Thermal Properties Of Gas Research Articles

An enhanced compressible two-phase flow model with detailed chemistry under the adaptive mesh refinement frame

In the present study, an enhanced compressible two-phase flow model is advanced, considering the effect of chemical reactions within a detailed mechanism. In this model, two immiscible fluids (liquid and gaseous mixture) are accurately separated with the resolved interface. Unlike the classical five-equation two-phase flow model, the thermal properties of gases are no longer assumed to be constant but rather vary as functions of temperature. A modified mechanical relaxation procedure is proposed and employed at the gas-liquid interface to prevent the occurrence of nonphysical pressure oscillation. In the gaseous mixture, numerous gas components are included and resolved by their mass fraction among the gaseous mixture. In this model, the heat release effect is simulated by a detailed chemistry. Furthermore, the numerical results of several benchmark problems in one dimension and two dimensions demonstrate the efficacy of the proposed compressible multiphase flow model, such as the air shock tube, the gaseous detonation tube, the shock-droplet interaction, and especially the detonation-droplet interaction that has received little focused interest and investigations. Moreover, a self-developed adaptive mesh refinement strategy is performed for a high efficiency of numerical solving.

Thermal resonance model for micro-oscillators in the vicinity of a geometric boundary

This study explores the damping behavior of micro-oscillators within the transitional flow regime between molecular flow and viscous flow, including the presence of a neighboring geometric boundary. The damping is described by a model based on standing thermal waves (STW), which form a thermal resonance depending on the pressure and on the gap width to the boundary. This concept was first introduced in a previous paper for a nitrogen atmosphere and is now examined for seven further gases (He, Ne, Ar, Kr, CO2, N2O, SF6). The distance between the micro-oscillator and the confining geometry, given by an Al plate, is in the range of 150 µm to 3500 µm. Fitting the thermal wave model to the experimental data shows very good agreement and explains the convex region for the measured quality factor Q in the transition from the molecular to the viscous flow regime. The evaluation of the thermal resonance model shows a strong correlation between the ambient pressure at which thermal resonance occurs and the thermal properties of the gas (i.e. thermal diffusivity a and adiabatic index κ) including the gap width h which is in agreement with the proposed theory. This opens up the possibility of using micro-oscillators to measure the thermal properties of gases in a very precise way, comparable to the thermal wave resonator cavity principle, but with a much simpler and smaller setup.

A Robust Miniaturized Gas Sensor for H2 and CO2 Detection Based on the 3ω Method.

Gas concentration monitoring is essential in industrial or life science areas in order to address safety-relevant or process-related questions. Many of the sensors used in this context are based on the principle of thermal conductivity. The -method is a very accurate method to determine the thermal properties of materials. It has its origin in the thermal characterization of thin solid films. To date, there have been very few scientific investigations using this method to determine the thermal properties of gases and to apply it to gas measurement technology. In this article, we use two exemplary gases ( and ) for a systematical investigation of this method in the context of gas analysis. To perform our experiments, we use a robust, reliable sensing element that is already well established in vacuum measurement technology. This helix-shaped thin wire of tungsten exhibits high robustness against chemical and mechanical influences. Our setup features a compact measurement environment, where sensor operation and data acquisition are integrated into a single device. The experimental results show a good agreement with a simplified analytical model and FEM simulations. The sensor exhibits a lower detection limit of 0.62% in the case of , and only 0.062% in case the of at an excitation frequency of 1. This is one of the lowest values reported in literature for thermal conductivity sensors.

Thermal calculations and NOx emission analysis of a micro gas turbine system without a recuperator

A thermal calculation based on a table of thermal properties of gas was carried out for a micro gas turbine system without a recuperator. The performance parameters of the micro gas turbine system were obtained. The results of the thermal calculations were verified using ASPEN PLUS, and it shows that the thermal calculations fit well with the ASPEN simulation results. Based on this thermal calculation method, the variation of the performance parameters of the micro gas turbine system under different pressure and temperature ratios was analyzed. The results show that there is no optimum pressure ratio within the general design parameters of micro gas turbines, which leads to extreme values of thermal efficiency. The NOx generation in the combustion chamber of the micro gas turbine based on the Zeldovich mechanism was modeled and analyzed by coupling the 1-D thermal calculation model with the NOx emission model. The relationship between NOx generation rate, molar fuel factor, the characteristic pressure, and the characteristic temperature was obtained. The results of the analysis show that, in terms of controlling NOx emissions from a gas turbine, the use of an increased pressure ratio has a significant advantage over an increased temperature ratio to improve the thermal efficiency of the micro gas turbine.

