Heap leaching is a process extensively used by the mining industry to recover metals from low-grade ores and large quantities of submarginal material resources. Understanding flow through a packed particle bed is important to enhance the performance of heap leaching with respect to design and operating considerations. Complex fluid behavior in porous media, such as film flow, fragmentation, coalescence of droplets, and rivulet flow with or without meandering, has been widely observed in laboratory experiments. In this study, to provide detailed information of momentum and mass transfer phenomena in a granular bed direct numerical simulations (DNS) were performed. In this case the liquid-gas flow through a granular bed was considered comprised of monosized, spherical, solid particles arranged randomly in a cylindrical container. The volume of fluid (VOF) method was used to compute velocity field as well as liquid volume fraction distributions in the container. The results obtained suggest that the liquid phase distribution in the bed is mainly controlled by surface tension and particle induced turbulence appears to have insignificant effects. These results allow us to obtain a better understanding of the fundamental physics governing unsaturated fluid flow. This finding seems to have a significant impact in the design of efficient multi-phase reactors for heap leaching and bioleaching processes. (c) 2006 Elsevier Ltd. All rights reserved.