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•Simulations are performed to study micromixing in a laminar flow micromixer.•Micromixing is modelled directly with CFD and indirectly with a lamellar model.•Micromixing performance ...is evaluated using the Villermaux-Dushman protocol.•Both approaches provide results that are in good agreement with experimental data.•The lamellar model is much less computationally intensive than the CFD approach.
The CFD simulation of fast reactions in laminar flows can be computationally challenging due to the lack of appropriate sub-grid micromixing models in this flow regime. In this work, simulations of micromixing via the implementation of the competitive-parallel Villermaux/Dushman reactions in a T-micromixer with square bends for Reynolds numbers in the range 60–300 are performed using both a conventional CFD approach and a novel lamellae-based model. In the first, both the hydrodynamics and the concentration fields of the reaction species are determined directly using a finite volume approach. In the second, the hydrodynamic field from the CFD calculations is coupled with a Lagrangian model that is used to perform the chemical reactions indirectly. Both sets of results are compared with previously published experimental data and show very good agreement. The lamellar model has the advantage of being much less computationally intensive than the conventional CFD approach, which requires extremely fine computational grids to resolve sharp concentration gradients. It is a promising solution to model fast chemical reactions in reactors with complex geometries in the laminar regime and for industrial applications.
Understanding crystal growth kinetics is of great importance for the development and manufacturing of crystalline molecular materials. In this work, the impact of additives on the growth kinetics of ...benzamide form I (BZM-I) crystals has been studied. Using our newly developed crystal growth setup for the measurement of facet-specific crystal growth rates under flow, BZM-I growth rates were measured in the presence of various additives previously reported to induce morphological changes. The additives did not have a significant impact on the growth rates of BZM-I at low concentrations. By comparison to other systems, these additives could not be described as “effective” since BZM-I showed a high tolerance of the additives’ presence during growth, which may be a consequence of the type of growth mechanisms at play. Growth of pure BZM-I was found to be extremely defected, and perhaps those defects allow the accommodation of impurities. An alternative explanation is that at low additive concentrations, solid solutions are formed, which was indeed confirmed for a few of the additives. Additionally, the growth of BZM-I was found to be significantly affected by solution dynamics. Changes in some facet growth rates were observed with changes in the orientation of the BZM-I single crystals relative to the solution flow. Of the two sets of facets involved in the growth of the width and length of the crystal, the {10l̅} facets were found to be greatly affected by the solution flow while the {011} facets were not affected at all. Computational fluid dynamics simulations showed that solute concentration has higher gradients at the edges of the leading edge {10l̅} facets, which can explain the appearance of satellite crystals. {10l̅} facets were found to show significant structural rugosity at the molecular level, which may play a role in their mechanism of growth. The work highlights the complexities of measuring crystal growth data of even simple systems such as BZM-I, specifically addressing the effect of additives and fluid dynamics.
Apparently simple detectors, Resistive Plate Chambers actually incorporate a range of physical situations somewhat more complex than those found in most other gaseous detectors. These include the ...interplay between materials with different electrical characteristics, space-charge dominated avalanches evolving in very high electric fields and the propagation of fast signals on heterogeneous multiconductor transmission lines. In this article the state-of-the-art of physical modelling of many of these aspects is reviewed and sometimes expanded, while aspects still requiring further work are highlighted.
Process analytical technology (PAT) has developed significantly since its introduction in pharma where many in situ analytical probes and measuring devices are now commercially available, replacing ...the use of off-line quality control measurements that are typically laborious and time intensive. The use of PAT instrumentation should not interfere with the process itself and subsequently should have no effect on the product whilst measuring representative samples. Implementation of these devices is typically arbitrary using empirical means. Therefore, the objective of this study is to highlight the use of computational fluid dynamics modeling to investigate the effect of interfacing parameters and process parameters of an inline near-infrared (NIR) probe used to determine the viscosity of a non-Newtonian micellar liquid. The parameters investigated for the probe were immersion depth, immersion angle, gap size, and fluid velocity. The results conclude that the immersion angle and depth should both be optimized to prevent stagnant fluid accumulating in the measuring gap ensuring that the NIR measurements are representative of the bulk. The gap size determines the optical pathlength and therefore was also investigated against an existing predictive viscosity model showing no changes in model performance with varying gap size. The use of computational modeling to develop a digital twin prior to PAT implementation at the equipment design stage ensures the technology can perform at its best and will also aid in calibration transfer studies.
Graphical Abstract
•The flow in a CIJs mixer is studied with the PLIF flow visualization technique.•Three flow regimes are observed in the range 50<Re<600.•The jets’ flow imbalance always influences negatively the ...mixing quality.•The mechanism of eddy engulfment is a key aspect in the reduction of mixing scales.
