Critical Temperature Of Water Research Articles

Working fluid selection based on critical temperature and water temperature in organic Rankine cycle

This paper examines the thermal performance of working fluids in the entire evaporation temperature region up to near-critical temperature of working fluids in the organic Rankine cycle (ORC). The variation and tendency of the net power output with water temperature and correlated with the critical temperature of working fluids is investigated. Four characteristic curves of the net power output at particular water temperature (Tw_turn, Tw_app, Tw_tran and Tw_up) and their temperature difference (ΔT_turn=Tw_turn-Tcr, ΔT_app=Tw_app-Tcr) are obtained to evaluate the working fluids. The curve at “applicable water temperature (Tw_app)” is a demarcation to differentiate the net power output from low to high. The “upper water temperature (Tw_up)” is an upper limit of the water temperature to yield the higher net power output. A relation is built that the suitable water temperature is within the Tw_app and Tw_up of the working fluid.

On correlating water solubility in ill-defined hydrocarbons

Saturated water solubility values in hydrocarbon liquids span more than four orders of magnitude and are characterized by high relative error. Development of reliable correlations is particularly challenging for ill-defined and asymmetric hydrocarbon mixtures where fluid characterization and pseudo binary phase behavior type are uncertain. In this work, predictive correlations targeting this application, below the critical temperature of water, are explored and two promising models are compared with computation methods available in the literature. The model inputs include easily measurable properties (hydrogen mass fraction, fluid density at ambient conditions) as well as KWatson, mean molar mass and the average boiling point of the hydrocarbon mixture. These latter three inputs are complex and frequently difficult to define parameters encountered in refinery characterization of ill-defined organic mixtures. Models comprising one or two input variables were fit using a training data set comprising pure hydrocarbons and Athabasca bitumen. The average deviation of the models from these reference experimental data was found to be comparable to the uncertainty of the reference data in most cases. However most of the models exhibited high deviation and bias relative to the test data set comprising ill-defined hydrocarbon mixtures. Two models are shown to be robust numerically, insensitive to the uncertainty of input variables, and applicable irrespective of the pseudo binary phase behavior type with water (Type II, Type IIIa, or Type IIIb) up to their upper critical end point (UCEP). At temperatures above the UCEP, a hydrocarbon rich liquid phase only arises for Type IIIb pseudo binary mixtures. In this region, above 647K, correlation extrapolation options beyond the range of experimental data are discussed, and only fluid-specific Henry-like constant models are proposed.

A practical method for the estimation of oil and water mutual solubilities

A simple model is proposed for the calculation of oil and water mutual solubilities as a function of temperature using the hydrocarbon specific gravity and Watson-K factor as correlating parameters. The model parameters were determined using a single consistent set of high quality solubility data collected at the water or hydrocarbon saturation pressures at temperatures from 273K and 573K but primarily from 298K to 398K. The hydrocarbon in water solubilities ranged over 11 orders of magnitude while the water in hydrocarbons solubilities ranged over 4 orders of magnitude. Hydrocarbon types ranged from low molecular weight paraffins such as n-pentane to heavy aromatics such as anthracene. The average absolute error in the estimated solubilities of water in hydrocarbons over 621 data points was 34% and approached the suggested underlying uncertainty in the reference data (30%). The average absolute error in the estimated solubilities of hydrocarbons in water over 964 data points was 88% and exceeded the suggested underlying uncertainty in the reference data (30%).The model can be extended to higher temperatures using a procedure based on activity coefficients or equations of state and is easily adapted to work with ill-defined hydrocarbon mixtures. Prediction and correlation of solubilities of water in kerosene, heavy oils, and bitumen were made at temperatures, pressures, and compositions far removed from the original data used for model construction. The correlation failed near the critical temperature of water because under these conditions, the properties hydrocarbon-rich phases in the mixtures on which the correlation is based (Type II and Type IIIa phase behaviour according to the van Konynenburg and Scott naming scheme) and those of water+heavy hydrocarbons (Type IIIb phase behaviour) diverge. A separate NRTL based correlation is presented for the mutual solubility of water+heavy oils at temperatures close to the critical temperature of water.

