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Effective Darcy‐scale contact angles in porous media imbibing solutions of various surface tensions
Author(s) -
Weisbrod Noam,
McGinnis Thomas,
Rockhold Mark L.,
Niemet Michael R.,
Selker John S.
Publication year - 2009
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2008wr006957
Subject(s) - imbibition , contact angle , surface tension , porous medium , materials science , distilled water , infiltration (hvac) , wetting , salinity , porosity , geotechnical engineering , mechanics , soil science , mineralogy , chemistry , composite material , thermodynamics , environmental science , geology , chromatography , physics , botany , germination , oceanography , biology
Surface tensions of high‐salinity solutions are significantly different from those of pure water. Our objective was to develop and test a methodology to determine whether these surface tension effects predictably alter imbibition into dry and moist porous media. Static and dynamic experiments were performed using four grades of quartz sand to determine the effects of solution salinity on imbibition. Results were quantified as apparent contact angles between the sand and three solutions (pure water, 5 molal NaNO 3 , and n‐hexane). Contact angles determined using a static method in initially air dried sand ranged from 23° to 31°, with the same values found for both water and the NaNO 3 solution. Effective contact angles determined for the air‐dried sand using a dynamic method based on a modified version of the Green and Ampt model were about twice those found using the static method, averaging 45° and 62° for water and the NaNO 3 solution, respectively. In prewetted sands, the dynamic imbibition data yielded apparent contact angles of 2° and 21° for water and the NaNO 3 solution, respectively, with the latter value comparing well to a predicted value of 25° for the NaNO 3 solution solely on the basis of surface tension contrast. The results of this study indicate that on the Darcy scale, saline solutions appear to follow the relationship of nonzero contact angles with other miscible fluids of different surface tensions used to prewet the sand grains, in agreement with the macroscale infiltration results of Weisbrod et al. (2004).