Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session L06: Reactive Mixing |
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Chair: Douglas Kelley, University of Rochester Room: 205 |
Monday, November 25, 2019 1:45PM - 1:58PM |
L06.00001: Comparing laminar flows for efficient reactive mixing Daniel Troyetsky, Thomas D. Nevins, Douglas H. Kelley As a chemical reaction occurs, a front is formed at the boundary between reacted and non-reacted regions. We wish to quantify the efficiency of reactive mixing by a variety of shear flows by understanding how fronts evolve over time. A more efficient flow causes the reacted region to grow more quickly. To do this we have performed numerical simulations of chemical reactions in the presence of two-dimensional, laminar shear flow using both the one-dimensional Eikonal approximation, which assumes fronts are thin curves with an inherent burning speed, as well as the two-dimensional advection-reaction-diffusion equation, which captures the dynamics of reactant concentration through both space and time. We find that the key factor in improving mixing efficiency is to maximize the absolute velocity difference in the flow. We have also developed an analytical solution to model these front dynamics and have successfully predicted the final front shape and growth rate for six unique flow profiles. [Preview Abstract] |
Monday, November 25, 2019 1:58PM - 2:11PM |
L06.00002: Reactive mixing in a shear flow Emilie Guilbert, Christophe Almarcha, Henri Lhuissier, Bloen Metzger, Emmanuel Villermaux We investigate the interaction between chemical reaction and diffusion on a moving substrate and by means of an original chemical reaction between two transparent reactants (fluorescin and potassium ferricyanide) which produce a fluorescent product in water (fluorescein) with tunable kinetics. A blob of fluorescin in a cell filled with potassium ferricyanide is advected in a simple shear flow. The blob deforms into an elongated strip diffusing from its borders at a shear-dependent rate. Depending on the ratio of the mixing time to the reaction time (Damkh\"oler number $Da$), several regimes are identified: When $Da>1$, the product concentration remains constant in the reaction zones until the reactive borders overlap, while when $Da<1$ the product concentration increases linearly in time at a rate controlled by the reaction only. The mixing-controlled decay rate of the final product concentration after the reaction is completed is described as well. [Preview Abstract] |
Monday, November 25, 2019 2:11PM - 2:24PM |
L06.00003: Flow Characteristics of Mixing in Continuous Flow Supercritical Carbon Dioxide Material Synthesis Reactor Courtney Otani, Elizabeth Rasmussen, John Kramlich, Igor Novosselov Supercritical carbon dioxide (sCO2) is being increasingly employed for advanced clean energy research including turbomachinery, electronics cooling, and more recently material synthesis. Understanding the fluid mechanics that dictate optimum operation is key to wide-spread application. The research presented here focuses on the mixing section of a continuous flow sCO2 material synthesis reactor. Modeling the transient and multiphase mixing between sCO2 and precursor materials gives insight into optimizing reactor conditions for uniform and controllable crystallization growth. Therefore, the commonly used counter-current design as well as three others are analyzed using computational fluid dynamics (CFD) to determine the flow characteristics of various geometries. Velocity and temperature contour plots and profiles are presented to identify regions with high vorticity, large temperature gradients, areas of stagnation, and boundary layer effects. Comparison of these results highlight the attributes and inefficiencies of different mixing section geometries. [Preview Abstract] |
Monday, November 25, 2019 2:24PM - 2:37PM |
L06.00004: In-line spectroscopic diagnostics to investigate mixing-limited consecutive-competitive reaction systems Gokul Pathikonda, Michael Ahmad, Mustafa Usta, Irfan Khan, Cyrus Aidun, Devesh Ranjan Many complex industrial processes involve mixing-limited reaction chemistry in highly turbulent and complex environments. The proportions of reaction products (`reaction yield') involving consecutive-competitive reactions have long been known to depend on characteristics of turbulent mixing, necessitating the need for better injector designs for turbulent control. The relevant experimental studies frequently require the ability to measure the chemical reaction products in complex turbulent environments. We present a novel in-line spectroscopic measurement to study the reaction between 1-Napthol and Diazotized Sulfanilic acid. The concentrations of mono- (primary) and di-azo (secondary) reaction products averaged diametrically are measured using visible-light absorption spectroscopy at various distances from the injector. The diagnostic is characterized using bench-top measurements of known concentrations, and implemented on a co-flowing jet injector facility. Preliminary results demonstrating the effect of viscosity gradients on reaction yield is presented. It was noticed that an increase in the viscosity gradients in the reaction environments (owing to disparity in viscosity of inlet liquids) significantly alters the selectivity of the overall reaction. [Preview Abstract] |
