Vapor Partial Pressure Research Articles

Vaporization and thermodynamics of ceramics in the Y2 O3 -ZrO2 -HfO2 system.

The Y2 O3 -ZrO2 -HfO2 system is a promising base for a wide range of high-temperature materials including ultra-high-temperature ceramics. At high temperatures of synthesis and application of these ceramics the components may vaporize selectively, leading to changes in chemical composition and exploitation properties of the materials. Therefore, study of the vaporization processes of ceramics based on the Y2 O3 -ZrO2 -HfO2 system is of great importance. The thermodynamic properties of the Y2 O3 -ZrO2 -HfO2 system obtained in the present study can be used for the prediction and modeling of the physicochemical properties of ultra-high-temperature ceramics. The present study was carried out by the high-temperature Knudsen effusion mass spectrometric method using the MS-1301 mass spectrometer, which was designed to study the physicochemical properties of non-volatile compounds. Vapor species effusing from the tungsten twin effusion cell, which was used for vaporization of the samples under study, were ionized by electron ionization with an ionization energy of 30 eV. The gaseous phase over the samples of the Y2 O3 -ZrO2 -HfO2 system was shown to consist of the YO, ZrO, ZrO2 , HfO and O vapor species at a temperature of 2660 K. The YO, ZrO, ZrO2 , HfO and O partial vapor pressures were obtained in a wide concentration range by the complete isothermal vaporization method, which allowed determination of the activities of Y2 O3 , ZrO2 and HfO2 , Gibbs energies of mixing and excess Gibbs energies of the Y2 O3 -ZrO2 -HfO2 system at 2660 K. Negative deviations from the ideal behavior were shown in the solid solutions of the Y2 O3 -ZrO2 -HfO2 system at 2660 K. The excess Gibbs energies found in the present study were approximated using the Redlich-Kister representation. The possibility of application of the Kohler method to estimate the excess Gibbs energies of the Y2 O3 -ZrO2 -HfO2 system was considered.

Strong Dependence of Contact Angle on Pressure

Although the usual pressures typically only slightly affect the properties of condensed phases and their surface layers, in physical chemistry of surfaces, it was found a quantity, the contact angle on the three-phase contact line, that is very sensitive to pressure. In experiments with an air bubble in water stuck to a solid surface, an increase in hydrostatic pressure of less than doubled gave an increase in the contact angle of more than 10o if the angle itself was sufficient but less than 90o. Сhanging the orientation of the liquid - gas surface. If the angle (no matter sharp or obtuse) is close to 90o, the mobility of the three-phase contact line arises as an alternative way to achieve equilibrium. To explain these phenomena, a thermodynamic theory is formulated. It is shown that with a fixed line of three-phase contact, an increase in pressure in a liquid always causes an increase in the contact angle. At the same time, an increase in the hydrostatic pressure of water by two times is equivalent to an increase in the partial pressure of water vapor inside the bubble by a factor of seven.

Implications of K, Cu and Zn isotopes for the formation of tektites

Abstract Tektites are mm to cm sized glassy objects generated through high-energy meteoroid impacts on the surface of the Earth under high temperature and pressure, and reducing conditions. They are the products of large-scale catastrophic events in Earth’s history and can be used to understand the behavior of moderately volatile elements (e.g., K and Zn) during impact vaporization events. Here, we report bulk K isotopic compositions of tektites from three different strewn fields and “in-situ” profile analysis of both K and Zn isotopes in one complete tektite. All tektites span a narrow range in their K isotopic compositions (δ41KBSE: −0.10 ± 0.03‰ to 0.16 ± 0.04‰), revealing no discernible K isotopic fractionation from the Bulk Silicate Earth (BSE) and upper continental crust materials, which is consistent with previous results. In contrast, Zn isotopes show a large variation (δ66Zn: −0.39 ± 0.02‰ to 2.38 ± 0.03‰) even within one specimen. In order to provide a coherent explanation for the different behavior of moderately volatile elements (K, Zn and Cu), we have conducted thermochemical calculations to compute the partial vapor pressures of Cu2O, K2O, and ZnO dissolved in silicate melts as a function of temperature, pressure, oxygen and chlorine fugacities. In a large range of the parameter space, the calculations show that Cu and Zn can be vaporized much easier than K and thus produce large isotopic fractionation. In contrast, the lithophile element K is more prone to remain in the silicate melt because of its very low activity coefficient in the melt, and thus the K isotopes remain unfractionated. This study provides new constraints on the formation of tektites and is consistent with a “bubble-stripping” model to explain the extreme water and volatiles depletion in tektites.

