Pressure-temperature Diagram Research Articles

Re-assessment of accumulators performance to identify VVER-1000 vulnerabilities against various break sizes of SB-LOCA along with SBO

After Fukushima Daiichi accident it is suggested to identify the vulnerabilities of nuclear power plants. In SB-LOCA along with SBO scenario, the passive safety systems can have a positive influence on the accident mitigation. This article aims to analyze the performance of passive accumulators (ACC) injection in the spectrum (10–100 mm break sizes) of SB-LOCA that simultaneously occurs with SBO in Bushehr Nuclear Power Plant (BNPP). The results showed that ACCs are not able to inject in the whole range of breaks, because the primary loop pressure is not decreased sufficiently in minimal breaks without operator intervention. Also, the Core Damage Times (CDT) have been calculated for this range of breaks based on 1204 °C of Peak Cladding Temperature (PCT) and Burst Pressure-Temperature Diagram (BPTD) to identify the vulnerable break size. Further, analysis showed that the range of smaller breaks has a shorter CDT (the 50 mm break is the most vulnerable break size) that can be improved by optimizing the set-points of accumulators.

Использование микроволновой спектроскопии для изучения состояния переохлажденной воды

Представлены методики экспериментов для изучения переохлажденной воды с использованием микроволновой спектроскопии. Одна методика связана с получением глубокого переохлаждения воды в порах силикатного материала, другая основана на получении аморфного состояния в образце пресного льда при его пластической деформации. Показаны возможности методик при изучении свойств переохлажденной воды. При атмосферном давлении и температуре –45 °С (на линии Видома) был определен интервал температур, в котором наблюдаются аномалии микроволновых потерь переохлажденной воды, находящейся в порах силикагеля. При пластической деформации поликристаллического льда наблюдали минимум фактора потерь в микроволновом диапазоне на линии Видома.
 
 
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CO2 storage in fractured nanopores underground: Phase behaviour study

In this paper, thermodynamic phase behaviour, implications, and strategies for the CO2 storage process in the fractured tight/shale reservoirs (i.e., nanoproes) with adsorptions are studied. First, an analytical equation of state is modified to calculate the nanoscale phase behaviour by considering the effects of pore radius and molecule–molecule interactions. Second, a new empirical correlation for calculating the adsorption thickness in nanopores is initially developed. The modified equation of state coupled with the new adsorption thickness correlation and fracture geometry equation is used to calculate the phase behaviour of confined pure and mixing CO2 streams in fractured nanopores with adsorptions. Third, the pressure–volume diagrams, pressure–temperature diagrams, and critical properties of 12 pure substances of CO2, N2, and alkanes of C1–10 and 12 binary and ternary CO2-dominated mixtures are studied. The calculated pressures for all cases in nanopores with and without the adsorptions and fractures are reduced with the system volume increases but increased by increasing the system temperature with constant compositions. The pressures in nanopores are always larger than those in bulk phase at small volumes but in good agreement at large volumes. In comparison with the N2 or C1–10, the pure CO2 is more easily transited to be a liquid or supercritical phase. Any additions of contaminations (e.g., N2 or C1–10) into the pure CO2 increase the pressures in the pressure–volume or temperature diagram while decrease the critical properties to different extent, especially in nanopores, wherein the N2 exerts the strongest effect and the effects of the alkanes are weakened with the carbon number increase. Overall, three optimum strategies are determined for CO2 storage projects in the deep tight/shale formations as follows: large pore radii, purified CO2 streams, and low temperatures.

Thermodynamic analysis of biodiesel production systems at supercritical conditions

This work reports thermodynamic analysis of systems involved in the biodiesel production using ethanol at supercritical conditions. PC-SAFT equation of state was used from ASPEN Plus simulator for modeling all investigated systems. Binary and ternary phase equilibrium data at high pressure and temperature were used to assess the PC-SAFT capability of predicting the thermodynamic behavior of the complex mixture of interest in this work. The results showed that the PC-SAFT is a reliable tool to represent the phase behavior of mixtures involving ethanol, vegetable oil, fatty acid, ethyl esters of fatty acid and glycerol. Phase behavior of the reaction system was evaluated under specified experimental conditions and considering different reaction conversions. Pressure-temperature diagrams demonstrated that the two-phase region for the reaction mixture decreases as the extension of reaction is increased. The PC-SAFT equation of state was used to estimate the density of the reactant mixture and the effect of this parameter over the residence of the reaction was assessed, where it was clearly demonstrated that the density of the mixture greatly affects the residence time calculation for the reactions of biodiesel production at high pressure conditions.

