Capillary Water Transport Research Articles

Boosting Water Evaporation by Construction of Photothermal Materials with a Biomimetic Black Soil Aggregate Structure.

Solar-driven interfacial evaporation is considered an efficient way to get fresh water from seawater. However, the low evaporation rate, surface salt crystallization, and low energy collection of the photothermal evaporation layer limit its further application in an outdoor freshwater field. And the aggregate structure design of the material itself is often ignored in solar-driven water evaporation. Black soil (BS), with a unique soil aggregate structure, is rich in tubular pores, which can be used for multilevel sunlight utilization and good capillary water transport. Based on the extraordinary photothermal properties and pumping capacity of BS, a reasonable unidirectional salt-collecting device is designed, which can realize long-term collection of mineral salts and continuous evaporation of seawater and generate electric energy in the continuous evaporation. Inspired by the unique aggregate structure, the photothermal material doping of halloysite and nigrosin will simulate the generation of this aggregate structure and retain a good water transport effect while obtaining multistage utilization of sunlight. The solar-driven evaporation rate of a nigrosin-halloysite solar steam generator is 1.75 kg m-2 h-1 under 1 kW m-2 mimic solar radiation; it can achieve stable salt leaching-induced voltage generation of 240 mV. This work demonstrates not only a solar evaporator that can continuously achieve desalination but also the design strategy of BS-like aggregate photothermal materials, which promotes the development of low-cost resource recovery and energy generation for practical outdoor seawater desalination.

Chalcedonite aggregate in lime mortars: Assessment of strength, microstructure, and durability

The constructions of historic buildings are on ground and sub-ground level often affected by various salts leeching in the constructions from surrounding environment due to non-existent or non-functional ground-water insulation. The salts dissolved in water are transported through capillary system of masonry and cause severe problems at air-construction interface where the water evaporates into the environment and salts accumulate in the outer-most layer destroying it in the process by the crystallization. To improve the durability of repair mortars and their ability to accumulate salts lightweight porous aggregate is used. This study focuses on the use of chalcedonite aggregate in such materials. Mortars based on aerial and natural hydraulic lime are prepared and the siliceous aggregate is replaced by chalcedonite sand. Fresh state properties of mortars likely to affect microstructure and/or durability e.g. air content in fresh mortar are determined. Flexural and compressive strength are studied at the ages of 28, 56, 90, 180, and 365 days, additionally at 90 days microstructural characteristics, durability to freeze–thaw cycles and salt crystallization resistance are studied. The use of highly porous aggregate leads to significant increase in amount of mixing water needed to achieve the same workability, while air content in fresh mortar and water retention value are only mildly affected. The substitution of aggregate leads to improvement in flexural strength however, compressive strength is decreased. The incorporation of lightweight porous aggregate causes significant increase in total open porosity of the mortars, their water absorption as well as increase in capillary water transport. Even though the significant increase in hygric properties, the durability to freeze–thaw cycling also increases. The improvement in salt crystallization resistance is observed mainly in the case of sulfate attack with only minor improvements in the solutions of nitrates and chlorides. The mortars with chalcedonite aggregate show results favourable for their utility as repair mortars, mainly in damp buildings, where the fast capillary water transport is highly beneficial.

Biomimetic Aerogel with Aligned Porous Structures from Ice Templating for Water Evaporation‐Induced Electricity Generation

AbstractWater evaporation is a ubiquitous natural process for collecting thermal energy from the environment. Carbon nanomaterial‐based aerogels are good candidates for use as hydroelectric generators (HEGs), permitting substantial interaction with water through electronic coupling, and have been considered for application in evaporation‐induced electricity generation. However, the water transport and electricity generation ability of the aerogels are affected by their pore structures. Inspired by the directional transport of the water vessel elements of the xylem, a biomimetic partially reduced graphene oxide aerogel (prGO) with an aligned porous structure is prepared, assisted by directional ice templating. The as‐prepared prGO aerogel presents a high capillary water transport rate and can efficiently transport water to the top, which is the basis for efficient current generation. This biomimetic prGO is scalable, providing an avenue for assembling other low‐dimensional carbon materials into high current output HEGs.