On Gas Ingression of Hermetic Packages

In this paper, a closed-form mathematic equation that governs gas ingression of hermetic packages is derived from first principles and applied to moist air and water vapor ingression conditions. The equation models internal gas partial pressure change as a function of time, external conditions, and package characteristics. The equation provides the theoretical basis for direct comparisons of ingression behaviors of different gases into hermetic packages. Comparing the rates of internal air pressure increase due to air ingression and water vapor partial pressure buildup due to water vapor ingression, the authors theorize that vacuum decay may present a greater challenge to the performance of microelectromechanical systems (MEMS) devices within hermetic packages than that of water vapor content induced corrosion failures. This paper also examines gas ingression of hermetic enclosures with multiple layers of seals.

Mass-Spectrometric Study of Evaporation of Perovskite

The evaporation of perovskite CaTiO3 at 1700–2200 K was studied by the high-temperature mass-spectrometric Knudsen effusion method. The molecular components typical of simple oxides and a small amount of complex gaseous oxide CaTiO3 were identified in the gas phase over perovskite. The partial vapor pressures of the molecular components of the gas phase over perovskite were compared with those corresponding to simple oxides; it was found that the character of evaporation of perovskite is mainly affected by the calcium component.

Physiological responses and thermal equilibrium of Jersey dairy cows in tropical environment.

Long-term assessments of thermal responses of housed Jersey cows raised in tropical conditions were performed to investigate the effect of climate environment on their physiological performance and thermal equilibrium. Twelve Jersey dairy cows with 326.28 ± 30kg of body weight, 17.66 ± 1.8 of milk yield, and 165.5 ± 6.8 of days in milking were assigned in two 12 × 12 Latin square designs. Air temperature, relative humidity, partial vapor pressure, direct and diffuse short-wave solar radiation and black globe temperature under the shade, and direct sunlight were recorded. Physiological responses as respiratory rate (RR, breaths min-1), ventilation (VE, Ls-1), proportion (%) of oxygen (O2) and carbon dioxide (CO2), saturation pressure (PS{TEXH}), and air temperature (TEXH, °C) of the exhaled air were assessed protected from solar radiation and rain. Rectal temperature (TR, °C), skin temperature (TEP, °C), and hair coat surface temperature (TS, °C) were also recorded. The thermal equilibrium was determined from biophysical equations according to the principles of the energy conservation law in a control volume. Exploratory and confirmatory analyses were performed from principal components and by the least square method, respectively. The cows were evaluated under range of ambient air temperature from 26 to 35°C, relative humidity from 27 to 89%, and short-wave radiation from 0 to 729Wm-2. Exploratory and confirmatory analyses demonstrated that a similar level of nocturnal and diurnal air temperatures evoked distinct (P < 0.05) responses for rectal (TR, °C) and skin (TEP, °C) temperatures, ventilation (VE, Ls-1), tidal volume (TV, L breaths-1), and oxygen consumption (∆O2, %) and carbon dioxide output (∆CO2, %), clearly revealing an endogenous rhythm dependence. In conclusion, these findings clarify how the circadian rhythmicity of the thermal environment and animal's biological clock dictate dynamics of heat generated by metabolism, dissipated to the environment and physiological parameters of the housed Jersey cows raised in tropical condition; therefore, it is fundamental to help us to understand how the Jersey dairy cows under tropics are affected by the climatic conditions, leading to better ways of the environmental management.

