Absorption Coefficients Of Gases Research Articles

Correlated k-Distribution Treatment of Cloud Optical Properties and Related Radiative Impact

AbstractA new scheme of water cloud optical properties is proposed for correlated k-distribution (CKD) models, in which the correlation in spectral distributions between the gaseous absorption coefficient and cloud optical properties is maintained. This is an extension of the CKD method from gas to cloud by dealing with the gas absorption coefficient and cloud optical properties in the same way.Compared to the results of line-by-line benchmark calculations, the band-mean cloud optical property scheme can overestimate cloud solar heating rate, with a relative error over 30% in general. Also, the error in the flux at the top of the atmosphere can be up to 20 W m−2 at a solar zenith angle of 0°. However, the error is considerably reduced by applying the new proposed CKD cloud scheme. The physical explanation of the large error for the band-mean cloud scheme is the absence of a spectral correlation between the gaseous absorption coefficient and the cloud optical properties. The overestimation of the solar heating rate at the cloud-top layer could affect the moisture circulation and limit the growth of cloud. It is found that the error in the longwave cooling rate caused by the band-mean cloud scheme is very small. In the infrared, the local thermal emission strongly affects the spectral distribution of the radiative flux, which makes the correlation between the gaseous absorption coefficient and cloud optical properties very weak. Therefore, there is no obvious advantage in emphasizing the spectral correlation between gas and cloud.

비분산 적외선 가스센서의 온도보상 알고리즘

본 논문에서는 써모파일을 사용한 비분산 적외선 메탄가스센서의 온도보상 알고리즘을 제시하였다. 가스측정을 위해 적외선 감지부에 내장된 써미스터의 출력전압과 분위기 온도와의 상관성을 도출하고, 협 대역통과 필터 특성과 온도 변화에 따른 센서모듈(광 공동과 적외선램프)의 출력전압 특성 및 메탄가스의 흡수계수와 광 경로에 따른 출력특성 해석을 통하여 가스센서 모듈의 온도보상 알고리즘을 도출하였다.온도보상 전 약 <TEX>$\pm$</TEX> 1,500 ppm 이상의 오차를 갖는 센서는 온도보상 알고리즘을 적용함으로써 <TEX>$20^{\circ}C$</TEX>온도변화 구간에서 최대 약 180 ppm 이하의 정밀한 센서모듈을 제작하였다. This paper describes the temperature compensation algorithm using thermopile detector for nondispersive infrared methane gas sensor. From the output voltage of thermistor that is attached onto the infrared detector, the ambient temperature was extracted. The effects of temperatures on the properties of sensor module (the characteristics of narrow bandpass filter, optical cavity and infrared lamp, and gas absorption coefficient times optical path length) have been introduced in order to implement the temperature compensation algorithm. Even though the measurement error of developed sensor module was in the range of <TEX>$\pm$</TEX> 1,500 ppm, after programming the temperature compensation algorithm, the developed sensor module shows a high accuracy less than +180 ppm error within <TEX>$20^{\circ}C$</TEX> temperature variation.

SLW-1 Modeling of Radiative Heat Transfer in Nonisothermal Nonhomogeneous Gas Mixtures With Soot

The spectral line weighted-sum-of-gray-gases (SLW) model consisting only of a single gray gas and of one clear gas is developed as an efficient spectral method for modeling radiation transfer in gaseous medium. The model is applied here in prediction of radiative transfer in nonisothermal and nonhomogeneous gas mixtures with nongray soot. The absorption spectrum of the gas mixture and soot particles is treated as a spectrum of a single effective gas, reducing the problem to the simplest case of the SLW model with a single gray gas and a clear gas. Good accuracy can be achieved by the optimal choice of the model’s gray gas absorption coefficient and its weight by application of the absorption-line blackbody distribution functions of individual species in the mixture calculated with a high-resolution spectral database. The SLW-1 model is validated by comparison with benchmark solutions using the line-by-line method, the SLW method with a large number of gray gases, and the SNB model.

