for bubble aspect ratio are compared to known correlations from the literature. The comprehensive and extensive bubble data obtained in this study will now be used as a source for the development of correlations needed in the validation of numerical simulations and models. The data are available from the authors on request.

An experimental investigation on CCFL characteristics during gas/low surface tension liquid counter-current two-phase flow in a small-scaling PWR hot leg typical geometry

A sharp increase in world energy demands which further results in another large progress in the development of nuclear energy establishes comprehensive developments on corresponding mitigation studies. Therefore, as a scenario of accident called LOCA is fundamentally considered, the related phenomena, i.e., the counter-current flow followed by flooding in the primary circuit of PWR, is of a great importance. The present work investigates characteristics of the flooding during a pair of gas/low surface tension liquid counter-current two-phase flow in a complex conduit representing a down-scaled of PWR hot leg typical geometry. Visual observations were obviously carried out to observe the flow phenomenology, while flow parameters were frequently varied. A typical result reveals that the gas flow rate to initiate the flooding decreases with the increase of liquid flow rate. Moreover, exhibiting locations of the onset called locus, a front flooding tends to occur during relatively low liquid flow rates while the higher liquid flow rates exhibit another flooding namely rear flooding. Accordingly, the present investigation provides a package of valuable information on a particular understanding towards the flooding characteristics to overcome the efforts on promoting safety managements on the operation of nuclear power plants..

An Integrated Modeling Approach for Vertical Gas Migration Along Leaking Wells Using a Compressible Two-Fluid Flow Model

Gas migration behind casings can occur in wells where the annular cement barrier fails to provide adequate zonal isolation. A direct consequence of gas migration is annular pressure build-up at wellhead, referred to as sustained casing pressure (SCP). Current mathematical models for analyzing SCP normally assume gas migration along the cemented interval to be single-phase steady-state Darcy flow in the absence of gravity and use a drift-flux model for two-phase transport through the mud column above the cement. By design, such models do not account for the possible simultaneous flow of gas and liquid along the annulus cement or the impact of liquid saturation within the cemented intervals on the surface pressure build-up. We introduce a general compressible two-fluid model which is solved over the entire well using a newly developed numerical scheme. The model is first validated against field observations and used for a parametric study. Next, detailed studies are performed, and the results demonstrate that the surface pressure build-up depends on the location of cement intervals with low permeability, and the significance of two-phase co-current or counter-current flow of liquid and gas occurs along cement barriers that have an initial liquid saturation. As the magnitude of the frictional pressure gradient associated with counter-current of liquid and gas can be comparable to the relevant hydrostatic pressure gradient, two-phase flow effects can significantly impact the interpretation of the wellhead pressure build-up.

Experimental Investigations and Numerical Studies of Two-Phase Countercurrent Flow Limitation in a Pressurized Water Reactor: A Review

Gas–liquid two-phase countercurrent flow limitation (CCFL) phenomena widely exist in nuclear power plants. In particular, the gas–liquid countercurrent flow limitation phenomena in a pressurized water reactor (PWR) during a loss-of-coolant accident (LOCA) or a small-break loss-of-coolant accident (SBLOCA) play an important role in nuclear reactor safety research. Over several decades, a series of experimental investigations and numerical studies have been carried out to study the CCFL phenomena in a PWR. For the experimental investigations, numerous experiments have been conducted, and different CCFL mechanisms and CCFL characteristics have been obtained in various test facilities simulating different scenarios in a PWR. The CCFL phenomena are affected by many factors, such as geometrical characteristics, liquid flow rates, and fluid properties. For the numerical studies, more and more numerical models were presented and applied to the calculations of two-phase countercurrent flow over the past several decades. It is considered that the computational fluid dynamics (CFD) tools can simulate most of the two-phase flow configurations encountered in nuclear power plants. In this paper, the experimental investigations and the numerical studies on two-phase countercurrent flow limitation in a PWR are comprehensively reviewed. This review provides a further understanding of CCFL in a PWR and gives directions regarding future studies. It is found that relatively fewer investigations using steam–water under high system pressures are performed due to the limitation of the test facilities and test conditions. There are a number of numerical studies on countercurrent two-phase flow in a PWR hot leg geometry, but the simulations in other flow channels were relatively rare. In addition, almost all of the numerical simulations do not include heat and mass transfer. Thus, it is necessary to investigate the effects of heat and mass transfer experimentally and numerically. Furthermore, it is of significance to perform numerical simulations for countercurrent two-phase flow with a fine computational grid and suitable models to predict the formation of small waves and the details in two-phase flow.

