Complete mixing

About: Complete mixing is a research topic. Over the lifetime, 331 publications have been published within this topic receiving 6540 citations.

Dispersed phase mixing: I. Theory and effects in simple reactors

Abstract: When drops in a two-liquid phase chemical reactor are able to mix with one another by coalescences and redispersions, any spread of concentration among the drops tends to be averaged out. This phenomenon can affect average reaction rate and selectivity in non first-order reactions or mass transfer rate controlled reactions in the dispersed phase. It was found that for mass transfer rate controlled reactions, or the equivalent zero-order reaction, quite large dispersed phase mixing rates are required to bring conversions close to the level obtained with complete mixing.

Micro T-mixer as a rapid mixing micromixer

Abstract: In this paper, micro T-mixers are fabricated and tested to investigate their feasibility as a rapid mixing micromixer. The micro T-mixers are fabricated out of a silicon substrate and bonded to a Pyrex glass plate to enable their mixing performances be observed and characterized. The mixing is characterized using a blue dye and a colourless liquid, the results are further verified by the hydrolysis reaction of dichloroacetyl phenol red. Different pressures are applied onto the inlets of the micro T-mixers and their corresponding mixing performances are observed with an optical microscope. Liquid streams break up into striations at progressively higher Reynolds number of flow and there exists a Reynolds number, between 400 and 500, when these striations disappear into uniform concentration across the mixing channel. The observations are further supported by computer simulations, which enable the fast mixing to be explained by the asymmetrical flow conditions at the inlets, in addition to the generation of vortices and secondary flow at the junction. It is shown that for a micro T-mixer with a mixing channel having a hydraulic diameter of 67 μm, an applied pressure of 5.5 bar is sufficient to cause complete mixing within less than a millisecond after the two liquids make contact.

Reactive Transport in Porous Media: A Comparison of Model Prediction with Laboratory Visualization

Abstract: Groundwater transport models that accurately describe spreading of nonreactive solutes in an aquifer can poorly predict concentrations of reactive solutes. The dispersive term in the advection-dispersion equation can overpredict pore-scale mixing, and thereby overpredict homogeneous chemical reaction. We quantified this experimentally by imaging instantaneous colorimetric reactions between solutions of aqueous CuSO4 and EDTA4- within a 30-cm long translucent chamber packed with cryolite sand that closely matched the optical index of refraction of water. A charge-coupled device camera was used to quantify concentrations of blue CuEDTA2- within the chamber as it was produced by mixing of the two reactants at different flow rates. We compared these experimental results with a new analytic solution for instantaneous bimolecular reaction coupled with advection and dispersion of the product and reactants. For all flow rates, the concentrations of CuEDTA2- recorded in the experiments were about 20% less than predicted by the analytic solution, thereby demonstrating that models assuming complete mixing at the pore scale can overpredict reaction during transport.

A barrier embedded chaotic micromixer

Abstract: Mixing enhancement has drawn a great attention to designing of micromixers, since the flow in a microchannel is usually characterized by a low Reynolds number (Re) which makes mixing quite a difficult task to complete. In this regard, we present a new chaotic passive micromixer, called a barrier embedded micromixer (BEM). In the BEM, chaotic flow is induced by periodic perturbation of the velocity field due to periodically inserted barriers along the top surface of the channel while a helical type of flow is obtained by slanted grooves on the bottom surface in the pressure driven flow. A T-channel and a microchannel with only slanted grooves were fabricated for the purpose of experimental comparison. Mixing performance has been experimentally characterized in two ways: (i) change of average mixing intensity by means of phenolphthalein and (ii) mixing patterns via a confocal microscope. Experimental results showed that BEM has better mixing performance than the other two. A characteristic required mixing length, defined in view of intensity change, increases logarithmically with Re in BEM. The confocal microscope images indicated that BEM could achieve almost complete mixing. The chaotic mixing mechanism, proposed in this study can be easily applied to integrated microfluidic systems, such as micro-total-analysis-systems, lab-on-a-chip and so on.

Fecal Bacterial Kinetics in Stabilization Ponds

Abstract: Fecal bacterial die-off is described by a first-order reaction assuming complete mixing, thus a series pond system is more efficient than a single pond of equal total volume. The death rate constant is reduced as the temperature falls and if thermal stratification takes place.