Comprehensive Thermodynamic Study of the Calcium Sulfate–Water Vapor System. Part 2: Physical Modeling of Adsorption Phenomena

We employ a rigorous thermodynamic modeling approach to investigate the water adsorption phenomena on two calcium sulfate compounds, AIII-CaSO4 and CaSO4·0.5H2O. In part 1 of this work ( Ind. Eng. Chem. Res., 2019, DOI: 10.1021/acs.iecr.9b00856), we prepared these two products by the dehydration of synthetic CaSO4·2H2O and obtained quantitative adsorption data as a function of the temperature and water vapor partial pressure. In this part, we develop macroscopic solution models (ideal and nonideal) to model monolayer adsorption on AIII-CaSO4. This allowed the calculation of the energies of adsorption for this phenomenon, evidencing a physisorption mechanism. For the CaSO4·0.5H2O, we interpreted the water adsorption using a multilayer adsorption model (BET model). For both materials, we showed that nitrogen adsorption data was not sufficient to represent their entire surface areas and porosity profiles compared to their water vapor sorption capacity.

Fundamental study on the vaporization of cesium and iodine dissolved in LiF-NaF-KF molten salt

As a basic study related to a severe accident of Molten Salt Reactor (MSR), the equilibrium vapor pressures over LiF-NaF-KF eutectic salt (46.5–11.5–42.0 mol%, FLiNaK) containing Cs and I as volatile Fission Product(FP) were measured by a transpiration method under pure Ar gas flow at the temperature ranging from 900 to 1100 K. As the result, the vapor pressures of Cs and I in molten FLiNaK were evaluated to be higher than those of other elements in the salt, and the vapor pressure of the solvent salt elements such as Li and K also increased with addition of CsI and CsF. The activity coefficients of CsI and CsF were derived from the partial vapor pressure of CsI and CsF calculated by assuming the gas phase equilibrium. Activity coefficients of CsI, 6 to 13 in this temperature range, showed strongly positive deviation from ideal solution while those of CsF were around unity. This peculiar activity coefficients suggest instability of CsI in the FLiNaK salt as suggested for LiF-ThF4-CsI salt by literature. The vaporization behaviors measured for the FLiNaK with different Cs/I ratio indicated strong interaction between Cs and I in FLiNaK salt.

Numerical modelling of flashing flow phase change in convergent-divergent nozzle: A sensitivity analysis

A sensitivity analysis of a computational fluid dynamics (CFD) model of flashing flow phenomenon including the thermal non-equilibrium effect is proposed in the present paper. The model uses a two-phase mixture approach and the phase-change process is based on the difference between the vaporization pressure and the vapour partial pressure. Thermal non-equilibrium effect is included in the model by a sub-routine for the boiling delay. A two-dimensional axisymmetric convergent-divergent nozzle is used as benchmark for the proposed study. Such geometry is representative of well-known applications in nuclear, refrigeration and energy engineering (e.g., primary flow in the motive nozzle of ejectors). The results are compared to experimental data and previous numerical results available in literature. Present results show good agreement with global and local experimental fluid dynamic quantities used to validate the model. The paper includes in the first part a brief description of physical phenomenon of flashing flow, the experimental benchmark geometry and operating conditions. In the second part, the physical model and the numerical modeling approach are reported, showing the validation and the results related to the sensitivity analyses of the artificial coefficients characterizing the modelling approach.

Thermochemistry of Nickel Trifluoride

The literature data on thermal behavior of crystalline nickel fluorides NiF3 and Ni2F5 in the higher oxidation states are analyzed. Their enthalpies of formation are calculated: ΔfHo(Ni[NiF6](cr), 0 K) = -1399.6 ± 6 and ΔfHo(Ni2F5(cr), 0 K) = −1370.5 ± 8 kJ/mol. The partial saturated vapor pressures in the NiF3–Ni2F5 and Ni2F5–NiF2 systems over a broad temperature range are determined. The technical impossibility to achieve a measurable pressure of NiF3 is shown. The findings are compared to the data for similar derivatives of 3d-block elements and ruthenium and platinum trifluorides. Ni2F5(cr) is suggested to be used as a fluorine accumulator.

