土壤气体扩散系数是研究土壤气体传输过程的一个重要参数,它随土壤质地、容重和孔隙的改变而变化,难以估算,为准确测定和研究其特征,依据气体扩散原理设计并研制了土壤气体扩散系数测定装置。以石英砂和砂质壤土为试验材料,利用该装置...土壤气体扩散系数是研究土壤气体传输过程的一个重要参数,它随土壤质地、容重和孔隙的改变而变化,难以估算,为准确测定和研究其特征,依据气体扩散原理设计并研制了土壤气体扩散系数测定装置。以石英砂和砂质壤土为试验材料,利用该装置研究了气体扩散系数与不同含水量和容重下的充气孔隙度间的关系。结果表明:砂质壤土原状土和装填土的气体扩散系数差别很小;土壤相对扩散系数随土壤总孔隙度减小而变小,且粒径较小的土壤具有相对较小的气体扩散系数;原状和装填砂质壤土的相对扩散系数与充气孔隙度之间的关系均可以用幂函数方程来拟合,方程中的参数与土壤质地密切相关,原状土非活性孔隙度为0。Buckingham模型的预测值与实测结果基本一致(均方根误差=0.008),但Millington and Quirk模型(均方根误差=0.032)和SWLR模型(均方根误差=0.023)的预测结果偏差较大。展开更多
The present work is concerned with determining the viscosity,diffusion,thermal diffusion factor and thermal conductivity of five equimolar binary gas mixtures including:CF4-He,CF4-Ne,CF4-Ar,CF4-Kr,CF4-Xe from the prin...The present work is concerned with determining the viscosity,diffusion,thermal diffusion factor and thermal conductivity of five equimolar binary gas mixtures including:CF4-He,CF4-Ne,CF4-Ar,CF4-Kr,CF4-Xe from the principle of corresponding states of viscosity by the inversion technique.The Lennard-Jones (12-6) model potential is used as the initial model potential.The calculated interaction potential energies obtained from the inversion procedure is employed to reproduce the viscosities,diffusions,thermal diffusion factors,and thermal conductivities.The accuracies of the calculated viscosity and diffusion coefficients were 1% and 4%,respectively.展开更多
The objective of this work is to study the gas desorption characteristics of the high-rank intact coal and fractured coal.The gas adsorption,mercury porosimetry and gas desorption experiments were carried out in this ...The objective of this work is to study the gas desorption characteristics of the high-rank intact coal and fractured coal.The gas adsorption,mercury porosimetry and gas desorption experiments were carried out in this study.Then,the theories of thermodynamics,diffusion mechanism and desorption kinetics were used to estimate the gas desorption characteristics.The results of gas adsorption experiments show that the initial isosteric adsorption heat of the intact coal is greater than that of the fractured coal,indicating that the gas molecules desorb more easily from fractured coal than intact coal.Using the mercury porosimetry,we find that the diffusion channels of fractured coal are more developed than those of intact coal.The difficult diffusion form dominates in the intact coal during the gas diffusing,while the easy diffusion form dominates in the fractured coal.The results of gas desorption experiments show that the initial gas desorption volume and velocity of the fractured coal are both greater than those of the intact coal.Using the Fick diffusion law,the study calculates the gas diffusion coefficients of the intact coal and fractured coal.The diffusion coefficients of the fractured coal are 2 times and 10 times greater than those of the intact coal at the time of 0-120 and 0-10 min,respectively.展开更多
Information on the most influential factors determining gas flux from soils is needed in predictive models for greenhouse gases emissions. We conducted an intensive soil and air sampling along a 2 000 m transect exten...Information on the most influential factors determining gas flux from soils is needed in predictive models for greenhouse gases emissions. We conducted an intensive soil and air sampling along a 2 000 m transect extending from a forest, pasture, grassland and corn field in Shizunai, Hokkaido （Japan）, measured CO2, CH4, N20 and NO fluxes and calculated soil bulk density （Pb）, air-filled porosity （fa） and total porosity （Ф）. Using diffusivity models based on either fa alone or on a combination of fa and 4, we predicted two pore space indices： the relative gas diffusion coefficient （Ds/Do） and the pore tortuosity factor （T）. The relationships between pore space indices （Ds/Do and T） and C02, CH4, N2O and NO fluxes were also studied. Results showed that the grassland had the highest Pb while fa and Ф were the highest in the forest. CO2, CH4, N20 and NO fluxes were the highest in the grassland while N20 dominated in the corn field. Few correlations existed between fa, Ф, Pb and gases fluxes while all models predicted that Ds/Do and T significantly correlated with CO2 and CH4 with correlation coefficient （r） ranging from 0.20 to 0.80. Overall, diffusivity models based on fa alone gave higher Ds/Do, lower τ, and higher R2 and better explained the relationship between pore space indices （Ds/Do and τ） and gases fluxes. Inclusion of Ds/Do and τ in predictive models will improve our understanding of the dynamics of greenhouse gas fluxes from soils. Ds/Do and τ can be easily obtained by measurements of soil air and water and existing diffusivity models.展开更多
The diffusion,viscosity and thermal conductivity coefficients of gases between two parallel solid walls have been obtained analytically based on the Green-Kubo relation under a hard-sphere model.They decrease nonlinea...The diffusion,viscosity and thermal conductivity coefficients of gases between two parallel solid walls have been obtained analytically based on the Green-Kubo relation under a hard-sphere model.They decrease nonlinearly as the Knudsen number defined as the ratio of the mean free path to the wall distance increases.This theoretical prediction was in good agreement by the DSMC results.展开更多
