Change In Internal Energy Research Articles

Turbulent/non-turbulent interfaces in temporally evolving compressible planar jets

Turbulent/non-turbulent interfaces (TNTIs) in compressible jets are studied with direct numerical simulations of temporally evolving compressible planar jets with jet Mach numbers MJ of 0.6, 1.6, and 2.6 ejected with a jet initial pressure equal to the ambient pressure. The flow properties near the TNTI are investigated with statistics computed on the local interfacial coordinate. The layer thicknesses are about 10-13η for the TNTI layer, 3η for the viscous superlayer, and 7-10η for the turbulent sublayer (TSL), where η is the Kolmogorov scale on the jet centerline. The TSL thickness divided by η decreases from 10 to 7 as MJ increases. The turbulent fluid is characterized with lower density, higher temperature, and lower pressure than the non-turbulent fluid, where these properties sharply change within the TNTI layer. The rate of change in internal energy near the TNTI is proportional to the initial kinetic energy of the jet, where the internal energy at the outer edge of the TNTI layer changes because of the diffusive/dilatational effects. The movement of entrained fluid is similar in compressible and incompressible jets. Compressibility affects the total entrainment rate via the total surface area of the TNTI, where the surface area of the TNTI per unit area of the plane perpendicular to the cross-streamwise direction decreases from 9.5 to 7.0 as MJ increases. Strongly compressive waves appear in the non-turbulent region at a high Mach number, where the imprints of these waves are found within the TNTI layer as strong pressure/temperature correlation and large values of pressure skewness.

Molecular dynamics study of deformation mechanisms of poly(vinyl alcohol) hydrogel

ABSTRACTMolecular dynamics (MD) simulations have been performed on the physically crosslinking poly(vinyl alcohol) (PVA) hydrogel to study the deformation mechanisms under uniaxial tensile conditions. The distributions of hydroxyl oxygens and dihedral angle and the number of hydrogen bonds have been analysed to study the structure of the hydrogel. The water content and temperature dependency of mechanical properties have been investigated. The energy contributions from the partially united atom potential have been calculated as a function of strain. It is found that the stress–strain curve comprises toe region, linear region and yield and failure region which is close to most biomaterials. In the toe and yield region, all the contributions to the internal energy change a little. However, in the linear region, the bond stretching and angle bending energy increase rapidly and mainly dominate the region, and the energy increases more rapidly with the increasing water content but the decreasing temperature. The degree of crosslinking decreases with the increasing deformation. The polymer chains occur significant torsional activity in the toe region. Hydrogen bonds are stable in the toe and yield region, but the hydrogen bonds between hydroxyl groups and waters decrease in the linear region.

Theoretical research on structural, electronic, mechanical, lattice dynamical and thermodynamic properties of layered ternary nitrides Ti2AN (A = Si, Ge and Sn)

Abstract First-principles density functional theory (DFT) calculations within generalized gradient approximation (GGA) are carried out to investigate the structural, electronic, mechanical, lattice dynamical and thermodynamic properties of Ti 2 AN (A = Si, Ge and Sn) MAX phases. The optimized geometrical parameters such as lattice constants ( a , c ) and the internal coordinates have been calculated. Electronic band structure and corresponding density of states (DOS) have been obtained. The analysis of the band structures and density of states have shown that these compounds are electrical conductors. The elastic constants have been ascertained using the stress-strain method. The isotropic elastic moduli, known as bulk modulus ( B ), shear modulus ( G ), young's modulus ( E ), poisson's ratio ( ν ), vickers hardness ( H v ) and linear compressibility coefficients ( α ) have been studied within framework of the Voigt–Reuss–Hill approximation for ideal polycrystalline Ti 2 AN (A = Si, Ge and Sn) MAX aggregates. Furthermore, the phonon dispersion curves as well as accompanying phonon density of states have been comprehensively computed. And also raman and infrared modes at the Γ point have been obtained. Within the thermodynamic properties, specific heat capacity, entropy, helmholtz free energy and internal energy changes were analyzed depending on the temperature of Ti 2 AN (A = Si, Ge and Sn) compounds. The obtained results are presented in comparison with present theoretical data for Ti 2 SiN. This is the first quantitative theoretical study of the electronic properties and other properties for Ti 2 GeN and Ti 2 SnN compounds and therefore theoretical results for these compounds need to be verified experimentally.

