Pure Water Vapor Research Articles

Osmotically Driven Water Vapor Transport in Unsaturated Soils

Knowledge of the transport processes of bulk fertilizers and other solutes in soils and porous media is vital to understanding the environmental and economic impacts of many agricultural and waste disposal practices. Previous experimental research shows that significant water movement can occur towards regions of high salt concentrations in unsaturated porous media. It is hypothesized that in unsaturated media, large gradients in aqueous osmotic potentials cause significant water‐vapor fluxes towards regions of high solute concentrations. A physically based model to describe this process is developed by combining existing theories of liquid‐water and water‐vapor transport with aqueous electrolyte theory. A simplified solution, demonstrating these water‐vapor transport processes, is compared with experimental results from discontinuous soil column experiments previously published by Wheeting (1925) The results confirm that large osmotic potentials created in the presence of high solute concentrations in unsaturated porous media, can account for the quantities of water vapor movement observed. This redistribution of pure water vapor complicates modeling of ion diffusion in these systems and is an important process to include in solute transport models when high solute concentrations exist in unsaturated soils.

High Temperature Corrosion Behaviour of some Boiler Steels in Pure Water Vapour

Six steel grades, T22, T23 (2 1/4 4 Cr), T91, T92, T122 (9-12%Cr) and TP347 (austenitic 18%Cr) were exposed during 32 weeks (= 5376 h) in pure water vapour at temperatures of 500, 550, 600 and 650°C. The corrosion kinetics, determined by gravimetric measurements (by oxides descaling), follows a parabolic law, except for the austenitic steel and the 2 1/4 Cr steels at the highest temperatures. The corrosion rates of the six steels may be high: 0,1 mm/year for the 9-12 %Cr at 650 °C for example. The favourable effect of chromium is strongly less high in steam than in other media (air, combustion gases…). The stainless steel TP347 in water vapour has a better corrosion resistance but after all mediocre because of an important scaling phenomenon.

Abnormal Oxidation of Stabilized Ferritic Stainless Steels in Water Vapor

The influence of water vapor on the high temperature oxidation of several stabilized ferritic stainless steels with various Si and Cr contents has been studied by thermogravimetry at 900°C in pure water vapor or dry oxygen, followed by the characterization of the oxide scales formed. Oxidation of Fe-Cr steels in pure water vapor was characterized by a non-protective breakaway oxidation due to the formation of iron oxide nodules on the sample surface. Decreasing the H 2 O partial pressure or increasing the Si or Cr content enhanced the oxidation resistance of the alloy by delaying the breakaway appearance. This abnormal oxidation is thought to be initiated by the arrival of oxygen- and hydrogen-containing species on the chromium depleted metal/oxide interface. The mechanism of the effect of water vapor is discussed and some assumptions proposed.

Raman Spectroscopy Determination of Residual Stresses at Room Temperature in Chromia Scales Grown on Pure Chromium in Oxygen and in Water Vapour

Raman spectroscopy was used for determining the stresses generated in the chromia scales formed on pure chromium by thermal oxidation in dry oxygen or in pure water vapour. After oxidation, the residual stresses in the oxide scale are compressive, and depend on several parameters, among which the oxidation conditions (nature and partial pressure of the oxidant) and oxide thickness. A stress gradient through the oxide scale was underlined by measurements on a taper section of the metal/oxide system. Compressive stresses seemed to be stronger at the oxide surface compared to the metal/oxide interface. In the case of oxide scales generated in water vapour, a duplex morphology was observed, and it was noticed that the stresses are lower in the equiaxed and fine grained inner layer than in the compact and coarse grained outer layer. These features let imagine partial relaxation of stresses by creep within the inner part of the scale grown in water vapour. In dry oxygen the poor adherence of the oxide induced rapid relaxation by buckling and spalling.

