The Hydrodynamics of Three Multiphase Reactors (Spouted Beds, Fluidized Bed and Bubble Column) Have Been Studied in Order to Identify the Main Transition Velocities Utrans. the Kolmogorov Entropy (KE) Algorithm is Applied to Gauge Pressure Fluctuations as a Universal Method for Utrans Identification. the Local KE Minima Are Used as Transition Indicators. It Has Been Found that the Boundaries of the Main Hydrodynamic Regimes (Packed Bed, Stable Spouting and Unstable Spouting) in Two Spouted Beds (0.076 and 0.152 M I.d.) Could Be Identified Easily by This Method. in the Smaller Bed the Utrans Values (0.783 and 0.885 M·s-1) Tend to Be Higher Than the Ones (0.563 and 0.631 M·s-1) in the Bigger Bed. in the Case of the Fluidized Bed (0.14 M I.d.), the Minimum Fluidization Velocity Was Identified at UG=0.121 M·s-1. at UG=0.151 and 0.377 M·s-1, Both the Fast Bubble and Slow Bubble Sub-Regimes of Bubbling Fluidization Were Identified. at UG=0.83 M·s-1, the Turbulent Fluidization Regime Was Established. the KE Values in a Bubble Column (0.14 M I.d.) Are Capable of Identifying Four Utrans Values (0.016, 0.03, 0.04 and 0.046 M·s-1). the Boundaries of a Gas Maldistribution Zone, Bubbly Flow Regime, Two Transition Sub-Regimes and Churn-Turbulent Flow Regime Are Thereby Delineated. © 2012 the Society of Chemical Engineers, Japan.