文摘土壤气体扩散系数是研究土壤气体传输过程的一个重要参数,它随土壤质地、容重和孔隙的改变而变化,难以估算,为准确测定和研究其特征,依据气体扩散原理设计并研制了土壤气体扩散系数测定装置。以石英砂和砂质壤土为试验材料,利用该装置研究了气体扩散系数与不同含水量和容重下的充气孔隙度间的关系。结果表明:砂质壤土原状土和装填土的气体扩散系数差别很小;土壤相对扩散系数随土壤总孔隙度减小而变小,且粒径较小的土壤具有相对较小的气体扩散系数;原状和装填砂质壤土的相对扩散系数与充气孔隙度之间的关系均可以用幂函数方程来拟合,方程中的参数与土壤质地密切相关,原状土非活性孔隙度为0。Buckingham模型的预测值与实测结果基本一致(均方根误差=0.008),但Millington and Quirk模型(均方根误差=0.032)和SWLR模型(均方根误差=0.023)的预测结果偏差较大。
基金Research Committees of Shiraz University and Shiraz University of Technology for supporting this project and making computer facilities available
文摘The present work is concerned with determining the viscosity,diffusion,thermal diffusion factor and thermal conductivity of five equimolar binary gas mixtures including:CF4-He,CF4-Ne,CF4-Ar,CF4-Kr,CF4-Xe from the principle of corresponding states of viscosity by the inversion technique.The Lennard-Jones (12-6) model potential is used as the initial model potential.The calculated interaction potential energies obtained from the inversion procedure is employed to reproduce the viscosities,diffusions,thermal diffusion factors,and thermal conductivities.The accuracies of the calculated viscosity and diffusion coefficients were 1% and 4%,respectively.
基金provided by the National Basic Research Program of China(No.2011CB201204)the Natural Science Foundation for the Youth of China(Nos.41202118 and 51204173)
文摘The objective of this work is to study the gas desorption characteristics of the high-rank intact coal and fractured coal.The gas adsorption,mercury porosimetry and gas desorption experiments were carried out in this study.Then,the theories of thermodynamics,diffusion mechanism and desorption kinetics were used to estimate the gas desorption characteristics.The results of gas adsorption experiments show that the initial isosteric adsorption heat of the intact coal is greater than that of the fractured coal,indicating that the gas molecules desorb more easily from fractured coal than intact coal.Using the mercury porosimetry,we find that the diffusion channels of fractured coal are more developed than those of intact coal.The difficult diffusion form dominates in the intact coal during the gas diffusing,while the easy diffusion form dominates in the fractured coal.The results of gas desorption experiments show that the initial gas desorption volume and velocity of the fractured coal are both greater than those of the intact coal.Using the Fick diffusion law,the study calculates the gas diffusion coefficients of the intact coal and fractured coal.The diffusion coefficients of the fractured coal are 2 times and 10 times greater than those of the intact coal at the time of 0-120 and 0-10 min,respectively.
基金Supported by the Japanese Society for the Promotion of Science (JSPS)the Ministry of Education of Japan (No. PI0701)
文摘Information on the most influential factors determining gas flux from soils is needed in predictive models for greenhouse gases emissions. We conducted an intensive soil and air sampling along a 2 000 m transect extending from a forest, pasture, grassland and corn field in Shizunai, Hokkaido （Japan）, measured CO2, CH4, N20 and NO fluxes and calculated soil bulk density （Pb）, air-filled porosity （fa） and total porosity （Ф）. Using diffusivity models based on either fa alone or on a combination of fa and 4, we predicted two pore space indices： the relative gas diffusion coefficient （Ds/Do） and the pore tortuosity factor （T）. The relationships between pore space indices （Ds/Do and T） and C02, CH4, N2O and NO fluxes were also studied. Results showed that the grassland had the highest Pb while fa and Ф were the highest in the forest. CO2, CH4, N20 and NO fluxes were the highest in the grassland while N20 dominated in the corn field. Few correlations existed between fa, Ф, Pb and gases fluxes while all models predicted that Ds/Do and T significantly correlated with CO2 and CH4 with correlation coefficient （r） ranging from 0.20 to 0.80. Overall, diffusivity models based on fa alone gave higher Ds/Do, lower τ, and higher R2 and better explained the relationship between pore space indices （Ds/Do and τ） and gases fluxes. Inclusion of Ds/Do and τ in predictive models will improve our understanding of the dynamics of greenhouse gas fluxes from soils. Ds/Do and τ can be easily obtained by measurements of soil air and water and existing diffusivity models.
基金supported by the National Natural Science Foundation of China (Grant No.10921062)
文摘The diffusion,viscosity and thermal conductivity coefficients of gases between two parallel solid walls have been obtained analytically based on the Green-Kubo relation under a hard-sphere model.They decrease nonlinearly as the Knudsen number defined as the ratio of the mean free path to the wall distance increases.This theoretical prediction was in good agreement by the DSMC results.