Major auxiliary equipment needs for the world energy network project

Many national energy projects have been pursued in Japan. Some of them are very important to control the emission of CO 2 from fossil fuel. The world energy network (WE-NET) project based on a hydrogen combustion gas turbine is one of the national projects and has a high target of thermal efficiency up to 60% or more (HHV) [Proc. IJPGC, Vol. 2, Baltimore, 1998, p. 293; Proc. IJPGC, Vol. 2, Baltimore, 1998, p. 433; Annual Summary Report on WE-NET, 1997; J. JSME, 100 (947) (1997) 1034; J. GTSJ, 27 (4) (1999) 217]. However, this new technology has to be developed by an application of a combined cycle for gas and steam turbines and special auxiliary equipment such as an oxygen supply plant and heat exchangers. The hydrogen combustion gas turbine will be operated by pure hydrogen and oxygen supplied and kept to produce a pure water vapor only. If other gaseous components are included in the combustion gas, the thermal efficiency of the combined cycle is decreased by the breakdown effect of a condenser vacuum. In this project, hydrogen may be imported from some foreign countries where it has to be produced by using clean and renewable energies, for example, hydropower or solar energy. On the other hand, the oxygen to be distilled from the air has to be supplied by auxiliary equipment of a liquid oxygen plant. This auxiliary equipment, however, will consume much power. In an existing type of the liquid oxygen plant, about 10% of the total power plant output has been consumed for the additional power of oxygen supply. In addition, the WE-NET combined cycle of the hydrogen combustion gas turbine will be supported by many heat exchangers that have to be checked for their technical problems. This paper has been highlighted at high performance design and setup of the major auxiliary equipment of the oxygen supply plant and the heat exchangers. The R&D prospect of their auxiliary equipment to attain a high thermal efficiency of the combined cycle in the WE-NET project will be discussed.

Passivation of iron by oxidation in H 2O and O 2/H 2O mixtures

In order to obtain insight in the oxidation mechanism of Fe(1 0 0) in oxygen and water and determine the rate limiting step in the oxidation, we studied the initial oxidation of Fe(1 0 0) in water vapor and water vapor/oxygen gas mixtures using ERD, XPS and ellipsometry. The hydrogen content of the oxide layer grown at room temperature was determined. The H/O ratio in the oxide layer amounted to 0.28±0.02. The formation of a H and Fe 3+ containing oxide significantly lowered the oxidation rate in O 2 compared with an equally thick oxide without H or Fe 3+. We discuss possible origins of the differences and show that cation diffusion properties of the oxide layer formed influences the oxidation rate. The oxidation rate in pure water vapor is determined by surface processes involving the adsorption/desorption/dissociation equilibrium. The oxidation rate in water/oxygen mixtures is limited by the rate of Fe cation diffusion through the grown oxide film.

A high precision calibration system for the simulation of cometary gasenvironments

For the calibration of comet mass spectrometers a novel calibrationsystem was designed to simulate the neutral gaseous atmosphere of comets. Thefacility consists of a fully automated three-chamber ultra-high vacuum systemwith a separate gas mixing unit. The molecular beam technique is used for thesimulation of the dynamic environment of comets. The gas mixing unit allowsone to produce molecular beams and static environments of pure water vapour,of mixtures of water vapour and minor gas constituents and also of a widerange of other gases which are expected in the environment of comets. Theuniqueness of this system lies in its emphasis on accuracy and long termstability both in the static and in the molecular beam mode. Of particularinterest is the determination of the absolute pressure for all gases in therange below 10-6 mbar and the determination of the molecular beamcharacteristics. Although it is optimized for cometary environments, thecalibration system is, by virtue of its versatility, well suited for thecalibration of various space instruments over an extended parameter range.

Environmental Scanning Electron Microscopy of the Dehydration of Gel Materials

The possibility of performing scanning electron microscopy under “environmental” conditions (ESEM); where the specimen does not have to be under high-vacuum conditions, or even coated to make it conductive, has existed for several years [1]. in particular it has been possible to image in conditions that allow the samples to remain fully hydrated during observation. This unique feature of the ESEM has been exploited to image the dehydration of aqueous protein gel materials which have been created under controlled conditions to produce a range of Gel types.Drops of several μl of the Gels were placed in the Peltier cooling stage of the FEI-Philips Electroscan E3, and allowed to stabilize at 4.1°C. Several drops of water were placed on the stagesurround to maintain a high vapor pressure of water around the sample. The chamber was then pumped down to the working pressure of 6 torr and then back-filled with pure water vapor following the technique of Cameron et.al. [2].

