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This study aims to design a new multi‐stage photoreactor with immobilized ZnO and assess its performance in reducing textile wastewater toxicity using solar energy. The electric conductivity measurement is retained as a detection method to obtain the residence time distribution (RTD) function. The RTD is then used to characterize the hydrodynamic behavior of the photoreactor and to evaluate its deviation from the distribution curves of ideal reactors. Solar experiments are conducted to demonstrate the performance of this multistage reactor towards the degradation of a textile azo dye namely Solophenyl Red 3BL (SR 3BL). The influence of the flow rate and the SR 3BL initial concentration (CO) are considered. The variation of the flow rate slightly influences the SR 3BL photodegradation efficiency and it is inversely proportional to its concentration. The study of the reuse of the immobilized catalyst shows that the degradation efficiency of 98% is reached even after multiple photocatalytic cycles. The figure of merit collector area per order was in the range of 35 to 110 m2/m3order. This result provides useful information for scaling up and estimating energy efficiency of the reactor. [ABSTRACT FROM AUTHOR]

CFD simulations are reported to compare hydrodynamic/axial dispersion in a classical helical-shaped and planar serpentine-shaped tubular reactor at a millimetric scale (1-5 mm) for the first time. A two-step simulation approach is validated against experimental data on residence time distribution in serpentine coils. The method is then used for parametric analysis to explore the impact of geometric parameters on the coiling factor and axial dispersion coefficient. Dean vortices in the coiling region are visualized. The findings from the parametric analysis are utilized to develop empirical correlations and Artificial Neural Network (ANN) models for estimating coiling factors and axial dispersion coefficients in both serpentine and helical coils. The absolute average relative error (AERR) in predicting the coiling factor is 3.5% for helical coils and 4.6% for serpentine coils. The AERR of the ANN model for predicting the axial dispersion coefficient is 14% for helical coils and 10% for serpentine coils. The study reveals that both axial dispersion coefficient and pressure drop are higher in serpentine coils compared to helical coils. Axial dispersion is found to be relatively unaffected by pitch (helical) or bend diameter (serpentine) and tube diameter but shows significant reduction with a decrease in pitch circle diameter (helical) or gap between bends (serpentine). The developed correlations and ANN models can aid in the precise sizing of tubular reactors designed as helical or serpentine coils. This is exemplified through a case study involving the synthesis of an ionic liquid, where the helical configuration demonstrated a performance advantage of approximately 6% over the serpentine configuration. [ABSTRACT FROM AUTHOR]

The quantitative analysis of a small sample size of soil may not provide an adequate representation of the overall field composition due to its significant heterogeneity. In other words, measuring the organic carbon content of a few grams of soil is not representative of the whole field. The aim of this experimental study is to carry out a global assessment of these types of parameters and investigate the relevance of reactive tracing methods. Reactive tracing consists of injecting into a porous medium a (non-inert) weakly retained tracer whose interaction with the medium is well characterized. Thus, by injecting a solution containing a low-mass organic solute, a breakthrough curve reflecting the distribution of the retention times is obtained. Its delay compared to that of a tracer of water makes it possible to determine the organic carbon fraction in the soil. This approach was applied with two types of organic solutes tracers: the phenol and the toluene in order to measure the organic carbon fraction. In parallel, soil samples were analyzed and characterized by different techniques of chromatography (HPLC), X-ray fluorescence and infrared. The results showed that toluene was not suitable for such measurements because of its high retention time compared to the average residence time of the fluid in the column. Regardless, it yields an organic carbon fraction value of 11%, which is close to the one determined analytically in the soil sample 15%. Phenol has a lower retention time and would therefore be more suitable for field measurements. However, it gives an organic carbon fraction that is five times lower. [ABSTRACT FROM AUTHOR]

This study investigates the performance of serpentine and wavy serpentine millireactors. Millireactors, with their microscale features, offer advantages such as heightened surface-to-volume ratio, improved heat transfer coefficients, and reduced mass transfer pathways. The serpentine and wavy serpentine millireactors, characterized by their channel structures, demonstrate superior energy efficiency, reaction speed, and scalability compared to conventional reactors. The focus of this research is on understanding the mass transfer rates and residence time distribution (RTD) in these millireactors, crucial for optimizing their design and operation. The residence time distribution studies providing insights into the mixing characteristics and overall flow behavior. The (RTD) data was fitted to different models. Mass transfer studies examine the movement of acetic acid between aqueous and organic phases, with the volumetric mass transfer coefficient (KLa) as a key parameter. Results from the serpentine millireactor indicate a partially mixed flow behavior with a dispersion number of 0.611, while the wavy serpentine millireactor exhibits a dispersion number of 0.130, indicating improved mixing efficiency. The mass transfer studies yield KLa values in the range of 0.31–1.42 min−1 and 0.49–2.71 min−1 for serpentine and wavy serpentine millireactors, respectively. Efficiency assessments reveal 72.31% and 83.21% for serpentine and wavy serpentine millireactors, respectively. The study concludes that the use of serpentine and wavy serpentine millireactors represents an effective method for process intensification, offering valuable insights for chemical engineering and process optimization applications. The results contribute to advancing the millireactor technology and its potential in continuous flow chemical manufacturing. [ABSTRACT FROM AUTHOR]

The Approximate Bayesian Computing (ABC) was used in this work to perform the selection and calibration of models in reactor dynamics. Five phenomenologically based hydrodynamic models on dead volume, flow deviation and retro-mix anomalies were evaluated and classified into two groups. The inverse problems were solved from experimental data obtained by the technique of residence time distribution (RTD) in positive step, using the methylene blue tracer in a stirred-tank reactor. The experiments evaluated the influence of volumetric flow, effluent outlet position, agitation position and rotation on the hydrodynamic characterization of the reactor. The results revealed that the most influential parameter in the first group was the dead volume, while in the second group, the retro-mix anomaly was highly sensitive to rotation. The ABC algorithm applied in this work used the Morozov discrepancy principle to select the tolerance in the final population. Tolerances for other intermediate populations were obtained from the median distance of each particle accepted in the previous population. The application of the Bayesian approach in RTD problems was excellent for the hydrodynamic characterization of reactors. The ABC SMC algorithm proved to be efficient for the calibration and selection of hydrodynamic models of reactors. The most influential anomaly in the flow was the dead volume. [ABSTRACT FROM AUTHOR]

