Adiabatic Index Research Articles

Compensation of composition variation-induced sensitivity changes in gas phase photoacoustics

Infrared photoacoustic (PA) spectroscopy is a widely used technique to monitor trace gas concentration changes during industrial processes where the bulk composition may vary considerably. However, the PA signal is prone to changes in bulk composition, leading to relative uncertainties in measurements of up to 10%, due to the complex dependence of the sensitivity of a PA system (S) on the thermal and acoustic properties of the gas sample. A novel calibration and concentration calculation method is proposed to keep the relative accuracy of the PA measurements in the few percentages range even in case of large-scale composition variations. The main novelty of the proposed method is that it tackles the complex dependence of the PA system's sensitivity in a way that while it varies the resonance frequency of the calibration gas, it keeps the heat capacity ratio of calibration gases at a constant value. We prove that it determines the analyte’s concentration with relative accuracy of about 1 %, even when the composition of the gas varies drastically. It rigorously compensates for the frequency and heat capacity ratio dependence of S and for the dependence of the half-width of the resonance curve of the PA cell on the thermal and acoustic properties of the gas. Although the reported demonstration measurements are executed in a relatively simple gas mixture, the proposed method has widespread applicability in high-precision monitoring.

Computational modeling of heat transfer and flow separation in supersonic cooled nozzles: Parametric study

Flow separation is necessary for the construction of a rocket engine nozzle. Regenerative cooling is one of the most significant criteria for the safety of wall nozzles because of the high temperature and pressure in the thrust chamber. A review of a comprehensive numerical investigation of the boundary layer separation and heat transfer in a 30??15? cooled nozzle is presented. The accuracy of the SST-V turbulence model in this study was numerically investigated. For this purpose and for a wide range of chamber conditions, the effects of various parameters, such as wall temperature, turbulent Prandtl number, and constant specific heat ratio vary from 1.31 to 1.4 for constant fluid properties for N2O, CH4, Cl2, and air, respectively. The variable specific heat ratio ranged from 1.39 to 1.66 for variable fluid properties for air, CH4, O2 and Helium, respectively, and we investigated how various parameters impact the position of flow separation and local wall heat transfer.

STABILITY OF MACROSCOPIC BODY COSMOLOGICAL MODEL IN RUBAN’S BACKGROUND

In this paper, the Barber Self-Creation theory of gravitation is used to examine the stability of the cosmological model in the Ruban’s background in the presence of macroscopic body. Exact solution is obtained by considering the relation between metric coefficients and radiation. The physical, kinematical, and thermodynamical aspects of the derived cosmological model have been examined. The relationship between sound speed, causality, and adiabatic index are used to discuss the stability of these models. Also, the discussion includes different energy conditions.

Relativistic shocks in conductive media

Context. Relativistic shocks are present in all high-energy astrophysical processes involving relativistic plasma outflows interacting with their ambient medium. While they are well understood in the context of relativistic hydrodynamics and ideal magnetohydrodynamics (MHD), there is a limited understanding of the properties related to their propagation in media characterized by finite electrical conductivity. Aims. This work presents a systematic method for the derivation and solution of the jump conditions for relativistic shocks propagating in MHD media with finite electrical conductivity. This method is applied to the numerical solution of the Riemann problem and the determination of the conditions inside the blastwave that is formed when ultrarelativistic magnetized ejecta interact with the circumburst medium during a gamma-ray burst. Methods. We derived the covariant relations expressing the jump conditions in a frame-independent manner. The resulting algebraic equations expressing the Rankine-Hugoniot conditions in the propagation medium’s frame were then solved numerically. A variable adiabatic index equation of state was used in order to obtain a realistic description of the post-shock fluid’s thermodynamics. This method was then employed for the solution of the Riemann problem for the case of a forward and a reverse shock, both of which form during the interaction of a gamma-ray burst ejecta with the circumburst medium. This allowed us to determine the kinematics of the resulting blastwave and the dynamical conditions in its interior. Results. Our solutions clearly depict the impact of the plasma’s electrical conductivity in the properties of the post-shock medium. Two characteristic regimes are identified with respect to the value of a dimensionless parameter that has a linear dependence on the conductivity. For small values of this parameter, the shock affects only the hydrodynamic properties of the propagation medium and leaves its electromagnetic field unaffected. No current layer forms in the shock front; thus, we refer to this as the current-free regime. For large values of this parameter, the ideal MHD regime has been retrieved. We also show that the assumption of a finite electrical conductivity can lead to higher efficiencies in the conversion of the ejecta energy into thermal energy of the blastwave through the reverse shock. The theory developed in this work can be applied to the construction of Riemann solvers for resistive relativistic MHD (RR4MHD).

