Is the water rising?

When a quantity is changing slowly it is difficult to know whetherit will continue to monotonically increase. This situation mayraise questions as to when there is a problem and what shouldbe done. Is the average level of the world's oceans rising?There is some evidence to support this contention. Is this situationa matter of concern that requires action, and what should thataction be? These are vexing questions. Ionising radiation certainly     

Heat conductivity of water near 4°C

The results of short-term nonsteady-state measurements do not confirm the view that the heat conductivity of water behaves abnormally in the vicinity of 4°C.Notation L thickness of the liquid layer, m - T temperature, K - q heat flux, W/m² - thermal conductivity, W/m·deg K. Indices 0 and L denote the beginning and end of the layer, respectively Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 2, pp. 339–342, August, 1980.     

Harvesting energy from water flow over graphene?

It is reported excitingly in a previous letter (Nano Lett. 2011, 11, 3123) that a small piece of graphene sheet about 30 × 16 μm(2) immersed in flowing water with 0.6 M hydrochloric acid can produce voltage ~20 mV. Here we find that no measurable voltage can be induced by the flow over mono-, bi- and trilayered graphene samples of ~1 × 1.5 cm(2) in size in the same solution once the electrodes on graphene are isolated from interacting with the solution, mainly because the H(3)O(+) cations in the water adsorb onto graphene by strong covalent bonds as revealed by our first-principles calculations. When both the graphene and its metal electrodes are exposed to the solution as in the previous work, water flow over the graphene-electrode system can induce voltages from a few to over a hundred millivolts. In this situation, the graphene mainly behaves as a load connecting between the electrodes. Therefore, the harvested energy is not from the immersed carbon nanomaterials themselves in ionic water flow but dominated by the exposed electrodes.     

Why are carbon nanotubes fast transporters of water?

Extraordinarily fast transport of water in carbon nanotubes (CNTs) in recent experiments has been generally attributed to the smoothness of the CNT surface. Using molecular dynamics simulations we investigate water flow in (16,16) CNTs and show that the enhanced flow rates over Hagen-Poiseuille flow arise from a velocity "jump" in a depletion region at the water nanotube interface and that the water orientations and hydrogen bonding at the interface significantly affect the flow rates. For nanotube with the same smooth wall structure but with more hydrophilic Lennard-Jones (LJ) parameters of silicon, the enhancement is greatly reduced because it does not have "free" OH bonds pointing to the wall as in CNTs that would reduce the number of hydrogen bonds in the depletion layer. Roughness in the tube walls causes strong hydrogen-bonding network and no significant flow enhancement is attained in rough tubes.     

Davies’ surface condition and singularities of deep water waves

Davies’ surface condition is an approximate free-surface condition on gravity waves progressing in permanent form on water of infinite depth. It is known that this condition preserves essential features of finite-amplitude waves including the highest one. This paper proposes a new surface condition that generalizes Davies’ idea of approximation and covers a fully nonlinear condition. Analytic continuation of the proposed surface condition allows us to explore singularities of solutions that dominate the flow. The results of singularity analysis elucidate the connection between Davies’ approximate solution and the fully nonlinear solution. In addition, it is shown that the nonmonotonic variation of wave speed with wave steepness can be predicted using a linear sum of a relatively small number of singularities. This suggests that a suitable choice of a parameter in the proposed surface condition can move singularities away from the flow field without changing their structure and may reduce numerical difficulties due to singularities for large-amplitude waves.     

Thermal properties and phase diagrams of water–hydrocarbon systems

The phase equilibria of immiscible binary systems (water–n-hexane, water–n-pentane) are investigated using a constant-volume piezometer. The measurements were performed under normal conditions, based on P,V,T,x-data obtained in the temperature range of 300–680 K, pressures up to 60 MPa, and in a wide range of densities. Based on the experimental data, we constructed phase diagrams in the P–T and T–x coordinates and determined the Krichevskii parameters for the system of water–n-hexane near the critical point of the pure solvent.     

