Dew Point Technique Research Articles

Use of Chilled Mirror /Dew-Point Method (WP4C) to Develop Soil Water Characteristic Curve for Coastal Silty Sand with a Comparison of the Existing Analytical Models

Soil Water Characteristic Curve (SWCC) is one of the methods to study the behaviour of unsaturated soil. This study presents the SWCC for Sri Lankan coastal silty sand developed using chilled mirror dew-point technique WP4C and compares the performance of a few prediction models. SWCC was also developed experimentally using pressure plate and suction-moisture sensors, to verify the results obtained using WP4C. The fitted SWCC curve was developed using Van Genuchten's (VG) model. The prediction models of Arya and Paris (1981), Aubertin et al. (2003), and Wang et al. (2017) were used to compare the performance using their own suggested values and the more suitable values for this study as the model parameters which were estimated using the least square method. This study shows that chilled mirror dew-point technique which is incorporated in WP4C instrument can be used as a fast and reliable experimental method to develop the SWCC for sandy soils compared to other experimental methods. The Wang et al. (2017) model is better suited for estimating the SWCC through analytical methods for this soil type, using either the recommended values in this study or proposed values by the authors for the modal parameters.

Suction effects on the tensile strength and unconfined compression of unsaturated soils

The soil-water characteristic curve is an important relation of unsaturated soils, that expresses the variation of the amount of water retained in the soil as a function of its suction. In these soils, drying or wetting can have a great influence on their resistance parameters. This work presents and discusses the effects of increased suction on the tensile strength and unconfined compression of unsaturated soils. Suction was evaluated using the filter paper and the dew point technique, while the resistance parameters were obtained through the “Brazilian Test” and uniaxial compression. Three different soils from Rio de Janeiro were studied: two young residual soils, in which the influence of the soil structure was also verified through tests on undisturbed and reconstituted samples, and a colluvial soil. The results allowed to conclude that the increase of suction, in a first moment, generates an increase in the resistance parameters of these soils. With the continuation of the drying process, the mechanical behaviour of the soils varied, being able to maintain the resistance or showing a drop related to high suction values.

Hydromechanical behavior and prediction of unsaturated loess over a wide suction range

Subgrade loess in arid and semi-arid regions subjected to high-suction conditions owing to low relative humidity and deep groundwater levels. Understanding the hydromechanical behavior of unsaturated compacted loess over a wide suction range is critical for resolving infrastructure problems in such areas. In this study, the water retention behavior of loess was investigated by imposing or measuring suction (s) using the axis translation technique, vapor equilibrium technique, and chilled mirror dew point technique. Triaxial tests were also performed to study the mechanical behavior of compacted loess under different net cell pressures (σ3n).The soil-water retention curves obtained using the different techniques are consistent. The degree of saturation and water content decreases significantly when s 0.5 MPa, indicating that undrained triaxial tests can be considered as those under constant suction. For the same σ3n, specimens show strain-hardening, shrinkage, and drum-shaped shear failure under low-s conditions and strain-softening, dilatancy, and oblique section splitting under high-s conditions. The failure deviator stress and cohesion of the compacted loess specimens increase with increasing s over the full s range (0–299.37 MPa). An equation to predict the shear strength of unsaturated loess over a wide s range is proposed. The intersection of the capillary water retention curve and adsorption water retention curve is set as a reference point (sR), where capillary degree of saturation is applicable for s ≤ sR and adsorption degree of saturation is added for s > sR. The predicted and measured shear strengths of the compacted loess specimens are in good agreement.