Kestabilan Pencucuhan Hidrogen dalam Persekitaran Gas Adi dalam Enjin Pencucuhan Mampatan

Hydrogen fuel promises a high engine efficiency and the ability to eliminate harmful emissions in an internal combustion engine. However, the ignition stability of hydrogen in compression ignition engine is unstable due to the high-auto ignition temperature of hydrogen. Noble gases such as argon, krypton and xenon have a larger molecular weight compared to nitrogen. Therefore, replacing nitrogen with noble gases appears to be a promising option due to their high specific heat ratio. This paper aims to investigate the ignition stability in a heavy molecular noble gases atmosphere in a CI engine. In this study, Converge CFD software simulates a singlecylinder compression ignition engine model based on the Yanmar NF19SK engine parameters. Hydrogen combustion in a noble gas atmosphere resulted in low ignition stability when operated at low intake temperature. Based on this study, we found that increasing intake temperature improves the ignition stability. As a result, argon is the most preferable among other noble gases. Nevertheless, future research should investigate the other noble gases’ capability under different parameters to improve the engine's thermal efficiency.

Charged stellar structure in f(R,ϕ) gravity admitting Chaplygin equation of state

The aim of this paper is to examine the singularity-free solutions for anisotropic stellar structures in [Formula: see text] theory of gravity, where [Formula: see text] denotes the Ricci scalar and [Formula: see text] represents the scalar field. For this purpose, we consider the spherically symmetric spacetime to discuss the stellar structures with anisotropic fluid. Moreover, the Einstein field equations are solved by using Chaplygin equation of state, and the Karori–Barua metric. To analyze the charged stellar structure, we use the matching conditions of spherically symmetric spacetime with the Reissner–Nordstrom exterior metric and develop some expressions for finding the unknown parameters. We further investigate the graphical behavior of energy density, pressure components, anisotropic component, equation of state parameters, equilibrium condition, stability analysis, adiabatic index and energy conditions. Conclusively, our considered stellar structures under observations are realistic, stable, and are free from any singularities.

Rapid Black Hole Spin-down by Thick Magnetically Arrested Disks

Black hole (BH) spin can play an important role in galaxy evolution by controlling the amount of energy and momentum ejected from near the BH into the surroundings. We focus on radiatively inefficient and geometrically thick magnetically arrested disks (MADs) that can launch strong BH-powered jets. With an appropriately chosen adiabatic index, these systems can describe either the low-luminosity or highly super-Eddington BH accretion regimes. Using a suite of 3D general relativistic magnetohydrodynamic simulations, we find that for any initial spin, an MAD rapidly spins down the BH to the equilibrium spin of 0 < a eq ≲ 0.1, very low compared to a eq = 1 for the standard thin luminous (Novikov–Thorne) disks. This implies that rapidly accreting (super-Eddington) BHs fed by MADs tend to lose most of their rotational energy to magnetized relativistic outflows. In an MAD, a BH only needs to accrete 20% of its own mass to spin down from a = 1–0.2. We construct a semi-analytic model of BH spin evolution in MADs by taking into account the torques on the BH due to both the hydrodynamic disk and electromagnetic jet components, and find that the low value of a eq is due to both the jets slowing down the BH rotation and the disk losing a large fraction of its angular momentum to outflows. Our results have crucial implications for how BH spins evolve in active galaxies and other systems such as collapsars, where the BH spin-down timescale can be short enough to significantly affect the evolution of gamma-ray emitting BH-powered jets.