A systems-integration approach to the optimization of macroscopic water desalination and distribution networks: a general framework applied to Qatar’s water resources

The objective of this article is to introduce an optimization-based approach for the integrated design and operation of macroscopic water networks. A structural representation approach is developed to embed all potential configurations of interest. This representation accounts for water resources, desalination plants, water users, wastewater treatment facilities, and storage. Water recycle/reuse is enhanced via the use of treated water. Water utilization is improved by minimizing the losses of discharged water resulting from the linkage of power plants and thermal desalination plants and the lack of integration between water production and consumption. Excess water is saved in storage systems or injected in aquifers for strategic (long-term) storage. The developed approach also accounts for the economic values of water uses and storage and for the cost of water production and allocation. An optimization formulation is developed and solved to determine the optimal operation of the infrastructure. The solution also determines the optimal monthly allocation and storage of water resources. A case study is solved for managing the water resources in the State of Qatar while accounting for desalination, distribution, and storage. The solution indicates that storage in tanks reaches its maximum capacity in less than a month while storage in aquifers continues throughout the year as a strategic step towards water security. The solution also illustrates the need to treat wastewater in addition to using desalination of seawater. The output water streams with different qualities are assigned to proper destinations.     

Enhancement of heat transfer by water–Al2O3 and water–TiO2 nanofluids jet impingement in cooling hot steel surface

Two different nanofluids, namely water–Al₂O₃ and water–TiO₂, were impinged in the form of jet on hot steel surface to remove high heat flux, and their performance was compared. The dimension of the test steel sample was 120 mm × 120 mm and 4 mm thickness. Four K-type thermocouples were embedded on the bottom surface of the plate to measure the transient temperature distribution. The time-temperature data were recorded by the help of a data acquisition system (make: CHINO, model: KR2000), and the results were analysed by ZAILA application software. Effect of impinging nanofluids with weight concentrations of 0.01%, 0.03%, 0.05% and 0.07% Al₂O₃ and TiO₂ nanoparticles on heat transfer from the hot surface was tested. The surface heat transfer coefficient (HTC) was computed from the time-temperature history recorded during experimentation. Experimental results revealed that addition of nanoparticles to the base fluid (water) surprisingly enhanced the heat transfer rate and HTC as expected. The heat transfer rate increased up to certain limit of nanoparticle concentrations, and then declined. Application of nanofluids for the steel strip cooling was found very effective in terms of heat transfer phenomena as compared to the conventional fluid cooling methods.     

A survey of ²²²Rn in drinking water in Mexico City

In Mexico City there are more than 22 millions of inhabitants (10 in the metropolitan area and 12 in the suburban zone) exposed to drinking water. The local epidemiological authorities recognised that exposure to radon contaminated drinking water is a potential health hazard, as has been considered worldwide. The United States Environmental Protection Agency has proposed a limit of 11.1 Bq l(-1) for the radon level in drinking water. In Mexico a maximum contamination level of radon in drinking water has not yet even considered. In this work, a (222)Rn study of drinking water in Mexico City has revealed a range of concentrations from background level to 3.8 Bq l(-1). (222)Rn was calculated using a portable degassing system (AquaKIT) associated with an AlphaGUARD measuring system. Samples from 70 wells of the water system of the south of the Valley Basin of Mexico City and from houses of some other political administrative divisions of Mexico City were taken.     

Adsorption properties of shungite in purification of water–alcohol solutions

Shungite adsorption properties to remove higher alcohols and other impurities from water–alcohol solutions is studied by the methods of nitrogen adsorption, thermogravimetric analysis, wetting, temperature-programmed desorption mass spectrometry, and FTIR spectroscopy. Shungite is shown to be able to effectively sorb impurities from water-alcohol solutions to form fairly strong adsorption systems. Heat treatment 180°C in vacuum results in almost complete decomposition of the adsorption systems, thus providing recovery and a slight increase of the specific surface and sorptive volume of shungite. The present findings demonstrate the theoretical possibility of recovery of adsorption centers on the shungite surface, which would extend its usable life as a sorbent.     

