Transport Coefficients Of Gas Research Articles

Investigations on carbon-sequestration optimization of recycled coarse-aggregate and its effects on concrete performances

Recycled coarse-aggregate (RCA) derived from waste concrete can be re-used for concrete preparation, which is now limited due to its drawbacks such as micro-cracks, high-porosity, and reduced concrete strengths. To remedy these deficiencies, carbon-sequestration was employed to enhance RCA and the conditions were optimized, including the temperature (20 °C–40 °C), pressure (0.1 MPa–0.3 MPa), time (5 h–24 h) and initial water content (25%–75 %). There parameters were optimized based on the orthogonal test with scheme L9(34), which was evaluated based on RCA carbon-sequestration amount as well as its properties. With the optimized parameters, RCA was enhanced as CRCA. Both RCA and CRCA were utilized to fully replace natural coarse-aggregate (NCA) in concrete and concrete basic performances were investigated systematically, including strengths, shrinkage and medium transport properties. The results show that the effects of carbon-sequestration time and initial water-content of aggregate on the carbon-sequestration efficiency of RCA are the most significant. The optimized parameters were 30 °C temperature, 0.3 MPa pressure, 24 h time and 25 % initial water content with the maximum amount of carbon-sequestration at 8.42 %. The carbon-sequestration reduced the width of the recycled aggregate interfacial transition zone (ITZ) in concrete, increased the microhardness of ITZ and mortar, and decreased the porosity of CRCA. The CRCA elevated the compressive strength, splitting tensile strength and flexural strength of the concrete (28d) by 13.5 %, 8.5 % and 7.4 %, respectively. The drying shrinkage at 28d of RCA-concrete was decreased by 12.0 % when RCA was replaced with CRCA, however with the CRCA value still 16.2 % higher than that of NCA-concrete. Moreover, CRCA can decrease the medium transport coefficients of water, chloride, and gas in concrete when compared with the RCA-concrete while they are still greater than those of NCA-concrete.

Analytical structure of the binary collision integral and the ultrarelativistic limit of transport coefficients of an ideal gas

Analytical structure of the binary collision integral and the ultrarelativistic limit of transport coefficients of an ideal gas

Rainstorm and strong wind weathers largely increase greenhouse gases flux in shallow ponds

Shallow-water ponds represent the hotspots of greenhouse gas (GHG) emissions. Most current studies focus on the temporal dynamics for GHGs in water, with little consideration given to the effects of weather changes. In this study, we measured and compared the concentrations and fluxes of CO2, CH4, and N2O from a pond in Northeast China under different meteorological conditions. Results showed that the rates of CO2, CH4, and N2O emissions from pond into the atmosphere during strong winds were 85.85 ± 7.55 mmol m−2 d−1, 22.05 ± 6.80 mmol m−2 d−1, and 10.87 ± 0.72 μmol m−2 d−1, respectively, significantly higher than those measured during non-rain weather. Among which, over 88 % of CH4 emissions were contributed by ebullition. Meanwhile, the CO2 and N2O flux were also significantly higher during heavy rainfall, reaching 100.05 ± 19.76 mmol m−2 d−1 and 5.90 ± 1.03 μmol m−2 d−1, respectively. Strong winds and precipitation induced sediment disturbances, high gas transport coefficients, reduced photosynthesis and oxygen greatly promoted the GHGs escape evasion. Wind speed, air pressure, solar radiation, and dissolved oxygen in water were important influencing factors. Our results emphasize the importance of capturing short-term weather disturbance events, especially rainstorm and strong winds, to accurately assess the annual GHG budget from these shallow water ecosystems.