Shock temperature and reflectivity of precompressed H2O up to 350 GPa: Approaching the interior of planets** Project supported by the National Key Research and Development Program of China (Grant No. 2017YFA0403200) and the Science Challenge Project (Grant No. TZ2016001).

Using a combination of static precompression and laser-driven shock compression, shock temperature and reflectivity of H2O have been measured up to 350 GPa and 2.1 × 104 K. Here, two calibration standards were applied to enhance temperature measurement reliability. Additionally, in temperature calculations, the discrepancy in reflectivity between active probe beam wavelength and self-emission wavelength has been taken into account to improve the data’s precision. Precompressed water’s temperature–pressure data are in very good agreement with our quantum molecular dynamics model, suggesting a superionic conductor of H2O in the icy planets’ deep interior. A sluggish slope gradually approaching Dulong–Petit limit at high temperature was found at a specific heat capacity. Also, high reflectivity and conductivity were observed at the same state. By analyzing the temperature–pressure diagram, reflectivity, conductivity and specific heat comprehensively at conditions simulating the interior of planets in this work, we found that as the pressure rises, a change in ionization appears; it is supposedly attributed to energetics of bond-breaking in the H2O as it transforms from a bonded molecular fluid to an ionic state. Such molecular dissociation in H2O is associated with the conducting transition because the dissociated hydrogen atoms contribute to electrical properties.

Phase behaviour for the (CO2 + 1-butyl-2-pyrrolidone) and (CO2 + 1-octyl-2-pyrrolidone) systems at temperatures from (313.2 to 393.2) K and pressures up to 28 MPa

Phase equilibrium for two binary systems, (CO2 + 1-butyl-2-pyrrolidone) and (CO2 + 1-octyl-2-pyrrolidone) mixture, were measured at five experimental temperatures of (313.2, 333.2, 353.2, 373.2 and 393.2) K and pressure from (4.45 to 28.72) MPa. The (vapour + liquid) equilibria for the 1-butyl-2-pyrrolidone and 1-octyl-2-pyrrolidone play a significant role as organic solvents in numerous industrial processes. Both (CO2 + 1-butyl-2-pyrrolidone) and (CO2 + 1-octyl-2-pyrrolidone) binary mixture systems have critical mixture curves that represent maximums in pressure-temperature diagram between the critical temperatures of CO2 and 1-butyl-2-pyrrolidone or CO2 and 1-octyl-2-pyrrolidone. The (CO2 + 1-butyl-2-pyrrolidone) and (CO2 + 1-octyl-2-pyrrolidone) systems display type-I phase behaviour. The experimental results for the (CO2 + 1-butyl-2-pyrrolidone) and (CO2 + 1-octyl-2-pyrrolidone) binary systems are correlated with Peng-Robinson equation of state including two (kij, ηij) adjustable parameters.

The Homogeneity Range of Crystalline Tris(8-hydroxyquinoline)gallium

An experimental procedure has been developed for constructing p i –T diagrams (partial vapor pressure of the ligand-forming component–temperature) for luminescent metal complexes with symmetric organic ligands. The partial 8-hydroxyquinoline vapor pressure–temperature diagram has been constructed for tris(8-hydroxyquinoline)gallium electrophosphor (Gaq3) in the temperature range 300–617 K at 8-hydroxyquinoline vapor pressures 10–3–104 Pa, where the homogeneity ranges of different Gaq3 polymorphs have been determined. Structure-sensitive properties of crystalline materials can be tailored by changing synthesis conditions within the homogeneity range of a phase.

Phase behaviors of deeply supercooled bilayer water unseen in bulk water

Akin to bulk water, water confined to an isolated nanoslit can show a wealth of new 2D phases of ice and amorphous ice, as well as unusual phase behavior. Indeed, 2D water phases, such as bilayer hexagonal ice and monolayer square ice, have been detected in the laboratory, confirming earlier computational predictions. Herein, we report theoretical evidence of a hitherto unreported state, namely, bilayer very low density amorphous ice (BL-VLDA), as well as evidence of a strong first-order transition between BL-VLDA and the BL amorphous ice (BL-A), and a weak first-order transition between BL-VLDA and the BL very low density liquid (BL-VLDL) water. The diffusivity of BL-VLDA is typically in the range of 10-9 cm2/s to 10-10 cm2/s. Similar to bulk (3D) water, 2D water can exhibit two forms of liquid in the deeply supercooled state. However, unlike supercooled bulk water, for which the two forms of liquid can coexist and merge into one at a critical point, the 2D BL-VLDL and BL high-density liquid (BL-HDL) phases are separated by the highly stable solid phase of BL-A whose melting line exhibits the isochore end point (IEP) near 220 K in the temperature-pressure diagram. Above the IEP temperature, BL-VLDL and BL-HDL are indistinguishable. At negative pressures, the metastable BL-VLDL exhibits a spatially and temporally heterogeneous structure induced by dynamic changes in the nanodomains, a feature much less pronounced in the BL-HDL.

