Wet Side Research Articles

Alternation of wet and dry sides during partial rootzone drying irrigation enhances leaf ethylene evolution

Soil drying increases endogenous ABA and ACC concentrations in planta, but how these compounds interact to regulate stomatal responses to soil drying and re-watering is still unclear. To determine the temporal dynamics and physiological significance of root, xylem and leaf ABA and ACC concentrations in response to deficit irrigation (DI) or partial rootzone drying (PRD-F) and re-watering, these variables were measured in plants exposed to similar whole pot soil water contents. Both DI and PRD-F plants received only a fraction of the irrigation supplied to well-watered (WW) plants, either to all (DI) or part (PRD-F) of the rootzone of plants grown in split-pots. Both DI and PRD-F induced partial stomatal closure, increased root ABA and ACC accumulation consistent with local soil water content, but did not affect xylem or leaf concentrations of these compounds compared to WW plants. Two hours after re-watering all (DI-RW) or part of the rootzone (PRD-A) to the same soil water content, stomatal conductance returned to WW values or further decreased respectively. Re-watering the whole rootzone had no effect on xylem and leaf ABA and ACC concentrations, while re-watering the dry side of the pot in PRD plants had no effect on xylem and leaf ABA concentrations but increased xylem and leaf ACC concentrations and leaf ethylene evolution. Leaf water potential was similar between all irrigation treatments, with stomatal conductance declining as xylem ABA concentrations and leaf ACC concentrations increased. Prior to re-watering PRD plants, accounting for the spatial differences in soil water uptake best explained variation in xylem ACC concentration suggesting root-to-shoot ACC signalling, but this model did not account for variation in xylem ACC concentration after re-watering the dry side of PRD plants. Thus local (foliar) and long-distance (root-to-shoot) variation in ACC status both seem important in regulating the temporal dynamics of foliar ethylene evolution in plants exposed to PRD.

Numerical study and experimental validation on heat and water transfer through polymer membrane by applying a novel enhancement technique

Abstract In the present study, a three dimensional numerical simulation is performed to investigate the heat and water transfer enhancement in a polymer membrane humidifier with partially blocked channel. The experimental tests are also conducted for validation purposes. The thermal-hydraulic performance factor (JF) is introduced as the main parameter to evaluate the humidifier performance with considering pressure drop. The higher value of JF indicates the higher heat transfer with the lower pressure drop. When there are equal mass flow rates at both wet and dry sides, three ranges of flow rates are identified. At low flow rates (less than 4.4 mg/s), with and without considering pressure drop, the blocked humidifier shows weaker performance than the simple humidifier, so blocking is not recommended under any circumstances. At moderate flow rates (between 4.4 mg/s and 6.65 mg/s), regardless of pressure drop, the performance of the blocked humidifier is better than that of the simple humidifier, and with considering the pressure drop, the blocked humidifier performs weaker. At high flow rates (greater than 6.65 mg/s), with and without considering pressure drop, the blocked humidifier performs better than the simple humidifier. The same trend holds for the case of constant dry side flow rate with the variable wet side flow rate.

Influence of Fibers on Hydro-Mechanical Properties of Bentonitic Mixtures

This paper reports the influence of fibre inclusion on the hydro-mechanical properties of bentonitic mixtures at varying compaction states. Pond ash–bentonite and sand–bentonite mixtures are synthesized by adding 20% commercial bentonite to pond ash and sand respectively. Discrete polypropylene fibres ranging from 0 to 1% are added to the mixtures. The hydro-mechanical properties of specimens; compacted to either standard or modified Proctor density; are investigated for a wide range of molding water content varying from dry to wet side of optimum. Though the inclusion of fibre has insignificant effect on optimum moisture content and maximum dry density of mixtures, the compressive strength, failure strain, unit cohesion and frictional angle of the compacted specimens are found to increase whereas the volumetric shrinkage strains are found to decrease irrespective of the molding water content. Both unreinforced and reinforced specimens exhibited the maximum unconfined compressive strength at relative water contents of 90% and 80% when compacted to standard and modified Proctor density respectively. With an addition of 1% fibre, these values are found to increase by 2 to 3 times. The specimens compacted at dry of optimum did not show any significant variation in hydraulic conductivity whereas specimens compacted at wet of optimum exhibited an increased hydraulic conductivity with fibre content. However, specimens compacted at optimum moisture content showed an insignificant change in hydraulic conductivity with increase in fibre content. Furthermore, the increase in volumetric shrinkage strain with relative water content is reduced as the fibre content increases.

