A Chemical Probe for Characterising Turbulent Micromixing

Durandal, Cédric; Lemenand, Thierry; Valle, Dominique Della; Peerhossaini, Hassan

doi:10.1115/fedsm2006-98146

Cited by 3 publications

(2 citation statements)

References 13 publications

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“…The intrinsic parameter characterizing the absolute magnitude of the reaction apparent kinetics is the micromixing time t m (the inverse of a mixing rate), which can be considered the key parameter of chemical reactor performance for rapid reactions. The mixing time can be related to the segregation index by using physical models [26][27][28][29].…”

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Micro-mixing measurement by chemical probe in homogeneous and isotropic turbulence

Lemenand

Valle

Habchi

et al. 2017

Chemical Engineering Journal

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h i g h l i g h t sValidation of a micro-mixing model under homogeneous and isotropic turbulence (HIT). HIT is obtained by a system of oscillating grids placed in a vessel. Chemical probe measurements are carried out by the iodide/iodate reaction system. IEM and EDD models are tested. EDD model provides the more accurate quantitative characterization of micro-mixing. Keywords: Active grid turbulence Chemical probe IEM (Interaction by Exchange with the Mean) model EDD (Engulfment, Deformation and Diffusion) model Homogeneous and isotropic turbulence Micro-mixing LDV a b s t r a c tThe chemical probe is commonly used to evaluate the performance of chemical reactors. By a localized injection of chemical reagents, it is possible to measure the local micro-mixing, which is readily related to the selectivity of chemical reactions, since mixing at the molecular scale is the limiting factor for a wide range of chemical systems. The raw result of the chemical-probe method is a segregation index that allows comparison of different situations (various locations in the reactor, various Reynolds numbers, various geometries, etc.). Beyond the qualitative assessment provided by this segregation index, it is possible to obtain the intrinsic micro-mixing time by means of a micro-mixing model, describing the temporal evolution of a chemical reaction whose rate is governed by the micro-mixing. Here a key step is the choice of micro-mixing model. Several micro-mixing models available in the literature have been used in some specific cases without evaluating their appropriateness for the problem in hand. The main difficulty in this evaluation is that the real flows often do not fully satisfy the basic model assumptions, in particular the condition of homogeneous and isotropic turbulence (HIT).The present work aims at assessing the validity of a micro-mixing model under ''ideal" experimental conditions, i.e. HIT with no mean flow, to avoid the bias due to the flow gradients. The HIT is obtained here by a system of oscillating grids placed in a vessel. The chemical probe measurements carried out by the iodide/iodate reaction system are applied to the two most commonly used phenomenological models in the literature: the IEM (Interaction by Exchange with the Mean) and the EDD (Engulfment, Deformation and Diffusion) models. The benchmark for the micro-mixing models is based on comparison of the local turbulent kinetic energy (TKE) dissipation rate both drawn from the micro-mixing time by the theoretical model of Bałdyga and the reference direct experimental determination by laser Doppler velocimetry measurements. It is shown that the engulfment model EDD seems the more appropriate to analyze the chemical data and provide a quantitative characterization of micro-mixing.Ó 2016 Elsevier B.V. All rights reserved. IntroductionUnderstanding of the mechanisms that underlie turbulent mixing and convective transfer is fundamental in many technological applications -chemical, pharmaceutical, food, and cosmetic, for http://dx.

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confidence: 99%

Micro-mixing measurement by chemical probe in homogeneous and isotropic turbulence

Lemenand

Valle

Habchi

et al. 2017

Chemical Engineering Journal

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“…1. The segregation index can be related further to the mixing time by using physical models Bourne, 1989, 1999;Fournier et al, 1996b;Durandal et al, 2006;Falk and Commenge, 2010). Section 2 presents in detail the iodideiodate method, which is used in the present study since it presents the best accuracy among other chemical probe methods (Durandal et al, 2006).…”

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A new adaptive procedure for using chemical probes to characterize mixing

Habchi

Valle

Lemenand

et al. 2011

Chemical Engineering Science

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The M Number: A Novel Parameter to Evaluate the Performance of Static Mixers

Medina

Thomas

Eldredge

et al. 2019

Journal of Fluids Engineering

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Static mixers (SM) have become standard equipment in the process industries. They are widely used in applications that involve chemical reactions, heat transfer, blending of fluids, or a combination of these. Compared to mechanically agitated vessels, SMs consume less energy, require less maintenance, and can provide mixing with shorter residence time. Assessment of the performance of SM provides a means to categorize and rank the available devices and new designs, which in turn facilitates selection for specific applications. Applying the second law efficiency (SLE) principle, we derived and proposed a novel mixing parameter, the M number, which is a dimensionless ratio of mixing level to energy loss. The parameter is compared to an industry-standard method of mixing evaluation that relies on the coefficient of variation (CoV) change across the mixer. Both CoV and the M number are used to evaluate mixing performance from computational fluid dynamics (CFD) results for a static mixer for various inlet conditions. Unlike the CoV-based parameters considered, the M number offers the advantages of accounting for energy loss and the natural mixing effects of the system. In addition, an empirical relationship is obtained that relates the M number to the Reynolds number (Re). Potential applications for the M number are discussed and its limitations are noted. Work in progress includes investigation with other SM.

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A Chemical Probe for Characterising Turbulent Micromixing

Cited by 3 publications

References 13 publications

Micro-mixing measurement by chemical probe in homogeneous and isotropic turbulence

Micro-mixing measurement by chemical probe in homogeneous and isotropic turbulence

A new adaptive procedure for using chemical probes to characterize mixing

The M Number: A Novel Parameter to Evaluate the Performance of Static Mixers

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