Critical Temperature Of Water Research Articles

Excess, Partial, and Molar Volumes of n-Alkanes in Near-Critical and Supercritical Water

Densities of solutions of n-pentane, n-hexane, n-heptane, and n-octane in near-critical and supercritical water were measured at pressures between 4 and 38 MPa and temperatures from 643.15 to 648.15 K over the entire composition range. The measurements were performed at three isotherms: 643.15, 647.05, and 648.15 K. A constant-volume piezometer was used to measure the PVTx data. The overall accuracy of the pressure, density, temperature, and mole fraction data are ±0.15%. ±0.5%, ±10mK and ±0.0002, respectively. From these results, excess and partial molar volumes were determined. The uncertainties of the derived results are given. Analysis of the results for dilute water + n-alkane mixtures showed that partial molar volume of n-alkane (solute) and excess molar volume of the mixture near the critical point of pure water (solvent) exhibit remarkable anomalies. The experimental values of molar volumes are compared with predicted values based upon scaling theory. Analysis of the results confirms the prediction of scaling theory that along the critical temperature and pressure of water the limiting partial molar volume of alkane as mole fraction x → 0 is proportional to x−γ/βδ, where γ/βδ ≍ 0.79. Our results contribute to understanding of supercritical solubility in near-critical fluids.

The Effect of Pressure on Deuterium-Hydrogen Fractionation in High-Temperature Water

The pressure dependence of deuterium-hydrogen (D-H) fractionation in water to 500°C and 200 megapascals has been calculated from high-temperature, high-pressure spectroscopic data. Pressure effects have a maximum at the critical temperature of water (20 per mil between 22 and 200 megapascals). Even larger effects are predicted for vaporlike densities from molecular dynamics simulations and molecular orbital calculations. Pressure effects explain many of the large discrepancies in published mineral-water D-H fractionation curves. Possible applications to natural examples include mineral-water isotope geobarometry.

Some critical transitions in pool flash evaporation

To improve the fundamental understanding of the physics of the flash evaporation process, pool flash evaporation experiments were conducted in a 152 mm diameter chamber with initial water temperatures of 40–80°C, and superheats of 2–7°C. Several critical transition points were identified or discovered: (1) a critical time at which the rate of ebullition and evaporation diminishes abruptly, (2) an initial water temperature (T i ) at which the non-equilibrium temperature difference attains a minimum, (3) a critical initial water temperature at which the expected observed trend of decreasing non-equilibrium temperature difference (NETD) with decreasing depth reverses itself and (4) a critical initial pool depth at which ϖ 2 (NETD) ϖT i 2 , changes sign from positive at smaller depths to negative at larger depths.

Absorption and Fluorescence Studies of Acridine in Subcritical and Supercritical Water

The isobaric acid/base equilibrium between acridine and the acridinium cation was measured from ambient temperature to 380 °C (above the critical temperature of water, Tc = 374 °C) using absorption spectroscopy. At 3500 psia, the isobaric protonation of acridine is shown to be exothermic up to approximately 315 °C. Above 315 °C, protonation becomes endothermic due to changes in the dielectric constant of water with temperature, which has a profound influence on the solvation of ions. The results are interpreted using a modified Born equation to account for the temperature-dependent changes in acridinium cation and proton solvation. The absorption and fluorescence spectra and the fluorescence lifetime of acridine are sensitive to changes in solvent−solute hydrogen bonding. Hydrogen bonding between acridine and water is observed to decrease from ambient temperature to the critical temperature. A relatively rapid change in hydrogen bonding occurs between 100 and 200 °C.

Mutual solubilities of hydrocarbons and water: III. 1‐hexene; 1‐octene; C10C12 hydrocarbons

AbstractThis article completes the analysis of high‐temperature mutual solubilities of hydrocarbons and water. Part I (Tsonopoulos and Wilson, 1983) presented benzene, cyclohexane, and n‐hexane, while Part II (Heidman et al., 1985) extended the investigation to ethylbenzene, ethylcyclohexane, and n‐octane. Part III presents experimental data up to the three‐phase critical end point for C6, C8, and C10 1‐alkenes, n‐decane, n‐butylcyclohexane, m‐diethylbenzene, p‐diisopropylbenzene, cis‐decalin, tetralin, 1‐methylnaphthalene, and 1‐ethylnaphthalene. The thermodynamic analysis of Henry's constants for hydrocarbons in water is extended to the critical temperature of water, while the solubility and volatility of water in hydrocarbons are successfully correlated with several modifications of the Redlich‐Kwong equation of state.

