Gas Temperature Distribution Research Articles

Conductive Heat Transfer Through Nanoconfined Gas: From Continuum to Free-Molecular Regime

In the past few decades, great efforts have been devoted to studying heat transfer on the nanoscale due to its importance in multiple technologies such as thermal control and sensing applications. Heat conduction through the nanoconfined gas medium differs from macroscopic predictions due to several reasons. The continuum assumption is broken down; the surface forces which extend deeper through the gas medium become prominent due to the large surface-to-volume ratio, and, finally, the gas molecules are accumulated nonuniformly on the solid surfaces. In this work, to better understand the combination of these phenomena on the heat conduction through the nanoconfined gas medium, we present a series of molecular dynamics simulations of argon gas confined between either metals or silicon walls. The gas density is set so that gas experiences a wide range of Knudsen numbers from continuum to the free molecular regime. It is observed that the intrinsic characteristics of the solid determine the gas density distribution near the walls and consequently in the bulk region, and these distributions control the heat conduction through the gas medium. While the nanochannel walls have their most significant impact on the density and temperature distributions of the rarefied gas, the pressure and the heat flux across the gas domain converge toward a plateau as the gas becomes denser. We propose new analytical formulas for calculating the gas pressure, induced heat flux, and effective thermal conductivity through the strongly nanoconfined gas, which incorporates the wall force field impacts on the gas transport characteristics for the Knudsen number in the range of 0.05 to 20.

Analysis of inversion error characteristics of stellar occultation simulation data

Atmospheric stellar occultation observation technology is an advanced space-based detection technology that can measure the vertical distribution of trace gas composition, temperature, and aerosol content in a planet’s atmosphere. In this study, an inversion algorithm of the onion-peeling method was constructed to invert the transmittance obtained from the forward mask. The method used a three-dimensional ray-tracing simulation to obtain the transmission path of the light in the Earth’s atmosphere. The relevant parameters were then combined in the high-resolution transmission molecular absorption (HITRAN) database, and line-by-line integration was performed to calculate the atmospheric transmittance. The transmittance value was then used as an input to calculate the vertical distribution of oxygen molecules when using the single-wavelength inversion of the onion-peeling method. Finally, the oxygen molecule content was compared with the value attained by the Mass Spectrometer and Incoherent Scatter Radar Extended (MSISE00) atmospheric model to determine the relative error of our model. The maximum error was found to be 0.3%, which is low enough to verify the reliability of our algorithm. Using Global-scale Observations of the Limb and Disk (GOLD) measured data to invert the oxygen number density, we calculated its relative deviation from the published result to further verify the algorithm. The inversion result was affected by factors such as prior data, the absorption spectral line type, the ellipticity of the Earth, and the accuracy of the orbit. Analysis of these error-influencing factors showed that the seasons and the Earth’s ellipticity affected the accuracy of the model only 0.001% and could therefore be ignored. However, latitude and solar activity had a greater impact on accuracy, on the order of 0.1%. The absorption line type affected the accuracy of the model by as much as 1%. All three of these factors therefore need to be considered during the inversion process.

Effects of air supply optimization on NOx reduction in a structurally modified municipal solid waste incinerator

The reduction of NOx (nitrogen oxides) emission remains the key challenge in the incineration of MSW (municipal solid waste). The flame position, gas temperature and heat load distribution can be optimized by adopting suitable air supply methods, and the NOx generation as well as the NOx emission will be reduced. In this study, numerical models of a 350 t/d MSW incinerator were established to study the effects of different air supply methods (such as different ratios of primary air and secondary air, ratios of secondary air guns, supply methods of over-fired air). Results indicated the combustion state and flowing characteristics were effectively improved, which suppressed the initial generation of NOx and promoted the NOx removal efficiency of SNCR process. Reducing the ratio of primary air could significantly avoid the NOx generation, the initial production of NOx decreased by 8.39% when the ratio of primary air was reduced to 65%. With the arrangement of over-fired air, temperature distribution was more evenly, and significant promotion effects on SNCR (selective non-catalytic reduction denitrification) process were obtained. The maximum SNCR efficiency reached 62.81% with NOx emission at outlet was less than 100 mg/Nm3, which was 23.95% higher than before.

