Pure Water Vapor Research Articles

Optical study of surface melting on ice

We have used an optical reflection technique to measure the thickness of water films existing on the surfaces of isolated single H2O ice crystals, at temperatures below O°C. The crystals were grown in situ from pure water vapor. When investigated under these conditions the water films were found to be of finite thickness at all T up to and including the triple point, indicating incomplete wetting of water on ice, or incomplete surface melting. The maximum film thickness detected was approximately 200 Å. At TTR water drops appeared on the ice facets, observed by interference microscopy. Their contact angles were consistent with the above findings. The addition of air to the atmosphere caused the film thickness to diverge on some orientations of the surface, i.e. it caused complete wetting or complete surface melting.

Measurement of Water Activity Above 100°C

ABSTRACTThe method is based on equilibration of the sample with an atmosphere of pure water vapor at constant pressure. Water activity is calculated from the sample temperature at equilibrium. A curve describing ×= f(aw) at constant water vapor pressure (isobar) was established for microcrystalline cellulose and potato starch, within the range 100–150°C. The precision of the method was evaluated and an empirical model, based on the GAB equation, was developed to fit experimental data. Determination were specifically with isobars at 1 bar, but isobars at other pressures could be determined by modifying the system.

A far wing line shape theory and its application to the foreign-broadened water continuum absorption. III

The far wing line shape theory developed previously and applied to the calculation of the continuum absorption of pure water vapor is extended to foreign-broadened continua. Explicit results are given for H2O–N2 and H2O–CO2 in the frequency range from 0 to 10 000 cm−1. The theory is based on the quasistatic and binary collision approximations and assumes for the interaction potential an isotropic Lennard-Jones part and the leading anisotropic multipolar (dipole–quadrupole) term. For H2O–N2, the positive and negative resonant frequency average line shape functions and absorption coefficients are calculated for a number of temperatures between 296 and 430 K for comparison with existing laboratory data. In general, the agreement is very good, especially at the higher temperatures for which the experimental absorption is larger and the corresponding error limits are smaller. For H2O–CO2 for which no experimental data exists, the calculations are made only at 296 K. Because of the significantly different line shapes for self vs foreign broadening, the ratio of the corresponding continuum absorption coefficients varies widely as a function of the frequency. The implications of this for absorption in the Earth’s atmosphere are discussed briefly.

A far wing line shape theory and its application to the water vibrational bands (II)

A far wing line shape theory based on the binary collision and quasistatic approximations that is applicable for both the low and high frequency wings of vibration–rotational bands is presented. This theory is applied in order to calculate the frequency and temperature dependence of the continuous absorption coefficient for frequencies up to 10 000 cm−1 for pure water vapor. The calculations are made assuming an interaction potential consisting of an isotropic Lennard-Jones part with two parameters that are consistent with values obtained from virial data and the anisotropic dipole–dipole part, together with measured line strengths and positions of allowed transitions. The results are compared with existing laboratory data in the 2400–2700 cm−1 window and in the 3000–4300 cm−1 band center region, with field measurements in the 2000–2225 cm−1 region and with a recent experimental measurement near 9466 cm−1. The overall good agreement, together with even better agreement with the more accurate laboratory data in the 300–1100 cm−1 window presented previously, allows us to conclude that both the magnitude and temperature dependence of the water vapor continuum can be accounted for by our comprehensive far wing line shape theory without the introduction of any adjustable parameters. Refinements of the present theory and extension to foreign-broadened absorption are also discussed briefly.

Diffusional limitations on the kinetics of dehydration reactions of hydrated barium chloride

The dehydration kinetics of BaCl 2·2H 2O powders were examined as a function of water vapor pressure, sample bed depth, particle diameter and temperature. The conversion behavior was modeled in both the kinetic and the combined diffusion and kinetic limited regimes with modified forms of the Avrami-Erofe'ev equation. Kinetic data were obtained by thermogravimetric techniques and by calorimetry. Structural data for intermediates and products were obtained by X-ray diffraction and optical microscopy. Dehydrations were conducted isothermally between 317 and 335 K either under vacuum or in controlled pure water vapor atmospheres ranging from 40 to 6.67 × 10 2 Pa. The dehydration rate decreased as the water vapor pressure, sample bed depth and particle diameter increased. The estimated effective bed diffusivity is 1.0×10 −6 cm 2 s −1. After a critical pressure was exceeded, severe reductions in rate were observed. The dehydration of BaCl 2·2H 2O proceeded stepwise via the crystalline monohydrate above about 80 Pa at 317 K; below this pressure the crystalline monohydrate was not observed. Transient increases in water vapor pressure in the sample bed caused crystallization of the monohydrate under conditions where it did not otherwise form.

