| Summary: | The influence of the hydrodynamics (flow rates <i>Q</i>, specific energy dissipation rate ε) on the micromixing in a two-step microreactor with intensively swirled flows (MRISF-2) was studied experimentally. Three methods of liquid input into the reactor were compared: (i) through the upper tangential and axial nozzles (TU1, Ax); (ii) through two upper tangential nozzles (TU1, TU2); (iii) through the upper and lower tangential nozzles (TU1, TL2). Segregation index <i>X</i><sub>s</sub> used as a measure of micromixing level was determined by means of iodide iodate reaction method. The Bernoulli equation for a device with two inputs and one output was derived to assess the energy consumption. It was revealed that in MRISF-2 up to 99.8–99.9% of input energy is dissipated, i.e., transformed into liquid element deformations thus resulting in better micromixing. For each of three liquid inputs, the dependence ε = <i>f</i>(<i>Q</i>) could be fairly approximated by an exponent ε = <i>A</i><sub>1</sub><i>Q<sup>n</sup></i><sup>1</sup>, with <i>n</i><sub>1</sub> ≈ 3.0. For connection (TU1, TU2) the dependence <i>X</i><sub>s</sub> = <i>f</i>(ε) falls linearly for <i>Q</i> > 2 L/min, but for the low flow rates (<i>Q</i> ≈ 1 L/min) there is an unusually small <i>X</i><sub>s</sub> value; the effect of good micromixing is caused by the kinetic energy concentrated in a small volume of liquid near the neck. The best behavior in terms of micromixing was achieved for the (TU1, Ax) connection scheme: the level of <i>X</i><sub>s</sub> ≈ 0.01 for ε ≈ 30 W/kg, and comes down with growing ε to <i>X</i><sub>s</sub> ≈ 0.002 for ε ≈ 30,000 W/kg. These values are 50 and 250 times lower compared to the mixing in a lab glass with a magnetic stirrer, as shown in our previous work. The parameters of dependencies <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>X</mi><mi mathvariant="normal">s</mi></msub><mo>=</mo><msub><mi>A</mi><mn>3</mn></msub><msup><mi mathvariant="sans-serif">ε</mi><mrow><msub><mi>n</mi><mn>3</mn></msub></mrow></msup></mrow></semantics></math></inline-formula> were found for (TU1, Ax) and (TU1, TL2).
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