Compressibility Research Articles

Predicting imidazolium ionic liquid properties with a simple molecular volume-based SAFT-VR Mie approach

Each thermodynamic model requires a distinct set of parameters for each component and these parameters must be transferable beyond their original estimation domain to accurately predict a variety of thermodynamic properties. Previous work introduced and evaluated a novel parametrization method for the solubility of ionic liquids in CO2 or CH4 [Chem. Eng. Sci. 2024, 285, 119610]. This methodology provides a fast and efficient way to evaluate ionic liquids by requiring only their molecular volume. In this study, the approach is extended to include both pure ionic liquids, examining properties such as density, isobaric heat capacity, isobaric expansivity, isothermal compressibility, and speed of sound, as well as their mixtures with ethanol or water, focusing on speed of sound, and excess enthalpy. Ionic liquids are modeled as both non-associating and associating components. Overall, the approach demonstrates good estimates and holds potential for extension to other models and systems.

Dynamic recrystallization mechanisms and microstructure evolution of a novel Al-Zn-Mg-Cu-Zr alloy by isothermal compression

The dynamic recrystallization (DRX) behavior and microstructure evolution of a novel Al-Zn-Mg-Cu-Zr alloy was investigated by isothermal compression tests at temperature of 350–470 °C and strain rate of 0.0001–1 s−1. The results showed that the flow behavior revealed typical dynamic recovery (DRV) characteristics at a high strain rate (1 s−1), while exhibited a DRX shape when the strain rate decreased. The critical strains (εc) of the DRX decreased with the decrease of strain rate or the increase of deformation temperature. A low temperature was conductive to precipitation behavior, the coarse precipitates and dispersed Al3Zr particles would pin the dislocations and substructures, which inhibit the DRX process. The DRX mechanism of the Al-Zn-Mg-Cu-Zr alloy was dominated by continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) during the hot deformation process, upon increasing the temperature and decreasing the strain rate, there was a transition point of DRX mechanism from DDRX to CDRX. Moreover, the linear relationship between the Zener-Hollomon (Z) parameter and DRX grain size was established for the further exploration of the transition of the dominant DRX mechanism.

Physicochemical and catalytic behavior of binary mixtures of n-alkyl imidazolium bromide ionic liquids with poly (ethylene glycol)-400: Application of flory statistical theory

In this work, Flory statistical theory is employed to predict the important physicochemical properties namely density, isothermal compressibility, internal pressure, coefficient of volume expansion, energy of vaporization, heat of vaporization, cohesive energy density, solubility parameter and polarity index for three binary mixtures of PEG-400 + [CnMim][Br], where n=4, 6, and 8 at different temperatures (T= 298.15 K, 308.15 K, and 318.15 K). Furthermore, the applicability of Flory statistical theory to predict certain physicochemical properties has been verified. Excess properties viz., excess enthalpy, excess Gibbs free energy, and excess entropy are also determined for these binary mixtures. The variation of energy of vaporization, heat of vaporization, solubility parameter and excess parameters are used to analyze the catalytic behavior and prevalent molecular interactions of these mixtures.

Liquid Piston Compression Heat Transfer Prediction via Thermal‐Resistance Network: Simulation, Experimental Validation, and Liquid Carryover Evaluation

Liquid piston compressors gain attention due to their potential for more efficient and isothermal compression compared to traditional solid piston compressors. Liquid piston compressors use a liquid column instead of a solid piston, allowing for innovative mechanisms to enhance heat transfer and achieve near‐isothermal compression. However, a validated analytical model for heat transfer in liquid piston compressors is still needed to understand the exhaust phase within a liquid piston. In this work, a thermal network model, able to predict the polytropic index to within 8% of the experimental results, is proposed. Moreover, thorough experimentation is conducted to measure the amount of liquid carried over to better understand the exhaust phase. In the results, it is revealed that the piston carries over 13–21 mL of liquid within the exhaust gas for 10–23 s of stroke. Notably, the difference in liquid carried over for the three‐stroke times is not statistically significant, indicating that the liquid carried over is a function of liquid piston design and not stroke time. Finally, most liquid piston applications consider only water; hence, for the first time, this research assesses the stability of a cycle using a nonflammable hydraulic fluid (Fuchs 46 M red) to enhance compressor longevity and material compatibility.

