Equilibrium Vapor Research Articles

Rationale for Soil‐Gas Sampling to Improve Vapor Intrusion Risk Assessment in China

Rationale for Soil‐Gas Sampling to Improve Vapor Intrusion Risk Assessment in China

Changes on diametral compression behaviour of compacted marls due to drying

Cracking due to desiccation can compromise the behaviour of earth structures built with compacted clayey soils by promoting water access and consequent volume changes on further wetting. Tensile strength therefore is important to be considered when studying the behaviour of such structures, and in particular its dependence on the degree of saturation or water content. The influence of water content in tensile behaviour of compacted marls was investigated by performing diametral compression tests (Brazilian splitting tests), where axial deformations were measured besides strength. The samples were prepared by compaction at optimum point using standard compaction energy (optimum water content 16%) and then dried by vapour equilibrium to reach water contents between 5% and 16%. The correspondence between water content and suction was done by using the drying branch of the water retention curve, measured using WP4 equipment (Water Dewpoint Potentiometer). Good relationships were found between tensile strength and the water content (and suction). In addition, the study was completed with the analysis of other parameters such as the semi-contact angle created in the loaded area and the stiffness of the material, which also showed changes with water content.

Numerical investigation on water exchange of shale samples

Interest in the hydraulic and mechanical characterization of shales has grown in recent years, because of their application in the context of energy geotechnics. In the frame of nuclear waste disposal shales are considered as host formations for the placements of nuclear waste at high depths. In the frame of hydrocarbon production they are considered as unconventional reservoirs, from which extracting natural gas. Understanding how fluids flow through shales is then a key aspect for both fields of application. This paper focuses on the analysis of the transport of water vapour through laboratory samples. After reviewing the balance and flow laws that govern the transport of fluid in unsaturated porous media, a simplified model is put forward. The model was implemented in a commercial finite element code, and it was used to reproduce the results of a literature study on wetting and drying of Opalinus Clay shale samples, imposed through the vapour equilibrium technique. Back analysis of the water content and volume strains of these specimens suggests that existing models underestimate the actual flow rate of water vapour which takes place at low suctions. The current interpretation also seems to be consistent with microstructural investigations on the interconnection between large pores of this material.

Developing a high capacity axis translation apparatus for gas shale testing

Gas shales are usually partially saturated due to hydrocarbon generation and often have a low in-situ degree of saturation less than 40 %. During stimulation, substantial fluid imbibition into the formation occurs due to high suction. Recent research on these shales showed that changes in saturation strongly affect the strength and elastic properties, as well as their hysteretic behavior. To date, most experimental methodologies were based on total suction control by the vapor equilibrium technique. We postulate that the more representative in-situ conditions can be reproduced by capillary pressure control using the axis translation technique. The main challenge, however, is that the capillary pressure range is limited and far from sufficient to bring gas shales to partially saturated conditions. This paper introduces our recent progress in developing a high capacity axis translation apparatus for gas shales testing. Four high air entry value (HAEV) filter candidates were tested and evaluated for their performances and suitability

Thermo-physical behavior of borosilicate glasses in the presence of high-level radioactive liquid waste constituents

Elemental composition of high-level radioactive liquid waste (HLW) from samples of various batches was assessed by using side-on-view inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Under robust condition (Mg ratio, 10.2 ± 0.4 at RF power 1.3 kW), t he plasma excitation temperature (Texe, 9925 ± 1950 K) was calculated using the Boltzmann plot method. Thermal behavior of major constituents (> 1 g L−1) of HLW, such as nitrates of Na+, Fe3+, Cs+, Nd3+, and UO22+ , were studied using simultaneous thermal analyzer. Subsequently, the thermal stability of five and seven components borosilicate glasses was studied in detail with the above nitrates individually added as additives. Vapor pressure of sodium metaborate (NaBO2, one of the major vapor species from the glass melt in the off-gas system during vitrification of HLW) was estimated using transpiration thermogravimetry. Based on mass loss, the equilibrium vapor pressures (2.51–26.37 Pa) over a temperature span of 1233.15–1343.15 K were estimated. The molar enthalpy of vaporization (ΔvapH°) for sodium metaborate was calculated to be 287.84 ± 0.94 kJ mol−1 using the experimental data.

