Effect Of Water Density Research Articles

Statistical analysis of microalgae supercritical water gasification: Reaction variables, catalysis and reaction pathways

Despite the large number of research performed on the supercritical water gasification (SCWG) of microalgae, majority of them are specific to feed microalgae species and certain range of reaction conditions, obscuring the general understanding of the reaction. Here reported data on SCWG of microalgae are compiled and analyzed using multiple linear regression multivariate analysis, in an attempt to comprehensively understand the reaction. It is found that for non-catalytic reactions, variables such as reaction temperature, reaction time and feed concentration exert strong positive effect toward carbon gasification efficiency (CGE) of microalgae SCWG, while reaction pressure, water density, nitrogen content of feed microalgae (representing the proportion of protein in the feed), sulfur content and ash content show limited influence. Over Ru-based catalysts, the effect of feed concentration is weak but water density seems to show apparent correlation with CGE. The present analyses indicate that non-catalytic SCWG of microalgae is positive order on feed concentration with weak effect of water density, while with Ru-based catalysts the reaction is likely to be positively influenced by water density with weak effect of feed concentration. Based on these findings, reaction path differences between non-catalytic and Ru-catalyzed microalgae SCWG are discussed.

Investigation of hydrogen diffusion in supercritical water: A molecular dynamics simulation study

Supercritical water gasification of coal is an efficient method for hydrogen production. The diffusion of hydrogen is the key to completely gasification at moderate condition. The researches have been done about hydrogen diffusion in liquid water and there is little information about hydrogen diffusion in supercritical water, especially for typical supercritical water gasification conditions. In this article, Molecular dynamics (MD) simulation of hydrogen diffusion in water is carried at the temperature ranging from ambient to supercritical. The results show that at ambient condition, the calculation of diffusion coefficient is 0.37 × 10−8 m2/s, which is reliable compared with references. However, the diffusion coefficient is 217.80 × 10−8 m2/s at 973 K, 250 atm where the temperature is far away from the critical point that most empirical equations do not fit our calculation well due to the unique of supercritical water. It is revealed that the diffusion coefficient at supercritical conditions quite obeys the Arrhenius equation. Our calculated activation energy is 19.41 kJ/mol. Effects of water density and viscosity are discussed. These results are expected to provide fundamentals for optimization of supercritical water gasification process.

Low linear energy transfer radiolysis of supercritical water at 400 °C: in situ generation of ultrafast, transient, density-dependent "acid spikes".

There is growing interest in the radiation chemistry of supercritical water (SCW), as its use as a coolant in a nuclear reactor (Generation IV) is the logical evolution of the current (Generation III or less) water-cooled reactors. However, current knowledge about the potential effects of water radiolysis in a Gen-IV supercritical water-cooled reactor (SCWR) is incomplete. In this work, Monte Carlo track chemistry simulations of the low linear energy transfer (LET) radiolysis of SCW (H2O) at 400 °C are used in combination with a spherical "spur" model to study the effect of water density on the in situ radiolytic formation of H3O+ ions and the corresponding abrupt, transient, highly acidic pH response ("acid spikes") that is observed immediately after irradiation. The magnitude and duration of this acidic pH effect depend on the water density in the considered range of 0.15-0.6 g cm-3. It is strongest at times less than a few tens of picoseconds with the pH remaining nearly constant at ∼1.6 and 1.9 for the highest ("liquid-like") and lowest ("gas-like") density, respectively. At longer times, the pH gradually increases for all densities and finally reaches a constant value corresponding to the non-radiolytic, pre-irradiation concentration of H3O+, due to the autoprotolysis of water. Our results show that the lower the density of the water, the longer the time required to reach this constant value, ranging from ∼50 ns at 0.6 g cm-3 (pH ∼ 5.6) to ∼1 μs at 0.15 g cm-3 (pH ∼ 8.5). The generation of these highly acidic pH fluctuations around the "native" radiation tracks, though local and transient, raises questions about the potential implications of this effect in proposed Gen-IV SCW-cooled reactors regarding corrosion and degradation of materials.