Анализ внезапного выброса газоугольной смеси из полости конической формы, сформированной в процессе выброса

Indispensable attributes in underground coal mining are methane and coal dust of various particle sizes. When they are mixed, coal-gas mixtures are formed, predisposed to various hazardous and extremely hazardous gas-dynamic phenomena, primarily to sudden emissions, accompanied by formation of cavities in the coal massif and intensive release of coal-gas mixtures from these cavities into the mine workings. The article deals with the problem of a one-dimensional stationary flow of a gas-coal mixture in an underground cone-shaped cavity formed during a sudden release. The Euler equation of motion and the continuity equation are used as the basic equations. As a result of their transformation, an ordinary differential equation of the first order is obtained, for which the Cauchy problem is formulated. The solution to the Cauchy problem is a transcendental equation with respect to the desired Mach numbers. The roots of the transcendental equation are calculated using the MathCAD mathematical software suite. Upon finding the Mach numbers, the remaining parameters of the mixture are determined, i.e. the pressure, density and temperature of the gas-coal mixture at any point in the conical region, including their critical values. Graphs are constructed that were used as the basis to establish some regularities of the one-dimensional stationary flow of a gascoal mixture in a conical region. In particular, it was found that with an increase in the Mach number, parameters of the gas-coal mixture decrease non-linearly, and with an increase in the Poisson's adiabatic index, the pressure and temperature decrease, and the density increases.

Evaluation of one-dimensional models to predict chatter in spring-loaded pressure relief valves for gas service

Literature models proposed to avoid valve instabilities in safety valves for gas service are evaluated. The phenomena occurring during the opening of the safety valve are described to introduce possible sources of instabilities. Models from the last thirty years are classified based on the hypothesis of the source, creating the classifications balance-based and pressure wave models. The experiments used by their authors to validate the models are evaluated. A sensitivity analysis of five models is conducted based on set pressure, inlet line diameter, ratio of specific heats and moving mass. The model results are also compared to experimental data with different gases and set pressures. In all cases the trends of the balance-based models do not match that of the pressure wave models. Compared to measurements with different set pressures, none of the tested models did both match the trends and predict a reliable inlet line length. Comparing against measurements with varying set pressure, the three percent rule only predicted a reliable inlet line length in 2 out of 5 cases. The predicted increasing trend according to the three percent rule did not match the measured trend of decreasing maximum permissible inlet line length. Based on phenomena like the spindle friction and lubrication not being included as model input parameter, and authors finding non-reproducible measurement setups, it is concluded that the instability of a safety valve is a rather stochastic process without considering additional parameters throughout the lifecycle of the safety valve.

Relativistic configurations of Tolman Stellar structures in Gauss–Bonnet gravity

The purpose of this study is to discuss the charged stellar structure in the background of the [Formula: see text] theory of gravity. The Einstein–Maxwell equations defined in the appearance of charge by utilizing the Tolman–Kuchowicz spacetime are described by spherically symmetric spacetime. To analyze the charged stellar structure, we use the matching conditions of spherically symmetric spacetime with the Reissner–Nordström exterior metric and develop some expressions for examining the energy density, radial pressure and tangential pressure, respectively. We address the energy conditions to verify our model’s viability for the SAX J1808.4-3658 star. Some other physical features, such as energy density, pressure components, anisotropic parameters, equation of state parameters, stability analysis, adiabatic index, Tolman–Oppenheimer–Volkoff equation, mass-radius relationship, compactness and redshift, have been investigated. We observe that our results are physically viable, free from geometrical and physical singularities, which provide circumstantial evidence for the existence of viable and stable compact star.