Hydro-mechanical behavior of expansive soils with different dry densities over a wide suction range

Many civil engineering projects are related to hydro-mechanical behavior of unsaturated expansive soils over a wide suction range, which was investigated by imposing suctions on an expansive soil using the axis-translation technique and the vapor equilibrium technique with saturated salt solution in this paper. Water retention test results on compacted expansive soil show that void ratio keeps decreasing along with increasing the suction in an entire suction range (from 0 to about 1000 MPa), and the soil–water retention curves in terms of gravimetric water content versus suction relation are independent of the dry density or void ratio when the suction is higher than 250 kPa. Therefore, the mechanical tests on an unsaturated expansive soil with constant water content can be considered as that at constant suction when suction is higher than 250 kPa. The stress–strain behavior at different constant suctions in the entire suction range measured from triaxial shear tests under a constant net confining stress shows that the strength and stress–strain curve of specimens with higher suction are higher than those with lower suction and the higher the suction, the more dilative the specimens. The strain softening appears when the suction is higher than a specific value and the appearance of strain softening is related to the sliding surface. The tested compacted expansive soil with extremely high suctions (i.e., 38.0 and 368 MPa) shows distinct peak strength, strain-softening and dilative behavior.

Phase Equilibrium Measurements of the Methacrolein–Methacrylic Acid–Water Ternary System at 101.3 kPa

In this work, the isothermal liquid–liquid equilibrium (LLE) and isobaric vapor–liquid equilibrium (VLE) of the methacrolein–methacrylic acid–water ternary mixture were systematically measured using an LLE cell and improved Rose–Williams still under atmospheric pressure. The thermodynamic consistency of LLE data and VLE data was tested by the Othmer–Tobias and Van Ness methods, respectively. The NRTL, UNIQUAC, and Wilson activity coefficient models have been conducted to correlate binary parameters in prediction phase equilibrium based on experimental data. The reliability of three models in equilibrium calculations has been analyzed in detail. All three models are in good agreement with the experimental data.

Effect of environmental relative humidity in the tensile strength of layering in slate stone

Slate is a natural stone widely used for building, for which is subjected to regulations and standards in order to be commercialized. As far as the influence of water is considered, only detailed studies are compulsory when the water absorption is higher than 0.60%. However, the mechanical behavior of this layered material depends on water content, which is function of the relative humidity of the environment, and not considered in existing standards. In order to investigate its influence on foliation tensile strength, an experimental study was performed, which consists on carrying out Brazilian tests in slate samples with known water content, applied and controlled by using vapor equilibrium technique. This technique allows controlling the relative humidity of the environment surrounding the material and that of the air on its pores. Relative humidities between 55% and 92% were applied during the tests and defined considering climate data from the north of Spain. Despite the maximum water content tested in the slates was low (0.10%) in comparison with its saturation content (0.57%), the experimental results show a decreasing of the foliation tensile strength that reaches up to three times less with an increment of the environmental relative humidity of 37%. The results achieved can be important in order to quantify the layering weakness due to a natural alteration factor such as the environmental relative humidity. Moreover, the procedure employed is proposed as a convenient method for adequating each variety of slate stone to different climates according to its vulnerability to water.

Mechanical behavior of GMZ bentonite pellet mixtures over a wide suction range

High-density bentonite pellet mixtures have been proposed as candidate materials for filling technological voids in the deep geological disposal repository of high-level radioactive waste (HLW). Water vapour transfer plays a major role in the function formation of the unsaturated engineering barrier system, due to the existing high thermal gradients generated by the decay heat released from the canister. In this work, series of suction controlled swelling pressure tests, swelling deformation tests and compression tests were conducted on GMZ bentonite pellet mixtures. Results show that, for the specimen hydrated by the vapour equilibrium technique, no collapse was observed on the evolution curve of swelling pressure. However, for that wetted by the osmotic technique, a collapse of swelling pressure was observed after the first peak value. For specimens hydrated with suction-control, a collapse on the evolution curve of swelling strain was only observed under high vertical stresses. In addition, the unloading curves of specimens exhibited a linearity at the high suction stage and a bi-linearity at the low suction stage. The swelling pressure determined by the swell-consolidation method was higher than that determined by the constant-volume method.

The investigation on the vapor-liquid phase equilibrium of (trifluoromethane + difluoromethane) system at temperatures ranging from (223.150 to 273.150) K

The trifluoromethane (R23) and difluoromethane (R32) are widely used in refrigeration and chemical industry. The isothermal vapor plus liquid equilibrium (VLE) data for the R23 plus R32 system were determined experimentally at six temperatures from 223.150 K to 273.150 K. Two models were employed to regress the experimental VLE data: Peng–Robinson (PR) equation of state with the one-parameter van der Waals (vdW) mixing rule; Peng–Robinson equation of state combined non-random two-liquid (NRTL) activity coefficient model with the modified Huron-Vidal two-order (MHV2) mixing rule. The maximum average absolute relative deviation of pressure (AARDp) and average absolute deviation of vapor phase mole fraction (AADy) for PR-vdW are 2.71% and 0.0175, respectively, while the maximum AARDp and AADy for PR-MHV2-NRTL are 1.53% and 0.0148, respectively.

