Two-phase Line Research Articles

Simulation of the THF hydrate-water interfacial free energy from computer simulation.

In this work, the tetrahydrofuran (THF) hydrate-water interfacial free energy is determined at 500 bar, at one point of the univariant two-phase coexistence line of the THF hydrate, by molecular dynamics simulation. The mold integration-host methodology, an extension of the original mold integration technique to deal with hydrate-fluid interfaces, is used to calculate the interfacial energy. Water is described using the well-known TIP4P/Ice model, and THF is described using a rigid version of the TraPPE model. We have recently used the combination of these two models to accurately describe the univariant two-phase dissociation line of the THF hydrate in a wide range of pressures from computer simulation [Algaba et al., J. Chem. Phys. 160, 164718 (2024)]. The THF hydrate-water interfacial free energy predicted in this work is compared with the only experimental data available in the literature. The value obtained, 27(2) mJ/m2, is in excellent agreement with the experimental data taken from the literature, 24(8) mJ/m2. To the best of our knowledge, this is the first time that the THF hydrate-water interfacial free energy is predicted from computer simulation. This work confirms that the mold integration technique can be used with confidence to predict the solid-fluid interfaces of complex structures, including hydrates that exhibit sI and sII crystallographic structures.

Prediction of the univariant two-phase coexistence line of the tetrahydrofuran hydrate from computer simulation.

In this work, the univariant two-phase coexistence line of the tetrahydrofuran (THF) hydrate is determined from 100 to 1000bar by molecular dynamics simulations. This study is carried out by putting in contact a THF hydrate phase with a stoichiometric aqueous solution phase. Following the direct coexistence technique, the pressure is fixed, and the coexistence line is determined by analyzing if the hydrate phase grows or melts at different values of temperature. Water is described using the well-known TIP4P/Ice model. We have used two different models of THF based on the transferable parameters for phase equilibria-united atom approach (TraPPE-UA), the original (flexible) TraPPe-UA model and a rigid and planar version of it. Overall, at high pressures, small differences are observed in the results obtained by both models. However, large differences are observed in the computational efforts required by the simulations performed using both models, being the rigid and planar version much faster than the original one. The effect of the unlike dispersive interactions between the water and THF molecules is also analyzed at 250bar using the rigid and planar THF model. In particular, we modify the Berthelot combining rule via a parameter ξO-THF that controls the unlike water-THF dispersive interactions. We analyze the effect on the dissociation temperature of the hydrate when ξO-THF is modified from 1.0 (original Berthelot combining rule) to 1.4 (modified Berthelot combining rule). We use the optimized value ξO-THF = 1.4 and the rigid THF model in a transferable way to predict the dissociation temperatures at other pressures. We find excellent agreement between computer simulation predictions and experimental data taken from the literature.

Inspection Based Corrosion Rate Mapping for Remaining Strength and Remaining Life of Two-Phase Geothermal Steel Piping

Geothermal as green energy has many advantages for power generation due to cleanness, zero waste, and renewable. However, during the operational period, corrosion and scaling in two-phase geothermal steel piping are two main challenges that can cause leaks, reduce flow performance, and reduce safety. Therefore, the two-phase geothermal steel piping remaining strength and life analysis are conducted to manage its integrity. This paper presents a case study on the corrosion rate mapping, excessive corrosion, and scaling for a two-phase flow line in Well Pad B, one of the geothermal production facilities in Unit 1 Dieng, PT Geo Dipa Energi. The data used for this assessment refer to the results of the wall thickness inspection; meanwhile, the data used for scaling and corrosion analysis refer to field observation results. The results of the remaining strength calculation, using both ASME B31G Original and Modified methods, indicate that the remaining strength of all tested points was deemed acceptable in 2020. The remaining life calculation, based on API 579, reveals that the longest remaining life is 9.08 years and the shortest is 0.83 years in the long-term scenario. In the short-term scenario, the longest remaining life is 57.29 years and the shortest is 11.01 years. The corrosion rate is classified as Class I, based on the total key species, with a predictive corrosion rate value > 1.3 mm/year or 51.1 mpy (poor level). In the long-term scenario, the highest corrosion rate recorded is 258.7 mpy (unacceptable level), while the lowest is 39 mpy (fair level). In the short-term scenario, the highest corrosion rate observed is 23 mpy (fair level), and the lowest is 9 mpy (good level). Furthermore, based on the calculation of the Ryznar Stability Index, the fluid has the potential to generate heavy scale, with an RSI value of 4.1.