High‐temperature oxidation of nickel and chromium studied with an in‐situ environmental scanning electron microscope

AbstractInvestigations of the morphology of metal oxide scales formed at high temperatures in oxidative environments are usually undertaken after exposure of the samples is completed. In this study, an environmental scanning electron microscope (ESEM) was used as a tool for the in‐situ observation of oxide scale formation. Pure nickel and chromium samples were oxidized at a temperature of 973 K in either pure oxygen or water vapour at a pressure of 667 Pa. The evolution of an oxide scale was followed in‐situ for up to 3 h. The morphology of the developing oxide scales was found to be a function of the metal substrate and the gaseous species. The growth mechanisms of the different metal oxide scales are reviewed and related to the analysed in‐situ images. Emphasis is placed on the relationship between oxidation mechanism and scale morphology. Nickel is seen to oxidise by outward diffusion of nickel probably on oxide grain boundaries when exposed to oxygen. Water vapour changes the scale morphology and a duplex‐type scale arises due to preferential overgrowth. The scale which develops due to chromium oxidation in oxygen is a fine‐grained, thin, and dense layer. In contrast, water vapour leads to whisker growth on chromium and an open, felt‐like structure forms. The applicability of the ESEM to the study of such systems is demonstrated, and its limitations are outlined. The results are encouraging examples of the possibilities which the in‐situ ESEM technique possesses.

Monte Carlo simulation of phase equilibria of aqueous systems

In this article, an overview of recent achievements in Monte Carlo molecular simulation of aqueous systems is presented. Semi-empirical two-body potential models introduced recently allow accurate representation of the pure water vapor–liquid equilibria, including the critical region. Furthermore, these models are used for the calculation of water–hydrocarbon low and high pressure phase equilibria. Efficient methodologies for the simulation of highly dense system(s) and systems of long chain molecules are discussed. In all cases, simulation results are compared against experimental data. Limitations of approximate molecular models are discussed.

Continuous absorption of water vapor and a problem of the absorption enhancement in the humid atmosphere

Our recent studies of the nonlinear continuum absorption of the pure water vapor have been extended on a case of the air broadening. The nonlinear absorption dependence has been derived for inhomogeneous optical mediums. The absorption of water within the air atmosphere and the Rayleigh scattering are taken into account in order to describe in situ experiments and the good coincidence with measurements in the short-wave region is observed for the optical depth calculated up to the wavenumbers of 20 000 cm −1 . First, an old hypothesis, that the absorption anomaly in water clouds in comparison with traditional modeling should be, in particular, explained by the continuum absorption of water, may be confirmed by the present calculations. Second, since the previous parametrization to be made for the pure water vapor continuum has been saved, our approach based on the radical hypotheses describing the continuum by nonlinear terms has been validated as a successful attempt to decide an important applied problem. On the whole, this enhancement problem of comparison of the absorption measured and modeled in the visible spectral region is presented in two forms, when the excess absorption either of a few orders of magnitude or approximately of 10% is observed for the transparency windows or bands, respectively. The solution of this problem in the present paper is suggested by modeling of the full absorption spectrum (nonlinear continuum+linear absorption contribution mainly from the central part of lines) within the wide spectral region. There is a discussion of the interaction of the microwave band of water with the UV bands of the gases presented and the band enhancement problem, in detail, is considered for the near-infrared band 10 500– 10 900 cm −1 .

Thermal Oxidation of Metallic Niobium by Water Vapor

The behavior of metallic niobium in pure water vapor (without added oxygen) was studied between 800 and 1000°C. Linear kinetics curves were observed (except for a short initial period) with a homographic influence of H2O pressure. Hydrogen additions in the gas phase largely modified the reaction rates. The oxide formed (NbO2) is different from that predicted by thermodynamics (Nb2O5). Taking into account all these experimental observations, a mechanism is proposed in which the limiting step is oxygen incorporation into the oxide lattice.

