An Experimental Investigation of the Motion of Gas-Liquid Displacement Interface in an Artificial Porous Medium

The study of flow and transport in porous media has relevance in many industrial, environmental (Geologic sequestration of CO2) and biological disciplines. In many engineering applications we require the knowledge of the velocity field for flow through porous objects. Historically, simplified models such as Darcy’s law [1,2], provide a reasonable description of the flow in the interior for single phase flow but require empirical coefficients to match the boundary conditions with the outer flow. The scientific basis for understanding flow and transport phenomena in porous media has largely been developed from experimental and theoretical studies in “bulk” or macroscopic systems in which coupled behavior at the pore scale is not measured or observed directly. To understand the flow behavior at the pore scale, flow characterization in porous media is very important. Multiphase, immiscible, low Re flow through a simulated porous media is studied experimentally. The experimental test cell, Figure 1, designed in collaboration with the Department of Energy, National Energy Technology Laboratory (DOE NETL), was manufactured from an optically clear polycarbonate material. It has a lattice type pattern of 2.5 mm pores bodies interconnected by angular capillary throats varying in size from 200 μm to 1000 μm. The experimental flow loop (Figure 2), utilizes air as the displacing fluid and sodium iodide (NaI) solution in water as the defending fluid. Air is provided at a constant pressure at the inlet. The refractive indices of the NaI solution and the optically clear test cell are matched to facilitate the observance of the air-liquid interface motion. Experimental data recorded with respect to time are the inlet gage pressure, delta pressure, inlet to outlet, across the test cell, volume flow rate at the outlet and the position of the displacement interface as the invading fluid, air, displaces the defending fluid, NaI solution. Parameters that can be varied in the experiment are viscosity ratio, micro and macro capillary number, the bond number and the volume flow rate. The details of the test loop are provided in Figure 2. The figure shows the piping arrangement to fill the test cell with the NaI solution and supplying the air for the tests. A CCD camera (Redlake ES 1.0 cross-correlation camera; resolution: 1008 × 1018 pixels) equipped with a 20 mm Micro Nikkor lens (Nikon) and a data acquisition system consisting of a PC and a PIXCI D2X frame grabber card (EPIX) is utilized to obtain a series of digital images as the invading air enters the test cell through the inlet manifold and makes way through the liquid until the breakthrough to the exit manifold. The pore scale velocity of the displacement interface is determined using a “Difference Threshold Technique” developed at Case Western Reserve University (CWRU), Laser Flow Diagnostics Lab (LFDL), Department of Mechanical and Aerospace Engineering. The difference threshold technique developed to processing the images is described in the next section.