Skip to main content
NCBI home page
NIHPA Author Manuscripts logoLink to NIHPA Author Manuscripts
. Author manuscript; available in PMC: 2018 Nov 1.
Published in final edited form as: Water Resour Res. 2017 Oct 26;53(11):9519–9527. doi: 10.1002/2017WR021717

The Gas-absorption/Chemical-reaction Method for Measuring Air-water Interfacial Area in Natural Porous Media

Ying Lyu 1,2,3,4, Mark L Brusseau 4,5,*, Asma El Ouni 4, Juliana B Araujo 4, Xiaosi Su 3,6
PMCID: PMC5898451  NIHMSID: NIHMS929442  PMID: 29662253

Abstract

The gas-absorption/chemical-reaction (GACR) method used in Chemical Engineering to quantify gas-liquid interfacial area in reactor systems is adapted for the first time to measure the effective air-water interfacial area of natural porous media. Experiments were conducted with the GACR method, and two standard methods (x-ray microtomographic imaging and interfacial partitioning tracer tests) for comparison, using model glass beads and a natural sand. The results of a series of experiments conducted under identical conditions demonstrated that the GACR method exhibited excellent repeatability for maintaining constant water saturation and for measurement of interfacial area (Aia). Coefficients of variation for Aia were 3.5% for the glass beads and 11% for the sand. Estimated maximum interfacial areas (Am) obtained with the GACR method were statistically identical to independent measures of the specific solid surface areas of the media. For example, the Am for the glass beads is 29 (±1) cm−1, compared to 32 (±3), 30 (±2), and 31 (±2) cm−1 determined from geometric calculation, N2/BET measurement, and microtomographic measurement, respectively. This indicates that the method produced accurate measures of interfacial area. Interfacial areas determined with the GACR method were similar to those obtained with the standard methods. For example, Aias of 47 and 44 cm−1 were measured with the GACR and XMT methods, respectively, for the sand at a water saturation of 0.57. The results of the study indicate that the GACR method is a viable alternative for measuring air-water interfacial areas. The method is relatively quick, inexpensive, and requires no specialized instrumentation compared to the standard methods.

Keywords: gas absorption, interfacial area, fluid-fluid interface

Introduction

It is well established that the air-water interface is critically important for numerous applications in environmental, geologic, and hydrologic systems, given its influence on fluid flow, contaminant transport, and mass and energy transfer. For example, fluid-fluid interfacial area is a fundamental variable necessary to describe and quantify pore-scale fluid configuration and flow in multiphase systems (e.g., Brusseau et al., 2006; Dalla et al., 2002; Gray and Hassanizadeh, 1991; Hassanizadeh and Gray, 1993; Joekar-Niasar and Hassanizadeh, 2012; Reeves and Celia, 1996). In addition, adsorption at the air–water interface can have a major impact on the retention of chemical contaminants and colloids for contaminant transport, water treatment, and subsurface remediation applications (e.g., Costanza and Brusseau, 2000; Fang et al., 2013; Wang et al., 2016; Zevi et al., 2012). The fluid-fluid interface is also critical for mass and energy transfers, such as evaporation, volatilization, gas exchange, and heat flow.

The significance of fluid-fluid interfacial area for porous-media systems has driven the development and application of methods for its characterization and quantification. The methods available to measure fluid-fluid interfacial area in natural porous media include mass-balance tracer tests (Anwar et al., 2000, 2001; Araujo et al., 2015; Karkare and Fort, 1996; Schaefer et al., 2000), aqueous and gas-phase interfacial partitioning tracer tests (Brusseau et al., 1997, 2006, 2007, 2008, 2010, 2015; Cho and Annable, 2005; Costanza and Brusseau, 2002; Dobson et al., 2006; Jain et al., 2003; Kim et al., 1997, 1999; McDonald et al., 2016; Narter and Brusseau, 2010; Peng and Brusseau, 2005; Saripalli et al., 1997, 1998; Zhong et al., 2016), and pore-scale imaging (Al-Raoush, 2009; Al-Raoush and Willson, 2005; Brusseau et al., 2006, 2007, 2008, 2009; Costanza-Robinson et al., 2008; Culligan et al., 2004, 2006; Ghosh and Tick, 2013; McDonald et al., 2016; Porter et al., 2010; Prodanovic et al., 2006; Schnaar and Brusseau, 2005, 2006a, 2006b). Each of the methods has certain constraints that can complicate their use. For example, high-resolution imaging methods require access to specialty instrumentation and the application of complex image-processing tools. The aqueous tracer-based methods typically employ surfactant compounds as interface tracers, which in some cases can have deleterious impacts on measurements. These impacts can be ameliorated with thorough experimental control, but tracer-based methods are also typically relatively time consuming.