Effect of liquid viscosity on the gas–liquid two phase countercurrent flow in the wellbore of bullheading killing

Studying the gas–liquid two-phase countercurrent flow under high liquid viscosities is key in designing the well-killing parameters of the bullheading method; however, currently, in-depth research on this issue is limited. Herein, using a self-designed vertical visualization wellbore gas–liquid two-phase flow experimental system with a tube diameter of 0.1 m and liquid viscosity in the range of 1–50 mPa s, a simulation experiment of bullheading killing was conducted. The effects of liquid viscosity on the bubble morphology, bubble migration, and gas–liquid countercurrent flow pattern were analyzed, and the mechanism of back pressing of gas during the well-killing process of the bullheading method in a large-scale tube was revealed. Moreover, the influencing factors and variation in the critical displacement of bullheading were analyzed. The results revealed that the stability of Taylor bubbles increased and the number of small bubbles decreased with the increase in liquid viscosity, resulting the gradual shrinkage or disappearance of the churn flow and bubbly flow, expansion of the region of slug flow, and downward movement of the transition boundary between bullet-cup flow and slug flow. On approaching the critical liquid displacement during the process of simulated bullheading, Taylor bubbles rapidly dissociated into small bubbles and turned around during the rising process, forming a gas–liquid downward flow, following which the gas was successfully pressed back. In addition, our analysis revealed that the press-back effect is not always positively correlated with the viscosity of the kill fluid. The critical displacement of the well-killing fluid first decreased and then increased with an increase in the liquid viscosity. Finally, based on the experimental results, an improved calculation method for the critical displacement of bullheading considering the influence of liquid viscosity was established, which could provide important theoretical guidance for the parameter design of bull heading.

Statistical Analysis Of Bubble Parameters From A Model Bubble Column With And Without Countercurrent Flow

Bubble columns are widely used in numerous industrial processes, because of their advantages in operation, design and maintenance compared to other multiphase reactor types. In contrast to their simple design, the generated flow conditions inside a bubble column reactor are quite complex, especially in continuous mode with counter-current liquid flow. For the design and optimization of such reactors precise numerical simulations and modelling is needed. These simulations and models have to be validated with experimental data. For this reason experiments were carried out in a laboratory-scale bubble column with shadow imaging technique with and without countercurrent liquid flow. In the experiments two types of gases –relatively badly soluble air and good soluble CO2 – are applied and the bubbles were generated with three different capillary diameters. With changing gas and liquid flow rates overall 108 different flow conditions were investigated. The gathered data has been statistically evaluated over the whole 1 m measurement area and bubble parameters have been obtained such as bubble diameter, velocity, aspect ratio, bubble motion direction and inclination. The analysis of these parameters shows, that the countercurrent liquid flow has a noticeable influence on the bubble parameters, especially on the bubble velocity and motion direction. In the case of CO 2 bubbles remarkable bubble shrinkage has been observed at counter-current liquid flow due to the enhanced mass transfer. The comprehensive and extensive bubble data obtained in this study will now be used as a source for the validation of numerical simulations and models.