With consumers becoming more aware of the health risks associated with obesity, the food industry has begun to seek better ways to produce healthier frozen desserts. Making such products has been a challenge, as it is difficult to control the taste quality of a product while also attempting to maintain its nutritional value and decrease the amount of fat and sugar it contains. The difficulty is made greater by a lack of understanding of the freezing process. Essentially, commercial ice cream products are crystallized inside a component called a scrape surface freezer (SSF), which contains a high-speed rotational beater, a dasher, and blades for mixing and scraping the ice cream mixture from the walls of the cylinder. In this study, the complex mixing, scraping, and freezing processes of an SSF were modeled using computational fluid dynamics (CFD) to evaluate and understand these processes virtually because they are extremely difficult to evaluate physically. Therefore, a CFD simulation model was developed to comprehend the complex nature of heat transfer and fluid dynamics. The computational outcomes were validated by means of two experimental comparisons: an axial profile of the temperature occurring inside the SSF and a profile depicting particle residence time. The CFD results aided in the visual identification of details pertaining to such flow patterns as high shear stress and recirculating zones. This study should provide a basis for the SSF designs based on advanced computational models, with the result being a more efficient, costeffective way to produce healthier versions of frozen desserts. [ABSTRACT FROM AUTHOR]

Gas aspiration through ladle shroud, during the teeming of a ladle into a tundish, has been investigated via physical and mathematical modeling. To this end, a volume of fluid‐based two‐phase turbulent flow model (in conjunction with the standard k–ε turbulence model) and a full‐scale two‐strand bloom casting tundish have been applied. Both flow and residence time distribution measurements are carried out in the full‐scale tundish system, adopting well‐established measurement techniques. Computational results, supported appropriately with experimentally measured data, indicate that gas aspiration alters flow and turbulence profoundly in the vicinity of the shroud entry zone. Early reversal of jetting flow toward the free surface, due to the buoyancy of the entrained gas, increases the overall intensity of motion in the tundish, creating more mixing flow volumes at the expense of plug flow volume. Most importantly, however, gas aspiration through shroud tends to drastically cut down interactions between the down coming liquid jet metal and the pouring box, making the specific design and shape of a pouring box redundant toward desirable flow modification. Finally, it is shown that strong surface flows and turbulence, generated due to gas aspiration, can be suitably damped by deploying a set of weirs, increasing plug flow volume in tundish. [ABSTRACT FROM AUTHOR]

Understanding the residence time distribution (RTD) of a continuous hydrothermal reactor is of great significance to improve product quality and reaction efficiency. In this work, an on-line measurement system is attached to a continuous reactor to investigate the characteristics of RTD. An approach that can accurately fit and describe the experimental measured RTD curve by finding characteristic values is proposed for analysis and comparison. The RTD curves of three experiment groups are measured and the characteristic values are calculated. Results show that increasing total flow rate and extending effective reactor length have inverse effect on average residence time, but they both cause the reactor to approach a plug flow reactor and improve the materials leading. The branch flow rate fraction has no significant effect on RTD characteristics in the scope of the present work except the weak negative correlation with the average residence time. Besides, the natural convection stirring effect can also increase the average residence time, especially when the forced flow is weak. The analysis reveals that it is necessary to consider the matching of natural convection, forced flow and reactor size to control RTD when designing the hydrothermal reactor and working conditions. [ABSTRACT FROM AUTHOR]

Regulatory authorities recommend using residence time distribution (RTD) to address material traceability in continuous manufacturing. Continuous virus filtration is an essential but poorly understood step in biologics manufacturing in respect to fluid dynamics and scale‐up. Here we describe a model that considers nonideal mixing and film resistance for RTD prediction in continuous virus filtration, and its experimental validation using the inert tracer NaNO3. The model was successfully calibrated through pulse injection experiments, yielding good agreement between model prediction and experiment (R2> ${R}^{2}\gt $ 0.90). The model enabled the prediction of RTD with variations—for example, in injection volumes, flow rates, tracer concentrations, and filter surface areas—and was validated using stepwise experiments and combined stepwise and pulse injection experiments. All validation experiments achieved R2> ${R}^{2}\gt $ 0.97. Notably, if the process includes a porous material—such as a porous chromatography material, ultrafilter, or virus filter—it must be considered whether the molecule size affects the RTD, as tracers with different sizes may penetrate the pore space differently. Calibration of the model with NaNO3 enabled extrapolation to RTD of recombinant antibodies, which will promote significant savings in antibody consumption. This RTD model is ready for further application in end‐to‐end integrated continuous downstream processes, such as addressing material traceability during continuous virus filtration processes. [ABSTRACT FROM AUTHOR]

This paper introduces an in-line dye tracer experiment to measure the residence time functions in continuous concrete processing. These functions quantify the material-system interdependency and can be used to compare different material-system combinations and for quality and process control. A Rhodamine B solution was used as the tracer material and detected by measuring the color intensity using a digital image processing technique. The experiment was validated on a 3D concrete printing system by comparing the results of impulse, step-up and step-down inputs with different tracer quantities. The results show that a high signal-to-noise ratio can be obtained with low tracer concentrations. For the examined combination of material and system, an impact on the original process was only observed for the step-up inputs at high tracer quantities. It is concluded that the presented method is cost-effective and non-labor-intensive and, therefore, has the potential for wide adoption and integration in automated workflows. [ABSTRACT FROM AUTHOR]

Constant and proper mixing of water in fish farms is essential for creating maximum uniformity, minimizing stagnant areas, properly distributing oxygen, and removing solid waste from the bottom of the ponds. The effect of the inflow installation mode and inflow momentum force in octagonal ponds was examined on the hydrodynamic flow mixing by laboratory modeling. For this purpose, the inflow was analyzed in three modes with angles of 90, 60, and 30° and the inflowing force at four levels with values of 0.004, 0.009, 0.013, and 0.018 N by the residence time distribution curve and hydraulic efficiency of octagonal ponds. The laboratory modeling results revealed that the inflow at the 90° mode for all four-momentum forces does not form an eddy current and short circuit in the pond's flow, as the result of which the hydraulic efficiency of the pond falls in the weak range. To improve the hydraulic efficiency of the pond, the inflow was installed at 60 and 30° modes; the results demonstrated 2.68 and 3.26 times higher efficiency than the 90° mode. Moreover, for all three inflow installation modes, the hydraulic efficiency had an inverse relationship with the inflow momentum force.

