Gas Thermodynamic Properties Research Articles

Method for considering real gas equations of state in through-flow programs

Numerical methods are significant in the turbomachine design process and off-design analysis. One of these methods is the through-flow method in the meridional plane, which is utilized in an early design phase. It provides a robust and quick numerical turbomachinery analysis by only giving a few characteristic geometric parameters.This work shows an extension of the through-flow method by considering real gas equations of state (EOSs) in throughflow programs. This is implemented in an in-house through-flow program called tFlow. This enables the method to support a more reliable calculation regarding, for instance, carbon dioxide (CO2) in a high-pressure region, where the gas does not behave like an ideal gas. The incorporation of real gas EOSs is validated with two-dimensional (2D) calculations of nozzle flows and with quasi-three-dimensional (3D) calculations of supercritical CO2 (sCO2) centrifugal compressors. A straightforward method for modifying the Riemann inlet boundary conditions for real gases is presented enabling a quick extension of through-flow codes to real gases and providing a stable solution process. Look-up tables (LUTs) are used instead of common high-degree polynomials to solve the real gas thermodynamic properties and reduce the computation time by a factor of about 20. Additionally, the calculation results verify the application of the Jameson–Schmidt–Turkel (JST) scheme in terms of real gas EOSs. Finally, the predictions are compared against 1D solutions for 2D cases and against the experimental data of the sCO2-HeRo compressor for 3D cases.

Slug flow parameters applied to dynamic riser analysis

Slug flow is a typical pattern in the petroleum production system. Its main feature is intermittency. This feature influences the riser dynamic behavior due to the coupling of its geometric configuration and time and space variation of internal fluid parameters. Although the studies that illustrate slug flow intermittency and dynamic riser behaviors have been growing recently, this discussion still needs to be expanded. Most slug models proposed in the literature are simplified and do not adequately capture the intermittency to a proper riser dynamic influence determination. Previous models neglected at least one of the following slug flow mechanisms: random features, bubble shape, liquid slug aeration, wake, and pipeline inclination effects. This paper aims to cover all these phenomena and present a model that provides realistic slug flow data for any riser analysis program. The dynamic riser analysis is not the scope of this paper. This article used a new slug tracking model that captures the intermittency to study the influence of the internal flow over the dynamic riser behavior. The model considers the liquid slug hold-up and its change over the pipe, the oil and gas thermodynamic properties, and the geometrical transition from typically horizontal plane interfaces to vertical concentric bubble shapes. The slug tracking model tests use three gas and liquid ratios (0.55, 0.7, and 0.82) with a 2.05 m/s constant mixture velocity. The maximum relative pressure deviation was 24.1. Time and space analysis of the slug flow parameters demonstrates the slug tracking capacity to reproduce the intermittency of the bubble and liquid slug lengths, void fractions, velocities, and pressures. This intermittence is essential to describe the internal slug flow influence on the structure behavior.

Theoretical calculations to investigate thermodynamic properties of 2D electron gas in InP/InPBiN quantum structure

The electronic band structure of InP/InNPBi has been theoretically investigated within the framework of the band anticrossing (BAC) model. The matched InP/InNPBi heterostructure has been proposed as an interface that confines electrons in a 2D sheet. The physical parameters of this structure are determined considering the BAC model and based on the self-consistent calculation of coupled Schrodinger-Poisson equations. Thermodynamic properties of the quantum gas of noninteracting electrons are investigated by calculating the chemical potential (μ), the magnetization (M), and the specific heat capacity (Cv) in the presence of a quantizing magnetic field and a finite temperature. The effect of characteristic parameters of the structure (broadening parameter, doping level, and effective mass) on the thermodynamic properties of gas is discussed. More interest is focused on the study of the evolution of Cv as a function of temperature for different estimated effective masses of InNPBi material.

An Apparent Permeability Model in Organic Shales: Coupling Multiple Flow Mechanisms and Factors.