Effect of pendant ester groups on gas transport property of 6FDA-BAPP/6FAP copolyimide membrane

Despite the various methods that have been developed, controlling the microstructure of polyimide membranes to achieve excellent separation performance based on target gases remains a challenge. One such method involves rearranging polyimides containing ortho-hydroxyl groups into polybenzoxazoles at temperatures above 400 °C, which can effectively distort the backbones and improve gas diffusion. However, this approach is limited by the extremely high conversion temperatures required and low conversion degrees achieved. The esterification process of the polyimide, which contains ortho-hydroxyl groups to the imide ring, represents a simple and effective approach to enhance the membrane's competitiveness in gas separation without undergoing thermal rearrangement at high temperatures. The polyimide was prepared by the polycondensation of 4,4'-(Hexafluoro isopropylidene) diphthalic anhydride (6FDA), 2,2-double (4,4-amino phenoxy) propane (BAPP), and 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane (6FAP). Microstructures and gas transport coefficients were analyzed when the esterification of 6FDA-BAPP/6FAP was conducted using acetic anhydride and caproic anhydride. In CO2/N2 separation, a-6FDA-BAPP/6FAP exhibits CO2 permeability of 1279.41 ± 66.93 Barrer and perm-selectivity of 40.80 ± 2.27, owing to the significantly improved affinity to CO2. The membrane of c-6FDA-BAPP/6FAP exhibit the further improved CO2 permeability and deteriorated perm-selectivity, due to a leveling effect on the diffusion of CO2 and N2 caused by the pendant caproates with longer alkyl chains. The results confirmed that the gas separation performance of polyimide membrane containing ortho-hydroxyl groups is sensitive to the pendant group.

Investigation of methane mass transfer and sorption in Marcellus shale under variable net-stress

Natural gas in shale exists as free and adsorbed gas, subject to prevailing pore pressures and stress conditions. Accordingly, to accurately estimate/predict the shale gas recovery potential, a central requirement is to represent gas transport and sorption behavior under varying stress conditions. The objective of this work is to facilitate the interpretation of laboratory-scale experiments, at relevant conditions, in an attempt to bridge the gap in scales between laboratory- and field-scale observations.We have conducted a series of high-pressure experiments on a full-diameter core sample from the Marcellus shale. These include gas loading (pressure-decay) and depletion (production) experiments with pure methane (CH4) at variable stress conditions to characterize transport and sorption behavior under reservoir-relevant conditions. We have formulated and applied a novel integral model for mass transfer and storage in multi-porosity shale systems that allows us to effectively investigate transport and sorption phenomena: We delineate gas transport by interpreting helium (He) pressure-decay experiments and demonstrate how to use the information gained to calculate the relevant transport coefficients of CH4 and other gases. A separate measurement of the CH4 sorption isotherm on a smaller sample (a shale cube) was interpreted and combined with the transport description to predict the production behavior of CH4 from the experiments with the full-diameter core.Our experiments demonstrate that the representation of sorption hysteresis is crucial for predicting and guiding shale gas production: At the end of both gas production experiments, approximately 20% of the initial gas in place remained in the core. Without accounting for sorption hysteresis, our modeling demonstrates that the CH4 production could be overestimated by 10%. We demonstrate that our integral, triple-porosity model provides an effective approach for the interpretation and prediction of gas transport and sorption behavior during loading and production experiments on shale cores under variable net-stress conditions.In summary, our work combines measurements and modeling of mass transfer and sorption in shales at different scales to validate a characterization approach that facilitates an improved understanding of shale gas production. Furthermore, the triple-porosity model utilized in our work defines a potential pathway for the translation of laboratory-scale experimentation to larger-scale applications.

Study on the influence of metal phase transition on transport coefficient calculation of gas–metal plasma mixtures

