Measurement Of Interfacial Area Research Articles

Experimental investigation of nozzle submergence depth on steam cavity thermal characteristics in direct contact condensation

Direct contact condensation has found wide applications in an industrial sector because of its enormous mass and heat transfer capabilities. In the current experimental investigation, effect of submergence depth has been analyzed on the thermal characteristics of steam plume issuing into water tank from two geometrically different steam spray nozzles i.e. converging–diverging (CD) nozzle and straight pipe (SP) nozzle. The steam cavity images were taken using high-speed camera which were processed by MATLAB image-processing tool for the measurement of steam-water interfacial area. It was observed that axial temperature distribution rises with the increase in submergence depth while for radial temperature distributions reverse was found to be true. Additionally, the temperatures at nozzle exit were noted to be independent of submergence depth. The heat transfer coefficient decreases as the steam pressure, water temperature and submergence depth is increased for both the nozzles and found in range of 1.661–2.91 MW/m2·K and 1.472–1.989 MW/m2·K for the CD and SP nozzle, respectively. Moreover, the effect of submergence depth was found to be almost negligible at the higher submergence depth values.

Determining air-water interfacial areas for the retention and transport of PFAS and other interfacially active solutes in unsaturated porous media

The objective of this work was to determine the methods that produce the most representative measurements and estimations of air-water interfacial area specifically for the retention and transport of PFAS and other interfacially active solutes in unsaturated porous media. Published data sets of air-water interfacial areas obtained with multiple measurement and prediction methods were compared for paired sets of porous media comprising similar median grain diameters, but one with solid-surface roughness (sand) and one without roughness (glass beads). All interfacial areas produced with the multiple diverse methods were coincident for the glass beads, providing validation of the aqueous interfacial tracer-test methods. The results of this and other benchmarking analyses demonstrated that the differences in interfacial areas measured for sands and soil by different methods are not due to errors or artifacts in the methods but rather the result of method-dependent differential contributions of solid-surface roughness. The contributions of roughness to interfacial areas measured by interfacial tracer-test methods were quantified and shown to be consistent with prior theoretical and experiment-based investigations of air-water interface configurations on rough solid surfaces. Three new methods for estimating air-water interfacial areas were developed, one based on the scaling of thermodynamic-determined values and the other two comprising empirical correlations incorporating grain diameter or NBET solid surface area. All three were developed based on measured aqueous interfacial tracer-test data. The three new and three existing estimation methods was tested using independent data sets of PFAS retention and transport. The results showed that the method based on treating air-water interfaces as smooth surfaces as well as the standard thermodynamic method produced inaccurate air-water interfacial areas that failed to reproduce the multiple measured PFAS retention and transport data sets. In contrast, the new estimation methods produced interfacial areas that accurately represented air-water interfacial adsorption of PFAS and associated retention and transport. The measurement and estimation of air-water interfacial areas for field-scale applications is discussed in light of these results.

A novel approach for wettability estimation in geological systems by fluid–solid interfacial area measurement using tracers

Wettability plays a vital role in many applications of flow in porous media and affects Darcy scale flow parameters by influencing the fluid–solid interfacial area. Therefore, quantifying the fluid–solid interfacial area can provide a way to measure wettability at the Darcy scale. Here, we experimentally explore a dual-tracer method, which can also be scaled to large geological reservoirs to quantify the fluid–solid interfacial area during the multiphase flow through a porous medium for different wetting conditions. Using our experiments, we demonstrate the influence of different saturations, wettability and flow conditions on the solid–liquid interfacial area. When oil is in the residual phase, we observe that the solid–water interfacial area increases with the increase in water saturation for the water-wet and mixed-wet cases. However, the water–solid interfacial area decreases with an increase in water saturation for the oil-wet case. We increase the water saturation by increasing the water flow rate; therefore, the anomalous behaviour seen in the oil-wet case can be attributed to the rearrangement of oil and water at higher water flow rates. When both oil and water are flowing, the solid–water interfacial area increases with water saturation for all the wettability cases and increases in water wettability as anticipated.Synopsis: Wettability measurements at Darcy-scale give a broad idea of overall subsurface wetting conditions for application in CO2 sequestration, ground-water remediation or oil recovery.

