The effects of the presence of vertical internal tubes and their diameters on the local gas holdup and bubble dynamics, including the specific interfacial area, bubble chord length, and bubble velocity were investigated in a 6 in. bubble column for the air-water system by using a four-point optical fiber probe technique. Two different diameters, 0.5-inch, and 1-inch, of vertical internals equally covering 25% of the column's cross-sectional area (CSA) were used to represent the heat-exchanging tubes utilized in the Fischer Tropsch (FT) process. For both sizes, the vertical internals were uniformly distributed over column CSA. The experiments were performed using the air-water system, in a 6-inch bubble column at superficial gas velocities of 20, 30, and 45 cm/s. The experimental results indicated that the presence of vertical internals and their diameters have a significant effect on the hydrodynamic properties of the bubble column reactor at high superficial gas velocities. The local gas holdup significantly increased in the core region and decreased at the wall regions when the 0.5-inch vertical internals were used. Contrarily, the 1-inch vertical internals enhanced the gas holdup near to the wall regions. Additionally, the bubble chord length and the bubble rise velocity were found to be larger in the presence of vertical internals, especially at high superficial gas velocities. The specific interfacial area with the 0.5-inch internal was much lower than bubble column without vertical internals, but while using 1-inch internals, it was enhanced in the wall regions.