Water Transfer Mechanism Research Articles

The Influence of Two Surfactants on Infiltration into a Water‐Repellent Soil

Water‐repellency which affects infiltration, evaporation, erosion, and other water transfer mechanisms through soil has been observed under several natural conditions throughout the world. Surfactants can be used to mitigate the consequences of soil water repellency. The infiltration rates of two surfactants applied at concentrations of 500, 1000, 3000, and 5000 mg L−1 were measured on laboratory columns of sand treated to create a stable water‐repellent system. All of these surfactant solutions had a surface tension equal to 0.035 N m−1 Drop‐penetration times (DPT) of these solutions were also measured for these solutions. An aqueous ethanol solution with an identical surface tension as the surfactant solutions was also used. The DPT decreased and the infiltration rate increased as the surfactant solution concentration increased. The results are explained by adsorption of surfactant which caused an increase in surface tension of the solution. Adsorption of surfactants enhanced soil rewetting so that treated columns that were dried had high subsequent infiltration rates with water. Because the adsorption of surfactants greatly affects infiltration, prescription of surfactant treatment on a theoretical basis is not feasible. Although some basic concepts can be established, the utility of surfactants in managing water repellent systems will depend on empirical observations.

The Influence of Two Surfactants on Infiltration into a Water-Repellent Soil

Water-repellency which affects infiltration, evaporation, erosion, and other water transfer mechanisms through soil has been observed under several natural conditions throughout the world. Surfactants can be used to mitigate the consequences of soil water repellency. The infiltration rates of two surfactants applied at concentrations of 500, 1000, 3000, and 5000 mg L−1 were measured on laboratory columns of sand treated to create a stable water-repellent system. All of these surfactant solutions had a surface tension equal to 0.035 N m−1 Drop-penetration times (DPT) of these solutions were also measured for these solutions. An aqueous ethanol solution with an identical surface tension as the surfactant solutions was also used. The DPT decreased and the infiltration rate increased as the surfactant solution concentration increased. The results are explained by adsorption of surfactant which caused an increase in surface tension of the solution. Adsorption of surfactants enhanced soil rewetting so that treated columns that were dried had high subsequent infiltration rates with water. Because the adsorption of surfactants greatly affects infiltration, prescription of surfactant treatment on a theoretical basis is not feasible. Although some basic concepts can be established, the utility of surfactants in managing water repellent systems will depend on empirical observations.

Osmotic swelling behavior of globules of W/O/W emulsion liquid membranes

The osmotic swelling behavior of water-in-oil-in-water (W/O/W) type emulsion liquid membranes (ELMs) was investigated. Using an optical microscope equipped with a camera, the changes in the size of the W/O/W globules were monitored over a long period of time (up to about 4 h). The osmotic pressure gradient between the internal and external aqueous phases was induced by creating a concentration difference of d-glucose between the two aqueous phases. The results indicate that the swelling ratio, defined as the ratio of globule diameter at time t to globule diameter at t=0, decreases with the increase in ϕ W/O(0) (initial volume fraction of internal aqueous phase droplets). The swelling ratio generally increases with the increase in the concentration of surfactant present in the membrane (oil) phase. The permeation coefficient of water also increases with the increase in the surfactant concentration. With the increase in ϕ W/O(0) up to about 0.42, the permeation coefficient decreases only slightly. However, with further increase in ϕ W/O(0), a sharp reduction in the permeation coefficient occurs. The mechanism of water transfer in ELMs of the present work is reasoned to be the diffusion of hydrated surfactants.

Investigation of the mechanism of water transfer in catalysts and adsorbents

Drying is a key stage in numerous technological processes in the preparation of adsorbents and catalysts. A very efficient method preserving the quality of dried material is adsorption-contact drying (ACD). To calculate the rate of the mass transfer in the process of the ACD, it is necessary to have the data on the ratio between the gas-phase and liquid-phase transfer of moisture. A method to determine the rates for gas-phase and liquid-phase transfer of moisture in the process of mass transfer in porous materials is suggested. The data obtained agree well with the existing theoretical concepts about the liquid-phase transfer of moisture under the mechanical contact of two porous bodies.