Gas Temperature Effect in Methane DBD Reactor for Hydrogen Production

Numerical investigation of gas temperature distribution in a dielectric barrier discharge (DBD) for plasma reactor in pure methane gas (CH<sub>4</sub>) were carried out by using one-dimensional fluid model. This physical approach was based essentially on electrons and ions transport equation resolution coupled with Poisson's equation for two parallel electrodes plates. In the present work, the heat transport equation was solved in order to determine the gas heating behavior in the discharge DBD. The numerical model was applied in the case of a gas pressure of 350 torr and sinusoidal voltage excitation at period frequency of 50 kHz. The results obtained by this model show the time variations of charged particles, the electric field, and the electrical characteristics of CH<sub>4</sub> DBD. The gas heating development in the discharge reactor becomes important in the vicinity of the dielectrics. The effect of operation discharge parameters such as the applied voltage, the secondary electron-emission coefficient (γ) as well as the gas pressure have been analyzed and discussed. The findings suggest that the increase of gas temperature in CH<sub>4</sub> DBD reactor affects the improvement of discharge behavior and consequently the hydrogen production.

Analysis on helium stratification erosion by vertical steam jet using the CUPID code

This paper presents a validation of a computational fluid dynamics (CFD) code (CUPID) for predicting the erosion of helium stratification by a vertical steam jet. For the validation of CUPID, CFD grade experimental data obtained from the PANDA facility in the framework of the OECD/NEA HYMERES-2 project was used. To predict the stratification erosion phenomena appropriately, the turbulence model and radiative heat transfer model need to be employed as major physical models. Therefore, the standard k–ε turbulence model, including the buoyancy term, was applied, and a sensitivity study was carried out to investigate the effect of buoyancy production in the turbulence dissipation rate equation on the predicted helium concentration. Additionally, a radiative heat transfer model (P-1) was implemented by applying the appropriate parameter for the calculation, and the predicted gas temperature distributions with and without radiative heat transfer were compared. First, the physical models were validated for a baseline test case in which the vertical steam jet did not interact with any flow obstacles. Then, a second validation was carried out as a blind benchmark calculation where the experimental data were released after the calculation results had been submitted. The CUPID calculations for the helium concentration and gas temperature were very close to the measured data and showed that the analysis models can be used to accurately predict the gas mixing phenomena in the containment.

X-ray spectra of circumgalactic medium around star-forming galaxies: connecting simulations to observations

ABSTRACT The hot component of the circumgalactic medium (CGM) around star-forming galaxies is detected as diffuse X-ray emission. The X-ray spectra from the CGM depend on the temperature and metallicity of the emitting plasma, providing important information about the feeding and feedback of the galaxy. The observed spectra are commonly fitted using simple one-temperature (1-T) or two-temperature (2-T) models. However, the actual temperature distribution of the gas can be complex because of the interaction between galactic outflows and halo gas. Here, we demonstrate this by analysing 3D hydrodynamical simulations of the CGM with a realistic outflow model. We investigate the physical properties of the simulated hot CGM, which shows a broad distribution in density, temperature, and metallicity. By constructing and fitting the simulated spectra, we show that, while the 1-T and 2-T models are able to fit the synthesized spectra reasonably well, the inferred temperature(s) does not bear much physical meaning. Instead, we propose a lognormal distribution as a more physical model. The lognormal model better fits the simulated spectra while reproducing the gas temperature distribution. We also show that when the star formation rate is high, the spectra inside the biconical outflows are distinct from those outside, as outflows are generally hotter and more metal enriched. Finally, we produce mock spectra for future missions with the eV-level spectral resolution, such as Athena, Lynx, the Hot Universe Baryon Surveyor, and theX-ray Imaging and Spectroscopy Mission.