Heat transfer and wetting behaviour of falling liquid films in inclined tubes with structured surfaces

This study examines wetting behaviour and evaporation heat transfer of a falling liquid film inside a circular tube carrying grooves at its internal surface. The experiments include five different structures (four helical, one longitudinal) and one smooth tube (Cu, d i ≈ 27 mm ) with counter-current flow of liquid (downwards) and vapour (upwards). Results are obtained for liquid propane films ( P r = 2 . 79 , R e smooth tube = 160 − 645 ) at different twisting angles and height of the grooves, tube inclination angles ( β = 0° − 20° from the vertical), mass flow rates (from 5 kg/h up to 20 kg/h) and driving temperature differences (2 K, 3 K and 4 K) mainly at a film inlet temperature of 293.15 K. For wetting behaviour investigations the liquid film is visually observed at the lower end of the tube. The experiments reveal that the internal structures used lead to a strong improvement in both wetting behaviour and heat transfer, even up to inclination angles of 20° . The amount of capillary transported liquid within the grooves coupled with groove geometry itself are the main impacts on wetting behaviour and will be discussed within this paper. • Helically twisted structures resulting better wetting and heat transfer. • Greater groove mass flow rate supportive for greater heat transfer. • High aspect ratios supportive for high heat transfer. • Driving temperature difference influences wetting and heat transfer. • Small inclination with small influence on heat transfer.

CFD Modeling of Pulsed Disc and Doughnut Column: Prediction of Axial Dispersion in Pulsatile Liquid–Liquid Two-Phase Flow

Numerical simulations of liquid–liquid counter-current two-phase flow in pulsed disc and doughnut columns (PDDCs) are performed. The simulation methodology comprises two steps. In the first step, t...

Investigation of hydrodynamic behavior in random packing using CFD simulation

Computational fluid dynamics (CFD) simulations of countercurrent gas–liquid flow in random packings of Raschig rings were carried out in this study. This model used gravity simulation to construct the random packing structure, and a volume expansion-recovery method to improve the meshing quality. A simple feedback control scheme was applied to control the gas inlet flow rate so that pressure drop can be estimated. The generated characteristics of the packing structure such as the number of packing elements, dry surface area and porosity were found to be close to experiments. CFD predictions of hydrodynamics properties are also validated by the experimental data using a small column section. The results indicate that our CFD model was able to capture the essential hydrodynamics behavior of the gas–liquid countercurrent flow. Hence, the approach presented in this study can be used as a basis for studying the effect of detailed packing-geometry design on hydrodynamic and mass transfer characteristics.

Efficiency of Mixture Separation in Distillation Columns with Structured Packings under Conditions of Dynamically Controlled Irrigation

The paper presents the results of an experimental study of separation efficiency and distribution of flow parameters over the cross-section of the distillation columns. The experiments were carried out on the large-scale research setup “Large Freon Column” with the diameter of 0.6 and 0.9 m. Experimental data were obtained at uniform and non-uniform irrigation of the Mellapak 350.Y and Sulzer 500X structured packings by the controlled liquid distributor. The mixture of refrigerants R114 and R21 was used as the working liquid at the pressure of 3 bar in the column. The liquid distributor with independently controlled valves for each drip point was used for controlled packing irrigation. Local temperature distributions of the liquid phase and counter-current vapor flow in the cross-section and over the packing height were recorded using a sequence of fast-response temperature sensors. Periodic irrigation of the structured packing can affect large-scale non-uniformity of mixture composition and flow parameter distribution over the cross-section and height of the transfer unit. Significantly non-uniform packing irrigation within a separate semiperiod leads to rearrangement of the structure of large-scale non-uniformity inside the packing.The new method for dynamically controlled irrigation of the packing is suggested. This method is aimed at destruction of stationary large-scale maldistribution over the column cross-section and achievement of higher separation efficiency of a completely wetted packing.

