Gas Equation Of State Research Articles

A parameter determination method of powder burn model based on Levenberg-Marquardt optimization

ABSTRACT The powder burn model is a mathematical model used to characterize the combustion behavior of energetic materials. In this paper, a parameter determination method for the powder burn model is proposed based on the Levenberg-Marquardt (L-M) optimization algorithm, establishing connections between internal ballistics parameters and powder burn model parameters. Taking a 4/1 single-base propellant as an example, the detailed fitting process is presented, and error analysis is conducted. The fittings of the gas state equation and reaction rate equation of powder burn model converge at the 15th and 22nd iterations, respectively. Both fittings displayed a high level of accuracy, with an R-squared value of 0.999. The comparison with the results of the closed bomb experiments demonstrates excellent agreement between pressure-time curves calculated by the powder burn model and the internal ballistics model, confirming their suitability for describing the combustion behavior of propellants. This method provides a foundation for numerically simulating the internal ballistics combustion behavior of energetic materials.

Internal Pressure-Temperature Coupling Analysis Method for Thermal Decomposition of GFRP Composites Based on the Overlapping Elements Method.

A method of internal pressure-temperature coupling analysis for the thermal decomposition of GFRP composites under high-temperature conditions was established, which incorporates coupled calculations of heat transfer equations, the Arrhenius equation, Darcy's law, and the ideal gas state equation. Using the overlapping mesh method, the coupling calculation of temperature and internal pressure is realized based on the UMATHT and USDFLD user subroutines developed. Specifically, two user subroutines, UMATHT-1 and UMATHT-2, are used to define the heat transfer equation and gas diffusion equation separately. Numerical simulations are conducted to simulate the polymers' thermal decomposition in high-temperature environments. For glass fiber/vinyl ester composites and glass fiber/phenolic composites, the predicted temperature and pressure values are in good agreement with experimental measurements, and porosity and permeability are then analyzed. Due to the accumulation of thermal decomposition gases, inter-pressure within the material surged and reached a peak value. After that, it began to decrease, but the factors affecting the pressure decrease vary at different positions. Specifically, the pressure closest to the heating surface is influenced by the combined effects of decomposition rate, permeability, and porosity, while the pressure far away from the heating surface is only affected by the initial permeability. The pressure in the intermediate region may be influenced by both increased porosity and initial permeability.

Molecular CO2 Storage: State of a Single-Molecule Gas.

CO2 evolution is one of the urgent global issues; meanwhile, understanding of sorptive/dynamic behavior is crucial to create next-generation encapsulant materials with stable sorbent processes. Herein, we showcase molecular CO2 storage constructed by a [60]fullerenol nanopocket. The CO2 density reaches 2.401 g/cm3 within the nanopore, showing strong intramolecular interactions, which induce nanoconfinement effects such as forbidden translation, restricted rotation, and perturbed vibration of CO2. We also disclosed an equation of state for a molecular CO2 gas, revealing a very low pressure of 3.14 rPa (1 rPa = 10-27 Pa) generated by the rotation/vibration at 300 K. Curiously enough, the CO2 capture enabled to modulate an external property of the encapulant material itself, i.e., association of the [60]fullerenol via intercage hydrogen-bonding.

How negative feedback and the ambient environment limit the influence of recombination in common envelope evolution

ABSTRACT We perform 3D hydrodynamical simulations to study recombination and ionization during the common envelope (CE) phase of binary evolution, and develop techniques to track the ionic transitions in time and space. We simulate the interaction of a $2\, \mathrm{M_\odot }$ red giant branch primary and a $1\, \mathrm{M_\odot }$ companion modelled as a particle. We compare a run employing a tabulated equation of state (EOS) that accounts for ionization and recombination, with a run employing an ideal gas EOS. During the first half of the simulations, ∼15 per cent more mass is unbound in the tabulated EOS run due to the release of recombination energy, but by simulation end the difference has become negligible. We explain this as being a consequence of (i) the tabulated EOS run experiences a shallower inspiral and hence smaller orbital energy release at late times because recombination energy release expands the envelope and reduces drag, and (ii) collision and mixing between expanding envelope gas, ejecta and circumstellar ambient gas assists in unbinding the envelope, but does so less efficiently in the tabulated EOS run where some of the energy transferred to bound envelope gas is used for ionization. The rate of mass unbinding is approximately constant in the last half of the simulations and the orbital separation steadily decreases at late times. A simple linear extrapolation predicts a CE phase duration of ${\sim}2\, {\rm yr}$, after which the envelope would be unbound.