A new understanding of the sub-[formula omitted] enthalpy relaxation in metallic glasses

We performed a study of the sub-Tg enthalpy relaxation effect in a bulk Zr-based metallic glass by means of calorimetric and shear modulus measurements. It is found that the increase of the heat absorption in the supercooled liquid state due to sub-Tg preannealing can be well described by a kinetic equation derived within the framework of the Interstitialcy theory. This equation assumes that the heat effects are controlled by the relaxation of the shear modulus occurring upon heating. It is revealed that the heat absorbed during temperature rise up to the supercooled liquid region linearly increases with the shear modulus measured near the room temperature. It is argued that this relationship is determined by a change of glass internal energy, which is controlled by the shear moduli of glass and maternal crystal.On the other hand, it is suggested that sub-Tg enthalpy relaxation as well as relaxation of the shear modulus are governed by concentration changes of interstitialcy-type defects inherited from the melt. This approach, in particular, allows explanation of a new dependence of the heat absorbed during sub-Tg enthalpy relaxation experiment as a function of the preannealing time at temperatures well below Tg.Overall, the obtained results give further clear confirmation of a major role of the shear elasticity in relaxation phenomena in metallic glasses.

The saturated and supercritical Stirling cycle thermodynamic heat engine cycle

On the assumption that experimentally validated tabulated thermodynamic properties of saturated fluids published by the National Institute of Standards and Technology are accurate, a theoretical thermodynamic cycle can be demonstrated that produces a net-negative entropy generation to the universe. The experimental data on the internal energy can also be used to obtain a simple, empirical equation for the change in internal energy of a real fluid undergoing isothermal expansion and compression. This demonstration provides experimental evidence to the theory that temperature-dependent intermolecular attractive forces can be an entropic force that can enhance the thermodynamic efficiency of a real-fluid macroscopic heat engine to exceed that of the Carnot efficiency.

Molecular dynamics simulations on homogeneous condensation of R600a refrigerant

Molecular Dynamics (MD) simulations have been employed to study the homogeneous condensation phenomenon of R600a (isobutane) refrigerant in the vapor compression refrigeration system. The molecular system consists of superheated vapor isobutane in a cuboid simulation cell with periodic boundary conditions in all directions. A more physically reliable thermostat and a barostat are applied to control the temperature and pressure of the cell containing the molecules. Based on AHRI standard 460 rating conditions, the simulations started from the initial configuration of vapor phase isobutane system, and once the equilibration is established at 361K with 1atm, the system is suddenly cooled to the ambient temperature of 308K and is set under the condensing pressure of 7.1658bar corresponding to the saturation temperature at 325K of the compound at supersaturation ratio 1.548. The density, internal potential energy, and volume changing with time of superheated vapor molecules in the homogeneous condensation process of the system are investigated. The results show that vapor molecules have underwent a rapid phase transition to the subcooled liquid at a certain critical time period. Subcritical clusters of isobutane molecules are formed in the preliminary part of the simulations, which then aggregate to generate the critical condensate nucleus over time. An examination of the radial distribution functions (RDFs) shows that the bonding and non-bonding interactions are formed in the vapor and liquid phases of isobutane. It is truly consistent with the internal potential energy and phase change properties. The computed densities of both phases agree well with the NIST standard reference thermodynamic and transport property data of the compound. A comparative study is executed through several simulations for various values of supersaturation and undersaturation ratios with different numbers of molecules to investigate the critical time of phase transition in the homogeneous condensation process.

Calculation of proppant-carrying flow in supercritical carbon dioxide fracturing fluid

As a new clear and efficient fracturing fluid, supercritical carbon dioxide (SC-CO2) has many advantages in the development of unconventional oil and gas resources, such as no harm to the reservoir, improving the reservoir permeability and fluid flow resistance, quickly completely flowing back after fracturing. Based on the principle of suspension energy balance, an equilibrium flow rate model of proppant-carrying flow of SC-CO2 is derived, and calculation errors are 3.32% and 4.54%, respectively, compared with equilibrium flow rates obtained from experiments under different density and particle sizes. By considering the change of fluid internal energy and flow work, filtration characteristics, physical parameters, and SC-CO2–rock adsorption in the SC-CO2 fracturing process, a proppant-carrying flow calculation model of the SC-CO2 fracturing fluid is established based on temperature–pressure field coupling, fracture and filtration zone coupling, and SC-CO2 fluid and proppant coupling. In the experiment, the heights of nine groups of proppant embankments were measured, and the average model prediction error value is 3.43%. SC-CO2 has a similar proppant-carrying capacity to that of clear water under the high Reynolds number condition. Based on the proppant-embankment prediction model of SC-CO2 fracturing, through analyzing proppant-carrying characteristics of the SC-CO2 fracturing fluid, the proppant concentration distribution and proppant embankment section are obtained at different fracturing times. According to the calculation, as the fracturing fluid pumping rate increases, proppant density and proppant particle size will decrease, the viscosity of the SC-CO2 fracturing fluid system will increase, and proppant accumulation height can be reduced over a small range, while proppant accumulation length will experience a greater increase along the fracture length direction. During field operation of SC-CO2 fracturing, the proppant pumping process should be optimized according to the proppant embankment section and proppant concentration should be choose increased in small steps to meet fracture propping requirements.