The effective gas-liquid interfacial area, through its control of mass transfer and chemical reaction rates, is a fundamental parameter for the design and operation of reactor systems used in many chemical engineering applications. A standard method developed in chemical engineering to measure gas-liquid interfacial area is based on absorption of a gaseous compound that can undergo chemical reaction in liquid solution. This method is referred to as the gas-absorption/chemical-reaction (GACR) method. A widely used reaction system for the GACR method is CO2-NaOH. This method has been applied to numerous types of reactors, including rotating bed (Luo et al., 2012; Tsai and Chen, 2015; Yang et al., 2011), packed column (Kolev et al., 2006; Pubanik and Vogelpohl, 1974), stirred cell (van Woezik and Westerterp, 2000), and bubble column (Maceiras et al., 2010). These reactor systems typically have extremely high porosities (> 90%) due to the use of structured packing media such as stainless steel wire mesh, Rachel rings, Pall rings, etc that are designed to provide large surface area for gas-liquid contact.

The objective of this study is to adapt the GACR method for novel application to natural geomedia in environmental systems, which have much lower porosities compared to the chemical-engineering systems for which the method was originally designed. Column experiments are conducted using model glass beads and a natural sand to determine if this method can produce accurate and robust measurements of air-water interfacial area for geomedia. Interfacial areas are also measured using interfacial partitioning tracer tests (IPTT) and x-ray microtomography (XMT), two standard methods, to allow comparison of results.

Materials and Methods

GACR Theory

The system comprises a gas containing a constituent that can react with a reagent present in a gas-immiscible liquid, wherein the liquid-phase reagent is insoluble in the gas. The amount of gas constituent that transfers into the liquid (absorption) is a function of the gas-liquid interfacial area, the mass-transfer properties, and the rate of the reaction. If the reaction rate is sufficiently fast, the gas constituent will be consumed immediately upon transfer into the liquid (i.e., at the liquid side of the gas-liquid interface), with no additional reaction within the bulk liquid. Under this condition, the depletion of the gas constituent from the gas phase (and the generation of the reaction product in solution) is proportional to the magnitude of fluid-fluid interfacial area, thus providing a means for the latter’s determination.

The NaOH–CO2 system was used in this study because of its simple and well-described reaction kinetics and readily available equilibrium data (e.g., Svoboda and Rylek, 1979):

2NaOH+CO2=Na2CO3+H2O (1)

Reaction (1) can be treated as a pseudo first-order reaction when there is minimal change in the concentration of OH− in solution (NaOH is in excess), the condition for which is described by the following inequality (Sharma and Danckwerts, 1970):

Dk2cOHkL2<1+cOH2Ci (2)

where D is the diffusion coefficient of CO2 in solution (m2/s), k2 is the second-order rate constant between CO2 and OH− (m3/kmol·s), kL is the liquid side mass transfer coefficient (m/s), cOH is concentration of OH− in solution (kmol/m3), and ci is concentration of CO2 at the gas–liquid interface (kmol/m3), and is assumed to be in equilibrium with the bulk gas phase.

The absorption rate, Ra (kmol/s) can be expressed as equation (3) according to Danckwerts’ mass-transfer model (Sharma and Danckwerts, 1970):

Ra=AciDk2cOH+kL2 (3)

where A is the total interfacial area in the packed column (m2). The absorption rate Ra can be determined from the formation rate of Na2CO3 (e.g., Kasturi and Stepanek, 1974; Yang et al., 2011), with the concentration of Na2CO3 in the effluent solution measured by titration. When the inequality (4) is satisfied,

Dk2cOHkL2>3 (4)

the chemical reaction is sufficiently rapid such that it is not sensitive to kL (Sharma and Danckwerts, 1970; Mohanty et al., 2007), and the kL2 term in equation 3 can be ignored. With this consideration, and introducing the pseudo first-order rate coefficient, k1 (= k2cOH), the absorption rate can be expressed as:

Ra=AciDk1 (5)

The procedure for determining A first involves measuring Ra from the GACR experiment, as noted above. Equation 5 is then solved for A, with values for D, k1, and ci determined as described in the Supplemental Materials. The effective volume-normalized specific gas-liquid interfacial area (in our case, air-water interfacial area) in the system is determined as Aia = A/V, where Aia has units of m−1, V is the volume of the packing (m3), and A is obtained from Equation (5).

The theoretical maximum specific interfacial area can be calculated from Am = Aia/(1−Sw), where Sw is water saturation (Brusseau et al., 2007, 2008). Aia values obtained with each of the measurement methods can be used to estimate Am values with the corresponding Sws. The Am represents the theoretical maximum specific interfacial area associated with conditions of vanishing small Sw, wherein the remaining water exists as a thin film (equivalent to single molecule thickness) solvating the solid surface. Under this condition, the air-water interfacial area approaches a value nearly identical to the specific solid surface area. Hence, the Am can be compared to measures of the specific solid surface area to evaluate the robustness of measured interfacial areas (Brusseau et al., 2007, 2008). The Am values obtained in this manner are estimates, whose representativeness of the true maximum depends on system conditions (e.g., linearity of the interfacial area – fluid saturation function).