Using coarse-grained models to examine structure-property relationships of diblock-arm star polymers

Molecular dynamics simulations were used to verify that diblock-arm star polymers (SPs) can be accurately described using coarse-grained models. Each arm of the SPs examined consist of an inner polyethylene block and an outer polyethylene oxide block. A sixteen-arm SP with arm chemistry -CH224-CH2OCH26-H was mapped to a MARTINI coarse-grained representation and compared to results from atomistic simulations of an identical chemistry and architecture. Results for radius of gyration, radial distribution functions, and occupied volumes all show agreement with the atomistic model and reproduce general trends with respect to temperature. Additional measurements of interfacial area and anisotropy reveal that our model does not demonstrate crystallization of the polyethylene blocks at low temperatures as observed in the atomistic model which can be ascribed to the reduction in degrees of freedom that follow from coarse-graining. Calculated values for relaxation times agree with the general trends from the atomistic simulations. Nineteen additional coarse-grained star polymers were examined in order to investigate structure-property relationships that arise by varying arm number and arm length. The ability to model these chemical species at this resolution will allow for simulations of polymeric nanocarriers in more complex environments including at increased concentrations and near surfaces. This work demonstrates an important first step in work that will enable improved design of these polymeric nanoparticles for drug delivery applications.

Solid-fluid interfacial area measurement for wettability quantification in multiphase flow through porous media

Quantification of wettability inside a porous medium is challenging. Most of the currently available methods use either a proxy surface of the porous solid or a small sample of the porous medium for wettability quantification. Recognizing that more wetting fluid has more interfacial area with porous solid, we develop a tracer method to quantify the solid-liquid interfacial area for a porous medium. We use two tracers for a fluid-phase, an ideal tracer, and an adsorbing tracer. The ideal tracer follows the flow path, and the adsorbing tracer dynamically adsorbs on the porous surface. We use the tracers’ mean residence time to quantify the solid-liquid interfacial area during multiphase flow in a porous medium. We conduct the tracer flow experiments at various saturations for a given wettability condition. We observe a monotonic behaviour of the wetted area with the fluid saturations. At the same residual saturation, oil has 10% less interfacial area with the porous solid in comparison to water. This difference in contact area can be used for quantifying the wettability using our methodology.

Testing the validity of the miscible-displacement interfacial tracer method for measuring air-water interfacial area: Independent benchmarking and mathematical modeling

The interfacial tracer test (ITT) conducted via aqueous miscible-displacement column experiments is one of a few methods available to measure air-water interfacial areas for porous media. The primary objective of this study was to examine the robustness of air-water interfacial area measurements obtained with interfacial tracer tests, and to examine the overall validity of the method. The potential occurrence and impact of surfactant-induced flow was investigated, as was measurement replication. The column and the effluent samples were weighed during the tests to monitor for potential changes in water saturation and flux. Minimal changes in water saturation and flux were observed for experiments wherein steady flow conditions were maintained using a vacuum-chamber system. The air-water interfacial areas measured with the miscible-displacement method completely matched interfacial areas measured with methods that are not influenced by surfactant-induced flow. This successful benchmarking was observed for all three media tested, and over a range of saturations. A mathematical model explicitly accounting for nonlinear and rate-limited adsorption of surfactant at the solid-water and air-water interfaces as well as the influence of changes in surface tension on matric potentials and flow was used to simulate the tracer tests. The independently-predicted simulations provided excellent matches to the measured data, and revealed that the use of the vacuum system minimized the occurrence of surfactant-induced flow and its associated effects. These results in total unequivocally demonstrate that the miscible-displacement ITT method produced accurate and robust measurements of air-water interfacial area under the extant conditions.

Low-concentration tracer tests to measure air-water interfacial area in porous media

The aqueous-based interfacial tracer method employing miscible-displacement tests is one method available for measuring air-water interfacial areas. One potential limitation to the method is the impact of tracer-induced drainage on the system. The objective of this study was to investigate the efficacy of a low-concentration tracer test method for measuring air-water interfacial area. Tracer concentrations and analytical methods were selected that allowed the use of tracer input concentrations that were below the threshold of tracer-induced drainage. Multiple tracer tests were conducted at different water saturations. Interfacial areas increased from 34.8 to 101 cm−1 with the decrease in saturation from 0.86 to 0.62. The method produced relatively robust measurements of air-water interfacial area, with coefficients of variation ranging from 6 to 26%. A variably saturated flow and transport model that accounts for the effects of tracer on interfacial tension, and the retention of tracer at the air-water and solid-water interfaces, was used to test for potential tracer-induced drainage. The simulations showed that the use of low tracer-input concentrations eliminated this phenomenon. This is consistent with the measured data for effluent-sample masses, which exhibited minimal change during the tests, and with the observation that the interfacial areas obtained with the low-concentration-tracer method were consistent with values measured with two methods that are not influenced by tracer-induced drainage. These results demonstrate that the low-concentration miscible-displacement tracer test method is an effective approach for measuring air-water interfacial areas in porous media.