Effects of Annealing Parameters on Epitaxial Graphene on SiC Substrates

The effects of annealing on epitaxial graphene on SiC substrates with various conditions are investigated. Results show that high pressure hydrogen atmosphere is more effective to decouple the epitaxial graphene from SiC substrate than that of a relative lower pressure process. Besides, the characteristic 2D-peak of graphene in Raman spectra disappeared with an annealing temperature 1000 °C, which means that the epitaxial graphene layer was decomposed in this condition. The study also shows that the decomposition of graphene can be effectively suppressed by increasing carbon vapor partial pressure through introducing ethylene during high pressure hydrogen annealing at 1000 °C. And the epitaxial graphene is successfully transferred to quasi free standing graphene by the annealing with an appropriate flow of ethylene.

Water Column Separation at Turbine Start up Loading

According to authors knowledge this is the first case of water column separation that happened, not during load rejection, but during the turbine start and loading to full power output. To control the transient flows in water courses, the wicket gates of turbine are the primary flow regulators. The minimum pressure during transient operations of hydroelectric turbine units may cause a water column separation and the subsequent re-joining creates forces that could damage turbine runners, non-rotating parts, and the whole machine house. This condition occurs when a local pressure drops below the vapour pressure or partial pressure of gases (air). The instant pressure rises from collapse of voids have the potential to crack internal linings of water conductors and connections between steel and concrete, and may damage hydraulic machines, air valves, penstock valves, or gates. The damage may not be evident immediately but would be observed after repetitive transients. All calculations and measurements of transients must be completed for analysis of the water column separation, following existing guidelines, though there is no standards and recommendation on the subject of waterhammer and hydraulic vibrations. This paper presents an approximate analysis of water column separation based on the pressures measured on site.

On the effective spectral emissivity of clear skies and the radiative cooling potential of selectively designed materials

Thermophotonic devices are optically designed to be spectrally selective in order to reject heat to outer space through atmospheric windows of low thermal absorption. The determination of thermal equilibrium temperatures for thermophotonic devices requires the knowledge of the effective spectral emissivity of the sky. In this work, individual contributions of participating gases and aerosols to the spectral values of the sky emissivity are analyzed in the entire infrared spectrum as well as in seven distinct bands for which water vapor either dominates or is virtually transparent to infrared radiation. We also propose high-fidelity correlations for the effective sky emissivity as functions of the normalized ambient partial pressure of water vapor (pw) for both broadband and for the seven spectral bands. The correlations are derived using a combination of ground experimental data, high resolution spectral data for the main atmospheric constituents and spectral models to reconstruct the spectral distribution of infrared thermal radiation from the atmosphere to the ground. These results enable direct calculation of the equilibrium temperature and cooling efficiency of radiative cooling devices in terms of meteorological conditions observed at the surface level. For hot and dry conditions, the passive radiative coolers have a cooling potential of 150.8 W m−2 while for humid conditions, the coolers are mostly ineffective.

The water vapour self- and foreign-continua in the 1.6 µm and 2.3 µm windows by CRDS at room temperature

New measurements of the water vapour continuum in the 1.6 µm and 2.3 µm windows are obtained at room temperature using highly stable and sensitive cavity ring down (CRD) spectrometers.In the 1.6 µm window, self-continuum cross-sections, CS, are derived for 30 selected spectral points between 5700 and 6850 cm−1 using pressure ramps of pure water vapour (up to 15 Torr). Purely quadratic pressure dependence is obtained for each measurement point. Compared to our previous dataset (Mondelain et al., 2014), the retrieved Cs values are more accurate and show a general agreement. The spectral coverage is extended both on the high and low frequency edges of the 1.6 µm window. In addition, new CS values are derived in the 5120–5137 cm−1 interval extending to higher energy the coverage of the 2.3 µm window. The measurements near 5700 cm−1 and 5130 cm−1 are found lower than the MT_CKD_3.2 values by a factor of about 2 and 1.5, respectively.Foreign-continuum cross-sections, CF, are newly obtained in the 2.3 µm window from CRDS spectra of moist air in flow regime. Spectra were recorded for different water vapour partial pressures while maintaining the total pressure constant in the high finesse CRDS cavity. After subtraction of the monomer and self-continuum contributions, CF values were derived from the linear variation of the foreign-continuum absorption with the water vapour partial pressure. CF values determined at four spectral points between 4430 and 5000 cm−1 are larger by up a factor of five than the corresponding MT_CKD values. Considering these CRDS data at room temperature and literature values at 400 K the temperature dependence of the foreign-continuum is confirmed to be weak.

