Unconfined Pool Boiling ANSYS Fluent Tutorial

Description

This project investigates the saturated water pool boiling inside a cylindrical chamber. Pool boiling is defined as boiling from a hot surface immersed in a large volume of stagnant liquid. The liquid may be at its boiling point, in which case the term saturated pool boiling is used, or below its boiling point which is called subcooled pool boiling.

The motion of the liquid induced by the boiling process and the velocities are assumed to be low in academic experimental applications where conditions such as ONB (Onset of Nucleate Boiling), DNB (Departure from Nucleate Boiling), and CHF (Critical Heat Flux) are examined. However, pool boiling is unusual in industrial equipment and applications where extreme conditions such as burnout may occur.

The geometry of the present project is designed in Design Modeler and meshed in ANSYS Meshing software. The mesh type is structured and the element number is equal to 8,750.

Unconfined Pool Boiling Methodology

The Eulerian multiphase model was used in this project to simulate the pool boiling inside the mentioned chamber. The RPI boiling sub-model is enabled and different forces including drag, lift, wall lubrication, turbulent dispersion, along with virtual mass force are enabled. Also, wall adhesion option is enabled to model the vapor bubbles detachment realistically.

Boiling mass transfer mechanism is also activated and appropriate correlations are used for bubble departure diameter, frequency of bubble departure, nucleation site density, and area influence coefficient. Moreover, the bubble waiting time coefficient for the quenching model correction was set to 0.5.

Furthermore, energy equation is enabled to calculate the temperature change inside the domain. Also, realizable k-epsilon model is used to solve for the turbulent fluid equations. The present study is performed in steady format and 2D axisymmetric model is used to simulate the problem inside a cylindrical coordinate.

Gravity is also enabled to induce the upward motion of vapor due to the density difference. This difference exists between water and vapor.

Conclusion

Finally, the results related to the boiling process is obtained and presented. As seen in the volume fraction contour for the vapor phase, vapor tends to move upward. This motion causes a convective motion inside the water culminating in multiple nucleation sites.

Moreover, it can be easily seen that how the shapes of generated bubbles change. Also, its visible how they exchange mass with the surrounding water (condensation) as they ascend toward the outlet.