Experimental and computational thermal analysis of partial-body cryotherapy

During the partial body cryotherapy, human surface is cooled with gas for several minutes. For this, special heat and mass exchanger is used – a cryocabin. From a thermal engineering viewpoint, to improve this empirical treatment, detailed data are needed on the temperature and velocity of the cooling gas, as well as on the biological tissues cooling. For this, current study proposes an improved human, partial body cryotherapy simulation models and study of the partial body cryotherapy heat transfer problem in a single system “equipment-gas-biotissue” using experiment and computer simulation. For the first time the cryoexposure duration up to 420 s was analyzed. The data on the actual cooling gas temperature and velocity distributions, skin and internal biotissue temperature, bioheat flux for the considered typical gas supply mode is obtained. The impact of body mass index, external thermal resistance (body hair) and internal structure of a body parts on cooling dynamics is analyzed. This information is expected to be useful for understanding the effect-exposure correlation of the cryotherapy and in the design of the cryotherapy equipment.

Study of UV Ne II line shapes in the cathode sheath of an abnormal glow discharge

We report results of an experimental and theoretical study of complex UV line shapes of Ne II 369.421 nm, Ne II 370.962 nm, Ne II 371.308 nm, and.Ne II 372.711 nm lines in the cathode sheath (CS) region of an abnormal DC glow discharge in pure neon. Two sets of experimental profiles and electric field distributions, one for discharge with tungsten and the other with titanium cathode, were obtained by means of the optical emission spectroscopy (OES) and theoretically studied by the iterative CS kinetic model. It is shown that our theoretical model enables the determination of the most important CS parameters (e.g. the thickness of the CS region, and the theoretical distributions of electric field and gas temperature) and thereupon based accurate theoretical predictions of the experimentally observed profiles of the studied lines.

Study on Distribution of Wellbore Temperature in Gas Drilling with Gradient Equations

Precise calculation of gas temperature profile is the key to gas drilling design. It is traditionally assumed that the gas temperature distribution in the wellbore is equal to the formation temperature, without considering the influence of fluid flow and Joule-Thomson cooling effect. This paper puts forward a gradient equation method for gas temperature distribution in wellbore considering gas flow and Joule-Thomson local cooling of the bit. The method applies pressure, temperature, density, and velocity equations to gas flow in drillstrings and annulus. The solution of the gradient equation is in the form of the fourth-order Runge-Kutta equation. Bottom wellbore temperatures measured at depths of 700 to 2000 m in an actual well are consistent with those predicted by the gradient method. Due to the Joule-Thomson cooling effect at the bit nozzle, the temperature drops by about 30°C. The sensitivity analysis is carried out by gradient method, and the results show that the temperature drop range of different nozzle sizes can reach 60°C due to the Joule-Thomson cooling effect. Stable temperature curves can be established within a few minutes of the gas cycle. Due to the influence of gas flow and Joule-Thomson cooling, the gas temperature in the wellbore deviates significantly from the geothermal temperature in the formation under the flow condition. The temperature of the gas in drillstrings increases as the drill depth increases and then decreases rapidly near the bottom of the hole. As the gas flows upward along the annulus, the gas temperature rises first, surpasses the formation temperature, and then decreases gradually along the geothermal gradient trend.

Application of Planar Laser Rayleigh Scattering for Measurement of Gas Temperature Distributions in Effusion Jet Cooled Panels Exposed to High Temperatures