Laboratory studies of water vapor absorption in the atmospheric window at 213 GHz

Absolute absorption rates of water vapor have been measured in the atmospheric window between the rotational lines at 183 and 321–325 GHz. Measurements have been carried out for pure water vapor and mixtures with N 2 at atmospheric pressure. Pressure and temperature dependences are compared with models involving different lineshapes and different types of continua.

Jet emission spectroscopy of OH and OD near 1850 Å: First observation of a 2Π→2Π electronic transition of OD

The complex many-line systems observed at around 1850 Å from discharges containing H2O or D2O [A. Michel, Z. Naturforsch. 12a, 887 (1957); P. Felenbok and J. Czarny, Annu. Astrophys. 27, 244 (1964)] have been reinvestigated at high resolution in the emission from supersonic jet expansions. Mixtures of He with D2O produce a conspicuous progression of red shaded bands that overlap the many-line spectra but have not been reported before. The new transitions originate at large internuclear distance in a single 2Π vibronic level of OD at 88 294 cm−1 above the minimum of the ground-state potential, and they end on high vibrational levels, v″=13,...,18, of X 2Π. Term values and spectroscopic parameters for the initial and final states have been determined; the upper state, labeled C′2Π, is inverted with a spin-orbit interaction that is close to the A value of X 2Πi. Analogous bands of OH have not been detected, and in contrast with the many-line emissions of both isotopes which persist in the presence of Ar as well as of He and in discharges through pure water vapor, the new C′2Π→X 2Π bands of OD appear only in mixtures with He. Guided by ab initio calculations for the 2Π excited states of OH [E. F. van Dishoeck and A. Dalgarno, J. Chem. Phys. 79, 873 (1983)], the interpretation of the experimental results concludes that all of the observed emission at around 1850 Å originates in a group of more or less strongly mixed 2Π levels which reflect the radiative properties and excitation characteristics of two interacting stable diabatic states and which escape predissociation by a repulsive third 2Π state.

Determination of Sorption Rate and Apparent Solid-Side Diffusivity of Pure H2O in Silica Gel Using a Constant Volume/Variable Pressure Apparatus

Silica gel-water vapor is commonly suggested as a working media for solar-powered desiccant cooling systems since the system can be regenerated at relatively low temperatures. In the present study the sorption rates of water vapor by regular density silica gel particles were measured in the pressure range of 1–25 torr using a constant volume/variable pressure apparatus. The sorption rate was determined from recorded time variation of water vapor pressure in a test unit of known volume during the sorption process. The mass transfer film resistance was eliminated by evacuating the system and by introducing pure water vapor into the test unit. The apparent solid-side diffusivity was obtained by matching the analytical solution of the simultaneous heat and mass transfer governing equations to the experimental data. The uptake measurements had been performed for three particle sizes of silica gel (150 μm, 1 mm, and 3 mm). The tests were performed sequentially in small steps over a range of initial silica gel moisture content ranging from near zero up to 0.25 kg H2O per kg dry silica gel. The effect of moisture content and particle size on the sorption rate and apparent diffusivity were determined. The effect of charging on time variation of pressure was evaluated and used for correction on all sorption data.

Temperature dependence of water-vapor absorption in linewings at 190 GHz

Absolute absorption rates of water vapor have been measured in the high-frequency wing of the 183 GHz rotational line. Measurements have been carried out for pure water vapor and mixtures with N 2 at atmospheric pressure. Pressure and temperature dependences are compared with models involving different types of lineshapes.

Intercomparing shortwave radiation codes for climate studies

As a second step of the international program of Intercomparison of Radiation Codes Used in Climate Models (ICRCCM), an intercomparison of shortwave radiation models was initiated. Among the 26 codes that participated in the comparison were very detailed (line‐by‐line), narrow‐band (high‐spectral resolution), as well as highly parameterized (low‐spectral resolution) models. A considerable spread was detected in the response of these models to a set of well‐defined atmospheric profiles. Substantial discrepancies exist among models even for the simplest case of pure water vapor absorption with standard deviation ranging from 1% to 3% for the downward fluxes at the surface and from 6% to 11% for the total atmospheric absorption. The divergences in downward surface flux increase to nearly 4% when all absorbers and the molecular scattering are considered. In cloudy conditions the divergences range from 4% to 10%, depending on the cloud optical thickness. Another major uncertainty that has been identified is the spectral averaging of the scattering properties which can result in very significant errors for low spectral resolution codes. Since these errors appear to be systematic, they may induce unrealistic feedback mechanisms in numerical climate models. The amplitude of the differences between models is in many cases larger than the accuracy required for the achievements of several objectives of the World Climate Research Program. While reference solutions for the absorption and scattering in atmospheres can be obtained based on the state‐of‐the‐art spectroscopic knowledge and rigorous computational techniques, the absolute tests of the validity of the radiation algorithms would be comprehensive field experiments in which the radiative and all relevant atmospheric parameters are measured to a high degree of accuracy.

