Thermal Conductivity Of Gas Mixtures Research Articles

A model for effective thermal conductivity of porous carbon materials in FCM fuel pellets

The application of fully ceramic microencapsulated (FCM) fuels to light water reactors and small modular reactors are attracting great interest. The porous carbon buffer layer is the main release volume for gas products, and it is the important part for transferring the fission heat. In this study, a theoretical model for effective thermal conductivity of porous carbon materials is developed and verified, which depends on the current porosity, the thermal conductivity of gas mixture and PyC skeleton. In this model, the temperature-pressure dependence of thermal conductivity for the released gas mixture is considered, with the fitting relation based on the existing experimental data. The porosity, the amounts of released gas mixture in the pores and the pore pressure are considered to evolve with burnup. Appearance of a buffer-IPyC gap is also involved. The effects of initial porosity of buffer layer, appearance of a buffer-IPyC gap, different kernel materials and irradiation temperature on the effective thermal conductivity are investigated. The effect of uncertainties in the thermal conductivity of dense PyC skeleton material is also analyzed. This work is expected to provide a fundamental basis for further precise simulation of the in-pile thermo-mechanical coupling behavior in FCM fuel pellets.

Development of a simple CO2 sensor based on the thermal conductivity detection by a thermopile

A simple and effective thermal conductivity based CO2 gas sensor has been successfully developed. The CO2 sensor consists of a modified IR thermopile sensor without an IR window. The thermopile is heated by the AC current that is applied through the output terminals of the device, which in turn leads to a temperature gradient generating a DC output voltage. The gas exposed to the thermopile simultaneously cool down the thermopile. Thus, the thermopile can simultaneously serve as a heater and temperature sensor. The built-in sensors possess low production costs, low power consumption and are easily manufactured. From the conducted experiments, the sensor can work well, and the results can be validated with the established theory, as evidenced by the RMS error of 0.787. The measurement results are also in a good agreement with the model predictions Mason and Saxena for the thermal conductivity of gas mixtures.

Multi-scale modelling of heat transfer in polyurethane foams

The influence of morphology and cell gas composition on heat insulation properties of polyurethane (PU) foams was investigated using a multi-scale mathematical model. The polymer absorption coefficient was determined from quantum chemical computations. Reverse non-equilibrium molecular dynamics was used to calculate the thermal conductivity of polymer and gas mixtures relevant to PU foams. The equivalent foam conductivity was calculated using homogeneous phase approach. The individual models were coupled together using suitable surrogate models within MoDeNa framework. To validate the proposed model 9 foam samples were prepared using different recipes, their morphology was characterized and their thermal conductivity was measured. The difference between experimental and predicted values was comparable to experimental error. Developed multi-scale model was used to identify the most suitable relation for the calculation of thermal conductivity of gas mixtures in PU foams and to quantify the influence of foam density, cell size, and strut content on heat insulation properties of PU foams.

On thermal conductivity of gas mixtures containing hydrogen

A brief review of formulas used for the thermal conductivity of gas mixtures in CFD simulations of rocket combustion chambers is carried out in the present work. In most cases, the transport properties of mixtures are calculated from the properties of individual components using special mixing rules. The analysis of different mixing rules starts from basic equations and ends by very complex semi-empirical expressions. The formulas for the thermal conductivity are taken for the analysis from the works on modelling of rocket combustion chambers. $$\hbox {H}_2{-}\hbox {O}_2$$ mixtures are chosen for the evaluation of the accuracy of the considered mixing rules. The analysis shows that two of them, of Mathur et al. (Mol Phys 12(6):569–579, 1967), and of Mason and Saxena (Phys Fluids 1(5):361–369, 1958), have better agreement with the experimental data than other equations for the thermal conductivity of multicomponent gas mixtures.

Unsteady state thermochemical performance analyses of solar driven steam methane reforming in porous medium reactor

A unsteady state thermochemical reaction model was developed by Monte Carlo Ray Tracing (MCRT) and Finite Volume Method (FVM) coupled for steam methane reforming in a porous medium thermochemical reactor. Concentrated solar irradiation was adopted as the source of high-temperature process heat. The transient state thermochemical reaction model combined conduction, convection, and irradiative heat transfer with temperature dependent thermochemical reactions. Along with modified P1 approximation, the local thermal non-equilibrium (LTNE) model was used to investigate the thermal performance of porous medium solar thermochemical reactions in order to provide more temperature information. The modified-Sutherland model for calculating thermal conductivity of gas mixture was introduced in the thermochemical reaction model to provide higher calculating precision. The temperature distribution, reactants, and products variation with time were analyzed. Effects of mixture model, sudden change of solar irradiance on the solar thermochemical reaction were also analyzed. The results illustrated that the modified-Sutherland model for calculating the conductivity of gas mixture was recommended for the thermochemical reaction analyses.