Numerical simulation of the diesel engine starting considering air pre-heating in the intake system

BACKGROUND: Low temperature of the intake air is one of the reasons of difficult starting of a cold diesel engine in conditions of negative outside temperatures. For a reliable staring of a cold diesel engine, it is necessary to have the temperature at the end of the compression stroke higher than the fuel self-ignition temperature. As the temperature at the end of the compression stroke is defined, first, by the temperature at the end of the intake stroke, the mentioned condition can be satisfied with preliminary warming of the air entering in a cylinder. AIMS: The article is devoted to solving the task related to development of a mathematical model of a diesel engine taking into account air pre-heating in the intake system and ensuring simulation of the pre-starting mode, starting and operation of a diesel engine in conditions of low negative outside temperature. METHODS: The enhanced mathematical model of a diesel engine basing on heat mechanics (thermodynamics of opened systems) which reflects main features of an internal combustion engine (ICE) as the system transforming energy in time domain is proposed in the article. The mathematical model’s equation system is based on laws of conservation of energy and mass, solid bodies’ motion equation and includes differential equations of changing of temperature and density of the working body in a cylinder, in the intake system and in the ICE’s crankcase, the ideal gas state equation as well as differential equations of changing of rotation velocity and rotation angle of an engine’s crankshaft. RESULTS: The mathematical model was tried out on the example of the 1Ch9.5/8.0 multi-purposed air-cooled diesel engine. The results of simulation of the pre-starting mode, starting and operation of the diesel engine taking into account air pre-heating in the intake system are presented in the article. CONCLUSIONS: Implementation of air pre-heating at the intake in the design of diesel engines is the most effective way of ensure starting of the engines at low negative outside temperature. The obtained results help to develop recommendations of choosing power and operation modes of pre-heating devices for ensuring starting and operation of diesel engines in conditions of low negative outside temperatures.

Numerical simulation and experiment of double chamber brake based on CFD

The artillery firing process will instantly produce high-temperature and high-pressure gunpowder gas, this process will produce shock waves. The gunpowder gas has a limited effect on the projectile during the firing and ballistic after-effects period, however, it has a very obvious effect on the stability of the gun body, and the reduction of the stability of the gun body directly affects the firing accuracy and the safety of the firing personnel. Based on the method of Computational Fluid Dynamics (CFD), numerical simulation is carried out, and the structure and flow parameters of the muzzle flow field are obtained by using three-dimensional Euler's control equation, gas equation of state, and k-epsilon model, as well as dynamic mesh technology. By comparing the flow parameters of the brake before and after optimization, and analyzing the results obtained from the 8-round firing experiments, the efficiency of the optimized brake is increased by 8.2%, and the deviation between the experimental data and the simulation results is only 10.5%, which not only verifies the accuracy of the numerical simulation calculations but also verifies the optimized brake's good retracting effect. The results of the study can provide a reference for the optimization and design of the double-chamber brake.

Bubble-Induced Strong Thermal Contraction for Graphene

Abstract The thermal expansion coefficient (TEC) of van der Waals (vdW) layered structures is of crucial importance in governing the dependability and longevity of advanced optoelectronic equipment. Bubbles are commonly found within layered structures, yet their impact on the thermal expansion coefficient of the structure is still not well understood. We derive an analytical formula that describes the influence of bubbles on the variation in length, utilizing both the elastic membrane theory and the improved van der Waals gas state equation. The results demonstrate that as the temperature increases, bubbles can induce significant thermal contraction in few-layer graphene structures. The analytical predictions are validated through molecular dynamic (MD) simulations, confirming the accuracy and reliability of the proposed model. These findings hold significant value in enhancing our understanding of the dependability and durability of functional equipment that relies on van der Waals layered structures.

A level-set method for ultrasound-driven bubble motion and tissue deformation

Ultrasound-driven bubble collapse and resulting tissue deformation are numerically investigated by combining a level-set method for determining the liquid–gas and liquid–solid interfaces and a full Eulerian method to solve the unified governing equations for both solid and fluid phases. The fluid compressibility effect is considered by employing the van der waals and Tait equations of state for gas and liquid, respectively, and a semi-implicit pressure correction method is used to effectively capture ultrasound and shock waves. Two tissue models, treating tissue as a viscoelastic solid or as a fluid with large surface tension, are compared in terms of the bubble expansion and compression processes and tissue deformation patterns. Computations are also carried out to investigate the influences of ultrasonic pulse amplitude, ultrasound frequency, and bubble-tissue distance on the bubble-tissue interaction.