Phase behavior in binary and ternary water-salt systems at high temperatures and pressures

Abstract

Excited-State Proton Transfer Reactions in Subcritical and Supercritical Water

The isobaric rates of excited-state deprotonations of 2-naphthol by acetate and borate anions exhibit only modest deviations from Arrhenius-like behavior from ambient temperature to nearly the critical temperature of water (Tc = 374 °C). In contrast, the rates of deprotonation by ammonia and water exhibit marked deviations from Arrhenius-like behavior and go through a maximum at high temperatures. These observations establish a fundamental difference in how the rates of charge-generating reactions, such as proton transfers to neutral molecules like ammonia and water, and those in which ionicity is unchanged, such as proton transfers to acetate and borate anions, depend on temperature. The loss of local water structure and changes in dielectric constant with temperature have a much more profound influence on the charge-generating reactions. These results are interpreted using transition state theory and compared with several molecular dynamics−free energy perturbation simulations. At temperatures above 250...

Volumetric properties of aqueous 1-1 electrolytes near and above the critical temperature of water III. Experimental densities and apparent molar volumes of CsBr(aq) to the temperature 725.5 K and the pressure 38.0 MPa, comparison with other 1-1 electrolytes, and extrapolations to infinite dilution for NaCl(aq)

A vibrating-tube densitometer was used for measuring differences in densities between CsBr(aq) and water from molalities of 0.0024 mol·kg-1 to 0.50 mol·kg-1, at temperatures between 604.4 K and 725.5 K, and at pressures from 18.4 MPa to 38.0 MPa. The temperature and molality dependences of the derived apparent molar volumes are compared with those for the other 1-1 electrolytes. Anomalous behavior was observed for dilute solutions in the region of low density of water (Po;o < 350 kg·m-3) where the salts with the lowest ionic radii had the least negative values of the apparent molar volumes. This behavior indicates that the ion pairs with the smallest distance of closest approach have the least negative apparent molar volumes. Using the Pitzer parametric equation and a simplified model describing ion-pairing in dilute solution, the partial molar volumes at infinite dilution were estimated when the density of water was greater than 280 kg·m-3. Under these conditions, there was no evidence that critical-point phenomena invalidated the estimate.

Liquid-vapor fractionation of oxygen and hydrogen isotopes of water from the freezing to the critical temperature

The equilibrium fractionation factors of oxygen and hydrogen isotopes between liquid water and water vapor have been precisely determined from 25 to 350°C on the VSMOW-SLAP scale, using three different types of apparatus with static or dynamic techniques for the sampling of water vapor. Our results for both oxygen and hydrogen isotope fractionation factors between 25 and 100°C are in excellent agreement with the literature (e.g., Majoube, 1971). Our results for the hydrogen isotope fractionation factor above 100°C also agree quantitatively with the literature values of Merlivat et al. (1963) and Bottinga (1968). The results for the hydrogen isotope fractionation factor obtained in this study and from most of the literature were regressed to the equation, 10 3Inα 1−v(D) = 1158.8( T 3 10 9 ) −1620.1 ( T 2 10 6 ) + 794.84( T 10 3 ) −161.04 + 2.9992( 10 9 T 3 ), from 0°C to the critical temperature of water (374.1°C) within ± 1.2(1σ) ( n = 157); T( K). The cross- over temperature is 229 ± 13° C (1σ). Our values for the oxygen isotope fractionation factor between liquid water and water vapor are, however, at notable variance with the only dataset available above 100°C in the literature ( Bottinga, 1968), which is systematically higher (av. + 0.15 in 10 3 In α 1−v( 18O)) with large errors (± 0.23 in 1σ). Our results and most of the literature data below 100°C were regressed to the equation, 10 3 In α 1−v( 18O) = −7.685 + 6.7123( 10 3 T ) − 1.6664( 10 6 T 2 ) + 0.35041 ( 10 9 T 3 ), from 0 to 374.1°C within ± 0.11 (1σ)( n = 112); T( K). A third water-steam isotope geothermometer, using the ratio of ΔδD/Δδ 18O given by water and steam samples, is readily obtained from the above equations. This geothermometer is less affected by incomplete separation of water and steam, and partial condensation of steam than those employing the oxygen and hydrogen isotopic compositions alone.