1732 MEMS技術を用いた熱線濃度計(OS1-3 機械工学が支援する微細加工技術III,OS1 機械工学が支援する微細加工技術)

This experimental study aims at measurement concentration of jet diffusion The hot wire concentration sensor to measure the concentration of components in binary mixture of gases is described The concentration sensor consists of a concentration probe, a vacuum pump, a hot wire amplifier And the concentration probe consists a brass some nozzle, a brass tube, tungsten hot wire to measure gas thermal conductivity of gas mixture Now, this concentration sensor is produced by using the MEMS technology This sensor is a composition on the chip such as a sonic nozzle, the micro channels, and the hot film sensors

0110 2成分気体に対応した濃度計の研究(OS1-2 噴流,後流および剥離流れの流動解析と応用,オーガナイズドセッション)

This experimental study aims at measuring concentration of jet diffusion. Hot-wire concentration sensor to measure the concentration of the components in a binary mixture of gases is described. The concentration sensor consists of a concentration probe, a vacuum pump, a hot-wire amplifier. And the concentration probe consists of a brass sonic nozzle, a brass tube, a tungsten hot-wire to measure gas thermal conductivity of gas mixture. There are two main parameter in King's equation which are velocity and thermal conductivity. The sonic nozzle decreases the effect of velocity. The new probe calibrated with helium jet. The calibration curve was made with helium-air mixture. And the time constant was 0.9 ms. Contour of velocity and concentration of helium jet diffusion was measured.

Thermal Conductivity of Carbon Dioxide–Methane Mixtures at Temperatures Between 300 and 425 K and at Pressures up to 12 MPa

The thermal conductivities of carbon dioxide and three mixtures of carbon dioxide and methane at six nominal temperatures between 300 and 425 K have been measured as a function of pressure up to 12 MPa. The measurements were made with a transient hot-wire apparatus. The relative uncertainty of the reported thermal conductivities at a 95% confidence level is estimated to be ±1.2%. Results of the low-density analysis of the obtained data were used to test expressions for predicting the thermal conductivity of nonpolar mixtures in a dilute-gas limit developed by Schreiber, Vesovic, and Wakeham. The scheme was found to underestimate the experimental thermal conductivity with deviations not exceeding 5%. The dependence of the thermal conductivity on density was used to test the predictive scheme for the thermal conductivity of gas mixtures under pressure suggested by Mason et al. and improved by Vesovic and Wakeham. Comparisons reveal a pronounced critical enhancement on isotherms at 300 and 325 K for mixtures with methane mole fractions of 0.25 and 0.50. For other states, comparisons of the experimental and predicted excess thermal conductivity contributions showed a smaller increase of the experimental data with deviations approaching 3% within the examined range of densities.

Prediction of the Thermal Conductivity of Gas Mixtures Using Direct Simulation Monte Carlo Method

Prediction of the Thermal Conductivity of Gas Mixtures Using Direct Simulation Monte Carlo Method

Thermal Conductivity of Nitrogen-Methane Mixtures at Temperatures Between 300 and 425 K and at Pressures Up to 16 MPa

The thermal conductivities of nitrogen and three mixtures of nitrogen and methane at six nominal temperatures between 300 and 425 K have been measured as a function of pressure up to 16 MPa. The relative uncertainty of the thermal conductivity measurements at a 95% confidence level is estimated to be less then 1%. The data obtained and the results of the low-density analysis were used to test two prediction methods for the thermal conductivity of gas mixtures under pressure and for the thermal conductivity of dilute polyatomic gas mixtures. Reasonable agreement was found with expressions for predicting thermal conductivity of nonpolar mixtures in a dilute-gas limit developed by Schreiber et al. The scheme underestimates the experimental thermal conductivity with deviations not exceeding 3%. The prediction scheme for the thermal conductivity of gas mixtures under pressure suggested by Mason et al. and improved by Vesovic and Wakeham underestimates the experimental thermal conductivities throughout, likely due to its use of the Hirchsfelder–Eucken equation at the low-density limit.