Assessing XMT-Measurement Variability of Air-Water Interfacial Areas in Natural Porous Media.

This study investigates the accuracy and reproducibility of air-water interfacial areas measured with high-resolution synchrotron x-ray microtomography (XMT). Columns packed with one of two relatively coarse-grained monodisperse granular media, glass beads or a well-sorted quartz sand, were imaged over several years, encompassing changes in acquisition equipment, improved image quality, and enhancements to image acquisition and processing software. For the glass beads, the specific solid surface area (SSSA-XMT) of 31.6 ±1 cm-1 determined from direct analysis of the segmented solid-phase image data is statistically identical to the independently calculated geometric specific solid surface area (GSSA, 32 ±1 cm-1) and to the measured SSSA (28 ±3 cm-1) obtained with the N2BET method (NBET). The maximum specific air-water interfacial area (Amax) is 27.4 (±2) cm-1, which compares very well to the SSSA-XMT, GSSA, and SSSA-NBET values. For the sand, the SSSA-XMT (111 ±2 cm-1) and GSSA (113 ±1 cm-1) are similar. The mean Amax is 96 ±5 cm-1, which compares well to both the SSSA and the GSSA values. The XMT-SSSA values deviated from the GSSA values by 7-16% for the first four experiments, but were essentially identical for the later experiments. This indicates that enhancements in image acquisition and processing improved data accuracy. The Amax values ranged from 74 cm-1 to 101 cm-1, with a coefficient of variation (COV) of 9%. The maximum capillary interfacial area ranged from 12 cm-1 to 19 cm-1, for a COV of 10%. The COVs for both decreased to 5-6% for the latter five experiments. These results demonstrate that XMT imaging provides accurate and reproducible measurements of total and capillary interfacial areas.

Measurement of Bubble Size, Gas holdup and Interfacial Area in Bubble Columns using Image Processing Techniques

Bubble sizes in bubble column affect transfer processes. Therefore, it’s important to calculate bubble size and interfacial area. Bubble size distribution (BSD) in a bubble column of rectangular cross section with dimensions 0.2m x 0.02m was measured using photographic method (400 fps) for air-water system. Gas holdup, Sauter-mean bubble diameter, aspect ratio and specific interfacial area were estimated from BSD. Effect of superficial gas velocity and static bed height on these parameters was investigated. The bubble size distribution exhibited mono-modal distribution showing the presence of non-uniform homogeneous bubbling regime. The frames of video were analysed using image processing steps to obtain major and minor axis of elliptical bubbles. Values of d32, , and ai were estimated from the data. The value of d32 increased with increasing Ug but is independent of Hs. The values of d32 were somewhat higher than the values reported by other investigators. The value of ai increases with increasing Ug and with decreasing Hs. Present values of compared well with the data reported in literature.

Interfacial area measurement with new algorithm for grouping bubbles by diameter

Many industrial systems make use of two-phase flows for processing or safety applications. Modeling these flows is essential for ensuring safety and engineering optimization. In general, these flows are modeled using the two-fluid model. Two key parameters in the two-fluid model are void fraction and interfacial area concentration. To improve model accuracy, the bubbles are typically broken up into groups based on transport properties and modeled separately. Such models must be validated using experimental data, which is often collected using intrusive probes such as electrical conductivity or optical void probes. Current algorithms for converting the signals from these instruments into void and interfacial area measurements struggled with missing interfaces due to signal rise and fall time. These types of instruments also use the chord length to classify the “group” of a bubble, which can lead to incorrect grouping behavior. In this paper, a new dynamic signal processing method and a grouping algorithm based on calculating bubble diameter have been introduced in an attempt to correct these inaccuracies. The ability of the new algorithm is to correctly identify smaller bubbles and to more accurately identify bubble signals is demonstrated by comparison of the output logic pulse for both the old and new algorithms with the same input signal. The new bubble size calculation means that a number of bubbles that were previously classified as “spherical/distorted” are now classified as “cap/slug/churn” bubbles. This leads to changes in average bubble properties. While these changes were expected in several cases, the increase was larger than the reported uncertainty of the instruments. This may indicate significant shortcomings in data analyzed using the previous algorithms. Additional data collection and analysis is required in order to evaluate this possibility. However, the new algorithm has a significant weakness: the bubble diameter calculation increases the computational t ime by an order of magnitude.