Abstract This experimental study examines the use of planar laser Rayleigh scattering to measure instantaneous gas temperature distributions at different heights above the surface of an effusion cooled plate. An experimental test rig was used to model combustor conditions with a bulk crossflow temperature of 1500 K. Carbon dioxide was used as coolant at multiple blowing ratios ranging from 1.12 to 11.1. A “temperature-pegging” methodology was used to process Rayleigh light scattering images to create high resolution and accurate temperature images at heights of 2, 2.75, and 3.5 mm above the surface of a prototypical effusion plate. Measured temperature distributions were used to calculate root-mean-square (RMS) distributions, and were also converted to film effectiveness maps based on the upstream crossflow gas and effusion coolant temperatures. It is found that the film cooling region spreads upstream with increasing effusion jet blowing ratio parameter. The RMS deviation of gas temperatures over each measurement plane shows that the RMS fluctuations are low inside and outside the effusion film, but are high near the film edge. At a given height above the effusion panel, the RMS fluctuations decrease in the film region with increasing blowing ratio. Film effectiveness follows similar trends with high film effectiveness region expanding with increasing effusion jet blowing ratios.

Investigation of transport processes in a commercial hot wall CVD reactor with multi-substrates for high-quality pyrocarbon deposition

A 3D CFD model is developed to illustrate the complex reacting flow in the commercial hot-wall CVD reactor using detailed gas and surface chemistry. This helps to understand multi-species transport and their interplay with the gas and surface reactions for pyrocarbon (PyC) deposition. The detailed transport phenomena models with temperature-dependent physical properties are incorporated into the model to improve accuracy. Valuable information such as microscopic local variations in gas velocity, temperature, and species distributions is obtained, which otherwise difficult to acquire experimentally. A sensitivity analysis is also performed to realize how the operating conditions affect the distributions of intermediate species and, ultimately, the growth rate of PyC. The understanding gained in this study is further used to optimize the CVD reactor to obtain high-quality PyC. The response surface methodology is employed to examine the interactions among various operating parameters that influence film performance.

The effect of particle size and volumetric loading on the gas temperature distributions in a particle-laden flow heated with high-flux radiation

The instantaneous, spatially resolved gas-phase temperature distribution within a particle-laden flow heated using high-flux radiation has been measured for a series of heating fluxes, particle volumetric loadings and particle diameters using two-colour laser induced fluorescence of toluene. The temperature of the gas downstream from the start of the heating region was found to increase with an increase in heat flux, an increase in particle loading and a decrease in particle diameter. Coherent regions of high and low temperature in the instantaneous flow associated with spatial variations in the particle distribution were identified for all particle diameters investigated. The time-averaged gas-phase temperature on the jet axis was found to increase approximately linearly with distance in the region downstream from the heating beam to the edge of the measurement region investigated, indicating near-constant convective heat transfer due to the large temperature difference between the gas and radiatively heated particles throughout this region. The axial gradient of gas-phase temperature with distance was also calculated using a simplified, one-dimensional heat transfer model. The difference between the model and measurements was, on average, less than 20%, with the magnitude of this difference found to increase with a decrease in particle diameter and an increase in particle loading.

UV Fluorescence Traces Gas and Lyα Evolution in Protoplanetary Disks

Abstract Ultraviolet spectra of protoplanetary disks trace distributions of warm gas at radii where rocky planets form. We combine Hubble Space Telescope Cosmic Origins Spectrograph observations of H2 and CO emission from 12 classical T Tauri stars to more extensively map inner disk surface layers, where gas temperature distributions allow radially stratified fluorescence from the two species. We calculate empirical emitting radii for each species under the assumption that the line widths are entirely set by Keplerian broadening, demonstrating that the CO fluorescence originates further from the stars r ∼ 20 au than the H2 r ∼ 0.8 au . This is supported by 2D radiative transfer models, which show that the peak and outer radii of the CO flux distributions generally extend further into the outer disk than the H2. These results also indicate that additional sources of Lyα photons remain unaccounted for, requiring more complex models to fully reproduce the molecular gas emission. As a first step, we confirm that the morphologies of the UV–CO bands and Lyα radiation fields are significantly correlated and discover that both trace the degree of dust disk evolution. The UV tracers appear to follow the same sequence of disk evolution as forbidden line emission from jets and winds, as the observed Lyα profiles transition between dominant red wing and dominant blue wing shapes when the high-velocity optical emission disappears. Our results suggest a scenario where UV radiation fields, disk winds and jets, and molecular gas evolve in harmony with the dust disks throughout their lifetimes.

