Measured Mass Transfer Coefficients in Porous Media Using Specific Interfacial Area

Bulk and intrinsic mass transfer processes across interfaces between nonaqueous phase liquids (NAPLs) and water were studied in water-saturated columns. Columns packed with different grain sizes of sand were used to create various NAPL-water interfacial areas along with different NAPL saturations. The intrinsic mass transfer coefficients were estimated from the bulk mass transfer coefficients, and the specific interfacial areas were measured using tracer studies. The bulk mass transfer coefficients increased with increasing NAPL-water specific interfacial area as well as NAPL saturation and pore velocity and with decreasing grain sizes. Moreover, the bulk mass transfer coefficients were correlated with NAPL-water specific interfacial area rather than NAPL saturation and were more sensitive at high NAPL-water interfacial areas than at low interfacial areas. In contrast, the intrinsic mass transfer coefficients were nearly independent of specific interfacial area and NAPL saturation but dependent on pore velocity. Reduction of NAPL saturation by dissolution caused a linear decrease in the bulk mass transfer coefficients.