A Calibrated Computational Fluid Dynamics Model for Simulating the Rotating Disk Apparatus

Summary Reaction kinetics between calcite and acid systems have been studied using the rotating disk apparatus (RDA). However, simplifying assumptions have been made to develop the current equations used to interpret RDA experiments to enable solving them analytically in contrast to using numerical methods. Previous work has revealed inadequacies of some of these assumptions, which necessitates the use of a computational fluid dynamics (CFD) model to investigate their impact on the RDA results. The objectives of the current work are to develop a calibrated CFD and proxy model to simulate the reaction in the RDA and use this model to estimate the diffusion coefficient and the reaction rate coefficient of the reaction in the RDA. The present work developed the first calibrated CFD model to determine the diffusion coefficient and the reaction rate coefficient in the RDA with minimum assumptions in the hydrochloric acid (HCl) carbonate reaction. More specifically, the model relaxes the constant fluid properties, infinite acting reactor boundaries, and constant reaction surface area assumptions. The proxy model obtained results in reduced computational time with minimal compromise on accuracy. Finally, the proposed model showed an improvement of 63% in predicting the reaction kinetics between calcite and HCl compared to traditional methods.

An Alternative Kinetic Model of the Iodide-Iodate Reaction for Its Use in Micromixing Investigations

The Villermaux-Dushman method, one of the most extensively used test reaction systems for micromixing characterization, has been widely criticized for years due to uncertainties regarding the incomplete dissociation of sulfuric acid and the proposed kinetic study by Guichardon et al. In this work, a renewed study of the kinetics of the iodide-iodate reaction is presented, using perchloric acid to avoid issues concerning incomplete acid dissociation. The experimental results are in good agreement with the fifth order rate law for the iodide-iodate reaction. The reaction rate coefficient strongly depends on the ionic strength and can be modeled with a Davies-like equation. When implemented in the incorporation model, the kinetic model presented in this study can be used to estimate micromixing times that are in line with the theoretical engulfment time. This is observed in two different reactors with low and high intensity of mixing: an unbaffled stirred vessel and a rotor-stator spinning disc reactor. The results from the latter are also compared with the second Bourne reaction, giving very similar micromixing times. The use of sulfuric acid in combination with the kinetic model from Guichardon et al. also provides micromixing times of the same order of magnitude; presumably their kinetic model indirectly accounts for the second proton dissociation rate in the overall reaction rate coefficient. The kinetic model presented in this study in combination with perchloric acid is suggested as an alternative to characterize micromixing behavior. <pre><br><br></pre>

An Alternative Kinetic Model of the Iodide-Iodate Reaction for Its Use in Micromixing Investigations

The Villermaux-Dushman method, one of the most extensively used test reaction systems for micromixing characterization, has been widely criticized for years due to uncertainties regarding the incomplete dissociation of sulfuric acid and the proposed kinetic study by Guichardon et al. In this work, a renewed study of the kinetics of the iodide-iodate reaction is presented, using perchloric acid to avoid issues concerning incomplete acid dissociation. The experimental results are in good agreement with the fifth order rate law for the iodide-iodate reaction. The reaction rate coefficient strongly depends on the ionic strength and can be modeled with a Davies-like equation. When implemented in the incorporation model, the kinetic model presented in this study can be used to estimate micromixing times that are in line with the theoretical engulfment time. This is observed in two different reactors with low and high intensity of mixing: an unbaffled stirred vessel and a rotor-stator spinning disc reactor. The results from the latter are also compared with the second Bourne reaction, giving very similar micromixing times. The use of sulfuric acid in combination with the kinetic model from Guichardon et al. also provides micromixing times of the same order of magnitude; presumably their kinetic model indirectly accounts for the second proton dissociation rate in the overall reaction rate coefficient. The kinetic model presented in this study in combination with perchloric acid is suggested as an alternative to characterize micromixing behavior. <pre><br><br></pre>

