Compressibility Research Articles

Morse fluids in the immediate vicinity of the critical point: Calculation of thermodynamic coefficients

The previously proposed approach for the microscopic description of the critical behavior of Morse liquids based on the cell fluid model is applied to the case where the parameters of the Morse interaction potential correspond to alkali metals (sodium and potassium). The critical temperatures, densities, and pressures obtained for sodium and potassium agree with the experimental results. The thermodynamic coefficients (isothermal compressibility, density fluctuations, and thermal expansion) of sodium are investigated in the supercritical temperature region. Numerical calculations of thermodynamic coefficients are performed close to the critical point, where carrying out theoretical and experimental research is challenging. The change in compressibility with increasing density at various temperature values is traced. The behavior of density fluctuations approaching the critical point is shown for different temperatures. The variation in the magnitude of the thermal expansion with increasing temperature for different pressure values is illustrated.

A Neural-Network-Optimized Hydrogen Peroxide Pairwise Additive Model for Classical Simulations.

We have developed an all-atom pairwise additive model for hydrogen peroxide using an optimization procedure based on artificial neural networks (ANNs). The model is based on experimental molecular geometry and includes a dihedral potential that hinders the cis-type configuration and allows for crossing the trans one, defined between the planes that have the two oxygen atoms and each hydrogen. The model's parametrization is achieved by training simple ANNs to minimize a target function that measures the differences between various thermodynamic and transport properties and the corresponding experimental values. Finally, we evaluated a range of properties for the optimized model and its mixtures with SPC/E water, including bulk-liquid properties (density, thermal expansion coefficient, adiabatic compressibility, etc.) and properties of systems at equilibrium (vapor and liquid density, vapor pressure and composition, surface tension, etc.). Overall, we obtained good agreement with experimental data.

Thermodynamic and Thermal Analyze of N,N-Dimethylformamide + 1-Butanol Mixture Properties Based on Density, Sound Velocity and Heat Capacity Data.

The present paper contains data on the density (ρ), sound velocity (u), and specific heat capacity cp of the mixture of N,N-dimethylformamide + 1-butanol (DMF + BuOH) determined in the entire concentration range of solution and in the temperature range (293.15-318.15) K. The analysis of thermodynamic functions such as isobaric molar expansion, isentropic and isothermal molar compression, isobaric and isochoric molar heat capacity, as well as their excess functions (Ep,mE,KS,mE,KT,mE,Cp, mE,CV, mE) and also VmE was undertaken. The analysis of changes in the physicochemical quantities was based on consideration of the system in terms of intermolecular interactions and resulting changes in the mixture structure. The results available in the literature were confusing during the analysis and became the reason for our decision to thoroughly examine the system. What is more, for a system whose components are widely used, there is very scarce information in the literature regarding the heat capacity of the tested mixture, which was also achieved and presented in this publication. The conclusions drawn from so many data points allow us to approximate and understand the changes that occur in the structure of the system due to the repeatability and consistency of the obtained results.

New Correlation for Predicting Undersaturated Oil Compressibility for Mishrif Reservoir in the Southern Iraqi Oil Fields

Reservoir fluids properties are very important in reservoir engineering computations such as material balance calculations, well testing analyses, reserve estimates, and numerical reservoir simulations. Isothermal oil compressibility is required in fluid flow problems, extension of fluid properties from values at the bubble point pressure to higher pressures of interest and in material balance calculations (Ramey, Spivey, and McCain). Isothermal oil compressibility is a measure of the fractional change in volume as pressure is changed at constant temperature (McCain). The most accurate method for determining the Isothermal oil compressibility is a laboratory PVT analysis; however, the evaluation of exploratory wells often require an estimate of the fluid behavior prior to obtaining a representative reservoir sample. Also, experimental data is often unavailable.Empirical correlations are often used for these purposes.This paper developed a new mathematical model for calculating undersaturated oil compressibility using 129 experimentally obtained data points from the PVT analyses of 52 bottom hole fluid samples from Mishrif reservoirs in the southern Iraqi oil fields. The new undersaturated oil compressibility correlation developed using Statistical Analysis System (SAS) by applying nonlinear multiple regression method. It was found that the new correlation estimates undersaturated oil compressibility of Mishrif reservoir crudes in the southern Iraqi oil fields much better than the published ones. The average absolute relative error for the developed correlation is 7.16%.