Cluster generation in expansions of pure water vapour and of mixtures with carbon dioxide

The condensation of pure superheated water vapour and of a mixture with carbon dioxide in a supersonic jet behind a sonic nozzle has been investigated by the nozzle molecular beam method. The relation of source temperature, pressure, and nozzle diameter necessary for fully developed condensation has been determined for the pure vapour. By using the retarding potential technique, the cluster size distribution function and the dependence of the mean cluster size on the nozzle source conditions have been obtained. Mass-spectrometric measurements of the beam composition in a mixture expansion have revealed the presence of both homogeneous and heterogeneous clusters. The fully developed condensation in CO2-H2O mixture was found to begin at a smaller total source pressure than in pure water vapour or carbon dioxide.

Fatigue resistance of steels: Boardman, B. Metals Handbook 10th Edn (ASM International, Materials Park, Ohio, 1990) Vol. 1, pp 673–688

In the recent literature, the influence of lean fuel, type of fuel, velocity profile and the flow direction on the performance operation of solid oxide cells (SOCs) is commonly investigated. SOCs generate electricity when they operate in fuel cell mode (SOFC – Solid Oxide Fuel Cell) or produce hydrogen in electrolysis mode (SOEC – Solid Oxide Electrolyzer Cell). They consist of several layers, including two porous electrodes separated by a gas-tight electrolyte. Typical anode porosity (fuel electrode in SOFC mode) varies from 20% to 50% (after sintering). The porosity value may limit the mass transport and the overall performance of SOC. This work investigates computationally and experimentally, the existing challenge such as diffusion mechanism in porous medium using the example of SOC electrode. A set of mass transport models (Fick's laws, modified Fick's law, Maxwell-Stefan Model, Dusty Gas Model) are described and discussed, highlighting their similarities, differences, advantages, and disadvantages as well as restrictions in usage. Finally, a detailed computational fluid dynamics (CFD) model of the diffusive transport in porous electrode was elaborated and validated. An experimental campaign was conducted using anode supported SOC, fabricated at the Institute of Power Engineering in Poland. Simulations were performed of the mass transport of pure hydrogen and pure water vapor or carbon dioxide (substitute of real product of electrochemical reaction in SOC for validation purposes) through porous anode. Tests were conducted in the wide flow range 10 [ml/min] up to 200 [ml/min] for both gases. The results demonstrate that hydrogen mole fractions reached similar values (0.5–0.6) at both outlets only for the maximum residence time or high porosity of anode. This implies that residence time and gas diffusion can be controlled by a combination of operating and microstructural parameters and can be estimated by numerical simulation using computational fluid dynamics. The main motivation and outcome of this work were to reduce the cost and time required for the optimization of the mass transport process through SOC's porous electrode.

Developments in geothermal energy in Mexico—part thirty-six. The commissioning of a heat pump assisted brine purification system

Any system which extracts useful energy from a geothermal source is limited by the effectiveness of the heat transfer between the geothermal fluid, which has a tendency to scale, and the relevant components of the system. A heat pump can be used to maintain a temperature difference between two vessels containing pure water and geothermal brine which is sufficient to enable pure water vapour to flow continuously from the geothermal brine vessel to the pure water vessel. A mechanical vapour compression heat pump using R114 as the working fluid and designed to deliver more than 50 kW of heat has been incorporated in a brine purification system at the Los Azufres geothermal field. This system has been successfully commissioned and is operating as designed and theoretically predicted.

Silica coatings on strongly passivated substrates

Silicon dioxide can be deposited by pyrolysis of silicon alkoxide onto highly passivating substrates such as stainless steels ( e.g. AISI 316L), superalloys (H34CT), and titanium and its alloys. Before silicon dioxide deposition the passivating layer has to be removed, and a strongly adherent, dense oxide layer has to be re-formed (pre-oxidation). The substrate composition, in particular the carbon content, is the determining factor for the type of surface preconditioning used; this pretreatment is necessary for the complete removal of the chromium-rich passivating layer. Mechanical grinding, honing and polishing, chemical wet etching, electrochemical polishing and gas phase etching are typical treatments considered for surface preparation; these treatments replace partially or completely the reduction of the passivating oxide layer by means of the carbon in the substrate, which occurs above 780 °C. For the final mechanical operation only diamond should be considered (tool, abrasive); the use of other materials tends to contaminate the surface and leads to the formation of mixed oxides during the pre-oxidation. The pre-oxidation itself is performed under pure water vapour, moist nitrogen or isopropanol; in some cases (titanium and its alloys) preconditioning under pure nitrogen must be carried out. Internal stresses must be relieved before the pre-oxidation and silicon oxide deposition treatments. It was also found that, during the pyrolysis of silicon alkoxide, the reactor atmosphere must have some water vapour, which can be produced by an adequate evaporator or by dehydration of isopropanol.