Drying of cable backfill by vapour diffusion balanced by capillary water suction: a laboratory experiment with altered groundwater levels

The performance of underground infrastructures, such as an electrical transmission cable, is strongly affected by transmission-induced high temperatures, which have an impact on the properties of the cable and the electric load. Therefore, it is essential to determine if a high load will cause a dry out of a sandy thermal backfill close to the cable. This paper aims at describing processes and establishing criteria for when a dry out can occur. Processes that are addressed are e.g., vapour diffusion and capillary water transport. Criteria of interest are e.g., groundwater levels and capillarity of soil. A new pilot laboratory experiment, with varying groundwater levels, was developed to investigate the dry out of the cable sand in close proximity to an operating cable. The experimental results show that a thermal backfill can withstand a dry out, at a high current load in a cable, if there is a capillary contact to a groundwater level 2 m below the backfill material.

Multiphase, multidimensional modeling of proton exchange membrane water electrolyzer

The water in a proton exchange membrane water electrolyzer (PEMWE) used for hydrogen production undergoes a multiphase flow, which makes it difficult to analyze the mass transfer phenomenon and predict the performance of the PEMWE. Therefore, the multiphase flow in the PEMWE requires a comprehensive study. This work theoretically investigates multiphase mass transfer along with the electrochemical reaction in a PEMWE using a three-dimensional computational modeling approach. First, the model was validated based on an in-house experiment, and a good agreement was achieved. Subsequently, the spatial distribution of species and the electrochemical process were investigated, and the liquid water saturation level was monitored. It was observed that the high current density results in low liquid saturation in the cathode. Oxygen is accumulated under the land owing to its longer diffusion path. Higher temperatures increase and decrease liquid saturation in the cathode and anode, respectively, because they weaken the capillary transport of water inside the porous layer. The concentration overpotential is significantly lower than the activation overpotential. Furthermore, it was found that the high porosity and low contact angle of the porous material aid the capillary transport of water inside the diffusion layer.

Unclogged Janus Mesh for Fog Harvesting.

Janus membranes with asymmetric surface wettability have been extensively utilized in various fields, including fog harvesting, because of their novel liquid transport properties. However, Janus membranes have an inherent disadvantage in terms of aerodynamic efficiency in harvesting fog because of the clogged water bridges caused by the small pore size. In the present work, we applied Janus wettability to mesh geometry with systematically varying hole sizes. For a clogged mesh with a small hole size, capillary water transport to the mesh back via the wettability gradient in the direction of fog flow helps harvest more fog by enhancing water drainage, similarly to the Janus membrane. The advantage of the capillary water transport extends to a clog-free mesh with larger hole sizes but more preferably to a Janus mesh with a superhydrophilic back, which presents the highest level of fog-harvesting yield because of the fast shedding frequency and short onset time. In contrast, a Janus mesh with a superhydrophobic front, which also has a wettability gradient along the fog flow, produces a lower fog-harvesting performance, particularly at slow fog speeds, because of the dropwise deposition of large water drops that locally disturb fog flow around a protruding water surface. On the other hand, the other type of Janus mesh with a superhydrophilic front is observed to minimize this disadvantage in the local fog flow by virtue of the filmwise deposition. It is also found that some Janus treatments can help protect mesh holes from clogging up by either forming a thin water meniscus or resisting water transport through the mesh holes.