Impact of Cosmic Filaments on the Gas Accretion Rate of Dark Matter Halos

Abstract We investigate the impact of cosmic filaments on the gas accretion rate, M ̇ gas , of dark matter halos in filaments, based on cosmological hydrodynamic simulation. We find that for halos less massive than 1012.0 M ⊙, M ̇ gas of halos residing in prominent filaments (with width D fil > 3 Mpc h −1) is lower than halos residing in tenuous filaments (D fil < 3 Mpc h −1) by 20%–30% at z = 0.5 and by a factor of 2–3 at z = 0. However, M ̇ gas depends weakly on the physical distance between halo center and the spine of filaments from high redshift to z = 0 and only shows a clear difference between the inner and outer regions in prominent filaments at z = 0. We further probe the thermal properties of gas in prominent and tenuous filaments, which appear in relatively highly and intermediate overdense regions, respectively. The gas in prominent filaments is hotter. Around 26%, 38%, and 45% of gases in prominent filaments are hotter than 106 K at z = 1.0, 0.5, and 0.0, respectively. The corresponding fractions in tenuous filaments are merely ∼6%, 9%, and 11%. The suppressed gas accretion rate for low-mass halos in prominent filaments at z ≲ 0.5 may result from the hotter ambient gas, which could provide a physical processing mechanism to cut down the supply of gas to halos before they enter clusters. This process partially meets the need of the preheating mechanism implemented in some semianalytical models of galaxy formation but works only for ∼20% of halos at z < 1.

Equation of liquid, gas, and fluid state for methane

Using methods and approaches, previously developed by the authors, a new fundamental low-parametric equation of state for methane (in the form of the reduced Helmholtz function) has obtained to describe the thermodynamic properties. It allows describing the thermal properties of gas, liquid, and fluid at pressures of up to 20 MPa with sufficiently high accuracy close to the experimental one (with the exception of the critical region). The sound speed and caloric properties of methane have been calculated without involving any caloric data, with the exception of ideal gas enthalpy. The values of speed of sound, isochoric heat capacity, and other thermodynamic properties obtained by calculations are in good agreement with the experimental data.

Thermal modeling of indirect water heater in city gate station of natural gas to evaluate efficiency and fuel consumption

In this paper, a comprehensive model of indirect water heater for a pressure reduction station of natural gas has been presented. Effiiency and fuel consumption of heater have been estimated by applying energy and mass conservation equations. Three terms of energy including heat absorbed by natural gas, heat transferred to environment from stack and heat loses to environment from heater body have been evaluated. Thermal properties of natural gas has been calcualated using AGA8 state equation. Therefore, the model is a function of climate, heater geometry and natural gas characteristics including temperature, pressure and its composition. The results are compared with data recorded from real station in Iran (Arak, Kheriabad and Malekabad stations) and very good agreement has been observed. Reducing temperature and increasing pressure of inlet gas, thickening glass wool insulation and rising fire tube radius led to an increase in heater’s thermal efficiency from 20 to 60% and consequently fuel consumption of heater was reduced. Finally, choosing the sutible geometery yeilded a higher heater efficincy with a raise from 44% to 70%.