Hydrodynamics of countercurrent gas–liquid flow in inclined packed beds – A prospect for stretching flooding capacity with small packings

Hydrodynamics of the inclined bed, which was randomly packed with small packings, was subject to gas–liquid countercurrent flow for different column inclination angles (0–20° from vertical position) and liquid-feed nozzle positions, while sweeping fluid throughputs ranged to encompass trickling flow up to the flooding point, was studied using electrical capacitance tomography. The embedded and overhead nozzles behaved differently with respect to the attainment of the flooding point. In the case of the overhead nozzle, pressure drop and liquid saturation increased with gas and liquid throughputs though leading to considerably widened flooding capacity as the column shifted from verticality. Decreasing pressure gradients and liquid saturations were measured with gradually slanting column axis at the expense of liquid maldistribution inside the bed. The latter effect was the consequence of gas–liquid segregation that accompanied liquid accumulation near the bottommost column wall. One distinction of this flow structure was a peculiar stratified pulse flow regime, which was observed as a prelude to flooding in tilted beds. The inception of this flow regime, stimulated by gas–liquid interactions in the gas-rich upper region, was a function of gas and liquid flow rates. Bed-obliquity, which delayed flooding in this particular flow regime, is regarded as a potential method in prospective catalytic processes that are to be carried out in the countercurrent packed beds which contain small packings.

Two-phase flow phenomena along an adiabatic riser – An experimental study at the test-facility GENEVA

Long adiabatic riser geometries with low system pressures are present in a lot of energy and petrochemical processes. Natural-circulation systems are an appropriate solution to save operating and maintenance costs. Under certain circumstances natural-circulation systems tend to unstable mass flow, especially in the riser section. The pressure gradients can stress the construction materials and affect the heat transfer. This paper focuses on GENEVA test-facility and its natural-circulation circuit with heat input by steam condensation. The GENEVA test-facility is explained in detail with focus on the local void fraction measurement system in the adiabatic riser section. The differences to former natural circulation test-facilities are particular emphasized. Therefore a transient experiment is presented and analysed. Moreover the influence of flow restrictions at the downcomer outlet is explained and an experimental method is presented, to determine the maximum natural circulation mass flow of the natural-circulation circuit. Besides, a comparison between the two different riser inner diameters, which were used during the experiments, is presented. The convective heat transfer is analysed by taking into account different dimensionless numbers. A variety of experiments were performed up to 100kWel input power from the evaporators. Flashing and geysering as two types of occurred instabilities are stated and discussed in comparison to former test-facilities. Further phenomena like water hammer and counter current liquid flow are investigated. Based on these analyses constructive solutions can be derived, to stabilize the presented natural-circulation two-phase flow system.

Two-phase flow measurements under static and dynamic conditions for modeling the top kill process

An experimental study on bubble (slug) rise inside a pipe filled with static liquid and bull heading of a gas flow with a liquid flow is presented. The bubble rise velocity (BRV) was measured inside a pipe with different inclinations and is compared with two well-known models. The static tests have been performed with three different liquids: water, CaCl brine mixture, and non-Newtonian fluid (Xanvis™). A model is proposed, based on the drift flux method, to predict the bubble rise velocity. Dynamic well killing (or top kill) is also examined, whereby a continuous gas flow is suppressed with a counter current liquid flow. Flow tests at different angles from vertical were undertaken to investigate the effect of inclination on the liquid flow rate needed to bullhead the gas flow. A simple empirical model based on the results is proposed to predict the results in actual wells.

Calculation and Analysis of Liquid Holdup in Lower Blast Furnace by Model Experiments

A hydromechanics experiment on the countercurrent flow of gas and liquid simulating the flow conditions in the lower blast furnace was carried out. A cold model of a packed bed with various packing materials and liquids was used to study the holdup of liquid. Correlations for static holdup, dynamic holdup, and total holdup were obtained. A good agreement was found between the calculated and experimental data. A mathematical model simulating the flow fields was applied to study the effect of liquid holdup in blast furnace. The results of the model calculation show that static holdup is the determinant of the total holdup of molten materials when the blast furnace works in stable condition. The slag phase generally reaches flooding holdup ahead of the hot metal. The radial distribution of gas flow is almost not influenced by the holdup of molten materials, but it has a greater influence on the pressure drop. The size of coke has far greater influence on static holdup than liquid properties does. The study is useful for acquiring a deeper understanding of the complex phenomena in the blast furnace and for determining appropriate operational actions under different production conditions.