Ultrasonic, transport and vibrational frequency analysis of non-aqueous peptide + electrolyte solutions

Ultrasonic method finds extensive application in investigating various physicochemical parameters involving molecular interactions in liquid mixtures. The density, viscosity and ultrasonic velocity measurements were carried out in non-aqueous peptide and electrolyte solutions at different concentrations and temperatures to illustrate the intermolecular interactions prevailing in the solutions. The main transport parameters such as adiabatic compressibility, internal pressure and free volume have been computed using the measured values. These parameters were utilized to interpret the intermolecular interactions existing in the mixture of glycyl-glycine and potassium ascorbate in non-aqueous formamide medium. The ultrasonic results are corroborated with the vibrational frequency analysis of the peptide and ascorbate solutions.

Molecular interaction between ester with ethanol at different temperature using ultrasonic technique

In this work, thermodynamic and acoustic properties of binary liquid mixtures of ethyl propionate with ethanol are determined at various temperatures and under ambient pressure. Experimental ultrasonic velocity, density, and viscosity of binary mixtures were measured at different temperatures of 308 K, 313 K, 318 K, 323 K, 328 K, and 333 K. Acoustical parameters such as acoustic impedance (Z), adiabatic compressibility (βa), Intermolecular free length (Lf), relaxation time (τ), internal pressure (π), and thermodynamic parameters like Gibb’s free energy (ΔG) and enthalpy (H) have been computed from the above primary parameters. The excess free length (LfE), excess internal pressure (πE) and excess enthalpy (HE) were derived using experimental data. Negative excess values are obtained for the binary system (ethyl propionate + ethanol). The non-linear variations are found for the thermo -acoustic parameters which imply the presence of complex formation in the binary system. The obtained results have been discussed in detail.

Is the Outflow-Layer Inertial Stability Crucial to the Energy Cycle and Development of Tropical Cyclones?

Abstract This study revisits the issue of why tropical cyclones (TCs) develop more rapidly at lower latitudes, using ensemble axisymmetric numerical simulations and energy diagnostics based on the isentropic analysis, with the focus on the relative importance of the outflow-layer and boundary layer inertial stabilities to TC intensification and energy cycle. Results show that although lowering the outflow-layer Coriolis parameter and thus inertial stability can slightly strengthen the outflow, it does not affect the simulated TC development, whereas lowering the boundary layer Coriolis parameter largely enhances the secondary circulation and TC intensification as in the experiment with a reduced Coriolis parameter throughout the model atmosphere. This suggests that TC outflow is more likely a passive result of the convergent inflow in the boundary layer and convective updraft in the eyewall. The boundary layer inertial stability is found to control the convergent inflow in the boundary layer and depth of convection in the eyewall and thus the temperature of the energy sink in the TC heat engine, which determines the efficiency and overall mechanical output of the heat engine and thus TC intensification. It is also shown that the hypothesized isothermal and adiabatic compression legs at the downstream end of the outflow in the classical Carnot cycle are not supported in the thermodynamic cycle of the simulated TCs, implying that the hypothesized classical TC Carnot cycle is not closed. It is the theoretical maximum work of the heat engine, not the energy expenditure following the outflow downstream, that determines the mechanical work used to intensify a TC.

Revealing hot deformation behavior of inconel X-750 superalloy: A novel hot processing map coupled with grain boundary engineering

In this work, a series of isothermal hot compression tests were performed at the temperature of 900–1150 °C with the strain rate ranging from 0.01 to 10s−1 in Inconel X-750 alloy (referred as Alloy X-750). Based on the flow stress data, the back-propagation artificial neural network model was utilized to accurately predict the flow stress at elevated temperatures. Subsequently, by constructing a modified hot processing map coupled with the variation of Σ3n (n = 1, 2, and 3) twin boundaries fraction, the optimal processing parameters were determined to be in the range of 1100–1150 °C and 1-10s−1 for Alloy X-750. Moreover, the possibility of grain boundary engineering via hot deformation were also evaluated by using some critical quantification descriptors of twin related domains (TRDs), such as the number of grains in the TRDs, the lengths of the longest chain, and the average TRDs size. All the results can further verify the validity of modified hot processing map. Finally, the high-temperature flow behavior combined with the relevant microstructure characterization showed that discontinuous dynamic recrystallization is considered as the predominant softening mechanism, while the continuous dynamic recrystallization and particle-stimulated nucleation also additionally contribute to the recrystallization nucleation during the hot deformation of Alloy X-750.