It is of great significance to study shale apparent permeability under the action of multiple flow mechanisms and factors because shale reservoirs possess complex pore structures and flow mechanisms. In this study, the confinement effect was considered, with the thermodynamic properties of gas being modified, and the law relating to the conservation of energy adopted to characterize bulk gas transport velocity. On this basis, the dynamic change of pore size was assessed, from which shale apparent permeability model was derived. The new model was verified by three steps: experimental and molecular simulation results of rarefied gas transport, shale laboratory data, and comparison with different models. The results revealed that, under the conditions of low pressure and small pore size, the microscale effects became obvious, which significantly improved gas permeability. Through comparisons, the effects of surface diffusion and matrix shrinkage, including the real gas effect, were obvious in the smaller pore sizes; nevertheless, the stress sensitivity effect was stronger in larger pore sizes. In addition, shale apparent permeability and pore size decreased with an increase in permeability material constant and increased with increasing porosity material constant, including internal swelling coefficient. The permeability material constant had the greatest effect on gas transport behavior in nanopores, followed by the porosity material constant; however, the internal swelling coefficient had the least effect. The results of this paper will be important for the prediction and numerical simulation of apparent permeability relating to shale reservoirs.

Self-similar analysis of gas dynamics for van der Waals gas in slipping flow after normal shock wave

A self-similar model of gas dynamics and heat transfer behind the shock wave was developed with allowance for the effects of slippage and dissipation. The model takes into account the impact of the following factors: shock wave intensity (U∞/Us), physical properties (Prandtl number Pr), thermodynamic gas properties (van der Waals numbers Waa, Wab), slippage effects (Knundsen number Kn), and dissipation (Brinkman number Br), as well as the relation of the temperatures of the flow and the wall (T0/Tw). The numerical solution was performed with the help of MATLAB software, as well as an in-house code written using the programming language C++ to verify the accuracy of calculations. The study demonstrated that for the case at hand, the Reynolds analogy holds under the influence of all mentioned factors provided that Pr = 1, except for the conditions when the effects of mechanical energy dissipation become significant. The paper presents the results of calculations of the velocity and temperature profiles, friction, and heat transfer coefficients (Nusselt numbers).

A new calculation method for the free electron fraction of an ionization chamber in the ultra-high-dose-per-pulse regimen

The free electron fraction is the fraction of electrons, produced inside the cavity of an ionization chamber after irradiation, which does not bind to gas molecules and thereby reaches the electrode as free electrons. It is a fundamental quantity to describe the recombination processes of an ionization chamber, as it generates a gap of positive charges compared to negative ones, which certainly will not undergo recombination.The free electron fraction depends on the specific chamber geometry, the polarizing applied voltage and the gas thermodynamic properties. Therefore, it is necessary to evaluate such fraction in an accurate and easy way for any measurement condition.In this paper, a simple and direct method for evaluating the free electron fraction of ionization chambers is proposed.We first model the capture process of the electrons produced inside an ionization chamber after the beam pulse; then we present a method to evaluate the free electron fraction based on simple measurements of collected charge, by varying the applied voltage. Finally, the results obtained using an Advanced Markus chamber irradiated with a Flash Radiotherapy dedicated research Linac (ElectronFlash) to estimate the free electron fraction are presented.The proposed method allows the use of a conventional ionization chamber for measurements in ultra-high-dose-per-pulse (UHDP) conditions, up to values of dose-per-pulse at which the perturbation of the electric field due to the generated charge can be considered negligible.

Triple-Nozzle Thermo-Compressor: Geometrical Investigation and Comparison with Single-Nozzle Thermo-Compressor

Primary nozzle is one of the most important factors which has a large influence on the performance of thermo-compressors. Most of studies carried out until now, have been performed on single-nozzle thermo-compressors. In this paper, an actual industrial thermo-compressor is considered and the purpose is to study the effect of increasing primary nozzle number on the performance of this thermo-compressor. For this purpose, a triple-nozzle thermo-compressor is simulated numerically and its performance is compared with single-nozzle thermo-compressor. Ideal gas thermodynamic properties are considered to simulate the compressible flow within the thermo-compressor and numerical result is validated using the experimental result. In addition, the effects of variation in mixing chamber convergence angle and position of nozzles at the radial direction in triple-nozzle thermo-compressor are investigated. The numerical results show that at the same condition, a triple-nozzle thermo-compressor is able to provide superior critical back pressure and entrainment ratio than single-nozzle thermo-compressor. The proximity of nozzles (with 34% changes in radial distance) increases the critical back pressure about 8% and decreases the entrainment ratio about 5%. By increasing mixing chamber convergence angle about 66%, the value of critical back pressure decreases about 29% and the value of entrainment ratio decreases about 16% in single nozzle-thermo-compressor and 10% in triple-nozzle thermo-compressor. Also, by 8% reduction of mixing chamber convergence angle, the critical back pressure decreases 6% but entrainment ratio decreases about 2% in single-nozzle thermo-compressor and increases about 3% in triple-nozzle thermo-compressor.