A temperature effect analysis of the KRITZ-1 benchmark based on keff decomposition and using the JENDL-4.0 and ENDF/B-VII.1 libraries

This paper provides a comparison between multiplication factors within the UO2 fuelled cores that were measured during the original KRITZ-1 experiments performed in the early 1970s. Results were calculated using the MCNP6.1 code and the most recent cross section libraries, ENDF/B-VII.1 and JENDL-4.0. The results of this study reveal a good level of agreement between calculated and measured outcomes; indeed, the maximum relative error of calculated keff from experimental data does not exceed 0.5% (absolute value) for all cores and for both evaluations. The reactivity temperature coefficient, expressed as the temperature dependence of the reactivity, was examined into details using the seven factors that incorporate the keff parameter rather than just the five that exist in the literature. In order to better investigate the influence of differences in neutron cross sections we also quantified the temperature effect on the five factors of the infinite multiplication factor on each one separately by admitting a pin cell model.Calculated thermal and fast non-leakage probabilities using JENDL-4.0 are found to overestimate the ones calculated using ENDF/B-VII.1 for all temperatures, possibly because the JENDL-4.0 library overestimates some absorptions, especially in the resonance region of fissionable nuclides. This discrepancy between the libraries decreases with increasing temperature, however, while the inverse tends to occur in the case of standard deviations. Our assessment has shown that the temperature coefficient in the thermal temperature range is linked to thermal spectrum and water density effects, while within the epithermal temperature range this is strongly dependent on the thermal shapes of the cross sections of the uranium isotopes; the resonance escape probability highlights that the error is mainly due to the Doppler broadening effect.

Effect of water density on the oxidation behavior of alloy A-286 at 625 °C – A TEM study

In this study the effect of water pressure on oxidation behavior of Alloy A-286 is assessed at 625 °C for 1000 h. The pressure values selected are 0.1, 8 and 29 MPa, representing steam, subcritical and supercritical conditions. Transmission electron microscopy (TEM) is used to study the oxide formation on the surface. A-286 sample exposed to supercritical water forms an oxide layer, about 1 μm, containing Fe2O3, spinel and Cr2O3. In addition, isolated internal oxidation, up to 10 μm, has taken place during the exposure. Recrystallization of substrate material is also observed. A-286 exposed to steam shows little oxidation. The oxide formed on the surface is only ∼200 nm thick and it is comprised of a top layer of Cr2O3 and a thin sub-layer of SiO2, as well as limited grain boundary oxidation in the form of spinel (Cr, Fe, Ti)3O4 and TiO2. In contrast, the sample tested under subcritical condition suffered from excessive external and internal oxidation, with about 20 μm of Fe2O3 on the external surface, followed by a partially oxidized zone (up to 20 μm) containing Cr2O3 on the prior grain boundaries and discrete Cr2O3 particles within the grain. The weight gain of A-286 exposed to subcritical condition is several orders of magnitude greater than that seen under steam condition.

Effects of temperature changes on soil hydraulic properties

Accurate simulation of the effects of temperature on soil water movement processes is lacking in the study of hydrothermal interactions in soil systems. Previous research has proposed some likely mechanisms (e.g., surface tension-viscous flow) to explain soil hydraulic properties in relation to temperature, but little research has focused on the temperature dependence of soil particles (e.g., thermal expansion). Using simulation analyses and experimental data, the effect of temperature on soil hydraulic properties was explored focusing on the thermal effect of water surficial properties and soil particle characteristics. Two temperature coefficients, λ, representing the thermal effect of water surficial properties and c, representing the thermal effect of soil particle characteristics are introduced into soil hydraulics formulae to represent temperature dependence. Results show that temperature-dependent changes in water surficial properties including kinematics viscosity, surface tension and water density effects on soil hydraulic properties. Changes in temperature also affect soil particles, soil porosity and the interactive surface between liquid and solid, especially in heavy loam with high clay content. Expected soil hydraulic properties were calculated at three temperatures in two soil types and then compared to corresponding experimental results. Comparison of predicted and experimental soil hydraulic properties revealed overall similarities with a few exceptions. This study represents an initial simulation study of the effects of temperature on soil hydraulic properties.