An Alternative Kinetic Model of the Iodide-Iodate Reaction for Its Use in Micromixing Investigations

The Villermaux-Dushman method, one of the most extensively used test reaction systems for micromixing characterization, has been widely criticized for years due to uncertainties regarding the incomplete dissociation of sulfuric acid and the proposed kinetic study by Guichardon et al. In this work, a renewed study of the kinetics of the iodide-iodate reaction is presented, using perchloric acid to avoid issues concerning incomplete acid dissociation. The experimental results are in good agreement with the fifth order rate law for the iodide-iodate reaction. The reaction rate coefficient strongly depends on the ionic strength and can be modeled with a Davies-like equation. When implemented in the incorporation model, the kinetic model presented in this study can be used to estimate micromixing times that are in line with the theoretical engulfment time. This is observed in two different reactors with low and high intensity of mixing: an unbaffled stirred vessel and a rotor-stator spinning disc reactor. The results from the latter are also compared with the second Bourne reaction, giving very similar micromixing times. The use of sulfuric acid in combination with the kinetic model from Guichardon et al. also provides micromixing times of the same order of magnitude; presumably their kinetic model indirectly accounts for the second proton dissociation rate in the overall reaction rate coefficient. The kinetic model presented in this study in combination with perchloric acid is suggested as an alternative to characterize micromixing behavior. <pre><br><br></pre>

Investigation of chlorine wall decay in an old, decommissioned metallic pipe using a pipe section reactor

The study investigates the kinetics of free chlorine depletion in tap water from the Sofia distribution network. The overall decay rates, the bulk reaction rate coefficient, the wall reaction rate coefficient and the influence of mass transfer have been determined in a laboratory pipe section reactor (PSR), testing an old decommissioned metallic pipe. In total, 23 series of experiments were performed under different initial free chlorine concentrations and different hydraulic conditions. The applicability of different chlorine decay mathematical models has been investigated. A new model was proposed, combining zero order bulk reactions and first order wall reactions, describing the laboratory results with Nash-Sutcliffe efficiency coefficients over 0.99. The obtained values for the wall reaction coefficient vary in the range 0.008–0.030 m/h, decreasing exponentially with increasing initial chlorine concentration.

The low temperature D+ + H2 → HD + H+ reaction rate coefficient: a ring polymer molecular dynamics and quasi-classical trajectory study

The D+ + H2 → HD + H+ reaction rate coefficient has been calculated at low temperatures (20–100 K) by ring polymer molecular dynamics and quasi-classical trajectory methods.

Diffusion and Heterogeneous Reaction in Porous Media: The Macroscale Model Revisited

Diffusion and reaction in porous media have been studied extensively due to the wide range of applications in which this transport phenomenon is involved. In particular, in chemical reactor engineering, reactive mass transfer is crucial to understand the performance of porous catalyst particles immersed in chemical reactors. Due to the disparity of characteristic lengths between the pores and the porous particles, this type of process is usually modeled by means of effective-medium equations, in which the solid and fluid phases are conceived as a pseudo-continuum. For conditions in which the pore-scale Thiele modulus (or Kinetic number) is much smaller than unity, it is reasonable to assume that the effective diffusivity involved in the effective-medium model is only a function of the porous medium geometry. However, a long debate has existed in the literature concerning the extensive use of this assumption for situations in which the Kinetic Number does not satisfy the above mentioned constraint. In addition, the functionality of the effective reaction rate coefficient with the Kinetic number has not been sufficiently studied. In this work we address these issues by means of the volume averaging method. Our analysis is focused on cases in which the Kinetic number can reach values up to 1. Interestingly, for this particular condition, the use of the intrinsic diffusivity tensor is justified. In addition, by means of Maclaurin series expansions, the effective reaction rate coefficient is shown to be acceptably approximated as a first-order function. These two conclusions for the effective medium coefficients constitute the major contributions from this work. In addition, the predictions from the upscaled model are validated by comparison with direct numerical simulations under steady and transient conditions.