Impacts of soil type and crop species on permanent wilting of plants

The lack of a continuous network of water-filled pores necessary for the flow of water in the soil has been related to the wilting of plants as well as to the limitations of soil sample equilibrium in pressure plates. The objectives of this study were: (i) to quantify deviations of the soil water content measured in pressure plates and dew point measurements at a matric potential of −15,000 hPa (commonly defined as the permanent wilting point), (ii) to determine the soil matric potential at which the physiological wilting of different plant species occurs in soil with contrasting texture, and (iii) to evaluate if the wilting of plants occurs at the hydraulic cut-off in soil. An experiment was conducted to determine the soil matric potential at which wilting of sunflower (Helianthus annuus L.), maize (Zea mays L.) and soybean (Glycine max L.) occurs in four soils with clay contents ranging from 7 to 57%. Soil water retention characteristics were determined by the pressure chamber and the dew point technique. Soil water retention data were fitted to empirical models for estimates of soil matric potential and water content at the hydraulic cut-off. The water contents at −15,000 hPa in samples equilibrated in pressure plates was similar to those obtained from the dew point method in our soils. Our results show that physiological wilting of plants is both plant species and soil dependent. In soils with low clay contents, different plant species wilted at similar water contents. However, in the clayey soils, the different crops showed different abilities in the uptake of water from the soil, where soybean wilted at significantly lower water contents than the other two species. The values of matric potential at the permanent wilting point found in our study were considerably lower than −15,000 hPa, suggesting that the commonly used definition of permanent wilting point as water content at −15,000 hPa is incorrect.

Estimation of soil texture from permanent wilting point measured with a chilled‐mirror dewpoint technique

AbstractSoil texture is an important factor governing a range of physical properties and processes in soil. The clay and fine fractions of soil are particularly important in controlling soil water retention, hydraulic properties, water flow and transport. Modern soil texture analysis techniques (x‐ray attenuation, laser diffraction and particle counting) are very laborious with expensive instrumentation. Chilled‐mirror dewpoint potentiameters allows for the rapid measurement of the permanent wilting point (PWP) of soil. As the PWP is strongly dictated by soil texture, we tested the applicability of PWP measured by a dewpoint potentiameter in predicting the clay, silt and sand content of humid tropical soils. The clay, silt, and sand content, organic matter and PWP were determined for 21 soils. Three regression models were developed to estimate the fine fractions and validated using independent soil data. While the first model showed reasonable accuracy (RMSE 16.4%; MAE 13.5%) in estimating the clay, incorporating the organic matter into the equation improved the predictions of the second model (RMSE 17.3%; MAE 10.9%). When used on all soil data, the accuracy of the third model in predicting the fine fraction was poor (RMSE 31.9%; MAE 24.5%). However, for soils with silt content greater than 30%, the model prediction was quite accurate (RMSE 7–12%; MAE 7–9%). The models were used to estimate the sand content and soil textures of soils, which proved relatively accurate. The dewpoint potentiometer can serve a dual purpose of rapidly estimating the PWP and the clay, fine fraction, and soil texture of soils in a cost efficient way.

Phase equilibria of (water + [EMIM] bromide) and (water + [EMIM] tosylate)

This work presents a detailed phase equilibria study on the aqueous solutions of two hydrophilic ILs that are solid at room temperature: 1-ethyl-3-methylimidazolium bromide ([EMIM][Br]) and 1-ethyl-3-methylimidazolium tosylate ([EMIM][TOS]). The melting temperatures of the pure ILs were measured to discriminate between existing literature data that show some disparity. Solid-liquid equilibrium (SLE) data for (water + [EMIM][Br]), so far lacking in the literature, were determined by a dynamic method over the major portion of the entire composition range. Using a chilled mirror dew point technique, extensive and accurate vapor-liquid equilibrium (water activity) measurements were further conducted for the aqueous solutions of both ILs. The temperature and concentration dependences of the activity data were correlated simultaneously by an extended NRTL model, whereby establishing a common description of pertinent equilibria and related thermodynamic behavior of these systems. Good performance of this model was verified against other experimental data from the literature and this work. In particular, correct predictions of experimental SLE data proved the model to extrapolate well beyond the temperature range of data underlying the correlation. Excess thermodynamic properties calculated from the model revealed that these systems exhibit large negative deviations from Raoult's law, a strongly exothermic mixing and, except for (water + [EMIM][TOS]) in the water-rich region, positive excess entropies. Comparing the two ILs, the observed deviations from ideality are always more pronounced for [EMIM][Br], which indicates that [Br]– is a more hydrophilic anion than [TOS]–. The observed pattern of thermodynamic behavior was rationalized on the molecular level by means of simple MD simulations. They showed that while there are more H-bonds formed between water and [TOS]–, these bonds are weaker than those between water and [Br]–.

