Mixing time is defined as the time required for achieving a certain degree of homogeneity of injected tracer in a unit operation vessel. It has been used as a key parameter for assessing the performance of amixing system. From an experimental standpoint

several techniques have been developed for measuring the mixing time. Based on the disturbances to flow

they can be classified into two groups: non-intrusive and intrusive. However

depending on the type of data generated

they can be also classified into direct measurements and indirect measurements (Eulerian and Lagrangian). Since the techniques available for measuring mixing times in an agitated tank do not provide the same information

its choice depends on several factors

namely: accuracy

reproducibility

suitability

cost

sampling speed

type of data

and processing time. A review of the experimental techniques reported in the literature in the last 50 years for themeasurement of mixing time in stirred vessels under single and gas-liquid flowconditions with Newtonian and non-Newtonian fluids in the laminar and turbulent regimeis made

and a comparison between these techniques is also presented.