Using optical index matching to visualize solute transport and perform particle tracking in a synthetic porous medium
Abstract
Optical visualization techniques are heavily used in experimental fluid mechanics. In flow studies addressing natural objects (fractured or porous rocks), they are difficult to utilize as they often require transparent solid objects. Even if the solid objects in the experimental setup happen to be transparent to light, the existence of complex boundaries between the fluid and the surrounding solid phase leads to distorsion of the images through light refraction at the interfaces, unless the solid and fluid are nearly perfectly matched in optical index. This is in particularly true for porous media, due to the many optical interfaces present in the system. We present here an experimental setup addressing the visualization of solute transport and particle advection in a synthetic porous medium consisting of glass beads. The fluid is a mixture of benzol and ethanol mixed in a proportion that ensures a good an optical index matching as possible between the fluid and the beads. At fluid preparation, we monitor the index matching by measuring the transmission of a laser beam through a box containing a sample porous medium. The matched fluid allows monitoring of solute dispersion inside the porous medium. The influence of the index mismatch on the uncertainty of the measurements has been estimated using available theories. Successful attempts at tracking colloidal particles advected inside the porous medium are also presented. The simple tracking algorithm requires that particles not too close to each other be monitored at a large enough acquisition frequency For analog experiments in which a transparent porous medium can be used, this technique can be a reasonable choice with respect to more elaborate and expensive techniques such as X-ray tomography or MRI.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- Bibcode:
- 2007AGUFM.H53E1467M
- Keywords:
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- 1895 Instruments and techniques: monitoring