Thermal conductivity and effective diffusion coefficient for vibrational energy: carbon dioxide (350-2000K)

Abstract. Heat transport in snowpacks is generally thought to occur through two independent processes: heat conduction and latent heat transport carried by water vapor. This paper investigates the coupling between both these processes in snow, with an emphasis on the impacts of the kinetics of the sublimation and deposition of water vapor onto ice. In the case where kinetics is fast, latent heat exchanges at ice surfaces modify their temperature, and therefore the thermal gradient within ice crystals and the heat conduction through the entire microstructure. Furthermore, in this case, the effective thermal conductivity of snow can be expressed by a purely conductive term complemented by a term directly proportional to the effective diffusion coefficient of water vapor in snow, which illustrates the inextricable coupling between heat conduction and water vapor transport. Numerical simulations on measured three-dimensional snow microstructures reveal that the effective thermal conductivity of snow can be significantly larger, up to about 50 % for low-density snow, than if water vapor transport is neglected. Comparison of our numerical simulations with literature data suggests that the fast kinetics hypothesis could be a reasonable assumption to model snow physical properties. Lastly, we demonstrate that under the fast kinetics hypothesis the effective diffusion coefficient of water vapor is related to the effective thermal conductivity by a simple linear relationship. Under such condition, the effective diffusion coefficient of water vapor is expected to lie in the narrow 100 % to about 80 % range of the value of the diffusion coefficient of water vapor in air for most seasonal snows. This may greatly facilitate the parameterization of water vapor diffusion of snow in models.

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Impact of water vapor diffusion and latent heat on the effective thermal conductivity of snow

The Cryosphere ◽

10.5194/tc-15-2739-2021 ◽

2021 ◽

Vol 15 (6) ◽

pp. 2739-2755

Author(s):

Kévin Fourteau ◽

Florent Domine ◽

Pascal Hagenmuller

Keyword(s):

Thermal Conductivity ◽

Diffusion Coefficient ◽

Heat Conduction ◽

Water Vapor ◽

Effective Thermal Conductivity ◽

Latent Heat ◽

Effective Diffusion Coefficient ◽

Effective Diffusion ◽

Water Vapor Transport ◽

Fast Kinetics

Abstract. Heat transport in snowpacks is understood to occur through the two processes of heat conduction and latent heat transport carried by water vapor, which are generally treated as decoupled from one another. This paper investigates the coupling between both these processes in snow, with an emphasis on the impacts of the kinetics of the sublimation and deposition of water vapor onto ice. In the case when kinetics is fast, latent heat exchanges at ice surfaces modify their temperature and therefore the thermal gradient within ice crystals and the heat conduction through the entire microstructure. Furthermore, in this case, the effective thermal conductivity of snow can be expressed by a purely conductive term complemented by a term directly proportional to the effective diffusion coefficient of water vapor in snow, which illustrates the inextricable coupling between heat conduction and water vapor transport. Numerical simulations on measured three-dimensional snow microstructures reveal that the effective thermal conductivity of snow can be significantly larger, by up to about 50 % for low-density snow, than if water vapor transport is neglected. A comparison of our numerical simulations with literature data suggests that the fast kinetics hypothesis could be a reasonable assumption for modeling heat and mass transport in snow. Lastly, we demonstrate that under the fast kinetics hypothesis the effective diffusion coefficient of water vapor is related to the effective thermal conductivity by a simple linear relationship. Under such a condition, the effective diffusion coefficient of water vapor is expected to lie in the narrow 100 % to about 80 % range of the value of the diffusion coefficient of water vapor in air for most seasonal snows. This may greatly facilitate the parameterization of water vapor diffusion of snow in models.

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Diffusion of Heavy Oil in SiO2 Model Catalyst and FCC Catalyst

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.550-553.158 ◽

2012 ◽

Vol 550-553 ◽

pp. 158-163 ◽

Cited By ~ 2

Author(s):

Zi Yuan Liu ◽

Sheng Li Chen ◽

Peng Dong ◽

Xiu Jun Ge

Keyword(s):

Diffusion Coefficient ◽

Pore Size ◽

Effective Diffusion Coefficient ◽

Pore Diameter ◽

Effective Diffusion ◽

Model Catalyst ◽

Average Pore ◽

Diffusion Factor ◽

Fcc Catalyst ◽

Fcc Catalysts

Through the measured effective diffusion coefficients of Dagang vacuum residue supercritical fluid extraction and fractionation (SFEF) fractions in FCC catalysts and SiO2model catalysts, the relation between pore size of catalyst and effective diffusion coefficient was researched and the restricted diffusion factor was calculated. The restricted diffusion factor in FCC catalysts is less than 1 and it is 1~2 times larger in catalyst with polystyrene (PS) template than in conventional FCC catalyst without template, indicating that the diffusion of SFEF fractions in the two FCC catalysts is restricted by the pore. When the average molecular diameter is less than 1.8 nm, the diffusion of SFEF fractions in SiO2model catalyst which average pore diameter larger than 5.6 nm is unrestricted. The diffusion is restricted in the catalyst pores of less than 8 nm for SFEF fractions which diameter more than 1.8 nm. The tortuosity factor of SiO2model catalyst is obtained to be 2.87, within the range of empirical value. The effective diffusion coefficient of the SFEF fractions in SiO2model catalyst is two orders of magnitude larger than that in FCC catalyst with the same average pore diameter. This indicate that besides the ratio of molecular diameter to the pore diameter λ, the effective diffusion coefficient is also closely related to the pore structure of catalyst. Because SiO2model catalyst has uniform pore size, the diffusion coefficient can be precisely correlated with pore size of catalyst, so it is a good model material for catalyst internal diffusion investigation.

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