The geometric specific solid surface area (GSA) for a porous-medium pack can be calculated as GSA = 6(1−n)/d, where n is porosity and d is median grain diameter (L). Solid surface areas were measured using the standard nitrogen/Brunauer-Emmett-Teller (N2/BET) method (Pharmaceopeia, 2017). Solid surface areas were also measured by direct XMT analysis of the solids (methods used for XMT are presented in the SM).

Materials

Two porous media were used for the experiments. The relevant physical properties of the porous media are presented in Table 1. The first is an ideal glass-bead medium with a particle diameter of 1.16 mm. These beads have smooth surfaces, as illustrated by the concordance of specific solid surface areas determined with N2/BET measurement and geometric calculation. The second is a 45/50 mesh natural quartz sand with a median diameter of 0.35 mm. This medium has significant microscopic surface roughness, denoted by the significantly larger N2/BET solid surface area compared to the calculated geometric area. All of the chemicals used in this study were analytical grade and all solutions were prepared with ultra-pure water. The theory supporting the application of the GACR method is presented in the following section, followed by the methods used for the experiments.

Table 1.

Properties of the porous media.

Item Value
Packing media Glass beads Sand
Diameter of packed porous medium, mm 1.16 0.35
Porosity of packed porous medium 0.38 0.35
Particle density of porous media, g/cm3 2.20 2.64
Bulk density of packed porous media, g/cm3 1.41 1.71
Open in a new tab

Bulk density ρb = Total packing mass/Total packing volume

Methods

The apparatus used for the GACR method is shown in Figure SM1. The column used for the GACR experiments was constructed of polypropylene with dimensions of 1.4 cm inner diameter and 7 cm length. The column was oriented vertically for all experiments. Flow distributors were placed in contact with the porous media on the top and at the bottom of the column to help promote uniform fluid distribution and to support the media. A separator was placed at the bottom of the column to facilitate separation of the gas and solution. Effluent gas samples were collected from the outlet into a sealed conical flask, and liquid effluent samples were collected into 50 mL vials.

The column was dry packed and weighed to determine the bulk density of the packed porous medium. The pack was then saturated with water to gravimetrically determine porosity. Water was injected at a low flow rate during saturation to attempt to minimize trapped air. Results of our prior work have demonstrated that there is minimal trapped air, particularly for these coarse media (Brusseau et al., 2008). Gas was then injected briefly at the top of the column using a high flow rate to drain the pack to the target water saturation of 0.43 and 0.57 for the glass beads and sand, respectively. Any intraparticle microporosity possessed by the media is anticipated to be water-filled at these and much lower water saturations, and thus not a factor in characterizing interfacial area. The NaOH solution was injected at the top of the column at a steady flow rate (~14 mL/min) to initiate the GACR test. The concentration of NaOH in the injected solution was constant at ~1.5 M for each experiment. Concurrently, gas containing 4.6% CO2 (in a balance of nitrogen) was injected at the top of the column. Concurrent liquid and gas flow as opposed to countercurrent flow was used due to the low porosity of the porous media.

The NaOH concentration, solution temperature, CO2 concentration, and gas pressure were measured prior to entry of the fluids into the column. Liquid and gas effluent samples were collected every 5 minutes to determine the concentrations of NaOH and Na2CO3 in solution and the concentration of CO2 in the gas. Samples were collected until the effluent concentrations of all constituents were steady. The packed column was flushed with pure water after each experiment until constituent concentrations in the effluent solution were below detection.

The concentration of CO2 was measured using a CO2 analyzer (Smart Bell plus, UEI Test Instrument Company, USA). Gas pressure was measured with a static pressure meter (EM201SPKIT, UEI Test Instrument Company, USA). The gas flow rate was measured with a direct-read rotameter (FLDA3412C, UEI Test Instrument Company, USA) placed between the gas cylinder and the column. The concentration of NaOH and Na2CO3 were measured by titration with 0.5 M HCl solution.

A set of preliminary experiments was conducted to characterize the impacts of operational variables, including liquid and gas volumetric flow rates, solution concentration, and temperature, and to determine optimal operation conditions for the selected system and media (Ying and Brusseau, 2017). The results of these tests determined that gas and liquid flow rates of approximately 1000 and 14 ml/min, respectively, and a NaOH concentration of ~1.5 M produced optimal results. Conditions for treating the reaction system as pseudo first-order were fully satisfied. Multiple experiments under identical conditions were then conducted for each porous medium to test for method repeatability. The measured interfacial areas are compared to independent measurements to evaluate accuracy and representativeness.

The methods used for the XMT and IPTT measurements are similar to those successfully employed in prior work. Details are provided in the SM.

