Session: 08-11: Computational Fluid Dynamics (CFD) and Applications - XI

Paper Number: 136496

136496 - Numerical Simulation of Pool Boiling With Two-Fluid and Grid-Resolved Wall Model 

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. Hence, the presented new grid resolved model of pool boiling is especially useful for the prediction of pool boiling under high heat fluxes and critical heat flux conditions pertinent to the cooling of nuclear fuel elements. Examples of critical heat flux predictions on the heated flat surfaces are presented too. Presented simulations are obtained with the in-house computer code based on the modified Semi-Implicit Method for Pressure Linked Equations (SIMPLE) type numerical method 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.    

Presenting Author: Milan Petrovic University of Belgrade, Faculty of Mechanical Engineering

Presenting Author Biography: Dr Milan M. Petrovic, research associate, studied at the Faculty of Mechanical Engineering; University of Belgrade and obtained BSc, MSc and PhD degrees respectively in 2010, 2012 and 2021. He has been employed at the Faculty of Mechanical Engineering; University of Belgrade as a research assistant from 2013 to 2021 and as a research associate from 2021 till now. The research field of Dr Petrovic involves modelling of various thermal-hydraulics processes in thermal power plants, such as: pool and flow boiling in energetic equipment, steam accumulation systems, two-phase transport in pneumatic conveying systems and flue gas desulphurization. Dr Petrovic is the author of 11 papers published in leading international journals, several papers in proceedings of international conferences and one patent.

Authors:

Milan Petrovic University of Belgrade, Faculty of Mechanical Engineering
Vladimir Stevanovic University of Belgrade
Milica Ilic University of Belgrade, Innovation Centre of the Faculty of Mechanical Engineering
Sanja Milivojevic University of Belgrade, Faculty of Mechanical Engineering