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

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.

Measurement of interfacial area from NMR time dependent diffusion and relaxation measurements

The interfacial area between two immiscible phases in porous media is an important parameter for describing and predicting 2 phase flow. Although present in several models, experimental investigations are sparse due to the lack of appropriate measurement techniques. We propose two NMR techniques for the measurement of oil-water interfacial area: (i) a time dependent NMR diffusion technique applicable in static conditions, similar to those used for the measurement of the solid specific surface of a porous media, and (ii) a fast relaxation technique applicable in dynamic conditions while flowing, based on an interfacial relaxation mechanism induced by the inclusion of paramagnetic salts in the water phase. For dodecane relaxing on doped water, we found an oil interfacial relaxivity of 1.8μm/s, large enough to permit the measurement of specific interfacial surface as small as 1000cm2/cm3. We demonstrate both NMR techniques in drainage followed by imbibition, in a model porous media with a narrow pore size distribution. While flowing, we observe that the interfacial area is larger in imbibition than in drainage, implying a different organization of the oil phase. In a carbonate sample with a wide pore size distribution, we evidence the gradual invasion of the smallest pores as the oil-water pressure difference is increased.

Void fraction, bubble size and interfacial area measurements in co-current downflow bubble column reactor with microbubble dispersion

Microbubbles dispersed in bubble column reactors have received great interest in recent years, due to their small size, stability, high gas-liquid interfacial area concentrations and longer residence times. The high gas-liquid interfacial area concentrations lead to high mass transfer rates compared to conventional bubble column reactors. In the present work, experiments have been performed in a downflow bubble column reactor with microbubbles generated and dispersed by a novel mechanism to determine the gas-liquid interfacial area concentrations by measuring the void fraction and bubble size distributions. Gamma-ray densitometry has been employed to determine the axial and radial distributions of void fraction and a high speed camera equipped with a borescope is used to measure the axial and radial variations of bubble sizes. Also, the effects of superficial gas and liquid velocities on the two-phase flow characteristics have been investigated. Further, reconstruction techniques of the radial void fraction profiles from the gamma densitometry's chordal void fraction measurements are discussed and compared for a bubble column reactor with dispersed microbubbles. Empirical correlations are also proposed to predict the Sauter mean bubble diameter. The results demonstrate that the new bubble generation technique offers high interfacial area concentrations (1000–4500 m2/m3) with sub-millimeter bubbles (500–900µm) and high overall void fractions (10–60%) in comparison with previous bubble column reactor designs.

Uncertainty analysis of an interfacial area reconstruction algorithm and its application to two group interfacial area transport equation validation

Wire mesh sensors (WMS) are state of the art devices that allow high resolution (in space and time) measurement of 2D void fraction distribution over a wide range of two-phase flow regimes, from bubbly to annular. Data using WMS have been recorded at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) (Lucas et al., 2010; Beyer et al., 2008; Prasser et al., 2003) for a wide combination of superficial gas and liquid velocities, providing an excellent database for advances in two-phase flow modeling.In two-phase flow, the interfacial area plays an integral role in coupling the mass, momentum and energy transport equations of the liquid and gas phase. While current models used in best-estimate thermal-hydraulic codes (e.g. RELAP5, TRACE, TRACG, etc.) are still based on algebraic correlations for the estimation of the interfacial area in different flow regimes, interfacial area transport equations (IATE) have been proposed to predict the dynamic propagation in space and time of interfacial area (Ishii and Hibiki, 2010). IATE models are still under development and the HZDR WMS experimental data provide an excellent basis for the validation and further advance of these models. The current paper is focused on the uncertainty analysis of algorithms used to reconstruct interfacial area densities from the void-fraction voxel data measured using WMS and their application towards validation efforts of two-group IATE models.In previous research efforts, a surface triangularization algorithm has been developed in order to estimate the surface area of individual bubbles recorded with the WMS, and estimate the interfacial area in the given flow condition. In the present paper, synthetically generated bubbles are used to assess the algorithm’s accuracy. As the interfacial area of the synthetic bubbles are defined by user inputs, the error introduced by the algorithm can be quantitatively obtained. The accuracy of interfacial area measurements is characterized for different bubbles sizes and shapes, and for different WMS acquisition frequencies. It is found that while convex shapes are successfully analyzed by the reconstruction algorithm, some difficulties are faced with bubbles presenting internal cavities.Utilizing the experimental HZDR database, the performance of the current two-group IATE model is evaluated. While the qualitative propagation of interfacial area is predicted sufficiently well, there is a discrepancy in magnitude between the model’s prediction and the experimental results. Overall, the study suggests that differences exist in the incidence of interaction mechanisms between small and large diameter pipes and further efforts are needed in order to extend the range of validity of current IATE models.

