11 - Isothermal nucleation and bubble growth in porous media at low supersaturations

Abstract

This chapter presents the nucleation and growth of bubbles in porous media, which are the problems encountered in processes such as pressure depletion and boiling. of the chapter describes the basic principles of nucleation and bubble growth in the bulk, some of the results obtained in past within the framework of percolation and pore network models are discussed. In particular, results of experiments of liquid-to-gas phase change by pressure decline of supersaturated CO2 solutions in 2D transparent etched networks are reported in order to understand the phenomena in porous media. The observations confirm the heterogeneous nature of nucleation, that is, the decisive role of the capillary roughness of the pore walls. Contrary to the bulk or Hele-Shaw cells, gas clusters have irregular and ramified shapes typical of invasion percolation patterns. As a result, the growth rate of a single gas cluster is different than the growth rate of an isolated single bubble in the bulk. Numerical simulations of the growth pattern and of the growth rate of a single gas cluster are performed with a numerical automaton. Based on a pore network modeling technique and on a set of hypotheses derived from the observations, this automaton is first validated by comparing the numerical results with the experimental data. Then the automaton is used to explore the influences of the Jakob number, pressure decline rate, bond number, and wettability. The closure of the macroscopic mass balance equations is discussed. The chapter briefly describes the phenomenology of nucleation process and presents the particular aspects of the phenomenon in porous media.