M.Hilman Gumelar Syafei, Ahmad Indra Siswantara, Muhammad Arif Budiyanto, Irvan Syah, Illa Rizianiza, Angga Septiyana
Falling liquid films are widely utilized due to their excellent heat and mass transfer performance combined with short residence times. Previous studies have employed two-dimensional (2D) CFD simulations to investigate the hydrodynamics of falling films on vertical tube surfaces. However, two-dimensional models fail to represent circumferential velocity gradients, whose presence is critical because they may induce tangential velocity components. This study examines the hydrodynamics of palm-based vegetable oil falling film flow over the outer surface of a vertical tube across different flow rates. The analysis particularly addresses tangential velocity distributions through three-dimensional (3D) transient isothermal CFD simulations with a Volume of Fluid (VOF) multiphase model. The results show that for flow rates of 15 LPM (Re≈25) or higher, the film remains smooth over a longer distance before undergoing a sudden transition to three-dimensional wavy flow in the lower section. In contrast, at lower flow rates, wave formation begins much earlier, approximately 0.3–0.5 m downstream of the inlet. The axial velocity profiles in the upper section exhibit semi-parabolic, symmetric shapes, while at the lower sections, both 1 LPM and 18 LPM cases exhibit asymmetric distributions, indicating circumferential velocity gradients. Tangential velocity is most pronounced in the lower sections, reaching maximum values of 0.159 m/s, 0.081 m/s, 0.088 m/s, and 0.0802 m/s for flow rates of 1, 3, 9, and 18 LPM, respectively. © 2026 Elsevier Inc.
Department of Mechanical Engineering, Faculty of Engineering, Universitas Indonesia, Depok, Indonesia; Department of Mechanical Engineering, Faculty of Engineering, Universitas Negeri Semarang, Semarang, Indonesia; Department of Mechanical Engineering, Faculty of Engineering, Institut Teknologi Kalimantan, Balikpapan, Indonesia; Technology Center for Aeronautics, National Research and Innovation Agency – BRIN, Bogor, Indonesia