Effect of water density on heterogeneous catalytic water gas shift reaction in the presence of Ru/C, Pd/LaCoO3 and Fe3O4 in supercritical water

Water gas shift reaction in the presence of heterogeneous catalysts such as Ru/C, Pd/LaCoO3 and Fe3O4 was examined in supercritical water at 673K from 0.1 to 0.5g/cm3 of water densities. These catalysts catalyzed water gas shift reaction and the main products were CO2 and H2. CH4 was formed from CO and H2 produced by water gas shift reaction in the presence of Ru/C. CO conversion tended to decrease with increasing water density for all catalysts, which means that water essentially suppressed heterogeneous catalytic water gas shift reaction in supercritical water. The kinetics of water gas shift reaction was analyzed with an elementary-like reaction model using fugacity. The model calculation represented the trend of experimental results and revealed that the suppression of water gas shift reaction in high water density region was probably because water would cover on active sites and stabilize the adsorbed species on catalyst to decrease the ratio of vacancy of active sites on catalyst.

Determination of the Nickel/Nickel Oxide Phase Transition and Henry's Constant in Hydrogenated Subcritical and Supercritical Water

The objective of this study is to determine the temperature dependence of the nickel/nickel oxide phase transition using additions of dissolved hydrogen in subcritical and supercritical water. The dissolved hydrogen at the Ni/NiO boundary was measured by direct exposure of nickel coupons at 320 to 450°C and 25 MPa. The stable form of nickel at each exposure condition was determined by optical examination and confirmed by nuclear reaction analysis. Henry's law constant as a function of temperature was determined in-situ by measuring the fugacity of hydrogen through a palladium-silver tube using known dissolved hydrogen concentrations. Below 320°C, Henry's constant decreases linearly up to the critical temperature, above which the slope becomes temperature independent. The effect of water density on Henry's law constant was determined. A thermodynamic model for hydrogen fugacity at the Ni/NiO phase boundary was developed and was shown to agree with the measured data. The deviation in the fugacity at the critical temperature was accounted for by the inclusion of activity of water in the model, highlighting the importance of thermodynamic properties of solvents in high temperature oxidation.

Theoretical Analysis and Experimental Study on Heat-Transfer in Cryogenic Gas Atomization Jet Cooling Nickel-Base Alloy

Based on pool film boiling, Heat transfer coefficient and cooling model are established when fogdrop jet into cutting zone to cool high temperature wall. Through the transient experiment of cryogenic gas atomization jet cool high temperature nickel-base alloy surface with different water dose. The water dose achieving the best cooling effect is 2 ml/min, 4ml/minand 6ml/min under the nickel-base alloy surface temperature at 300 ℃, 500 ℃and 650 ℃. Then the effect of water density to heat transfer coefficient is discussed. Water dose to the best cooling effect must be equivalent to the amount of water that materials can vaporize and participate in the phase-change heat transfer under certain temperature. When achieving optimal cooling effect, the number of fogdrops participating in phase-change heat transfer are the most , and heat transfer coefficient reaches the maximum.

Effect of water density on the response of Square Tension Leg Platform

Effect of water density on the response of Square Tension Leg Platform

Theoretical Analysis and Experimental Study on Heat-Transfer in Cryogenic Gas Atomization Jet Cooling Nickel-Base Alloy

Based on the pool film boiling, Heat transfer coefficient and cooling model are established When fogdrop jet into cutting zone to cool high temperature wall. Through the transient experiment of cryogenic gas atomization jet cooling high temperature nickel-base alloy surface with different water dose. The water dose achieving the best cooling effect is 2 ml/min, 4ml/minand 6ml/min under the nickel-base alloy surface temperature at 300 °C, 500 °Cand 650 °C. Then the effect of water density to heat transfer coefficient is discussed. It is indicated that the water dose to the best cooling effect must be equivalent to the amount of water that materials can vaporize and participate in the phase-change heat transfer under certain temperature. When achieving optimal cooling effect, the number of fogdrops participating in phase-change heat transfer to cool high temperature wall are the most , and the heat transfer coefficient reaches the maximum.

