Computational Analysis of a Single Air Bubble Rising in Quiescent Water Under Temperature Variations

Two-phase fluid flow is widely encountered in petroleum, chemical, nuclear, and energy applications. Computational fluid dynamics (CFD) by ANSYS Fluent 17.2 has been employed in this work to simulate the rise of a single air bubble through stagnant water at different temperatures (0 °C, 25 °C, and 50 °C). In addition, a user-defined function(UDF)was developed and implemented to incorporate phase-change behavior and temperature-dependent properties. This study investigates how the buoyancy-driven bubble dynamics will be responsive to changes in liquid viscosity, surface tension, and density. The results demonstrated that increasing the temperature of water enhances the bubble rise velocity significantly; the bubble rose approximately 18-30% faster at 50 °C compared with 0 °C due to the reduction in viscosity and interfacial tension. Additionally, the bubble behavior in 30% saline water was compared to pure water at ambient temperature, 25 °C. Salinity increased the rise velocity by 12-17% due to the reduction in the surface tension, while effective viscosity remained lower. All these results indicate that the variations in thermophysical properties dominate the bubble hydrodynamics, while the effects of boundary conditions remain almost the same for various temperature levels.