Experimental investigation of pressure drop and heat transfer in minichannel with smooth and pin fin surfaces

This study investigates pressure drop and heat transfer characteristics in a minichannel heat exchanger experimentally. The experimental testing was carried out on a minichannel with a hydraulic diameter of about 2.5 mm, with smooth and embedded with circular pin-fins. The testing was conducted with different hot fluids, air and water, over different Reynolds numbers ranges, and over different heat capacity ratios (0.25, 0.5, 0.75, and 1). The experimental study of the pressure drop covers a Reynolds number range between 100-1900 for the hot water, and Reynolds number range between 500-10,000 for the hot air. The hot fluid flows through a channel with an inline arrangement with a 1750 pin fin, while the cold fluid flows through a smooth channel. Increasing flow rates resulted in an increase in pressure drop and heat transfer coefficients. When using pin-fins surface instead of smooth surface, the overall heat transfer coefficient (U) increased by 190% when water is used as the heat transfer fluid (HTF), and the same coefficient increased by 42% when air is used as the heat transfer fluid. Similarly, the difference in pressure drop is low in the case of water-water, while in the case of air-water, the difference in pressure drop is more substantial as Reynolds number increases.

Ferrimagnetic quantum phase transitions and Weyl-Kondo semimetal in a dimerized organic polymer

We study the ferrimagnetic quantum phase transitions (QPTs) and thermodynamics of a dimerized organic polymer, which is described as a periodic Anderson-like model using Green’s function theory. In the absence of magnetic field, it is shown that the Kondo coupling could destroy the Dirac semimetal and induce spin splitting, and the dimerization could open up an energy gap. In a magnetic field, the ferrimagnetic and ferromagnetic insulators as well as Weyl-Kondo semimetal are unveiled. The mechanism of Kondo-singlet competition with dimer-singlet is unveiled to account for the 1/3 magnetization plateau. The field induces second and first order QPTs in the small and large hybridization limit, which is demonstrated by the field scaling of Grüneisen ratio and temperature scaling of specific heat at low temperatures, providing novel thermodynamic means to diagnose the order of QPTs.

A novel flux splitting based on wave-particle splitting for ideal magnetohydrodynamics

A novel flux splitting method based on wave-particle splitting is developed for one-dimensional ideal magnetohydrodynamics. While ideal magnetohydrodynamics (MHD) equations are non-convex with non-homogeneous flux as opposed to their hydrodynamic counterparts, the present flux splitting methods cannot develop Riemann solver. The proposed approach based on wave-particle method referred as Advection Magnetic-direction Wave Particle Splitting (AMWPS) scheme splits the flux into four parts: the wave-like total pressure part, the wave-like normal magnetic part, the particle-like advection part and the particle-like tangential magnetic part. The particle-like parts can be solved by the scheme developed by Toro and Vazquez-Cendon (TV scheme) and we propose a novel approach to the solution of Riemann problem formed by the wave-like parts including total pressure sub-flux and normal magnetic sub-flux. As for the ordered wave foliation in MHD and other limitations in wave structure, we also analyze the relation between plasma β and specific heat ratio γ. The advantage of AMWPS is that it can sharply capture isolated, stationary Alfven wave discontinuity. Several one-dimensional and two-dimensional MHD problems have been tested to highlight the accuracy, positivity preservation and robustness of AMWPS scheme and comparative studies show that AMWPS significantly outperforms the Riemann solver named Harten, Lax and Leer for contact wave (HLLC) in most cases.

An acceptable study of anisotropic dark energy stars in modified [formula omitted] gravity

