The equilibrium humidity of dispersed solids at different temperatures

The use of the free energy of water vapor as a unique characteristic of saturated air permits the level of dehydration of dispersed solids to be determined unambiguously. The moist air diagram is computed for compensation of the moisture fluctuation of the surrounding air, corresponding to a change of the temperature of drying.Notation F₁ free energy of water vapor in air - F₂ free energy of bound water in dispersed solid - T₁ temperature of drying air, °C - T₂ temperature of dispersed solid, °C - T₃ temperature of air in laboratory, °C - P₁ water vapor pressure (absolute air humidity) - p_s saturated water vapor pressure at temperature T₁ - relative humidity of air, % - R gas constant - M molecular weight of water - W moisture content of dispersed solid - L₂ internal binding energy (thermal effect) of water in dispersed solid Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 20, No. 5, pp. 787–791, May, 1971.     

Microwave Determination of Water Mole Fraction in Humid Gas Mixtures

A small volume (65?cm³) gold-plated quasi-spherical microwave resonator has been used to measure the water vapor mole fraction x _w of H₂O/N₂ and H₂O/air mixtures. This experimental technique exploits the high precision achievable in the determination of the cavity microwave resonance frequencies and is particularly sensitive to the presence of small concentrations of water vapor as a result of the high polarizability of this substance. The mixtures were prepared using the INRIM standard humidity generator for frost-point temperatures T _fp in the range between 241?K and 270?K and a commercial two-pressure humidity generator operated at a dew-point temperature between 272?K and 291?K. The experimental measurements compare favorably with the calculated molar fractions of the mixture supplied by the humidity generators, showing a normalized error lower than 0.8.     

Experiments on saturated vapor pressure of aqueous lithium bromide solution at high temperatures

This work mainly focuses on the determination of the saturated vapor pressure of LiBr aqueous solution with mass fraction ranging from 43.14 to 65.26 wt% at high temperature experimentally. First, the measurement of the saturation vapor pressures is conducted in deionized water as well as in LiBr aqueous solution at a lower temperature. The experimental result has a good agreement with the literature value, which verified the reliability and accuracy of the experimental apparatus. Second, measurement of the saturated vapor pressure of LiBr aqueous solution with mass fraction ranging from 43.14 to 65.26 wt% is systematically carried out in the 156.06~257.84 °C temperature range. Based on the saturated vapor pressure data at lower temperature, a correlation for predicting the saturated vapor pressure data of the LiBr aqueous solution is obtained, which is also available for high temperature condition. Therefore, this work will be very helpful for the modeling and design of high temperature LiBr/H₂O absorption heat transformers.     

Saturator Efficiency and Uncertainty of NMIJ Two-Pressure Two-Temperature Humidity Generator

The primary dew-point standard of National Metrology Institute of Japan (NMIJ) over the dew-point range of  −10 °C to 95 °C is a humidity generator based on the two-pressure two-temperature method. In this generator, the dew-point temperature of generated air is calculated by using the pressure and temperature, assuming that the air in the saturator is in equilibrium with liquid water. Therefore, the evaluation of the degree of saturation of water vapor in the saturator is important. In this study, the saturation efficiency of the NMIJ two-pressure two-temperature humidity generator has been re-evaluated. The NMIJ humidity generator has a presaturator that consists of a water bath and a bubbling element that can supply water vapor to the airflow into the main saturator. The amount of water vapor in the air output from the PS is altered by changing the PS temperature. The dew-point temperatures of the generated air were measured by a chilled-mirror hygrometer under various conditions of PS pressure and temperature. The saturator efficiency of the generator has been evaluated from the relationship between the measured dew-point temperature and the PS temperature. When the temperature of the PS was lower than that of the saturator, the amount of water in the air was insufficient to achieve saturation. When the temperature of the PS was slightly higher than that of the saturator, saturation was obtained.     

Humidity sensors using KH2PO4-doped porous (Pb,La)(Zr,Ti)O3

Humidity sensing devices were prepared by using fine porous (Pb, La)(Zr, Ti)O₃ (PLZT) particles with ferroelectricity instead of insulating metal oxides such as alumina and zircon. The impedance of PLZT with 1 wt %. KH₂PO₄ was 10⁶ and lower than that of zircon with 3.8 wt % KH₂PO₄ by a factor of 10² in a dry atmosphere. In addition, the impedance in a humid atmosphere was controlled by the adding of potassium dihydrogen phosphate and changed by about four orders of magnitude in the humidity region 0 to 90% relative humidity at 1 kHz for samples burnt at 700° C. The humidity dependence of impedance is mainly governed by the change of coverage of adsorbed water. The hydrophilicity is affected by the burning temperature and lanthanum content of PLZT used as starting particle for porous PLZT ceramics burnt with KH₂PO₄. From complex impedance analysis it is confirmed that the resistive component inserted in parallel with the capacitive component decreases steeply with an increase in humidity, while the capacitive component is poorly dependent on the humidity.     