Impinging stream dryers (ISDs) are effective for removing moisture from particulate materials because of the complex multiphase transport of air particles in ISDs. Nowadays, computational techniques are powerful to simulate multiphase flows, including dilute and dense-phase gas–solid flows and hence, the use of a reliable computational model to simulate the phenomena and design a dryer has recently received more attention. In this study, computational fluid dynamics, combined with the discrete element method (CFD-DEM) and falling drying rate model, were used to predict the multiphase transport phenomena of parboiled paddy in a coaxial ISD. The design of an impinging stream pattern for improving residence time in a drying chamber of ISD was also investigated. The results showed that the CFD-DEM, in combination with the falling drying model, could be well-utilized to predict the particle motion behavior and lead to more physically realistic results. The predicted change of moisture content in parboiled paddy was in good agreement with the experimental data for 17 cycles of drying. Although the prediction of mean residence time was lower than the experimental data, the predicted mean residence time was a similar trend to the experimental data. For ISD design, the simulation revealed that the use of two stages of impinging stream region (two streams collide at the top of the drying chamber at the first stage and then the gas particles flow on the incline floor to collide with the other stream at second stage) in a drying chamber could increase the residence time approximately 75% and reduce drying cycle from 17 to 10 cycles when it was considered at the same final moisture content. [ABSTRACT FROM AUTHOR]

BACKGROUND: The determination of the residence time distribution of an entire process or process step in integrated continuous biomanufacturing is required for process understanding, traceability determination and to efficiently handle process disturbances. When recombinant proteins such as monoclonal antibodies are captured by continuous precipitation and two‐stage filtration, the question arises whether simple salt is suitable as a tracer or whether a labeled protein is required. RESULTS: We have investigated the use of various inert tracers, sodium nitrate (NaNO3) due to its absorbance at UV 280 nm, and fluorescently labeled or unlabeled antibodies to determine the RTD of the product at steady‐state and in the start‐up and shut‐down phases. All tracers are suitable for measuring the RTD of the precipitated antibody for individual unit operations. For interconnected unit operations, if the product is concentrated, the RTD can be determined with labeled or unlabeled antibodies, because it is not possible to concentrate salts in a microfiltration unit. The duration of the start‐up and shut‐down phases depends on the concentration factor applied in two‐stage filtration, and the number of reactor volumes required to reach steady state corresponds to the concentration factor. Around 1.6 reactor volumes are required for the shutdown phase for 99% wash‐out. CONCLUSION: The integrated process has a plug flow characteristic, which is advantageous as the process can react quickly when process deviations occur. © 2024 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

The information available in daily plant operation data is not fully exploited by polymer reaction engineers: what do the catalytic olefin polymerization plants tell? In this article, a method is proposed to increase catalyst and process know‐how, based on experimentally acquired production rate results, coming from a continuous tandem reactor polymerization process. The polymer reaction engineering methodology is also discussed in detail for connecting the catalyst reaction performance to the expected activity profile and yield for batch operation, together with the residence time distribution effect for continuous operation. The potential of the proposed methodology is highlighted with a theoretical example and the effectiveness of the method is demonstrated with an applied example, accurately estimating deactivation parameter values for two catalysts based on plant information and, validated based on small‐scale polymerization experiments. [ABSTRACT FROM AUTHOR]

A new idea to deal with the backmixing problem in a scaled-up multi-inlet vortex mixer is proposed in this paper. Firstly, a Reynolds-averaged Navier–Stokes–large-eddy simulation hybrid model was used to simulate the flow field in a vortex mixer, and the numerical simulation results were compared with those from a particle image velocimetry experiment in order to validate the shielded detached eddy simulation model in the rotating shear flow. Then, by adding a series of columns in the mixing chamber, the formation of wake vortexes was promoted. The flow field in the vortex mixer with different column arrangements were simulated, and the residence time distribution curves of the fluid were obtained. Meanwhile, the degree of backmixing in the vortex mixer was evaluated by means of a tanks-in-series model. In the total ten cases related with four groups of variables, it was found that increasing the diameter of the column was the most efficient for weakening the backmixing in the vortex mixer. Specifically, the vortexes made the kinetic energy of the fluid more evenly distributed in the center of the mixing chamber, thereby eliminating the low-pressure area. After structural adjustment, the number of equivalent mixers was increased by 55%, and the peak number of residence time distribution curves was reduced from four to one. [ABSTRACT FROM AUTHOR]

The present study proposes an analytical solution to a linearized Boussinesq equation considering unsteady downslope river stage, spatio-temporal rainfall recharge, and bedrock seepage. This analytical solution alleviates the limitations of the previous studies like varying river boundary, leaky aquifer bed, and non-uniform recharge simultaneously. The time-dependent river stage depicts the seasonal water level variation in the river, whereas the leakage from the confined to the unconfined aquifer or vice versa represents the bedrock seepage. The analytical expression is derived using the separation of variable method along with a variable transformation technique. The proposed solution is validated using nonlinear numerical and linearized analytical solution. The study highlights that the aquifers with higher bedrock conductivity tend to have a higher inflow rate to the aquifer from the river during monsoon season and a higher outflow rate to the river from the aquifer in the lean period. The analysis also illustrates that for a relatively flat catchment area, with the rise of the water level in the river, there is a reverse flow from the river to the aquifer. Further, the stream stage variation rate is found to be pivotal in deciding the duration of flow direction alteration and volume of water released from the aquifer. Furthermore, a sensitivity analysis is performed to assess the influence of flow parameters on the discharge function. The discharge is found to be positively sensitive to hydraulic conductivity, aquifer slope, and recharge. Finally, the residence time distributions corresponding to various bedrock seepage conditions are examined. Results indicate that the residence time for the various conditions tends to exhibit the heavy-tailed distributions. [ABSTRACT FROM AUTHOR]

