This paper describes a novel hydrodynamic principle for online process control of flow rate ratios and mixing between two concurrent flows in our recently introduced centrifugal micromixer (Ducree et al., 2003 and Ducree et al., 2004). These flows are contacted in an asymmetric, planar Y-structure on a rotating disk and subsequently driven through a common radial mixing channel. We show that the ratio of the incoming flow rates is statically seeded by the asymmetry of the inlets. The ratio can dynamically be adjusted by the frequency of rotation to realize a feedback process control. Furthermore, a new mechanism of quasi instantaneous mixing is activated by the sense of rotation. The proposed hydrodynamic mechanism is validated by experiments and simulations.