In most industrial applications, plasma has an important feature that the erosion products produced by plasma will undergo a phase transition and affect the properties of plasma mixtures. Calculating the transport coefficients of the plasma mixtures, usually, gas–metal mixtures, is an important approach to study this feature. However, most transport coefficient calculation methods have some difficulties in dealing with the solid and liquid components of gas–metal plasma mixtures. In this study, a modified method for calculating transport coefficients of gas–metal plasma mixtures containing solid and liquid status is proposed, considering that the liquid and solid components are usually in the form of clusters. Based on this modified method, the influence of the metal phase transition on the transport coefficients of gas–metal plasma mixture is explored with the example of H2–Cu plasma mixture. The findings revealed in this study are as follows: (1) The modified calculation method is applicable for not only gas–metal plasma mixtures but also other plasma mixtures containing solid and liquid status. (2) Ignoring the metal phase transition in the calculation of transport coefficients of gas–metal plasma mixtures will inevitably produce considerable variances. (3) The variances, caused by ignoring the metal phase transition, are tightly associated with the pressure, the proportion of metal, and the unbalanced degree of gas–metal plasma mixtures. In summary, the variances caused by ignoring the metal phase transition might be ignorable only when the pressure, proportion of metal, and unbalanced degree of gas–metal plasma mixture are all in extremely small values.

Computational study of temperature and density perturbations on atmospheric dynamics

This study examines the perturbation effect of temperature and density of moist air on atmospheric variables at 9°1’48″N, 38°44’24″E and 6.324 km above the Earth’s surface. The atmosphere is a compressible neutral moist air flowing on a rotating Earth as a model and it’s basic atmospheric parameters such as gas constant, transport coefficients, mixing ratio and specific heat capacities are considered to be temperature dependent and the Earth’s gravity changes with latitude and altitude. To describe the dynamics, we carried out a numerical computation using finite difference method on an unstaggered grid. Our results revealed that the response of all the variables have a plane wave pattern, in which specific heat capacities (SHCs), resultant wind speed (RWS) and water vapor mixing ratio (MR) increase with time at each latitude but vertical wind speed (VWS), specific enthalpy (SE) and pressure decrease with time at each latitude. The increase of MR with time is the result of water vapor flux into the air parcel and the decrease of SE and increase of RWS with time is the result of thermal energy to mechanical energy transformation. The decrease of VWS with time is the effect of the viscous force due to temperature dependence of viscosity.

Gas permeameter for polymers and nanocomposites: a new equipment

Information on the gas transport coefficients in the permeation of homogeneous semipermeable materials such as semicrystalline polymers under extreme pressures and temperatures is rarely found in the literature. Therefore, the objective of this work is to showcase innovation regarding the accuracy and usability of the medium pressure and temperature gas permeameter suitable for polymeric and polymeric nanocomposite plates built by the authors, which was tested with nitrogen at 1 MPa and 69 °C (342.15 K) permeating pure high density polyethylene samples (HDPE) and HDPE samples with added nanoclay, redoing the tests published in a previous work on the subject. The results were compared against data obtained previously and information present in the literature, validating the permeameter presented in this work, which is capable of analyzing gas permeability under the described conditions with greater accuracy and ease of operation than the previous model for the values of the transport coefficients of nitrogen permeating HDPE, demonstrating that the implemented improvements and advances were adequate, allowing the measurement of the transport properties of gases permeating polymeric and nanocomposite plates, necessary information for the design of risers for the transportation of oil and natural gas, for example.

Kinetic theory of granular particles immersed in a molecular gas

The transport coefficients of a dilute gas of inelastic hard spheres immersed in a gas of elastic hard spheres (molecular gas) are determined. We assume that the number density of the granular gas is much smaller than that of the surrounding molecular gas, so that the latter is not affected by the presence of the granular particles. In this situation, the molecular gas may be treated as a thermostat (or bath) of elastic hard spheres at a fixed temperature. The Boltzmann kinetic equation is the starting point of the present work. The first step is to characterise the reference state in the perturbation scheme, namely the homogeneous state. Theoretical results for the granular temperature and kurtosis obtained in the homogeneous steady state are compared against Monte Carlo simulations showing a good agreement. Then, the Chapman–Enskog method is employed to solve the Boltzmann equation to first order in spatial gradients. In dimensionless form, the Navier–Stokes–Fourier transport coefficients of the granular gas are given in terms of the mass ratio$m/m_g$($m$and$m_g$being the masses of a granular and a gas particle, respectively), the (reduced) bath temperature and the coefficient of restitution. Interestingly, previous results derived from a suspension model based on an effective fluid–solid interaction force are recovered in the Brownian limit ($m/m_g \to \infty$). Finally, as an application of the theory, a linear stability analysis of the homogeneous steady state is performed showing that this state is always linearly stable.