Oxygen Exchange Processes between Oxide Memristive Devices and Water Molecules

Resistive switching based on transition metal oxide memristive devices is suspected to be caused by the electric‐field‐driven motion and internal redistribution of oxygen vacancies. Deriving the detailed mechanistic picture of the switching process is complicated, however, by the frequently observed influence of the surrounding atmosphere. Specifically, the presence or absence of water vapor in the atmosphere has a strong impact on the switching properties, but the redox reactions between water and the active layer have yet to be clarified. To investigate the role of oxygen and water species during resistive switching in greater detail, isotope labeling experiments in a N₂/H₂¹⁸O tracer gas atmosphere combined with time‐of‐flight secondary‐ion mass spectrometry are used. It is explicitly demonstrated that during the RESET operation in resistive switching SrTiO₃‐based memristive devices, oxygen is incorporated directly from water molecules or oxygen molecules into the active layer. In humid atmospheres, the reaction pathway via water molecules predominates. These findings clearly resolve the role of humidity as both oxidizing agent and source of protonic defects during the RESET operation.     

A phenomenological comparison of some heavy metal fluoride glasses in water environments

The details of corrosive attack by water on several heavy metal fluoride glasses are given. The glasses studied contain either ZrF₄ or HfF₄ as primary constituents, or, are composed of the fluorides of zinc, thorium, barium and either yttrium or ytterbium. Polished specimens were subjected either to room temperature (RT) liquid water or to 100% relative humidity at room temperature. The degree of surface corrosion is correlated to preparatory and compositional effects. Thermogravimetric analysis (TGA) was utilized to determine the extent of corrosion as a function of temperature and as a function of time at constant temperature in an atmosphere of RT helium saturated with water.     

Characterization of the Humidity Calibration Chamber by Numerical Simulations

At the Centre for Metrology MIKES of VTT Technical Research Centre of Finland (VTT MIKES), we have been developing a humidity calibration apparatus for radiosondes within an EMRP Project Metrology for Essential Climate Variables. The minimum air temperature and absolute humidity are \(-80\,^{\circ }\hbox {C}\) and 2.576 \(\times \) \(10^{-4} \,\hbox {g}\cdot \hbox {m}^{-3}\) (corresponding the dew-point temperature \(-90\,^{\circ }\hbox {C}\)), respectively. Recent developments for the apparatus extend its pressure operation range down to 7 hPa (abs). When operating in such dry conditions, the efficiency in calibration is highly limited by the time of humidity stabilization in a measurement chamber: Because the water vapor pressure is very low, the adsorption and desorption of water molecules at the chamber walls have a significant effect on the spatial and temporal humidity differences in the chamber. Inhomogeneity in humidity field inside the calibration chamber increases calibration uncertainty. In order to understand how varying parameters such as pressure, temperature, inflow speed and geometry of chamber effect on stabilization time of humidity field, computational fluid dynamics simulations were developed using Comsol software. Velocity and pressure of fluid, water vapor diffusion, temperature as well as adsorption/desorption of water molecules on the chamber walls were included in the simulations. Adsorption and desorption constants for water on the measurement chamber wall were determined experimentally. The results show that the flow speed and the surface area are the dominant parameters affecting the stabilization time of a calibration chamber. It was also discovered that more homogenous water vapor concentration field is obtained at low pressures.     

Isothermal Vapor–Liquid Equilibrium Data for Water + Diisopropanolamine,Water + <Emphasis Type="Italic">N</Emphasis>-Methyldiethanolamine and Diisopropanolamine + <Emphasis Type="Italic">N</Emphasis>-Methyldiethanolamine Systems

Accurate modeling of thermodynamic vapor–liquid equilibrium of aqueous amines and amine mixtures is essential for the design of new CO₂ capture processes. Isothermal vapor–liquid equilibrium data were measured for the binary systems of water?+?diisopropanolamine (DIPA), water?+?N-methyldiethanolamine (MDEA) and DIPA?+?MDEA by using headspace gas chromatography at 423 K. The DIPA?+?MDEA system has azeotrope. The experimental binary vapor–liquid equilibrium data of water?+?DIPA, water?+?MDEA and DIPA?+?MDEA binary systems were well correlated with NRTL model.     