Scaling Flat Plate Overall Effectiveness Measurements

AbstractLow temperature experiments are often performed on models of cooled turbine components in order to predict the temperature of the actual turbine component at engine conditions. Designing the scaled experiment properly takes care beyond simply matching the freestream Reynolds number. For instance, it is well known that for the overall effectiveness to match that at engine conditions, the Biot number of the experimental model must match that of the engine component. Somewhat less clear is the method by which one must scale the coolant flowrate. Widely used coolant flowrate parameters have generally been informed based on the results of adiabatic effectiveness experiments and it remains unclear how well these parameters also allow for matched overall effectiveness, which is highly dependent on internal cooling. In the present work, overall effectiveness distributions were measured on a flat plate with three rows of zero-degree compound angle 7-7-7 shaped holes. The influence of various thermodynamic gas properties was examined using several foreign gases as the coolant while matching coolant flowrate parameters M, I, and ACR. It is shown that the thermal conductivity of the coolant plays an outsized role in the overall effectiveness, but this is not accounted for with any of the traditional coolant flowrate parameters. With significant thermal conductivity variations possible between the coolant and freestream gas at both engine and experimental conditions, consideration of this effect is of vital importance to the experimentalist.

PyGeochemCalc: A Python package for geochemical thermodynamic calculations from ambient to deep Earth conditions

Over the past half century, techniques for evaluating the thermodynamics of water-rock interactions from ambient to deep Earth conditions have advanced incredibly and in myriad directions. As these tools for analyzing the thermodynamic states of geochemical species as a function of temperature, pressure, and composition have multiplied, so too have the possibilities for tracing water-rock interaction from ambient to deep conditions on Earth and beyond. Yet, the aqueous geochemical community still lacks a centralized platform for incorporating this constantly updating thermodynamic data into aqueous geochemical models. Here, we introduce PyGeochemCalc (PyGCC), a community-driven, open-source Python package that meets this need by providing a consolidated set of functions for calculating the thermodynamic properties of gas, aqueous, and mineral (including solid solutions and variable-formula clays) species, as well as reactions amongst these species, over a broad range of temperature and pressure conditions. The PyGCC package utilizes the revised Helgeson-Kirkham-Flowers (HKF) equation of state, and newly proposed density-based extrapolations based upon it, to calculate the thermodynamic properties of aqueous species; a choice of equations of state and electrostatic models (including the Deep Earth Water (DEW) model) to calculate thermodynamic and dielectric properties of water; and heat capacity functions to calculate thermodynamic properties of minerals and gases. Additionally, PyGCC integrates these functions to generate thermodynamic databases for various geochemical programs, including the Geochemist's Workbench (GWB), EQ3/6, TOUGHREACT, and PFLOTRAN, with straightforward possibilities for extension to other simulators. The various functions in the package can also be modularly utilized, and introduced into other modeling tools, as desired. In this paper, we detail the capabilities of PyGCC and the equations it relies on for calculating thermodynamic properties of water, aqueous species, and gases. Although the fundamental thermodynamic data necessary for state-of-the-science PyGCC calculations will necessarily evolve as our collective geochemical knowledge base expands, PyGCC's open source, community-driven design will allow for users to keep pace via rapid implementation of these advancements in this modern geochemical tool.

Data Programs at NBS/NIST: 1901–2021

A detailed overview is provided of the vast number of innovative data programs over 120 years at the National Bureau of Standards (NBS)/National Institute of Standards and Technology (NIST). These programs provide critically evaluated data used throughout the world. The NBS was founded in 1901 through an act of Congress and in 1988 renamed as the NIST. Measurement and dissemination of scientific data to support competitiveness in American industry has been the core of its mission from the beginning. The National Standard Reference Data System (NSRDS) at NBS was established in 1963, followed by the SRD Act of 1968 to establish data evaluation centers and coordinated comprehensive programs to ensure that reliable reference data are easily accessible by scientists, engineers, and the general public. The Journal of Physical and Chemical Reference Data (JPCRD), started in 1972, has now published 50 volumes. NSRDS and JPCRD publications have provided widely employed print databases in many areas of science; these databases were expanded to computer databases in the 1980s and then to web-based databases in the 1990s. The data programs at NBS/NIST provide critically evaluated data in areas such as the thermodynamic properties of gas- and condensed-phase compounds, their multicomponent mixtures as well as chemical reactions, ceramic-phase equilibria, crystallographic data, refrigerants, water/ice/steam, gas-phase ionic species, atomic energy levels and molecular spectra, molecular mass spectra and peptide mass spectra, chemical kinetics, the CODATA fundamental constants of nature, and the International Union of Pure and Applied Chemistry International Chemical Identifier (InChI).