Dynamic recrystallization mechanisms of as-forged Al–Zn–Mg-(Cu) aluminum alloy during hot compression deformation

The thermal deformation behavior of as-forged Al–Zn–Mg-(Cu) aluminum alloy at strain rate 0.001–1 s−1, temperature 663–783 K and deformation degree 0–60% was studied by isothermal compression test, and an accurate strain-compensated Arrhenius constitutive equation was established. Based on the microstructure characteristics of compressed specimens, the effects of strain rate, temperature and strain on dynamic recrystallization (DRX) behavior and substructure evolution were determined. The results show that the alloy undergoes discontinuous dynamic recrystallization (DDRX), continuous dynamic recrystallization (CDRX) and geometric dynamic recrystallization (GDRX) simultaneously at high temperature and low strain rate (743 K, 0.001–0.01 s−1), where CDRX includes microshear band assist (MSBA), homogeneous increase of misorientation (HIM) and progressive lattice rotation near grain boundaries (LRGB). However, with decreasing temperature and increasing strain rate, GDRX basically disappears, and DDRX becomes the main DRX mechanism. At medium to high strain rate (0.1∼1 s-1), high-density dislocations accumulate at the grain boundaries and numerous microshear bands form inside grains during the early deformation stage. The misorientation angles of these pre-existing geometrically necessary boundaries gradually increase with temperature and strain, ultimately transforming into subgrains and DRX grains.

Constitutive modeling for elevated temperature flow behavior of a novel Cr-Si alloyed hot stamping steel

The flow behavior of a novel Cr-Si alloyed hot stamping steel (Cr-Si steel) at elevated temperature was investigated via isothermal compression tests on a Gleeble-3500 thermomechanical simulator with a temperature range of 600 ∼ 900 °C and a strain rate range of 0.1 ∼ 10 s−1. Subsequently, the Arrhenius-type constitutive model, comprising strain compensation, was established in accordance with the friction and adiabatic heating corrected stress-strain curves. Furthermore, the predictability and prediction accuracy of the constitutive model were verified. The results reveal that at a constant strain rate, the flow stress of the Cr-Si steel initially increases as the strain increases before tending to stabilize, owning to the combined effects of work hardening and dynamic recovery. The peak flow stresses decrease as the temperatures increase and the strain rates decrease. The constitutive model can accurately predict the elevated temperature constitutive relationship of the Cr-Si steel during the hot stamping process.

Hot Deformation Behavior and Processing Maps of an As-Cast Al-5Mg-3Zn-1Cu (wt%) Alloy.

One of the key issues limiting the application of Al-Mg-Zn-Cu alloys in the automotive industry is forming at a low cost. Isothermal uniaxial compression was accomplished in the range of 300-450 °C, 0.001-10 s-1 to study the hot deformation behavior of an as-cast Al-5.07Mg-3.01Zn-1.11Cu-0.01Ti alloy. Its rheological behavior presented characteristics of work-hardening followed by dynamic softening and its flow stress was accurately described by the proposed strain-compensated Arrhenius-type constitutive model. Three-dimensional processing maps were established. The instability was mainly concentrated in regions with high strain rates or low temperatures, with cracking being the main instability. A workable domain was determined as 385-450 °C, 0.001-0.26 s-1, in which dynamic recovery (DRV) and dynamic recrystallization (DRX) occurred. As the temperature rose, the dominant dynamic softening mechanism shifted from DRV to DRX. The DRX mechanisms transformed from continuous dynamic recrystallization (CDRX), discontinuous dynamic recrystallization (DDRX), and particle-stimulated nucleation (PSN) at 350 °C, 0.1 s-1 to CDRX and DDRX at 450 °C, 0.01 s-1, and eventually to DDRX at 450 °C, 0.001 s-1. The eutectic T-Mg32(AlZnCu)49 phase facilitated DRX nucleation and did not trigger instability in the workable domain. This work demonstrates that the workability of as-cast Al-Mg-Zn-Cu alloys with low Zn/Mg ratios is sufficient for hot forming.

Constitutive model of 25CrMo4 steel based on IPSO-SVR and its application in finite element simulation

Optimizing the forming process of high-speed railway axles requires establishing an accurate model of the flow behavior of 25CrMo4 steel. In this regard, this study investigated the thermal deformation behavior of 25CrMo4 axle steel by conducting isothermal compression tests using a Gleeble-1500 thermal simulator within a certain temperature range (1323–1423 K) and strain rate range (0.01–1.0 s−1). In order to establish the constitutive relationship model of 25CrMo4 steel at high temperature, this study uses an intelligent algorithm (IPSO-SVR) combining improved particle swarm optimization and support vector regression. The study also analyzed the predictive performance of the model and examined the impact of key parameters of PSO and SVR on prediction accuracy. Subsequently, the study utilized the predicted data of the IPSO-SVR model as input to the finite element software to numerically simulate high-temperature deformation. The research results indicate that the IPSO-SVR constitutive model has high prediction accuracy and can effectively characterize the dynamic mechanical properties of 25CrMo4 steel. Therefore, this method provides a feasible and effective solution for finite element simulation.