Application of Acrylate Latex Emulsion as the Binder for Coating Aluminum Substrate by Silica-Gel Powder

The adsorbent coated exchangers are the main part of adsorption refrigeration systems. Although coated exchangers are commercially available, the coating technique and the binder used are seldom revealed and left as a challenge for researchers. Dip-coating is the most commonly used coating technique. However, the variety of binders used indicates that choosing the appropriate binder is still a matter of trial-and-error. A series of experiments were performed to introduce acrylic latex emulsion (ALE) and bitumen emulsion as the new binder for coating silica-gel powder on aluminum. The results indicate coats created by both emulsion binders are stable but the bitumen emulsion keeps its stability for about 10[Formula: see text]min after mixing with water and silica-gel powder. The effect of ALE binder and water concentrations on water vapor equilibrium and desorption kinetics was investigated. The outcomes indicated that the sample containing 0.8[Formula: see text]g water/g silica-gel, 0.08[Formula: see text]g ALE binder/g silica-gel shows the fastest desorption kinetic and the minimum capacity loss. The mechanical stability of this sample was evaluated by the shear test and the pull-off test. The measured values show that the prepared laminate withstands up to 27[Formula: see text]N/cm2 shear stress and 18[Formula: see text]N/cm2 tensile stress.

Experimental study on salt–metal organic framework composites for water absorption

In this article, MIL-101(Cr) powder material was successfully prepared by hydrothermal synthesis and combined with different mass fractions of CaCl2 by immersion method to obtain MIL-101(Cr)/CaCl2 composite materials. The physical properties of the adsorbent were determined by X-ray powder diffraction, N2 adsorption/desorption isotherm, TGA and FTIR. The water vapor adsorption performance of MOFs was tested by a gravimetric instrument to analyze the underlying mechanism. Results indicated that the specific surface area, total pore volume, and pore size distribution of micropores and mesopores of MIL-101(Cr)/CaCl2 composites decreased with increasing CaCl2 content. When P/P0 = 0.9, the water vapor equilibrium adsorption capacities of MIL-101(Cr), MIL-101(Cr)/CaCl2-10%, MIL-101(Cr)/CaCl2-20%, and MIL-101(Cr)/CaCl2-30% were 1.05, 0.88, 1.13, and 1.35 g/g, respectively. MIL-101(Cr)/CaCl2-30% agglomerated after water absorption, so MIL-101(Cr)/CaCl2-20% was selected as the final experimental material. The water vapor adsorption heat of MIL-101(Cr)/CaCl2-20% was 42–58 kJ/mol, which is close to the evaporation enthalpy of water (44 kJ/mol at 25 °C). The analysis of the adsorption kinetics showed the relatively uniform adsorption rate of MIL-101(Cr)/CaCl2-20%. Overall, MIL-101(Cr)/CaCl2-20% exhibited superior water vapor adsorption performance and have great potential for application to adsorption heat pumps.

Improving water retention capacity of an aeolian sandy soil with feldspathic sandstone

The Mu Us sandy land in China’s Shaanxi Province faces a critical water shortage, with its aeolian sandy soil endangering the regional eco-environment. Here we investigated the effects of feldspathic sandstone on water retention in an aeolian sandy soil from the Mu Us sandy land. Feldspathic sandstone and aeolian sandy soil samples were mixed at different mass ratios of 0:1 (control), 1:5 (T1), 1:2 (T2), and 1:1 (T3). Soil-water characteristic curves were determined over low- to medium-suction (1–1000 kPa) and high-suction (1000–140 000 kPa) ranges, by centrifuge and water vapor equilibrium methods, respectively. Results showed that the addition of feldspathic sandstone modified the loose structure of the aeolian sandy soil mainly consisting of sand grains. The van Genuchten model described well the soil-water characteristic curves of all four experimental soils (R2-values > 0.97). Soil water content by treatment was ranked as T2 > T3 > T1 > control at the same low matric suction (1–5 kPa), but this shifted to T2 > T1 > T3 > control at the same medium- to high-suction (5–140 000 kPa). T2 soil had the largest saturated water content, with a relatively high water supply capacity. This soil (T2) also had the largest field capacity, total available water content, and permanent wilting coefficient, which were respectively 17.82%, 11.64%, and 23.11% higher than those of the control (P-values < 0.05). In conclusion, adding the feldspathic sandstone in an appropriate proportion (e.g., 33%) can considerably improve the water retention capacity of aeolian sandy soil in the study area.

