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Measurement of fluid contents and wetting front profiles by real-time neutron radiography
Authors:M R Deinert  J -Y Parlange  T Steenhuis  J Throop  K Ünlü  K B Cady  
Institution:

a Nuclear Science and Engineering, Cornell University, Ithaca, NY 14853, USA

b Biological and Environmental Engineering, Cornell University, Ithaca, NY 14853, USA

c Mechanical and Nuclear Engineering, Pennsylvania State University, College Station, PA, 16802-1412, USA

d Theoretical and Applied Mechanics, Cornell University, 219 Kimball Hall, Ithaca, NY 14853, USA

Abstract:Few methods exist for measuring rapidly changing fluid contents at the pore scale that simultaneously allow whole flow field visualization. We present a method for using real-time neutron radiography to measure rapidly changing moisture profiles in porous media. The imaging technique monitors the attenuation of a thermal neutron beam as it traverses a flow field and provides measurements every 30 ms with an image area >410 cm2 and a spatial resolution not, vert, similar0.05 cm. The technique is illustrated by measuring the variation in moisture content across a wetting front moving at constant velocity through SiO2 sand. The relative contributions of the hydraulic conductivity and diffusivity terms in Richards' equation to the total fluid flux within the wetting front region were also measured. The diffusivity was found to rise from zero to a peak value within the wetting front region before falling off while the conductivity was found to rise monotonically. The reliability of the technique was checked via mass balance.
Keywords:Author Keywords: Transient flow  Wetting front  Real-time neutron radiography  Diffusivity  Image analysis  Fingered flow
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