Measuring the Heating and Cooling of the Interstellar Medium at High Redshift: PAH and [C ii] Observations of the Same Star-forming Galaxies at z ∼ 2

Abstract Star formation depends critically on cooling mechanisms in the interstellar medium (ISM); however, thermal properties of gas in galaxies at the peak epoch of star formation (z ∼ 2) remain poorly understood. A limiting factor in understanding the multiphase ISM is the lack of multiple tracers detected in the same galaxies, such as Polycyclic Aromatic Hydrocarbon (PAH) emission, a tracer of a critical photoelectric heating mechanism in interstellar gas, and [C ii] 158 μm fine-structure emission, a principal coolant. We present ALMA Band 9 observations targeting [C ii] in six z ∼ 2 star-forming galaxies with strong Spitzer IRS detections of PAH emission. All six galaxies are detected in dust continuum and marginally resolved. We compare the properties of PAH and [C ii] emission, and constrain their relationship as a function of total infrared luminosity (L IR) and IR surface density. [C ii] emission is detected in one galaxy at high signal-to-noise (34σ), and we place a secure upper limit on a second source. The rest of our sample are not detected in [C ii] likely due to redshift uncertainties and narrow ALMA bandpass windows. Our results are consistent with the deficit in [C ii]/L IR and PAH/L IR observed in the literature. However, the ratio of [C ii] to PAH emission at z ∼ 2 is possibly much lower than what is observed in nearby dusty star-forming galaxies. This could be the result of enhanced cooling via [O i] at high-z, hotter gas and dust temperatures, and/or a reduction in the photoelectric efficiency, in which the coupling between interstellar radiation and gas heating is diminished.

The Importance of Quantum Pressure of Fuzzy Dark Matter on Lyα Forest

Abstract With recent Lyα forest data from BOSS and XQ-100, some studies suggested that the lower mass limit on the fuzzy dark matter (FDM) particles is lifted up to . However, such a limit was obtained by ΛCDM simulations with the FDM initial condition and the quantum pressure (QP) was not taken into account, which could have generated non-trivial effects in large-scale structures. We investigate the QP effects in cosmological simulations systematically, and find that the QP leads to further suppression of the matter power spectrum at small scales, as well as the halo mass function in the low-mass end. We estimate the suppressing effect of QP in the 1D flux power spectrum of Lyα forest and compare it with data from BOSS and XQ-100. The rough uncertainties of thermal gas properties in the flux power spectrum model calculation were discussed. We conclude that more systematic studies, especially with QP taken into account, are necessary to constrain FDM particle mass using Lyα forest.

The simple fundamental equation of state for liquid, gas, and fluid of xenon

To describe the thermodynamic properties of xenon, a new fundamental low-parametric equation of state (in the form of reduced Helmholtz energy) is obtained with the help of the methods and approaches developed by the authors. It allows us to describe the thermal properties of gas, liquid, and fluid with a sufficiently high accuracy close to the accuracy of experiment in a range from the density in the ideal gas state to the density at the triple point, excluding the critical region. The caloric properties and speed of xenon sound are calculated without involving any caloric data, with the exception of ideal gas enthalpy. The values of isobaric heat capacity, sound speed, and other thermodynamic properties obtained by calculations are in good agreement with the experimental data.

Thermal and magnetic properties of electron gas in toroidal quantum dot

One-electron states in a toroidal quantum dot in the presence of an external magnetic field have been considered. The magnetic field operator and the Schrodinger equation have been written in toroidal coordinates. The dependence of one-electron energy spectrum and wave function on the geometrical parameters of a toroidal quantum dot and magnetic field strength have been studied. The energy levels are employed to calculate the canonical partition function, which in its turn is used to obtain mean energy, heat capacity, entropy, magnetization, and susceptibility of noninteracting electron gas. The possibility to control the thermodynamic and magnetic properties of the noninteracting electron gas via changing the geometric parameters of the QD, magnetic field, and temperature, was demonstrated.