A flamelet LES of turbulent dense spray flame using a detailed high-resolution VOF simulation of liquid fuel atomization

A numerical framework used to model dense spray flames is proposed. In this framework, the liquid fuel (acetone) atomization is solved by a detailed high-resolution VOF simulation, and the Eulerian components of liquid droplets are transformed into Lagrangian droplets, which are stored in a database at a certain downstream cross-section. Then, the combustion process is solved by a LES/FPV (flamelet progress variable) adopting the pre-stored database of Lagrangian droplets (i.e., the position, size, and velocity of each droplet) as the inlet boundary conditions. This framework is a one-way coupling between a VOF simulation and a combustion simulation. The validity of this approach is investigated by comparing the computations with the experiments of the Sydney Piloted Needle Spray Burner. The VOF simulation shows that the volume flux of the droplets at the nozzle exit fluctuates both temporally and spatially and the larger droplets tend to be located away from the center axis compared to the small droplets. The computed breakup length is in good agreement with the empirical correlation. In the database of the Lagrangian droplets for the LES/FPV of spray flames, the location of the sampling cross-section, the sampling time, and the threshold value for Eulerian–Lagrangian (E-L) transformation strongly affect the properties of the Lagrangian droplets, and are critical for the successful use of the LES/FPV. Two spray flames with different recess distances are computed using their optimal pre-stored droplets databases and both show generally good agreement with the experiments in terms of the gas temperature and droplet size distributions. The spray flame with a longer recess distance, which is more representative of a dilute spray, is considered to have a longer and wider premixed core than that with a shorter recess distance representing a dense spray. The discrepancy in the prediction of denser spray flames becomes more evident leading to over-predictions of gas temperature further downstream. Reasons for this behavior are discussed in the text.

Bench Tests for Exhaust Gas Temperature Distribution in an Aircraft Piston Engine with and without a Turbocharger

Bench Tests for Exhaust Gas Temperature Distribution in an Aircraft Piston Engine with and without a Turbocharger

Development of the model and the method for determining the influence of the temperature of gunpowder gases in the gun barrel for explaining visualize of free carbon at shot

A phenomenon that is present in almost every shot is highlighted. It manifests itself in the muzzle discharge as a certain amount of free carbon. The thermochemical reaction of Boudouard-Bell (disproportionation of carbon monoxide) was determined, which explains the formation of free carbon in the gunpowder gases during the firing process. A feature of this reaction is the formation of a condensed phase of carbon during the firing process after the gasification of the gunpowder charge. The reason is revealed that does not allow describing the formation of free carbon during firing on the basis of existing models of internal ballistics processes. It is the lack of taking into account the temperature distribution of the gunpowder gases along the length of the gun barrel and its change. A mathematical model is proposed that makes it possible to estimate the temperature distribution during the shot. A method has been developed for solving the problem of internal ballistics with the ability to determine the temperature of gunpowder gases along the length of the gun barrel at different times and at different positions of the projectile in the barrel. The original model is built using generally accepted assumptions. Modeling results can only be estimated. For this reason, the method is based on simple calculations, which makes it possible not to involve high-power computing equipment. The modeling of the temperature distribution of gunpowder gases in the space of the gun barrel between the charging ball and the moving projectile in the model system is carried out. The possibility of changing the length of the zone of the Boudouard-Bell reaction (the zone of formation of free carbon) depending on the initial data is shown. The use of a fresh gunpowder charge and a degraded one is simulated. Full and reduced charges are considered. The simulation results showed the reason for the possibility of initiating a secondary muzzle discharge flash both from the front side and from the side of the muzzle brake.

