| Influence of Filling Ratio on Flow Pattern in a Two-Phase Closed Thermosiphon at Fixed Confinement Number |
| Paper ID : 1022-ICEEM2025 (R2) |
| Authors |
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Ahmed G. Rahma *1, Frédy Abadassi2, Abdellah Ghenaim2, Pierre François1, Yannick Hoarau1, Denis Funfschilling1, Abderahmane Marouf1 1Université de Strasbourg, CNRS, ICUBE UMR 7357, 67000 Strasbourg, France 2INSA Strasbourg, CNRS, ICUBE UMR 7357, 67000 Strasbourg, France |
| Abstract |
| This study presents a two-dimensional numerical investigation of the influence of filling ratio (FR) on flow patterns in a two-phase closed thermosiphon under sub-atmospheric pressure conditions, using the commercial CFD software STAR-CCM+. Simulations were performed on a 500 mm copper tube with an inner diameter of 20.2 mm, subjected to a constant heat input and output of 172.9 W. The filling ratio varied from 20% to 120%. Key dimensionless numbers (including the Bond number (Bo), Confinement number (Co), Weber number (We), and Froude number (Fr) were used to characterize the dominant force interactions governing two-phase flow behavior. The results showed that all cases were operating within the gravity-dominated regime, where buoyancy was the primary driving mechanism, with additional influence from surface tension due to confinement effects. Lower FRs (20–80%) exhibited high evaporation rates, intense bubble activity, and vapor entrainment, with insufficient liquid bridges to form stable slug flow. At higher FRs (100–120%), flow patterns were characterized by transient slugs, thicker liquid columns, and a noticeable shift from latent to sensible heat transfer in the condenser. The spatiotemporal evolution of the vapor volume fraction (αV) revealed delayed nucleation and expanded bubble fluctuation zones as the FR increased. This study offers valuable insights for optimizing the design and operation of passive two-phase thermal management systems using CFD-based methods. |
| Keywords |
| Two-phase thermosiphon, Filling ratio, Flow patterns, Sub-atmospheric pressure, Numerical simulation, Dimensionless numbers. |
| Status: Accepted |