Measured Moisture Profiles Research Articles

Detailed investigation of capillary active insulation materials by 1H nuclear magnetic resonance (NMR) and thermogravimetric drying

Capillary active interior insulation materials are an important and innovative approach to minimize energy losses of historical buildings. In an experimental setup, we investigate the development of moisture profiles under realistic boundary conditions to determine the liquid moisture conductivity for two different interior insulation materials. The moisture profiles were determined by destructive sample cutting with subsequent thermogravimetric drying as well as directly measured by the non-destructive method NMR, which has a higher spatial resolution and even enables repetitive measurements during the course of the experiments. We observed that the moisture profiles obtained from both methods showed good agreement, when compared at the low spatial resolution of sample cutting. This raises confidence in the method of simple mechanical sample cutting. In the next step, the liquid moisture conductivity was calculated using an inverse modelling approach based on both measured moisture profiles separately. Then, we compared the pore-size distributions of the investigated samples based on NMR T2-relaxation-time distributions, mercury intrusion porosimetry and indirect determination from pressure plate and sorption isotherm measurements. Moreover, the measured T2-relaxation-time distributions across the sample depth may give further insight into the saturation degree of the different pore sizes.

Retrieving soil moisture profiles based on multifrequency polarimetric radar backscattering observations. Theoretical case study

ABSTRACT In this theoretical work, a dual-frequency polarimetric method is proposed for measuring moisture profiles in the topsoil up to 0.30 m thick. A case of measuring soil moisture profiles, which monotonically changes with depth, during 37 days after irrigation is considered. Original values of backscattering coefficients are calculated by the Oh model and by the small perturbation method at frequencies of 5.4 GHz and 435 MHz, respectively. In these calculations, we used measured moisture profiles and spectroscopic refractive mixing dielectric model of non-saline mineral soil with a clay fraction of 9.1%. Soil moisture profiles are retrieved by solving the inverse problem, the cost function of which is constructed based on the co- and cross-polarized ratios, calculated at two frequencies for the measured and modelled soil moisture profiles. An exponential function is used as a modelled soil moisture profile. It is shown that the standard deviation between the retrieved and measured soil moisture values in the surface layer 0.30 m thick appears to be ≤0.02 m3 m−3 (theoretical limit), and the determination coefficient is 0.881. The study shows a promising path towards developing multi-frequency radar systems for remote sensing of soil moisture profiles using satellites-based and unmanned aerial vehicles air-based platforms.

Comparison of TDR and X-ray method for determining moisture transport parameters

This work compares two methods, the X-ray method and the time domain reflectometry (TDR) method, which are used for determining moisture transport parameters, such as moisture diffusivity, w-λ profile and absorption coefficient. Both methods are suitable for measuring instantaneous moisture content profiles during water transfer through a porous material. However, while the X-ray method is fully non-destructive, the TDR measurement requires installation of TDR probes into the measured material and the obtained results can be influenced by the quality of the contact between the TDR probe and material.The moisture transport parameters were determined from the measured moisture profiles during the process of water uptake, realized on calcium silicate samples. The same measurement arrangement and sample treatment were applied for both methods. The moisture diffusivity moisture dependence was calculated using Boltzmann transformation.The moisture transport parameters obtained by the TDR method were sufficiently close to the values obtained from the X-ray measurement.

Identification of Moisture Diffusivity of Autoclaved Aerated Concrete in the Form of Smooth Two-Variable Function

The identification of moisture diffusivity of autoclaved aerated concrete as a function of both temperature and moisture content is presented. At first, a series of laboratory experiments at various temperatures is carried out. Then, the measured moisture profiles along the sample are analyzed using inverse analysis. For the definition of moisture diffusivity an empirical formula is chosen and its parameters are identified by genetic algorithm. In this way, a single inverse analysis procedure is conducted that allows for the identification of one global smooth moisture diffusivity function depending on both temperature and moisture content. Since the hygrothermal performance of wall assemblies has a significant effect on energy efficiency of building envelopes, the identified material parameter may help to increase the accuracy of energy related calculations.