Mapping of optimum operating condition for LiBr–water refrigeration cycles

In this work, optimum operating condition maps are generated covering wide ranges of refrigeration and sink temperatures for single- and double-effect LiBr–water vapour absorption refrigeration cycle. These optimum condition maps will be useful to choose optimum operating conditions while designing LiBr–water cycle for desired applications. Methodology for generating such maps is discussed in detail, which can also be used for other absorption refrigeration cycles with various working fluids. Three configurations of LiBr–water absorption refrigeration cycles, single effect, double-effect series flow and double-effect parallel flow, are analysed with the most accurate thermodynamic property correlation available in the literature. Sensitivity of cycle performance to various operating variables such as generator, absorber and condenser temperatures is determined. Second law analysis shows that when a higher temperature heat source is available, double-effect cycles are more effective over single effect as they have higher coefficient of performance.     

Hydrogen peroxide versus water synthesis of bioglass–nanocrystalline hydroxyapatite composites

This article reports a comparison of the structural and textural properties of bioglass–hydroxyapatite (HA) composites obtained in the SiO₂–CaO–P₂O₅ system by sol–gel method, with different amounts of hydrogen peroxide (3% H₂O₂) or water (H₂O). X-ray diffraction, Raman, and FT-IR spectroscopy reveal the presence of nanocrystalline HA. Scanning electron microscopy images illustrate that the HA phase is mainly distributed on the glass surface. The results point out that the sintering at 550 °C of a sol–gel derived SiO₂–CaO–P₂O₅ bioglass leads to a single crystalline phase of HA, and validate a new processing method for obtaining bioglass–HA composites. Structural analyses of the investigated composites indicate the existence of a silicate network built up from Q₃ and Q₂ units. The replacement of water with hydrogen peroxide has as consequence the increase of depolymerization degree of silica network. Textural properties were investigated with N₂-adsorption technique. The composites prepared with hydrogen peroxide exhibit a more uniform and narrow mesoporous distribution that recommends them for drug uptake and release applications. It was found that the specific surface area and pore volume are clearly influenced by the H₂O₂(H₂O):TEOS molar ratio.     

Mechanism of silver nano-particles formation on α-alumina using supercritical water

Supercritical water impregnation is a novel method, which utilizes high diffusivity of the fluid with hydrothermal synthesis allowing nano-particles to deposit on porous materials in well-dispersed condition. In this work, silver nano-particles were deposited on the surface of α-alumina supports using metal acetate solution. TEM-EDS analyses clearly identified the silver particle of two kinds, those deposited on α-alumina surface and those gathering in bulk phase. Their particle size distribution showed differences in propensity, implying that particle formation were via different mechanism. The difference in particle deposition mechanism was also confirmed from the results of other operational factors investigated. Furthermore, the mechanism of particle deposition to alumina support surface have been proposed based on the experimental results and reported observation of nucleation and particle growth steps during the hydrothermal synthesis. In addition, the mechanism of silver particle formation has been discussed in detail.     

Heterocyclic methacrylates for clinical applications–further studies of water sorption

The room temperature polymerizing system comprising poly(ethyl methacrylate)-tetra hydrofurfuryl methacrylate (PEM/THFMA) has potential in orthopaedic and dental applications, and earlier work has shown it to have unusual water absorption characteristics. This aspect has been studied in further detail, by studying the water absorption behaviour from some biological solutions, and the effect of the addition of an antibiotic (gentamicin). For comparison purposes, a parallel system whereby tetrahydrofuryl methacrylate was replaced by hydroxyethyl methacrylate (PEM/HEMA), was studied. In the case of PEM/THFMA, water uptake was substantially reduced when absorption was carried out from solutions (from about 30% in water to about 1.5% in solutions of higher concentrations), and the corresponding diffusion coefficient increased (by a factor of several hundred). The addition of gentamicin increased uptake, but the extent of increase also decreased in solutions. It was concluded that uptake was related to the osmolarity of the external solution, and also on the presence of osmotic sites within the polymer; hence the uptake process appears to be governed by chemical potential considerations. At the higher uptakes, there was evidence of water clusters. In marked contrast, the uptake by the PEM/HEMA system was independent of the osmolarity of the external solutions, presumably due to the hydrophilic nature of HEMA.     