Developments in geothermal energy in Mexico—part sixteen. The potential for heat pump technology

Mexico possesses large amounts of geothermal brine at temperature which are too low to enable electricity to be generated efficiently and economically. Any system which extracts useful energy from a geothermal source is limited by the effectiveness of the heat transfer between the geothermal fluid, which has a tendency to scale, and the relevant components of the system. A heat pump can be used to maintain a temperature difference between two vessels containing pure water and geothermal brine, which is sufficient to enable pure water vapour to flow continuously from the geothermal brine vessel to the pure water vessel. The hot water produced can then be used to operate an absorption cooling system which can be used to store food. Alternatively a heat pump can be employed to increase the temperature of the hot water to produce low pressure stream.

Linewidths and linestrengths in the ν2 band of HTO as measured with a tunable diode laser

A tunable lead-salt diode laser coupled to a digital data recording system was used to accurately measure linestrengths and linewidths of several vibrational-rotational transitions in the ν 2 band of HTO. A dilute sample of tritiated water was placed in a multipass cell, and measurements were made both in pure water vapor and with a mixture of air and water vapor. Self-broadening coefficients, air-broadening coefficients, and linestrengths were determined for seven of the stronger HTO lines in the 1260- to 1385-cm −1 region.

Nitric acid cloud formation in the cold Antarctic stratosphere: a major cause for the springtime ‘ozone hole’

Large depletions in stratospheric ozone were first reported by Farman et al. [1] at Halley Bay (76 °S), and confirmed by satellite observations [2]. Chubachi [3] gives a detailed account of ozone decreases and temperatures in the lower stratosphere during the spring of 1982 at 69 °S. There is now evidence [2] for annual declines in total ozone by ~6 and 3 % in regions of total ozone minima and maxima, respectively, from September to mid-October since the late 1970s. We propose here a chemical mechanism for the formation of the ozone hole. It involves removal of gaseous odd nitrogen by ion- and/or aerosol-catalysed conversion of N2O5 and ClONO2 to HNO3 vapour, followed by heteromolecular HNO3–H2O condensation, leading to HNO3–H2O aerosols. At an altitude of 17 km, these processes start at temperatures below 205 ± 5 K, well above the condensation temperature of pure water vapour. We propose that the absence of gaseous odd nitrogen and catalytic methane oxidation reactions driven by sunlight in early spring lead to large OH concentrations which rapidly convert HCl to ClOX. Catalytic reactions of ClOX and BrOX cause drastic ozone destructions and can account for the springtime ‘ozone hole’ first observed by Farman et al. [1]. By our model the depletion would be mainly due to emissions of industrial organic chlorine compounds. Arctic regions may also become affected. The depletion lasts while HNO3, but not HCl, is incorporated in the particles in the temperature range 205 ± 5 to 192 K.

Temperature dependence of water-vapor absorption in the wing of the 183 GHz line

Absolute absorption rates of water vapor have been measured in the laboratory in the high-frequency wing of the 183 GHz line. Measurements have been carried out for pure water vapor and mixtures with N 2 at atmospheric pressure. Pressure- and temperature-dependences are compared with models involving several types of lineshapes.

Pore structure and kinetics of the thermal decomposition of Al(OH)3

AbstractThe isothermal decomposition of gibbsite (aluminum hydroxide) was studied under controlled, pure water vapor pressures from 50 to 3,000 Pa over the temperature range from 458 to 508 K; the effect of sample particle size was also investigated. The partial conversion to boehmite (AlOOH) and the subsequent formation of a ρ‐transition alumina product phase were followed with respect to the reactor operating conditions. Nitrogen and water vapor adsorption measurements were used to evaluate the chemical kinetics of the formation of ρ‐alumina in terms of an interface velocity, and to interpret the observed dependencies on temperature and water vapor pressure. An adsorption/decomposition model is presented for these kinetics. The interpretation is consistent with the observation that decomposition rate is inversely proportional to the square of the water vapor pressure. The apparent activation energy of 342 ± 15 kJ/mol includes a water adsorption energy, as well as the chemical decomposition contribution of 260 ± 20 kJ/mol.

Microgravimetric measurements of water vapour sorption on hydrated cement pastes

To study the pore structure of hydrated cement pastes, differing in pretreatment and chemical composition, water vapour sorptlon experiments have been used. The experiments were carried out at 25.0°C in a pure water vapour atmosphere, up to relative vapour pressures of 0.98. The amount of water adsorbed or desorbed was determined gravimetrically using a Cahn 2000 microbalance. The set-up developed for this purpose and some experimental results are presented.