In the context of this work, mixing refers to macromixing unless otherwise specified, and the following definitions are used to avoid confusion related to the concept of mixing time: Local mixing time refers to the time required to bring a locally measured tracer concentration within 5 % of equilibrium. The time-scale of (macro)mixing is the time required to reduce the concentration's standard deviation in the whole volume to 5 % of mean. The time-scale is thus a global measure of mixing efficiency . For convenience, the mixing rate is defined as the inverse of the time-scale.