Examining mechanical properties of various pharmaceutical excipients with the gravitation-based high-velocity compaction analysis method

The compression physics of powders must be considered when developing a suitable tablet formulation. In the present study, the gravitation-based high-velocity method was utilized to analyze mechanical properties of eight common pharmaceutical excipients: two grades of lactose, anhydrous glucose, anhydrous calcium hydrogen phosphate, three grades of microcrystalline cellulose and starch. Samples were compressed five times consecutively with varying pressure and speed so that Setup A produced higher pressure and longer contact time than Setup B. The important parameters obtained from samples were porosity profiles, compaction pressure, contact time, internal energy change and the amount of elastic recovery. All acquired data was only based on distance-time profile of the compression event. Lactose and glucose fragmented effectively while calcium hydrogen phosphate remained in rearrangement phase, due to its hardness and insufficient pressure applied. Microcrystalline cellulose samples showed plastic behaviour and starch was most elastic of all the samples. By utilizing the method, examined excipients could be categorized according to their compression behaviour in an accurate and cost-efficient manner.

Photoluminescence and stress-luminescence of non-piezoelectric ZnS:Cu amorphous materials

In this work, the non-piezoelectric ZnS:Cu amorphous powder was sintered at 1100 °C. The dominant photoluminescent emission peak at ∼484 nm can be found upon a ∼365 nm light excitation. An obvious stress-luminescence of ZnS:Cu, appearing reproducibly strong visible emission under mechanical pulse load, is found. The stress-luminescence mechanism of the non-piezoelectric ZnS:Cu amorphous powder may be attributed to the internal energy change under the mechanical pulse load.

Increase in the thermodynamic efficiency of the working process of spark-ignited engines on natural gas with the addition of hydrogen

The work is devoted to the substantiation and practical implementation of a new approach for estimating the change in internal energy by pressure and volume. The pressure is measured with a calibrated sensor. The change in volume inside the cylinder is determined by changing the position of the piston. The position of the piston is precisely determined by the angle of rotation of the crankshaft. On the basis of the proposed approach, the thermodynamic efficiency of the working process of spark ignition engines on natural gas with the addition of hydrogen was estimated. Experimental studies were carried out on a single-cylinder unit UIT-85. Their analysis showed an increase in the thermodynamic efficiency of the working process with the addition of hydrogen in a compressed natural gas (CNG).The results obtained make it possible to determine the characteristic of heat release from the analysis of experimental data. The effect of hydrogen addition on the CNG combustion process is estimated.

Thermodynamics and computation during collective motion near criticality.

We study self-organization of collective motion as a thermodynamic phenomenon in the context of the first law of thermodynamics. It is expected that the coherent ordered motion typically self-organises in the presence of changes in the (generalized) internal energy and of (generalized) work done on, or extracted from, the system. We aim to explicitly quantify changes in these two quantities in a system of simulated self-propelled particles and contrast them with changes in the system's configuration entropy. In doing so, we adapt a thermodynamic formulation of the curvatures of the internal energy and the work, with respect to two parameters that control the particles' alignment. This allows us to systematically investigate the behavior of the system by varying the two control parameters to drive the system across a kinetic phase transition. Our results identify critical regimes and show that during the phase transition, where the configuration entropy of the system decreases, the rates of change of the work and of the internal energy also decrease, while their curvatures diverge. Importantly, the reduction of entropy achieved through expenditure of work is shown to peak at criticality. We relate this both to a thermodynamic efficiency and the significance of the increased order with respect to a computational path. Additionally, this study provides an information-geometric interpretation of the curvature of the internal energy as the difference between two curvatures: the curvature of the free entropy, captured by the Fisher information, and the curvature of the configuration entropy.