Experimental Study of the Effect of Temperature on Water Solubility in Natural Rhyolite Melt to 100 MPa

The effect of temperature on water solubility in rhyolite melt was experimentally determined at 850–1200°C and 22–100 MPa. A natural high-silica rhyolite glass was equilibrated with pure water vapor, and the water content in the quenched glass was determined by IR spectroscopy. The results demonstrate that water solubility in rhyolite melt has a negative temperature dependence, which becomes weaker at high temperatures and low water contents. This temperature dependence can be modeled adequately on the basis of ideal mixing of water species and anhydrous rhyolite melt components. The model reproduces both the present and previously published solubility data for water in rhyolitic melts to 100 MPa and over a wide range of temperature from near the solidus to 1200°C, thereby permitting calculation of water saturation under varying temperature conditions. At 50–100 MPa, an increase in the fraction of excess water as a result of a rise in temperature can cause a four- to eight-fold increase in the fractional amount of volumetric expansion above that caused by pure thermal expansion, per unit temperature rise. Thus, the negative temperature dependence of water solubility could be of fundamental importance in the development of gravitational instability in shallow, water-saturated silicic magma chambers.

Oxygen removal of codeposited a-C:D layers from tokamak tiles

To investigate the thermo-oxidative removal of hydrogen from codeposited layers formed in tokamaks, codeposited specimens from a TFTR bumper limiter tile and from JET and DIII-D divertor tiles have been exposed to O 2 gas at 523 and 623 K. From D-content measurements, derived erosion rates were found to be several micrometers per hour, with faster erosion rates obtained for thicker codeposits. Erosion rates at 523 K could be increased by increasing the O 2 pressure above the nominal pressure of 2.1 kPa; at 21 kPa, the initial erosion rate was ∼5 times as fast. To study the effect of water on the film erosion and D removal rates, specimens were exposed to pure water vapour. Although water vapour alone was found to decrease the D-content of the films after `short' exposures, `long-term' exposures to H 2O had no additional effect, consistent with an isotope exchange mechanism. Exposure to air led to similar erosion rates as observed with O 2, for an equivalent O 2 partial pressure, indicating that the other constituents in air had no significant effect on the chemistry.

Numerical Solutions of Three-Dimensional Non-Grey Gas Radiative Transfer Using the Statistical Narrow-Band Model

Three-dimensional non-grey gas radiation analyses were conducted using the statistical narrow-band model along with up-dated band parameters. The exact narrow-band averaged radiative transfer equation was solved using a ray-tracing method. Accurate numerical results were presented for non-grey real gas radiative transfer in a three-dimensional rectangular enclosure containing (i) an isothermal pure water vapor at 1000 K and 1 atm, (ii) an isothermal and inhomogeneous H2O/N2 mixture at 1000 K and 1 atm, and (iii) a nonisothermal and homogeneous mixture of CO2/H2O/N2 at 1 atm.

An experimental integrated absorption heat pump effluent purification system. Part I: operating on water/lithium bromide solutions

The merits of single stage absorption heat pumps coupled to simple distillation for effluent treatment are discussed. An experimental integrated absorption heat pump effluent purification system (IAHPEPS) was built and operated with water–lithium bromide as a working mixture. This unit has been used to raise the temperature and hence, the vapour pressure of the impure water contained in one vessel, to the point where pure water vapour will distil from impure effluent solution (tap water or brine) and condense in a second vessel used to collect pure water. Pure effluent production rates of between 0.5 and 4.3 kg h −1 were obtained. The actual coefficient of performance ( COP A) and the heat pump effectiveness varied from 1.1 to 1.4 and 0.58 to 0.72, respectively. The results from the small scale system indicate the likely results from industrial scale units which could be operated with low quality heat such as waste heat, solar or geothermal resources.