Modeling swelling soils for disposal barriers

A fully coupled advanced formulation for heat, liquid and gas transfer in unsaturated deforming soils is presented. Balance equations are rooted in the theory of mixtures. A double porosity model, which is believed to be especially relevant when simulating expansive soils, is proposed to characterize the water transfer mechanism. Another relevant feature of the framework developed, is the incorporation of a consistent elastoplastic model to describe stress‐ strain relationships in unsaturated soils. A flexible FE computer program was developed, including an array of alternative numerical strategies and constitutive equations to enhance its capabilities. The experimental results of a hydration and heating experiment performed on confined expansive bentonite were satisfactorily compared with model simulations. # 2000 Elsevier Science Ltd. All rights reserved.

Water and solute transfer between a prairie wetland and adjacent uplands, 1. Water balance

The hydrology and water quality of lakes and wetlands are controlled by the exchange of water and solutes with adjacent uplands. We studied a small catchment in Saskatchewan, Canada, to evaluate the mechanisms of water and solute transfer between the wetland and the surrounding upland. Detailed measurements of hydrologic processes (precipitation, runoff, evapotranspiration, and subsurface flow) and chloride distribution are combined to improve the estimate of the transfer flux. This paper describes hydrologic processes and Part 2 describes the solute transport processes. Large snowmelt runoff occurs in the catchment, which transfer 30–60% of winter precipitation on the upland into the wetland to form a pond in the center. Snowmelt water and summer precipitation infiltrate under the central pond. Infiltration accounts for 75% of water leaving the central pond and evapotranspiration accounts for 25%. Most of the infiltrated water flows laterally in the shallow subsurface to the wet margin of the pond and further to the upland, where it is consumed by evapotranspiration without recharging deep groundwater. The net recharge rate of the aquifer underlying the catchment is only 1–3 mm year −1. Snowmelt runoff transfers water from the upland to the wetland, and shallow subsurface flow transfers water in the opposite direction. When the two processes are combined, they provide the paths for cyclic transport of solutes.

IR absorption characteristics of an IR moisture sensor and mechanism of water transfer in fluidized bed granulation

Monitoring of moisture content by an infrared (IR) moisture sensor during fluidized bed granulation is a necessary way to control granule growth; however, this method requires prior investigation of IR absorption characteristics indicating the relationship between granule moisture content and IR absorption. In this contribution. for a better understanding of this IR absorption characteristics, fluidized bed granulation and drying were conducted at various powder samples and operating conditions with monitoring of moisture content by an IR moisture sensor. The effects of powder properties such as water absorbing potential and diameter on the IR absorption characteristics were investigated experimentally. Based on the results obtained, the water transfer mechanism among particles was analyzed, and factors which determined the IR absorption characteristic during fluidized bed granulation and drying were discussed.

Water transfer in mixed water-in-oil emulsions studied by differential scanning calorimetry

Water transfers are observed within complex systems containing aqueous phases separated by a membrane or an oil phase, such as biological cells or multiple emulsions. In order to better understand water transfer mechanism, a system made of a mixed water-in-oil (W/O) emulsion containing two kinds of aqueous droplets — pure water and a 30 % urea solution — was developed. Water transfer from pure water droplets to urea solution droplets was evidenced by Differential Scanning Calorimetry (DSC). Finally the mixed emulsion contains one kind of droplets made of a diluted urea solution which composition is in agreement with formulation and data obtained from experiments performed on single W/O emusions which dispersed phase is a diluted urea solution of the same composition. These mixed emulsions have been pictured as a three-fluid phases system containing two aqueous phases separated by a plane oil membrane. From a homogeneous solubility-diffusion model applied to a quasi-stationnary regime, the water intra-diffusion coefficient has been obtained and compared to the value calculated from the Stokes-Einstein equation. A factor ten makes the discrepancy between the two values, the value deduced from the model being the highest. A possible influence of the emulsifier molecules has been evoked.

Evaluating water fluxes of field-grown alfalfa from diurnal observations of natural isotope concentrations, energy budget and ecophysiological parameters

In this work, the isotopic composition of water in soil, plant and atmospheric vapour has been used to investigate the flow processes in an alfalfa canopy during a typical summer day under Mediterranean climate. In addition to the stable isotopes of water, energy budget, leaf water potential and stomatal conductance were used in an integrated approach to a better understanding of the mechanisms of water transfer. The daily enrichment cycle of 18O and 2H in the leaves can be described by a physical model assuming that one of the important factors influencing the daily variation of 18O and 2H content is the daily humidity cycle. The isotopic composition of the input water can be either determined by the collar water or by the water of the soil layers supplying water to the active roots. There is no fractionation during water uptake by the roots. Total resistance to water flow in alfalfa calculated using an Ohm's law analogue was similar to other reported values. However, alfalfa contains internal stores of water. Differences between transpiration and root water uptake can be interpreted as indicating that these internal stores contribute substantially to transpiration during the day. Upshifts and downshifts in the isotopic composition of leaves are due to contributions from these internal stores and can probably result from a modification of the values of the kinetic fractionation factor in relation to the changes in the aerodynamical regime and the stomatal opening.