Disinfection is an important step in deep drinking water treatment technology. This study applies computational fluid dynamics to investigate and optimize the hydrodynamics inside the ozone contactor. ANSYS Fluent was used to solve all the control equations. A step method is used to simulate the residence time distribution. The mean residence time is simulated under the Eulerian framework. The deflectors are installed in chambers to direct flow. The deflectors allow for a more uniform flow and a longer mean residence time within the contactor. The baffling factor showed that the deflectors could reduce the short-circuit effect in the contactor and improve the disinfection efficiency by 34.6% compared to the original reactor. The Morrill factor coefficient is improved by 22.8% compared to the original reactor. According to the Aral-Demirel index, contactors with deflectors are significantly better than other baffle-type contactors. The presence of the deflectors increased the microbial inactivation efficiency from 95.3 to 96.5%. The optimal deflector height should be controlled between 30 and 60 mm. [ABSTRACT FROM AUTHOR]

Understanding the flow dynamics of chemical species is important for characterizing, analyzing, and designing chemical reactors. Computational fluid dynamics (CFD) provides accurate flow patterns, but this approach can be computationally expensive for large or complex geometries. To overcome this limitation, a new Lagrangian‐based method is developed using smoothed particle hydrodynamics (SPH) to forecast the flow patterns and residence time distribution of two different fluids for various reactor geometries: (laminar, fractal, T‐mixer, Hartridge–Roughton (H‐R) mixer and packed bed with a gyroid internal packing) and compared the results with computational fluid dynamics (CFD) simulations. The SPH method is less accurate than the CFD analysis, but it obtained the approximate flow behavior much faster. Consequently, the SPH method has significant potential as a first screening technique to optimize reactor topologies and internal packing structures. [ABSTRACT FROM AUTHOR]

In the present study, the hydrodynamic behaviour of a three‐dimensional bubbling fluidized bed reactor was studied using the finite volume method and granular kinetic theory. The effect of two types of gas distributors (i.e., perforated and porous plates) on the gas/solid hydrodynamic was investigated. The residence time distribution model was utilized to check the deviation of the gas flow pattern from the ideal flow patterns for two types of distributors. The parameters indicating the degree of back‐mixing, such as mean residence time and dimensionless variance, were calculated. Also, the model was verified through the comparison of the particle velocity with experimental data obtained by the particle image velocimetry–digital image processing (PIV‐DIA) technique. It was found that the gas flow pattern in the present bubbling fluidized bed is closer to the mixed flow than the plug flow pattern. It was also found that the porous plate distributor gives more uniform hydrodynamic distributions of gas and solid in the bed, which results in better gas–solid mixing due to the formation of the smaller bubbles. [ABSTRACT FROM AUTHOR]

The fate of nutrients and contaminants in fluvial ecosystems is strongly affected by the mixing dynamics between surface water and groundwater within the hyporheic zone, depending on the combination of the sediment's hydraulic heterogeneity and dune morphology. This study examines the effects of hydraulic conductivity stratification on steady‐state, two‐dimensional, hyporheic flows and solute residence time distribution. First, we derive an integral transform‐based semi‐analytical solution for the flow field, capable of accounting for the effects of any functional shape of the vertically varying hydraulic conductivity. The solution considers the uneven distribution of pressure at the water‐sediment interface (i.e., the pumping process) dictated by the presence of dune morphology. We then simulate solute transport using particle tracking. Our modeling framework is validated against numerical and tracer data from flume experiments and used to explore the implication of hydraulic conductivity stratification on the statistics and pdf of the residence time. Finally, reduced‐order models are used to enlighten the dependence of key residence time statistics on the parameters characterizing the hydraulic conductivity stratification. Key Points: A new integral transform‐based semi‐analytical solution for hyporheic flows in stratified sediments is provided and tested against dataThe impact of hydraulic conductivity stratification on residence time distribution and its statistics is quantitatively analyzedROMs are used to approximate key residence time statistics in the space of variability of parameters characterizing the conductivity profile [ABSTRACT FROM AUTHOR]

This paper initially involves three main processing parameters: screw speed, feeding speed, and initial material moisture content, exploring the RTD of materials inside the extruder barrel under varying parameters and clarifying the impact of parameter variations on RTD. Finally, machine vision technology was utilized to link extruded product images to texture features, and a texture prediction model based on image features was established using a Back Propagation (BP) neural network. Particle Swarm Optimization (PSO) and Genetic Algorithm (GA) were applied to optimize the BP neural network. The results indicate that the feeding speed has a stronger impact than the screw speed on the extrusion process, and an increase in the initial material moisture content tends to shorten the RTD. Specifically, an increase in screw speed results in a denser product structure, while higher feeding speeds lead to reduced pore size in the microstructure. As the initial material moisture content increased from 55% to 70%, the average residence time MRT decreased from 265.21 s to 166.62 s. Additionally, elevated moisture content causes a more porous microstructure. After optimizing the texture prediction model of extruded products through the application of Particle Swarm Optimization and Genetic Algorithm models, it was discovered that the Genetic Algorithm was more effective in reducing errors (p < 0.05) than the Particle Swarm Optimization algorithm. It was found that the Particle Swarm Optimization model exhibited better prediction performance. The results of the prediction indicated a significant association between the image features of the product and hardness, resilience, and chewiness, as corroborated by correlation coefficients of 0.93913, 0.94040, and 0.94724, respectively. [ABSTRACT FROM AUTHOR]

The flow behaviors of highly viscous fluid falling film outside the vertical tube were investigated by theoretical analysis and numerical simulation. Based on gas-liquid two-phase flow methods, a new insight into flow behaviors, which mainly referred to the film thickness distribution, surface renewal frequency and residence time distribution of the highly viscous fluid falling film outside the vertical tube, were provided. Moreover, the correlation between film thickness and fluid viscosity and flow rate was established through model analysis. The numerical simulation results of film thickness were in good agreement with the experimental and theoretical values. The film surface dilated at the beginning of the falling film, and then gradually reached stable state with the largest thickness value. The distribution curve of falling film velocity from wall surface to free surface was in line with the typical Nusselt semi-parabolic profile. Normally, a large flow rate or a low fluid viscosity corresponds to a high surface renewal frequency and a narrow residence time distribution of falling film flow. The dimensionless residence time distribution of falling film flow showed little difference under different conditions, which indicates that the vertical tube falling film flow has a good application prospect in the production of high viscosity materials with uniform quality. [ABSTRACT FROM AUTHOR]

