Energy Dissipation Rate and Micromixing in a Two-Step Micro-Reactor with Intensively Swirled Flows.

Abstract

The influence of the hydrodynamics (flow rates Q, 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 Xs 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 = f(Q) could be fairly approximated by an exponent ε = A1Qn1, with n1 ≈ 3.0. For connection (TU1, TU2) the dependence Xs = f(ε) falls linearly for Q > 2 L/min, but for the low flow rates (Q ≈ 1 L/min) there is an unusually small Xs 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 Xs ≈ 0.01 for ε ≈ 30 W/kg, and comes down with growing ε to Xs ≈ 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 Xs=A3εn3 were found for (TU1, Ax) and (TU1, TL2).