Vacuum freezing type ice slurry production using ethanol solution 1st report: Measurement of vapor–liquid equilibrium data of ethanol solution at 20 °C and at the freezing temperature

In this study, an original method for the production of ice slurry from ethanol solution without using a refrigerator is proposed. This system has advantages compared with similar existing systems using materials other than ethanol solution. In this paper, the vapor–liquid equilibrium data of ethanol solution at 20 °C and at the freezing temperature are measured, which is necessary to calculate the COP of this ice slurry producing system. In the experiments, two experimental methods are proposed to measure the saturated pressure and the vapor composition of ethanol solution. Each method has an advantage in their operating temperature range. As a result, the vapor–liquid equilibrium diagrams of ethanol solution at 20 °C and at the freezing temperature, and approximations of saturated pressure of various concentrations of ethanol solution for varying liquid temperature, are obtained.     

Saturated vapor pressure over AgGaGeS4 crystals

The vaporization behavior of AgGaGeS₄ crystals has been studied using vapor pressure measurements (gradient heating under dynamic vacuum, frozen equilibrium method, and membrane measurements). AgGaGeS₄ has been shown to vaporize incongruently, losing predominantly GeS₂. The total saturated vapor pressure over AgGaGeS₄ crystals has been measured, and has been represented by a best fit equation. The results are discussed in relation to earlier data on the melting point and melting behavior of AgGaGeS₄ crystals.     

Tuning Surface Wettability and Adhesivity of a Nitrogen‐Doped Graphene Foam after Water Vapor Treatment for Efficient Oil Removal

An environment‐friendly water vapor treatment for realizing a highly hydrophobic (contact angle ≈147.5°) and oleophilic N‐doped graphene foam (NGF) for efficiently removing oil from oil/water emulsions is presented. 3D porous networks of NGF with high N content are prepared by subjecting a mixture of graphene oxide and 5 vol% pyrrole to a hydrothermal process; the mixture is then freeze‐dried and annealed under a N₂ atmosphere. The surface wettability and adhesivity are tuned through water vapor treatment by forming a low‐surface‐energy hydrocarbon layer, with no chemical modification. The effectiveness of the hydrophobic/oleophilic NGF in removing oil from an oil/water emulsion is demonstrated.     

Determination of saturated vapor pressure of organic substances from the triple to critical point

Methods are given of extrapolating the saturated vapor pressure of substances of “atmospheric range” to the entire liquid phase region from the triple to critical point. The extrapolation of the pT parameters from room temperature to the triple point is performed by simultaneous processing of vapor pressure and of differences between the heat capacities of ideal gas and liquid. The liquid-vapor equilibrium in the region from the normal boiling temperature to the critical point is predicted by the law of corresponding states of L.P. Filippov using the experimentally obtained pT data and values of density of liquids. Experimental facilities are described for determining the saturated vapor pressure by the comparison ebulliometric method and for determining the low-temperature heat capacity by the vacuum adiabatic calorimetry. The methods of extrapolating the vapor pressure are tested with standard substances for which reliable pT data are available for the entire liquid phase region.     

The behavior of a cloud of emissions of high moisture content in the surface layer of the atmosphere

The propagation in the atmosphere of instantaneous emissions which largely consist of water vapor is treated in a three-dimensional formulation. The regularities are studied of the evolution of the hydrodynamic, concentration, and temperature fields depending on the parameters which define the state of the atmosphere (temperature and humidity), as well as on the temperature and moisture content of the cloud of emissions.     

A digital hygrometer

A digital hygrometer using a polyimide capacitive humidity sensor is developed. The capacitance change of the sensor due to adsorption of water vapor in the atmosphere is detected by a switched-capacitor digital capacitance bridge controlled by a one-chip microcomputer and is displayed as relative humidity with 0.1% resolution. The accuracy of the hygrometer calibrated by a two-point method is solely determined by the temperature dependence and the long-term drift of the dielectric sensitivity of the sensor and is estimated to be 2%     

Near-critical NaCl-H2O: An equation of state and discussion of anomalous properties