The flow in a Confined Impinging Jets (CIJs) mixer was studied with Planar Laser Induced Fluorescence. Two key aspects influencing the flow regimes and mixing quality were studied: the impact of the jets’ Reynolds number (Re) in the range 50<Re<600; and the effect of the jets’ flow imbalance, maintaining the flow rate of one of the injectors fixed and varying the other. Mixing mechanisms and scales are studied from the acquired flow images, and the mixing degree is quantified from the calculation of the Intensity of Segregation (Danckwerts, 1952). In balanced flow conditions, i.e., equal volumetric feeding rates, when the best mixing performance is observed, three flow regimes are observed: for Re<103 the flow is steady with complete segregation of the two feeding jet streams; for Re=104 the flow tends to an oscillatory periodic laminar flow regime; for Re>104 the flow evolves to a self-sustained chaotic laminar regime with strong mixing dynamics. With the increase of Re it is observed the formation of smaller mixing scales in the flow and an increase on the mixing quality. The visualized mixing scales are compared with theoretical models existing in the literature for the estimation of the striation thickness, leading to the conclusion that, in the studied flow regimes, the statistical theory of turbulent diffusion does not provide a realistic physical description of the flow. Furthermore, the jets’ mass flow imbalance is shown to always influence negatively the mixing quality. This is observed even when the flow imbalance results in the increase of the flow rate of one of the jets, increasing the amount of energy supplied to the system for dissipation. Results of this work show that the mechanism of eddy engulfment promoted by the two chaotically oscillating impinging jets, in the laminar regime, is a key aspect in mixing by CIJs.
Heterogeneous catalyst pellets evaluation is performed in smaller and smaller reactors with the main objective of reducing catalyst development costs. Downscaling raises the question: is there a ...lower limit to the number of pellets that ought to be tested in a reactor so that the results do not depend on which pellets are sampled? Major sources of variability among a catalyst pellet population are dimensions and many parameters that can be grouped as “intrinsic kinetic activity” (porosity, tortuosity, active phase repartition and availability).
In this paper, we present a methodology to estimate the incertitude induced by variability on size and kinetics on the evaluation of the apparent kinetic constant in a fixed bed reactor. Analytical expressions are presented to predict this incertitude for sphere and cylinder shaped pellets, with a first order kinetic law in two limiting cases: the absence of mass transfer limitations and presence of severe internal mass transfer limitations. The predicted incertitude scales as the square root of sample population: downsizing increases the incertitude. We propose criteria to evaluate the minimum number of pellets to sample, so that sampling induced variability is lower than an acceptable incertitude, expressed in °C. This acceptable incertitude could be for example a fraction of the experimental temperature incertitude.
•Methodology to evaluate the consequences of testing small catalyst samples in fixed beds.•Explicit equation to evaluate the incertitude for spherical and cylindrical pellets.•Criterion on minimum number of pellets required for a low variability catalytic test.•Incertitude scales with the square root of sample population.
The mitigation of human-induced climate change is of crucial importance for the sustainability of humankind. For this aim the RPC community has exerted considerable effort over the last decade to ...reduce the greenhouse gases emission from RPC detectors. These included searching for new eco-friendly gases, implementing recovery and/or recirculation systems, improving gas tightness and using new materials and approaches in detector conception and operation for the reduction of gas flow rates. Along this line of work, we present here an RPC architecture aimed at a dramatic reduction of gas use in chambers meant for low particle rate (below ten of Hzċcm−2) operation. Two glass chambers were tested for more than six months with zero gas flow, showing no evidence of time-related effects, allowing to consider that permanently sealed RPCs may be within reach, with obvious practical and environmental advantages.
Ice cream is a complex product containing four different phases that affect its microstructure. Viscosity is a critical ice cream quality parameter that is typically measured using off-line ...methodologies, such as rheometry. In-line viscosity measurements allow continuous and instant analysis compared to off-line methodologies, yet they still constitute a challenge. This work focused on the preliminary study of the potential application of near-infrared (NIR) and Raman spectroscopy as analytical tools to assess the viscosity of ice cream mixes. Historically, partial least squares regression (PLSR) is a standard algorithm used for analysis of spectral data and in the development of predictive models. This methodology was implemented over a range of viscosity values, obtained by varying the ice cream fat content and homogenization conditions. Individual PLSR models showed some predictive ability and better performance compared to the integrated model obtained by data fusion. Lower prediction errors and higher coefficients of determination were obtained for NIR, making this technique more suitable based on model performance. However, other considerations should be accounted during the selection of the best method, such as implementation limitations. This study offers a preliminary comparison of the spectroscopic methods for quantitative analysis of viscosity of aged ice cream mixes and a starting point for an in-situ application study.
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