Effects of water density on acid-catalytic properties of TiO2 and WO3/TiO2 in supercritical water

The effects of water density on the acid-catalytic properties of TiO2 and WO3/TiO2 catalysts in supercritical water at 400°C were investigated by using the kinetic analysis of the dehydration reaction of glycerol. The reaction selectivity of TiO2 and WO3/TiO2 catalysts and the apparent-reaction orders for water indicated that the acid-catalytic properties of these two catalysts show different dependence on water density. In the reaction using TiO2, the contribution of Lewis acid sites in TiO2 was large at a low water density, while the contribution of Brönsted acid sites in TiO2 increased with increasing water density. On the other hand, the reaction using WO3/TiO2 was mainly catalyzed by Brönsted acid sites in WO3/TiO2 even at a low water density, and the nature of Lewis/Brönsted acid sites in WO3/TiO2 was not influenced by the water density.

Effect of water density and air pressure on partial oxidation of bitumen in supercritical water

Partial oxidation of bitumen was examined in supercritical water from 653 to 723K at a water/oil ratio from 0 to 3 and up to 5.1MPa of initial air pressure. The contents in the reactor were separated into water rich phase and oil rich phase. Most of oxygen was quickly consumed within 30min and the main gases produced were CO, CO2 and methane. The low temperature gave higher CO/(CO+CO2) ratio and suppressed coke formation. The amount of total gas tended to decrease and the ratio of CO/(CO+CO2) increased about two times by the increase in water/oil ratio from 0.5 to 3. The high water/oil ratio was preferred for selective partial oxidation to produce CO, which means that the effect of the enhancement of partial oxidation by supercritical water was probably larger than that of CO oxidation by water and water gas shift reaction. The increase in initial air pressure increased the amount of CO and CO2 and decreased the ratio of CO/(CO+CO2). The total oxidation route was enhanced under high air pressure.

Water density effects on methanol oxidation in supercritical water at high pressure up to 100 MPa

Reaction kinetics of methanol oxidation in supercritical water at high pressure condition (420 °C; 34–100 MPa; ρ = 300–660 kg/m 3) was investigated. Pseudo-first order rate constant for methanol decomposition increased with increasing water density. Effects of supercritical water on the reaction kinetics were investigated using a detailed chemical kinetics model. Incorporating the effect of diffusion in a reduced model revealed that overall kinetics for SCWO of methanol is not diffusion-limited. Roles of water as a reactant were also investigated. The dependence of sensitivity coefficient for methanol concentration and rate of production of OH radical on water density indicated that a reaction, HO 2 + H 2O = OH + H 2O 2, enhanced the OH radical production and thereby facilitated the decomposition of methanol. It is presumed that concentration of key radicals could be controlled by varying pressure intensively.

The role of hydrogen-bonding interactions in acidic sugar reaction pathways

Previously, theoretical multiple sugar (β- d-xylose and β- d-glucose) reaction pathways were discovered that depended on the initial protonation site on the sugar molecules using Car–Parrinello-based molecular dynamics (CPMD) simulations [Qian, X. H.; Nimlos, M. R.; Davis, M.; Johnson, D. K.; Himmel, M. E. Carbohydr. Res. 2005, 340, 2319–2327]. In addition, simulation results showed that water molecules could participate in the sugar reactions, thus altering the reaction pathways. In the present study, the temperature and water density effects on the sugar degradation pathways were investigated with CPMD. We found that changes in both temperature and water density could profoundly affect the mechanisms and pathways. We attributed these effects to both the strength of hydrogen bonding and proton affinity of water.

P-141 超臨界水ガス化反応における水密度の影響(ポスター2,ポスター発表)

P-141 超臨界水ガス化反応における水密度の影響(ポスター2,ポスター発表)

Aqueous Electrolyte Ionization over Extreme Ranges as Simple Fundamental Relation with Density and Believed Universal; Sodium Chloride Ionization from 0^o^ to 1000^o^C and to 1000 MPa (10000 Atm.)