Measurement of NAPL-water interfacial areas and mass transfer rates in two-dimensional flow cell.

The nonaqueous-phase liquid (NAPL)-water interfacial area and the mass transfer rate across the NAPL and water interface are often key factors in in situ groundwater pollution treatment. In this study, the NAPL-water interfacial area and residual NAPL saturation were measured using interfacial and partitioning tracer tests in a two-dimensional flow cell. The results were compared with previous column and field experiment results. In addition, the mass transfer rates at various NAPL-water interfacial areas were investigated. Fe2+-activated persulfate was used for in situ chemical oxidation remediation to remove NAPL gradually. The results showed that the reduction of NAPL-water interfacial areas as well as NAPL saturation by chemical oxidation caused a linear decrease in the interphase mass transfer rates (R2 = 0.97), revealing the relationship between mass transfer rates and interfacial areas in a two-dimensional system. The NAPL oxidation rates decreased with the reduction of interfacial areas, owing to the control of NAPL mass transfer into the aqueous phase.

The two-phase flow IPTT method for measurement of nonwetting-wetting liquid interfacial areas at higher nonwetting saturations in natural porous media.

Interfacial areas between nonwetting-wetting (NW-W) liquids in natural porous media were measured using a modified version of the interfacial partitioning tracer test (IPTT) method that employed simultaneous two-phase flow conditions, which allowed measurement at NW saturations higher than trapped residual saturation. Measurements were conducted over a range of saturations for a well-sorted quartz sand under three wetting scenarios of primary drainage (PD), secondary imbibition (SI), and secondary drainage (SD). Limited sets of experiments were also conducted for a model glass-bead medium and for a soil. The measured interfacial areas were compared to interfacial areas measured using the standard IPTT method for liquid-liquid systems, which employs residual NW saturations. In addition, the theoretical maximum interfacial areas estimated from the measured data are compared to specific solid surface areas measured with the N2/BET method and estimated based on geometrical calculations for smooth spheres. Interfacial areas increase linearly with decreasing water saturation over the range of saturations employed. The maximum interfacial areas determined for the glass beads, which have no surface roughness, are 32±4 and 36±5 cm-1 for PD and SI cycles, respectively. The values are similar to the geometric specific solid surface area (31±2 cm-1) and the N2/BET solid surface area (28±2 cm-1). The maximum interfacial areas are 274±38, 235±27, and 581±160 cm-1 for the sand for PD, SI, and SD cycles, respectively, and ~7625 cm-1 for the soil for PD and SI. The maximum interfacial areas for the sand and soil are significantly larger than the estimated smooth-sphere specific solid surface areas (107±8 cm-1 and 152±8 cm-1, respectively), but much smaller than the N2/BET solid surface area (1387±92 cm-1 and 55224 cm-1, respectively). The NW-W interfacial areas measured with the two-phase flow method compare well to values measured using the standard IPTT method.