In this work, we investigate a stable spherically symmetric relativistic stellar configuration within the framework of f(R,G) gravity. Here, we consider the stellar object filled by a mixture of two non-interacting isotropic ordinary matter and anisotropic dark energy (DE) in the fluid state, named by ‘dark energy star’. Also, these two stated fluids are related by a direct proportional condition between matter density and DE density. In particular, we have used Krori-Barua (K-B) matric potentials to solve the field equations. The whole discussion is performed corresponding to a fixed functional form f(R,G)=R+λR2+G10 with a constant λ. Again, in order to verify the well-behaved nature of our obtained stellar system, we have checked several attributes of our proposed DE stellar structure with a detailed graphical representation. For this connection, we have chosen three compact stars like, SAX JI808.4-3658, PSR J1614-2230, and 4U1820-30, with mass (M) and radius (R). We have shown the stability of our stellar system by exploring several tests via causality conditions, adiabatic index, Tolman-Oppenheimer-Volkoff equation, and Harrison-Zeldovich-Novikov criteria. Further, we have shown that ordinary matter and DE maintain their own characters by discussing energy conditions. Finally, based on the whole discussion, we have concluded that our proposed DE stellar system is stable and also maintains all physical acceptability requirements in f(R,G) gravity.

Propagation of magnetogasdynamics spherical shock wave in a gravitating gas with radiation heat flux

This article presents a mathematical model for characterizing the dynamic behavior of spherical shock waves in a self-gravitating, radiating ideal gas with the presence of an azimuthal magnetic field, emphasizing adiabatic conditions. The analysis assumes that the environment just ahead of the shock wave is stationary, and it accounts for variations in density, magnetic field, and fluid velocity within the disturbed medium just behind the shock front. Furthermore, the impact of thermal radiation within the context of an optically thin limit is incorporated into the energy equation of the governing system. Employing the Lie invariance method, the set of partial differential equations governing the flow within this medium is transformed into a system of nonlinear ordinary differential equations through the use of similarity variables. Four distinct cases of similarity solutions are derived by selecting different values for the arbitrary constants associated with the generators. Among these four cases, only two yield similarity solutions, one assuming a power-law shock path and the other an exponential-law shock path. In the case of a power-law shock path, the resulting set of nonlinear ordinary differential equations is numerically solved using the 4th-order Runge-Kutta method in MATLAB software. The article thoroughly discusses the influence of various parameters, including γ (adiabatic index of the gas), Ma−2 (Alfvén–Mach number), ϕ (ambient density exponent), and G0 (gravitational parameter), on the flow properties. The findings are presented graphically to provide a comprehensive understanding of the effects of these parameters.

Changing the working conditions of the mineral wool cupola during the transition from an open type to a closed one

The widespread use in the industry of mine furnaces of the wagon type requires the organization of management of their gasdynamic and thermal regime. In the mode of operation of a cupola with an open grate, its thermal mode is characterized mainly by the peripheral movement of gases with a significant difference in the ratio of heat capacities of gas flows and materials. The use of forced removal of exhaust gases from the shaft furnace contributes to an earlier transition from a peripheral to a predominantly central movement mechanism. By increasing the degree of rarefaction on the grate to 0,71‒0,73 bar, it is possible to increase the level of melt temperature, temperature pressure and air blast flow, exhaust gas temperature while improving the conditions of heat exchange between gases and heated materials. This process will be accompanied by a continuous decrease in the productivity of the unit with an improvement in the stability of the melting process. A further increase in the level of rarefaction on the grate contributes to the gradual transition of the mechanism of movement of gases from the peripheral to the central one with a deterioration in the parameters of the wagon melting.

Thermal Characteristics of Dry Gas Seal in Startup Process Considering Microscale Effects

The heat generated during the startup process of dry gas seals, such as the friction heat of the asperities, viscous shear heat, and the expansion heat of the gas film, easily leads to seal failure and endangers the stable operation of turbomachinery. This study combines the statistically modified contact model and the average Reynolds equation by considering the adiabatic index and the microscale effects of dry gas seals to explore the heat generation characteristics of dry gas seals formed in series at multiple times. In particular, the change laws and influencing factors among the components, including the friction heat of asperities and the shear heat and expansion heat of the gas film and total heat, are investigated. A comparative analysis indicates that the slip flow effect increases the total heat during the startup process. The friction heat is much greater than expansion heat and shear heat. Despite constant acceleration, exponential acceleration, or Harrison acceleration, the heat changes are uneven during the startup process. In particular, the heat changes sharply in the early stage and slowly in the later stage. The Harrison acceleration mode is the most conducive to sealing stability.