A framework for soil-water modeling using the pedostructure and Structural Representative Elementary Volume (SREV) concepts

Current soil water models do not take into account the internal organization of the soil medium and consequently ignore the physical interaction between the water film at the surface of solids that form the soil structure and the structure itself. In this sense, current models deal empirically with the physical soil properties, which are all generated from this soil water and soil structure interaction. As a result, the thermodynamic state of the soil water medium, which constitutes the local physical conditions of development for all biological and geochemical processes within the soil medium, is still not well defined and characterized. This situation limits modeling and coupling the different processes in the soil medium since they all thermodynamically linked to the soil water cycle. The objective of this article is to present a complete framework for characterizing and modeling the internal soil organization and its hydrostructural properties resulting from interaction of its structure with the soil water dynamics. The paper builds on the pedostructure concept, which allowed the integration of the soil structure into equations of water equilibrium and movement in soils. The paper completes the earlier framework by introducing notions of soil-water thermodynamics that were developed in application to the concept of the Structural Representative Elementary Volume (SREV). Simulation of drainage after infiltration in the Yolo loam soil profile, as compared to measured moisture profile using the measured soil characteristic parameters, showed a high degree of agreement. This new modeling framework opens up new prospects in coupling agro-environmental models with the soil medium, recognizing that the soil organization, hydro-structural, and thermodynamic properties are the foundation for such coupling.

Experimental investigation and theoretical modelling of absolute convective drying of starch

Starch is a granular, hygroscopic, capillary-porous material with an intricate structure. It is known that drying starch till 0% moisture is a physical treatment that modifies starch properties. However, depending upon the heat and mass transfer mechanisms prevalent in the drying system, starch properties are modified in a unique manner. Therefore, the drying operation itself needs to be thoroughly understood. Potato starch was treated in an oven at three high-temperature levels (110, 130 and 140°C) and for three sample thicknesses (2.8, 5.6 and 11.2mm). It was observed that drying of starch with moisture content in the hygroscopic range occurred only in the 2nd falling rate period. Two existing theoretical, drying models, one based upon the Krischer Theory and the other based upon the Percolation Approach, were considered apt for modelling the oven drying. Both models describe the experimentally measured moisture profiles well. During drying, transition from one water sub-population to another was smooth. The effective diffusion coefficient decreased with moisture content and increased with temperature, but did not follow Arrhenius’ Law above 130°C.

Determination of moisture diffusivity in porous materials using gamma-method

In the present paper, results of an experimental gamma ray study of moisture transfer processes in porous material are reported. Evolution of moisture profiles in porous concrete samples during sorption and capillary moistening has been examined. Measured moisture profiles were used to determine, by the Boltzmann–Matano method, the coefficient of moisture diffusion versus moisture content of the material under various moistening conditions.

Testing MACRO (version 5.1) for pesticide leaching in a Dutch clay soil

Testing of pesticide leaching models against comprehensive field-scale measurements is necessary to increase confidence in their predictive ability when used as regulatory tools. Version 5.1 of the MACRO model was tested against measurements of water flow and the behaviour of bromide, bentazone [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one-2,2-dioxide] and imidacloprid [1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine] in a cracked clay soil. In keeping with EU (FOCUS) procedures, the model was first calibrated against the measured moisture profiles and bromide concentrations in soil and in drain water. Uncalibrated pesticide simulations based on laboratory measurements of sorption and degradation were then compared with field data on the leaching of bentazone and imidacloprid. Calibrated parameter values indicated that a high degree of physical non-equilibrium (i.e. strong macropore flow) was necessary to describe solute transport in this soil. Comparison of measured and simulated bentazone concentration profiles revealed that the bulk of the bentazone movement in this soil was underestimated by MACRO. Nevertheless, the model simulated the dynamics of the bentazone breakthrough in drain water rather well and, in particular, accurately simulated the timing and the concentration level of the early bentazone breakthrough in drain water. The imidacloprid concentration profiles and its persistence in soil were simulated well. Moreover, the timing of the early imidacloprid breakthrough in the drain water was simulated well, although the simulated concentrations were about 2-3 times larger than measured. Deep groundwater concentrations for all substances were underestimated by MACRO, although it simulated concentrations in the shallow groundwater reasonably well. It is concluded that, in the context of ecotoxicological risk assessments for surface water, MACRO can give reasonably good simulations of pesticide concentrations in water draining from cracking clay soils, but that prior calibration against hydrologic and tracer data is desirable to reduce uncertainty and improve accuracy.

