A. Ahmadi et al., Calculation of the effective properties describing active dispersion in porous media: from simple to complex unit cells, ADV WATER R, 24(3-4), 2001, pp. 423-438
Dissolution of a trapped non-aqueous phase liquid (NAPL) in soils and aquif
ers is a matter of great interest for the remediation of contaminated geolo
gical structures. In this work, the Volume Averaging Method is used to upsc
ale the "active dispersion" phenomenon, taking into account both dispersion
and dissolution of the NAPL. The method provides a macroscopic equation in
volving a dispersion tensor, additional convective terms and a linear form
for the interfacial mass flux. These "effective properties" are related to
the pore-scale physics through closure problems. These closure problems are
solved over periodic unit cells representative of the porous structure. Tw
o alternative approaches are considered. The first involves a finite volume
formulation of the closure problems and therefore a detailed discretisatio
n of the pore structure. The second is based on a "network modeling" of the
pore space and appears as a natural alternative for overcoming the limitat
ions of the first approach (simple unit cells containing a small number of
pores). The two approaches are presented and the influence of NAPL volume f
raction and the orientation of the average velocity field are studied in te
rms of the Peclet number for simple unit cells and more complex ones contai
ning a thousand pores. (C) 2001 Elsevier Science Ltd. All rights reserved.