Synthesis of single-crystal perovskite PbCrO3 through a new reaction route at high pressure

ABSTRACTAs a new member in the family of Mott system, perovskite PbCrO3 has recently been uncovered to exhibit fantastic structural transition under pressure, coupled with magnetic, electronic, and ferromagnetic transitions, which provide many opportunities for understanding of correlated system. However, it is still challenging to synthesize high-quality single-crystal PbCrO3, leading to the limited exploration of this Mott compound. In this work, we formulate a new high-pressure reaction route for preparation of high-quality PbCrO3 crystals between PbCl2 and Na2CrO4 at high pressure of 5–10 GPa and at high temperature of 750–1500°C. Because of the formation of reaction byproduct NaCl, the final product can readily be separated by washing with water. The obtained sample is in the form of single crystal with crystallite size up to 200 μm. In addition, combined with X-ray diffraction measurement, a tentative pressure-temperature synthesis diagram of PbCrO3 is mapped out from the reaction between PbCl2 and Na2CrO4 and the reaction mechanism is also explored in detail.

Thermodynamic assessment of the Mo-S system and its application in thermal decomposition of MoS2

The Mo-S system is crucial to extractive metallurgy, tribology, and various possible applications in design and fabrication of novel two-dimensional (2D) materials. First-principles calculations were utilized to compute the enthalpies of formation of molybdenum sulfides at 0 K and the heat capacity of Mo2S3 up to 960 K. A critical evaluation of the thermodynamic properties, phase equilibria, and phase diagram information in the literature was carried out to facilitate the thermodynamic optimization of the Mo-S system. The obtained thermodynamic description of the Mo-S system can satisfactorily represent most of the reliable thermodynamic and phase diagram information. Pressure-temperature (P-T), pressure-composition (P-x), and temperature-composition (T-x) diagrams of the Mo-S system were utilized to study the thermal decomposition of MoS2 for raw Mo production. Reduced pressure and high temperature are thermodynamically favorable conditions for the MoS2 reduction process.

Surface reconstruction of InAs (001) depending on the pressure and temperature examined by density functional thermodynamics

A detailed understanding of the atomic configuration of the compound semiconductor surface, especially after reconstruction, is very important for the device fabrication and performance. While there have been numerous experimental studies using the scanning probe techniques, further theoretical studies on surface reconstruction are necessary to promote the clear understanding of the origins and development of such subtle surface structures. In this work, therefore, a pressure-temperature surface reconstruction diagram was constructed for the model case of the InAs (001) surface considering both the vibrational entropy and configurational entropy based on the density functional theory. Notably, the equilibrium fraction of various reconstructions was determined as a function of the pressure and temperature, not as a function of the chemical potential, which largely facilitated the direct comparison with the experiments. By taking into account the entropy effects, the coexistence of the multiple reconstructions and the fractional change of each reconstruction by the thermodynamic condition were predicted and were in agreement with the previous experimental observations. This work provides the community with a useful framework for such type of theoretical studies.

Continuous biodiesel production in supercritical two-step process: phase equilibrium and process design

A supercritical biodiesel production process via transesterification of vegetable oil with methanol, using CO2 as co-solvent is designed, simulated, and validated with experimental data. A preliminary study of the liquid-vapor equilibrium of the reacting mixture at different compositions was done to determine the supercritical conditions, by means of pressure-temperature diagrams. Under supercritical conditions, the presence of a single phase increases the reaction kinetics, avoiding the limitation by interphase mass transfer, and enabling to carry out the process with low residence time. The proposed process is based on two fixed-bed catalytic reactors in series, with intermediate glycerol separation. CO2 used as co-solvent decreases the critical temperature, enabling to carry out the process in milder conditions. The intermediate glycerol separation displaces the chemical equilibrium towards higher conversion of triglyceride, increasing biodiesel yield. The results of a complete experimental study are used to validate the model, through a comparison with the simulations result.