Concentration-dependent diffusivity and anomalous diffusion: A magnetic resonance imaging study of water ingress in porous zeolite

Magnetic resonance imaging is employed to study water ingress in fine zeolite powders compacted by high pressure. The experimental conditions are chosen such that the applicability of Boltzmann's transformation of the one-dimensional diffusion equation is approximately satisfied. The measured moisture profiles indicate subdiffusive behavior with a spatiotemporal scaling variable eta=x/t(gamma/2) (0<gamma<1). A time-fractional diffusion equation model of anomalous diffusion is adopted to analyze the data, and an expression that yields the moisture dependence of the generalized diffusivity is derived and applied to our measured profiles. In spite of the differences between systems exhibiting different values of gamma a striking similarity in the moisture dependence of the diffusivity is apparent. This suggests that the model addresses the underlying physical processes involved in water transport.

Infiltration into inclined fibrous sheets

The flow from line and point sources through an inclined fibrous sheet is studied experimentally and theoretically for wicking from a saturated region and flow from a constant-flux source. Wicking from a saturated line generates a wetted region whose length grows diffusively, linearly or tends to a constant, depending on whether the sheet is horizontal or inclined downwards or upwards. A constant-flux line source generates a wetted region which ultimately grows linearly with time, and is characterized by a capillary fringe whose thickness depends on the relative strength of the source, gravitational and capillary forces. Good quantitative agreement is observed between experiments and similarity solutions.Capillary-driven and constant-flux source flows issuing from a point on a horizontal sheet generate a wetted patch whose radius grows diffusively in time. The flow is characterized by the relative strength of the source and spreading induced by the action of capillary forces, gamma. As gamma increases, the fraction of the wetted region which is saturated increases. Wicking from a saturated point corresponds to gamma = gamma(c), and spreads at a slower rate than from a line source. For gamma < gamma(c), the flow is partially saturated everywhere. Good agreement is observed between measured moisture profiles, rates of spreading, and similarity solutions.Numerical solutions are developed for point sources on inclined sheets. The moisture profile is characterized by a steady region circumscribed by a narrow boundary layer across which the moisture content rapidly changes. An approximate analytical solution describes the increase in the size of the wetted region with time and source strength; these conclusions are confirmed by numerical calculations. Experimental measurements of the downslope length are observed to be slightly in excess of theoretical predictions, though the dependence on time, inclination and flow rate obtained theoretically is confirmed. Experimental measurements of cross-slope width are in agreement with numerical results and solutions for short and long times. The affect of a percolation threshold is observed to ultimately arrest cross-slope transport, placing a limitation on the long-time analysis.

A Sharp Drying Front Model

The drying of materials is often described by nonlinear diffusion equations. Up to now the only way to solve these equations is by numerical simulations. Recently an analytic solution has been proposed for the drying problem. Based on this solution a sharp drying front model is presented. Measured moisture profiles during drying and the drying curve of gypsum are compared with approximate models.

Experimental analysis of coupled water and chloride transport in cement mortar

Abstract Coupled water and chloride transport in cement mortar is analyzed experimentally in the paper. Samples with initial moisture content corresponding to 45% relative humidity are subjected to one-sided sodium chloride-in-water solution uptake, and moisture profiles and chloride concentration profiles are determined in three chosen time intervals. In the evaluation of measured moisture profiles and chloride concentration profiles, diffusion model is employed. Moisture diffusivity is determined as function of moisture content and chloride diffusion coefficient as function of chloride concentration using two methods commonly used for analysis of moisture profiles, namely the double integration method and the Matano method. The highest values of both coefficients are obtained by Matano method for the curves corresponding to 24 h exposure to the solution, the lowest values by Matano method for 168 h, the results obtained by double integration method are in between. The complementary experiments with distilled water as penetrating liquid performed for the sake of comparison do not show this feature. It is observed that water transport in the initial time period is for the chloride solution faster and in later times slower than for distilled water. Therefore, the observed differences in the calculated apparent values of moisture diffusivity and chloride concentration coefficients are attributed to the fact that Cl− and Na+ ions are adsorbed on the pore walls faster than water molecules. This effect should be included into the mathematical models using ion binding isotherms.

