Complete-mixed units are designed such that the contents of the tank are completely mixed. A slug or continuous dye tracer injected at the inlet of a complete-mixed unit would result in a dye distribution at the outlet as shown in Figure 8-8(b). 18 Due to their nature, mechanically mixed rapid mixers tend to have complete-mixing characteristics or those of an arbitrary-flow system (Figure 8-8(c)). In an arbitrary-flow unit, partial mixing between that of a plug-flow unit and that of a complete-mixed unit is encountered.