Applicability Evaluation of Natural Gas State Equations at Low Temperatures

The paper analyzes the possibility of operating range expanding of natural gas state equations for low temperatures. The state equations of natural gas and methods of estimating the compressibility factor, entrenched in modern national and international standards, were analyzed. It has been shown that the range of their applicability is limited to a temperature value of 250 K, however, these temperature limitations is not restricted bystate equations directly butstipulated by the lack of reliable data about natural gas compressibility factor values at temperatures below 250 K and methods for complementary errorcalculation that may arise. The results of comparison of values of natural gas compressibility factor as a function of temperature at pressure of 1.3 and 6 MPa calculated by means of the most widely used state equations are presented. It was found that the results of the calculation according to the considered methods have satisfactory convergence within the range of 220 K, that generally confirms the applicability of modern state equations for low temperatures. In its turn, the effect of assumptions applied nowadays to definegas volume flow rateon flow metering error showed that application of substitutive compressibility values may result in significant complementary systematic error. This indicates the practicability of expanding the database of compressibility factor values for natural gas for low temperatures, as well as developmentof a standard to assess the value of the corresponding complementary error.

Simulation and experimental investigation of high-pressure pneumatic pilot-driven on/off valve with high transient performances for compressed air ejection

A high-pressure pneumatic pilot-driven on/off valve (HPPV) that quickly switches an air inlet line on and off was designed to meet the requirements of a compressed air ejection device with high pressure, high flow rate, and continuous ejection. An HPPV multi-physics field simulation model was established using AMESim simulation software based on the bond graph modeling approach that considered mechanical, gas flow, pipe heat exchange, and pilot valve operation, and experiments were conducted to check the simulation model accuracy. The effects of real gas thermodynamics, pipeline heat exchange, and pilot valve operation on the simulation model accuracy and those of different initial parameter conditions on the dynamic characteristics of the HPPV were investigated in the validated simulation model. The results indicated that the tolerance between simulation and experiment was less than 7.3%, so the simulation model was realistic and reliable. In addition, among the different influencing factors, the pipeline heat transfer significantly affected the simulation model accuracy, and the tolerance between the simulation results without considering the pipeline heat exchange and the experimental results exceeded 10%. The real gas thermal effect slightly affected the simulation model accuracy, and the tolerance between the simulation results under the action of each gas state equation was less than 3%. The pilot valve operation affected only the opening and closing moments of the HPPV and had no effect on the simulation model accuracy. The dynamic characteristics of the HPPV were stable and reliable under different initial parameter conditions.

Phase transitions in systems of particles with only hard-core interactions

This article contains our comments and views on the status of the current understanding of phase transitions in systems in thermodynamic equilibrium with only hard-core interactions, based on our work in this area. The equation of state for the hard sphere gas in d-dimensions is discussed. The universal repulsive Lee-Yang singularity in the complex activity plane, and its relation to the directed and undirected polymer models are outlined. We also discuss orientationally disordered crystalline mesophases, and some of their models.

Modulational instability of ion-acoustic waves in a dense quantum plasma

Modulational instability of ion-acoustic (IA) waves is investigated in an unmagnetized quantum plasma by adopting an equation of state for Fermi electron gas. To this end, a basic set of one-dimensional quantum hydrodynamic equations is reduced to a nonlinear Schrödinger equation using the reductive perturbation method. Quantum corrections are described using a nondimensional quantum parameter H proportional to the quantum diffraction parameter. Based on normalized electron temperature and chemical potential, new quantum criteria of modulational instability for IA waves are obtained and analyzed. Moreover, formation of rogue waves due to the modulational instability of IA waves and propagation of modulated IA packets in the form of bright and dark envelope solitons are examined for two different types of astrophysical plasma regions: white dwarf stars and warm dense matter.