Moisture transport and steel rebar corrosion in repair composites incorporating Nano-Fibrillated Cellulose (NFC)

Repair of deteriorating concrete infrastructure remains a major challenge. The concern is that current repair materials are not able to prevent premature failure after a repair has been performed. Thus, an engineered repair mortar that can enhance the durability of repaired composites by mitigating moisture transport and its debilitating influence on deterioration mechanisms such as steel rebar corrosion would be highly coveted. In this study, the influence of reinforcing a repair mortar with 0.1% by volume of Nano-Fibrillated Cellulose (NFC) on the capillary water transport in monolithic and composite specimens was investigated. Micro Computed Tomography (CT) imaging was also utilized in evaluating the microstructure of sorptivity test specimens. Thereafter, the influence of repair mortars on the corrosion behavior of deformed steel rebar was investigated via natural and accelerated tests. In these tests, concrete substrates had an embedded rebar in it, and repair mortars were applied on the top creating a composite specimen with a repair interface. Some of the parameters measured were surface resistivity, half-cell potential, overlay delamination time, residual rebar pullout load and rebar corrosion degree.Sorptivity tests indicated that the NFC is indeed capable of refining the pore structure through internal curing and thus reducing the capillary uptake of water. Moreover, the tendency of the NFC to entrap micro voids, especially near the repair interface, thereby indirectly reducing moisture transport and saturation of composite specimens was confirmed by CT imaging. Natural and accelerated corrosion test results demonstrated that NFC addition inhibited rebar corrosion as indicated by reduced rebar corrosion degree and delayed delamination of the repair overlay. The NFC also provided superior surface resistivity and a higher rebar pullout load capacity after corrosion.

고분자 전해질 연료전지의 다공 전달층 내부 모세관 물 전달에 대한 공극 네트워크 해석

본 논문은 고분자 전해질 연료전지에서의 전극 침수(electrode flooding) 현상에 대한 이해와 물 관리의 개선을 목표로 전극을 구성하는 소수성 다공 전달층(PTL) 내부에서 물의 모세관 전달 과정을 연구하였다. 공극 크기가 상이한 미세 다공층(MPL)과 기체 확산층(GDL)으로 구성된 다공 전달층에서의 물의 미세 전달 현상을 해석하기 위하여 정상 상태 다층(multi-layer) 공극 네트워크 모델을 개발하였다. 또한, 다공 전달층 내의 정상 상태 수분 포화도가 얻어진 이후 물이 포함된 공극 네트워크를 통한 기체확산 계산이 추가적으로 수행되었다. 해석 결과는 미세 다공층의 두께가 증가함에 따라 활발한 모세관 핑거링(capillary fingering)에 의해 물 전달 경로의 병합이 용이해지며 그 결과로 미세 다공층에서의 물 배출(breakthrough) 지점의 개수와 기체 확산층에서의 물의 체적 함량이 감소함을 보여주었다. 또한, 다층다공 전달층에서 최대 확산량을 얻기 위한 최적의 미세 다공층 두께가 존재함이 확인되었다.

A stably cross-linked ink on filter paper with 1D transport for efficient photothermal water treatment

Photothermal water evaporation using natural solar energy has been attracted more attentions due to wide applications such as water purification, sterilization, power generation and energy conservation. This article reports a low-cost and stable material for efficient generation of water vapor as well as saline and pollution water treatment. The hierarchically porous material consisting of nanoporous carbon and microporous paper is prepared by simply depositing and chemically cross-linking colloidal ink onto a filter paper. A stably homogeneous nanocarbon deposition is formed over microfibers in the paper. The nanocarbon particles greatly increase the surface area of pristine paper (from negligible to 12 m2 g−1) and light absorption. The carbon modified paper allows high water evaporation rate of 1.34 kg h−1 m−2 from a nanoporous carbon film, continuous capillary water transport in the micropores of paper, as well as minimal convective loss to bulk water due to 1D low contact area with water. The pore sizes of filter papers on the water evaporation together with the controlling of surface temperature and evaporating rate are also performed. Finally, this water solar evaporation system is applied for desalination and wastewater purifying (including heavy metal ion and organic pollutions). A safe freshwater is obtained after treatment. This study demonstrates the potential application of chemical modification of inked filter paper to achieve high evaporation rate and efficiency by rational design. A low-cost and stable material for efficient generation of water vapor and wastewater treatment was brought out, which is prepared by simply depositing and cross-linking colloidal ink onto a filter paper. The carbon modified paper allows efficient light absorption, high water evaporation rate from a nanoporous carbon film, continuous capillary water transport in the micropores of paper, as well as minimal energy loss.