Monday, November 25, 2019 2:37PM - 2:50PM |
L06.00005: Experimental investigation of disparate viscosity turbulent mixing in a coaxial jet mixer Michael Ahmad, Gokul Pathikonda, Mustafa Usta, Irfan Khan, Cyrus Aidun, Devesh Ranjan Industrial chemical processes often involve continuous mixing of streams of reactants at different viscosities. In contrast to streams of constant viscosity, the variable viscosity streams provoke different mechanisms for turbulence and mixing, which are known to affect chemical yield. These mechanisms need thorough study to enable predictive modeling of such phenomena. Thus, simultaneous PIV and PLIF are employed to measure the turbulent and mixing dynamics in a confined, co-annular jet flow with viscosity ratios up to 40. This data reveal the effects of the imposed viscosity gradients on the nature in which the jet spreads into the co-flow. Evidently, the viscosity disparity largely confines the vortical structures to the lower viscosity fluid resulting in larger and more intermittent scalar structures in the higher viscosity fluid. This overarching phenomena reflects itself within realizations of the mean velocity and scalar fields, but also the Reynold stresses and turbulent and scalar dissipation. These observations allude to differences in expected chemical yield. This study is performed concurrently with a computational effort to develop insight for SGS models of turbulent mixing within mediums with viscosity gradients. [Preview Abstract] |
Monday, November 25, 2019 2:50PM - 3:03PM |
L06.00006: Competitive-consecutive reaction of liquids with disparate viscosity Mustafa Usta, Gokul Pathikonda, Michael Ahmad, Irfan Khan, Devesh Ranjan, Cyrus Aidun Competitive-consecutive reactions between liquids with disparate viscosity come along with several challenges due to high Schmidt (Sc) number and high reaction rates. The relevant scales at high Sc for a scalar become much smaller than turbulent dissipative scales. Higher reaction rates turn the problem into mixing limited reactions. In this study, we employ large-eddy simulation (LES) to investigate the effect of viscosity ratio on the reaction yields. The focus is on the co-axial jet and jet in crossflow mixing. In addition to the computations, the experimental setup features PIV and PLIF measurements to resolve the velocity and the mixture fraction. The investigations reveal that the mixing and reaction characteristics are considerably affected by the viscosity ratios of the liquids. The results for the mixing will be presented with comparison to experiments for the viscosity ratio of up to 40. The chemical reaction results; and the challenges in the subgrid scale modeling of variable viscosity, high Schmidt number, and high reaction rates will be presented for various viscosity ratios. [Preview Abstract] |
Monday, November 25, 2019 3:03PM - 3:16PM |
L06.00007: Experimental Study of a Turbulent Liquid Flame. Michael Le Bars, Baptiste Isnard, Christophe Almarcha Turbulent deflagrations are of fundamental importance for industrial applications and security issues. When the environment is congested by numerous obstacles, the turbulence generated by the blast upstream of the front strongly influences the flame speed and its acceleration. Our objective is to characterize experimentally turbulent premix combustion so as to improve its modeling and predictability. In particular, we aim at collecting experimental data for a critical analysis of flame velocity models, based on detailed non-intrusive measurements of local turbulence and front parameters. We investigate the coupling between turbulence and the premixed flame interface thanks to a so-called liquid flame, using an autocatalytic chemical reaction [1]: this chemical reaction generates an intermediate product that increases the reaction rate, leading to the building-up of a front with the final products in close similarity with premixed combustion. In our system, the turbulence is generated by 2 oscillating grids. PIV-PLIF measurements allow simultaneously quantifying the turbulence rate and the front evolution. The experimental results are used to challenge the predictions from classical theoretical and numerical models. [1] Shy et al. Combust. Flame 1999. Pocheau \& Harambat PRE 2006. [Preview Abstract] |
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