Results and Discussions

GACR Results

A series of experiments were conducted under identical-as-possible conditions to test method repeatability. A total of 18 tests were conducted for the glass beads and 5 for the sand. The results are presented in Table 2. The water saturation of the pack was measured gravimetrically before and after each experiment. It remained constant (within measurement error) for both the glass beads and sand throughout the series of experiments. The essentially constant water saturations indicate that fluid displacement was uniform during the experiments.

Table 2.

Measured specific solid surface areas and air-water interfacial areas of glass beads and sand.

Glass beads Sand
SSSA-N2/BET a, cm−1 30 ± 2 1370 ± 90
SSSA-Geometric b, cm−1 32 ± 3 111 ± 8
SSSA-XMT c, cm−1 31 ± 2 107 ± 13
Water Saturation- GACR method 0.43 0.57
Aia d- GACR, cm−1 16.4 ± 1 47 ± 5
Am- GACR, cm−1 29 ± 1 109 ± 11
Am- XMT, cm−1 30 ± 1 103 ± 4
Am- IPTT, cm−1 31 ± 8 216 ± 17e
Open in a new tab

± values represent 95% confidence intervals.

a

specific solid surface area measured using the N2/BET method

b

specific solid surface area deteremined using geometric calculation [GSA = 6(1−n)/d, where n is porosity and d is particle diameter]

c

specific solid surface area measured by direct characterization of the solid phase with x-ray microtomography.

d

Aia denotes air-water interfacial area

e

determined from data reported in Brusseau et al. (2015)

The mean specific air-water interfacial areas, Aia, are 16.4 and 47 cm−1 for the glass beads and sand, respectively. The value for the glass beads is significantly smaller due to the larger particle diameter, as has been demonstrated in prior studies (e.g., Anwar et al., 2000; Costanza-Robinson and Brusseau, 2002; Cho and Annable, 2005; Peng and Brusseau, 2005; Dobson et al., 2006; Costanza-Robinson et al., 2008; Brusseau et al., 2009). The coefficients of variation (COV) for air-water interfacial area are 3.5% for the glass beads and 11% for the sand. These results demonstrate very good repeatability for the method. The COV values are similar to or smaller than those typically reported for the interfacial partitioning tracer method (e.g., Brusseau et al., 2007, 2008, 2015; Dobson et al., 2006).

An advantage of using the model glass beads is that their geometric specific solid surface area (GSA) can be accurately calculated due to their uniform particle-size distribution, smooth surface, and near-perfect sphericity. The GSA for the glass-bead pack is 32 (±3, 95% confidence interval) cm−1 (Table 2). This value is statistically identical to the specific solid surface area of 30 (±2) cm−1 measured using the N2/BET method. The maximum air-water interfacial area, Am, for the glass beads is 29 (±1) cm−1, which is statistically identical to the N2/BET and GSA solid surface areas. This indicates that the GACR method produced robust measurements of air-water interfacial area.

The Am for the sand is 109 (±11) cm−1. This value is statistically identical to the GSA determined for the sand (111 ±8 cm−1). The concordance indicates that the GACR method also produced robust measurements of air-water interfacial area for the sand. The Am (and GSA) is however significantly smaller than the N2/BET solid surface area of 1370 (±90 cm−1). This disparity suggests that the GACR method does not characterize interfacial area associated with the microscopic surface roughness present in the sand under the extant conditions.

XMT and IPTT Results

X-ray microtomography produced robust imaging of the solids and fluids, as illustrated in Figure 1. The air-water interfacial areas measured with the XMT method are presented in Figure 2. Inspection of the data reveals robust measurements were obtained for both media, with high r-squared values. The Am determined from these data is 30 (±1) cm−1 for the glass beads (Table 2). The specific solid surface area measured for the glass beads by direct characterization of the solids with XMT is 31 (±2) cm−1. The Am from the XMT data is statistically identical to the XMT-based solid surface area value, both of which are also statistically identical to the GSA and N2/BET solid surface areas. Similarly, consistent results were obtained for the sand, with an Am of 103 (±4) cm−1 compared to GSA and XMT solid surface areas of 111 (±8) and 107 (±13) cm−1, respectively (Table 2). These results demonstrate the accuracy of the XMT method for measuring interfacial area, as has been reported previously (Brusseau et al., 2007, 2008, Narter and Brusseau, 2010).

Figure 1.

Figure 1

Figure 1

Open in a new tab

Figure 2.

Figure 2

Open in a new tab

The breakthrough curves obtained from the IPTT experiments for the glass beads are presented in Figure 3. The mean retardation factor for the interfacial tracer was 2.2 (± 0.2) for a water saturation of 0.24. The interfacial area and Am are 23 (±4) and 31 (±5) cm−1, respectively. Notably, the Am is similar to the N2/BET, GSA, and XMT specific solid surface areas (Table 2), indicating that the IPTT method produced robust measurement of air-water interfacial area. Similar results were reported for a related IPTT method used to measure interfacial area between organic liquid and water for the same glass beads used herein (Narter and Brusseau, 2010).