Most studies focus on the "clockwise sequential" switching manner for a four-compartment periodic anaerobic baffled reactor (PABR), while the exploration of the "every second" option on the feasibility for real industrial wastewater treatment is rarely reported. Hence, a PABR-treating traditional Chinese medicine wastewater was run continuously in "every second" switching manner with both switching period T and hydraulic residence time of 48 h. Satisfactory start-up performance was achieved during the operation of a climbing average organic load rate at approximately 1, 2, 4, and 6 kg chemical oxygen demand (COD) m-3 d-1 for 12, 24, 24, and 6 days, respectively. The average COD removal was 87.20% after the second lifting of OLR and 89.98% after the third one. Denaturing gradient gel electrophoresis and its cluster analysis showed that the microbial communities in each compartment adapted their structure in response to the periodically changing micro-ecology conditions. Moreover, the residence time distribution test with tap water in the clean PABR was carried out in experiments and computational fluid dynamics (CFD) simulation, both of which were in good agreement. The CFD model output visualized the flow velocity field and hydrodynamic-mass transport inside the PABR. Optimization of operation pattern in PABR including switching manner and frequency depended on both the type of waste being treated and the flexibility of biomass to periodically changing micro-ecology conditions. [ABSTRACT FROM AUTHOR]

Accurate measurement of solution tracer concentration in residence time distribution (RTD) tests can be difficult in low volumetric flowrate systems where solution must be accumulated over a period before there is sufficient volume for a tracer concentration measurement. This is encountered with laboratory-scale heap leaching column salt tracer RTD tests. Step-up tracer experiments were used to show how this results in tracer concentration underestimation (due to mixing effects) and loss of profile features, such as tracer concentration step changes. A tracer measurement setup was conceived to overcome this. It was designed to have well-defined flow which could be described using a compartment model of a plug flow and well-mixed volume in series. The model was used to calculate "true" tracer concentrations from the measured values (correlation coefficients greater than 0.983). It was demonstrated to be effective at both correcting tracer concentration magnitudes and restoring lost profile features. [ABSTRACT FROM AUTHOR]

Sloshing is the movement of fluid in a partially filled vessel subjected to external motions. Although sloshing causes intense forces and instability to floating structures, the internal motion of liquid caused by external forces might be useful for devices that require mixing. For offshore floating photobioreactors, sloshing induced by external ocean wave forces are desirable, as the movement of liquid is able to bring about mixing and mass transfer for the nutrients and gas in the microalgae culture. The objective of this study is to investigate the correlation between the regular wave-induced sloshing of different motions (surge, heave, and pitch) on the mixing behaviour of the novel offshore floating photobioreactor designed to utilize the ocean surface waves for the effects of mixing. To determine the residence time distribution (RTD) of the stagnant volume of the photobioreactor, dissolved solids were injected into the system. The concentration of dissolved solids was measured using a total dissolve solid (TDS) sensor. The mixing caused by sloshing motion had the highest intensity during pitching motion. A homogenous solution was formed just after 65.9 s for the filling ratio of 30 %, with the rotation angle of 8 degrees and frequency of 0.21 Hz. Thus, wave-induced sloshing is able to generate intense mixing to the medium during pitching motion but still has non-ideal behaviours, such as bypass and dead zones during horizontal and vertical motion. [Display omitted] • Proposed novel floating photobioreactor to utilize the ocean surface waves for mixing. • Study on effects of surge, heave, and pitch on the mixing behavior of floating photobioreactor. • Mixing induced by sloshing is maximum with pitching motion. [ABSTRACT FROM AUTHOR]

As the primary carrier for storing and transporting particles, the silo is widely used in the production process. The RTD is a promising method for studying the silo discharge process and has not been studied enough. This paper presents a study on the residence time distribution (RTD) and flow pattern of particles in a two-dimensional flat-bottom batch discharge silo under gravity using experiments and the discrete element method (DEM). Meanwhile, a multi-simulation averaging method is proposed to eliminate local fluctuations in the residence time. The results are as follows. The mean flow rate is 16.85 g·s − 1  in simulations, which is only 2.7% larger than the experimental value. In the central area of the silo, the residence time contour lines take on elliptical shapes and the trajectories of particles are straight lines. The particles are distributed along the elliptical residence time contour lines all the time during the discharge process until they flow out of the silo. The particles near the side wall of the silo swiftly flow with a constant acceleration to the central line of the silo along the upper horizontal surface, which has become avalanche slopes, and then flow down the outlet together with the particles in the radial flow region. In this study, an elliptical distribution law during the silo discharge process was funded for the first time. An improved radial flow model was proposed with a higher accuracy and clearer physical meaning, which will be helpful in silo design and scaling up in industrial applications. [ABSTRACT FROM AUTHOR]

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A hydrodynamic modelling of a continuous-flow single-channel (CFSC) reactor was highlighted by means of Residence Time Distribution (RTD) experimental approach using stimulus response technique and three inlet flowrates (43.66, 79.40 and 115.10 L.h−1). Axial dispersion model (ADM) was applied for approximating the RTD experimental curves in order to check the flow patterns homogeneity and identify the possible flow deviations. The CFSC reactor was then evaluated for river water treatment by electrocoagulation process. At 43.66 L.h−1, dead zones were diagnosed within the CFSC reactor and corresponding experimental RTD curve deviated from ADM. At high inlet flowrates, the hydrodynamic behaviour was highly plug-flow (Pe > 100) without flow malfunctions and a satisfactory agreement was obtained between RTD experimental curves and ADM. In contrast, at 43.66 L.h−1, the CFSC reactor exhibited higher turbidity removal (of about 91.7%) compared to high inlet flowrates, indicating that the treatment efficiency depends mainly on coagulant dose electro-dissolved per unit of time rather hydrodynamic condition. However, the associated operating cost was relatively high at 43.66 L.h−1. As for the effect of initial water quality, it was observed that, for the same coagulant dose electro-dissolved, the treatment efficiency dropped as the initial turbidity of water decreased. [Display omitted] • Hydrodynamic modelling of the CFSC reactor is highlighted by RTD approach and ADM. • Dead zones phenomena occur at Re = 243, thus, hydrodynamic deviates from ADM. • At 243 < Re < 639, the removal yield depends on coagulant dose rather hydrodynamic. • Decrease in Re enhances the treatment yield while increasing the operating cost. • The treatment is less effective for river water with low initial turbidity (20 NTU). [ABSTRACT FROM AUTHOR]