Experimental study on the effect of the critical temperature of water on the preparing and occurring of large earthquakes

The features of fracturing and dissolving of Yunnan marble in distilled water near the critical temperature have been studied experimentally. The results indicate that the mechanical parameters of the samples (fracture strength, Young’s Modulus, shear fracture energy and fracture toughness) drop with the temperature of the environment water, near the critical temperature (380°C), these parameters have sudden changes (drop), then keep stable values roughly. The contents of some chemical materials in the water, PH value and conductivity at every experiment temperature have been analysed and measured. At 380°C, there all exist sudden changes. According to the results, it is pointed out that the sudden changes are related to strong stress corrosion of water near its critical temperature to the rock and the exist and its migration of the water solution near the critical temperature in the crust have important significance to the earthquake source process, the formation cause of the low-focal depth earthquakes in the crust.

The Viability of pH Measurements in Supercritical Aqueous Systems

The measurement of pH of aqueous systems at high temperature is becoming increasingly important because of the need to monitor the chemistry of nuclear power plant cooling water systems and the cycle chemistry of fossil‐fueled power reactors. We have previously shown that the yttria‐stabilized zirconia pH sensor can be used for accurate pH measurements of aqueous systems up to 320°C. This paper describes the viability of pH measurement of aqueous systems up to and above the critical temperature of water.

Temperature Effects on Generation and Entrainment of Bubbles Induced by a Water Jet

A simple experiment simulating the jet feature of breaking waves is conducted to study quantitative effects of the water temperature on the generation of bubbles at the air–water interface and their entrainment into the water column. The results indicate that there is a critical water temperature for the inception of bubbles. Such a critical temperature can be attributed to changes of the surface tension and viscosity, both of which decrease as water temperature increases. Field measurements of the bubble entrainment depth, bubble size spectrum, and whitecap coverage are shown to have similar temperature dependencies as our observations.

Volumetric properties of aqueous 1-1 electrolyte solutions near and above the critical temperature of water II. Densities and apparent molar volumes of LiCl(aq) and NaBr(aq) at molalities from 0.0025 mol·kg −1 to 3.0 mol·kg−1, temperatures from 604.4 K to 725.5 K, and pressures from 18.5 MPa to 38.0 MPa

A vibrating-tube densitometer was used for measuring differences in densities between water and LiCl(aq) and NaBr(aq) at molalities from 0.0025 mol·kg−1 to 3.0mol·kg−1, at temperatures from 604.4 K to 725.5 K, and pressures from 18.5 MPa to 38.0 MPa. The density differences and the derived apparent molar volumes are tabulated.

Volumetric properties of aqueous 1-1 electrolyte solutions near and above the critical temperature of water I. Densities and apparent molar volumes of NaCl(aq) from 0.0025 mol·kg −1 to 3.1 mol·kg −1, 604.4 K to 725.5 K, and 18.5 MPa to 38.0 MPa

Differences between densities of NaCl(aq) and water were measured with a vibrating-tube densitometer from 0.0025 mol·kg−1 to 3.1 mol·kg−1, 604.4 K to 725.5 K, and 18.5 MPa to 38.0 MPa. The density differences and apparent molar volumes of NaCl are tabulated and the accuracy of the results is discussed.

Changes in insulation of body tissue and wet suits during underwater exercise at various atmospheric pressures

To clarify the independent changes of insulations of body tissues (Itissue) and wet suit (Isuit) in the wet-suited subject during underwater exercise, overall heat flow from the skin (Htissue) and wet suit (Hsuit) and esophageal (Tes), skin (Tsk), and wet suit temperatures were measured at 1, 2, and 2.5 atmospheres absolute (ATA) at critical water temperature (Tcw). The average Tcw in nine wet-suited men (23-38 yr) was 22.3 +/- 0.2, 26.3 +/- 0.2, and 28.0 +/- 0.4 degrees C (SE) at 1, 2, and 2.5 ATA, respectively. At Tcw of each pressure male volunteers wearing 5-mm neoprene wet suits completed three 2-h experiments while immersed up to the neck. During one experiment the subjects remained at rest, and in the other two they exercised on an underwater ergometer at two different intensities (2 and 3 met). Tes significantly declined (P less than 0.05) over 2 h from 37.1 to 36.5 degrees C during rest in each pressure. The 2-met exercise prevented Tes from falling in all pressures, and the 3-met exercise elevated Tes by 0.2-0.3 degrees C. There was no exercise-dependent difference in Isuit, but a pressure-dependent difference was remarkable. The Itissue at rest was identical for all pressures; however, it progressively decreased as a function of exercise intensity. It is concluded that overall Itissue is entirely determined by work intensity at Tcw, but not by atmospheric pressure. On the contrary, Isuit at Tcw is solely dependent on the pressure, but not on the work intensity.