Parameters of the collisionally broadened R22 absorption line of the 1000–0001 transition of the CO2 molecule

A frequency stabilized, tuneable CO2 laser is used to measure the unsaturated absorption coefficients of pure carbon dioxide gas at pressures of 1 and 100 Torr and temperatures of 296–700 K. The radiative transition probability and the temperature dependence of the collisional self-broadening coefficient are determined for the R22 absorption line of the 1000-0001 transition of the CO2 molecule. The exponent on the temperature is found to depend on the method used to determine the collisional self-broadening coefficient.

The SLW-1 model for efficient prediction of radiative transfer in high temperature gases

A reduced SLW model consisting of a single gray gas and a clear gas is developed as an efficient spectral method for modeling radiation transfer in high temperature gases. It is shown that the SLW-1 model is not simply a reduction of the SLW method to the case of a single gray gas. Good accuracy can be achieved by the optimal choice of the model’s gray gas absorption coefficient and its weight by application of the Absorption-Line Blackbody Distribution Function (ALBDF), which is calculated with a high-resolution spectral database. Different approaches to the construction of the SLW-1 model are shown. The SLW-1 model absorption spectrum still has the line structure corresponding to the real gas absorption spectrum, which is maintained with fixed spectral intervals in non-uniform medium with the help of the reference approach. The validation of the SLW-1 model is performed by comparison with (i) benchmark solutions obtained by the line-by-line method and (ii) the SLW method with a large number of gray gases. Formulation of the SLW-1 method is also shown with the Two-Flux method and P-1 differential approximation.

A closure study of aerosol hygroscopic growth factor during the 2006 Pearl River Delta Campaign

Measurements of aerosol physical, chemical and optical parameters were carried out in Guangzhou, China from 1 July to 31 July 2006 during the Pearl River Delta Campaign. The dry aerosol scattering coefficient was measured using an integrating nephelometer and the aerosol scattering coefficient for wet conditions was determined by subtracting the sum of the aerosol absorption coefficient, gas scattering coefficient and gas absorption coefficient from the atmospheric extinction coefficient. Following this, the aerosol hygroscopic growth factor, f(RH), was calculated as the ratio of wet and dry aerosol scattering coefficients. Measurements of size-resolved chemical composition, relative humidity (RH), and published functional relationships between particle chemical composition and water uptake were likewise used to find the aerosol scattering coefficients in wet and dry conditions using Mie theory for internally- or externally-mixed particle species [(NH4)2SO4, NH4NO3, NaCl, POM, EC and residue]. Closure was obtained by comparing the measured f(RH) values from the nephelometer and other in situ optical instruments with those computed from chemical composition and thermodynamics. Results show that the model can represent the observed f(RH) and is appropriate for use as a component in other higher-order models.

Measurement technique for methane concentration by wavelength scanning of a distributed-feedback laser

A new technique which takes advantage of distributed-feedback (DFB) laser wavelength scanning to measure methane concentration is presented. A wavelength scan of the methane absorption peak at 1665.9 nm is realized using sawtooth modulation of the current injected to a DFB laser. A reference methane gas cell is used to find the methane absorption peak around 1666 nm, and normalization is used to reduce outside influences such as power drift and fiber loss. The concentration is derived by arithmetic processing of the absorption coefficient of the methane gas. An application test is carried out in a coal mine and a long-term precision of 0.05% is achieved.

Measurement technique for methane concentration by wavelength scanning of a distributed-feedback laser

A new technique which takes advantage of distributed-feedback (DFB) laser wavelength scanning to measure methane concentration is presented. A wavelength scan of the methane absorption peak at 1665.9 nm is realized using sawtooth modulation of the current injected to a DFB laser. A reference methane gas cell is used to find the methane absorption peak around 1666 nm, and normalization is used to reduce outside influences such as power drift and fiber loss. The concentration is derived by arithmetic processing of the absorption coefficient of the methane gas. An application test is carried out in a coal mine and a long-term precision of 0.05% is achieved.