Comparative evaluation of sultry indices in the mid-south of Iran

The sultry phenomenon is considered one of the climactic events of south shorelines of Iran which are associated with humidity and high air temperature. The importance and necessity of this phenomenon on the subject of applied studies especially bioclimatology will be regarded if increasing of its severity leads to human discomfort as well as asthma and hard breathing. The main objective of this study was to conduct a comparative investigation into the estimation indices for sultry conditions in the southern half of Iran. To achieve research objectives, the hourly data for partial vapor pressure, air temperature, relative humidity, and wind speed were collected from 12 synoptic stations over a 15-year period (1995–2009). The following five indices were used to differentiate between sultry and non-sultry days: the actual vapor pressure more than or equal to 18.8 hPa (Scharlau criterion), equivalent temperature index (more than 56 °C), physiological deficit index (less than 45 hPa), the approximated heat stress index, and the sultry severity index (Castens-Lancaster criterion). To compare these indices, two quantitative and qualitative criteria were considered. The results obtained from quantitative analysis of these indices showed that the Scharlau and Castens-Lancaster criteria were the most coordinated indices in determining sultry conditions. Suitable coordination was obtained only in half the studied stations for the physiological deficit index of less than 45 hPa. The lowest coordination was between the approximated heat stress index and the equivalent temperature index of more than 56 °C. The results obtained from the qualitative evaluation of the sultry estimation indices showed that the Scharlau criterion was more capable of estimating sultry conditions since it exhibited such characteristics as robustness, tractability, transparency, sophistication, extendability, and dimensionality. In general, the conducted quantitative and qualitative analyses showed that the Scharlau criterion was the most appropriate, homogeneous, and concrete index for monitoring sultry conditions in southern Iran.

Multifactor performance analysis of reversible solid oxide cells based on proton-conducting electrolytes

Reversible solid oxide cells (rSOCs) based on proton-conducting electrolytes represent a relatively new and cost-effective possibility for carrying out chemical-to-electrical energy conversion in direct and reverse directions with very high efficiency and low environmental impact. Here we report our findings regarding a modernised approach of rSOC testing, which differs from the traditional characterisation of electrochemical cells, consisting in volt-ampere measurements and impedance spectroscopy analysis under open circuit voltage (OCV) conditions. Expanding the bias range from 0.4 to 1.6 V, the designed rSOC was studied in different (fuel cell, OCV, electrolysis cell) modes and its performance was successfully correlated with ohmic and electrode electrochemical responses depending on the measurement temperature and water vapour partial pressure in oxidant gas. On the basis of this approach, the following new results can be formulated: (i) the ohmic resistance of the proton-conducting electrolytes is a variable parameter depending on the bias in contrast to the convenient oxygen-ionic conductors, for which it is assumed to be a constant; (ii) the electrolyte exhibits predominating proton transport with an activation energy of ∼0.3 eV over the whole bias range; (iii) the output parameters should be correlated with the ohmic and polarisation resistances determined at certain biases (a voltage corresponding to the maximal power density realisation or a thermoneutral voltage) instead of those measured under OCV mode. Concluding, this approach allows the main external factors affecting the rSOC’s performance to be disclosed along with proposed means for its future optimisation in the applied direction.