Thermal Efficiency of Solar Steam Generation Approaching 100 % through Capillary Water Transport

Solar-driven interfacial water evaporation yield is severely limited by the low efficiency of solar thermal energy. Herein, the injection control technique (ICT) achieves a capillary water state in rGO foam and effectively adjusts the water motion mode therein. Forming an appropriate amount of capillary water in the 3D graphene foam can greatly increase the vapor escape channel, by ensuring that the micrometer-sized pore channels do not become completely blocked by water and by exposing as much evaporation area as possible while preventing solar heat from being used to heat excess water. The rate of solar steam generation can reach up to 2.40 kg m-2 h-1 under solar illumination of 1 kW m-2 , among the best values reported. In addition, solar thermal efficiency approaching 100 % is achieved. This work enhances solar water-evaporation performance and promotes the application of solar-driven evaporation systems made of carbon-based materials.

Thermal Efficiency of Solar Steam Generation Approaching 100 % through Capillary Water Transport

AbstractSolar‐driven interfacial water evaporation yield is severely limited by the low efficiency of solar thermal energy. Herein, the injection control technique (ICT) achieves a capillary water state in rGO foam and effectively adjusts the water motion mode therein. Forming an appropriate amount of capillary water in the 3D graphene foam can greatly increase the vapor escape channel, by ensuring that the micrometer‐sized pore channels do not become completely blocked by water and by exposing as much evaporation area as possible while preventing solar heat from being used to heat excess water. The rate of solar steam generation can reach up to 2.40 kg m−2 h−1 under solar illumination of 1 kW m−2, among the best values reported. In addition, solar thermal efficiency approaching 100 % is achieved. This work enhances solar water‐evaporation performance and promotes the application of solar‐driven evaporation systems made of carbon‐based materials.

Vertically Aligned Janus MXene-Based Aerogels for Solar Desalination with High Efficiency and Salt Resistance.

Solar desalination is an effective way of converting solar energy to heat for seawater purification. The structure of absorbers and salt resistance are two crucial parameters for water transport and desalination stability. Here, we designed a vertically aligned Janus MXene aerogel (VA-MXA) with hydrophobic upper layer and hydrophilic bottom layer. Compared with irregular porous channels, such regulatable and well-ordered vertical array structure gives competitive advantage in the capillary water transport, light absorption, and vapor escape. MXene, which possesses a theoretical light-to-heat conversion efficiency of 100%, combined with the Janus structure, can efficiently convert light to heat and prevent the photothermal layer from "direct bulk water contact" with the hydrophobic upper layer, thus decreasing heat loss, while the hydrophilic bottom layer submerged in water can quickly pump water upward through the vertically aligned channels with low transport resistance and, meanwhile, enable effective inhibition of salt crystallization due to rapid dissolution with continuously pumping water. With a vertically aligned and Janus structure by flexible design, the Janus VA-MXA exhibited a high conversion efficiency (87%) and stable water yield for 15 days (∼1.46 kg·m-2·h-1) under 1 sun. About 6 L·m-2 of freshwater was output daily from seawater.