Ultrastructural Morphology of the Peritoneum: New Findings and Speculations on Transfer of Solutes and Water during Peritoneal Dialysis

The mechanisms of water and solute transfer across exchange vessels still are one of the most important and unsolved questions of modern physiology. During the last few years, several investigators have developed a combined approach trying to correlate physiological studies with ultrastructural observations ( 1-4) .The understanding of the transfer mechanisms across the peritoneal membrane during peritoneal dialysis is an even more complicated issue. There is a need to integrate the known (as well as the unknown) about capillary physiology with the yet-unclear role of the mesothelial layer during dialysis -a situation which can be hardly called nonnal physiology. This review brings together recent findings and views of both morphology and physiology of the peritoneal dialysis system.

Factors influencing changes in moisture content during storage of freeze-dried vaccines in vials

Previous studies have demonstrated that the water content of freeze-dried vaccines increases during storage. The reasons for these variations in water content are discussed in this paper. Different possible mechanisms have been considered: microleakages at the closure sealing point, water vapour transfer through the closure (permeation, loss and uptake of water by the stopper). Several types of vials and closures were studied, under different conditions of storage. Regardless of the vial form selected, the probability of microleakages was low. The stopper would seem to play an important role in the water transfer mechanisms. The moisture content of the stopper determines its equilibrium relative humidity (ERH) and whether there will be moisture transfer between the stopper and the vial contents and between the stopper and the storage atmosphere.

A Study of the Water Permeability of the Gills of Freshwater- and Seawater-adapted Trout (Salmo gairdneri): Mode of Action of Epinephrine

Water permeability of trout gills (Salmo gairdneri) was studied in vitro with fish adapted to freshwater (FW) and to seawater (SW). In adapted fish, diffusional water permeability is less in SW than in FW, whereas the apparent osmotic water permeability is invariant. The ratio of osmotic to diffusional water permeabilities is greater than unity. This result demonstrates the existence of two water transfer mechanisms, diffusion and bulk transport. Osmotic permeability is increased threefold by an instantaneous change of external salinity, while diffusional permeability remains unchanged under the same circumstances. The addition of 10⁻⁶M epinephrine to the perfusion liquid leads to an increase of diffusional permeability in FW-adapted fish (+110%) and in SW-adapted individuals (+60%). Osmotic permeability increases in both cases (+30%). In the course of rapid transfer experiments, epinephrine does not modify the behavior of diffusional fluxes, while it does attenuate the osmotic flux rectification mechanis...

The efficiency of a drinking fountain

In this experiment the efficiency of a water drinking fountain was studied. Efficiency was defined in terms of the percentage of water actually consumed in relation to the water that flows from the drinking fountain, the dringing time, the water consumed per user and the electricity required to cool the water. For this purpose four different spout diameters were used and the water pressure was regulated to give two different water trajectory heights for each spout diameter setting. This resulted in eight different flow rates. The results of the study indicated that the water fountain is a highly inefficient water transfer mechanism and that extreme flow rates worsened the efficiency of the system. The intermediate spout nozzle diameters proved to be superior with regard to all the effeciency statistics.

A study of the mechanism of water transfer across frog skin by a comparison of the permeability of the skin to deuterated and tritiated water.

1. Frog abdominal skins were placed between the two half-cells of a modified version of Ussing's frog skin apparatus.2. The rate of equilibration of deuterated and tritiated water across the skin was followed at pH 5.0, 6.9, and 8.0 with Ringer solution bathing both surfaces of the skin; and at pH 7.0 with sulphate Ringer solution bathing both surfaces of the skin.3. The ratio of the permeability coefficients for the influx of deuterated and tritiated water had a mean value over all the experiments of 0.9954 +/- 0.0207, n = 27, indicating that no isotope effect was observable within the limits of accuracy of the experimental method.4. The thickness of the unstirred layers associated with the frog skin was measured, and, from the data obtained, values of the true permeability coefficients for each isotope were calculated.