Investigation of radiative heat transfer in fixed bed biomass furnaces

This paper presents an investigation of the radiative heat transfer process in two fixed bed furnaces firing biomass fuels and the performance of several widely used models for calculation of radiative heat transfer in the free-room of fixed bed furnaces. The simple optically thin (OT) model, the spherical harmonic P1-approximation model, the grey gas model based on finite volume discretization (FGG), and the more accurate but time consuming spectral line weighted-sum-of-grey-gases (SLW) model are investigated. The effective mean grey gas absorption coefficients are calculated using an optimised version of the exponential wide band model (EWBM) based on an optical mean beam length. Fly-ash and char particles are taken into account using Mie scattering. In the investigated updraft small-scale fixed bed furnace radiative transfer carries heat from the bed to the free-room, whereas in the cross-current bed large-scale industry furnace, radiative transfer brings heat from the hot zones in the free-room to the drying zone of the bed. Not all the investigated models can predict these heat transfer trends, and the sensitivity of results to model parameters is fairly different in the two furnaces. In the small-scale furnace, the gas absorption coefficient predicted by using different optical lengths has great impact on the predicted temperature field. In the large-scale furnaces, the predicted temperature field is less sensitive to the optical length. In both furnaces, with the same radiative properties, the low-computational-cost P1 model predicts a temperature field in the free-room similar to that by the more time consuming SLW model. In general, the radiative heat transfer rates to the fuel bed are not very sensitive to the radiative properties, but they are sensitive to the different radiative heat transfer models. For a realistic prediction of the radiative heat transfer rate to the fuel bed or to the walls, more computationally demanding models such as the FGG or SLW models should be used.

Particle effects on the emissivity and temperature of optically thick, mixed media retrieved by mid-IR emission spectroscopy

Passive diagnostics offer new ways of obtaining real-time data for the control and modeling of industrial furnaces. It has been proposed elsewhere that from the intensity profile between 3.8 and 4.7 μm one may derive the temperature of a gas–particle medium and the particle emissivity ( ε p) at 3.95 μm. This technique applies to large columns of combustion products with enough CO 2. The temperature is retrieved by finding the best fit between Planck's function and the intensity profile between 4.56 and 4.7 μm, which is that of a blackbody due to CO 2 saturation. Here we consider the effect of particles on the intensity profile and, therefore, on the retrieved temperature and particle emissivity. We derive an analytic approximation of the effective emissivity for an optically thick gas–particle mixture that includes emission and absorption due to particles and gases, along with isotropic particle scattering. The derivation follows the method of embedded invariance and has been used already for particle-only clouds. It yields a spectral solution that is applicable in other infrared regions where gas and particle optical thicknesses are large. A key parameter ( χ) is the ratio of the gas absorption coefficient to the particle extinction coefficient. For χ=1 and ε p=0.5, particle effects decrease the gas band profile by 5% from that of a blackbody. For χ<1 and ε p<0.5, particle effects on the calculated temperature and particle emissivity are noticeable and particle effects should be considered. If χ is known, an iterative procedure may be used to calculate temperature and particle emissivity. We illustrate this procedure with data from a coal-fired boiler. Accounting for particle effects, temperatures were 4% higher (at about 1500 K) and particle emissivities 28% lower (for ε p within 0.3–05) than without considering these effects.