Capillary Transport of Water in Cracked and Non-cracked UHPFRC Specimens

Capillary Transport of Water in Cracked and Non-cracked UHPFRC Specimens

Reactive Transport Modeling of Swelling Processes in Clay‐sulfate Rocks

AbstractSwelling of clay‐sulfate rocks often causes large problems in geotechnical applications such as tunneling. The primary mechanism inducing the increase in rock volume is the chemical transformation of anhydrite to gypsum, which is triggered by the ingress of groundwater. In the present study, a novel conceptual and numerical modeling approach is developed that emphasizes the effect of groundwater flow in conjunction with the associated availability of water and changing geochemical conditions on the chemical transformation of anhydrite to gypsum. A reactive transport model was developed and hydraulic, reactive, and solute transport as well as mechanical model parameters were estimated through an inversion process, constrained by geodetic ground heave measurements from a study site in Staufen, Germany. The conceptual model of the swelling process was implemented numerically through a dual‐domain modeling approach, whereby the mobile domain accounts for solute transport along discontinuities, and the immobile reactive domain represents the matrix. A mass transfer process accounts for diffusive and/or capillary water transport into the matrix, where the rate‐limited transformation of anhydrite to gypsum takes place. The model calculates heave at the land surface depending on water inflow, the transformation of anhydrite into gypsum and the local stress conditions exerted by overburden pressure. The results show that the proposed reactive transport modeling approach is suitable to quantify the observed swelling‐induced heave at the study site with a plausible parameterization. The study also highlights that diffusion is a decisive factor for the effective rate of anhydrite dissolution and, therefore, the overall chemical transformation process.

Adsorption and movement of water by skin of the Australian thorny devil (Agamidae: Moloch horridus).

Moisture-harvesting lizards, such as the Australian thorny devil Moloch horridus, have remarkable adaptations for inhabiting arid regions. Their microstructured skin surface, with channels in between overlapping scales, enables them to collect water by capillarity and passively transport it to the mouth for ingestion. We characterized this capillary water transport for live thorny devils using high-speed video analyses. Comparison with preserved specimens showed that live lizards are required for detailed studies of skin water transport. For thorny devils, there was no directionality in cutaneous water transport (unlike Phrynosoma) as 7 µl water droplets applied to the skin were transported radially over more than 9.2 mm. We calculated the total capillary volume as 5.76 µl cm−2 (dorsal) and 4.45 µl cm−2 (ventral), which is reduced to 50% filling by the time transportation ceases. Using micro-computed tomography and scanning electron microscopy of shed skin to investigate capillary morphology, we found that the channels are hierarchically structured as a large channel between the scales that is sub-divided by protrusions into smaller sub-capillaries. The large channel quickly absorbs water whereas the sub-capillary structure extends the transport distance by about 39% and potentially reduces the water volume required for drinking. An adapted dynamics function, which closely reflects the channel morphology, includes that ecological role.

Absorption Characteristics of Lightweight Concrete Containing Densified Polystyrene

The environmental impacts of the construction industry can be minimised through using waste and recycled materials to replace natural resources. Results are presented of an experimental study concerning capillary transport of water in concrete incorporating densified expanded polystyrene (EPS) as a novel aggregate. A new environmentally friendly technique of densifying was used to improve the resistance to segregation of EPS beads in concrete. Twelve concrete mixes with three different water/cement ratios of 0.6, 0.8 and 1.0 with varying novel aggregate content ratios of 0, 30, 60 and 100% as partial replacement for natural aggregate by equivalent volume were prepared and tested. Total absorption, absorption by capillary action, and compressive strength was determined for the various concrete mixes at different curing times. The results indicated that there is an increase in total water absorption (WA) and capillary water absorption (CWA) and a decrease in compressive strength with increasing amounts of the novel aggregate in concrete. However, there is no significant difference between the CWA of control and concretes containing lower replacement level.

Morphometric analysis of polygonal cracking patterns in desiccated starch slurries.

We investigate the geometry of two-dimensional polygonal cracking that forms on the air-exposed surface of dried starch slurries. Two different kinds of starches, made from potato and corn, exhibited distinguished crack evolution, and there were contrasting effects of slurry thickness on the probability distribution of the polygonal cell area. The experimental findings are believed to result from the difference in the shape and size of starch grains, which strongly influence the capillary transport of water and tensile stress field that drives the polygonal cracking.