Thermal Transport and Thermal Polarization of Water in the Supercooled Regime.

The behavior of water in the deep supercooled regime has attracted significant interest, motivated by the hypothesis of the second critical point of water. Previous studies indicated the existence of a water anomaly, characterized by a minimum in the thermal conductivity of water. Here, we employ nonequilibrium molecular dynamics computer simulation and the TIP4P/2005 water force field to investigate the thermal conductivity of supercooled water targeting four different isobars, 1, 200, 700, and 1200 bar. We demonstrate using NEMD simulations the existence of minima in thermal conductivity associated with the maximum isothermal compressibility and the minimum speed of sound in water, hence establishing a firm connection with the second critical point of liquid water. Moreover, we demonstrate that thermal gradients polarize supercooled water with a thermal polarization coefficient of several mV/K. We explain the thermal polarization effect using a theoretical formulation introduced recently that connects the thermal polarization effect to the isobaric thermal expansion coefficient.

Deformation Behavior and Microstructural Evolution of Ti–6.5Al–2Zr–1Mo–1V Alloy during Isothermal Hot Compression

In this investigation, the effects of different deformation passes—namely, single pass and multipass—on the microstructural evolution and deformation mechanisms in the Ti–6.5Al–2Zr–1Mo–1V alloy are analyzed. It is observed that following a single‐pass hot compression, the extent of lamellar α phase spheroidization enhances as the temperature increases. During multipass hot compression, there is a gradual reduction in the size and concentration of equiaxed α phase, alongside an increase in spheroidization. Dislocation density escalates to 15.88%, while the proportion of high‐angle grain boundaries (HAGBs) diminishes to 75.24%. Static recrystallization occurring during the holding process facilitates dislocation annihilation. The dynamic phase transformation mechanism manifests through interfacial permeation at the primary α phase. Strain localization at the boundaries or sub‐boundaries of the primary α phase, which exhibit minimal curvature, induces elevated shear stress, thereby promoting the shearing of the primary α phase and reducing its presence. Texture components predominantly observed are <‐12‐10>//Z0 and <0001>//Z0, transitioning from <‐12‐10> to <0001> with increasing strain.

Speed of sound and isothermal compressibility in a magnetized quark matter with anomalous magnetic moment of quarks

We study the characteristics of quark matter under the influence of a background magnetic field with an anomalous magnetic moment of quarks at finite temperature and quark chemical potential in the framework of a Polyakov loop extended Nambu-Jona-Lasinio model. In the presence of a magnetic field, the speed of sound and isothermal compressibility become anisotropic with respect to the direction of the background magnetic field, splitting into parallel and perpendicular directions with respect to the magnetic field. Though the qualitative nature of parallel and perpendicular components of squared speed of sound appear similar, they differ in magnitude at lower values of temperature. The parallel and perpendicular components of isothermal compressibility decrease with increasing temperature, indicating a trend towards increased incompressible strongly interacting matter. On inclusion of the anomalous magnetic moment of quarks, the perpendicular component of isothermal compressibility becomes greater than the parallel component. Additionally, we investigate the quark number susceptibility normalized by its value at zero magnetic field, which may indicate the presence of magnetic fields in the system. Published by the American Physical Society 2024

Potential of carbide strengthened economical wrought nickel-based alloy for high temperature

A carbide strengthened wrought Ni-based superalloy is developed. The alloy depends on carbide dispersion strengthening. A high deformation plasticity in homogeneous alloy is shown in the 1100–1200 °C isothermal compression test and the improvement of microstructure can be achieved by recrystallization. After aging at 850–900 °C, the carbide strengthened wrought alloy appears excellent tensile strength. Carbide exists higher microstructure stability than γ′ in the same condition. The herein reported results reflect the potential of the economical wrought Ni-based superalloy to service above 800 °C.