Figure 3.

Figure 3

Open in a new tab

Comparison of Methods

For the glass beads, the GACR method produced a mean air-water interfacial area of 16 cm−1 for a water saturation of 0.43, whereas the XMT method produced an area of 16 cm−1 for a water saturation of 0.48. In addition, the Am obtained from the GACR method (29 ±1 cm−1) is statistically identical to the Am values obtained from the XMT and IPTT methods. For the sand, air-water interfacial areas of 47 and 44 cm−1 were measured with the GACR and XMT methods, respectively, for a water saturation of 0.57. The sand Am values obtained with the two methods are also similar (109 ±11 cm−1 vs 103 ±4 cm−1). These results show that the GACR method produced measurements of air-water interfacial area that are very consistent with the two standard methods.

Air-water interface consists of capillary-related interfacial area associated with contacts between bulk fluids (terminal meniscii, pendular rings, wedges) and film-related area associated with thin water films solvating solid surfaces. An advantage of the XMT method compared to the IPTT method is that the former can quantitatively differentiate between capillary and film area. The maximum capillary interfacial areas measured for the glass beads and sand are 6 and 20 cm−1, respectively. These values are significantly smaller than the interfacial areas measured with the GACR method. This indicates that the GACR method measures the combined capillary + film interface.

As noted above, the Am values for the sand obtained with the GACR and XMT methods are similar to each other and to the GSA. Conversely, the GACR and XMT values are significantly smaller than the IPTT Am value determined for the sand, which is 216 (±17) cm−1 (Table 2). As discussed above, the sand has a significant amount of microscopic surface roughness. The disparity indicates that the GACR method does not characterize interfacial area associated with the microscopic surface roughness present in the sand under the conditions employed.

Conclusion

The results of this study demonstrate that the GACR method produces robust measurement of air-water interfacial area for natural geomedia. The apparatus employs standard components, and measurements can be completed within tens of minutes. Both of which are advantages compared to the standard methods available. In addition, compared to the IPTT method, the GACR method is not influenced by constraints that can deleteriously affect IPTT-based measurements, such as non-interface tracer retention (e.g., solid-phase adsorption) and tracer-induced changes in fluid distributions. Hence, the GACR method appears to be a viable alternative method for measuring air-water interfacial area in natural porous media.

One factor of great interest for any interfacial-area measurement method is the range of fluid saturation over which the method can be used effectively. Given the dependence of the GACR method on liquid flow, the effective range is likely limited to liquid saturations of greater than 0.3-0.4, similar to the aqueous-phase IPTT method. One possible approach to extend the effective range would be to operate the system with single-phase (gas) flow, so that liquid saturations could be reduced. This is the principle of operation for the gas-phase IPTT method. The system would need to be designed, and operational variables set, such that the conditional requirements of the GACR method are satisfied. The apparatus employed herein was designed to be as simple as possible, and thus did not use more advanced flow-control devices. The use of a vacuum system coupled with a two-phase flow regulator, for example, could perhaps provide greater flexibility for optimizing the system conditions. The GACR method, similar to the IPTT-based methods, measures primarily the flow-accessible interfacial area. The effectiveness of the method for geomedia with high fractions of fine particles requires investigation.

Supplementary Material

Text SI-S01

Key Points.

  • -

    The GACR method for measuring air-water interfacial area is developed for environmental geomedia systems

  • -

    The method produced accurate measurements for a model glass bead medium and for a natural sand

  • -

    The method is relatively quick, inexpensive, and requires no specialized instrumentation

Acknowledgments

This research was supported by the NIEHS Superfund Research Program (P42 ES04940). The first author was supported by a scholarship from the China Scholarship Council during their stay at the University of Arizona. We thank Matt Narter for his assistance. All data used to support this work are reported in the manuscript in the respective tables and figures. The authors thank the editor and reviewers for their constructive comments.

Footnotes

The authors state no conflicts of interest related to this work.