A Refined Two-Channel Microwave Radiometer Liquid Water Path Retrieval for Cold Regions by Using Multiple-Sensor Measurements

Traditional two-channel microwave radiometers (MWRs) are widely used to measure cloud liquid water path (LWP); however, the retrieved LWPs are subject to relatively large uncertainties, particularly for low LWP clouds. By reformulating the statistical retrieval method with clear-sky measurements as a reference, a simple method is presented to significantly reduce uncertainties in the LWP retrieval due to errors in MWR calibration, uncertainties in the absorption coefficients of atmospheric gases, and variations in the vertical profiles of temperature and pressure. The improvement is illustrated by comparing the statistics of the erroneous clear-sky LWP for the Department of Energy's Atmospheric Radiation Measurement Program Climate Research Facility observations at the North Slope of Alaska site and by comparing LWP retrieved with a multiple-sensor algorithm and LWP retrieved based mainly on MWR measurements. This letter also demonstrates the importance of using correct water cloud temperature and temperature-dependent water absorption coefficients for MWR LWP retrieval over cold regions. This approach can be easily implemented for combined MWR, ceilometer, and surface meteorological measurements.

ANALYSIS OF THE TURBULENT, NON-PREMIXED COMBUSTION OF NATURAL GAS IN A CYLINDRICAL CHAMBER WITH AND WITHOUT THERMAL RADIATION

This work presents a numerical simulation of the non-premixed combustion of natural gas in atmospheric air in an axis-symmetric cylindrical chamber, focusing on the effect of thermal radiation on the temperature and chemical species concentration fields and the heat transfer. The simulation is based on the solution of the mass, energy, momentum and the chemical species conservation equations. Thermal radiation exchanges in the combustion chamber is computed through the zonal method, and the gas absorption coefficient dependence on the wavelength is resolved by the weighted-sum-of-gray-gases model. The turbulence is modeled by the standard k − ϵ model, and the chemical reactions are described by the E–A (Eddy Breakup–Arrhenius model). The finite volume method is employed to treat the differential equations. Among other results, the solution of the governing equations allows the determination of the region where combustion takes place, the distribution of the chemical species, the velocity fields and the heat transfer rate by convection and radiation. The results indicate that while thermal radiation has a strong effect on the temperature field and heat transfer, its effect on the chemical reactions rates is of less importance. The numerical results are compared to experimental results obtained by Garréton and Simonin (1994).

Experimental and computational study of a lifted, non-premixed turbulent free jet flame

The results of an experimental and modelling study of a lifted, non-premixed methane turbulent free jet flame issuing into still air are presented. Detailed in-flame measurements, including the gas temperature, oxygen and NO concentration distributions, are made. In a parallel computational study, a radiative mixedness–reactedness flamelet combustion model is employed to simulate the experimental flame. A comprehensive radiation heat transfer model based on the discrete transfer method of solution of the radiative transport equation, together with the wide-band model for gas absorption coefficients, was used. The NO formation and emission was also calculated using a post-processing approach. Validation of the numerical results against the experimental data shows generally good quality combustion predictions in the near burner region. However, predictive difficulties are encountered in the downstream region, particularly for the oxygen concentration. The NO predictions reveal discrepancies when compared with measurements in the fuel rich part of the flame. The in-flame experimental data, with the aid of the predictions, has provided an enhanced understanding of combustion and NO characteristics of the lifted, non-premixed turbulent free jet flame.

Prediction of theStandard AtmosphereProfiles of Temperature, Pressure, and Density with Height for the Lower Atmosphere by Solution of the (S−S) IntegralEquations of Transferand Evaluation of the Potential for Profile Perturbation by Combustion Emissions