On the possible locus of the liquid-liquid critical point in real water from studies of supercooled water using the TIP4P/Ice model.

One of the most accepted hypothesis to explain the anomalous behavior of water is the presence of a critical point between two liquids, the liquid-liquid critical point (LLCP), buried within the deep supercooled regime. Unfortunately, such hypothesis is hard to be experimentally confirmed due to fast freezing. Here, we show that the TIP4P/Ice water potential shifted by 400 bar can reproduce with unprecedented accuracy the experimental isothermal compressibility of water and its liquid equation of state for a wide pressure and temperature range. We find, both by extrapolation of response function maxima and by a Maxwell construction, that the location of the model LLCP is consistent with previous calculations. According to the pressure shift needed to recover the experimental behavior of supercooled water, we estimate the experimental LLCP to be located around 1250 bar and 195K. We use the model to estimate the ice nucleation rate (J) in the vicinity of the hypothesized LLCP experimental location and obtain J = 1024 m-3 s-1. Thereby, experiments where the ratio between the cooling rate and the sample volume is equal or larger than the estimated nucleation rate could probe liquid-liquid equilibrium before freezing. Such conditions are not accessible in common experiments with microdroplets cooled at a few kelvin per second, but they could be, for instance, using nanodroplets of around 50nm radius observed in a millisecond timescale.

Hot Deformation Behavior and Processing Maps of Pure Copper during Isothermal Compression.

In this study, pure copper's hot deformation behavior was studied through isothermal compression tests at deformation temperatures of 350~750 °C with strain rates of 0.01~5 s-1 on a Gleeble-3500 isothermal simulator. Metallographic observation and microhardness measurement were carried out of the hot compressed specimens. By analyzing the true stress-strain curves of pure copper under various deformation conditions during the hot deformation process, the constitutive equation was established based on the strain-compensated Arrhenius model. On the basis of the dynamic material model proposed by Prasad, the hot-processing maps were acquired under different strains. Meanwhile, the effect of deformation temperature and strain rate on the microstructure characteristics was studied by observing the hot-compressed microstructure. The results demonstrate that the flow stress of pure copper has positive strain rate sensitivity and negative temperature correlation. The average hardness value of pure copper has no obvious change trend with the strain rate. The flow stress can be predicted with excellent accuracy via the Arrhenius model based on strain compensation. The suitable deforming process parameters for pure copper were determined to be at a deformation temperature range of 700~750 °C and strain rate range of 0.1~1 s-1.

Revealing the ultra-high high-temperature compressive mechanical properties and deformation mechanism of a heterostructured AlNp/Al nanocomposite

Heterostructured materials have attracted increasing attention owing to their superior mechanical properties. In this work, the high-temperature mechanical property and deformation mechanism of a heterostructured AlNp/Al composite were revealed by isothermal compression tests. The results showed that the superior compressive strength of the AlNp/Al composite could be maintained at both room temperature and high temperature of 300–500 °C during the whole deformation process. The strong pinning effect of the dispersive AlN nanoparticle (AlNp) on the matrix grains could prevent grain boundary softening and grain growth, as well as the special layered heterogeneous structure and network structure could avoid high temperature softening. The hot deformation mechanism of the AlNp/Al composite could be affected by the strain rate and deformation temperature. It was confirmed that continuous dynamic recrystallization (CDRX) dominated the whole deformation process when deformed at low strain rates (0.0001–0.01 s−1) and high temperatures (400–500 °C); while dynamic recovery (DRV) was the main mechanism at high strain rate (0.1–1 s−1) and low temperature (300–350 °C) Furthermore, the strain rate sensitivity exponent (m) was used to assess the relationship between peak stress and deformation temperature and strain rate, which could predict the instability region of the composite. It shows that the simultaneous action of high temperatures and high strain rates should be avoided during hot deformation. This work shed light on the microstructure design of the high-strength heat-resistant aluminum matrix composite.