A differential CO2 profile probe approach for field measurements of soil gas transport and soil respiration#

AbstractBackgroundGas exchange between soil and atmosphere is of great importance for greenhouse gas cycles. As gas transport in soil is generally dominated by diffusion, the soil gas diffusion coefficient (DS) is crucial to understand fluxes between soil and atmosphere. Estimating DS is still a great source of uncertainty when calculating soil gas fluxes such as soil respiration from soil gas profiles. In situ measurement of the effective exchange coefficient (Deff) not only reduces this uncertainty, but also allows to quantify non‐diffusive transport processes in addition to the purely diffusive exchange (DS), which cannot be investigated by laboratory measurements or the application of soil gas diffusivity models. Even though several methods for in situ Deff measurement exist, they often lack in the temporal resolution to identify short‐term effects on Deff or require laborious set‐ups, which makes them unsuitable for a fast and mobile application.AimsOur objective was to test an improved profile probe for model‐based soil gas flux analyses that allows in situ monitoring of (1) soil CO2 profiles with high temporal resolution, (2) soil gas transport coefficients, including non‐diffusive transport processes, (3) soil–atmosphere CO2 flux, and (4) soil respiration profiles.MethodsWe developed a CO2 profile probe with build‐in sensors that can easily be installed in soil to gain continuous CO2 concentration profiles. The probe includes the option to inject CO2 as a tracer gas to estimate Deff. To account for changes in natural CO2 concentrations in the soil, we tested two approaches: firstly, a differential approach using two probes, an injection probe and a reference probe, and secondly, a stand‐alone approach in which changes in natural CO2 concentrations are estimated by a statistical model using its main environmental drivers. The resulting tracer gas profiles were used to fit a finite element gas diffusion model to derive Deff. Using the derived Deff values and the CO2 profiles allowed calculating CO2 fluxes. The approach was tested with controlled laboratory experiments using different mineral substrates to compare the diffusivity estimates of the in situ method with laboratory measurements on soil cores. Additional laboratory experiments included artificial CO2 sources to simulate soil respiration in order to evaluate the gradient‐based estimation of soil respiration profiles. In a second step, both approaches were tested under natural conditions in the field.ResultsThe derived Deff values agreed well with laboratory measurements of DS and DS‐transfer functions. The artificial CO2 sources could accurately be estimated with the gradient method. In the field under calm conditions, both approaches for the estimation of the changing natural CO2 profile gave comparable results. Under windy conditions, the stand‐alone approach gave unrealistically high values, whereas the differential approach using a reference profile still gave reliable results. We observed a clear relationship between Deff and wind‐induced pressure pumping in the topsoil. The estimated surface CO2 efflux agreed well with chamber measurements.ConclusionsThis new set‐up enables monitoring of diffusive and non‐diffusive soil gas exchange and soil respiration in situ with high resolution and relatively low effort.

Transport coefficients for granular gases of electrically charged particles

We consider a dilute gas of electrically charged granular particles in the homogeneous cooling state. We derive the energy dissipation rate and the transport coefficients from the inelastic Boltzmann equation. We find that the deviation of the velocity distribution function from the Maxwellian yields overshoots of the transport coefficients, and especially, the negative peak of the Dufour-like coefficient,$\mu$, in the intermediate granular temperature regime. We perform the linear stability analysis and investigate the granular temperature dependence of each mode, where the instability mode is found to change against the granular temperature. The molecular dynamics simulations are also performed to compare the result with that from the kinetic theory.