Experimental study on performance of membrane humidifiers with different configurations and operating conditions for PEM fuel cells

In this study on humidifiers for polymer electrolyte membrane (PEM) fuel cell application, the experimental outcome of two air-to-air planar membrane humidifiers with three different internal flow patterns including cross, parallel and counter flows are investigated under isothermal and insulated boundary conditions. At all temperatures and flow rates, the conditions of higher performance, corresponding to highest water recovery ratio (WRR) and lowest dew point approach temperatures (DPAT), are encountered in the counter flow case, in contrary to the cross flow configuration. The insulation condition with dry inlet temperature at 30 °C and wet inlet temperature at 60 °C has a higher WRR index compared to isothermal condition at 60 °C but is lower than isothermal condition at 30 °C. The DPAT in humidifier with insulation condition is approximately equal to that obtained in isothermal condition at 60 °C but is much higher than what results in isothermal condition at 30 °C. It can be deduced that the temperature of the wet side inlet plays a key role in the humidifier performance.

Aging effects on the swelling behavior of compacted bentonite

Due to its favorable low permeability, high swelling potential, and high retention capacity for radionuclides, the compacted bentonite has been considered as suitable buffer/backfill materials for construction of deep geological repository for disposal of high-level radioactive waste (HLW). However, prior to placing the compacted bentonite brick around the canister, several months to several years may elapse, which could affect the swelling behavior. In this study, the aging effect was experimentally investigated by performing a series of swelling tests on the compacted bentonite samples (prepared at both dry and wet sides with different water contents) that had been aged for 0, 7, 14, 30, 60, and 90 days. The microstructure features prior to wetting were also investigated by means of scanning electron microscopy (SEM), together with the determination of the electrical conductivity (EC) value. Results showed the axial strain and the swelling pressure decreased as the aging time increased for samples prepared at both dry and wet sides. Moreover, the EC value decreased as the aging time increased. These phenomena could be explained by the new bonding between soil particles created by aging, which was confirmed by the SEM observations.

Evaluation of resilient modulus and unconfined compressive strength of subgrade

Subgrade soil is the important material as the foundation for supporting the pavement layers and the repeated load of vehicle traffic. To characterize the stiffness and strength behavior of subgrade due to traffic loading in structural pavement design can be determined by resilient modulus and unconfined compressive strength test. In this study, laboratory test of resilient modulus and unconfined compressive strength used to investigate (1) the effect of moisture content of the changes of stiffness and strength characteristics, (2) the correlation between the resilient modulus and elasticity modulus. The soil sample prepared at five type of compacted soils, at the dry side (OMC-20%OMC and OMC-10%OMC), OMC and at the wet side (OMC+10%OMC and OMC+20%OMC) . The result shows the moisture content has a significant effect on cohesive soil, the resilient modulus, modulus elasticity and stress value increase with the increase of moisture content until reaching the optimum moisture content (OMC) and then decrease with the increase of moisture content on the wet side of OMC point. By comparing both resilient modulus and unconfined compressive strength result from ANOVA statistics analysis can be concluded that there is no difference in stiffness between resilient modulus and modulus elasticity methods.