This analytical solution, believed to be original here, to the 1D formulation of the (1905−1906) integral (S−S) Equations of Transfer, governing radiation through the atmosphere, is developed for future evaluation of the potential impact of combustion emissions on climate change. The solution predicts, in agreement with the Standard Atmosphere experimental data, a linear decline of the fourth power of the temperature, T4, with pressure, P, and, at a first approximation, a linear decline of T with altitude, h, up to the tropopause at about 10 km (the lower atmosphere). From these two results, with transformation using the Equation of State, the variations of pressure, P, and density, ρ, with altitude, h, are also then obtained, with the predictions again, separately, in substantial agreement with the Standard Atmosphere data up to 30 km altitude (1% density). The analytical procedure adopts the standard assumptions commonly used for numerical solutions of steady state, one dimensionality, constant flux directional parameter (μ), and a gray-body equivalent average for the effective radiation absorption coefficient, k, for the mixed thermal radiation-active gases at an effective (joint-mixture) concentration, p. Using these assumptions, analytical closure and validation of the equation solution is essentially complete. Numerical closure is not yet complete, with only one parameter at this time not independently calculated but not required numerically for validation of analytical closure. This is the value of the group-pair (kp)o representing the ground-level value of (kp), the product of the effective absorption coefficient and concentration of the mixed gases, written as a single parameter but decomposable into constituent gases and/or gas bands. Reduction of the experimental value of (kp)o to values of k for a comparison with relevant band data for water and CO2 shows numerical magnitudes substantially matching the longest wavelength bands for each of the two gases. Allowing also for the maximum absorption percentages, α°, of these two bands for the two gases, respectively, 39% for water and 8.5% for CO2, these values then support the dominance of water (as gas and not vapor) at about 80%, compared with CO2 at about 20%, as the primary absorbing/emitting (“greenhouse”) gas in the atmosphere. These results provide a platform for future numerical determination of the influence on the T, P, and ρ profiles of perturbations in the gas concentrations of the two primary species, carbon dioxide and water, and it provides, specifically, the analytical basis needed for future analysis of the impact potential from increases in atmospheric carbon dioxide concentration, because of fossil-fuel combustion, in relation to climate change.

Effect of radiative transfer of heat released from combustion reaction on temperature distribution: A numerical study for a 2-D system

Both light and heat are produced during a chemical reaction in a combustion process, but traditionally all the energy released is taken as to be transformed into the internal energy of the combustion medium. So the temperature of the medium increases, and then the thermal radiation emitted from it increases too. Chemiluminescence is generated during a chemical reaction and independent of the temperature, and has been used widely for combustion diagnostics. It was assumed in this paper that the total energy released in a combustion reaction is divided into two parts, one part is a self-absorbed heat, and the other is a directly emitted heat. The former is absorbed immediately by the products, becomes the internal energy and then increases the temperature of the products as treated in the traditional way. The latter is emitted directly as radiation into the combustion domain and should be included in the radiation transfer equation (RTE) as a part of radiation source. For a simple, 2-D, gray, emitting–absorbing, rectangular system, the numerical study showed that the temperatures in reaction zones depended on the fraction of the directly emitted energy, and the smaller the gas absorption coefficient was, the more strong the dependence appeared. Because the effect of the fraction of the directly emitted heat on the temperature distribution in the reacting zones for gas combustion is significant, it is required to conduct experimental measurements to determine the fraction of self-absorbed heat for different combustion processes.

Radiation affected ignition and flame propagation for solid fuel in a cylindrical enclosure

Ignition and flame propagation for pyrolysing fuel in a cylindrical enclosure has been examined in this study. The pyrolysing fuel of cylindrical shape was located both eccentrically and concentrically inside an outer cylinder that was sustained at high temperature. Due to gravity, buoyancy motion was inevitably incurred in the enclosure, and this was found to affect the flame initiation and propagation behaviour. Radiative heat transfer also played an important role in the thermo-fluid mechanical behaviour because of the high temperature involved in the problem. Numerical studies have been performed for various parameters such as the Grashof number, overheat ratio, gas absorption coefficient and vertical fuel eccentricity. The flame behaviour and initiation were observed to be totally different depending on the Grashof number. Due to absorbed radiant energy, the radiative gas played a significant role in flame evolution. The location of flame onset was also affected by both the vertical eccentricity of the inner pyrolysing fuel and the thermal conditions applied. The heating process and the flow field development were found to govern flame initiation and propagation.