References

  1. Al-Raoush RI. Impact of wettability on pore-scale characteristics of residual nonaqueous phase liquids. Environ Sci Technol. 2009;43(13):4796–4801. doi: 10.1021/es802566s. [DOI] [PubMed] [Google Scholar]
  2. Al-Raoush RI, Willson CS. A pore-scale investigation of a multiphase porous media system. J Contam Hydrol. 2005;77:67–89. doi: 10.1016/j.jconhyd.2004.12.001. [DOI] [PubMed] [Google Scholar]
  3. Anwar AHMF. Experimental determination of air–water interfacial area in unsaturated sand medium. New Approaches Characterizing Groundwater Flow; Proceedings of XXXI IAH Congress; Munich, Germany. September 10–14; 2001. pp. 821–825. [Google Scholar]
  4. Anwar AHMF, Bettahar M, Matsubayashi U. A method for determining air–water interfacial area in variably saturated porous media. J Contam Hydrol. 2000;43:129–146. [Google Scholar]
  5. Araujo JB, Mainhagu J, Brusseau ML. Measuring air–water interfacial area for soils using the mass balance surfactant-tracer method. Chemosphere. 2015;134:199–202. doi: 10.1016/j.chemosphere.2015.04.035. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Bhat RDV, Kuipers JAM, Versteeg GF. Mass transfer with complex chemical reaction in gas–liquid systems: two step reversible reactions with unit stoichiometric and kinetic orders. Chem Eng J. 2000;76:127–152. [Google Scholar]
  7. Brusseau ML, Popovicova J, Silva JAK. Characterizing gas-water interfacial and bulk-water partitioning for gas-phase transport of organic contaminants in unsaturated porous media. Environ Sci Technol. 1997;31:1645–1649. [Google Scholar]
  8. Brusseau ML, Peng S, Schaar G, Costanza-Robinson MS. Relationships among air-water interfacial area, capillary pressure, and water saturation for a sandy porous medium. Water Resour Res. 2006;42:W03501. article. [Google Scholar]
  9. Brusseau ML, Peng S, Schnaar G, Murao A. Measuring air-water interfacial areas with X-ray microtomography and interfacial partitioning tracer tests. Environ Sci Technol. 2007;41:1956–1961. doi: 10.1021/es061474m. [DOI] [PubMed] [Google Scholar]
  10. Brusseau ML, Janousek H, Murao A, Schnaar G. Synchrotron X-ray microtomography and interfacial partitioning tracer test measurements of NAPL-water interfacial areas. Water Resour Res. 2008;44:W01411. doi: 10.1029/2006WR005517. article. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Brusseau ML, Narter M, Schnaar S, Marble J. Measurement and estimation of organic liquid/water interfacial areas for several natural porous media. Environmental Science & Technology. 2009;43:3619–3625. doi: 10.1021/es8020827. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Brusseau ML, Narter N, Janousek H. Interfacial partitioning tracer test measurements of organic-liquid/water interfacial areas: application to soils and the influence of surface roughness. Environmental Science & Technology. 2010;44:7596–7600. doi: 10.1021/es101312n. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Brusseau ML, El Ouni A, Araujo JB, Zhong H. Novel methods for measuring air–water interfacial area in unsaturatedporous media. Chemosphere. 2015;127:208–213. doi: 10.1016/j.chemosphere.2015.01.029. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Cho J, Annable MD. Characterization of pore scale NAPL morphology in homogeneous sands as a function of grain size and NAPL dissolution. Chemosphere. 2005;61:899–908. doi: 10.1016/j.chemosphere.2005.04.042. [DOI] [PubMed] [Google Scholar]
  15. Costanza MS, Brusseau ML. Contaminant vapor adsorption at the gas-water interface in soils. Envrion Sci Technol. 2000;34:1–11. [Google Scholar]
  16. Costanza-Robinson MS, Brusseau ML. Air-water interfacial areas in unsaturated soils: Evaluation of interfacial domains. Water Resour Res. 2002;38:13-11–13-17. [Google Scholar]
  17. Costanza-Robinson MS, Harrold KH, Lieb-Lappen RM. X-ray microtomography determination of air-water interfacial area-water saturation relationships in sandy porous media. Environ Sci Technol. 2008;42(8):2949–2956. doi: 10.1021/es072080d. [DOI] [PubMed] [Google Scholar]
  18. Culligan KA, Wildenschild D, Christensen BSB, Gray WG, Rivers ML, Tompson AFB. Interfacial area measurements for unsaturated flow through a porous medium. Water Resour Res. 2004;40:12413. [Google Scholar]
  19. Culligan KA, Wildenschild D, Christensen BSB, Gray WG, Rivers ML. Pore-scale characteristics of multiphase flow in porous media: A comparison of air-water and oil-water experiments. Adv Water Resour. 2006;29(2):227–238. [Google Scholar]