The formation of hot gaseous haloes around galaxies

We use a suite of hydrodynamical cosmological simulations from the Evolution and Assembly of GaLaxies and their Environments (EAGLE) project to investigate the formation of hot hydrostatic haloes and their dependence on feedback mechanisms. We find that the appearance of a strong bimodality in the probability density function (PDF) of the ratio of the radiative cooling and dynamical times for halo gas provides a clear signature of the formation of a hot corona. Haloes of total mass $10^{11.5}-10^{12}{\rm{M}}_{\odot}$ develop a hot corona independent of redshift, at least in the interval $z=0-4$ where the simulation has sufficiently good statistics. We analyse the build up of the hot gas mass in the halo, $M_{\rm{hot}}$, as a function of halo mass and redshift and find that while more energetic galactic winds powered by SNe increases $M_{\rm{hot}}$, AGN feedback reduces it by ejecting gas from the halo. We also study the thermal properties of gas accreting onto haloes and measure the fraction of shock-heated gas as a function of redshift and halo mass. We develop analytic and semianalytic approaches to estimate a `critical halo mass', $M_{\rm{crit}}$, for hot halo formation. We find that the mass for which the heating rate produced by accretion shocks equals the radiative cooling rate, reproduces the mass above which haloes develop a significant hot atmosphere. This yields a mass estimate of $M_{\rm{crit}} \approx 10^{11.7}{\rm{M}}_{\odot}$ at $z=0$, which agrees with the simulation results. The value of $M_{\rm{crit}}$ depends more strongly on the cooling rate than on any of the feedback parameters.

Heat transfer performances of honeycomb regenerators with square or hexagon cell opening

Honeycomb regenerators with varied cell openings are applied to regenerative combustion systems. A three-dimensional unsteady numerical model, which calculate the gas flow and gas-solid heat transfer in regenerators with square or hexagon cell openings is developed by computational fluid dynamics package, FLUENT. The radiative transfer equation is employed to calculate radiative heat transfer in gas and is added in gas energy conservation equation as a source term. Convection coupled with radiation is used in gas-solid boundary condition. Moreover, temperature-dependent thermal properties of gas and solid are considered in the model. By comparing simulation results with experimental data from the literature, the numerical model is verified. The effects of different cell opening shapes on gas-solid interface heat flux, gas temperature profile and energy recovery ratio are compared. The simulation results show that there is a higher outlet air temperature and energy recovery ratio in square opening cells than hexagon opening cells. Furthermore, the influences of cell opening side length and switching time on air preheating effect and pressure loss are investigated in regenerators with the two different openings.

Simple fundamental equation of state for liquid, gas, and fluid of argon, nitrogen, and carbon dioxide

A new fundamental low-parametric equation of state in the form of reduced Helmholtz function for describing thermodynamic properties of normal substances was obtained using the methods and approaches developed earlier by the authors. It allows us to describe the thermal properties of gas, liquid, and fluid in the range from the density in ideal-gas state to the density at a triple point (except the critical region) with sufficiently high accuracy close to the accuracy of experiment. The caloric properties and sound velocity of argon, nitrogen, and carbon dioxide are calculated without involving any caloric data, except the ideal gas enthalpy. The obtained values of isochoric heat capacity, sound velocity, and other thermodynamic properties are in good agreement with experimental (reliable tabular) data.

The influence of variations of the elemental composition on the thermal properties of gas behind shock fronts

The homogenization of inhomogeneities in the elemental composition of the interstellar medium due to stellar evolution and weak mixing are inevitably related to the action of shocks. This paper considers the influence of variations in the elemental composition on the thermal and ionizational evolution of a collisional gas with the solar metallicity that is cooled behind a shock front with a velocity of 50–120 km/s. The intensities of lines of heavy elements in plasma cooling behind a shock front depend not only on variations in the elemental composition, but also on the shock velocity, due to the different values of the critical density for the transition to the equilibrium level populations in atoms and ions of heavy elements. This circumstance can be used to determine the elemental composition of cool and warm gas of the interstellar medium, as well as the thermal history of the gas.

The impact of the SZ effect on cm-wavelength (1–30 GHz) observations of galaxy cluster radio relics

