In this work, the impact of the vertical internals on the flow regimes and their transition velocities has been studied in a 0.14m inside diameter gas-solid fluidized bed. The identification of the flow regimes was accomplished statistically (standard deviation) and chaotically (Kolmogorov entropy) by analyzing the pressure drop fluctuations. Circular configurations of vertical tubes with two different sizes (0.0254 and 0.0127 m diameter), two kinds of solid particles of Geldart B type (glass beads and aluminum oxide), and a wide range of superficial gas velocities (0.15-1.2 m/s) have been implemented in this study. Generally, it was demonstrated that the vertical internals have a significant effect on the flow regimes, transition velocities, and transition velocity ranges of each individual flow regime. However, such effect is a function of the physical properties of the used solid particles in which the turbulent transition velocity (U-c) decreased in the case of glass beads and increased in the case of aluminum oxide for both of the configuration designs of vertical internals used in the present work. In addition, the 0.0254m vertical internals type has been shown to be more efficient either in minimizing the turbulent transition velocity (U-c) and superficial gas velocity within the range of slugging flow regime and increasing the range of the superficial gas velocity within the range of bubbling flow regime or in reducing the pressure drop and pressure fluctuations inside the bed. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.