Thermophysical properties of aqueous solutions of the 1-ethyl-3-methylimidazolium tricyanomethanide ionic liquid

Thermophysical behavior of the binary system [water+1-ethyl-3-methylimidazolium tricyanomethanide ionic liquid (IL)] was thoroughly characterized through systematic measurements of (vapor+liquid) equilibria (water activity aw), mixing enthalpy, density, viscosity, and refractive index. The measurements were performed in the entire composition range and/or specifically in the highly dilute IL region, at T=298.15K or as a function of temperature in the range from (288.15 to 318.15)K. Effective experimental methods minimizing IL sample consumption, using flow arrangements, instrument couplings and high degree of automation were preferably employed. In particular, the aw determination based on the chilled-mirror dew point technique and implemented by an AquaLab 4TE instrument was identified as a generally superior approach to study VLE of (water+IL) systems. Excess thermodynamic properties (Gibbs free energy, enthalpy, heat capacity, and volume) and property deviations from the linear mixing rule (viscosity, refractive index) were evaluated, Padé approximants being used to correlate adequately their complex composition dependences. The extensive aw data were processed by a two-step procedure fitting first the temperature dependence at each isopleth and subsequently the composition dependence at each isotherm. Good estimates could be thus obtained for derivative thermal properties (enthalpy, heat capacity). Alternatively, the water activity and excess enthalpy data were correlated simultaneously by a NRTL-type model, providing their compact, thermodynamically consistent and adequate representation. Despite small absolute values of excess Gibbs free energy (GE), the system is revealed to be highly nonideal, the small GE resulting from close compensation of its large enthalpy and entropy contributions. Large endothermic effects and an enhanced increase of entropy upon mixing found for this system indicate relative weakness of interactions between unlike molecules and a massive structure breakage in the solution. Positive values of excess volume and negative values of viscosity and refractive index deviations found in the major part of the composition range corroborate this general energetic and structural pattern, although the situation appears to be more complicated in the highly dilute IL region, where these properties congruently exhibit a sign inversion.

Water Activities and Osmotic Coefficients of Aqueous Solutions of Five Alkylaminium Sulfates and Their Mixtures with H2SO4at 25oC

Alkylaminium sulfates are frequently detected in ambient aerosols, and are believed to be important in the nucleation of new particles in the atmosphere, despite the comparatively low gas phase concentrations of amines. In this study, water activities and osmotic coefficients have been measured, using a chilled mirror dew point technique, of aqueous mixtures of sulfuric acid and the following alkylaminium sulfates: methylaminium, ethylaminium, dimethylaminium, diethylaminium, and trimethylaminium sulf-ate. The samples were prepared by mixing solutions of the five corresponding amines and aqueous sulfuric acid and determining the exact aminium to sulfate molar ratios by ion chromatography. The results were correlated using an extended Zdanovskii–Stokes–Robinson equation to enable concentration/water activity rela-tionships to be calculated over the entire composition range from pure aqueous sulfuric acid to pure aqueous aminium sulfate. Water activities and osmotic coefficients for aminium:sulfate ratios o...

