Neutron tomography of axisymmetric flow fields in porous media

A significant problem in the study of fluid transport in porous media is the ability to visualize the structure of the flow field when moisture contents vary rapidly in space and time. Here we present a method for determining the radial and vertical saturation profiles within axisymmetric preferential flow fields using neutron radiography. Flow fields such as these are surprisingly common in nature and determining the three-dimensional structure of their wetting front region has proven difficult. In this work, the moisture profiles are determined using a simple algorithm for algebraic computed tomography, which gives the three-dimensional structure of the moisture profile with a temporal resolution that is limited only by the desired noise level. The algorithm presented can be translated to radiography done using X-rays or light and is applicable to any rotationally symmetric object.

► An algorithm that can perform rapid tomography on axisymmetric flow fields.
► First 3-D reconstruction of the wetting front of a preferential flow field.
► Reconstructions are 10 second averages of the flow field.
► Advances the application of neutron radiography to study of fluid transport.