Thermodynamic Properties of Fluids from Speed of Sound: Integration Along Isentropes

The equations connecting speed of sound with other thermodynamic properties of gases and liquids, suitable for numerical integration with respect to temperature, density, and pressure, along isentropes, are derived. Algorithms of their solution are given too. They are tested with several substances (e.g., Ar, N2, O2, CH4, CO2, and H2O) in wide ranges of pressure and temperature. Average absolute deviation of thermal properties is 0.0129% in supercritical gaseous phase, 0.0308% in transcritical gaseous phase, and 0.0009% in liquid phase. Corresponding deviations of caloric properties are 0.1706%, 0.1863%, and 0.0702%, respectively.

Analysis of the second virial coefficient, and application to rare gas mixtures

Abstract The second virial coefficients characterize the real-gas non-ideality caused by the interaction between molecular pairs and ensure a link between macroscopic thermodynamic properties and microscopic molecular interactions because they depend on intermolecular interaction energy and temperature. Therefore, the second virial coefficients that are suitable for calculating the thermodynamic properties of gases used in the many fields in this work are preferred. In this study, a semi-analytic representation for the second virial (SV) coefficient over exponent–spline-Morse-spline-van der Waals potential (ESMSV), investigating the thermodynamic properties of rare gases, is presented. In the study the series formulae of the hypergeometric function, exponential function, gamma function, Meijer function, and binomial expansion have used in the suggested method. The numerical approach has been used mostly to evaluate the SV coefficient with ESMSV potential in literature. This unified formula can be applied and tested for rare gases. The obtained results for the SV coefficient over ESMSV potential of 4He–4He, 4He–Ne, 4He–Ar, 4He–Kr, 4He–Xe, Ne–Ne, O2–O2, and Ar–O2 rare gases have been compared with alternative experimental data and numerical calculations and shown that semi-analytical expression can be successfully applied to evaluate simple fluids.

Stationary Mach Configurations with Pulsed Energy Release on the Normal Shock

We obtained a theoretical analysis of stationary Mach configurations of shock waves with a pulsed energy release at the main (normal) shock and a corresponding change in gas thermodynamic properties. As formation of the stationary Mach configuration corresponds to one of two basic, well-known criteria of regular/Mach shock reflection transition, we studied here how the possibility of pulsed energy release at the normal Mach stem shifts the von Neumann criterion, and how it correlates then with another transition criterion (the detachment one). The influence of a decrease in the “equilibrium” gas adiabatic index at the main shock on a shift of the solution domain was also investigated analytically and numerically. Using a standard detonation model for a normal shock in stationary Mach configuration, and ordinary Hugoniot relations for other oblique shocks, we estimated influence of pulsed energy release and real gas effects (expressed by decrease of gas adiabatic index) on shift of von Neumann criterion, and derived some analytical relations that describe those dependencies.

Numerical Comparison of Transpiration Cooling Designs Using Real Gas Effects and Approximate Gas Model

In the severe high-temperature environment caused by aerodynamic heating, the vibrational excitation, dissociation and ionization of gas may successively occur, which are known as real gas effects. Under the real gas effects, the thermodynamic properties of gas vary drastically and significantly influence the performances of the active thermal protection system of hypersonic vehicles, especially in the case with coolant outflow, for example transpiration cooling. This paper numerically investigates the transpiration cooling performance with the consideration of the interaction between coolant outflow and hypersonic flow under the real gas effects. The mathematical models and coupled numerical strategy are firstly validated by experimental data, then the influences of real gas effects on the transpiration cooling of a wedged leading edge (WLE) are studied under a flight Mach number range from 8 to 12 and a flight height of 40 km. The analysis and discussions of the numerical results reveal some important phenomena and demonstrate the need to consider real gas effects.