Measurement of Taylor bubble shape in square channel by microfocus X-ray computed tomography for investigation of mass transfer

This paper addresses the measurement of the dynamic evolution of Taylor bubble volume and interfacial area during mass transfer. Carbon dioxide (CO2) Taylor bubbles were placed in countercurrent water flow in a square channel. Microfocus X-ray radioscopy enabled the measurement of volumetric dissolution rates. The measurements were calibrated by microfocus X-ray computed tomography scans of non-dissolving air Taylor bubbles. The reconstruction algorithm was adapted to correct the slight position shift of the Taylor bubble during the tomographic scan. The obtained three-dimensional representation of the Taylor bubble's shape enabled the measurement of Taylor bubble's true volume and interfacial area, which were correlated to the two-dimensional radioscopic measurements. The volumetric dissolution rates were measured in a square milli-channel with hydraulic diameter of dh=6mm. Furthermore, the thin film region of the constricted Taylor bubble's surface near the planar channel walls was extracted from the data and the ratio to the total Taylor bubble surface was computed.

Interfacial area measurements and surface area quantification for spray absorption

Abstract Sprays are widely used in the chemical industry for absorption operations such as gas conditioning and flue gas desulphurization. Despite the wide usage, spray absorption is poorly understood. For absorption applications, the rate of transfer of solute gas into all of the liquid drops is a strong function of the surface area of drops and hence the dropsize. Experimental measurements of dropsize at multiple locations within the spray plume and robust computation of the cumulative surface area of the drops is required to ascertain the liquid surface area availability. Further, the efficiency of spray contactors can be conveniently expressed in terms of the effective gas–liquid interfacial area measured using the standard chemical technique. The liquid surface area and the effective gas–liquid contact area inside spray columns can differ from each other on account of the large degree of absorption occurring during the process of atomization, and the internal stagnancy of small drops. Further, drop break-up, drop-drop interactions, collision of the spray plume with the column wall, and wall flow affect the liquid surface area availability and the effective gas–liquid contact area to varying degrees. As a result, it is essential to quantify both, the liquid surface area as well as the effective gas–liquid area inside spray columns to gain a fundamental understanding. Present study addresses this gap. Dropsize measurements using a Phase Doppler Interferometer (PDI), robust cumulative drop surface area quantification, and effective interfacial area measurements with the CO2-0.1 N NaOH system inside a 0.2 m ID laboratory spray column are presented. The effect of L/G ratio and gas–liquid contact height on the effective interfacial area and the cumulative drop surface area are elucidated. The effective interfacial area measurements are compared to results of previous researchers. Further, a methodology to compare the cumulative drop surface area with the effective interfacial area measurements is presented. Results from the study shows that a great degree of mass transfer does occur in the region in the vicinity of the nozzle tip. A large difference is observed in the cumulative drop surface area and the effective interfacial area on account of the large degree of CO2 absorption taking place during the process of atomization and the large number of internally stagnant drops. This work provides a fundamental insight into spray absorption and will guide in nozzle selection and robust design of spray columns.

Measuring air–water interfacial area for soils using the mass balance surfactant-tracer method

There are several methods for conducting interfacial partitioning tracer tests to measure air–water interfacial area in porous media. One such approach is the mass balance surfactant tracer method. An advantage of the mass-balance method compared to other tracer-based methods is that a single test can produce multiple interfacial area measurements over a wide range of water saturations. The mass-balance method has been used to date only for glass beads or treated quartz sand. The purpose of this research is to investigate the effectiveness and implementability of the mass-balance method for application to more complex porous media. The results indicate that interfacial areas measured with the mass-balance method are consistent with values obtained with the miscible-displacement method. This includes results for a soil, for which solid-phase adsorption was a significant component of total tracer retention.

Aeration performances of a gabion stepped weir with and without capping

The stepped spillway design has been used for more than 3,300 years. A simple structure is the gabion stepped weir. A laboratory study was performed herein in a large size facility. Three gabion stepped weirs were tested with and without capping, as well as a flat impervious stepped configuration. For each configuration, detailed air–water flow measurements were conducted systematically for a range of discharges. The observations highlighted the seepage flow through the gabions and the interactions between seepage and overflow. The air–water flow properties showed that the air concentration, bubble count rate and specific interface data presented lower quantitative values in the gabion stepped weir, compared to those on the impervious stepped chute, while higher velocities were measured at the downstream end of the gabion stepped chute. The re-oxygenation rate was deduced from the integration of the mass transfer equation using air–water interfacial area and velocity measurements. The aeration performances of the gabion stepped weir were lesser than on the flat impervious stepped chute, but for the lowest discharge. For the two configurations with step capping, the resulting flow properties were close to those on the impervious stepped configuration.