Magnus Aa. Gjennestad successfully defends his PhD.

Magnus Aa. Gjennestad successfully defends his PhD Tuesday, the 24th of November, Magnus Aashammer Gjennestad successfully defends his PhD, entitled: “Modelling of two-phase equilibrium, stability and steady-state flow in porous media”. The opponents of the defence were Prof. Professor Rainer Helmig from the Universität Stuttgart in Germany, Professor Luis González Macdowell from the Universidad Complutense in Spain and Professor Ursula Gibson from NTNU. The administrator of the Committee was Professor Ursula Gibson from NTNU.

The thesis of Magnus concerns fundamental aspects of coexistence and flow of two fluid phases within porous media. Specifically, the focus has been on thermodynamic stability and equilibrium on the scale of a single pore and on macroscopic steady-state properties of immiscible two-phase flow. In the thesis, capillary models were derived for free and adsorbed droplets and bubbles, and thick films in a pore. The thermodynamic stability of these structures in a specific pore geometry was mapped out and the effect of pore size and the pore being open or closed w.r.t. exchange of particles with the surroundings is explored. Equilibrium structures were found. The thermodynamic stability of thin films with a disjoining pressure was also examined in open and closed systems. Numerical methods were presented in the thesis that enable stable and fast time integration of a pore network model. These eliminate previous problems with numerical instabilities observed at low capillary numbers. The new methods extend the range of capillary numbers for which the pore network model is a tractable alternative and enables e.g. future studies of Haines jumps in the low capillary number regime. The thesis also addresses the computational challenges associated with calculating the thermodynamic stability limits of multi-component mixtures and the identification of extrema as minima, maxima or saddle points in variational calculus.

I have had the pleasure to work with Magnus both in SINTEF before and after his PhD, and be one of the advisors of his thesis. His work establishes a solid foundation to build on to create a thermodynamic framework for the heterogeneous structures that exist in porous media. The defence was carried out interactively through Zoom, and a picture of Magnus, his advisors and the opponents can be found below.