Changes in mineralogy and microstructure of a lime-treated silty soil during curing time

Lime treatment is widely applied to improve the workability and long-term durability of soils. In this study, the curing time effect on the mineralogy and microstructure of lime-treated soil was investigated. The soil samples were prepared with 2 % lime and statically compacted at dry (w = 17 %) and wet (w = 20%) sides of optimum. X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP) were performed on lime-treated soil at various curing times. The presence of XRD peaks attributed to portlandite even after 150 days curing time indicated that it was not totally converted in cementitious compounds after reaction with silica and alumina from clay minerals. By contrast, no obvious XRD reflections of well-crystallized cementitious compounds were identified. Furthermore, all samples compacted at dry and wet side of optimum exhibited bi-modal pore size distribution, with a decrease of macro-pore frequency with increasing water content. The microstructure changes with increasing curing time did not follow monotonic tendency. On the whole, the quantities of pores less than 0.006 μm and micro-pores increased and the quantity of macro-pores decreased with increasing curing time due to the possible creation of poorly crystallized or amorphous cementitious compounds.

The Effect of Dry and Wet Bulb Temperature Variation on the Performance of the Indirect Evaporative Cooler

The research is about designing and building up an evaporative cooling system, working by two- stages evaporative cooling system using outer air (pure air). The system is founded by designing and making a heat exchanger of orthogonal flow from Aluminum sheets of (30*60*40) cm, which represents the first stage of the system (indirect stage). The second stage (direct stage) of the system is represented by making an equipment of air washing (cylindrical) with (45 height, 60 width, 3 thickness) cm. The cooling system pulls outer air by a Centrifugal fan. The air passes through the heat exchanger pipes to be cooled tangibly (without moistening). Then it goes over the equipment of air washing to be cooled and cools the specified space. Computer software was designed by FORTRAN Language (FORTRAN 90) to predict the evaporative air cooler performance to know the proper environmental and design conditions of the system. Some variables were made to study their effect on the thermal performance of the system. The studied variable is to change the volumetric flow rate of air from (750 cfm) to (2000 cfm) of the dry side, and from (750 cfm) to (2500 cfm) of the wet side. The pipe length was changed from (20 cm) to (45 cm), and its diameter from (0.5 cm) to (3 cm). Those were the design changes. On the environmental changes, we studied the effect of changing the temperature on the dry or wet bulb of the system. The study is taken place in Tikrit University (34. 35N; 43.37 E), to determine the suitability of the weather conditions of the region for the work of the system. It was taken place in the late August for two consecutive days, with readings of 24 hours. The results show that the best quantity of the air supplied, which represent the best performance of the system (750 cfm) and (1000 cfm) for the wet side when the diameter (1-1.5 cm) and length is (45 cm). The results show also the possibility of the work of this system for the region mentioned because it is characterized by its hot and dry climate in the summer, as the efficiency of evaporative evaporator increases the hot and dry environment by 80%.

A generalised constitutive model for unsaturated compacted soils considering wetting/drying cycles and environmentally-stabilised line

A new Monash – Peradeniya – Kodikara (MPK) generalised model is presented, embodying a volumetric yield surface (i.e. loaded compaction yield surface) derived from constant water content testing, an environmentally-stabilised line representing the states achieved after a sufficient number of wetting/drying cycles, a constant plastic volumetric strain-based loading collapse yield curve and a soil water retention curve. The MPK generalised model has 16 parameters, including 10 parameters for mechanical behaviour. These 10 mechanical parameters can be determined by relatively simple constant water content tests, which is a major advantage of the model. The evolution of the plastic-strain-based soil water retention curves involves 6 parameters, some of which require calibration based on traditional SWRC testing under constant net stress. The equations for coupled hydro-mechanical behaviour were developed considering Bishop’s effective stress for the wet side of the air transition line and independent stress for the dry side of the air transition line, and the stress/strain conjugates were finally transformed to Bishop’s effective stress approach for the overall behaviour. The derived equations for the isotropic stress state were validated by reproducing a range of phenomenological observations, and the generalised MPK model is capable of reproducing most observed phenomenological behaviour, at least qualitatively.