Phase behavior of Athabasca bitumen + water mixtures at high temperature and pressure

Mixtures of hydrocarbons+water exhibit complex phase behaviors, and transitions in phase behavior classification also arise as hydrocarbon composition is varied. In this work, the phase behavior of Athabasca bitumen+water mixtures is reported, in the temperature range (522.1–644.0K) and the pressure range (4.2–35.7MPa). Pressure–temperature (at fixed composition) and pressure–composition (at fixed temperature) phase diagrams were prepared based on observations obtained using a view cell apparatus equipped with X-ray transmission tomography. Phase boundary and phase composition accuracy and precision were validated by reproducing phase diagrams for 1-methylnaphthalene+water and toluene+water mixtures available in the literature. The Athabasca bitumen+water pseudo-binary exhibits type IIIb phase behavior, based on the van Konynenburg and Scott classification scheme, as the composition difference between the water rich and Athabasca bitumen rich liquid phases remain large and liquid–liquid–vapor phase behavior persists up to the critical temperature of water. The reported phase diagrams are expected to provide benchmark data needed to define operating conditions for hydrocarbon resource production and refining processes based on the addition or exploitation of sub critical and near critical water.

Effect of Electric Field on Water Confined in Graphite and Mica Pores

We examined the influence of external electric field on the vapor–liquid coexistence curve and on structural properties of TIP4P/2005 water confined in hydrophobic and hydrophilic pores using all-atom molecular dynamics simulations. While the electric field increases the critical temperature of bulk water, the effect is contrary on the confined water. We clearly observe that the critical temperature of confined water decreases with increasing field strength. The current work strongly indicates that using electric field results in a decrease in the saturated liquid phase density and increase in the saturated vapor phase density of the confined water and can be used to modulate the evaporation rate of water under confinement. The effect of an electric field on the confined fluids is more pronounced at higher temperature. We also report that the critical density of water behaves differently in hydrophobic and hydrophilic pores. With increasing electric field, the critical density increases in hydrophobic pores; however, it is found to decrease in hydrophilic pores. We analyze the results using pair correlation functions and orientational, tetrahedral, and hydrogen bond distributions. Our investigation indicates that the presence of an electric field enhances the coordination number N(r) of the bulk phase. In contrast, the presence of an electric field reduces N(r) of the confined fluid. This is clearly reflected in the behavior of the critical temperature of bulk and confined water. Our structural analysis reveals that the application of an external field induces orientational order of dipole vector parallel to the field direction in bulk water, whereas its effects on dipole orientation is much less in confined systems. We also report that the hydrogen-bonding behavior in the vapor phase is responsible for the difference in critical density of water confined in hydrophobic and hydrophilic pores.

Thermodynamics of Si(OH)4 in the vapor phase of water: Henry’s and vapor–liquid distribution constants, fugacity and cross virial coefficients

The fugacity coefficients of Si(OH)4 are evaluated from solubilities of solid phases of SiO2 in the vapor phase of water. The virial equation of state, truncated at the third virial coefficient, is employed to describe the fugacity coefficients of Si(OH)4. The temperature dependencies of the second, B12, and the third, C112, cross virial coefficients for H2O–Si(OH)4 interactions are approximated by empirical relations. It is found that silica–water interactions in the vapor phase are significantly more non-ideal compared to water–water interactions. Knowledge of B12 and C112 allows calculation of solubilities of quartz (Q) and amorphous silica (AS) in steam up to the density of 200kgm−3 in satisfactory agreement with available data, and should provide reasonable solubility values at temperatures where no experimental results exist. The calculated values of the solubility of Q and AS in saturated vapor up to the critical temperature of water, Tc, are tabulated.The partial molar properties of dilute solutes close to the critical point of water are governed by the Krichevskii parameter, the value of which for Si(OH)4 is evaluated from available data (mainly vapor–liquid distribution constants for silica) to be equal to −187±10MPa. The knowledge of the thermodynamic properties of Si(OH)4 in the ideal gas state and in the state of the standard solution in liquid water allows calculating Henry’s constant, kH, for Si(OH)4 up to 623.15K at water saturation pressure P1∗. The theoretically-based equation, containing the Krichevskii parameter, allows extrapolating kH values all the way toward the critical temperature of water. This, in turn, makes possible calculation of the solubility of quartz and amorphous silica in liquid water at P1∗ at all temperatures up to Tc. The presented results should be useful for modeling solid–liquid–vapor, solid–vapor and liquid–vapor equilibria in the H2O–SiO2 system at steam densities up to 200kgm−3.