Phase behavior of metastable water based on fully ab initio simulations

Based on the strongly constrained and appropriately normed (SCAN) functional, phase behavior of metastable water is studied by ab initio molecular dynamics simulations. A clear van der Waals loop or two-phase coexistence line is observed in the simulated isotherms from 230 to 380 K, providing ab initio evidence for a first-order phase transition. The stability limit line formed by connecting the calculated spinodal points is observed to be a continuous reentrant curve, and the liquid-liquid critical point appears to be hidden at its minimum. The line of maximum density also tends to end at this minimum. These results suggest that the phase behavior of metastable water favors a critical-point-free scenario. Due to the potential limitations of the SCAN functional itself and the failure to take nuclear quantum effects into account, it remains to be further investigated whether the phase behavior of real water remains as predicted in the present work.

Phase separation of two-phase ammonia in horizontal T-junction at low mass velocity

Phase separation of a two-phase working fluid accompanies the thermal-hydraulic process in every system and device, with at least one T-junction used in a two-phase line. Adequate qualitative and quantitative prediction of phase separation in T-junction is critical for successful designing, e.g., refrigeration, thermal control, and fluid transport systems. Three simple T-junctions with different inlet and side diameters were tested in the horizontal position on two-phase ammonia at a saturation level of 40÷60 °C and mass velocities of 25÷150 kg·m−2s−1. Based on test data, it has been revealed that at the relative side branch mass flow rate above 0.6, the phase separation behaviour does not depend on inlet mass velocity, vapour quality, void fraction, flow patterns (stratified, slug and annular) and relative side branch diameter. A simplified empirical correlation has been proposed describing the ammonia test points with an error margin of ±15%.

Application of the lumped parameter line model to simulate electromagnetic transients in three-phase transmission lines with vertical symmetry

In this paper, we propose a transmission line model to represent three-phase untransposed transmission lines with vertical symmetry. Here, we decouple a transmission line into its propagation modes using Concordia's matrix, which is the proper orthogonal form of Clarke's matrix that has its columns normalised. Due to the usage of Concordia's matrix, the transmission line is decoupled into two coupled modes and one uncoupled mode. We represent the uncoupled mode by a single-phase transmission line, and the coupled modes by a two-phase transmission line without vertical symmetry. We compute voltages and currents for the single-phase transmission line using the classic Lumped Parameter Model. Voltages and currents in the two-phase transmission line are calculated using a cascade of coupled L circuits pairs. Modal voltages and currents are then transformed back to the phase domain. We compare the results obtained with the proposed model to those obtained with two well-known time domain models, the classic modal lumped parameter model and the lumped parameter model available in the Alternate Transients Program ATP. Results show that the proposed model agrees with time-domain models and has the advantage that is developed in the time domain without needing any inverse transformations.

Adiabatic compressibility of biphasic salt melts

Abstract The adiabatic compressibility along the two-phase saturation line was calculated for nine molten immiscible mixtures, namely, LiF + KBr, LiF + CsCl, LiF + RbBr, LiF + KI, LiF + CsBr, LiF + RbI, LiF + CsI, LiCl + AgBr, and NaCl + AgI, using experimental data on the sound velocity and density. It is shown that the ratio of compressibility of the equilibrium phases depends significantly on the sizes of the mixed ions. The dependence of the changes in compressibility in the distance and in the vicinity of the critical mixing point on the characteristics of the chemical bond between the ions is discussed.

