Optimization of micromixer with triangular baffles for chemical process in millidevices

Abstract

A new micromixer design (MTB – micromixer with triangular baffles and circular obstructions) was proposed aiming the combination of three mass transfer enhancements mechanisms: reduction of molecular diffusion path, split and recombination of streams and vortex generation. The geometric variables were also optimized considering the mixing performance and the required pressure drop. The optimal design was used for the mixing of different binary mixtures (vegetable oil/ethanol and water/ethanol) under the Reynolds number range from 0.01 to 200 and the chemical reaction process of vegetable oil transesterification with ethanolic solution of sodium hydroxide (biodiesel synthesis). High mixing index (M = 0.99) was observed for the oil/ethanol mixing for several channel heights (200 μm – 2000 μm) and widths (1500 μm – 3000 μm). The geometry W3000H400 (i.e., MTB with channel width of 3000 μm and height of 400 μm) was employed as the millireactor, providing a maximum oil conversion of 92.67% for a residence time of 30 s. For the water/ethanol mixing, the geometry W1500H200 was used. High mixing index (M = 0.99) was observed at very low Reynolds number (Re = 0.1) and also in higher Reynolds numbers of 50 and 100. Moreover, at Re = 0.1, high mixing index (M ≌ 0.90) was obtained already at 3.5 mm of channel length. However, for higher Reynolds number the fluids required longer distances to achieve superior mixing, about 10.5 mm at Re = 100. The MTB, unlike the ones found in the literature, can be used in microdevices (e.g., sensors) with low flow rates and in microdevices with large dimensions (eg, millidevices and milireactors) with high flow rates, allowing an easier application in chemical process aiming the commercial production.