Experimental study on heat and mass transfer of a multi-stage planar dehumidifier

Removing excessive moisture from the ambient air by means of a selective membrane in the membrane-based dehumidifier has become a new emerging technology. The present study pertains to the experimental work on heat and mass transfer of a multi-stage planar membrane dehumidifier. Commercial Nafion 212 membranes are applied in this membrane dehumidification system because of the large selectivity. The operating conditions of inlet dry air are fixed to maintain at temperature of 27ºC and relative humidity of 0.1% while performing dehumidification tests. Attention is mainly paid to examining the effects of various temperature, relative humidity and flow rate of the wet side inlet air on performance indexes including the dehumidification rate (DR), dew point approach temperature (DPAT), pressure loss (ΔP), and pumping power (Ω) in planar membrane-based dehumidifiers. Measured results show that increasing inlet temperature, relative humidity and flow rate of humid air in the wet channel enhances performance indexes, that is, higher DR, DPAT, ΔP and Ω. In addition, the counter flow configuration in the dehumidifier provides better mass and heat transfer performance compared to parallel flow configuration.

Experimental Study on the Response of Unsaturated Silt Due to Change in Drainage Conditions During the Triaxial Test Process

An experimental series is performed to study the response of unsaturated silt compacted on the dry and wet side of optimum water content due to change in drainage conditions during the triaxial test process. Soil samples were compacted at water content of 15% and 25% maintaining degree of compaction at 85%. The drainage conditions for pore air and pore water pressure was changed for isotropic consolidation, monotonic shear and water infiltration processes. The isotropic consolidation was performed by keeping pore air pressure drained and pore water pressure undrained. During monotonic shear both pore air and water pressures were undrained, whereas, the water infiltration was carried in fully drained conditions. The water infiltration was carried by keeping deviatoric stress and axial strain constant on the specimen. It was observed that the drainage conditions affect the deformation behavior of soil and results in a rapid decrease in specimen volume. Moreover, the stress paths for the specimens with constant deviatoric stress moved towards the failure line whereas the stress paths for the specimens with constant axial strain moved along the reference failure line.

Effects of microstructure on desiccation cracking of a compacted soil

Desiccation cracking has a significant influence on the hydro-mechanical behaviour of soils. Most previous studies focus on the desiccation cracking of slurry soil samples, whereas little attention has been paid to compacted soils. This study aims to investigate the effects of microstructure on the desiccation cracking of a compacted lean clay. Five soil samples are mixed with different water contents including 12.5%, 14.5%, 16.5% (optimum water content), 18.5%, and 20.5%, compacted to generate different initial soil microstructures. After compaction, the soil samples are subjected to saturation and then the same drying process. The pore size distribution of each soil sample is characterized by performing mercury intrusion porosimetry (MIP) test. The change in water content and the evolution of surface crack pattern during the drying process are continuously monitored. Experimental results show that the addition of water content during soil compaction significantly influences the microstructure and desiccation cracking behaviour of soils. With increasing compaction water content from the dry side to the wet side of the optimum water content, soil microstructure transits from an aggregate structure to a dispersed structure, resulting in the change of pore size distribution from bimodal to unimodal. For soils with aggregate structures, the desiccation cracks initiate simultaneously and distribute uniformly throughout the soil body. With decreasing water content, crack geometrical parameters such as surface crack ratio and crack density increase almost linearly. Comparatively, for soils with dispersed structures, more localized growth of primary and secondary cracks are observed and the crack geometrical parameters show a two-stage linear growth during drying. This study provides microstructural interpretations to important aspects of desiccation cracking in compacted clayey soils and may guide the design of clay materials for geotechnical engineering applications.

Transpiration Driven Electrokinetic Power Generator.

Transpiration is the process by which water is carried in plants from the roots to the leaves where evaporation takes place. Here, we report a transpiration driven electrokinetic power generator (TEPG) that exploits capillary flow of water in an asymmetrically wetted cotton fabric coated with carbon black. Accumulation of protons induced by the electrical double layer formed at the solid (carbon black)/liquid (water) interface gives rise to potential difference between the wet and dry sides. The conductive carbon black coating channels electrical current driven by the pseudostreaming mechanism. A TEPG of 90 mm × 30 mm × 0.12 mm yields a maximum voltage of 0.53 V, maximum current of 3.91 μA, and maximum energy density of 1.14 mWh cm-3, depending on the loading of the carbon black. Multiple TEPGs generate enough power to light up a light-emitting diode (20 mA × 2.2 V) or charge a 1 F supercapacitor.