Travelling Waves Solution of the Unsteady Flow Problem of a Collisional Plasma Bounded by a Moving Plate

The extension of the previous paper [Can. J. Phys. Vol. 88, (2010), 501–511] has been made. Therefore, the effect of the neutral atoms collisions with electrons and with positive ions is taken into consideration, which was ignored, for the sake of simplicity, in the earlier work. Thus, we will have multi-collision terms (electron–electron, electron–ion, electron– neutral) instead of one term, as was studied before for the sake of facilitation. These collision terms are needed to obtain the real physical situation. The new procedures will increase the ability of the research applications. This study is based on the solution of the BGK (Bhatnager–Gross–Krook) model of the nonlinear partial differential Boltzmann equations coupled with Maxwell’s partial differential equations. The initial-boundary value problem of the Rayleigh flow problem applied to the system of the plasma (positive ions + electrons+ neutral atoms), bounded by a moving plate, is solved. For this purpose, the traveling wave solution method is used to get the exact solution of the nonlinear partial differential equations system. The ratios between the different contributions of the internal energy changes are predicted via the extended Gibbs equation for both dia-magnetic and para-magnetic plasma. The results are applied to a typical model of laboratory argon plasma. 3D-Graphics illustrating the calculated variables are drawn to predict their behavior and the results are discussed.

Adsorption of organic molecules on a porous polymer surface modified with the supramolecular structure of melamine–cyanuric acid

The adsorption of organic molecules on the surface of a porous polymeric sorbent modified with a mixed cyanuric acid–melamine supramolecular structure is studied. The parameters of thermodynamic adsorption are considered and the contributions from intermolecular interactions to the Helmholtz energy of adsorption are assessed. Analysis of the molar changes in internal energy and adsorption entropy shows that the supramolecular structure formed on the surface could not exhibit dimension effects, indicating there were no cavities. The contributions from nonspecific interactions to the Helmholtz energy of adsorption generally fall, while those of specific interactions increase, indicating an increase in the polarity of the sorbent surface.

Thiolated gold nanoparticle solvation in near-critical fluids: The role of density, temperature, and topology.

We employ molecular dynamics simulations to study the structure and solvation thermodynamics of thiolated gold nanoparticles of size 1.2 and 1.6 nm with ligand of chain length 8-16 carbons in ethane and propane over a wide range of densities close to the critical isotherm. The Helmholtz free energy is estimated by explicitly calculating the change in entropy and internal energy of solvation, and the effect of density and temperature on fluctuation-driven inherent anisotropy in the ligand corona is characterized. Since the topological variation further accentuates this instantaneous asymmetry in the ligand cloud, the anisotropy with varying surface coverage and chain length is also studied including the solvent contributions to the entropic and energetic metrics. Our results are consistent with the experiment, suggesting a route of obtaining structural insights into solvation thermodynamics that could be useful for understanding the stability of nanoparticle dispersions.

Thermodynamic aspects of the coating formation through mechanochemical synthesis in vibration technology systems

On the basis of thermodynamic concepts of the process, we proposed an energy model that reflects the mechanochemical essence of coating forming in terms of vibration technology systems, which takes into account the contribution to the formation of the coating, the increase of unavailable energy due to the growth of entropy, the increase in the energy of elastic-plastic crystal lattice distortion as a result of the mechanical influence of working environment indenters, surface layer internal energy change which occurs as a result of chemical interaction of the contacting media. We proposed adhesion strength of the local volume modified through processing as a criterion of the energy condition of the formed coating. We established analytical dependence which helps to obtain the coating strength of the material required by operating conditions.

First-principles investigation on thermal properties and infrared spectra of imperfect graphene

In this study we used first-principles density functional theory to investigate the thermal and optical properties of graphene. Graphene phonon properties were first calculated by the density-functional perturbation theory and then used to acquire thermal properties such as the specific heat, free and total energy, and entropy, as well as the infrared and Raman spectra. Results show that the peaks of phonon density of states at about 40 and 45.5THz in the perfect graphene (G) were shifted to 40.5 and 46THz in the imperfect graphene (G-D), respectively. There are peaks at 16.5, 19, 25, and 43.5THz in the G-D curve, while there is no obvious peak at same frequencies in that of the G. The specific heat and entropy are lower for the G-D than for the G at temperature >280K, but the tendency is slightly reversed at temperature <200K. The total energy, change in vibrational internal energy, and change in the vibrational Helmholtz free energy are all lower for the G-D than for the G. The Helmholtz free energy for the G-D is higher at temperature >1300K, but lower at temperature below 1250K than for the G. In the infrared (IR) spectrum, no absorption peak exists for perfect graphene, but strong absorption is found at about 233, 830 and 1392cm−1 for the G-D. The character peak of sp2 carbon atom in-plane vibration in the Raman spectrum is shifted from 1589cm−1 for the G to 1530cm−1 for the G-D. The defects in the G-D caused the peaks and splits in the IR and Raman spectra.