Suction of Some Polyethylene Glycols Commonly Used for Unsaturated Soil Testing

In the laboratory, solutions of polyethylene glycols (PEGs) are used to control and apply suction in soils using the osmotic technique. In this study, the suctions of PEGs with molecular weights (Mr) of 1500, 4000, 6000, and 20 000 were measured at 25°C using the chilled-mirror dew-point technique. The mass ratio of PEG–water mixtures was varied between 0.09 to 1.09 g of PEG/g of water to cover a wide range of suction from 0.09 MPa to 12.2 MPa. The results showed that, in general, PEGs with low Mr generated greater suctions than those with higher Mr. The difference between suctions of PEGs 6000 and 20 000 was found to be minor. Concurrent with previous reports, analysis of the test results in terms of molality and molarity versus suction showed that PEGs with high M r generated greater suctions than those with lower Mr. For any PEG, both molal and molar concentrations tend to generate similar suctions at low concentrations, whereas the density effect of PEG–water mixtures was found to be significant at high concentrations in that suctions corresponding to molar concentrations were far greater than their molal series counterparts. In general, good agreements were noted between the suctions measured in this study and those reported in the literature for similar PEG types. New equations were proposed that independently related mass ratio, molality, and molarity to suction of the PEGs studied. Additionally, relationships were established between the measured % Brix values and suctions of the PEGs studied.

Assessing Errors and Accuracy in Dew‐Point Potentiometer and Pressure Plate Extractor Meaurements

Soil water potential can be determined quickly with a WP4 device, which uses a chilled mirror dew point technique. The instrument can be used to check the soil water potential of samples drained in a porous plate extractor (PPE). However, soil water potential measured in both devices on the same soil sample may not be in agreement, mainly in the wet‐end of the water retention curve. This work investigates this problem, and further evaluates how equilibrating soil samples in a PPE with different permeable material at the sample bottom (filter paper [FP], polyester fabric [PE], and synthetic knitwear [SK]) affects the final water potential. Soil samples (soil fraction <2 mm) of an Ultisol and an Oxisol were drained at 0.5 and 1.5 MPa pressure in a PPE and the water potential of these samples was measured in a WP4. Another fraction of the same soil was used to obtain a WP4 water retention curve. The permeable materials caused large differences in water retention at 0.5 MPa pressure (0.006 g g−1 in the Oxisol and 0.021 g g−1 in the Ultisol), and the FP allowed more water drainage than PE and SK, indicating the latter two should be avoided when using a PPE to determine water extraction. In both soils, the water potential measured in the WP4 was lower than −0.5 MPa for samples under 0.5 MPa pressure and greater than −1.5 MPa for samples under 1.5 MPa pressure. The increase of residual (fitted minus measured) in the WP4 water retention curve indicated that above −0.7 MPa the precision of WP4 measurements decreased drastically.

Errors in water retention curves determined with pressure plates: Effects on the soil water balance

Pressure plates apparatus are very common experimental devices utilized to measure the soil water retention curve. Many studies have demonstrated the lack of reliability of pressure plates apparatus when they are used to measure the soil water retention curve in the dry range, due to low plate and soil conductance, lack of hydrostatic equilibrium, lack of soil–plate contact and soil dispersion. In this research, we investigated measurements of soil water retention curves obtained with a combination of Stackman’s tables, pressure plates apparatus and the chilled-mirror dew point technique. Specifically, the aim of this research was: (a) to investigate the differences in the measured soil water retention curves by the different experimental methods, (b) evaluate relationships between the experimental differences and soil texture, (c) analyze the effect of experimental differences on hydraulic properties parameterization and (d) investigate the effects of the different parameters set on water transport computation. The results showed differences in measurements made by the combination of Stackman’s tables and Richards’ pressure plates apparatus as compared to the dew point method, for fine textured soils, while no significant differences were detected for coarse textured soils. Computed cumulative drainage and evaporation displayed lower values if soil water retention curves were obtained from data obtained with the Stackman’s tables and Richards’ pressure plates apparatus instead of the dew point method. In soils, where the soil water retention curve was measured with traditional methods (Stackman’s tables and Richards’ pressure plates apparatus) average cumulative drainage was 173mm, with respect to a combination of methods including the dew point methods, where the average cumulative drainage was 184mm. Average cumulative evaporation was 77mm for the traditional methods, while it was 91mm, for the combination of methods. Overall, when simulation models are used for studies related to solute transport, polluted soil remediation, irrigation management and others, erroneous measurement of the SWRC for fine textured soils, may lead to erroneous computation of the soil water balance.