In multi-stage spray dryers, agglomeration is forced by recirculating fine material into the nozzle zone. Drying droplets collide with dry particles and form agglomerates. The aim of this study was to achieve a more comprehensive understanding and control of agglomerate formation. Agglomerates with different properties were produced using a pilot spray drying plant. An increased air mass flow of the fluidized bed as well as a reduced solids content of the feed solution resulted in an increased number of primary particles per agglomerate. A residence time-based approach was then applied to determine the agglomeration efficiency, defined as the number of successfully adhered primary particles per recirculation. It ranged from 0.33 to 0.71 and was correlated to collision and sticking probabilities in the nozzle zone. This value is of importance both for process optimization and for the validation of simulation approaches. [ABSTRACT FROM AUTHOR]

A widely utilized tool in reactor analysis is passive tracers that report the residence time distribution, allowing estimation of the conversion and other properties of the system. Recently, advances in microrobotics have introduced powered and functional entities with sizes comparable to some traditional tracers. This has motivated the concept of Smart Tracers that could record the local chemical concentrations, temperature, or other conditions as they progress through reactors. Herein, the design constraints and advantages of Smart Tracers by simulating their operation in a laminar flow reactor model conducting chemical reactions of various orders are analyzed. It is noted that far fewer particles are necessary to completely map even the most complex concentration gradients compared with their conventional counterparts. Design criteria explored herein include sampling frequency, memory storage capacity, and ensemble number necessary to achieve the required accuracy to inform a reactor model. Cases of severe particle diffusion and sensor noise appear to bind the functional upper limit of such probes and require consideration for future design. The results of the study provide a starting framework for applying the new technology of microrobotics to the broad and impactful set of problems classified as chemical reactor analysis. [ABSTRACT FROM AUTHOR]

This article focuses on designing and analyzing a new method for mixing in process vessels. We propose using an air bubble curtain to accomplish the desired mixing. The air bubble curtain used in this study is made of an empty pipe with several holes through which air is pumped, which in turn produces a swarm of bubbles that causes pseudo-turbulent mixing in the tank filled with a liquid solution. A uniform distribution of bubbles within the tank was assured by maintaining a see-saw movement of the air bubble curtain. Mixing inside the tank was quantified by measuring the salt concentration in a laboratory model tank (30 cm × 30 cm × 30 cm) and a pilot-scale tank (200 cm × 100 cm × 100 cm). The optimal flow rates of air and the mixing time in both tanks that can achieve complete mixing were obtained from the experimental results. The proposed air bubble curtain can be of potential use in wastewater treatment, biotechnology, and aquaculture where turbulent mixing is required with minimum energy dissipation per unit mass. [ABSTRACT FROM AUTHOR]

Purpose: In continuous manufacturing (CM), the material traceability and process dynamics can be investigated by residence time distribution (RTD). Many of the unit operations used in the pharma industry were characterized by dead time–dominated RTD. Even though feasible and proper feedback control is one of the many advantages of CM, its application is challenging in these cases. This study aims to develop a feedback control, implementing the RTD in a Smith predictor control structure in a continuous powder blender line. Methods: Continuous powder blending was investigated with near-infrared spectroscopy (NIR), and the blending was controlled through a volumetric feeder. A MATLAB GUI was developed to calculate and control the concentration of the API based on the chemometric evaluation of the spectra. The programmed GUI changed the feeding rate based on the proportional integral derivative (PID) and the Smith predictor, which implemented the RTD of the system. The control structures were compared even on a system with amplified dead time. Results: In this work, the control structure of the Smith control was devised by utilizing the RTD of the system. The Smith control was compared to a classic PI control structure on the normal system and on an increased dead time system. The Smith predictor was able to reduce the response time for various disturbances by up to 50%, and the dead time had a lower effect on the control. Conclusions: Implementing the RTD models in the control structure improved the process design and further expanded the wide range of applications of the RTD models. Both control structures were able to reduce the effect of disturbances on the system; however, the Smith predictor presented more reliable and faster control, with a wider space for control tuning. [ABSTRACT FROM AUTHOR]

This work is a numerical study on the effects of the flow structures of the power-law fluid between two concentric cylinders with an upward laminar axial flow on levels of mixing and mean residence time through the Taylor Couette system. The cylindrical annular duct presents a radius ratio of 0.5 and an aspect ratio of 8. The inner cylinder is rotating while the outer one is kept at rest. The residence time distributions (R.T.D.) method and the mean residence time (Tm) are used to determine the number of tanks in series and the dispersion coefficient to evaluate levels of mixing. To this end, a pulsed input injection of a tracer is computing at the outlet of the annulus. As a main objective of this study, is to analyze the effect of the flow structure of a power-law fluid between two concentric cylinders on the mixing level and mean residence time in a Taylor Couette system. The novelty of our work is the use of power-law fluids as particles-carrying fluids. Several parameters, such as the axial Reynolds number (Re), the Taylor number (Ta), and the power-law index behavior (n), are used to show their impact on levels of mixing. It is shown that when n increases, the number of stirred tanks in series N increases for pseudoplastic fluids (n1), revealing high levels of mixing. The increase of the power-law index in the range of 0.61 increases the dispersion coefficient points to the well-mixing.

Impinging stream dryers (ISDs) are effective for removing moisture from particulate materials because of the complex multiphase transport of air particles in ISDs. Nowadays, computational techniques are powerful to simulate multiphase flows, including dilute and dense-phase gas–solid flows and hence, the use of a reliable computational model to simulate the phenomena and design a dryer has recently received more attention. In this study, computational fluid dynamics, combined with the discrete element method (CFD-DEM) and falling drying rate model, were used to predict the multiphase transport phenomena of parboiled paddy in a coaxial ISD. The design of an impinging stream pattern for improving residence time in a drying chamber of ISD was also investigated. The results showed that the CFD-DEM, in combination with the falling drying model, could be well-utilized to predict the particle motion behavior and lead to more physically realistic results. The predicted change of moisture content in parboiled paddy was in good agreement with the experimental data for 17 cycles of drying. Although the prediction of mean residence time was lower than the experimental data, the predicted mean residence time was a similar trend to the experimental data. For ISD design, the simulation revealed that the use of two stages of impinging stream region (two streams collide at the top of the drying chamber at the first stage and then the gas particles flow on the incline floor to collide with the other stream at second stage) in a drying chamber could increase the residence time approximately 75% and reduce drying cycle from 17 to 10 cycles when it was considered at the same final moisture content.