Quaternary ammonium salts as thermodynamic hydrate inhibitors in the presence and absence of monoethylene glycol for methane hydrates

The thermodynamic hydrate inhibition (THI) effect induced by three different quaternary ammonium salts (QASs) namely tetraethylammonium iodide (TEAI), tetramethylammonium bromide (TMAB) and tetraethylammoniun (TEAB) on the formation of methane gas hydrates has been investigated. The THI impact is also determined in the presence of monethylene glycol (MEG) for TMAB and TEAB. The inhibition capacity is examined by finding the average suppression temperature. Experiments are performed in the pressure range of 3.45–8.3 MPa at the concentration values of 1, 5 and 10 wt%. Hydrate liquid vapor equilibrium (HLVE) points are calculated by using isochoric thermodynamic cycle (T-cycle) method. COSMO-RS study is also performed to understand the THI behavior of the compounds by analyzing sigma profile. Along with it hydrate dissociation enthalpies (ΔHdiss) are considered. The results revealed that inhibition effect increased with increase in concentration. TMAB showed better impact on hydrate suppression as compared to TEAB and TEAI in pure as well as in mixture with MEG. Moreover, in thermodynamic modeling section, Dickens and Quinby-Hunt model is employed to predict HLVE data. The equilibrium temperatures predicted by model are compared with the experimental results and found to be in good agreement. Hence these compounds can be employed in THI applications and flow assurance schemes.

The SAFT for prediction of hydrate formation conditions of gas mixtures in the presence of methane, glycerol, ethylene glycol, and triethylene glycol

The statistical associating fluid theory (SAFT) equation of state is employed to calculate the fugacities of all components in the vapor and liquid phases in equilibrium with the coexisting hydrate phase. Since the SAFT takes into account the interactions of hard-sphere repulsion, hard chain formation, dispersion and association between molecules, it can successfully predict the inhibiting effect of methanol, glycerol, ethylene glycol, and triethylene glycol on the hydrate formation of gas mixtures containing methane, ethane, propane and carbon dioxide. The predictions were in excellent agreement with experimental data. However, the traditional cubic equations of state fail for systems containing water, alcohols and hydrocarbons in general.

Improved accuracy and precision of water stable isotope measurements using the direct vapour equilibration method

A method to measure the δ2 H and δ18 O composition of pore water in soil samples using direct vapour equilibration and laser spectrometry was first described in 2008, and was rapidly adopted. Here, we describe an improved setup to measure pore water δ2 H and δ18 O values through direct vapour equilibration with a laser spectrometer, combining a liquid and a vapour mode for water isotope analyses, and resulting in improved accuracy. We first tested new gas sampling bags as part of the equilibration protocol. Then, to assess measurement accuracy, vapour samples from equilibrated liquid waters of known isotope composition were measured in the liquid mode of the analyser using the new setup as well as the manufacturer's vapour mode. Various modes of preparing liquid water standards, namely equilibration, nebulisation, and vapourisation, were tested to determine the best calibration in terms of accuracy. Finally, the proposed modified liquid setup was validated by analysing water vapour equilibrated from soil pore water of a known composition. The δ2 H and δ18 O measurements were found to be more accurate by the modified liquid mode than by the factory-setup vapour mode. The strong and non-linear dependence of measured δ2 H and δ18 O values on H2 O concentration in vapour mode, especially at concentrations equal to the vapour pressure saturation typically found in laboratories, is problematic for corrections. Regarding calibration and standards, the use of two equilibrated liquid water standards was found to best calibrate measurements in the modified liquid setup. Finally, the modified liquid mode setup and its calibration, as described here, were shown to be appropriate for soil pore water analysis. The proposed modified setup results in more precise δ2 H and δ18 O soil pore water values than the usual protocols. An average standard deviation of 0.04‰ for δ18 O values and 0.3‰ for δ2 H values, based on 228 soil sample analyses, was obtained.

Humidity responsive single-layered film fabricated by hydrophilic titanium oxide nanotubes

We fabricated a humidity responsive film comprising a bundle of titanium oxide tubes, which changes its curvature corresponding to the relative humidity. The mechanism of changing the curvature of the film can be explained by adsorption, condensation, and evaporation of water molecules within the film. During adsorption, a liquid bridge is formed because of the growth of a water layer between tubes, thus contracting the tubes. When vapor pressure exceeds the equilibrium vapor pressure, condensation occurs at the meniscus of the liquid bridge, thus expanding the gap between tubes. We obtained the adsorption and desorption isotherms for the humidity responsive film by determining physical adsorption. Additionally, we demonstrated the varying motions of the humidity sensing film when a water droplet was applied on the surface. The sensor could distinguish between saturated and oversaturated humidity conditions, such as fog and rain, respectively, which is not possible using resistive humidity sensors. This humidity responsive film can be applied to environmental monitoring systems and possibly even to energy harvesting systems.

