CFD analysis of bubble microlayer and growth in subcooled flow boiling

• A new LES-microlayer model is introduced.
• Analogous to the unresolved SGS in LES, analysis of bubble microlayer was performed.
• The thickness of bubble microlayer was computed at both steady and transient states.
• The macroscale two-phase behavior was captured with VOF coupled with AMR.
• Numerical validations were performed for both the micro- and macro-region analyses.

A numerical study of single bubble growth in turbulent subcooled flow boiling was carried out. The macro- and micro-regions of the bubble were analyzed by introducing a LES-microlayer model. Analogous to the unresolved sub-grid scale (SGS) in LES, a microlayer analysis was performed to capture the unresolved thermal scales for the micro-region heat transfer by deriving equations for the microlayer thickness at steady and transient states. The phase change at the macro-region was based on Volume-of-Fluid (VOF) interface tracking method coupled with adaptive mesh refinement (AMR). Large Eddy Simulation (LES) was used to model the turbulence characteristics. The numerical model was validated with multiple experimental data from the open literature. This study includes parametric variations that cover the operating conditions of boiling water reactor (BWR) and pressurized water reactor (PWR). The numerical model was used to study the microlayer thickness, growth rate, dynamics, and distortion of the bubble.