Hydrothermal synthesis of Ni 2FeBO 5 in near-supercritical PWR coolant and possible effects of neutron-induced 10B fission in fuel crud

The hydrothermal synthesis of a nickel–iron oxyborate, Ni 2FeBO 5, known as bonaccordite, was investigated at pressures and temperatures that might occur at the surface of high-power fuel rods in PWR cores and in supercritical water reactors, especially during localized departures from nucleate boiling and dry-outs. The tests were performed using aqueous mixtures of nickel and iron oxides with boric acid or boron oxide, and as a function of lithium hydroxide addition, temperature and time of heating. At subcritical temperatures nickel ferrite NiFe 2O 4 was always the primary reaction product. High yield of Ni 2FeBO 5 synthesis started near critical water temperature and was strongly promoted by additions of LiOH up to Li/Fe and Li/B molar ratios in a range 0.1–1. The synthesis of bonaccordite was also promoted by other alkalis such as NaOH and KOH. The bonaccordite particles were likely formed by dissolution and re-crystallization by means of an intermediate nickel ferrite phase. It is postulated that the formation of Ni 2FeBO 5 in deposits of borated nickel and iron oxides on PWR fuel cladding can be accelerated by lithium produced in thermal neutron capture 10B(n,α) 7Li reactions. The process may also be aided in the reactor core by kinetic energy of α-particles and 7Li ions dissipated in the crud layer.

Influence of temperature on process performance of activated sludge in coking wastewater treatment plant

Coking wastewater contains toxic compounds such as ammonia, phenolics, cyanides, thiocyanate, and thiosulfate. In normal situation, these compounds can be 100% decomposed by activated sludge in the wastewater treatment plant. However, a new factor, high water temperature, caused by the covering of the basins, has been found to reduce the removal rate of the pollutants, especially the thiocyanate. Several remediation measures were applied to improve the biological process performance. A series of batch and continuous-flow biodegradation tests have demonstrated that the relatively low temperature ranging from 20 to 37°C attained perfect removal efficiency (∼100%) of SCN− from the coke plant wastewater. When the temperature is increased to 38, 39°C, the SCN− removal rate decreased to 30 ∼ 50% after 48 hours of temperature shift. Moreover, when the temperature is increased to 40 to 45°C, SCN− biodegradation is significantly decayed one day after the temperature shock, and the SCN− removal efficiency dropped gradually to 0%, with microbial deterioration during day 1 to day 4. Meanwhile, the COD removal has also decreased from 85% down to 45% at 45°C. Both laboratory verifications confirmed that 40°C should be the critical water temperature for the SCN− degrading microbe to function well in the activated sludge process. In order to stabilize the pollutant removing ability of the procedure, the water temperature of aeration basin is set to operate under 37°C. Four modifications were practiced on site to decrease the temperature of activated sludge. Only the last alternative measure worked well with the opened hand hole, 50% of total cover area, to discharge the water vapor and gas emission from the head space of aeration basin. The water temperature has dropped from 41 to 36°C in the early summer of June with ambient temperature of 37°C, suggesting that partially uncovering the basin does help maintain the water temperature. Finally, we suggest some measures that can be applied to establish a standard process on site in order to ensure that the aeration basin temperature stays under 37°C and that our biotreatment system can maintain its function in the future.

