Plug-flow mixing units are designed so that the fluid particles pass through the unit in the same sequence in which they enter. There is minimal longitudinal dispersion, and particles retain their identity and remain in the unit for a time equal to theoretical hydraulic detention time. In trace-profile study, an initial slug or continuous feed of dye tracer concentration C0 in a plug-flow unit would result in dye distributions at the outlet as shown in Figure 8-8(a).18 The theoretical hydraulic detention time t0 is obtained by dividing the unit volume by the flow rate.An excellent example of plug flow would be water flowing through a pipeline or in a series of completely mixed reactors. Due to their nature, static mixers are typically plug-flow type.