Environmental durability of z-pinned carbon fibre–epoxy laminate exposed to water

The influence of z-pins on the water absorption properties of a quasi-isotropic carbon fibre–epoxy laminate is assessed. Fibrous composite pins accelerate the moisture absorption rate and increase the total absorbed moisture concentration when the laminate is immersed in water. However, the moisture absorption properties of the laminate are not affected significantly by pins when exposed to hot and humid air. Water diffusion into the z-pinned laminate is aided by interfacial cracks between the pins and laminate. Also, the axial alignment of fibres within the composite pins in the through-thickness direction increases the water absorption rate. Pin pull-out tests reveal that water absorption reduces the mode I crack bridging traction load generated by pins by reducing the shear strength of the pin-laminate interface. This indicates that the mode I delamination toughness induced by pinning is weakened by moisture absorption.     

An air to water bridge: air sampling and analysis using tetraglyme

A water-soluble organic liquid is shown to scrub a wide variety of volatile organic compounds from air and gas streams. Gas pulled through impingers containing chilled tetraglyme (an organic solvent utilized in USEPA methods 3050A and 8240) is found to efficiently trap volatile Priority Pollutant, Hazardous Substance List and other organic species. A portion of the tetraglyme is subsequently dispersed into water and analyzed using conventional water analysis methodology. Practical quantitation limits of 100 ppbv have been demonstrated, and a potential to achieve lower limits of detection is clear. The method offers advantages over canister, adsorption tube, or Tedlar bag air-sampling techniques. Attributes include broad applicability, preservation of sample integrity ("plating out" of analytes is eliminated), freedom from water vapor interference, ready inclusion into water analysis methodology, simplicity, and low cost. Environmental laboratories with ordinary water/volatile organic analysis equipment are enabled to perform air-monitoring analyses without specialized hardware or expertise.     

Hydrodynamic influence on ship-hull vibration close to water bottom

The problem of a uniform ship-hull girder vibrating vertically close to water bottom is studied. A simple formula for the added mass is found by use of the method of matched asymptotic expansions. Results obtained from the present method and BEM are compared. They are in good agreement in the range considered here. The obtained added mass is used to predict the natural vibrations of a uniform beam vibrating close to water bottom. Numerical values show that the effects of shallow water are significant. The first- and second-order frequencies of the ship hull studied in this paper in deep water are about 1·4–3 times higher than those in shallow water.     

Nanostructured WO₃/BiVO₄ heterojunction films for efficient photoelectrochemical water splitting

We report on a novel heterojunction WO(3)/BiVO(4) photoanode for photoelectrochemical water splitting. The heterojunction films are prepared by solvothermal deposition of a WO(3) nanorod-array film onto fluorine-doped tin oxide (FTO) coated glass, with subsequent deposition of a low bandgap, 2.4 eV, visible light responding BiVO(4) layer by spin-coating. The heterojunction structure offers enhanced photoconversion efficiency and increased photocorrosion stability. Compared to planar WO(3)/BiVO(4) heterojunction films, the nanorod-array films show significantly improved photoelectrochemical properties due, we believe, to the high surface area and improved separation of the photogenerated charge at the WO(3)/BiVO(4) interface. Synthesis details are discussed, with film morphologies and structures characterized by field emission scanning electron microscopy and X-ray diffraction.     

Arsenic removal from water using calcined Mg–Al layered double hydroxide

Arsenic (As) in drinking water and its related toxicology are serious concerns nowadays. Development of better techniques related to removal of As from drinking water is an urgent need. Layered double hydroxide (LDH) or hydrotalcite-like compound with the general formula [M_1−x ²⁺ M _x ³⁺ (OH)₂] ^x+ A ^x−·nH₂O can be considered as a good adsorbent for the removal of toxic As from water. Due to large surface area and high anion exchange capacity of LDH, the compound may be a good adsorbent for the removal of As from contaminated water. In this study, the removal of As in aqueous solution by adsorption method based on the calcination–rehydration reaction was investigated in batch experiment at (30 ± 1)°C. Results showed the removal of 99.99% As from a solution of 0.1 ppm of As; the adsorbent required at saturation was 0.10 g/20 ml As solution with 90 min of exposure at (30 ± 1)°C. Factors like pH, adsorbent dose and shaking time influenced the rate of As removal. Experiment showed that the adsorption process follows the Freundlich-type adsorption isotherm. The explanation of adsorption phenomenon is supported by X-ray diffraction pattern.