Contribution to the problem of vapour-side corrosion of copper-nickel tubes in MSF distillers

The paper describes the vapour-side corrosion (VSC) of 70 Cu30Ni condenser tubes in some MSF distillers. Corrosion is first recognized by above-normal Cu 2+ content of the distillate and, at advanced stages, by the increase in electrical conductivity of the product water. Attack takes place at the inlets of tubes in the first high temperature cells and is located mainly at the lower part of the tube bundle. Corrosion starts after a long time of operating the distiller (the induction period). A “corrosion factor” is proposed to characterize tube failure in distillers. It is the number of tubes failing per 1000 operation hours, following the induction period. Corrosion is not due to assault on tube material by CO 2 resulting from the thermal decomposition of HCO 3 − and CO 3 2− ions of seawater. Corrosion involves the primary oxidation of the metal by air leaking through flanges, glands and/or gaskets, followed by dissolution in CO 2-loaded vapours condensing on the colder ends of the tubes. Analysis of the distillate reveals the presence of large quantities of O 2 in the vapour. A simple experimental set-up to simulate VSC in the laboratory is described. The results obtained therefrom clearly show that: (a) pure water vapour does not produce VSC; (b) CO 2-loaded vapours have no measurable effect on VSC; (c) the presence of air together with CO 2 is necessary to cause measurable VSC; (d) bombardment of the tubes with water droplets condensing at an upper level greatly accelerates material loss; and (e) dissolved Cu 2+ ions catalyze the dissolution of copper-nickel alloy. Mitigation of VSC can be either preventive or curative. Preventive measures involve the monitoring of the O 2 content of both brine and distillate, the performance of pressure tests on the distiller, and the change of old gaskets at reasonable intervals. Curative measures involve the plugging and extraction of failed tubes, the application of protective sleeves, and the eventual retubing of the condenser. A change of tube material might be an appealing alternative.

On the effect of ultraviolet radiation on water vapor absorption of submillimeter waves

The submillimeter absorption spectra of pure water vapor and a water vapor + dry air mixture are experimentally studied under the conditions of illumination of the gas sample by ultraviolet (UV) radiation. The measurements were carried out by a vacuum echelette spectrometer in the wave number range 21.5–56 cm−1 with spectral resolution 0.4–0.9 cm−1, using a DRT-375 mercury-vapor discharge lamp as the source of UV radiation. In contrast to the results of similar experiments performed by other researchers, the data presented here demonstrate the absence of a noticeable effect of the UV radiation on the absorption spectra of the gas samples used.

Investigation of ice-solid interfaces by force microscopy: Plastic flow and adhesive forces

The interaction between oxidized silicon atomic force microscope tips and vapor-deposited ice in a pure water vapor environment is studied using force curve measurements. The adhesive pull-off force and the indentation depth are approximately proportional to the maximum applied force for ice temperatures between −5 °C and −15 °C. A simple plastic flow model is used to deduce yield strengths comparable to previous macroscopic measurements at similar time scales (∼0.01 s). The rapid dynamics of ice surfaces above −20 °C allows the indentation to be partially filled in between force curves.

The respective role of oxygen and water vapor on the tribology of hydrogenated diamond-like carbon coatings

The tribological behavior of diamond-like carbon coatings (DLC) strongly depends on the chemical nature of the test environment. The present study proposes to explore the influence of water vapor and oxygen on the friction behavior of a hydrogenated DLC coating exhibiting ultralow friction in ultrahigh vacuum (friction coefficient below 0.01). Using a UHV tribometer, reciprocating pin-on-flat friction tests were performed in progressively increasing or decreasing partial pressures of pure oxygen and pure water vapor. The maximum gaseous pressures of oxygen and water vapor were 60 hPa and 25 hPa (1 hPa = 100 Pa), respectively, the second value corresponding to a relative humidity (RH) of 100% at room temperature. It was found that, for the pressure range explored, oxygen does not change the ultralow friction behavior of DLC observed in UHV. Conversely, water vapor drastically changes the friction coefficient at pressures above 0.5 hPa (RH = 2%), from about 0.01 to more than 0.1. Electron energy loss spectroscopy and in situ Auger electron spectroscopy have been performed to elucidate the friction mechanisms responsible for the tribological behaviors observed with the two different gaseous environments. In all cases no significant oxidation has been observed either inside the wear scars or in the wear debris particles. Ultralow friction is systematically associated with a homogeneous carbon-based transfer film. The higher friction observed at partial pressure of water vapor higher than 0.5 hPa, is associated with a thinner transfer film. Consequently friction seems to be controlled by the transfer film whose kinetics of formation strongly depends on the partial pressure of water vapor.