On the measurement of solute concentrations in 2-D flow tank experiments

摘要

In this study we describe and compare photometric and resistivitymeasurement methodologies to determine solute concentrations in porous mediaflow tank experiments. The first method is the photometric method, whichdirectly relates digitally measured intensities of a tracer dye to soluteconcentrations, without first converting the intensities to opticaldensities. This enables an effective processing of a large number of imagesin order to compute concentration time series at various points of the flowtank and concentration contour lines. This paper investigates perturbationsof the measurements; it was found both lens flare effects and imageresolution were a major source of error. Attaching a mask minimizes the lensflare. The second method for in situ measurement of salt concentrations inporous media experiments is the resistivity method. The resistivitymeasurement system uses two different input voltages at gilded electrodesticks to enable the measurement of salt concentrations from 0 to 300 g/l.The method is highly precise and the major perturbations are caused bytemperature changes, which can be controlled in the laboratory. The twomeasurement approaches are compared with regard to their usefulness inproviding data for benchmark experiments aimed at improving processunderstanding and testing numerical codes. Due to the unknown measurementvolume of the electrodes, we consider the image analysis method moreappropriate for intermediate scale 2D laboratory benchmark experiments forthe purpose of evaluating numerical codes.