A Validation of Fengyun4A Temperature and Humidity Profile Products by Radiosonde Observations

Fengyun4A is the first geostationary satellite with payload of the infrared hyperspectral sounder. The geostationary platform-based instrument can provide observational 3-dimensional fields of temperature and humidity with high scanning frequencies and spatial resolutions. The IR instrument-observed temperature (T) and relative humidity (RH) profiles are closely related to the cloud states. Radiosonde observations are used to validate the Fengyun4A T and RH profiles under different cloud-type sky conditions. The cloud-type information comes from the Himawari-8 satellite which has substantial observing overlap with Fengyun4A over Asia. Taking the radiosonde observation as the reference, Fengyun4A T profile has uncertainty of 2.1 K under clear sky, and 3.7 K under cloudy sky. When cloudy sky is divided into cloud-type skies, the categories have disparities in temperature biases, varying from positive to negative. It is found that most of cloud-type categories have uncertainties of 2.5–3.0 K. The RH profiles have an uncertainty of 18% under clear sky and 21% under cloudy sky in absolute value. On average, the RH biases show neural but positively biased at the dry side and negatively biased at the wet side in the scatter plot. The International Satellite Cloud Climatology Project (ISCCP) cloud type can help to extend the quality flag of the Fengyun4A temperature profile. The impacts from cloud types on IR sounding profiles should be considered in product development or applications.

Three-dimensional multiphase flow modeling of membrane humidifier for PEM fuel cell application

Purpose In this paper, a single module of cross-flow membrane humidifier is evaluated as a three-dimensional multiphase model. The purpose of this paper is to analyze the effect of volume flow rate, dry temperature, dew point wet temperature and porosity of gas diffusion layer on the humidifier performance.Design/methodology/approach In this study, one set of coupled equations are continuity, momentum, species and energy conservation is considered. The numerical code is benchmarked by the comparison of numerical results with experimental data of Hwang et al.Findings The results reveal that the transfer rate of water vapor and dew point approach temperature (DPAT) increase by increasing the volume flow rate. Also, it is found that the water recovery ratio (WRR) and relative humidity (RH) decrease with increasing volume flow rate. In addition, all mixed results decrease with increasing dry side temperature especially at high volume flow rates and this trend in high volume flow rates is more sensible. Although the transfer rate of water vapor and DPAT increases with increasing the wet inlet temperature, WRR and RH reduce. Increasing dew point temperature effect is more sensible at the wet side is compared with the dry side. The humidification performance will be enhanced with increasing diffusion layer porosity by increasing the wet inlet dew point temperature, but has no meaningful effect on other operating parameters. The pressure drop along humidifier gas channels increases with rising flow rate, consequently, the required power of membrane humidifier will enhance.Originality/value According to previous studies, the three-dimensional numerical multiphase model of cross-flow membrane humidifier has not been developed.

Factors determining species richness patterns of breeding birds along an elevational gradient in the Horn of Africa region.