The solubility and isotopic fractionation of gases in dilute aqueous solution. IIa. solubilities of the noble gases

A method for the analysis of precise gas solubility data is presented and applied to new determinations of the Henry constant, k2, for He, Ne, Ar, Kr, and Xe. The values of k2 are fitted to the same sets of temperature functions which we have tried for oxygen. Our previously proposed power series in 1/T, ln(k2/P )=a0+a1/T+a2/T2 (Mark I), gives the best 3-term fit within the temperature range 0–60°C. For use over the full range to the critical temperature of water, we have discovered a new function given by (T*)2ln(k2/P )=A0(T*)2+A1(1-T*)1/3+A2(1-T*)2/3(Mark II), where T*≡T/T c1 . It fits our data from 0–60°C nearly as well as Mark I; it fits high temperature data from other sources; and at the critical temperature of water it satisfies theoretical requirements. Expansion of Mark II reveals the relationship between Mark II and Mark I and leads to a 4-term smoothing function, ln(k2/P )=a−2(T*)−2+a−1(T*)−1+a0+a1T* (Mark III), which we believe gives the best values only for the 0–60°C range. Mark III is used to calculate values for $$\Delta \bar G^\theta ,\Delta \bar H^\theta ,\Delta \bar S^\theta $$ , and $$\Delta \bar C^\theta $$ , 0–60°C, and a procedure is empolyed to estimate the errors. Agreement is excellent between these results and those obtained from precise microcalorimetric measurements made by others. With the inclusion of pressure correction terms, Mark II yields the four thermodynamic function changes for use at high temperatures. With increasing temperature, these changes suddenly turn upward toward plus infinity as T c1 is approached. Essentially direct determinations of $$\Delta \bar C^\theta $$ for argon by other workers are in excellent agreement with our results. The symmetrical activity coefficient at infinite dilution, γ 2 ° is examined and the hypothetical properties of k2 are explored below 0°C. Mark II can be expressed in the reduced form (T*)2ln(k 2 * )=A1(1-T*)1/3+A2(1-T*)2/3, where k 2 * ≋k 2/(p c1φ2c1). A2 is a very good linear fit to A1, which suggests a characteristic temperature for water at 287.3 K.

Critical water temperature during water immersion at various atmospheric pressures.

The present work was undertaken to determine the effect of atmospheric pressure [ranging from a high altitude of 4,300 m above sea level or 0.6 atmospheres absolute (ATA) to depths of 10 m deep or 2 ATA] on the critical water temperature (Tcw), defined as the lowest water temperature a subject can tolerate at rest for 2 h without shivering, of the unprotected subject during water immersion. Nine healthy males wearing only shorts were subjected to immersion to the neck in water at 0.6, 1, and 2 ATA while resting for 2 h. Continuous measurements included esophageal (Tes) and skin (Tsk) temperatures, direct heat loss from the skin (Htissue), and insulation of the tissue (Itissue). The Tcw was significantly higher at 0.6 ATA than 1 and 2 ATA: however, Tcw at 1 ATA was identical to that at 2 ATA. The metabolic heat production remained unchanged among the pressures. During the 2-h immersion in Tcw, Tes was identical among all atmospheric pressures: however, Tsk was significantly higher (P less than 0.05) at 0.6 ATA and was identical between 1 and 2 ATA. The overall mean Itissue was near maximal during immersion in Tcw in each pressure, and no difference was detected among the pressures. However, Itissue at the acral extremities (arm, hand, and foot) decreased significantly at 0.6 ATA, and subsequently heat loss from these parts was increased, which elevated an extremity-to-trunk heat loss ratio to 1.4 at 0.6 ATA from 1.1 at 1 and 2 ATA.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of pressure on thermal insulation in humans wearing wet suits.