Gas transport and diffusion coefficients in a coupling coal system of matrix and nano-fracture: A molecular simulation study

Handling the gas transport mechanisms in fractured media is vital for the exploitation of coalbed methane (CBM). The gas storing and transport capability in coals relies to a great extent on the nano-structure. In this research, a combined matrix and nano-fracture system based on the double-porosity model was constructed. We aimed at providing molecular-level insights into the gas transport behaviors through simulation methods. The results demonstrated that the average density of methane in nano-fracture was obviously beyond that in matrix. Meanwhile, there was a significant equilibration time-lag between matrix and fracture. Gas molecules distributed in the nano-fracture had high diffusion rate. In addition, the adsorption layers were formed in the transition area between matrix and fracture with the increased densities. The gas molecules distributed in coal matrix randomly moved in pores. By contrast, the methane in nano-fracture and adsorption layers moved directionally along Z-axis and YZ plane, respectively. The simulated self- and transport diffusion coefficients were calculated, and the results turned out to coincide well with the experimental data. The diffusivity component parallel to fracture played a major role in the whole diffusion. There was a strong pressure dependence of diffusivity in the case of a small channel width. For the impact of surface geometry, the molecular velocity in the cylindrical system increased dramatically compared with that in the cubic block. The molecular simulation could be an effective means to correctly characterize the micro-transport properties of CBM molecules.

Equilibria and oscillations in a reversible mechanical system

The method of stochastic molecular modeling, developed by the authors for calculating the transport coefficients of rarefied gas in a free medium, is generalized to describe transport processes in confined conditions. The phase trajectories of the studied molecular system are simulated stochastically, and the simulation of the dynamics of the molecule is split into processes. First, its shift in the configuration space is realized, and then a possible collision with other molecules is played out. The calculation of all observables, in particular, the transport coefficients is carried out by averaging over an ensemble of independent phase trajectories. The interaction of gas molecules with the boundary is described by mirror or mirror-diffuse laws. The efficiency of the algorithm is demonstrated by calculating the selfdiffusion coefficient of argon in the nanochannel. The accuracy of modeling is investigated, its dependence on the number of particles and phase trajectories used for averaging. The viscosity of rarefied gases in the nanochannel has been systematically studied. It is shown that it is non-isotropic, and its difference along and across the channel is determined by the interaction of gas molecules with the channel walls. By changing the material of the walls, it is possible to significantly change the viscosity of the gas, and it can be several times greater than in volume, or less. The indicated anisotropy of viscosity is recorded not only in nano-, but also in microchannels.

Direct stochastic molecular modelling of transport processes in gases

The stochastic molecular modeling method (SMM) of transport processes in rarefied gases developed by the authors is systematically discussed in this paper. It is shown that, it is possible to simulate the transport coefficients of rarefied gas with high accuracy, using a relatively small number of molecules. The data of modeling the thermal conductivity coefficient are presented for the first time. The second part of the paper is devoted to the generalization of the SMM method for modeling transport processes in confined conditions. To describe the dynamics of molecules in this case, the splitting of their evolution by processes is used: first, the movement of molecules in the configuration space is simulated, and then their dynamics in the velocity space is imitated. Anisotropy of viscosity and thermal conductivity in nanochannels has been established. The interaction of gas molecules with walls is described by specular or specular-diffuse reflection laws. Gas viscosity can be either greater than in the bulk or less, depending on the law of gas interaction with the channel walls.

Hydrodynamics of granular gases of inelastic and rough hard disks or spheres. I. Transport coefficients.

The transport coefficients for dilute granular gases of inelastic and rough hard disks or spheres with constant coefficients of normal (α) and tangential (β) restitution are obtained in a unified framework as functions of the number of translational (d_{t}) and rotational (d_{r}) degrees of freedom. The derivation is carried out by means of the Chapman-Enskog method with a Sonine-like approximation in which, in contrast to previous approaches, the reference distribution function for angular velocities does not need to be specified. The well-known case of purely smooth d-dimensional particles is recovered by setting d_{t}=d and formally taking the limit d_{r}→0. In addition, previous results [G. M. Kremer, A. Santos, and V. Garzó, Phys. Rev. E 90, 022205 (2014)10.1103/PhysRevE.90.022205] for hard spheres are reobtained by taking d_{t}=d_{r}=3, while novel results for hard-disk gases are derived with the choice d_{t}=2,d_{r}=1. The singular quasismooth limit (β→-1) and the conservative Pidduck's gas (α=β=1) are also obtained and discussed.