A widely utilized tool in reactor analysis is passive tracers that report the residence time distribution, allowing estimation of the conversion and other properties of the system. Recently, advances in microrobotics have introduced powered and functional entities with sizes comparable to some traditional tracers. This has motivated the concept of Smart Tracers that could record the local chemical concentrations, temperature, or other conditions as they progress through reactors. Herein, the design constraints and advantages of Smart Tracers by simulating their operation in a laminar flow reactor model conducting chemical reactions of various orders are analyzed. It is noted that far fewer particles are necessary to completely map even the most complex concentration gradients compared with their conventional counterparts. Design criteria explored herein include sampling frequency, memory storage capacity, and ensemble number necessary to achieve the required accuracy to inform a reactor model. Cases of severe particle diffusion and sensor noise appear to bind the functional upper limit of such probes and require consideration for future design. The results of the study provide a starting framework for applying the new technology of microrobotics to the broad and impactful set of problems classified as chemical reactor analysis.

Biomass includes diverse raw materials of plant or animal origin that are biodegradable. It also constitutes a significant fraction of municipal waste burned in waste incineration plants. Grate technology is one of the more commonly used technologies in the thermal conversion of biomass. The mass transport of material on the grate is a complex issue. The article presents a model for determining selected mass flow parameters on the grate, primarily the distribution of residence time, degree of mixing, and dispersion. The model is a description of mechanical mass transport on the grates of thermal waste conversion devices and represents the kinetics of the processes occurring on the grate. It allows for the design of the details of the specific movement of the material particles on the grates depending on their size and density. In addition, experimental tests of flow parameters realized on a laboratory stand simulating the operation of the grate are presented. Tests were conducted on different types of grates and with selected types of biomass materials. They included variants of the operating parameters of the grates, such as the speed and pitch of the grates an their inclination, simultaneously with the fulfillment of the 1:1 scale condition of the size of the laboratory stand to the actual size of the industrial grate (its section). A general trend can be seen in the mean residence time of the material on the grate, which is higher in the case of a reciprocating grate. The degree of dispersion is mainly influenced for moving and reciprocating grates by the inclination angle of the grate. The analysis of the test results made it possible to clarify the mechanism of material mass transport on different types of grates. It is also proposed to use the results in modeling the process of biomass combustion in grate chambers as well as their design and operation. [ABSTRACT FROM AUTHOR]

Melt granulation for improving material handling by modifying particle size distribution offers significant advantages compared to the standard methods of dry and wet granulation in dust reduction, obviating a subsequent drying step. Furthermore, current research in pharmaceutical technology aims for continuous methods, as these have an enhanced potential to reduce product quality fluctuations. Concerning both aspects, the use of a planetary roller granulator is consequential. The process control with these machines benefits from the enhanced ratio of heated surface to processed volume, compared to the usually-applied twin-screw systems. This is related to the unique concept of planetary spindles flowing around a central spindle in a roller cylinder. Herein, the movement pattern defines the transport characteristics, which determine the energy input and overall processing conditions. The aim of this study is to investigate the residence time distribution in planetary roller melt granulation (PRMG) as an indicator for the material transport. By altering feed rate and rotation speed, the fill level in the granulator is adjusted, which directly affects the average transport velocity and mixing volume. The two-compartment model was utilized to reflect these coherences, as the model parameters symbolize the sub-processes of axial material transport and mixing. [ABSTRACT FROM AUTHOR]

The hydrodynamic performance of turbulent flows in circular pipes equipped with screen-type static mixers is numerically assessed in this study. A three-dimensional computational fluid dynamics model is used to study the effect of changing the operating conditions and reactor configuration on the flow field. The accuracy of the numerical results is validated by comparing pressure drop predictions to empirical correlations where a maximum relative error of 13.3% is recorded. The macro-mixing performance of screen type static mixers is also assessed using residence time distributions. The study shows that the flow through screens is three-dimensional by nature with secondary flows being prominent near the pipe walls. Moreover, the presence of the screen has a major impact on the turbulent velocity profile both up- and down-stream. The flow field and velocity gradients are interpreted using strain rate and vorticity. These parameters also show that the flow through screens is highly dispersive where 39.3% of the reactor volume has an extensional efficiency value greater than 0.6. This explains their good performance in processing multiphase flows and gives an insight on how to design systems that maximize this dispersive effect in their volume. The residence time distribution study shows that the presence of screens renders the flow closer to plug flow with the effect being more pronounced using finer mesh screens operating at high flow velocities. [ABSTRACT FROM AUTHOR]

A continuous process for preparation of magnesium hydroxide with a forced circulation tubular reactor is proposed. The residence time distribution of the liquid in the reactor at different flow rates is measured, and the parameters of the tanks‐in‐series model are obtained. Using soluble magnesium salt and ammonia as raw materials, magnesium hydroxide is prepared. The effect of the flow rates on the product quality is investigated. The results show that the smaller the flow rate, the longer the residence time of the liquid in the reactor and the better the dispersion and crystal morphology of the products. When the total volume of the reactor is 300 mL and the flow rates are 5–50 mL min−1, the values of the average residence time of the liquid are 3094–351 s and the parameters of tanks‐in‐series model are 1.05–1.52. The reactors are closer to the continuous stirred tank reactor. The average particle sizes of the magnesium hydroxide products are 2.32–2.47 µm, and the values of I001/I101 are 1.17–0.89. The crystal morphology is flaky. Being compared with that from magnesium sulfate, the magnesium hydroxide products from magnesium nitrate have smaller particle size and better dispersibility. [ABSTRACT FROM AUTHOR]