Interpretation of covolume in an extension of the Redlich–Kwong equation of state for real gases

Interpretation of covolume in an extension of the Redlich–Kwong equation of state for real gases

Numerical investigation of the effects of inlet conditions and wall heat transfer on subcritical/transcritical CO2 nozzle performance

In ejector-based refrigeration cycles and CO2 heat pump cycles, inlet flow state and wall heat transfer play an important role in improving nozzle performance. A CO2 two-phase nozzle model was firstly established. Then, the numerical model is validated by experimental data and void fraction correlation, and the effect of condensation coefficient and gas equation of state was analyzed. In addition, the CO2 flow behavior and the thermodynamic performance of the nozzle under different inlet gas phase volume fraction (GVF) and wall conditions (temperature and materials) were studied. The results show that although the GVF can reduce the critical mass flow rate of the nozzle, its adverse impact on the thermodynamic performance of the nozzle is more significant (The GVF varied from 0 to 0.6, with the former decreasing by 10.2% and the latter increasing by 25.1%). Low temperature on the wall will exacerbate the non-equilibrium phase transition, leading to an increase in the critical mass flow rate of the nozzle. At this time, high thermal conductivity walls will also exacerbate exergy losses, by using low thermal conductivity walls can improve the consequences. In addition, the study also found that the inlet supercooling degree (ISCD) should be set between 0 and 7 K, and excessive ISCD would lead to an increase in outlet humidity and a rise in critical mass flow.

An examination of the logotropic equation of state for Chaplygin gas and a generalized holographic model, as well as thermodynamic analysis utilizing scalar fields

This study proposes a method to reconstruct a generalized form of holographic dark energy and to analyse its cosmology, based on a logotropic equation of state. By assuming that the dark energy density is caused by holographic Ricci dark energy, one can calculate a scale factor for the universe’s overall energy density, provided by baryons, dark matter, and dark energy density. For the situation where the internal energy is in logarithmic form, the equation of state parameter is similarly obtained. In the following stage, a generalized Chaplygin gas is investigated using a logotropic equation of state, considering the scenario of a logarithmic internal energy. Modified generalized Chaplygin gas is also examined in the situation of logarithmic internal energy with logotropic equation of state, and related reconstruction is carried out. The generalized second law of thermodynamics is subsequently validated for event, particle, and Hubble horizons after taking into account the phantom and quintessence models using a logotropic technique.

Chemical Modeling of Constant-Volume Combustion of the Mixture of Methane and Hydrogen Used in Spark Ignition Otto Cycles

This paper develops a chemical model for a closed constant-volume combustion of a gaseous mixture of methane and hydrogen. Since the combustion is strongly dependent on temperature, pressure and fuel composition, these had chosen the actual corresponding thermodynamic systems in this kind of combustion, i.e., spark ignition (SI) reciprocating engines, to assess combustion parameters and flue gas composition. The actual cycles impose extra restrictive operational conditions through the engine’s-volumetric-compression ratio, the geometry of the combustion volume, the preparation method of the mixture of methane and hydrogen, (e.g., one fueling way of a homogeneous mixture obtained in a specific device or by two separate fueling ways for components), the cooling system and the delivered power. The chemical model avoided the unknown influences in order to accurately explain the influence of hydrogen upon constant-volume combustion and flue gas composition. The model adopted hypotheses allowing to generalize evaluated results, i.e., the isentropic compression and expansion processes, in closed constant-volume combustion caused by two successive steps that obey the energy and mass conservation laws, and the flue gas exhaust, which is also described by two steps, i.e., isentropic expansion through the flow section of exhaust valves followed by a constant pressure stagnation (this process, in fact, corresponds to a direct throttling process). The chemical model assumed the homogeneous mixtures of gases with variable heat capacity functions of temperatures, the Mendeleev—Clapeyron ideal gas state equation, and the variable chemical equilibrium constants for the chosen chemical reactions. It was assumed that the flue gas chemistry prevails during isentropic expansion and during throttling of exhaust flue gas. The chemical model allowed for evaluation of flue gas composition and noxious emissions. The numerical results were compared with those recently reported in other parallel studies.

Stationary solutions of the Schrödinger-Poisson-Euler system and their stability

We present the construction of stationary boson-fermion spherically symmetric configurations governed by Newtonian gravity. Bosons are described in the Gross-Pitaevskii regime and fermions are assumed to obey Euler equations for an inviscid fluid with polytropic equation of state. The two components are coupled through the gravitational potential. The families of solutions are parametrized by the central value of the wave function describing the bosons and the central density of the fluid. We explore the stability of the solutions using numerical evolutions that solve the time dependent Schrödinger-Euler-Poisson system, using the truncation error of the numerical methods as the perturbation. We find that all configurations are stable as long as the polytropic equation of state (EoS) is enforced during the evolution. When the configurations are evolved using the ideal gas EoS they all are unstable that decay into a sort of twin solutions that approach a nearly stationary configuration. We expect these solutions and their evolution serve to test numerical codes that are currently being used in the study of Fuzzy Dark Matter plus baryons.