Artificial Bee Colony-Artificial Neural Network (ABC-ANN) Hybrid Algorithm’s Performance on the Modeling of Thermodynamic Properties of a Refrigerant Gas (R404a)

ABSTRACT In this study, it was aimed to determine the thermodynamic properties of an environmentally friendly refrigerant (R404a) for both the saturated liquid–vapor region (wet vapor) and superheated vapor region, in the temperature range of 173–498°K, and the pressure range of 10–3600 kPa by using an adaptive artificial neural network algorithm. Performing the analysis of these gases with differential equations by using a computer is very time consuming and requires high computational power for calculation. Using numerical equations for modeling the thermodynamic properties of gasses to eliminate these drawbacks is a more accurate approach and this modeling can be accomplished with artificial intelligence algorithms such as the Artificial Neural Network (ANN). The proper selection of the activation function, which is one of the most important parameters for ANN, directly affects the validity of the model according to the problem and its application. In this study, an adaptive ANN was developed in which the optimal activation function combination was found by using the ABC algorithm and thus the error of the network were reduced when compared to the classical ANN. The improvements of in percentage errors were observed to increase from 7.55% to 76.68%. Finally, the accuracy of the numerical equations that describe the thermodynamic properties of R404a gas was increased. Using this technique helps to figure out the performance of the gas under related working conditions.

The influence of friction on gas parameters in the minimum section of nozzles

Processes of gas flow in nozzles, accompanied by the release of frictional heat, are presented in the form of polytropic processes. The polytropic process index n determines the degree of irreversibility of the gas flow process caused by the release of frictional heating. Relations are obtained to calculate the flow rate and thermodynamic properties of gas in the minimum section of the Laval nozzle and in the outlet section of the convergent nozzle at a pressure behind the nozzle less than the critical pressure. The gas calculated parameters (pressure, temperature, specific volume, velocity, cross-sectional area) in the minimum cross-section differ from the recommended values in the reference literature [1]. In particular, the gas pressure in the minimum cross section turns out to be higher than the critical pressure recommended in [1].

Alternative test method of internal arcing for replacing SF6 by air in SF6-insulated power equipment

To develop an alternative test method of internal arcing for replacing sulfur hexafluoride (SF6) by air in SF6-insulated power equipment, it is important for the public safety to clarify the thermal effect of hot SF6 and air from the equipment on the surroundings. In this study, an analytical model for evaluating the incident heat energy on a metal plate by exhausted hot gas was developed and validated. SF6-air mixtures with a range of gas thermodynamic and transport properties up to 30,000 K were modelled using computational fluid dynamics (CFD) to simulate the increase in pressure. The analytical results are investigated using the experimental results on SF6-air mixtures. Subsequently, a method of setting the test conditions for the internal arc testing in SF6-insulated power equipment, is proposed based on the analytical model. Using the mixture model, assuming an alternative arcing test for replacing SF6 by air in the SF6-insulated power equipment, the method of setting a current or the duration of current is demonstrated and verified. The results indicate that the current and duration of current can be set such that the incident heat energy on the metal plate by exhausted hot gas are approximately equalized. This study could establish an alternative test method of internal arc in SF6-insulated power equipment.

Transonic flows of single-phase supercritical fluids over thin airfoils

Abstract

Free electron gas and electron–positron pair equilibrium in a magnetic field

The thermodynamic properties of electron gas under the extreme conditions of high temperature, high matter density, and/or a strong magnetic field largely determine the behavior of matter in upper layers of neutron stars and accretion columns of magnetized neutron stars in binary systems. A strong magnetic field in these objects makes the motion of electrons across the field essentially quantum. The possible electron degeneracy and relativism of electrons are also important. When studying accretion onto a magnetar in a binary system, the intensive generation of electron–positron pairs in the quantizing magnetic field should also be taken into account. We consider in detail the thermodynamic properties of a gas of free electrons in strong magnetic fields, taking into account their relativism and degeneracy, as well as the equilibrium creation of electron–positron pairs in a high-temperature plasma in the presence of a quantizing magnetic field.

Rydberg impurity in a Fermi gas: Quantum statistics and rotational blockade

We consider the quench of an atomic impurity via a single Rydberg excitation in a degenerate Fermi gas. The Rydberg interaction with the background gas particles induces an ultralong-range potential that binds particles to form dimers, trimers, tetramers, etc. Such oligomeric molecules were recently observed in atomic Bose-Einstein condensates. In this work, we demonstrate with a functional determinant approach that quantum statistics and fluctuations have observable spectral consequences. We show that the occupation of molecular states is predicated on the Fermi statistics, which suppresses molecular formation in an emergent molecular shell structure. At large gas densities this leads to spectral narrowing, which can serve as a probe of the quantum gas thermodynamic properties.