February 26, 2021
16:30
Pour l’obtention du grade de Docteur en sciences de l’ingénieur et technologie
This thesis is a numerical study of turbulent thermal convection driven by free-surface evaporation in water pools. The studied physical phenomenon is closely related to the flow occurring in the early stages of a spent-fuel pool (SFP) loss-of-cooling accident (LOCA), such as that which occurred at Fukushima 2011. Here, the important interdependent physical phenomena are free-surface evaporation and turbulent thermal convection.
First, a configuration similar to turbulent Rayleigh-Bénard Convection (RBC) is investigated, but with a free-slip upper boundary condition approximating a free surface. Fixed temperature, boundary conditions are applied above and below, and the role of the free-slip and non-Oberbeck-Boussinesq effects on the mean flow properties are investigated. The free-slip is shown to play an important role on heat transfer in the domain and on the homogeneity of the thermal boundary layer heights.
Secondly, a representative evaporative heat flux is then prescribed uniformly as the thermal boundary condition above. Time-averaged properties of the flow, are shown to be influenced by the presence of the free surface and a novel Rayleigh number scaling of the Nusselt number is found. The latter shows a remarkably similar exponent to that of turbulent RBC, but where an increased prefactor accounts for the shear-free boundary.
Finally, a novel dynamic thermal boundary condition based on evaporative and convective heat losses at a free surface is developed and implemented and the role of aspect ratio on the large-scale circulation (LSC) state is investigated. The LSC is shown to switch from a stable single-roll, to a dual-roll state, changing the temperature and velocity fields at the free surface. However, no discernible impact on the evaporation rate is found. The results of this thesis are useful both academically and in industry with respect to the modelling of the early stages of an SFP-LOCA with system codes.
Jury members :
- Prof. Miltiadis Papalexandris (UCLouvain), supervisor
- Prof. Laurent Delannay (UCLouvain), chairperson
- Prof. Juray De Wilde (UCLouvain), secretary
- Prof. Laurence Rongy (ULB, Belgium)
- Dr. Vincent Deledicque (Bel V, Belgium)
- Dr. Holger Grosshans (National Metrology Institute, Germany)
Pay attention :
The public defense of William Hay scheduled for Friday 26 February at 16:30 will take place in the form of a video conference Teams