Abstract
Abstract. In this study we describe and compare photometric and resistivity measurement methodologies to determine solute concentrations in porous media flow tank experiments. The first method is the photometric method, which directly relates digitally measured intensities of a tracer dye to solute concentrations, without first converting the intensities to optical densities. This enables an effective processing of a large number of images in order to compute concentration time series at various points of the flow tank and concentration contour lines. This paper investigates perturbations of the measurements; it was found both lens flare effects and image resolution were a major source of error. Attaching a mask minimizes the lens flare. The second method for in situ measurement of salt concentrations in porous media experiments is the resistivity method. The resistivity measurement system uses two different input voltages at gilded electrode sticks to enable the measurement of salt concentrations from 0 to 300 g/l. The method is highly precise and the major perturbations are caused by temperature changes, which can be controlled in the laboratory. The two measurement approaches are compared with regard to their usefulness in providing data for benchmark experiments aimed at improving process understanding and testing numerical codes. Due to the unknown measurement volume of the electrodes, we consider the image analysis method more appropriate for intermediate scale 2D laboratory benchmark experiments for the purpose of evaluating numerical codes.
Highlights
Laboratory experiments are an excellent way of providing data to develop transport theories and validate numerical codes
Oswald et al (1997) and Oswald and Kinzelbach (2004) used the nuclear magnetic resonance (NMR) technique to derive concentration distributions of 3D benchmark experiments for density dependent flow. This method is very precise but it is limited to small flow tank experiments due to the size of the NMR tomograph
Reflected light is used for image analysis in most intermediate scale experiments (e.g. Oostom et al, 1992; Swartz and Schwartz, 1998, Wildenschild and Jensen, 1999; Simmons et al, 2002; Rahman et al, 2005; McNeil et al, 2006; Goswami and Clement, 2007). The advantage of this technique is that it can be used with non-transparent porous media material, e.g., sand and with thick flow tanks that prevent light transmission
Summary
Laboratory experiments are an excellent way of providing data to develop transport theories and validate numerical codes. Reflected light is used for image analysis in most intermediate scale experiments (e.g. Oostom et al, 1992; Swartz and Schwartz, 1998, Wildenschild and Jensen, 1999; Simmons et al, 2002; Rahman et al, 2005; McNeil et al, 2006; Goswami and Clement, 2007) The advantage of this technique is that it can be used with non-transparent porous media material, e.g., sand and with thick flow tanks that prevent light transmission. As opposed to Schincariol et al (1993), Swartz and Schwartz (1998) and McNeil et al (2006) we relate linearly measured intensities directly to concentrations without standardization to optical densities to enable processing of a large number of images with the aim of deriving breakthrough curves of a high temporal resolution. Inflow/outflow opening, third phase of saltpool experiment Brine injection, first phase of saltpool experiment
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