Experimental study on spray cooling under reduced pressures

Spay cooling is a complicated flow and heat transfer process affected by multi-factors among which the environmental pressure is extremely important. However the influence of pressure is not investigated sufficiently, especially the reduced pressure. In the present study, spray cooling under low initial environmental partial pressures and vapor partial pressures with R21 are investigated with a closed spray and condensation system. To study the influence of initial environmental partial pressure, different amounts of nitrogen are inflated into the vacuum flash chamber, while the vapor partial pressure is kept constant. To study the influence of vapor partial pressure, a cascade refrigerator is used to condense the vapor with different condensation temperatures so that the vapor partial pressure can be maintained or adjusted, while the initial environmental partial pressure is kept constant. The experimental results show that the spray cooling power increases monotonically with the increasing spray flow rate in the experimental range, while the cooling efficiency decreases with the increasing spray flow rate. The spray cooling power and cooling efficiency vary with the initial environmental partial pressure or the vapor partial pressure non-monotonously, which indicates there is an optimal pressure for the heat transfer performance. Besides, the mechanism of the non-monotonous variation trend is discussed based on the key aspects including flash evaporation, convection and boiling. Especially, the boiling heat transfer curve is applied to explain the trend.

AN OVERWIEW AND ANALYSIS OF DEPENDECIES FOR DETERMINING THE SATURATION PRESSURE OF WATER VAPORS

This paper reviews, describes and analyzes the accuracy of 24 dependencies for determining the partial pressure of saturated water vapor. An important indicator of this process is the partial pressure of water vapor in the air, and its maximum value is called saturated water vapor pressure or water vapor saturation pressure, or partial saturated water vapor pressure. The assessment is made against the accepted dependency of Hardy-Wexler. Conclusions and recommendations for simple and highly accurate dependencies ps = f(t) were made.

What is the best temperature-humidity index equation to indicate heat stress in crossbred dairy calves in a tropical environment?

ABSTRACT: The aim of this study was to determine among nine temperature-humidity index (THI) equations, the one that best represents the effects of heat stress on crossbred dairy calves reared in a tropical environment. Twelve male and female calves, aged 20 to 60 days, and raised in a tropical pen were evaluated. Respiratory (RR) and heart rates (HR), rectal (RT), body surface (BST), dry bulb (Tdb) and wet bulb (Tbw) temperatures, partial vapor pressure (Pv), relative humidity (RH) and dew point temperature (Tpo) were quantified in the morning and afternoon. Nine THI equations were calculated. The highest correlation between physiological variables and this was used to select the best THI equation. Averages for nine THI equations, Tdb, Twb, Pv, Tdp, RR, HR, RT, and BST were higher in the afternoon than in the morning, whereas that for RH was the opposite. The highest values for RT occurred at temperatures above 26.4°C and when humidity was below 55.5%. The Tdb and Pv correlations with RR (0.697 and 0.707), RT (0.703 and 0.706) and BST (0.818 and 0.817) were significant and positive, whereas the RH correlations with the same physiological variables were significant and negative (-0.622, -0.590 and -0.638, respectively). The best index was the THI sensible heat-based ( T H I = 3.43 + 1.058 x T d b - 0.293 x R H + 0.0164 x T d b x R H + 35.7), which was significantly correlated with RR (r=0.668 and r²=0.446), HR (r=0.259 and r²=0.067), RT (r=0.693 and r²=0.479) and BST (r=0.807 and r²=0.650). In conclusion, the THI sensible heat-based equation best represents the effects of heat stress on crossbred dairy calves reared in a tropical environment.

Mechanically stimulated thermal synthesis of lithium aluminates

The influence of the conditions of preliminary mechanical activation of a mixture of gibbsite and lithium carbonate in a planetary-type activator and the conditions of subsequent heat treatment on the phase composition of lithium aluminates is studied. It is shown that for the formation of γ-LiAlO2 it is necessary that at the stage of mechanical activation of the mixture an almost complete amorphization of aluminum hydroxide occurs, and the air heat treatment is carried out at a temperature above 750 °C. Thermal treatment of a mechanically activated mixture in the atmosphere with the partial water vapor pressure of below 1 Pa allows the synthesis of γ-LiAlO2 without significant amorphization of aluminum hydroxide at above 600 °C. For the synthesis of α-LiAlO2 preliminary mechanical activation should not lead to the amorphization of aluminum hydroxide, and the process of heat treatment in the air should be carried out at temperatures below 700 °C. The mechanism of formation of highly dispersed lithium aluminates during mechanical activation and subsequent heat treatment of a mixture of gibbsite and lithium carbonate is discussed.