Analysis of wall nucleation modeling for flow boiling in fluent

Understanding and predicting the process of wall nucleation are of great significance in numerical simulation of subcooled boiling flow since wall nucleation parameters partially constitute the boundary conditions of the vapor phase. However, in previous work, sensitivity study of wall nucleation models on prediction of two-phase transport in boiling flow is limited. Simulations using ANSYS Fluent bundled in ANSYS® Academic Student, release 18.2, were performed for an internally heated annulus channel and compared against existing data. Modeling of wall nucleation characteristics in forced convective boiling flow has been plagued by large uncertainty. However, new modeling has been shown to capture a wide range of system conditions and was developed against data taken in the same annulus test facility as the two-phase transport data. However, by implementing the improved nucleation modeling, significant under-predictions of void fraction is found at elevated pressure. To improve the prediction of void fraction profiles, large evaporation heat flux through inaccurate wall nucleation parameters is shown to be needed. This work suggests that the contribution of wall nucleation to the void fraction is overemphasized by the default net vapor generation modeling in Fluent. Other important modeling and parameter sensitivities are studied to isolate this issue in the nucleation dependence.