  20. Dalla E, Hilpert M, Miller CT. Computation of the interfacial area for two-fluid porous medium systems. J Contam Hydrol. 2002;56:25–48. doi: 10.1016/s0169-7722(01)00202-9. [DOI] [PubMed] [Google Scholar]
  21. Dobson R, Schroth MH, Oostrom M, Zeyer J. Determination of NAPL-water interfacial areas in well-characterized porous media. Environ Sci Technol. 2006;40:815–822. doi: 10.1021/es050037p. [DOI] [PubMed] [Google Scholar]
  22. Fang J, Xu MJ, Wang DJ, Wen B, Han JY. Modeling the transport of TiO2 nanoparticle aggregates in saturated and unsaturated granular media: effects of ionic strength and pH. Water Res. 2013;47:1399–1408. doi: 10.1016/j.watres.2012.12.005. [DOI] [PubMed] [Google Scholar]
  23. Ghosh J, Tick GR. A pore scale investigation of crude oil distribution and removal from homogeneous porous media during surfactant-induced remediation. J Contam Hydrol. 2013;155:20–30. doi: 10.1016/j.jconhyd.2013.09.003. [DOI] [PubMed] [Google Scholar]
  24. Gray WG, Hassanizadeh SM. Paradoxes and realities in unsaturated flow theory. Water Resour Res. 1991;27:1847–1854. [Google Scholar]
  25. Hassanissadeh SM, Gray WG. Thermodynamic basis of capillary pressure in porous media. Water Resour Res. 1993;29:3389–3405. [Google Scholar]
  26. Jain V, Bryant S, Sharma M. Influence of wettability and saturation on liquid-liquid interfacial area in porous media. Environ Sci Technol. 2003;37(3):584–591. doi: 10.1021/es020550s. [DOI] [PubMed] [Google Scholar]
  27. Joekar-Niasar V, Hassanizadeh SM. Analysis of fundamentals of two-phase flow in porous media using dynamic pore-network models: A review. Crit Rev Env Sci Technol. 2012;42:1895–1976. [Google Scholar]
  28. Karkare MV, Fort T. Determination of the air-water interfacial area in wet “unsaturated” porous media. Langmuir. 1996;12(8):2041–2044. [Google Scholar]
  29. Kasturi G, Stepanek JB. Two phase flow-III. Interfacial area in cocurrent gas-liquid flow. Chem Eng Sci. 1974;29:713–719. [Google Scholar]
  30. Ketcham RA, Carlson WD. Acquisition, optimization and interpretation of X-ray computed tomographic imagery: applications to the geosciences. Computers & Geosciences. 2001;27(4):381–400. [Google Scholar]
  31. Kim H, Rao PSC, Annable MD. Determination of effective air-water interfacial area in partially saturated porous media using surfactant adsorption. Water Resour Res. 1997;33:2705–2711. [Google Scholar]
  32. Kim H, Rao PSC, Annable MD. Gaseous tracer technique for estimating air-water interfacial areas and interface mobility. Soil Sci Soc Am J. 1999;63:1554–1560. [Google Scholar]
  33. Kolev N, Nakov S, Ljutzkanov L, Kolev D. Effective area of a highly efficient random packing. Chem Eng Process. 2006;45:429–436. [Google Scholar]
  34. Luo Y, Chu GW, Zou HK, Zhao ZQ, Dudukovic MP, Chen JF. Gas–liquid effective interfacial area in a rotating packed bed. Ind Eng Chem Res. 2012;51:16320–16325. [Google Scholar]
  35. Maceiras R, Alvarez E, Cancela MA. Experimental interfacial area measurements in a bubble column. Chem Eng J. 2010;163:331–336. [Google Scholar]
  36. McDonald K, Carroll KC, Brusseau ML. Comparison of fluid-fluid interfacial areas measured with X-ray microtomography and interfacial partitioning tracer tests for the same samples. Water Resour Res. 2016;52:5393–5399. doi: 10.1002/2016WR018775. [DOI] [PMC free article] [PubMed] [Google Scholar]
  37. Mohanty K, Das D, Biswas MN. Mass transfer characteristics of a novel multi-stage external loop airlift reactor. Chem Eng J. 2007;133:257–264. [Google Scholar]
  38. Narter M, Brusseau ML. Comparison of interfacial partitioning tracer test and high-resolution microtomography measurements of fluid–fluid interfacial areas for an ideal porous medium. Water Resour Res. 2010;46:W08602. doi: 10.1029/2009WR008375. [DOI] [PMC free article] [PubMed] [Google Scholar]
  39. Peng S, Brusseau ML. Impact of soil texture on air-water interfacial areas in unsaturated sandy porous media. Water Resour Res. 2005;41:W03021. article. [Google Scholar]
  40. Pharmacopeia, 846 Specific Surface Area Standard, USP. http://www.pharmacopeia.cn/v29240/usp29nf24s0_c846.html Accessed 2017.
  41. Porter ML, Wildenschild D, Grant G, Gerhard JI. Measurement and prediction of the relationship between capillary pressure, saturation, and interfacial area in a NAPL-water-glass bead system. Water Resour Res. 2010;46:W08512. article. [Google Scholar]