Моделирование теплопроводности разреженных газов стохастическим методом

One of the main successes of the kinetic theory of gases is the explicit calculation of the transport coefficients of rarefied gases. However, the greatest problems arise when calculating the thermal conductivity coefficient, especially for polyatomic gases. Also, when using different potentials, it is necessary to systematically calculate the so-called Ω-integrals, which in itself is a rather difficult task. For this reason, direct numerical molecular modeling of the processes of transfer of rarefied gases, in particular, the calculation of their transfer coefficients, is also relevant. A well-known method for such modeling is the molecular dynamics method. Unfortunately, until now this method is not available for modeling the processes of rarefied gas transfer. Under nor-mal conditions, the simulation cell should contain tens or even hundreds of millions of molecules during calculations. At the same time, the numerical implementation of the molecular dynamics method is accompanied by a systematic appearance of errors, which is the reason for the appearance of dynamic chaos. With this simulation, the true phase trajectories of the system under consideration cannot be obtained. Therefore, naturally, the idea of developing a method for modeling transport processes arises, in which phase trajectories are not calculated based on Newton's laws, but are simulated, and then are used to calculate any observables. In our works, we developed a method of stochastic molecular modeling (STM) of rarefied gas transfer processes, where this idea was implemented. The efficiency of the SMM method was demonstrated by calculating the coefficients of self-diffusion, diffusion, and viscosity of both monoatomic gases and polyatomic gases. At the same time, the possibility of modeling the most complex transfer process – the energy transfer process – has not yet been considered. This work aims to simulate the thermal conductivity coefficient by the SMM method. Both monoatomic (Ar, Kr, Ne, Xe) and polyatomic gases (CH4, O2) were considered.

The impact of pore structure and adsorption behavior on kerogen tortuosity

Diffusion tortuosity is an important microstructural parameter for computing effective gas transport coefficients in porous media. In this study, a realistic kerogen structure was built to quantitatively establish a clear understanding of the adsorption impact on diffusion tortuosity in the organic materials of shale. A molecular simulation study was employed to reconstruct a Type II-D kerogen model on a computational platform. A structure of five kerogen macromolecules was obtained through a series of NVT – NPT ensembles. There was a thorough characterization of the porosity and pore size distribution of the final structure. A grand canonical Monte Carlo method was used to compute the adsorption of methane for a pressure range up to 40 MPa. Freundlich and Langmuir models were employed to further parameterize the adsorption capacity. A molecular dynamics diffusion study was performed on the kerogen-adsorbed molecule configurations to obtain the effective diffusion, which was then used to estimate the tortuosity. Methane molecules follow tortuous pathways of diffusion, imposed by the heterogeneity and confinement of kerogen. The tortuosity is further impacted by the adsorption effect. Kerogen-methane interactions increase this tortuosity by a factor as high as 3.6 compared to an adsorption-corrected tortuosity.

Gas permeameter in polymer nanocomposite plates: construction and validation

Gas permeability in homogeneous semipermeable materials such as semicrystalline polymers is an inherent property of the material structure that results in the absorption of fluids from diffusion in their matrix. The ability of a gas to cross a semipermeable membrane more or less quickly is the object of research in various fields such as food and drug packaging industry, the chemical industry, and oil and natural gas explorations. In crude oil extraction, polymers minimize permeation and leakage in offshore hoses when materials are in contact with gases at high pressures and temperatures, preventing accidents with serious environmental and human impacts. As information regarding the transport coefficients of gases under extreme conditions is scarce in the literature, it was necessary to experimentally build and validate a device capable of providing reliable data on these properties. Thus, the aim of this paper is to describe a medium pressure gas permeameter in polymer nanocomposite plates, developed by the authors and sought to be validated with nitrogen at 1 MPa and 69 oC (342.15 K) in samples of high-density polyethylene both pure and with nanoclay, forming a polymer nanocomposite, considering the methods of obtaining the transport coefficients studied in the literature review of the standardized experimental techniques. The comparison of the results obtained with the data found in the literature suggests the validity of the equipment in presentation for the analysis of the gas permeability of different polymeric materials.