Prediction of Microstructure Evolution in Ball Mill Liner Forging Process

The liner is affixed to the inner side of the ball mill cylinder to protect the cylinder. Through isothermal compression experiments, Arrhenius constitutive models, peak strain models, critical strain models, dynamic recrystallization dynamic models, and grain size models suitable for the forging process of Mn–Cr–Ni–Mo steel used in ball mill liners were established. By utilizing Deform software, a 3D thermo‐force‐structure coupling model for the hot forging process of ball mill liners was constructed, and the volume fraction of dynamic recrystallization and average grain size during forging was predicted. The response surface model was employed to investigate how process parameters interacted with each other and affected microstructure uniformity in ball mill liners. After optimization, the optimal parameters were determined: initial forging temperature at 1200 °C, forging speed at 30 mm s−1, and friction coefficient at 0.3. Subsequently, a hot forging experiment on ball mill liners was conducted using these optimized parameters; samples were analyzed through backscattered electron diffraction device experiments and microscopic tissue observations. Results demonstrated that microstructural changes observed during actual forging processes aligned with numerical simulation results—thus verifying both the accuracy of the Mn–Cr–Ni–Mo steel material model and numerical simulation method.

A polycrystal plasticity-cellular automaton integrated modeling method for continuous dynamic recrystallization and its application to AA2196 alloy

Continuous dynamic recrystallization usually dominates the microstructural evolution in hot working of aluminum alloys, in which the high-angle grain boundaries of new grains mainly originate from the gradual increase in subgrain misorientation angles. In this work, an integrated computational method is proposed to simulate continuous dynamic recrystallization process of aluminum alloys by coupling three-dimensional cellular automaton and visco-plastic self-consistent models. The stress response, dislocation accumulation and recovery, and evolution of crystal orientations are computed in the context of polycrystal plasticity; the formation and rotation of subgrains, followed by stored energy and curvature-driven boundary migration, are captured and visualized by cellular automaton. The non-octahedral slip mode {110}<110> is additionally introduced to capture the 〈001〉 texture during hot compression. A universal cell topology deformation method is adopted to achieve an effective track of grain morphology evolution during plastic deformation. The proposed simulation framework is validated through simulating the isothermal uniaxial compression process of AA2196 alloy under different temperatures and strain rates. The orientation dependence of CDRX during compression is numerically reproduced by correlating the subgrain formation and rotation process with the activation state of slip systems. The simulated macroscopic flow stress, 3D microstructure and inherent microstructural characteristics such as subgrain size, subgrain boundaries and textures are in good agreement with the experimental results. The proposed method provides an effective and efficient tool for multi-scale simulation of hot forming process of aluminum alloys.

The influence of pressure-shift freezing based on the supercooling and pressure parameters on the freshwater surimi gel characteristics

In this study, the phase transition curve of grass carp surimi gel in the ice I region was mapped and fitted. Additionally, the average adiabatic compressibility of surimi gel was calculated to be 2.7℃/100 MPa in the range of 0–320 MPa. Building upon this, the study further investigated the impact of pressure-shift freezing (PSF) treatment based on supercooling and pressure coupling on the gel strength, texture profile analysis (TPA), and water-holding capacity of surimi gel. Compared with the low level of supercooling (supercooling value > -15℃) treatment, the PSF treatment with a higher supercooling degree (supercooling value ≤ -15℃) could enhance the strength and water-holding capacity of surimi gel. The morphology and distribution of ice crystals suggested that the diameter and size distribution of ice crystals in the sample were dependent on the combination of pressure level and supercooling. The combination of precise control of supercooling and pressure parameters is beneficial in improving the mechanical properties and water-holding capacity of surimi gel. This is of great value for developing high-quality surimi gel products and also offers a new research thread in the realm of high-pressure freezing.

Self-similar flow behind a shock wave in a gas under the effect of viscosity, heat conduction, and variable ambient density

Self-similar solutions have been investigated to describe the propagation of planar shock waves in a non-ideal gas generated by a piston under viscous stress and heat flux. The equation of state for non-ideal gas incorporates the correction in pressure and volume of the gas. The piston position and ambient density vary exponentially with time. Newton’s law of viscosity is used for the viscous stress and Fourier’s law of heat conduction is taken for heat flux. The viscosity coefficient is taken as constant whereas the thermal conductivity coefficient varies with temperature and density following the power law. The shock jump conditions have been derived for the viscous non-ideal gas using integral form of conservation laws. The shock Reynolds number Re s has been introduced to study the effect of viscosity on shock propagation in non-ideal gas. It is found that similarity solution exists only in an ideal gas under the condition that the ambient density exponent is equal to twice the shock position exponent. This study shows that shock Reynolds number Re s and heat conduction parameter Γ c can be used to control the variation of the flow variables and piston position significantly. The shock strength decreases with increase in the value of shock Reynolds number Re s but is independent of the heat conduction parameter Γ c . The pressure, density, and adiabatic compressibility have significant deviations from high to low viscous flow of ideal gas but the velocity and heat flux undergo negligible change. The results do not support the claim of negligible effect of viscosity in earlier studies and establish the impact of viscosity and heat flux on shock propagation in an ideal gas.