Water films and scaling of soil characteristic curves at low water contents

Individual contributions of capillarity and adsorptive surface forces to the matric potential are seldom differentiated in determination of soil water characteristic (SWC) curves. Typically, capillary forces dominate at the wet end, whereas adsorptive surface forces dominate at the dry end of a SWC where water is held as thin liquid films. The amount of adsorbed soil water is intimately linked to soil specific surface area (SA) and plays an important role in various biological and transport processes in arid environments. Dominated by van der Waals adsorptive forces, surface‐water interactions give rise to a nearly universal scaling relationship for SWC curves at low water contents. We demonstrate that scaling measured water content at the dry end by soil specific surface area yields remarkable similarity across a range of soil textures and is in good agreement with theoretical predictions based on van der Waals interactions. These scaling relationships are important for accurate description of SWC curves in dry soils and may provide rapid and reliable estimates of soil specific surface area from SWC measurements for matric potentials below ‒10 MPa conveniently measured with the chilled‐mirror dew point technique. Surface area estimates acquired by fitting the scaling relationship to measured SWC data were in good agreement with SA data measured by standard methods. Preliminary results suggest that the proposed method could provide reliable SA estimates for natural soils with hydratable surface areas smaller than 200 m2/g.

Total suction measurement of unsaturated soils with a device using the chilled-mirror dew-point technique

The total suction of a soil consists of two components: matric suction and osmotic suction. There are different techniques for measuring the total, matric and osmotic suction. The total suction of the soil is related to the water vapour pressure in the air space of the soil, and can be measured by devices capable of measuring relative humidity. A range of devices is available to measure relative humidity. In this paper, a device using the chilled-mirror dew-point technique with a selectable temperature environment was used to measure the relative humidity of a soil sample. Two residual soils of Singapore were used in the evaluation of the device for total suction measurement. The residual soils were compacted at various water contents and with three compaction efforts to provide soil samples of various suction values. The total suction of the compacted soil was measured and compared with its matric and osmotic suctions as independently measured using the null-type axis-translation apparatus and the pore fluid squeezer respectively. The time to equilibrium to obtain the total suction of the soil samples varied between a couple of minutes to about 18 min. The test results show that total suctions obtained using the device are always greater than the sum of the matric and osmotic suctions measured independently. The discrepancy increases as suction increases and is attributed to the limitations of the device for measuring the relative humidity of the soil samples accurately. However, by accounting for the discrepancy, the device can be used as a rapid means of determining the total suction of unsaturated soils.

Total suction measurement of unsaturated soils with a device using the chilled-mirror dew-point technique

The total suction of a soil consists of two components: matric suction and osmotic suction. There are different techniques for measuring the total, matric and osmotic suction. The total suction of the soil is related to the water vapour pressure in the air space of the soil, and can be measured by devices capable of measuring relative humidity. A range of devices is available to measure relative humidity. In this paper, a device using the chilled-mirror dew-point technique with a selectable temperature environment was used to measure the relative humidity of a soil sample. Two residual soils of Singapore were used in the evaluation of the device for total suction measurement. The residual soils were compacted at various water contents and with three compaction efforts to provide soil samples of various suction values. The total suction of the compacted soil was measured and compared with its matric and osmotic suctions as independently measured using the null-type axis-translation apparatus and the pore f...

Characterization of SiO 2 surface treatments using AFM, contact angles and a novel dewpoint technique

The properties of sensing surfaces are particularly important in chemical and biosensing since they affect the adhesion of sensing films and the sorption of analyte molecules onto the active area of the sensor. The objectives of this work were to study the effects of several surface treatments on glass and quartz using atomic force microscopy, contact angle measurements, and a novel dewpoint error technique, in order to develop a better understanding of the effects of these treatments. The dewpoint error technique was also examined as a novel method for measuring surface energy that may have advantages over contact angle measurements. Most significantly, chromic acid and oxygen/argon sputtering treatments were found to substantially decrease the contact angles of both glass and quartz. The surface roughness of glass was markedly increased by acetic acid, heated NaOH, and piranha etch while HCl and KOH caused the highest surface roughness for quartz. A reasonably good correlation was found between decreasing contact angles and increasing dewpoint error, suggesting that the dewpoint technique may provide a quantitative measure of surface energy without some of the drawbacks of contact angle measurements. There was no correlation found between surface roughness and contact angle hysteresis or dewpoint error.