Adiabatic compressibility along the two-phase saturation line for the molten (LiF + CsCl) system

The adiabatic compressibility, β, of the immiscible liquid mixture (LiF + CsCl) along the saturation line was experimentally investigated in the temperature range from the melting point to the critical mixing temperature using sound velocity values, u, measured by the pulse method, and density quantities, ρ, determined using the hydrostatic weight procedure based on the relationship β = u−2ρ−1. The coefficients of the temperature dependencies for the compressibility, sound velocity and density of the upper and lower equilibrium phases have opposite signs because of the superposition of the thermal motion intensity of the ions and the change in the phase compositions. The differences Δβ, Δu and Δρ for the equilibrium phases decrease with temperature elevation. The temperature dependencies of the compressibility, sound velocity and density difference are described using the empirical equations Δβ ≈ (Tc − T)1.004, Δu ≈ (Tc − T)1.003 and Δρ ≈ (Tc − T)0.504.

Assessment of all-solid-state lithium-ion batteries

All-solid-state lithium-ion batteries (ASSBs) are considered as next generation energy storage systems. A model might be very useful, which describes all contributions to the internal cell resistance, enables an optimization of the cell design, and calculates the performance of an open choice of cell architectures.A newly developed one-dimensional model for ASSBs is presented, based on a design concept which employs the use of composite electrodes. The internal cell resistance is calculated by linking two-phase transmission line models representing the composite electrodes with an ohmic resistance representing the solid electrolyte (separator). Thereby, electrical parameters, i.e. ionic and electronic conductivity, electrochemical parameters, i.e. charge-transfer resistance at interfaces and lithium solid-state diffusion, and microstructure parameters, i.e. electrode thickness, particle size, interface area, phase composition and tortuosity, are considered as the most important material and design parameters. Subsequently, discharge curves are simulated, and energy- and power-density characteristics of all-solid-state cell architectures are calculated. These model calculations are discussed and compared with experimental data from literature for a high power LiCoO2-Li10GeP2S12/Li10GeP2S12/Li4Ti5O12-Li10GeP2S12 cell.

Skeletonization application: Chinese calligraphy character representation and reconstruction

Chinese calligraphy is often used to perform the beauty of characters in Chinese culture and is quite suitable in the study of shape representation. The skeleton of a digital line pattern can be treated as the shape descriptor. However, the skeleton-biased and reconstruction-incomplete phenomena often exist in a skeletonization method, which results in the difficulty of using the skeleton to perform the beauty of Chinese calligraphy characters. To overcome this difficulty, skeletal line information derived from the skeletal points and indexed boundary points is defined, and its transformation is implemented by a procedure of two-phase skeletal line placement (SLP). Based on the SLP, an effective algorithm including the SLP-stroke for strokes, SLP-fork for forks, and SLP-end for the end parts of strokes is developed for constructing the skeletal line-based shape descriptor. Four indices of measurement of skeleton deviation, number of distorted forks, number of spurious strokes, and measurement of reconstructability are used to evaluate the performance of the proposed approach. Experimental results show that the skeleton-biased phenomenon can be greatly reduced and the pattern reconstructability close to 100% is achieved, thus confirming that the proposed skeletonization approach is suitable for the Chinese calligraphy character representation and reconstruction.

1.4Gsearch/s 2-Mb/mm2 TCAM Using Two-Phase-Pre-Charge ML Sensing and Power-Grid Pre-Conditioning to Reduce <italic>Ldi/dt</italic> Power-Supply Noise by 50%

This paper describes two power-supply noise ( Ldi/dt ) management techniques implemented in a 14-nm ternary content-addressable memory (TCAM) compiler that allows a $2\text {K} \times 640$ b instance to perform 1.4Gsearches/s while achieving a density of 2 Mb/mm2. This represents a 15% better performance and 10% better density than previous state-of-the-art TCAM. The first technique reduces the within-cycle noise by employing a two-phase match line (ML) pre-charge circuit which shuts off the pre-charge shoot-through current on easy-to-detect multi-bit mismatched MLs early in the cycle thereby approximately saving 60% of the ML power and reducing the within-cycle noise by 49.7%. The second technique is to reduce the multi-cycle noise by inserting targeted dummy search operations during low-current demand periods to flatten out current demand and reduce Ldi/dt noise by another 50%.