The effects of temperature and nutrient ratios on Microcystis blooms in Lake Taihu, China: An 11-year investigation

The temporal distribution of bloom-forming cyanobacteria- Microcystis and its correlation with related physical and chemical variables including the total nitrogen-to-total phosphorus ratio (TN:TP), the ammonium-to-nitrate ratio (NH 4-N:NO X -N), water temperature, and pH in the north part of Lake Taihu (Meiliang Bay) were investigated, using a continuous, 11-year record of environmental data (1992–2002) and phytoplankton species. A multivariate statistical analysis, canonical correspondence analysis (CCA), revealed a negative correlation between the Microcystis and TN:TP, and a positive correlation between the Microcystis and NH 4-N:NO X -N, water temperature and pH. Warm water temperature was the principal force driving Microcystis blooms, which were preceded declining concentrations of nitrogen compounds. Microcystis tended to dominate ( Microcystis contributed above 50% to total algal mass) in the north part of Lake Taihu during summer when the TN:TP mass ratio was less than 30, NH 4-N:NO X -N was below 1, and a critical water temperature ranged from 25 °C to 30 °C, respectively. Meanwhile, suspended solids (SS) concentrations exceeded 10 mg l −1 and pH exceeded 8.0 during blooms. Overall, this study advances our understanding of nutrient enrichment and high ambient temperature influences on Microcystis biomass.

Analysis of the scale up of a transpiring wall reactor with a hydrothermal flame as a heat source for the supercritical water oxidation

Experimental data from a tubular reactor and from a transpiring wall reactor (TWR) are used to analyze the scaling up of SCWO reactors operating with a hydrothermal flame as a heat source. Results obtained with the tubular reactor show that fluid velocity inside the reactor determines the minimum injection temperature at which a stable hydrothermal flame is formed. When the fluid velocity inside of the reactor is lower, the extinction temperature of the hydrothermal flame in that reactor is also lower. Using this reactor, extinction temperatures are always near or above the critical temperature of water. Total TOC removals are possible working with isopropyl-alcohol at temperatures between 650 and 700 °C and residence times of 0.5 s. Results of the TWR show that steady operation with a hydrothermal flame inside is possible even when reagents are injected at subcritical conditions as low as 170 °C. Temperature measurements show that reaction is not initiated in the injector but in the reaction chamber, where fluid velocity is lower than 0.1 s. This was explained by estimating that the flame front velocity of a hydrothermal flame is of the order of 0.1 m/s. Thus, it is expected that the flame is stabilized in the reaction chamber and not in the injector, where fluid velocities are higher than 2 m/s. A previously developed model of the TWR was modified in order to describe the ignition in the reaction chamber and not in the injector. The model reproduces satisfactorily experimental data and it was used to propose the design of scaled up reactors for SCWO with a hydrothermal flame inside.

GJ 1214b and the prospects for liquid water on super Earths

AbstractGJ 1214b is one of the first discovered transiting planets having mass (6.55 M⊕) and radius (2.678 R⊕) smaller than Neptune. To account for its low average density (1870 kg m−3), GJ 1214b must have a significant gas component. We use interior structure models to constrain GJ 1214b's gas envelope mass, and to explore the conditions needed to achieve within the planet pressures and temperatures conducive to liquid water. We consider three possible origins for the gas layer: direct accretion of gas from the protoplanetary nebula, sublimation of ices, and outgassing from rocky material. Despite having an equilibrium temperature below 647 K (the critical temperature of water) GJ 1214b does not have liquid water under most conditions we consider. Even if the outer envelope is predominantly sublimated water ice, in our model a low intrinsic planet luminosity (less than 2 TW) is needed for the water envelope to pass through the liquid phase; at higher interior luminosities the outer envelope transitions from a vapor to a super-fluid then to a plasma at successively greater depths.