Effect of water redistribution by two distinct saprotrophic fungi on carbon mineralization and nitrogen translocation in dry soil

Hydraulic redistribution (HR) of water from wet to dry soil compartments by non-differentiated mycelium was recently shown for the saprotrophic fungus Agaricus bisporus. The redistributed water triggered the carbon (C) mineralization in the dry soil. The potential of other saprotrophic fungal species and their mycelia networks for HR in soils is unknown. Here, we tested the potential for HR of the mycelial cord forming species Schizophyllum commune, compared it to capillary water transport in a sandy soil and assessed the impact of HR on C mineralization and enzyme activities in mesocosm experiments with dry and wet soil compartments using labeled water (2H) and labeled organic substrate (13C, 15N). Further, we determined nitrogen (N) translocation between the soil compartments by the mycelium of S. commune and A. bisporus. The flow velocity of redistributed water in single hyphae of S. commune was about 0.43 cm min−1 which is 1.5–2 times higher than in hyphae of A. bisporus, suggesting that cords enhance fungal HR. The amount of redistributed water was similar to capillary transport in the sterile sandy soil. Despite greater potential for HR, S. commune only slightly increased C mineralization and enzyme activity in the dry soil within 7 days. S. commune translocated N towards the organic substrate in the dry soil and used it for hyphal growth whereas A. bisporus redistributed N within the mycelial network towards the wet soil. Our results suggest that fungal hyphae have the potential to overcome capillary barriers between dry and wet soil compartments via HR and that the impact of fungal HR on C mineralization and N translocation is related to the foraging strategy and the resource usage of the fungus species.

Non-uniform agglomerate cathode catalyst layer model on the performance of PEMFC with consideration of water effect

We focus on the effect of cathode catalyst layer physical structure on the cell performance of proton exchange membrane fuel cell (PEMFC). At low polarization, high inlet humidification predicts better cell performance because of the more active surface in the CL. As polarization is extended near the mass transfer limited regime, high humidification only renders a flooded electrode and inferior cell performance. Catalyst layer with better capillary water transport parameters performs better than that with inferior water repulsion capability. Permeation in the gas diffusion layer (GDL) is important for efficient oxygen diffusion in mass transfer influenced regime. On the other hand, the permeability in catalyst layer only has secondary effect.The distribution of material properties in the CL is studied for the MEA fabrication strategy. The CL is divided into three sub-layers with changing material properties. With water effect considered, better performance is obtained for higher porosity near the GDL, higher electrolyte fraction in the agglomerate near the membrane. The effect of agglomerate particle size differs in the ohmic and mass transfer controlled regimes. Larger agglomerate size near GDL is preferred in the ohmic limited regime, while smaller size near GDL performs better if operated at mass transfer controlled regime.

EFFECT OF SANDSTONE ANISOTROPY ON ITS HEAT AND MOISTURE TRANSPORT PROPERTIES

Each type of natural stone has its own geological history, formation conditions, different chemical and mineralogical composition, which influence its possible anisotropy. Knowledge in the natural stones anisotropy represents crucial information for the process of stone quarrying, its correct usage and arrangement in building applications. Because of anisotropy, many natural stones exhibit different heat and moisture transport properties in various directions. The main goal of this study is to analyse several anisotropy indices and their effect on heat transport and capillary absorption. For the experimental determination of the anisotropy effect, five types of sandstone coming from different operating quarries in the Czech Republic are chosen. These materials are often used for restoration of culture heritage monuments as well as for other building applications where they are used as facing slabs, facade panels, decoration stones, paving, etc. For basic characterization of studied materials, determination of their bulk density, matrix density and total open porosity is done. Chemical composition of particular sandstones is analysed by X-Ray Fluorescence. Anisotropy is examined by the non-destructive measurement of velocity of ultrasonic wave propagation. On the basis of ultrasound testing data, the relative anisotropy, total anisotropy and anisotropy coefficient are calculated. Then, the measurement of thermal conductivity and thermal diffusivity in various directions of samples orientation is carried out. The obtained results reveal significant differences between the parameters characterizing the heat transport in various directions, whereas these values are in accordance with the indices of anisotropy. Capillary water transport is described by water absorption coefficient measured using a sorption experiment, which is performed for distilled water and 1M NaCl water solution. The measured data confirm the effect of anisotropy which is qualitatively the same as for the heat transport parameters. Summarizing the obtained results, it can be concluded that the anisotropy of sandstone should always be considered in planning the restoration works on the architectural heritage, in order to ensure compatibility between the original and replacement material. DOI: http://dx.doi.org/10.5755/j01.ms.21.3.7202