Determination of local energy dissipation rates in impinging jets by a chemical reaction method

To carry out controlled precipitation on a practical scale, the use of a tw o impinging jets mixer is explored in terms of its ability to deliver rapid micromixing. A system of parallel competing reactions developed by Villerm aux and co-workers is used to characterise the micromixing level in the dev ice as a function of feed flow rate and of its position in the reactor. The characteristic time for micromixing decreases with the feed flow rate and reaches values as small as 4 ms. Powers dissipated in the device are deduce d from the experiments using a simple micromixing model and correlate well with those calculated using computational fluid dynamics (Phoenics). Finall y, the energy dissipation rate in impinging jets is compared with the local energy dissipation rate of the impeller. Some rules of thumb for scale up are given. (C) 1999 Elsevier Science S.A. All rights reserved.