Gas–liquid countercurrent two-phase flow in a PWR hot leg: A comprehensive research review

Abstract Research into gas–liquid countercurrent two-phase flow in a model of pressurized water reactor (PWR) hot leg has been carried out over the last several decades. An extensive experimental data base has been accumulated from these studies, leading to the development of phenomenological correlations and scaling parameters of the countercurrent flow limitation (CCFL). However, most of the proposed correlations apply under a relatively narrow range of conditions, generally limited to the test section conditions and/or geometry. Moreover the development of mechanistic models based on the underlying physical processes has been limited. In contrast to this mechanistic form of modelling, the implementation of computational fluid dynamics (CFD) techniques has also been pursued, but the considerable robust three-dimensional (3D) closure relations for this application remain an unachieved goal due to lack of detailed phenomenological knowledge and consequent application of empirical one-dimensional experimental correlations to the multidimensional problem. This paper presents a comprehensive review of research work on countercurrent gas–liquid two-phase flow in a PWR hot leg and provides direction regarding future research on this topic. In the introductory section, the problems facing current research are described. In the following sections, recent experimental as well as theoretical research achievements are overviewed. In the last section, the problems that remain unsolved are discussed, along with some concluding remarks. It was found that only limited theoretical developments exist in the literature, however highly reliable experimental data are needed to support this effort. Additional work, both analytical and experimental, needs to be carried out on the effects of mass transfer on countercurrent flow limitation to improve the existing correlations and analytical models.

Revisiting large break LOCA with the CATHARE-3 three-field model

Some aspects of large break LOCA analysis (steam binding, oscillatory reflooding, top-down reflooding) are expected to be improved in advanced system codes from more detailed description of flows by adding a third field for droplets. The future system code CATHARE-3 is under development by CEA and supported by EDF, AREVA-NP and IRSN in the frame of the NEPTUNE project and this paper shows some preliminary results obtained in reflooding conditions. A three-field model has been implemented, including vapor, continuous liquid and liquid droplet fields. This model features a set of nine equations of mass, momentum and energy balance. Such a model allows a more detailed description of the droplet transportation from core to steam generator, while countercurrent flow of continuous liquid is allowed. Code assessment against reflooding experiments in a rod bundle is presented, using 1D meshing of the bundle. Comparisons of CATHARE-3 simulations against data series from PERICLES and RBHT full scale experiments show satisfactory results. Quench front motions are well predicted, as well as clad temperatures in most of the tested runs. The BETHSY 6.7C Integral Effect Test simulating the gravity driven reflooding process in a scaled PWR circuit is then compared to CATHARE-3 simulation. The three-field model is applied in several parts of the circuit: core, upper plenum, hot leg and steam generator, represented by either 1D or 3D modules, while the classic six-equation model is used in the other parts of the loop. An analysis of these first results is presented and future work is defined for improving the droplet behavior simulation in both the upper plenum and the hot legs.

Solids Residence Time Distribution in a Three-Phase Bubble Column Reactor: An Artificial Neural Network Analysis

Residence time distribution (RTD) study of solids in a three-phase pilot-scale bubble column photoreactor has been carried out in order to provide data for the development of an artificial neural network model usable for process optimisation. The experimental data indicated that the RTD of solids was a complex nonlinear function of gas and liquid velocities as well as the contacting pattern (co-current and countercurrent flow of gas and liquid). In this study, the solid particle RTD data were modeled using feed forward artificial neural networks (ANN). The networks were trained with 250- sets of input-output patterns using back-propagation algorithm. The trained networks were tested using 50-sets of RTD data previously unknown to the networks. Out of several configurations, a 3-layered network with 6-neurons in its hidden layer yielded optimal results with respect to the validation data. The optimal model and empirical data exhibited good agreement with a correlation coefficient of 0.995.