Mass transfer correlation for nonaqueous phase liquid volatilization in porous media

To investigate the Nonaqueous Phase Liquid (NAPL)vapor phase mass transfer, a series of NAPL volatilization experiments was carried out using toluene as the contaminant. Three sizes of glass beads and a medium silica sand were selected as the porous media. Experiments were performed for a NAPL saturation range of 13.871% and a pore gas velocity in the range of 0.1-2 cm/s. Previously, the interphase mass transfer process was characterized as a lumped parameter together with the interfacial area between the phases because of the complexity of the porous medium and the NAPL morphology. In this paper, actual vapor phase mass transfer was evaluated using the corresponding air-liquid interfacial area. The value of air-liquid interfacial area was calculated following the procedure presented in our previous studies. An empirical correlation for the actual NAPL-vapor phase mass transfer process was developed statistically for the variable zone of NAPL saturation, and the model showed that the interphase mass transfer is inversely related to the volumetric NAPL content and highly sensitive to the flow dynamics of the system. The correlation developed in this study may be useful for engineering computations concerning soil vapor extraction (SVE) of unsaturated sandy soil for higher range of NAPL saturation. Since the study was carried out only in the laboratory scale, further study needs to extend to a real contaminated site.