Phase behavior of system methane + hydrogen sulfide

An accurate description of the phase behavior of the CH4 + H2S system is given for temperatures from 70 K to the critical temperature of H2S and pressures up to 250 MPa. The study includes the solid phases of CH4 and H2S. A global pressure‐temperature diagram is presented. The types of temperature‐composition and pressure‐composition phase diagrams that can be encountered in the studied temperature and pressure ranges have been described. The temperature and pressure ranges where the phase behavior of the system changes have been identified and a representative phase diagram is presented for each range. Phase diagrams have been obtained through the solid–liquid–vapor equation of state proposed by Yokozeki. The parameters of the equation of state have been regressed on all the available phase equilibrium data for the considered system. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4090–4108, 2016

Stability hierarchy between Piracetam forms I, II, and III from experimental pressure–temperature diagrams and topological inferences

The trimorphism of the active pharmaceutical ingredient piracetam is a famous case of polymorphism that has been frequently revisited by many researchers. The phase relationships between forms I, II, and III were ambiguous because they seemed to depend on the heating rate of the DSC and on the history of the samples or they have not been observed at all (equilibrium II–III). In the present paper, piezo-thermal analysis and high-pressure differential thermal analysis have been used to elucidate the positions of the different solid–solid and solid–liquid equilibria. The phase diagram, involving the three solid phases, the liquid phase and the vapor phase, has been constructed. It has been shown that form III is the high-pressure, low-temperature form and the stable form at room temperature. Form II is stable under intermediary conditions and form I is the low pressure, high temperature form, which possesses a stable melting point. The present paper demonstrates the strength of the topological approach based on the Clapeyron equation and the alternation rule when combined with high-pressure measurements.

The Frenkel Line: a direct experimental evidence for the new thermodynamic boundary.

Supercritical fluids play a significant role in elucidating fundamental aspects of liquid matter under extreme conditions. They have been extensively studied at pressures and temperatures relevant to various industrial applications. However, much less is known about the structural behaviour of supercritical fluids and no structural crossovers have been observed in static compression experiments in any temperature and pressure ranges beyond the critical point. The structure of supercritical state is currently perceived to be uniform everywhere on the pressure-temperature phase diagram, and to change only in a monotonic way even moving around the critical point, not only along isotherms or isobars. Conversely, we observe structural crossovers for the first time in a deeply supercritical sample through diffraction measurements in a diamond anvil cell and discover a new thermodynamic boundary on the pressure-temperature diagram. We explain the existence of these crossovers in the framework of the phonon theory of liquids using molecular dynamics simulations. The obtained results are of prime importance since they imply a global reconsideration of the mere essence of the supercritical phase. Furthermore, this discovery may pave the way to new unexpected applications and to the exploration of exotic behaviour of confined fluids relevant to geo- and planetary sciences.

Identifying Liquid–Gas System Misconceptions and Addressing Them Using a Laboratory Exercise on Pressure–Temperature Diagrams of a Mixed Gas Involving Liquid–Vapor Equilibrium

This study focuses on students’ understandings of a liquid–gas system with liquid–vapor equilibrium in a closed system using a pressure–temperature (P–T) diagram. By administrating three assessment questions concerning the P–T diagrams of liquid–gas systems to students at the beginning of undergraduate general chemistry course, lack of understanding of the fundamental concepts concerning liquid–vapor equilibria, the ideal gas law, and boiling points was identified. A learning program for liquid–gas systems was then designed for students at the undergraduate general chemistry level to address this issue. It consists of a laboratory experiment and postlaboratory exercise and is intended to provide integrated student understanding. During the learning program, students actively used the related concepts to explain the physical chemistry of a liquid–gas system and integrated the concepts to explain practical systems in their daily lives using a P–T diagram. An outline of the learning program is reported on th...

Synthesis of monoclinicIrTe2under high pressure and its physical properties

In a pressure-temperature (P-T) diagram for synthesizing IrTe2 compounds, the well-studied trigonal (H) phase with the CdI2-type structure is stable at low pressures. The superconducting cubic (C) phase can be synthesized under higher temperatures and pressures. A rhombohedral phase with the crystal structure similar to the C phase can be made at ambient pressure; but the phase contains a high concentration of Ir deficiency. In this paper, we report that a rarely studied monoclinic (M) phase can be stabilized in narrow ranges of pressure and temperature in this P-T diagram. The peculiar crystal structure of the M-IrTe2 eliminates the tendency to form Ir-Ir dimers found in the H phase. The M phase has been fully characterized by structural determination and measurements of electrical resistivity, thermoelectric power, DC magnetization, and specific heat. These physical properties have been compared with those in the H and C phases of Ir1-xTe2. Moreover, magnetic and transport properties and specific heat of the M-IrTe2 can be fully justified by calculations with the density-functional theory presented in this paper.