Desolvation of polymers by ultrafast heating: Influence of hydrophilicity

Using molecular-dynamics simulation, we investigate the consequences of ultrafast laser-induced heating of a small water droplet containing a solvated polymer. Two polymers are studied: polyethylene as an example of a hydrophobic, and polyketone as an example of a hydrophilic polymer. In both cases, when the droplet is heated below the critical temperature of water, strong water evaporation is started, but the polymer remains in contact with a central water cluster. However, upon heating beyond the critical temperature, the hydrophilic polyethylene becomes completely desolvated, while polyketone still remains solvated. We analyze this behavior in terms of the intermolecular interactions and of the expansion dynamics of the heated droplet.

Effect of pH and Temperature on Corrosion of Nickel-Base Alloys in High Temperature and Pressure Aqueous Solutions

The properties of water change significantly across the critical point of water and these changes affect the degradation behavior of constructional alloys. The corrosion behavior of nickel-base alloys is investigated across the critical temperature of water at a constant pressure in aqueous solutions. At subcritical temperatures, the corrosion behavior of alloys of 625 and C-276 is influenced by the pH values of the aqueous solutions. In neutral pH, a thin surface oxide film develops on the substrate. In pH 2, Ni and Fe are selectively dissolved, and Cr and Mo form stable oxides. In pH 1, Cr, Ni, and Fe are dissolved from the substrate and Mo forms a stable oxide. At supercritical temperatures, no dealloying is observed independent of pH and a thin surface oxide film develops. Changes in water properties and thermodynamics explain the dealloying behavior of elements and the highest corrosion rate at high subcritical temperature.

Thermodynamic Properties of Aqueous Polyatomic Ions at Extreme Temperatures and Pressures

Recently a theoretical treatment (J. Phys. Chem. B 2009, 113, 2398-2404) was developed for predicting the standard state thermodynamic properties of electrolytes up to and beyond the critical temperature of water (1273 K and at pressures up to 1000 MPa). In general, the model requires sufficient data at 298.15 K including the Gibbs free energy of hydration and at two higher temperatures to fix two constants for each electrolyte. This communication describes an extension of this "two constant" theory to thermodynamic properties of polyatomic ions for which no accurate data for the Gibbs free energy of hydration exits at 298.15 K.

Hydrogen production by biomass gasification in supercritical water over Ni/γAl 2O 3 and Ni/CeO 2-γAl 2O 3 catalysts

Hydrogen production by supercritical water gasification (SCWG) is a promising technology for wet biomass utilization. Ni catalyst can realize the high gasification efficiency of biomass near the critical temperature of water. In this paper, Ni/γAl 2O 3 and Ni/CeO 2-γAl 2O 3 catalysts were prepared by an impregnation method. The catalyst performance for glucose gasification in supercritical water was tested in autoclave reactor. All experiments were carried out in the autoclave at 673 K, 24.5 MPa, and the concentration of glucose was 9.09 wt.%. The catalysts before and after reaction were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), BET specific surface area measurements, X-ray fluorescence spectrum (XRF) and Thermo-gravimetric analyses (TGA) in order to investigate on the chemical property and catalytic mechanism. The experimental results showed that hydrogen yield and hydrogen selectivity increased sharply with addition of Ni/γAl 2O 3 and Ni/CeO 2-γAl 2O 3 catalysts. The catalytic activity and H 2 selectivity of Ni/CeO 2-γAl 2O 3 was higher than that of Ni/γ-Al 2O 3 catalyst. The results revealed that carbon deposition and coking led to the deactivation of the catalysts. Ce in the Ni/CeO 2-γAl 2O 3 catalyst had a certain role in the inhibition of carbon deposition and coking.