A study on hot deformation behavior of 40Cr/Q345B bimetal

The hot deformation behavior of 40Cr/Q345B bimetal during hot compression bonding was studied using the isothermal compression method. A true stress–strain curve of the bimetal was obtained and modified to eliminate the effects of friction. The results show that the flow stress increases with decreasing deformation temperature and increasing strain rate. By analyzing the relationship of stress, deformation temperature, and strain rate, the constitutive equation of 40Cr/Q345B bimetal was obtained. The hot processing maps of 40Cr/Q345B bimetal under different strains are drawn. Through microstructure characterization, 40Cr/Q345B bimetal formed metallurgical bonding under the deformation process of this study. Combined with the hot processing map, microstructure, prior austenite grain, and microhardness distribution, it is proposed that the optimal deformation parameters of 40Cr/Q345B bimetal is 1050–1150°C and 0.02–0.4 s−1.

Physicochemical behaviour of 2-Pentanone + amine mixtures at three temperatures

Thermophysical properties viz. Isothermal compressibility (βT), internal pressure (Pi) along with their excess counterparts coupled with energy (ΔEvap) and enthalpy of vapourization (ΔHvap), cohesive energy density (CED), solubility parameter (δ), free volume (Vf) have been studied to understand the nature and extent of interactions between 2-pentanone and three amines (Pyridine, N-methylaniline, Aniline) over the range of temperatures. The investigation focuses on understanding the interactions present between amine and a carboxylic functional group. This helps to get a deeper insight into the functionality of the amide group which plays a crucial role in biologically complex systems. The study shows that the strength of interactions follows an order: Pyridine < N-methylaniline < Aniline with 2-Pentanone for all temperatures arising due to the capability of components to form H-bonding.

Measurement and prediction of the volumetric and acoustic properties of two biodiesel fuels up to 200 MPa

This work presents experimental data on sound velocities and densities for two biodiesel fuels, namely sunflower methyl ester and a blend of Palm, Rapeseed, and Soybean methyl esters at pressures ranging from atmospheric to 200 MPa and temperatures from 293.15 to 393.15 K. Speed of sound data were obtained up to 200 MPa using a pulsed echo method. Density was determined by measuring the period of a vibrating tube up to 100 MPa and by integrating the sound velocity between 100 and 200 MPa. These measurements were coupled to determine other properties, such as isothermal compressibility, isentropic compressibility, and acoustic impedance, which strongly influence the injection process in diesel engines. The experimental data were compared with a set of models previously developed to predict the density and sound velocity of biodiesels under high pressure based on their fatty acid ester composition.

Modified Voce-Type Constitutive Model on Solid Solution State 7050 Aluminum Alloy during Warm Compression Process

The 7050 alloy is a kind of Al-Zn-Mg-Cu alloy that is widely used for aircraft structures. Although the deformation behavior of the solid solution state 7050 aluminum alloy is critical for engineering and manufacturing design, it has received little attention. In this study, the room and warm compression behavior of the solid solution-state 7050 alloy was researched, and a modified model with variable parameters was built for the flow stress and load prediction. The isothermal compression tests of the solid solution-state 7050 alloy were performed under the conditions of a deformation temperature of 333–523 K, a strain rate of 10−3–10−1 s−1, and a total reduction of 50%. The strain-stress curves at different temperatures were corrected by considering interface friction. The flow stress model of aluminum was established using the modified Voce model. For evaluating the modified Voce model’s prediction accuracy, the flow stresses calculated by the model were compared with the experimental values. Consequently, for assessing its prediction abilities in finite element applications, the whole compression process was simulated in the finite element analysis platform. The results sufficiently illustrated that the modified Voce-type model can precisely predict the complex flow behaviors during warm compression. This study will guide the prediction of the warm compression load and the optimization of the heat treatment process of the alloy.

Acoustic, FTIR and Raman spectroscopic studies of aspartame and citric acid

aims: To study the molecular interactions between artificial sweetener and edible acid background: Ultrasonics, Material Science objective: To determine the molecular interactions between artificial sweetener and edible acids using acoustical parameters method: Acoustical parameters, spectroscopy and stability constant result: The molecular interactions and functional groups that are present is found conclusion: As the concentration increases, acoustical parameters like ultrasonic velocity, viscosity, density, Relaxation time, acoustic impedance while, other acoustical parameters like adiabatic compressibility and intermolecular free length decreases with the increases with concentration. This proves that there is a strong interaction between solute and solvent. other: Spectroscopy Experimental Study