Thermo-elastohydrodynamic analysis of the inhomogeneous foil bearing with misalignment

Purpose The misalignment is generally inevitable in the process of machining and assembly of rotor systems with gas foil bearings, but the exploration on this phenomenon is relatively less. Therefore, the purpose of this paper is to carry out the thermo-elastohydrodynamic analysis of the foil bearing with misalignment, especially the inhomogeneous foil bearing. Design/methodology/approach The rotor is allowed to misalign in two non-rotating directions. Then the static and dynamic performance of the inhomogeneous foil bearing is studied. The thermal-elastohydrodynamic analysis is realized by combining the Reynolds equation, foil deformation equation and energy equation. The small perturbation method is used to calculate the dynamic coefficients, then the critical whirl ratio is obtained. Findings The gas pressure, film thickness and temperature distribution distort when the misalignment appears. The rotor misalignment can improve the loading capacity but rise the gas temperature at the same time. Furthermore, the rotor misalignment can affect the critical whirl ratio which demonstrates that it is necessary to analyze the misalignment before the rotordynamic design. Originality/value The value of this paper is the exploration of the thermo-elastohydrodynamic performance of the inhomogeneous foil bearing with misalignment, the analysis procedure and the corresponding results are valuable for the design of turbo system with gas foil bearings.

Stereoscopic Micro PIV Investigation of Velocity Boundary Layer Near Piston Top of a Tumble Enhanced SI IC Engine

Stereoscopic Micro PIV Investigation of Velocity Boundary Layer Near Piston Top of a Tumble Enhanced SI IC Engine

Simulation of Temperature in Gas Drilling with Gradient Method

Accurate prediction of gas temperature profile is critical for designing gas drilling operations. Traditionally the gas temperature distribution in wellbore is assumed to equal the static formation temperature where the influences of fluid flow and Joule-Thomson cooling effect have not been considered. This work presents a gradient equation method to predict the gas temperature profile in the wellbore with considerations of gas flow and Joule-Thomson local cooling at drill bit. The method applies equations of pressure, temperature, density and velocity to gas flow inside drill string and annulus. The solution of the gradient equations takes the form of the fourth order Runge-Kutta equation. Bottom hole temperature measurement from depth 700m to 2000m in a real well is found consistent with the temperature values predicted by the gradient method, both showing 20℃ ~ 30℃ temperature drop due to the Joule-Thomson cooling effect at the bit nozzles. Result of sensitivity analyses with the gradient method indicates that the temperature drops due to the Joule-Thomson cooling effect can be up to 50℃, depending on nozzle size. The steady temperature profile can be established within minutes of gas circulation. Because of the influences of gas flow and Joule-Thomson cooling, the gas temperature in the wellbore significantly deviates from the formation geothermal temperature in flowing conditions. The gas temperature in the drill string increases with the well depth and then decreases rapidly toward the bottom of hole. As the gas flows up the annulus, the gas temperature first jumps up, overshoots the formation temperature, and then gradually decreases along the geothermal gradient trend.

Numerical Analysis on the Flue Gas Temperature Maintenance System of a Solid Fuel-Fired Boiler Operating at Minimum Loads

Currently, energy policy is associated with the increase in the share of renewable sources in systemic energy production. Due to this trend, coal-fired power units must increase their work flexibility. Adapting a coal power plant to work with a lower load often causes the issue of maintaining the temperature before the selective catalytic reduction (SCR) installation at a sufficiently high level. This paper presents a CFD analysis of the mixing area of two flue gas streams before the SCR installation with various methods for mixing flue gas streams. The novelty of the work is mixing the flue gas streams of different temperatures using a flap shape developed by the authors. A series of numerical simulations were performed to develop the location and method of introducing the higher temperature gas, obtaining a uniform distribution of the exhaust gas temperature. The simulation scheme was applied to a series of geometrical modifications of the boundary conditions. The tested solution using only a single, straight flap in the flue gas duct allows the amplitude to be reduced from 298 K to 144 K. As a result of the research, a mixing flap design was developed to reduce the initial temperature amplitude of the flue gas streams from 298 K to 43 K.