High water temperature tolerance in photosynthetic activity of Zostera japonica Ascherson & Graebner seedlings from Ago Bay, Mie Prefecture, central Japan

Photosynthetic activity of Zostera japonica seedlings was measured using a gas volumeter at 0 and 6 days in culture under eight light (0–800 μmol photons/m2/s) and ten water temperature conditions (5–35°C). Seedlings from Ago Bay, Mie Prefecture were cultured in incubators accurately controlled at each test temperature for 1 week. After 1 week, maximum gross photosynthesis (P maxg) appeared at 29°C and most seedlings cultured at 30–35°C bleached and withered. At the same time, the light compensation point (I c) increased only at 30°C during the culture period. As a result, the upper critical water temperature for survival was 29°C in Z. japonica seedlings, which agrees well with that for the southern boundary of Z. japonica around Japanese coast. It is necessary to monitor this species around this boundary as a bio-indicator for seawater warming.

Standard State Thermodynamic Properties of Completely Dissociated Hydrochloric Acid and Aqueous Sodium Hydroxide at Extreme Temperatures and Pressures

Standard state thermodynamic properties for completely dissociated hydrochloric acid were fixed by ionic additivity, using the data from other strong electrolytes perrhenic acid, sodium perrhenate, and sodium chloride from 298.15 to 598.15 K and at p(sat). The standard electrode potential for the important silver-silver chloride electrode system and the equilibrium constants for the volatility of HCl from aqueous solutions were then calculated and compared with literature data. Using the experimental data from this study and auxiliary data from literature, the logarithm of the molal association constant of HCl at the critical temperature of water and at 673.15 K up to 1000 MPa was predicted from the unified theory of electrolytes (UTE). The standard state thermodynamic properties for completely dissociated aqueous sodium hydroxide were also calculated by ionic additivity over the same temperature range from aqueous sodium chloride, hydrochloric acid, and the dissociation constant of water. The results were compared with literature data.

Temperature characteristics in seed germination and growth of Zostera japonica Ascherson & Graebner from Ago Bay, Mie Prefecture, central Japan

The optimal water temperature in seed germination and the upper critical water temperature in seedling growth were determined for Zostera japonica collected from Ago Bay, Japan. The relationship between the seed germination rates and seed storage period (0, 30, and 60 days) at 0°C was also examined. The optimal water temperature in seed germination was in the range 15–20°C regardless of the storage period, in which germination rates were up to 14%. Seedlings, grown from seeds up to 10 cm in total length, were cultured for 1 week at various water temperatures to measure their relative growth rates. The optimal water temperature in early growth was in the range 20–25°C; relative growth rates ranged from 3.8 to 4.2%. Seedlings could survive up to a water temperature of 29°C, but most seedlings withered at 30 or 35°C.

A Unified Theory of the Thermodynamic Properties of Aqueous Electrolytes to Extreme Temperatures and Pressures

A new theoretical treatment has been developed for predicting the thermodynamic properties of electrolytes up to and beyond the critical temperature of water (973 K and at pressures up to 1000 MPa). The model is based upon the classical Born equation corrected for non-Born hydration effects. The temperature and pressure behavior of electrolytes can now be accurately predicted from existing low temperature data. Only two constants are needed for each electrolyte at all temperatures and pressures, where data exist to test the theory.

Modelo teórico para el cálculo de las solubilidades mutuas entre gases no-polares y agua con sales disueltas

We propose a thermodynamic model for the equilibrium of non-polar gases, water and aqueous sodium chloride solutions valid to high pressures, high temperatures, and to high ionic strength solutions. The model couples Henry's Law and an equation of state to reproduce ex- perimental data in the aqueous phase and the gas-rich fluid phases. The standard state chemical potential of the solute in brines is related to the standard state chemical potential of the solute in pure water through a salting-out or Setschenov coefficient. The salting-out coefficients are obtained from experimental data. The model reproduces all crucial phenomena, including three phase equilibrium, at temperatures below the critical temperature of water. The modeling approach cannot account for gas-gas equilibrium phenomena that occur in the vicinity of the water critical point, nor for the hydrate-vapor-liquid equilibrium near the melting point of water.