  42. Prodanovic M, Lindquist WB, Seright RS. Porous structure and fluid partitioning in polyethylene cores from 3D X-ray microtomographic imaging. J Colloid Interface Sci. 2006;298(1):282–297. doi: 10.1016/j.jcis.2005.11.053. [DOI] [PubMed] [Google Scholar]
  43. Pubanik SS, Vogelpohl A. Effective interfacial area in irrigated packed columns. Chem Eng Sci. 1974;29:501–507. [Google Scholar]
  44. Reeves PC, Celia MA. A functional relationship between capillary pressure, saturation, and interfacial area as revealed by a pore-scale network model. Water Resour Res. 1996;32:2345–2358. [Google Scholar]
  45. Rivers ML. tomoRecon: High-speed tomography reconstruction on workstations using multi-threading. Proc Spie. 2012;8506 [Google Scholar]
  46. Rivers ML, Citron DT, Wang YB. Recent developments in computed tomography at GSECARS. Proc Spie. 2010:7804. [Google Scholar]
  47. Roberts D, Danckwerts PV. Kinetics of CO2 absorption in alkaline solutions—I Transient absorption rates and catalysis by arsenite. Chem Eng Sci. 1962;17:961–969. [Google Scholar]
  48. Saripalli KP, Kim H, Rao PSC, Annable MD. Measurement of specific fluid-fluid interfacial areas of immiscible fluids in porous media. Environ Sci Technol. 1997;31:932–936. [Google Scholar]
  49. Saripalli KP, Rao PSC, Annable MD. Determination of specific NAPL-water interfacial areas of residual NAPLs in porous media using the interfacial tracers technique. J Contam Hydrol. 1998;30(3-4):375–391. [Google Scholar]
  50. Schaefer CE, DiCarlo DA, Blunt MJ. Experimental measurement of air-water interfacial area during gravity drainage and secondary imbibition in porous media. Water Resour Res. 2000;36:885–890. [Google Scholar]
  51. Schnaar G, Brusseau ML. Pore-scale characterization of organic immiscible-liquid morphology in natural porous media using synchrotron X-ray microtomography. Environ Sci Technol. 2005;39:8403–8410. doi: 10.1021/es0508370. [DOI] [PubMed] [Google Scholar]
  52. Schnaar G, Brusseau ML. Characterizing pore-scale dissolution of organic immiscible liquid in natural porous media using synchrotron X-ray microtomography. Environ Sci Technol. 2006a;40(21):6622–6629. doi: 10.1021/es0602851. [DOI] [PubMed] [Google Scholar]
  53. Schnaar G, Brusseau ML. Characterizing pore-scale configuration of organic immiscible liquid in multiphase systems with synchrotron X-ray microtomography. Vadose Zone J. 2006b;5(2):641–648. [Google Scholar]
  54. Sharma MM, Danckwerts PV. Chemical methods of measuring interfacial areas and mass transfer coefficients in two fluid systems. Br Chem Eng. 1970;15:522–528. [Google Scholar]
  55. Svoboda K, Rylek M. Measurement of interfacial area and mass transfer coefficients by chemical method of CO2 absorption into aqueous solutions of NaOH in a model column with expanded metal sheet packing. Chem Eng Commun. 1979;3:399–411. [Google Scholar]
  56. Tsai CY, Chen YS. Effective interfacial area and liquid-side mass transfer coefficients in a rotating bed equipped with baffles. Sep Purif Technol. 2015;144:139–145. [Google Scholar]
  57. van Woezik BAA, Westerterp KR. Measurement of interfacial areas with the chemical method for a system with alternating dispersed phases. Chem Eng Process. 2000;39:299–314. [Google Scholar]
  58. Wang M, Gao B, Tang D. Review of key factors controlling engineered nanoparticle transport in porous media. J Haz, Mater. 2016;318:233–246. doi: 10.1016/j.jhazmat.2016.06.065. [DOI] [PubMed] [Google Scholar]
  59. Yang K, Chu GW, Zou HK, Sun BC, Shao L, Chen JF. Determination of the effective interfacial area in rotating packed bed. Chem Eng J. 2011;168:1377–1382. [Google Scholar]
  60. Zeebe RE. On the molecular diffusion coefficients of dissolved gases, and and their dependence on isotopic mass. Geochim Cosmochim Acta. 2011;75:2483–2498. [Google Scholar]
  61. Zevi Y, Gao B, Zhang W, Morales VL, Cakmak ME, Medrano EA, Sang WJ, Steenhuis TS. Colloid retention at the meniscus-wall contact line inan open microchannel. Water Res. 2012;46:295–306. doi: 10.1016/j.watres.2011.09.046. [DOI] [PubMed] [Google Scholar]
  62. Zhong H, El Ouni A, Lin D, Wang B, Brusseau ML. The two-phase flow IPTT method for measurement of nonwetting-wetting liquid interfacial areas at higher nonwetting saturations in natural porous media. Water Resour Res. 2016;52:5506–5515. doi: 10.1002/2016WR018783. [DOI] [PMC free article] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Text SI-S01
NIHMS929442-supplement-Text_SI-S01.pdf (231.4KB, pdf)

RESOURCES