Electromagnetic effects on static celestial objects in modified gravity

This paper aims to figure out the existence and development of some particular celestial bodies possessing charged anisotropic interiors in the framework of f(G,T) gravity. The modified field equations corresponding to a quadratic G2+ℵT model are established in which MIT bag model equation of state is employed to engage the role of bag constant, where ℵ symbolizes the coupling parameter. We then consider a Finch–Skea metric to uniquely solve the field equations. The resulting physical parameters are then explored graphically by using estimated data of five distinct compact stars PSR J1614-2230, Vela X-I, PSRJ1903+327, 4U1820-30 and Her X-I. Further, the regularity conditions, role of anisotropic pressure and viability criteria are investigated for different choices of the charge and bag constant. The stability is also determined through causality condition and the adiabatic index. We conclude that all the five charged star candidates correspond to viable and stable structures under the imposed constraints.

Numerical study of TC4-NiCr/EG+Water hybrid nanofluid over a porous cylinder with Thompson and Troian slip boundary condition: Artificial neural network model

The analysis is intended to demonstrate two-phase flow of hybrid dusty Eyring–Powell nanofluid flow over a porous cylinder with Thompson and Troian slip boundary condition. The combination of (C2H6O2) ethylene glycol (40 %) and (H2O) water (60 %) -based TC4 (TC4 is an alloy of titanium consisting of 90 % titanium, 6 % aluminium, and 4 % vanadium) was utilized to preparing the hybrid nanofluids. Ti–6Al–4V is another name for this alloy) and nickel-chromium (NiCr) nanoparticles flow properties after the mechanism has been filled with dusty particles. A new approach to the execution of an intelligent numerical computing solution is shown in this paper, which uses the Levenberg-Marquard algorithm to drive MLP feed-forward back-propagation ANN. Data were collected for the testing, certification, and training of the ANN model. The bvp4c with MATLAB solver is used to resolve nonlinear versions of well-known mathematical problems, such as those involving the skin friction coefficient, heat transfer rates, velocity, temperature, and other variables. The ANN model is designed to perform the following tasks: selecting data, building networks, training networks, and assessing their effectiveness via the use of the mean square error measure. The influence of key factors on the fluid transport characteristics is demonstrated via tables and graphs. The velocity profile is higher values, resulting in an amplification of the curvature parameter. The temperature rises when the radiation parameter values decline, and the specific heat ratio parameter exhibits a similar pattern. Higher values of the velocity slip parameter and melting factor both are decays on the Nusselt number. This type of theoretical investigation is a necessary aspect of many aircraft applications, including power production, cooling of electrical and propulsion reactors.

Ideal and non-ideal planar compressible fluid flows in radial equilibrium

Two-dimensional compressible flows in radial equilibrium are investigated in the ideal dilute-gas regime and the non-ideal single-phase regime close to the liquid–vapour saturation curve and the critical point. Radial equilibrium flows along constant-curvature streamlines are considered. All properties are therefore independent of the tangential streamwise coordinate. A differential relation for the Mach number dependency on the radius is derived for both ideal and non-ideal conditions. For ideal flows, the differential relation is integrated analytically. Assuming a constant specific heat ratio $\gamma$ , the Mach number is a monotonically decreasing function of the radius of curvature for ideal flows, with $\gamma$ being the only fluid-dependent parameter. In non-ideal conditions, the Mach number profile also depends on the total thermodynamic conditions of the fluid. For high molecular complexity fluids, such as toluene or hexamethyldisiloxane, a non-monotone Mach number profile is admissible in single-phase supersonic conditions. For Bethe–Zel'dovich–Thompson fluids, non-monotone behaviour is observed in subsonic conditions. Numerical simulations of subsonic and supersonic turning flows are carried out using the streamline curvature method and the computational fluid dynamics software SU2, respectively, both confirming the flow evolution from uniform flow conditions to the radial equilibrium profile predicted by the theory.