Equal Area Laws and Latent Heat ford-Dimensional RN-AdS Black Hole

We study the equal area laws ofd-dimensional RN-AdS black hole. We choose two kinds of phase diagrams,P-VandT-S. We employ the equal area laws to find an isobar which is the real two-phase coexistence line. Our calculation is much simpler to derive the critical value of the thermodynamic quantities. According to the thermodynamic quantities, we also study the latent heat of the black hole.

An Alternative Three-phase Transmission Lines Model in Phase Domain

The objective of this paper is to show an alternative model of a non-transposed three-phase transmission line with a vertical symmetry plane in phase domain. Due the line physical characteristics, it can be represented by a system consisting of a single?phase and a two-phase line. In this system, the equations describing the behavior of the values in single-phase line terminals are known, while the equations for two-phase line to be obtained. Using a transformation matrix written explicitly according to three-phase line parameters, it is possible to obtain the currents and voltages in phase domain of two-phase line. Then, modal values of three-phase line are converted into phase domain and thus obtain the analytical model for this line. To verify the performance of this model, it was used to simulate the energization of a 440 kV three-phase line and the results were compared to results obtained using a classical model.

Liquid Phase Behavior of 1-Butyl-1-methylpyrrolidinium Bis(trifluoromethylsulfonyl)imide with 1-Butanol or Hexan-1-ol: Measurements of Coexistence Curves, Density, and Interfacial Tension

The liquid–liquid equilibria of two binary systems containing 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide with butan-1-ol or hexan-1-ol at atmospheric pressure have been investigated. The two-phase line was observed as function of temperature using light scattering or visual detection. In addition, other physical properties such as the densities of phases in equilibrium and the interfacial tension were determined. The results obtained were compared with the literature and briefly discussed in terms of possible interactions that may occur in ionic liquid + alkan-1-ol solutions.

Calculation and Plot of Predominance Area Phase Diagram for Cu-S-O Ternary System

The typical chemical reactions of metal were analyzed in this paper, and the two-phase equilibrium line calculated model was obtained. By use of the physical properties database, the design of chemical reactions and the compounds were to be determined. Through the calculating the two-phase point and three-phase point ,the predominance area phase diagram algorithm based on the physical properties database was formed, which has clear physical meaning and accuracy calculation result, and also whose result was consistent with that of the literature.

Modified bundled-data as a new protocol for NoC asynchronous links

Asynchronous interconnection paradigm in NoCs has attracted many system designers in the recent years, through its different possible implementation strategies. In this paper, we present a new insight on how to categorize asynchronous protocols and explore a suitable protocol for the NoC asynchronous links. The new categorization criterion is based on the type of dependency between data transferring and handshaking tasks in a protocol. Furthermore, a new protocol called modified bundled-data (MBD) is introduced. MBD is a bundled-data-like protocol with two pairs of two-phase dual-rail encoded parity lines on the lateral sides of data lines, besides one two-phase acknowledgement line. The new protocol is evaluated by comparing its simulation results with those of bundled-data (BD) and dual-rail (DR) protocols on a 32-bit flit NoC asynchronous link. For this purpose, a new comprehensive interconnect model has been developed. The simulation results show that the new protocol's features such as power consumption, throughput, and latency are comparable with BD protocol's, while its signal integrity features are close to DR's.

Fault Analysis of Multiphase Distribution Systems Using Symmetrical Components

The paper presents a new approach for performing the fault analysis of multiphase distribution networks based on the symmetrical components. The multiphase distribution system is represented by an equivalent three-phase system; hence, the single-phase and two-phase line segments are represented in terms of their sequence values. The proposed technique allows the state of the art short-circuit analysis solvers to analyze unbalanced distribution networks. The fault currents calculated using the proposed technique is compared with the phase components short-circuit analysis solver. The obtained results for the IEEE radial test feeders show that the proposed technique is accurate. Based on the proposed method, the existing commercial grade short-circuit analysis solvers based on sequence networks can be utilized for performing unbalanced distribution systems.