Radio relics in galaxy clusters are believed to be associated with powerful shock fronts that originate during cluster mergers, and are a testbed for the acceleration of relativistic particles in the intracluster medium. Recently, radio relic observations have pushed into the cm-wavelength domain (1–30 GHz) where a break from the standard synchrotron power law spectrum has been found, most noticeably in the famous “Sausage” relic. Such spectral steepening is seen as an evidence for non-standard relic models, such as ones requiring seed electron population with a break in their energy spectrum. In this paper, however, we point to an important effect that has been ignored or considered insignificant while interpreting these new high-frequency radio data, namely the contamination due to the Sunyaev-Zel’dovich (SZ) effect that changes the observed synchrotron flux. Even though the radio relics reside in the cluster outskirts, the shock-driven pressure boost increases the SZ signal locally by roughly an order of magnitude. The resulting flux contamination for some well-known relics are non-negligible already at 10 GHz, and at 30 GHz the observed synchrotron fluxes can be diminished by a factor of several from their true values. At higher redshift the contamination gets stronger due to the redshift independence of the SZ effect. Interferometric observations are not immune to this contamination, since the change in the SZ signal occurs roughly at the same length scale as the synchrotron emission, although there the flux loss is less severe than single-dish observations. Besides presenting this warning to observers, we suggest that the negative contribution from the SZ effect can be regarded as one of the best evidence for the physical association between radio relics and shock waves. We present a simple analytical approximation for the synchrotron-to-SZ flux ratio, based on a theoretical radio relic model that connects the nonthermal emission to the thermal gas properties, and show that by measuring this ratio one can potentially estimate the relic magnetic fields or the particle acceleration efficiency.

Influence of dissolved gases on sonochemistry and sonoluminescence in a flow reactor

In the present work, the influence of gas addition is investigated on both sonoluminescence (SL) and radical formation at 47 and 248kHz. The frequencies chosen in this study generate two distinct bubble types, allowing to generalize the conclusions for other ultrasonic reactors. In this case, 47kHz provides transient bubbles, while stable ones dominate at 248kHz. For both bubble types, the hydroxyl radical and SL yield under gas addition followed the sequence: Ar>Air>N2>>CO2. A comprehensive interpretation is given for these results, based on a combination of thermal gas properties, chemical reactions occurring within the cavitation bubble, and the amount of bubbles. Furthermore, in the cases where argon, air and nitrogen were bubbled, a reasonable correlation existed between the OH-radical yield and the SL signal, being most pronounced under stable cavitation at 248kHz. Presuming that SL and OH originate from different bubble populations, the results indicate that both populations respond similarly to a change in acoustic power and dissolved gas. Consequently, in the presence of non-volatile pollutants that do not quench SL, sonoluminescence can be used as an online tool to qualitatively monitor radical formation.

Unified low-parametrical equation of state for engineering calculations of thermodynamic properties of substances

The new simple semi empirical equation of state for description of P --T data of normal substances was specified. New equation of state has 10 individual adjustable coefficients and it describes thermal properties of gas, liquid and fluid in the main with the accuracy within the error of experimental data, except of critical region. The caloric properties and the speed of sound of argon, nitrogen and carbon dioxide were calculated with the help of known thermodynamic equations and in general divergences between calculated and tabular caloric data do not exceed the experimental error. New equation can be used for engineering calculations at the deficit of experimental data, especially on the caloric properties of substances.

A low-parametric state equation for calculating the thermodynamic properties of substances in liquid and gaseous state

Using methods and approaches developed by the authors, a new low-parametric state equation for describing the thermal properties of normal substances is obtained that allows us to describe the thermal properties of gases, liquids, and fluids over a range of densities from the ideal gas state to the triple point, except for a critical region, with a high degree of accuracy close to that of an experiment. The caloric properties and speed of sound are calculated for argon, nitrogen, and carbon dioxide without using any caloric data except for the enthalpy of an ideal gas. It is established that the calculated values of enthalpy, heat capacity, the speed of speed of sound, etc., are in good agreement with the experimental (reliably tabulated) data.

Simple Self-Empirical Equation of State of Liquid and Gas for Engineering Calculations

The new simple semiempirical equation of state (EoS) for the description of P−ρ−T data of “normal” substances was specified. The new EoS has eight individual adjustable coefficients, and it describes the thermal properties of gas, liquid, and fluid with an accuracy within the error of experimental data, except for the critical region. The caloric properties and the speed of sound of argon, nitrogen, and carbon dioxide were calculated with the help of known thermodynamic equations, and in general divergences between calculated and tabular caloric data do not exceed the experimental error. The new equation can be used for engineering calculations at the deficit of experimental data, especially on the caloric properties of substances.