Prediction of flow stresses for a typical Nickel-Based superalloy during hot deformation based on constitutive equation

Abstract Utilizing the Gleeble-3500 thermal simulation testing machine, a series of isothermal constant strain rate thermal compression tests were executed to study the high-temperature rheological properties of the GH4169 alloy. These tests were carried out under deformation temperatures between 900°C and 1100°C, with strain rates from 0.001 to 1 s−1, and involved a deformation of 60%. The results reveal that the peak stress of the GH4169 alloy decreases as the temperature increases, and the strain rate decreases during hot deformation. The activation energy for thermal deformation is calculated to be 806.39 kJ/mol. Through regression analysis and polynomial fitting of true stress-strain curves from thermal compression tests, an Arrhenius constitutive equation integrating strain compensation for high-temperature deformation was established. The model exhibits an average relative error of 8.86% between predicted and experimental values, indicating the model’s good accuracy in predicting the alloy’s rheological behavior during thermal deformation. By adjusting the strain rate and deformation temperature, this model can be utilized to control the stress level in the hot working process.

Heat treatment, microstructure, texture, and mechanical properties of electron beam melted Ti6Al4V

The findings from the microstructural and textural analysis of as-printed and heat-treated electron beam melted Ti-6Al-4V (EBM-Ti64) samples are discussed in this work. The initial microstructures of both samples were characterized precisely. The as-printed microstructure exhibits aligned grain boundaries parallel to the building direction, with the presence of α platelets. In contrast, the heat-treated microstructure reveals a lamellar α/β structure with a considerably wide interlamellar spacing. This work addresses the transformations from β→α+ά and ά→α+β occurring when materials are heated up to below the β-transus temperature. While the ά→α˝+β transformation is deemed unlikely to take place, the process can still occur through spinodal decomposition of β,β→βV−poor+βV−rich→α˝+βV−rich where α˝ eventually transforms into α+β. A thorough characterization of three primary morphologies of the α phase was revealed. Due to exposure to high temperatures, as experienced in the environment of a rocket engine fan, it was necessary to conduct isothermal hot compression experiments on the homogenized EBM-Ti64 alloy. These experiments aim to investigate the hot deformation behavior within the temperature range of 250–350 °C and a strain rate of 10 s−1. The findings indicate that the modified Johnson-Cook constitutive model and its corresponding numerical simulation, based on stress-strain and work-hardening characteristics, effectively predict the flow behavior of this microstructurally complex alloy. Microstructure and mechanical properties of deformed as-printed and heat-treated samples at 250 ℃, 300 ℃, and 350 ℃ show that although dynamic recrystallization is not feasible under these conditions, we observe grain refinement and decreasing interlamellar spacing. These findings align with mechanical properties, where higher total strain and lower ultimate compression strength were noted as the testing temperature increased. Additionally, heat-treated materials exhibited inferior mechanical characteristics under each testing circumstance. Texture rotation (90 degrees) after deformation is evident in all pole figures. Considering the orientation distribution function maps, more intense <0001> fibre and {101̅0} <0001> textures were formed. Assessments of the slip systems revealed that the basal slip system has the lowest activity when considering texture orientations. Conversely, the most significant deformation contribution, particularly in the c-axis, comes from contraction twin and <c+a> 1st order pyramidal.