Transient modeling of non-isothermal, dispersed two-phase flow in natural gas pipelines

Unsteady-state or transient two-phase flow, caused by any change in rates, pressures or temperature at any location in a two-phase flow line, may last from a few seconds to several hours. In general, these changes are an order of magnitude longer than the transient encountered during single-phase flow. The primary reason for this phenomenon is that the velocity of wave propagation in a two-phase mixture is significantly slower. Interfacial transfer of mass, momentum and energy further complicate the problem. It is primarily due to the numerical difficulties anticipated in accurately modeling transient two-phase flow that the state of the art in this important area is restricted to a handful of studies with direct applicability to petroleum and gas engineering. A limited amount of information on the subject of two-phase transport phenomena is available in the petroleum engineering literature. Most of the publications for two-phase flow of gas assume that temperature is constant over the entire length of the pipeline. This study is the first effort to simulate the non-isothermal, one-dimensional, transient homogenous two-phase flow gas pipeline system using two-fluid conservation equations. The modified Peng–Robinson equation of state is used to calculate the vapor–liquid equilibrium in multi-component natural gas to find the vapor and liquid compressibility factors. Mass transfer between the gas and the liquid phases is treated rigorously through flash calculation, making the algorithm capable of handling retrograde condensation. The liquid droplets are assumed to be spheres of uniform size, evenly dispersed throughout the gas phase. The method of solution is the fully implicit finite difference method. This method is stable for gas pipeline simulations when using a large time step and therefore minimizes the computation time. The algorithm used to solve the non-linear finite difference thermo-fluid equations for two-phase flow through a pipe is based on the Newton–Raphson method. The results show that the liquid condensate holdup is a strong function of temperature, pressure, mass flow rate, and mixture composition. Also, the fully implicit method has advantages, such as the guaranteed stability for large time step, which is very useful for simulating long-term transients in natural gas pipeline systems.

Alternative proposal for Modal Representation of a Non-transposed Three-Phase Transmission Line with a Vertical Symmetry Plane

The objective of this paper is to show an alternative representation in time domain of a non-transposed three-phase transmission line decomposed in its exact modes by using two transformation matrices. The first matrix is Clarke's matrix that is real, frequency independent, easily represented in computational transient programs (EMTP) and separates the line into quasi-modes a, b and zero. After that, Quasi-modes a and zero are decomposed into their exact modes by using a modal transformation matrix whose elements can be synthesized in time domain through standard curve-fitting techniques. The main advantage of this alternative representation is to reduce the processing time because a frequency dependent modal transformation matrix of a three-phase line has nine elements to be represented in time domain while a modal transformation matrix of a two-phase line has only four elements. This paper shows modal decomposition process and eigenvectors of a non-transposed three-phase line with a vertical symmetry plane whose nominal voltage is 440 kV and line length is 500 km.

Decomposição modal de linhas de transmissão a partir do uso de duas matrizes de transformação

Este artigo mostra um processo alternativo de decomposição modal de linhas de transmissão trifásicas, não idealmente transpostas, que possuem um plano de simetria vertical. O processo baseia-se no uso de duas matrizes de transformação modal. Inicialmente utiliza-se a matriz de Clarke para decompor a linha em suas componentes <FONT FACE=Symbol>a, b</FONT> e zero. Devido ao fato de as componentes alfa e zero serem acopladas, as mesmas podem ser representadas como sendo uma linha bifásica sem um plano de simetria vertical. Em seguida esta linha bifásica é decomposta em seus modos exatos a partir do uso de uma matriz de decomposição modal adequada. O artigo descreve as características da linha bifásica que representa as componentes alfa e zero e mostra a aplicação do processo de decomposição modal em uma linha trifásica de 440 kV.