Numerical investigation on acoustic cavitation characteristics of an air-vapor bubble: Effect of equation of state for interior gases

The cavitation dynamics of an air-vapor mixture bubble with ultrasonic excitation can be greatly affected by the equation of state (EOS) for the interior gases. To simulate the cavitation dynamics, the Gilmore-Akulichev equation was coupled with the Peng–Robinson (PR) EOS or the Van der Waals (vdW) EOS. In this study, the thermodynamic properties of air and water vapor predicted by the PR and vdW EOS were first compared, and the results showed that the PR EOS gives a more accurate estimation of the gases within the bubble due to the less deviation from the experimental values. Moreover, the acoustic cavitation characteristics predicted by the Gilmore-PR model were compared to the Gilmore-vdW model, including the bubble collapse strength, the temperature, pressure and number of water molecules within the bubble. The results indicated that a stronger bubble collapse was predicted by the Gilmore-PR model rather than the Gilmore-vdW model, with higher temperature and pressure, as well as more water molecules within the collapsing bubble. More importantly, it was found that the differences between both models increase at higher ultrasound amplitudes or lower ultrasound frequencies while decreasing as the initial bubble radius and the liquid parameters (e.g., surface tension, viscosity and temperature of the surrounding liquid) increase. This study might offer important insights into the effects of the EOS for interior gases on the cavitation bubble dynamics and the resultant acoustic cavitation-associated effects, contributing to further optimization of its applications in sonochemistry and biomedicine.

Research on Characteristics of Hydrogen Dynamic Leakage and Combustion at High Pressure

Hydrogen is promoted as an alternative energy given the global energy shortage and environmental pollution. A scientific basis can be provided for the safe use and emergency treatment of hydrogen based on hydrogen leakage and combustion behavior. This study examined the stagnation parameters of dynamic hydrogen leakage and flame propagation in turbulent jets under normal temperatures and high pressure. Based on van der Waals’ equation of state for gas, a theoretical model for completely predicting stagnation parameters, outlet gas velocity, and flow rate changes in the process of high-pressure hydrogen leakage could be proposed, and the calculation result of this model was compared with the experimental result, with an error within ±10%. The progression and propagation of the flame in turbulent jets after ignition were recorded using the background-oriented schlieren image technology, and the propagation speed of flame from the ignition position downward and upward was calculated. Moreover, the influence of initial pressure, nozzle diameter, and ignition position on the flame propagation process and propagation speed was analyzed.

Numerical simulation and investigation of methane gas distribution and extraction in goaf with U-type ventilation of working face

The accumulated methane in goaf during coal mining may leak into the working face under the airflow influence, which is possibly causing disasters such as methane gas excessive at the working face and seriously threatening the mine safety. This paper first established a three-dimensional numerical model of the mining area under U-shaped ventilation, introducing the gas state equation, continuity equation, momentum equation, porosity evolution equation, and permeability evolution equation to simulate the airflow field and gas concentration field in the mining area under the natural state. The reliability of the numerical simulations is then verified by the measured air volumes at the working face. The areas in the mining area where gas is likely to accumulate are also delineated. Subsequently, the gas concentration field in goaf under the gas extraction state was theoretically simulated for different locations of large-diameter borehole. The maximum gas concentration in goaf and the gas concentration trend in the upper corner were analyzed in detail, and the critical borehole location (17.8m from the working face) was determined as the optimum location for gas extraction from the upper corner. Finally, a gas extraction test was carried out on-site to evaluate the application effect. The results show that the measured airflow rate has a small error with the simulated results. The gas concentration in the area without gas extraction is high, with the gas concentration in the upper corner being over 1.2%, which is greater than the critical value of 0.5%. The maximum reduction in gas concentration was 43.9%, effectively reducing the gas concentration in the extraction area after employing a large borehole to extract methane gas. The gas concentration in the upper corner and the distance of the borehole from the working face are expressed as a positive exponential function. The field engineering results show that the implementation of the large borehole at a distance of less than 17.8m from the working face can control the gas in the upper corner to less than 0.5%, effectively reducing the risk of gas in the upper corner. The numerical simulation work in this paper can provide some basic support for the design of an on-site borehole to extract gas from the mining void and reduce the gas hazard in coal mines.