APPLICATION OF A LOCAL-SPECTRUM CORRELATED MODEL TO MODELING RADIATIVE TRANSFER IN A MIXTURE OF REAL GAS MEDIA IN BIDIMENSIONAL ENCLOSURES

ABSTRACT Calculating radiative transport through nongray gases as combustion gases, atmospheric gases, and others is extremely difficult because of the strong spectral variation of the absorption coefficients of molecular gases. In the local-spectrum correlated model the spectral integration of the radiative transfer equation (RTE) is performed using one new gas absorption spectrum distribution function termed the cumulative wavenumber (CW). The CW model was first coupled with the discrete ordinates method to solve the transformed RTE. The accuracy of the model and algorithm first was examined for the one-dimensional homogeneous media, and results are compared with line-by-line calculations. It is found that the CW model is exact for homogeneous media, and inhomogeneous cases are examined. Then the CW model is implemented in a bidimensional enclosure with diffuse reflecting boundaries containing a mixture of real gases in isothermal and in strong nonisothermal cases. The spectral databases HITRAN and HITEMP are used to obtain the molecular absorption spectrum of the gases at different temperatures. Different cases are analyzed and results are compared.

An efficient approach for the implementation of the SNB based correlated- k method and its evaluation

The current implementation of the SNB based correlated- k method consumes a significant portion of the total cpu time on the on-line inversion of the cumulative distribution function. An approach was developed to pre-calculate the absorption coefficients of real gases from the inversion procedure. This approach results in significant improvement in the efficiency of the SNB based correlated- k method with slight loss in accuracy. This approach was evaluated against other implementation approaches of the SNB based correlated- k method in several non-isothermal and/or inhomogeneous problems.

Application of the full spectrum correlated- k distribution approach to modeling non-gray radiation in combustion gases

The treatment of radiative transport through combustion gases is rendered extremely difficult by the strong spectral variation of the absorption coefficients of molecular gases. In the full spectrum correlated- k distribution (FSCK) approach, a transformation is invoked, whereby the radiative transfer equation (RTE) is transformed from wavenumber to non-dimensional Planck-weighted wavenumber space after reordering of the spectrum. The reordering results in a relatively smooth spectrum, allowing accurate spectral integration with very few quadrature points. The numerical procedures, required to use the FSCK model for full-scale combustion applications, have been outlined in this article. The FSCK model was first coupled with the Discrete Ordinates Method (DOM) for solution of the transformed RTE. The accuracy of the model was then examined for a variety of cases ranging from homogeneous one-dimensional media to inhomogeneous multi-dimensional media with simultaneous variations in both temperature and concentrations. Comparison with line-by-line calculations shows that the FSCK model is exact for homogeneous media, and that its accuracy in inhomogeneous media is limited by the accuracy of the scaling approximation. Several approaches for effective scaling of the absorption coefficient are examined. The model is finally used for radiation calculations in a full-scale combustor, with full coupling to fluid flow, heat transfer and multi-species chemistry. The computational savings resulting from use of the FSCK model is found to be more than four orders of magnitude when compared with line-by-line calculations.

AN UNSTEADY CONDUCTION AND TWO-PHASE RADIATION IN A 2-D RECTANGULAR ENCLOSURE WITH GAS AND PARTICLES

A problem of combined conductive and two-phase radiative heat transfer in a two-dimensional rectangular enclosure with two-phase (gas-particles) media is analyzed. A two-phase radiative transfer equation (RTE) considering radiation by both gas and particles is studied. Its nonlinear integrodifferential RTE is solved using the discrete ordinates method (DOM, or so-called S N method). To validate the program, we compare the solution in a two-dimensional rectangular black enclosure with others. The DOM is then applied to the unsteady thermal development in two-phase media contained in a rectangular enclosure. A parametric study is performed by changing the gas and particle absorption coefficients, particle number density, particle emissivity, wall emissivity, and aspect ratio of the enclosure. The results confirm a significant effect of the two-phase radiation on the thermal development in the geometry. However, it is found that the conduction is predominant near the hot wall.