Rupture of polymers by chain scission

One of the distinguishing features of elastomeric materials, which consist of a network of flexible polymeric chains, is that the deformation response is dominated by changes in entropy. Accordingly, most classical theories of rubber-like elasticity consider only the entropy and neglect any changes in internal energy. On the other hand, the fracture of strongly cross-linked elastomers is essentially energy dominated, as argued in the well-known Lake–Thomas model for the toughness of elastomers. However, a single model unifying these two phenomena is still lacking. We provide a rational yet simple model for deformation and fracture of cross-linked polymers, based on two ingredients: (i) a non-Gaussian statistical mechanics model of polymer chains that accounts for the increase in energy due to the deformation of molecular bonds; (ii) a chain scission criterion based on the bond deformation energy attaining a critical value. Using this model, we can estimate the rupture stretch of elastomeric materials from fundamental quantities describing the polymer network. We use this model to relate the flaw sensitivity of elastomers to an intrinsic material length scale related to the network structure.

Refinement of the theoretical solubility model and prediction of solute solubility in mixed solvent systems

We have refined the non-polar (van der Waalls) and hydrogen bonding interaction term of STMIPE-AC (statistical thermodynamic molar intermolecular potential energy activity coefficient) model, which reduces the average error of the model in correlating the molar internal energy change on vaporization of pure liquids (62 solvents, 10 temperature points for each solvent) from 6.6% to 3.1%. The binary interaction parameters kij are fitted to the solubility data of solid solutes in pure solvents or estimated from a semi-empirical equation using a similar local composition method, and then they are used to predict the solute solubility in mixed solvents. The overall average relative error (ARE) in predicted solubility (15 solutes, 64 systems, 1091 data points) is 11.24%, which makes this model a practical approach for crystallization process development.

Change in Internal Energy and Enthalpy of Spinning Black Holes in XRBs and AGN Using Spin Parameter a* = 0.9

In the present research work, we have proposed a model for the change in the internal energy and enthalpy of the spinning black holes using first law of black holes in the case of spin parameter a*=0.9 and calculated their values in XRBs and AGN.

ЗАВИСИМОСТЬ ХАРАКТЕРИСТИКИ ТЕПЛОВЫДЕЛЕНИЯ ОТ СОСТАВА СМЕСИ НА ХОЛОСТОМ ХОДУ В ДВИГАТЕЛЕ, РАБОТАЮЩЕМ НА ГАЗОВОМ ТОПЛИВЕ

The idling mode for spark-ignition engines is characteristic, a significant uneven flow of the combustion process. Which is due to the fact that a fresh combustible mixture is strongly diluted with residual gases. The characteristics of flammability are largely determined by the preceding combustion cycle. The studies consisted of bench tests on the VAZ-2111 engine at idle and thermodynamic analysis of three successive indicator diagrams, obtained experimentally, reflecting the cycle before ignition was missed, a cycle witha pass and a cycle after ignition was missed. As a result of the thermodynamic analysis, the characteristics of the change in the work and the internal energy of the cycle for each interval of the indicator chart of one degree of rotation of the crankshaft are determined. On the basis of this, the characteristic of active heat release was obtained for all the investigated cycles. The presented results of the thermodynamic analysis of the combustion process make it possible to estimatewith more accuracy the effect of the composition of gas fuel on the heat release characteristic, since the analysis of the change in internal energy was carried out according to the author's technique, allowing its evaluation without determining the temperature and the quantity of the working fluid, which, with strong throttling, are practically unknown parameters. The results obtained showed the effect of the composition of the gas fuel and ignition misfire on the active heat release, and the efficiency of improving the stability of combustion for the economy of the engine. In this connection, the work is devoted to the analysis of the heat dissipation characteristics in experimental studies of new alternative gas fuels consisting of natural gas and hydrogen, which will allow us to better understand and quickly move to the design stage of new engines with increased efficiency of the combustion process at idle. This is certainly an important task, as modern trends in reducing the toxicity of automotive ICEs make it necessary to switch to gas fuels.