Coupling analysis of multi-annular temperature and pressure gradients in oil and gas wells considering fluid thermodynamic properties

A coupled prediction model for temperature and pressure is developed for the annulus of multiple casings to prevent damaging the integrity of oil and gas wells due to annular pressures. The complex structure of the oil and gas well requires dividing the calculation of the annular pressure into three stages based on the annulus level. The annular temperature and pressure gradients of the wellbore are then studied. The hydrostatic pressure changes of the annular fluid at different temperatures, pressures, and well depths are analyzed considering the influence of the isobaric expansion coefficient and isothermal compression coefficient in annular fluids. The pressure gradients of annular fluids A, B, and C with production time and well depth are discussed along with the deformation of production casings. Results show that the annular fluid density and hydrostatic pressure decrease with the increase of temperature, while they will increase with the increase of annular pressure. The annular pressure increases first and then decreases from the bottom of the well to the wellhead. The annular pressure increases the fastest in the early production stages.

Understanding the thermodynamic effects of chemically reactive working fluids in the Stirling heat pump

Within the realm of sustainable heating technologies, this study examines the performance of a Stirling heat pump employing chemically reactive working fluids in contrast to conventional inert counterparts. Reactive working fluids are energy vectors that enable the conversion of not only thermal but also chemical energy within the heat pump. The investigation spans a wide range of theoretical reactive gaseous mixtures, leveraging the ideal gas mixture thermodynamic model. Each fluid is characterized by an equilibrated chemical reaction, denoted as A2(g)⇄2A(g), and distinguished by a set of reaction coordinates: the standard entropy change of reaction and standard enthalpy change of reaction. The chemical reaction evolution and thermodynamic properties are observed in each transformation, and the overall coefficient of performance (COP) of the system is evaluated and benchmarked against that of comparable inert working fluids. It is observed that the exothermic reaction during isothermal compression significantly increases the thermal energy supplied to the heat sink, as well as the thermal energy density per unit maximum volume, by up to 269 %, compared to an inert gas system. However, for the majority of reactive fluids studied, chemical reactions introduce irreversibility in the internal regenerator due to heat transfer across a finite temperature difference, contrary to the case of inert working fluids, penalizing the COP. Consequently, a reduction of up to 28 % in the COP is observed. Nevertheless, there exists a range of reactive fluids, characterized by reversible heat exchange in the internal regenerator, offering increased thermal energy transfer to the heat sink without compromising the COP.

Electroplasticity mechanism of Ti2AlNb alloys under hot compression with the application of a lower electric current

In this study, a lower electric current (1.0–2.0 A/mm2) was applied during hot compression of Ti2AlNb alloys, and the mechanical response, microstructure evolution, and electroplasticity mechanism were investigated. The results showed that the maximum flow stress drop could reach 18.7 % after applying a lower electric current of 2.0 A/mm2, which confirms the existence of electroplasticity. The stress drop increased with increasing electric current density. However, the flow stresses of the samples in the isothermal compression test and those subjected to a 1.0 A/mm2 electric current compression test were similar, indicating that there is a threshold value for the electroplasticity effect on flow stress. The lower strain hardening rate caused by the electric current confirmed the electroplasticity effect, promoting the softening effect. Additionally, the lower average activation energy Q, affected by the electric current, implied the improvement of the deformability of the alloy due to the deformation mechanism of dynamic recovery (DRV), dynamic globularization, or dynamic recrystallization (DRX). The gradual reduction of dislocation density with increasing electric current density resulted in the stress drop, which can be ascribed to the directional drifting electrons colliding with dislocations, which promoted the movement of dislocations by arranging the dislocations in parallel. The local high temperature induced by the local Joule heating effect at the O lamella had a strong promoting effect on the globularization of the O lamella by producing uniform lattice distortion/local strain at the O/B2 interface. With increasing furnace temperature, the drifting electrons accelerated the transformation of LAGBs to HAGBs which promoted the appearance of dynamic recrystallization grains.