CLAYEY SOIL AMENDMENT BY HYDROPHILIC NANO BENTONITE FOR LANDFILL COVER BARRIER: A CASE STUDY

Methane and carbon dioxide are of major concern as greenhouse gases; the landfills have the problem of controlling these gases. Al Akaider in Jordan is the second biggest landfill suffers controlling gases as it lacks a cover design system. In this work, the main goal is to investigate the appropriateness of amended expansive clayey soil in Irbid as a cover barrier. The expansive soil is unwanted in construction projects, thus the modification of this expelled soil enables using it as a low cost landfill cover barrier. In this research, the effect of adding nano-clay material (Hydrophilic Nano Bentonite) on the geotechnical characteristics, hydraulic conductivity, and gas transport coefficients of the clayey soil are studied. The soil samples were obtained from Irbid city. Unconfined compressive strength and free swelling tests were performed on soil samples with different percentages of nano-clay added in the range (0.1% to 1.2%) by weight. The results indicated that the addition of nano-clay at low percentages increases the strength of expansive soil up to 315 kPa at 0.6% of nano-clay and the swelling potential decreased dramatically with the addition of nano-clay. The optimal percent of nano-clay was found to be 0.6%. The intrinsic permeability of the amended soil was 6.03×10–15 m2. The average values of fluid transport coefficients were determined at 25 °C. The hydraulic conductivity for water was about 6.5×10–10 m/s. Gas conductivity coefficients for CO2 and CH4 were 5×10–9 m/s and 2.5×10–9 m/s respectively. Gas diffusion coefficients for CO2 and CH4 were 3×10–6 m2/s and 4×10–6 m2/s respectively.

Rayleigh-Brillouin light scattering spectroscopy of air; experiment, predictive model and dimensionless scaling

ABSTRACT Spontaneous Rayleigh-Brillouin (RB) scattering experiments have been performed in air for pressures in the range 0.25–3 bar and temperatures in the range 273–333 K. The functional behaviour of the RB-spectral profile as a function of experimental parameters, such as the incident wavelength, scattering angle, pressure and temperature is analysed, as well as the dependence on thermodynamic properties of the gas, as the shear viscosity, the thermal conductivity, the internal heat capacity and the bulk viscosity. Measurements are performed in a scattering geometry detecting at a scattering angle and an incident wavelength of , at which the Brillouin features become more pronounced than in a right angles geometry and for ultraviolet light. For pressure conditions of 1–3 bar the RB-spectra, measured at high signal-to-noise ratio, are compared to Tenti-S6 model calculations and values for the bulk viscosity of air are extracted. Values of are found to exhibit a linear dependence on temperature over the measurement interval in the range . A temperature dependent value is deduced from a collection of experiments to yield: . These results are implemented in model calculations that were verified for the low pressure conditions (p<1 bar) relevant for the Earth's atmosphere. As a result we demonstrate that the RB-scattering spectral profiles for air under sub-atmospheric conditions can be generated via the Tenti-S6 model, for given gas-phase and detection conditions (p, T, , and θ), and for values for the gas transport coefficients. Spectral profiles for coherent RB-scattering in air are also computed, based on the Tenti-S6 formalism, and the predictions are compared with profiles of spontaneous RB-scattering. Finally data on RB-scattering in air, obtained under a variety of pressure, temperature, wavelength and scattering angles, are analysed in terms of universal scaling, involving the dimensionless uniformity parameter y and the dimensionless frequency x. Such scaling behaviour is shown to be well behaved for a wide parameter space and implies that RB-scattering spectra can be generated for a wide range of atmospheric applications of RB-scattering. The verification of this dimensionless scaling also shows that air can be treated as an ideal gas in the atmospheric regime, where .