The motion of input material in a rotary kiln is an important aspect of its operation. This can be observed especially in the case of the implementation of the hazardous waste incineration process in this device. The values of the flow parameters, mainly the residence time and the degree of mixing, can determine the proper and safe treatment of waste. The relationships that occur in the layer of solid material in a rotary kiln have not been completely recognized. This article presents a research method that involves an experiment on a laboratory stand simulating a rotary kiln in association with a dedicated algorithm. Multi-criteria tests were carried out. The adopted research method was the tracer method. It used a tracer which, subject to the same transport conditions as other material particles, provided information on the characteristic of the motion of tested materials in the rotating cylinder. The application based on the residence time distribution (RTD) algorithm returned information about the characteristics of the motion of the material in the rotary cylinder in terms of residence time distribution and the degree of mixing. This tracer method, together with stimulus impulses on the grate and a dedicated RTD algorithm, was used here as a sensor method to examine the characteristics of material motion on various grate systems. The data obtained as a result of this research may include, among others, the boundary conditions for numerical simulations of processes carried out in a rotary kiln. [ABSTRACT FROM AUTHOR]

This work reports the effect of scaling up annular centrifugal contactors (ACCs) upon the residence time distribution and the efficiency of extraction of uranium. The experiments were carried out in a multi-scale ACC platform of three ACCs with rotor diameters of 12, 25, and 40 mm. To enable direct comparison across all three scales of ACC, the residence time distributions were acquired by injecting dye into the solvent phase at a constant relative volume related to the ACC liquid holdup. Across all scales and flowrates, there was little difference in residence time distribution (<6 residence volumes), except for the smallest 12 mm rotor diameter ACC with a high solvent/aqueous feed ratio, which required 12 residence volumes, potentially due to internal circulation in the annulus. At low flowrates, the stage efficiency in all cases was >95%, and it improved further in larger rotor diameter ACCs. [ABSTRACT FROM AUTHOR]

β-ammonium tetramolybdate [β-(NH4)2Mo4O13] is an important product of molybdenum metallurgy because of its uniform crystal structure and excellent thermal stability. The yield of molybdenum strip produced with β-(NH4)2Mo4O13 as raw material and various processing properties have been significantly improved. However, the crystallization process of β-(NH4)2Mo4O13 is very complex, including neutralization, polymerization, nucleation, and crystal growth stages, resulting in a variety of polymerization morphology. In this work, a concentric structure reactor was used to segment these stages with directional regulation of each stage. Residence time distribution (RTD) was used to evaluate the simulation of flow field characteristics in the concentric structure reactor. Determination of the influence of inlet-outlet positions, size and position of paddle, and baffle setting on the fluid behavior in a single tank suggested measures to improve the abnormal flow condition and reduce the dead zone volume fraction. In the concentric structure reactor, the dead zone volume fraction was only 2.36% when the clapboards were arranged alternately in an up-down design, using an inlet flow rate of 100 mL/min. β-(NH4)2Mo4O13 was prepared continuously by adding aqueous ammonia and product slurry for crystallization in the concentric structure reactor. [ABSTRACT FROM AUTHOR]

This work is a numerical study on the effects of the flow structures of the power-law fluid between two concentric cylinders with an upward laminar axial flow on levels of mixing and mean residence time through the Taylor Couette system. The cylindrical annular duct presents a radius ratio of 0.5 and an aspect ratio of 8. The inner cylinder is rotating while the outer one is kept at rest. The residence time distributions (R.T.D.) method and the mean residence time (Tm) are used to determine the number of tanks in series and the dispersion coefficient to evaluate levels of mixing. To this end, a pulsed input injection of a tracer is computing at the outlet of the annulus. As a main objective of this study, is to analyze the effect of the flow structure of a power-law fluid between two concentric cylinders on the mixing level and mean residence time in a Taylor Couette system. The novelty of our work is the use of power-law fluids as particles-carrying fluids. Several parameters, such as the axial Reynolds number (Re), the Taylor number (Ta), and the power law index behavior (n), are used to show their impact on levels of mixing. It is shown that when n increases, the number of stirred tanks in series N increases for pseudoplastic fluids (n<1), indicating low levels of mixing while the parameter (N) decreases for dilatants fluids (n>1), revealing high levels of mixing. The increase of the power-law index in the range of 0.61 increases the dispersion coefficient points to the well-mixing. [ABSTRACT FROM AUTHOR]

An experimental study based on the pulse-response technique was performed in a Sulzer packed-bed column in order to establish the residence time distribution for four different liquid flow rates, namely 200, 400, 600 and 800 L/h and five different gas flow rates of 0, 5, 10, 15, 20 m³/h. Depending on the phase flow rate, comparisons with the axial distribution and the N-tanks-in-series models rendered good similarities. Furthermore, the axial dispersion coefficient and its dependence on the superficial velocity of the liquid phase, for various gas flow rates and also, on the F factor of the gas phase, for various liquid flow rates, have been established. [ABSTRACT FROM AUTHOR]

This short communication presents residence time distribution (RTD) measurements and modeling in a 16 m3 Siemens flotation cell, as the first RTD characterization in an industrial-scale pneumatic cell. The Siemens cell was installed as a pre-rougher machine in a Cu-Mo selective plant. This plant recovered molybdenite as an enriched product, depressing copper-bearing minerals. Irradiated non-floatable solid and Br82 in water solution were employed as solid and liquid tracers, respectively. The tracers were instantly injected into the Siemens cell, and the inlet and outlet concentrations were directly measured by external non-invasive detectors. From the flotation literature, three model structures for the RTDs were evaluated, including perfect mixing, one large perfect mixer and one small perfect mixer in series (LSTS), and N perfectly mixed reactors in series. A transport delay was incorporated for all models. The LSTS representation was more consistent with the experimental data, showing that the Siemens cell RTDs presented significant deviations with respect to perfect mixing and plug-flow regimes. From the industrial measurements, mean residence times of 4.1–5.2 min were estimated. [ABSTRACT FROM AUTHOR]

Mixing in low‐density polyethylene (LDPE) reactors is crucial regarding process safety as well as process efficiency. The extreme process conditions of pressures up to 3000 bar make it difficult to get an insight into LDPE reactors. This problem is tackled by a combined experimental and modeling approach. A poly(methylmethacrylate) duplicate of a laboratory high‐pressure reactor is set up to measure residence times and visualize flow lines. Experimental results are then compared to a computational fluid dynamics model. [ABSTRACT FROM AUTHOR]