AimTo document the species richness patterns of breeding birds along elevational gradients and explore its drivers in the Horn of Africa region.LocationHorn of Africa region.TaxonBreeding birds.MethodsDistributional data for breeding birds were collected. Elevational distribution data were extracted, interpolated, and assembled for all birds, passerines, and nonpasserines. In order to tease apart how different environmental factors contributed to the variation in species richness, we found it is necessary to divide the area into four subregions with different climatic regimes and topographic structure, namely western slope, eastern slope, wet side, and dry side. Then, the species richness in each 100‐m elevational band was counted along the elevational gradients of each subregion. Pearson's correlation analyses and ordinary least squares (OLS) regressions were used to examine the relationships between species richness and factors.ResultsThe variation in species richness followed hump‐shaped patterns for all subregions, although with peak values at different elevations. The bird species groups on the western and eastern slopes showed low and high plateaus with mid‐elevation peaks, respectively, but very low species diversities at the highest elevations. Species richness was significantly correlated with temperature range and productivity in each subregion. The temperature range, area, and productivity explained 82% of the species richness variations for all birds on the western slope.Main conclusionsThe separate analyses of four area subdivisions provide strong indications of how various factors interact. Productivity and temperature range were the major driving factors for shaping the richness patterns, but deviations from expected patterns suggest modifying roles of mist formation zones in the valleys that deeply intersect the large highlands in the west and rich riparian vegetation where water from cool and humid environments at high elevation reaches lower elevations in the arid east. Conservation is recommended in each subregion based on the elevational richness scenarios.

Wet side of the moon

The presence of water on the moon is now certain, less so its origin. New experimental findings support the idea of water being released from protonated lunar silicates due to heating from micro-meteorite impacts.

Performance analysis of a counter-flow indirect evaporative cooling system

A counter-flow regenerative indirect evaporative heat exchanger (RIEHX) was introduced and investigated. This paper aims to conduct an experimental study for the RIEHX to investigate the cooling performance under different operating conditions. The experimental prototype was able to adjust the inlet air flow rate and temperature. The thermal performance of the RIEHX was tested with variable inlet conditions. The experimental results have demonstrated that the supply air can be effectively cooled along the product air flow passages by transferring heat to the wet side of the RIEHX due to water evaporation. Under a constant inlet air velocity, the product air with a higher inlet temperature can obtain a larger temperature reduction. In addition, a lower air flow rate may enhance the cooling effect due to the increased contact duration between the air streams. The proposed system is able to improve the cooling effectiveness of the conventional plate-type indirect evaporative cooler.

Measuring near‐saturated hydraulic conductivity of soils by quasi unit‐gradient percolation—2. Application of the methodology

AbstractSarkar et al. (this issue) proposed a laboratory measurement method for obtaining the hydraulic conductivity of soil at near‐saturated moisture conditions, bridging the gap between measurements that can be obtained with the evaporation method in the medium dry region, and measurements of the saturated conductivity by traditional methods. The method is based on a tension infiltration on a limited part of the surface of a soil sample and drainage of the sample at the same tension, leading to a divergent flow field. Despite equal tensions at top and bottom of the sample (“unit gradient”), the water flux in the sample is smaller than the corresponding value of the soil hydraulic conductivity at the applied tension. From numerical analysis of the flow problem, they concluded that unsaturated conductivity can be obtained with an accuracy of 10% for all texture classes of the USDA soil texture triangle. In this paper, we test the methodology for three different soil types using an appropriate apparatus. The results match well with independent saturated conductivity measurements on the wet side, and with unsaturated conductivity measurements in the medium moisture range that were obtained with the evaporation method.

Nesting Habits of Harvest mice (<i>Micromys minutus</i>) in Semi-natural Grasslands of Paddy Fields on theCentralKanto Plain

“Ukiya no Sato” in the central part of the Kanto Plain, Japan, contains a mix of agricultural lands, such as paddy fields, and semi-natural grasslands, such as wetlands, and harvest mice (Micromys minutus) are found in both habitats. In this study, we investigated the nesting habits of harvest mice and the formation of semi-natural grasslands in this region to examine the conservation status of each. We observed many harvest mouse ball nests in the paddy fields on the plains, which were a long distance from the hilly and mountainous areas. It was inferred that the wetlands helped to maintain the mouse population through geographical and hydrological factors, as well as historical factors related to rural development. It was noteworthy that harvest mice in the study area particularly used the wetland species Carex dispalata as a nesting material and that the timing of leaf growth overlapped with the harvest mouse breeding season, indicating that this species was positively used as a nesting plant. From the viewpoint of conservation of the harvest mouse in the study area, it was considered necessary to shift to various plant communities in the wetland environment by improving the site condition closer to the wet side.