The system NaCl-H₂O near the critical point of pure water shows not only the remarkable properties of any two-component system near the critical point of one component but also an anomalous curvature of the T-x and P-x projections of the critical line in the range below mole fraction 0.0005. An equation of state is presented which is based on the Haar-Gallagher-Kell equation for pure water with a few terms involving the mole fraction of NaCl together with the temperature and density. Parameters in this equation were selected which yield a good representation of the entire vapor-liquid coexistence surface from 250 to 600°C and from the three-phase pressure to the critical pressure (or to the vapor pressure of pure water below its T _c). Derivatives of this equation yield densities, enthalpies, and heat capacities which are compared with experimental data. Also, the properties calculated for the vapor near the three-phase line are compared with those predicted by the successive hydration model previously developed for NaCl in steam in equilibrium with solid NaCl. Other related topics are discussed, including the anomalous features noted above.Special invited paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Gas-phase conversion of U,Sr, and Mo compounds into water-soluble forms in a nitrating atmosphere

Gas-phase conversion of uranyl molybdates UO₂MoO₄, UMo_1.7O_7.2, and UMo_0.4O_3.4, of strontium molybdate SrMoO₄, and of strontium uranate SrUO4 into water-soluble compounds in the NO_x–H₂O (vapor)–air or HNO₃ (vapor)–air atmosphere (hereinafter, nitrating atmosphere) was studied. The conversion of UO₂MoO₄, UMo_1.7O_7.2, and UMo_0.4O_3.4 in nitrating atmosphere results in formation of water-soluble uranium compounds and of the water-insoluble phase MoO₃·2H₂O. Rapid separation of the solution from the precipitate in reaction of UO₂MoO₄, UMo_1.7O_7.2, and UMo_0.4O_3.4 conversion products with water allows efficient transfer of U into the solution, with Mo remaining in the form of an insoluble precipitate. The conversion of SrMoO4 depends on the composition of the nitrating atmosphere. In the NO_x–H₂O (vapor)–air atmosphere, there is no SrMoO₄ conversion, whereas in the HNO₃ (vapor)–air atmosphere it is possible to reach ~85% conversion of SrMoO₄ into water-soluble Sr compounds. Complete conversion of SrUO₄ into water-soluble U and Sr compounds is reached when performing the gas-phase conversion at 130°С in both nitrating atmospheres. In the case of the HNO₃ (vapor)–air atmosphere, increasing the process temperature to 150°С leads to a decrease in the amount of water-soluble U(VI) phases.     

Phase Transition During Heat Treatment of Precursor Before YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−<Emphasis Type="Italic">δ</Emphasis></Subscript> Nucleation in TFA–MOD Method

This work presents a study of the evolution of the phases in the intermediate heat treatment process (IHP) which was after the pyrolysis process and before the crystallization of YBCO superconducting thin films. It was shown that the evolution of the solid solution could always take place whether with or without water vapor and oxygen. When water vapor is present in the atmosphere, the evolution temperature of the intermediate phase was lower than the one without vapor. The intermediate phase of Y₂Cu₂O₅ with the vapor was observed at 680 °C. By calculating the changes of Gibbs free energy of reactions possibly involved in the IHP, the priority reaction with water vapor was CuF₂>YF₃>BaF₂ when CuF₂, YF₃, and BaF₂ coexisted while CuF₂ and YF₃ prefer to react with BaO to form BaF₂ while they coexisted. The appearance of intermediate phase features could be illustrated through the calculation.     

Electrical and humidity sensing properties of lead(II) tungstate–tungsten(VI) oxide and zinc(II) tungstate–tungsten(VI) oxide composites

Lead(II) tungstate and zinc(II) tungstate were prepared by a solution route and sintered at 973 K in the form of cylindrical discs. Experimental results on PbWO₄ (PW) and WO₃ (WO) composites for humidity sensing are described. Sintered polycrystalline discs of PbWO₄ (PWWO-10), WO₃ (PWWO-01), ZnWO₄ (ZWWO-10) and composites of PW or ZW and WO in the mole ratios 8:2, 6:4, 4:6, 2:8 designated as PWWO and ZWWO-82, 64, 46 and 28, respectively and doped with 2 mol% of Li⁺ were studied. The composites were subjected to dc conductance measurements over the temperature range 373–673 K in air atmosphere from which activation energies were determined. The activation energy values for dc conductance were found to be in the range of 1.09–1.30 eV. The composites were identified by powder XRD data. The scanning electron microscopy (SEM) studies were carried out to study the surface and pores structure of the sensor materials. The composites were subjected to dc resistance measurements as a function of relative humidity in the range of 5–98% RH, achieved by different water vapor buffers thermostated at room temperature. The sensitivity factor (S_f=R_5%/R_98%) measured at 298 K revealed that PWWO-28 and ZWWO-46 composites have the highest humidity sensitivity factor of 17 615±3000 and 2666±550, respectively. The response and recovery time for these humidity sensing composites were good.