Nature of the first-order liquid-liquid phase transition in supercooled silicon.

The first-order liquid-liquid phase transition in supercooled Si is revisited by long-time first-principle molecular dynamics simulations. As the focus of the present paper, its nature is revealed by analyzing the inherent structures of low-density liquid (LDL) and high-density liquid (HDL). Our results show that it is a transition between a sp(3)-hybridization LDL and a white-tin-like HDL. This uncovers the origin of the semimetal-metal transition accompanying it and also proves that HDL is the metastable extension of high temperature equilibrium liquid into the supercooled regime. The pressure-temperature diagram of supercooled Si thus can be regarded in some respects as shifted reflection of its crystalline phase diagram.

Comparison of mantle lithosphere beneath early Triassic kimberlite fields in Siberian craton reconstructed from deep-seated xenocrysts

Mantle xenocrysts from early Triassic kimberlite pipes from Kharamai, Ary-Mastakh and Kuranakh fields in the Anabar shield of Siberia revealing similar compositional trends were studied to estimate the superplume influence on the subcratonic lithosphere mantle (SCLM). Pressure-temperature (PT) reconstructions using monomineral thermobarometry for 5 phases show division of the SCLM beneath the Kharamai field into 6 units: pyroxenitic Fe-rich (1–2 GPa) and Mg-rich (2–3 GPa) layers; middle with two levels of Gar-Sp pyroxenites at ∼3 and 4–5 GPa; Gar-dunite–harzburgites ∼4.5–6.5 GPa subjected to Ilm-Px vein metasomatism; and a Mg-rich dunite lower part. In the Anabar shield (Ary-Mastakh, Dyuken and Kuranakh fields) mantle lithosphere is composed of three large units divided into two parts: upper part with amphiboles and phlogopite; two levels of pyroxenites and eclogites at 3 and 4 GPa, and a lower part composed of refertilized dunites. Diagrams showing P-Fe#Gar clusters for garnets and omphacites illustrate the differences between SCLM of these localities. Differences of Triassic SCLM from Devonian SCLM are in simple layering; abundance of Na-Cr-amphiboles and metasomatism in the upper SCLM part, thick pyroxenite-eclogite layer and lower part depletion, heated from SCLM base to 5.0 GPa.Kharamai mantle clinopyroxenes represent three geochemical types: (1) harzburgitic with inclined linear REE, HFSE troughs and elevated Th, U; (2) lherzolitic or pyroxenitic with round TRE patterns and decreasing incompatible elements; (3) eclogitic with Eu troughs, Pb peak and high LILE content. Calculated parental melts for garnets with humped REE patterns suggest dissolution of former Cpx and depression means Cpx and garnets extraction. Clinopyroxenes from Ary-Mastakh fields show less inclined REE patterns with HMREE troughs and an increase of incompatible elements. Clinopyroxenes from Kuranakh field show flatter spoon-like REE patterns and peaks in Ba, U, Pb and Sr, similar to those in ophiolitic harzburgites. The PT diagrams for the mantle sections show high temperature gradients in the uppermost SCLM accompanied by an increase of P-Fe#Ol upward and slightly reduced thickness of the mantle keel of the Siberian craton, resulting from the influence of the Permian–Triassic superplume, but with no signs of delamination.

Density of Ethyl Acetate-Palm Oil Mixture in Supercritical Condition

The non-catalytic interesterification of palm oil in supercritical ethyl acetate in continuous system to produce biofuel is complex to understand thermodynamic properties during extreme condition, particularly density of two reactants. In this study, an indirect procedure for density measurement of palm oil and ethyl acetate mixture in a batch system at high temperature and pressure was experimentally investigated using isochoric method. Its apparatus comprise a constant volume reactor which was individually loaded with a mixture of ethyl acetate and palm oil in different molar ratios (10:1 to 30:1) and global densities (0.26 to 0.53 g/cm3). During temperature increment, the changing of pressure was recorded in real-time to obtain the pressure-temperature relationship. After measuring the change of pressure at various global densities, the pressure-temperature related specific global density diagram was successfully constructed. At high global densities and high molar ratios of ethyl acetate to palm oil, the transition point took place closing to the estimated critical point of the mixture. The results will be further employed as database for accurately residence time calculation in continuous reactor, especially for biofuel production from palm oil in supercritical ethyl acetate.