AbstractThe chemical nature of aqueous electrolyte ionization is illustrated by a simple relationship with water as a reactant believed to correlate ionization of aqueous sodium chloride approaching infinite dilution over the entire range of temperature and pressure [0 to 1000^o^C; 0.1 to 1000 MPa (10000 Atm)]. The derived equation accurately and smoothly describes the ionization constant of sodium chloride [K(NaCl)] in both water and water strongly diluted by inert solvent. Effects of water density on ionization are quantitatively and simply described that oppose conventional theory that ionization is a function only of dielectric constant, and theorists should apply this simplicity with density in understanding aqueous electrolyte ionization. There appears to be no substantive evidence for Pitzer's earlier proposal (1983) that K(NaCl) with decreasing very low densities (if known) would diverge sharply downward by several orders of magnitude. Classical ionization theories are limited in universal application, and it seems that theory must adjust to this observed simple fundamental relationship.

Effect of water density on the absorption maximum of hydrated electrons in sub- and supercritical water up to 400 °C

The optical absorption spectra of the hydrated electron (e(aq) (-)) in supercritical (heavy) water (SCW) are measured by electron pulse radiolysis techniques as a function of water density at three temperatures of 380, 390, and 400 degrees C, and over the density range of approximately 0.2-0.65 g/cm(3). In agreement with previous work, the position of the e(aq) (-) absorption maximum (E(A(max) )) is found to shift slightly to lower energies (spectral "redshift") with decreasing density. A comparison of the present E(A(max) )-density data with other measurements already reported in the literature in subcritical (350 degrees C) and supercritical (375 degrees C) water reveals that at a fixed pressure, E(A(max) ) decreases monotonically with increasing temperature in passing through the phase transition at t(c). By contrast, at constant density, E(A(max) ) exhibits a minimum as the water passes above the critical point into SCW. These behaviors are explained in terms of simple microscopic arguments based on the crucial role played by local density and configurational fluctuations (associated with criticality) in providing pre-existing polymeric clusters, which act as trapping sites for electrons.

Effect of Water Density on Methanol Oxidation Kinetics in Supercritical Water

We oxidized methanol in supercritical water at 500 degrees C to explore the influence of the water concentration (or density) on the kinetics. The rate increased as the water concentration increased from 1.8 to 5.7 mol/L. This effect of water density on the kinetics observed experimentally was quantitatively reproduced by a previously validated mechanism-based, detailed chemical kinetics model. In this model, reactions of OH radicals with methanol were the fastest methanol removal steps. The rates of these removal steps increased with water density at 500 degrees C because the OH radical concentration increased. The OH radical concentration increased with density because the rates of the steps H + H2O = OH + H2 and CH3 + H2O = OH + CH4, which produce OH radicals, increased. Thus, the main role of water in accelerating methanol oxidation kinetics at 500 degrees C is as a hydrogen donor to a radical (R) in steps such as R + H2O = OH + RH. This system provides a striking example of SCW being involved on the molecular level in the free-radical oxidation as a reactant in elementary steps.

Effect of Water Density on the Gasification of Lignin with Magnesium Oxide Supported Nickel Catalysts in Supercritical Water

Gasification of lignin biomass model compounds was examined in the presence of magnesium oxide supported nickel catalysts (Ni/MgO) in sub- and supercritical water from 523 to 673 K. The main gas products were methane, carbon dioxide, and hydrogen. The amount of gases produced increased with an increase in nickel loading on magnesium oxide. The highest total gas yield in a carbon basis was 78% with 20 wt % Ni/MgO catalyst at 673 K and 0.3 g/cm3 water density. In this system, the metal and support of Ni/MgO probably play different roles in gasification that MgO decomposed lignin to reactive intermediates and nickel promoted reaction between intermediates and water to form gases. The yield of methane and carbon dioxide increased with increasing water density but then decreased and leveled out to constant values, which indicates that water density affected the reaction kinetics.