Analytic solution for the non-linear drying problem

Recently, Landman, Pel and Kaasschieter proposed an analytic solution for a non-linear drying problem using a quasi-steady state solution. This analytic model for drying is explained here. An important consequence of this model is that the drying front has a constant speed when it is entering the material. This is also observed in experiments. On the basis of this constant drying front speed comparisons are made between the analytic model and numerical simulations. Finally comparisons are made between measured moisture profiles during drying and the analytic model.

Testing PESTLA using two modellers for bentazone and ethoprophos in a sandy soil

Two modellers tested the PESTLA model (version 2.3.1) against results of a field study on bentazone and ethoprophos behaviour in a sandy soil. Both modellers achieved an acceptable description of the measured moisture profiles but only after calibration of the soil hydraulic properties. Both could describe the bromide-ion concentration profiles measured at the end of the first winter reasonably well. However, both predicted that practically all bromide had leached out of the top 50 cm of the soil at the end of the second winter, whereas about 10% of the bromide dose remained in this layer. This is attributable to a systematic deviation of bromide transport from the concept assumed in the convection/dispersion equation and/or to the release of bromide from dead root remnants. Both modellers derived pesticide transformation and sorption parameters from laboratory studies with soil from the field. Both described bentazone movement reasonably well. Modeller 1 described the concentration profiles reasonably well, whereas Modeller 2 strongly overestimated the concentrations at the end of the study. This difference was mainly attributable to a difference in interpretation of the temperature dependence of the transformation rate of bentazone. Only Modeller 2 simulated ethoprophos behaviour. He simulated the persistence of ethoprophos in the top 20 cm very well during the first 200 days. However, thereafter the transformation in the field proceeded much faster than simulated. This is probably caused by accelerated transformation resulting from exposure of the top soil layer to about 1 mg kg −1 of ethoprophos over 200 days. Simulated penetration of ethoprophos was deeper than measured. By including accelerated transformation (admittedly on an ad-hoc basis) within the simulations, good agreement was achieved between measured and simulated penetration of ethoprophos. Calculations showed that the effect of calibrating water flow was substantial for bentazone but small for ethoprophos. However, the effect of calibration of water flow for bentazone was much smaller than the effect of the difference between the transformation rate parameters derived by the two modellers. We recommend that the guidance for deriving pesticide–soil input parameters be improved in order to reduce differences between modellers because a large influence of the person of the modeller on the outcome of model tests is unacceptable for methodological reasons.

Measurements of water transport in a gel by Overhauser magnetic resonance imaging

Overhauser imaging in a magnetic field of 16 mT was employed for a study of water transport during the drying process of an agar gel. The data illustrate important aspects of Overhauser imaging, such as the large sensitivity to small changes of local moisture, which may be attainable under appropriate conditions. The non-Fickian nature of the water transport process can be clearly inferred from the measured moisture profiles.

