A new adaptive procedure for using chemical probes to characterize mixing

Habchi, Charbel; Valle, Dominique Della; Lemenand, Thierry; Anxionnaz, Zoé; Tochon, Patrice; Cabassud, Michel; Gourdon, Christophe; Peerhossaini, Hassan

doi:10.1016/j.ces.2011.04.019

Cited by 25 publications

(13 citation statements)

References 45 publications

(56 reference statements)

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“…11. Principle of micro-mixing process with two chemical reactions of parallel-competitive type (adapted from Habchi et al [25]). tometer at 2606 m 2 mol À1 by Ferrouillat et al [48] and 2590 m 2mol À1 by Fournier et al [19].…”

Section: Methodsmentioning

confidence: 99%

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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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Section: Methodsmentioning

confidence: 99%

“…To obtain this value accurately, a series of conditions and hypotheses are necessary: i) the reaction is fully achieved locally, ii) the measurement is objective, i.e. there is no interference with the injection hydrodynamics, and iii) the need to target values of X S ''far" from 0 and 1 requires adapting concentrations to the flow turbulence level [25].…”

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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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“…By analogy we have considered a frequency, f corrugation , in the corrugated channel. It is defined as the ratio between the fluid velocity u, and the distance between two successive bends d bends (18.6 mm): (6) and this frequency has been multiplied by the measured mixing times t m . Fig.…”

Section: Mixing Timesmentioning

confidence: 99%

“…This allows an accurate control of the operating temperature which is one of the main barriers concerning the implementation of exo-or endo-thermal reactions in classical batch reactors. Moreover the corrugation of the reaction channel leads to the heat and mass transfers intensification while maintaining low Reynolds numbers [5][6][7][8][9]. Thus, by using heat exchanger/reactors many benefits are expected such as waste reduction, energy and raw materials saving, yield and selectivity increase, and cost reduction.…”

Section: Introductionmentioning

confidence: 99%

Characterization of the performances of an innovative heat-exchanger/reactor

Theron

Anxionnaz‐Minvielle

Cabassud

et al. 2014

Chemical Engineering and Processing: Process Intensification

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International audienceThe use of heat exchanger/reactors (HEX/reactors) is a promising way to overcome the barrier of poor heat transfer in batch reactors. However to reach residence time long enough to complete the chemistry,low Reynolds number has to be combined with both a plug flow behaviour and the intensification of heat and mass transfers. This work concerns the experimental approach used to characterize an innovative HEX/reactor. The pilot is made of three process plates sandwiched between five utility plates. The process stream flows in a 2 mm corrugated channel. Pressure drop and residence time distribution characterizations aim at studying the flow hydrodynamics. Identified Darcy correlations point out the transition between laminar and turbulent flow around a Reynolds number equal to 200. Moreover the flow behaves like a quasi-plug flow (Pe > 185). The heat transfer and mixing time have also been investigated. The ratio between the reaction kinetics and the mixing time is over 100 and the intensification factor ranges from5000 to 8000 kW m−3K−1. As a consequence, no limitations were identified which allows the implementation of an exothermic reaction. It has been successfully performed under severe temperature and concentration conditions, batchwise unreachable. Thus, it highlights the interest of using this continuous HEX/reactor

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“…The main interesting ways to intensify heat and mass transfers in heat exchanger/reactors are to insert 3D elements like metallic foams or fins [4][5][6] or to structure the flow path (2D or 3D) [7][8][9][10][11][12][13]. Such apparatuses have to address many points in terms of performances, but also in terms of polyvalence (the technology should not be dedicated to only one application), flexibility (to easily switch from one flow regime to another), competitiveness (too complex geometries lead to too high manufacturing and operating costs) and scale-up (performances have to be maintained during the scale-up procedure).…”

Section: Introductionmentioning

confidence: 99%

Influence of the meandering channel geometry on the thermo-hydraulic performances of an intensified heat exchanger/reactor

Anxionnaz‐Minvielle

Cabassud

Gourdon

et al. 2013

Chemical Engineering and Processing: Process Intensification

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In the global context of process intensification, heat exchanger/reactors are promising apparatuses to implement exothermic chemical syntheses. However, unlike heat exchange processes, the implementation of chemical syntheses requires to control the residence time to complete the chemistry. A way to combine the laminar regime (i.e. enough residence time) with a plug flow and the intensification of both heat and mass transfers is the corrugation of the reaction path. In this work, the experimental setup is based on plate heat exchanger/reactor technology. 7 millichannel corrugated geometries varying the corrugation angle, the curvature radius, the developed length, the hydraulic diameter and the aspect ratio have been designed and experimentally characterized (heat transfer, mixing times, pressure drops, RTD). The objectives were to assess their respective performances to derive some correlations depending on the channel design. The results confirmed the benefits of the reaction channel corrugation. Heat and mass transfers have been intensified while maintaining a plug flow behaviour in the usually laminar flow regime. Moreover, whatever the meandering channel's curvature radius, the results highlighted the relevance of considering the Dean number as the scale-up parameter. This dimensionless number, more than the Reynolds number, seems to govern the flow in the wavy channels.

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A new adaptive procedure for using chemical probes to characterize mixing

Cited by 25 publications

References 45 publications

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

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

Characterization of the performances of an innovative heat-exchanger/reactor

Influence of the meandering channel geometry on the thermo-hydraulic performances of an intensified heat exchanger/reactor

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