Fluid mixing during reaction

A combustion model for gaseous fuels based on the ratio of components was implemented assuming that all fluids which are mixed are also combusted [10]. The hypothesis is that mixing of reaction partners by diflusion is much slower than reaction kinetics. To calculate increasing of temperature during oxidation the global reaction... 

This section describes numerical and experimental means for the detailed characterization of multiphase flows. Flow behavior is closely linked to the transport processes of fluid mixing and axial dispersion and therefore affects the yield of chemical reactions performed in microchannel networks. Integrated multiphase flow sensors are potentially important for observing and controlling microreactor performance during continuous operation. 

Canon et al. (1977) simulated the flow, mixing, and reaction in the Paul and Treybal stirred reactor using a Monte Carlo coalescence and dispersion (C-D) method. In this method elements of the fluid are simulated by points that move according to the flow pattern in the vessel. These points have mass and composition representing some fraction of the fluid in the vessel. The points are caused to mix (coalesce), react, then disperse. The number of points undergoing C-D during each time increment is proportional to a C-D frequency. The local C-D frequency (coalescences/time/site) was found to be related to local turbulence as follows ... 

Fig. 22.5. Concentrations of components (sulfate, sulfide, carbonate, methane, and acetate) and species (O2 and H2) that make up redox couples, plotted against temperature, during a model of the mixing of fluid from a hot subsea hydrothermal vent with cold seawater. Model assumes redox couples remain in chemical disequilibrium, except between 02(aq) and H2(aq). As the mixture cools past about 38 °C, the last of the dihydrogen from the vent fluid is consumed by reaction with dioxygen in the seawater. At this point the anoxic mixture becomes oxic as dioxygen begins to accumulate.

Fig. 22.6. Redox potentials (mV) of various half-cell reactions during mixing of fluid from a subsea hydrothermal vent with seawater, as a function of the temperature of the mixture. Since the model is calculated assuming 02(aq) and H2(aq) remain in equilibrium, the potential for electron acceptance by dioxygen is the same as that for donation by dihydrogen. Dotted line shows currently recognized upper temperature limit (121 °C) for microbial life in hydrothermal systems. A redox reaction is favored thermodynamically when the redox potential for the electron-donating half-cell reaction falls below that of the accepting half-reaction.

Fig. 22.7. Thermodynamic driving forces for various anaerobic (top) and aerobic (bottom) microbial metabolisms during mixing of a subsea hydrothermal fluid with seawater, as a function of temperature. Since the driving force is the negative free energy change of reaction, metabolisms with positive drives are favored thermodynamically those with negative drives cannot proceed. The drive for sulfide oxidation is the mirror image of that for hydrogentrophic sulfate reduction, since in the calculation 02(aq) and H2(aq) are in equilibrium.

Fig. 30.1. Volumes of minerals precipitated during a reaction model simulating the mixing at reservoir temperature of seawater into formation fluids from the Miller, Forties, and Amethyst oil fields in the North Sea. The reservoir temperatures and compositions of the formation fluids are given in Table 30.1. The initial extent of the system in each case is 1 kg of solvent water. Not shown for the Amethyst results are small volumes of strontianite, barite, and dolomite that form during mixing.

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