Tropical Upper-Tropospheric Dry Regions from TOVS and Rawinsondes

Water vapor (WV) radiances from the TIROS-N Operational Vertical Sounder (TOVS) and rawinsondes during January 1979 are intercompared within the equatorial dry zone (EDZ) southwest of Mexico and the subtropical high (STH) southwest of Hawaii. Discrepancies are found when inferring upper-tropospheric moisture over the EDZ from different instrument platforms. This paper reconciles these discrepancies between radiances and operationally measured moisture profiles, quantifies the impact of trace amounts of upper-tropospheri WV on satellite-measured radiances, and summarizes limitations in the use of WV channel data for integrated precipitable water (PW) estimates. Contradictory upper-tropospheric moisture information is obtained over the EDZ when operational rawinsonde data and outgoing longwave radiation (OLR) are compared to TOVS WV radiances. However, no such contradiction is observed over the STH when all three data sources indicate dry conditions in the upper troposphere. This dryness is depicted in histograms of 6.7- and 7.3-µm WV brightness temperatures Tb, where a subset of excessively warm (dry) values exists within the STH but not the EDZ. It is shown that variations in small quantities of subtropopause moisture account for much of the WV Tb, discrepancy between these two regions; this moisture is not reported in operational rawinsonde data or detected in OLR. An upper-layer moisture boundary is defined linking TOVS and rawinsonde observations. This moisture boundary is the pressure level reached when moisture is integrated downward from 300 mb to a PW content of 0.6 mm. Operational rawinsonde limitations require that 300 mb be used for the top of our model atmosphere. Correlation imply that 70% of the upper-boundary elevation pressure (elevation) derived from rawinsonde data can be explained by WV Tb, variations. However, large standard deviations up to 55 mb are still present in boundary pressure estimated from WV radiances. Calculations from a radiative transfer model suggest that trace moisture between 100 and 300 mb, not normally available in operational soundings, causes the discrepancy. Analysis of special ship-launched rawinsondes confirm this hypothesis and demonstrate that up to 50% of the TOVS WV weighting functions can be attributed to tropospheric moisture above 300 mb; associated PW amounts may be as little as 0.2 mm. Accounting for this moisture could reduce errors in moisture boundary locations, estimated from TOVS, to less than 10 mb.

Moisture Movement in a Clay based Buffer Material under Isothermal Conditions

ABSTRACTSeveral series of one dimensional tests were performed to examine the moisture and soil water potential distributions in the buffer material compacted to a dry density of 1.67 Mg/m3 and volumetric water content of 0.28. Diffusivity parameters were calculated using the measured moisture profiles combined with the finite difference method. Powell’s optimization was used to determine the material parameters.It is experimentally demonstrated that the moisture distribution is highly dependent on the test boundary conditions. When volume change was allowed to take place during infiltration process, the buffer material adsorbs more water than in the case of no volume change. This is attributed to an increase in hydraulic conductivity by one order of magnitude. As the volumetric water content increases soil water diffusivity increases and soil water potential decreases.

On the falling‐rate period

AbstractA fixed bed of glass particles, wetted with water, was dried from above. The measured moisture profiles within the sample show that its surface is not completely dry during the falling‐rate period. Hence, the current view, according to which the moisture front retreats into the sample directly after reaching the critical moisture content, has to be revised. Assuming that parallel dry and wet channels form within the sample during the constant‐rate period, the onset of the falling‐rate period depends only on the diameter of these channels. If the moisture is distributed very finely, a large number of channels with a small diameter have to be considered. The falling‐rate period for this system occurs at low moisture contents. For a coarse distribution of moisture, fewer channels with a large diameter should be assumed. Their drying rates show the beginning of the falling‐rate period already at high moisture contents. A good agreement between measured and calculated drying rates could be achieved by fitting the channel diameter. Only for very low moisture contents, is the agreement poor. This is to be expected, because the measured moisture profiles show a completely dry sample surface for these moisture contents, indicating that the moisture front has already retreated into the sample.

Nuclear reaction analysis for measuring moisture profiles in graphite/epoxy composites

The absorption of moisture by epoxy resins and graphite/epoxy composites causes degradation of mechanical properties at elevated temperatures. In order to study the rate of moisture absorption and transport in fiber-reinforced epoxy, nuclear reaction analysis methods have been used to measure the localized moisture content in these materials. The experimental conditions have been determined for which the D( 3He, p) 4He reaction meets the particular requirements for measuring moisture profiles in composites. A description of the experimental procedures and the method of defining deuterium reference standards for measuring absolute concentrations of D 2O is presented. The technique has been applied to fully and partially saturated epoxy resin and composite specimens that have been subjected to various conditions of exposure. The moisture distribution has been measured through the thickness of composite specimens with 12 μm resolution and with a level of detectability of 0.01 wt.% D 2O. The measured profiles in composites are compared to calculations of classical diffusion models of water transport.