Prediction of the Thermal Conductivity of Gas Mixtures at Low Pressures

Three methods, namely, Mason–Saxena–Wassiljewa (MSW), Hirschfelder–Eucken (HE), and Schreiber–Vesovic–Wakeham (SVW), for predicting the thermal conductivity of nonpolar, multicomponent, molecular mixtures in the dilute-gas limit were tested against the available experimental data. Overall, the accuracy of the MSW method is judged to be of the order of ±6 to 8% while that of HE and SVW is ±2 to 3%. For the latter two methods this is a remarkably good agreement, considering the approximations made in deriving the prediction scheme from the kinetic theory results. The agreement achieved indicates that the HE and SVW methods can form the basis of accurate engineering estimation techniques for the thermal conductivity of gaseous mixtures at low pressures.

Thermal conductivity of gas mixtures

In continuation of our earlier work on binary mixtures (1992 J. Phys. B: At. Mol. Opt. Phys. 25 679), an empirical relationship to estimate the higher-order contributions to thermal conductivity of dilute monatomic multicomponent gas mixtures has been developed. This relationship is able to reproduce the exact contributions to within 0.2%. Finally, a method of estimating accurate values of thermal conductivity is outlined.

Empirical relationship for higher order contributions to thermal conductivity of gas mixtures

An empirical relationship to estimate the higher order contributions to thermal conductivity of monoatomic gas mixtures is reported. This relationship is able to reproduce the exact contributions within 0.2% for all the binary inert-gas mixtures.

The thermal conductivity of pure nitrogen and of mixtures of nitrogen and carbon dioxide at elevated temperatures and pressures

The thermal conductivities of nitrogen at 470 K and six mixtures of nitrogen and carbon dioxide at various temperatures have been measured as a function of pressure up to 25 MPa. The mixtures were measured at the following temperatures: one at 302 K, three at 380 K, one at 430 K, and one at 470 K. The data were used to test three prediction methods for the thermal conductivity of gas mixtures under pressure. Surprisingly good agreement was found with predictions using the corresponding-states method of Ely and Hanley. The predictions of the more theoretically based method of Mason et al. were low throughout, due partly to its use of the Hirschfelder-Eucken equation as the low-density limit, but also because the predicted density dependence rises too slowly. The simplified version of this method proposed by Svojskij gave slightly worse predictions, particularly at higher densities. The zero- density results for nitrogen are examined by comparing the zero-and first-density coefficients with the trends shown at lower temperatures.

Thermal conductivity of mixtures of polyatomic gases at low and moderate density

The paper discusses the prediction of the thermal conductivity of gas mixtures containing polyatomic components at low and moderate density. The prediction scheme adopted is based upon the rigorous kinetic theory of gases and makes use of other thermophysical properties of the pure gases and binary mixtures in the evaluation of the thermal conductivity. Comparisons with accurate experimental data indicate that only for systems in which the mass ratio of the species is near unity and for which inelastic collisions are rare, is a reliable prediction of the mixture thermal conductivity at low density possible. On the other hand, the density dependence of the thermal conductivity is quite accurately represented for most systems.

Generalization of experimental data regarding the thermal conductivity of gas mixtures from the structural point of view

On the basis of theoretical relationships and a generalization of experimental data, an equation is derived for calculating the thermal conductivity of binary mixtures of nonpolar gases.

Effect of molecular angular momentum on the thermal conductivity of a multicomponent gas mixture

The effects of molecular angular momentum (spin polarization) on the thermal conductivity of a multicomponent gas mixture are considered. The Wang Chang–Uhlenbeck approach to the kinetic theory of gases with internal states is used. Formal results are obtained for the thermal conductivity of a gas mixture of uniform composition. These results are given in terms of the quantum mechanical degeneracy-averaged cross section.

Thermal conductivity of mixtures with interpenetrating components

The basic principles of investigation of transport processes used in generalized conduction theory are formulated. Studies in which a structure with interpenetrating components has been used for determining electrical and thermal conductivity are analyzed. It is shown that using models of such structures it is possible to calculate the thermal conductivity of gas mixtures, liquid solutions, solid disperse systems, certain alloys, and granular and fibrous materials.

The thermal conductivity of gas mixtures at low temperatures. II

This article provides a review of the theoretical and experimental references devoted to the thermal conductivity of gas mixtures at low temperatures. We discuss the influence of quantum effects on the thermal conductivity of gas mixtures.

Erratum: Determination of the Eucken Factor from Relative Change in Thermal Conductivity of Gas Mixtures. Ortho–Para-hydrogen Mixtures at 77°K

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