Tin isotopes indicative of liquid–vapour equilibration and separation in the Moon-forming disk

The depletion in moderately volatile elements in the Moon relative to Earth and comparison of the isotope compositions of the Moon and Earth have placed important constraints on models of lunar formation. A liquid–vapour protolunar disk from a high-energy giant impact has been proposed to explain some of these constraints. Here we present high-precision tin isotope data for lunar rocks, measured by double-spike MC-ICP-MS (multicollector inductively coupled plasma mass spectrometry). The lunar rocks are enriched in light tin isotopes compared to the Earth (Δ124/116SnMoon–Earth = −0.48 ± 0.15‰). On the basis of our data and constraints on tin speciation, we show that this tin isotope fractionation is inconsistent with volatile loss from a lunar magma ocean. Instead, we propose a scenario with vigorous mixing between the protolunar disk and the Earth in high-energy conditions during the impact, followed by liquid–vapour equilibration and phase separation at around 2,500 K while the disk was cooling. This scenario is consistent with the depletion in moderately volatile elements and isotope composition of the Moon. Vigorous mixing between the protolunar disk and Earth followed by processes in the cooling disk may explain the enrichment in light isotopes of tin on the Moon relative to Earth, as found by analysis of lunar rocks and geochemical calculations.

SAPO-34 based zeolite coatings for adsorption heat pumps

In this work, at first, an overview on SAPO-34 zeolite coating for adsorption heat pumps is presented, highlighting current quality standard and open technological issues (i.e. the need for good mechanical and hydrothermal stability, high aging stability, etc.). Afterwards, we present an improved formulation of adsorbent composite coatings on aluminum support, having improved thermal and mechanical properties, especially when subjected to an impulsive stress. Specifically, the coated samples were prepared by dip-coating method starting from a water suspension of SAPO-34 zeolite and a hybrid polymer binder. Adhesive and mechanical properties were evaluated by pull-off test confirming the good interaction between metal substrate, filler and matrix. Adsorption equilibrium of water vapor on the adsorbent coating was measured in the range T = 30–150 °C and partial pressure of moisture equal to 11 mbar. It was found that binder does not affect the water adsorption capacity and adsorption rate of the original SAPO-34 zeolite.

Intercomparison of soil pore water extraction methods for stable isotope analysis and interpretation of hillslope runoff sources

AbstractIntercomparison of soil pore water extraction methods for stable isotope analysis has been a focus of recent studies in relation to plant source waters, which found a wide isotopic variance depending on the extraction method. Few studies have yet explored extraction effects for mobile pore waters that relate to hillslope runoff. This is because it is extremely difficult in natural systems to control the boundary conditions in order to assess and compare impacts of pore water extraction on resulting hillslope flow. With our new semicontrolled experiments on outdoor mini‐hillslopes, we studied mixing and runoff processes by means of stable isotopes of water and quantified relations between pore water extraction methods. We tested the null hypothesis that nondestructive and destructive pore water sampling methods sample the same soil water pool. Three hillslopes were mounted on load cells, filled with loamy sand textured soils from the Landscape Evolution Observatoryat Biosphere 2, equipped with soil moisture and temperature sensors, a bottom outflow, and a surface runoff gauge for isotope sampling. We followed the precipitation isotopic composition over and through the soil profile. One hillslope was instrumented with suction cups, on the second we installed sampling ports for in‐situ soil water vapour measurements, and the third hillslope was sampled destructively for applying the centrifugation and vapour equilibrium methods. All hillslopes were sampled at four depths (0–10, 10–20, 20–30, and 30–40 cm) at three different downslope positions.2H and18O analyses were performed via laser spectroscopy. We found no isotopic differences between rainfall, surface runoff, and bottom outflow. The in situ vapour ports' soil isotope data showed the widest spread over all hillslope positions and depths. Centrifugation's and suction cups' isotope results plotted closest to the local meteoric water line and within the range of hillslope runoff and bottom outflow data. Hillslope position did not influence the soil isotope results. These results suggest caution be used in the field when selecting an extraction technique for matching soil waters to runoff waters. Soil suction lysimeters and centrifugation appeared to be the most appropriate tools in this regard.