The present work was undertaken to determine the critical water temperature (Tcw), defined as the lowest water temperature a subject can tolerate at rest for 3 h without shivering, of wet-suited subjects during water immersion at different ambient pressures. Nine healthy males wearing neoprene wet suits (5 mm thick) were subjected to immersion to the neck in water at 1, 2, and 2.5 ATA while resting for 3 h. Continuous measurements of esophageal (T(es)) and skin (Tsk) temperatures and heat loss from the skin (Htissue) and wet suits (Hsuit) were recorded. Insulation of the tissue (Itissue), wet suits (Isuit), and overall total (Itotal) were calculated from the temperature gradient and the heat loss. The Tcw increased curvilinearly as the pressure increased, whereas the metabolic heat production during rest and immersion was identical over the range of pressure tested. During the 3rd h of immersion, Tes was identical under all atmospheric pressures; however, Tsk was significantly higher (P less than 0.05) at 2 and 2.5 ATA compared with 1 ATA. A 42 (P less than 0.001) and 50% (P less than 0.001), reduction in Isuit from the 1 ATA value was detected at 2 and 2.5 ATA, respectively. However, overall mean Itissue was maximal and independent of the pressure during immersion at Tcw. The Itotal was also significantly smaller in 2 and 2.5 ATA compared with 1 ATA. The Itissue provided most insulation in the extremities, such as the hand and foot, and the contribution of Isuit in these body parts was relatively small. On the other hand, Itissue of the trunk areas, such as the chest, back, and thigh, was not high compared with the extremities, and Isuit played a major role in the protection of heat drain from these body parts.

The system NaCl-H 2O: Relations of vapor-liquid near the critical temperature of water and of vapor-liquid-halite from 300° to 500°C

Vapor-liquid relations ( P- T- x) for the system NaCl-H 2O were determined experimentally at temperatures spanning the critical temperature of water ( T c ), the lowest temperature in the system at which critical behavior occurs. In addition, vapor-liquid-halite P- T- x(vapor) relations were determined from 300° to 500°C. Results show that at 373.0°C, immediately below T c , the vapor side of the isothermal vaporliquid P-x boundary has a shape quite different from that previously conceived. The NaCl content of the vapor increases with pressure in a smooth manner from the pressure of the three-phase assemblage (135 bars, 0.0029% NaCl), to a pressure just below that of the vapor pressure of pure water (0.012% NaCl at 184 bars). Above this pressure the boundary abruptly reverses and projects asymptotically to 0% NaCl in a beak-like shape at 218 bars, the vapor pressure of pure water. At 375.5°, slightly above T c , the asymptote disappears, and is replaced by a rounded nose. At progressively higher temperatures, the nose disappears and by 380°C the familiar symmetrical bell-shaped curve predominates with the critical point defined by the top of the bell. The P- T curve of the three-phase assemblage determined in the present study is in agreement with previous workers. The NaCl content of the three-phase vapor, however, is much higher than some literature values at temperatures above 410°C.

High Pressure Phase Equilibria andPVT‐Data of the Water‐Oxygen System Including Water‐Air to 673 K and 250 MPa

AbstractA high pressure autoclave with sapphire windows, auxiliary equipment and means and precautions needed for experiments with high pressure, high temperature oxygen are described. With water‐oxygen mixtures of different mole fractions,x, determinations were made of liquid‐gas phase equilibria conditions along “isopleths” between 500 and 660 K to 250 MPa. Molar volumes of the mixtures were measured at the three‐dimensional (PTx) phase equilibria surface and in the supercritical region at 673 K. The critical curve, an envelope for the isopleths, begins at the critical point of water (647 K), has a temperature minimum (640 K) at about 75 MPa and proceeds to 250 MPa at 663 K. Phase equilibria and critical curve data are given. The H2OO2critical PT curve is very close to the critical curve recently (10) determined for H2ON2. Values for the Henry‐constant from 300 K to 647 K for mixtures dilute in oxygen are presented. The Henry constant at room temperature has only about half the value of the Henry constant for nitrogen in water. At the critical temperature of water (647 K), however, both constants do not differ by more than the uncertainty of the determinations. The excess volume was calculated at 673 K from 30 to 250 MPa. All values are positive. The excess Gibbs energy and activity coefficients are presented. One isopleth for H2O‐air withx(H2O) = 0.80 was measured and molar volume values for this composition at 673 K between 33 and 280 MPa are given.