Pool Boiling: Water around an Horizontal Tube

Pool Boiling of Water around Horizontal Tube, CFD Simulation, ANSYS Fluent

Description

Pool boiling is one of the most important processes occurring across a wide range of small- and large-scale industries, from petrochemical plants to gas refineries and pharmaceutical manufacturing. This project simulates pool boiling around a cylindrical heater positioned within a rectangular pool filled with water — the heater causes water molecules near its surface to boil and transition into the vapor phase.

The geometry was built in SpaceClaim, with ANSYS Meshing used to generate a fine mesh grid totaling 92,151 cells.

Methodology

While several existing studies examine pool boiling under steady or pseudo-steady conditions, this project focuses specifically on transient pool boiling, aiming to capture and track individual vapor bubbles as they form and rise. The Eulerian multiphase model was used to represent the liquid water phase and the vapor bubble phase, incorporating drag, lift, wall lubrication, turbulent dispersion, turbulent interaction, virtual mass, and surface tension forces — all defined using correlations established in the literature.

Turbulent behavior around the bubble formation region near the cylindrical heater was captured using the Realizable k-epsilon model. The domain walls were treated as thermally insulated, while the cylindrical heater surface itself was maintained at 107°C to drive boiling in water initially at 100°C. An adaptive time step was used, with a minimum step of 10⁻⁵ s and an initial step of 10⁻⁴ s.

Conclusion

The results confirm that this simulation accurately captures bubble formation and rise, closely matching behavior observed in experimental studies. As expected, velocity and vapor volume fraction contours show bubbles forming within a thin layer surrounding the cylinder before rising toward the pool surface.

Heat flux and heat transfer coefficient contours further reveal a substantial flux generated at the heater wall, with a significant amount of heat escaping from the heater into the surrounding water. The simulation ultimately predicted a heat transfer coefficient of 1322 W/m²·K and a heater wall heat flux of 9055 W/m², quantifying the pool boiling heat transfer performance captured in this study.