Thermal transport of alkali halide aqueous solutions: a non-equilibrium molecular dynamics investigation

Electrolyte solutions are essential in various physical, chemical, and biological processes. Thermal fields induce ion mass fluxes in electrolyte solutions, creating stable salt concentration gradients at stationary conditions. The response of the salt to the thermal field is quite complex, as the ions move towards hot or cold regions depending on the composition of the solution. While these phenomena are well-known, the microscopic mechanism determining thermodiffusion is still poorly understood. In this study, we used non-equilibrium molecular dynamics simulations and the Madrid 2019 forcefield to investigate the thermal transport properties of several electrolyte solutions: {Li + , Na + , K + }Cl − and {Li + , Na + , K + }I − . We show that the reduction of the thermal conductivity with salt concentration is correlated with the modification of the isothermal compressibility and the molar mass of the solution. We also calculate the Soret coefficient of the solutions and compare our results with those of existing experiments. The Madrid 2019 forcefield reproduces the main experimental trends of chloride solutions and the stronger thermophilic response of lithium salts. Our results suggest a connection between the ability of cations (Na + , K + ) to disturb oxygen-oxygen correlations within the 0.35–0.5 nm inter-oxygen distance range and the thermophobicity of the solutions.

INVESTIGATION INTO THE THERMAL DEFORMATION BEHAVIOR AND THE ESTABLISHMENT OF A CONSTITUTIVE RELATIONSHIP FOR Mn-Cr-Ni-Mo STEEL

Isothermal compression tests were conducted on Mn-Cr-Ni-Mo steel at temperatures ranging from 1173 K to 1473 K and strain rates from 0.01 s–1 to 10 s–1 using a Gleeble-3800 thermal simulation tester. Four constitutive models for Mn-Cr-Ni-Mo steel, namely the Arrhenius model, Fields-Backofen model (F-B), original Johnson-Cook model (J-C), and the improved Johnson-Cook model (mJ-C) were established. A correlation coefficient (R) and the average absolute relative error (AARE) were employed to evaluate the predictive capability of these four models. Among them, the Arrhenius model exhibited superior accuracy in predicting the behavior of Mn-Cr-Ni-Mo steel. It and the isothermal thermal compression finite-element model were imported into Deform-3D software for a numerical simulation, aiming to analyze the distribution law of the equivalent stress field. A comparison was made between the time-stress data obtained from numerical simulation under different conditions and that from the isothermal compression tests. The results demonstrate good agreement between the time-stress curves of the numerical simulation and the experimental measurements, indicating that the established Arrhenius model can effectively simulate the thermal deformation of Mn-Cr-Ni-Mo steel. These research findings provide valuable fundamental data for simulating the plastic-deformation process of Mn-Cr-Ni-Mo steel.

Studies on interactions of L-glutamic acid with L-arabinose/D-xylose in aqueous medium: Ultrasonic velocity and acoustic parameter studies supported by FTIR spectroscopic investigation

Glutamic acid is a non-essential amino acid, meaning that the body can synthesize it on its own, and it doesn’t necessarily need to be obtained from the diet. Using an ultrasonic interferometer, the ultrasonic velocity at 293.15 K and 298.15 K and at experimental pressure P = 101 kPa were determined in order to evaluate and comprehend the synergy between non-essential amino acid and saccharides (L-arabinose/D-xylose) in an aqueous system. There is a direct correlation between the weak and strong molecular interactions that occur between the solution’s constituents and the propagation of ultrasonic sound waves through the experimental solutions. Using the ultrasonic velocity data, isentropic compressibility (Ks) apparent molar isentropic compressibility (Ks,ϕ) and isothermal compressibility (KT) were calculated. In addition to these characteristics, acoustic impedance (Z), internal pressure (πi), relative association (RA), molar free volume (Vf), molar free length (Lf) and surface tension (γ) were deduced and analysed to advocates potent ion- solvent interactions. In order to gain understanding of Glu-Glu and Glu- L-arabinose/D-xylose interactions in aqueous medium, these parameters were interpreted. Ion-solvent interactions are stronger than ion-ion interactions due to the greater and positive values of Ks0. Strong contacts occur between the polar segments of L-arabinose/D-xylose and the zwitterionic groups of Glu, and these interactions become stronger as the concentration of L-arabinose/D-xylose increases, as indicated by positive values of Ks,ϕ,tr0. The water structure is reformed during the solvation and ion association processes of Glu. Furthermore, the spectroscopic investigation has been conducted using the FTIR technique in order to verify the results obtained from acoustic studies. Predominant ion-hydrophilic/hydrophobic interactions prevail in the studied system is validated by FTIR study. Absorption band widening indicates that intermolecular hydrogen bonding predominates over intramolecular hydrogen bonding.