Limiting Activity Coefficients of Diols in Water by a Dew Point Technique

Limiting activity coefficients for 1,2-ethanediol (ethylene glycol), 1,2-propanediol (propylene glycol), 1,3propanediol, 1,2-butanediol, 1,3-butanediol, 1,Cbutanediol and 2,3-butanediol in water were measured over a range of temperatures (297-348 K). The recently developed dew point technique used in this investigation is especially suitable to this type of system with very low relative volatility (e.g., <0.5), where other methods are inapplicable. The experimental results were compared with extrapolated vaporliquid equilibrium (VLE) data, demonstrating the inadequacy of extrapolating VLE data to y for complex hydrogen-bonded systems. A one-parameter Wilson equation was used to characterize the results and to estimate y for water in the diols. Partial molar excess enthalpies at infinite dilution were estimated from the temperature derivative of the limiting activity coefficients. The results are discussed in terms of interand intramolecular hydrogen bonding.

High-temperature phase relations and thermodynamics in the iron-lead-sulfur system

The PbS activities in FeS-PbS liquid mattes were obtained at 1100 °C and 1200 °C by the dew-point method. Negative deviations were observed, and the liquid-matte solutions were modeled by the Krupkowski formalism. The liquid boundaries of the FeS-PbS phase diagram were derived from the model equations yielding a eutectic temperature of 842 °C atX Pbs = 0.46. A phase diagram of the pseudobinary FeS-PbS was also verified experimentally by quenching samples equilibrated in evacuated and sealed silica capsules. No terminal solid solution ranges could be found. Within the Fe-Pb-S ternary system, the boundaries of the immiscibility region together with the tie-line distributions were established at 1200 °C. Activities of Pb were measured by the dew-point technique along the metal-rich boundary of the miscibility gap. Activities of Fe, Pb, and S, along the miscibility gap were also calculated by utilizing the bounding binary thermodynamics, phase equilibria, and tie-lines.

A dew point technique for limiting activity coefficients in nonionic solutions

AbstractA new measurement technique for activity coefficients at infinite dilution has been developed involving the construction of a very dilute vapor phase and the accurate determination of its dew point. This method is especially applicable to systems of low solute relative volatility, precisely where other methods such as differential ebulliometry and headspace gas chromatography become less precise. Data are reported for γ∞ for N, N‐dimethylformamide, dimethylsulfoxide, and N‐methyl pyrrolidone in water over a range of temperatures.

Activities in Cu2S-FeS-SnS melts at 1200 °C

The dew-point technique was used to measure the vapor pressures of SnS over liquid sulfides of the system Cu2S-FeS-SnS at 1200 °C. Activities of SnS were generated from the measured vapor pressures of SnS. Activities of Cu2S and FeS were evaluated both in binary and ternary melts by Gibbs-Duhem calculations from the known SnS activity data. The systems Cu2S-SnS and Cu2S-FeS exhibit negative departures from ideal behavior, while FeS-SnS melts exhibit positive deviations.

The Moisture Content/Relative Humidity Equilibrium Relationship Of Wheat - A Review

ABSTRACT Thirty three sources of hygroscopic data for wheat are identified. Gravimetric methods predominate in the literature, followed by hygrometric methods which largely employ a dew Point technique for relative humidity determination. Hysteresis effects vary considerably in magnitude. The greatest difference between adsorption and desorption isotherms occurs in the 20–40% RH region. A table of equilibrium moisture contents interpolated from the data sets is presented for a Fixed set of temperatures and RH to enable comparison. The isotherm equations used to fit the data are also revewed. The Strohman-Yoerger, Modified-Oswin, Modified-Chung-Pfost, Chen-Clayton and Modified-Henderson equations are identified as the most suitable. Further investigation is needed to compare them.