The purpose of this study is to investigate heat/mass transfer and flow characteristics inside co-rotating disks with hub having ventilation holes. Naphthalene sublimation technique is employed to determine the local heat/mass transfer coefficients on the rotating disks using the heat and mass transfer analogy. Flow field measurements are conducted using Laser Doppler Anemometry (LDA) and numerical calculations are performed simultaneously to analyze the flow patterns induced by the disk rotation. The experiments are conducted for the Rossby number of 0.04, 0.1, and 0.35 to evaluate the influence of incoming flows through the holes on the hub. The basic flow structure in a cavity between co-rotating disks consists of three regions; the solid-body rotating inner region, the outer region with unsteady vortices and the shroud boundary layer region. The heat/mass transfer rates on the co-rotating disks are very low near the hub due to the solid-body rotation and increase rapidly in the outer region due to turbulence mixing. The modified hub with the ventilation holes enhances significantly the heat/mass transfer rates on the region near the hub.