# Active Mixing

Active mixers make use of a mechanical device to facilitate mixing. In this example a magnetic stir bar (driven by an external rotating magnetic field) is used to induce mixing. This simulation uses the Moving Objects model to simulate the magnetic stir bar. The magnetic interaction of the bar is not included but instead a rotational speed (RPM) of the bar is specified directly as a prescribed motion. In this case, there is no density variation, however, FLOW-3D can easily simulate multiple density components, i.e., miscible or immiscible fluids. The separation of immiscible fluids in FLOW-3D is based on a drift relationship.

This simulation demonstrates an active micro mixing process. The flow is from left to right. This is a one-fluid simulation with the bottom half (red) being seeded with passive scalars, or tracers, and therefore there is no density gradient.