Mixing patterns generated in stirred vessels for a wide range of Reynolds numbers were observed using a decolorization method based on the reaction between sodium thiosulfate and iodine. A relationship was established between the power number diagram (N-P-R-e diagram) and the shape of the isolated zone was observed. At low Reynolds numbers (laminar regime), the isolated zone resembled a doughnut ring, while a cylindrically rotating zone isolated at high Reynolds numbers (turbulent regime). Even with a small change in Reynolds number, the doughnut-ring-shaped isolated zone suddenly changed to a cylindrically rotating zone in an unbaffled vessel. The cylindrically rotating zone was not observed in baffled vessels at high Reynolds numbers. The clearance between the propeller impeller and the vessel bottom brought about a change in the mixing patterns, although the power consumption the remained constant.