Computational fluid dynamics (CFD) was used to investigate the film flow on rotating wheel for a horizontal twin-shaft reactor. The Volume of Fluid (VOF) model combined with the sliding mesh method was chosen to simulate the film formation process. The mechanism on a rotating wheel distinguishes itself from that on a regular solid disk. Bounded film with only one gas-liquid interface and unbounded film with two gas-liquid interfaces coexist due to the presence of an open window under certain operation conditions. The unbounded film inside open window is significantly thinner and returns more rapidly to the liquid pool. The minimum rotating speed for unbounded film formation decreases when the liquid viscosity increases. The open window on the rotating wheel can enhance the film flow and surface renewal, due to the interaction and transition between the unbounded film inside the open window zone and the bounded film on the ring and spoke zones, but this intensification is limited for highly viscous polymers. (C) 2018 Elsevier Ltd. All rights reserved.