Numerical Simulation of Pool Boiling With Two-Fluid Model and Grid-Resolved Heat Transfer Mechanisms

Abstract Most nucleate boiling simulations are based on the Eulerian modelling of bulk liquid-vapour two-phase flow and subgrid presence of all mechanistically partitioned heat transfer modes in fluid control volumes in contact with the heated wall. Such mechanistic partitioning heat transfer approach predicts the total heat flux from the heated wall towards the boiling two-phase mixture as the sum of (i) the single-phase convection heat transfer from the heated wetted wall not covered with the rising bubbles, (ii) the transient conduction caused by the rewetting of the heated wall hot spot after the bubble detachment, known as quenching heat flux and (iii) the evaporation heat flux. Here presented research introduces a new approach to the numerical modelling of pool boiling based on the grid resolved mechanisms of boiling heat transfer. The spots of bubble growth and the wetted areas are distinguished and two grid resolved modes of heat transfer are considered: the conjugate heat transfer from the heated wall to the rising bubble at the bubble footprint until the bubble departure and the conjugate heat transfer from the heated wall to the wetting liquid. The constituents of the heat transfer model at the footprint of the bubble growth are the bubble residence time and the bubble departure diameter. The presented model is validated by experimental data from the literature. It was shown that the model can predict the wall temperature transient at bubble footprint location as well as the mean wall superheating. Appropriate modelling of vapour generation at the discrete locations of the bubble growth enables good prediction of two-phase mixture pattern in the boiling pool, the void fraction distribution along pool height and swell level position. Further analysis includes the application of both subgrid and grid resolved modelling approaches to the simulation of pool boiling under high heat fluxes. It is shown that the subgrid wall boiling model does not predict adequately the wall temperature transient behaviour and the void fraction distribution in the boiling pool under high heat fluxes, while the grid resolved model provides plausible results. Presented simulations are obtained with the in-house computer code based on the modified Semi-Implicit Method for Pressure Linked Equations (SIMPLE) for the solving of mass, momentum and energy balance equation for each phase and appropriate closure laws for the prediction of vapour-liquid interface transport phenomena.