Thermal Conductivity in Supercritical Fluids

[Kasper_NYC]

Hi there,

Please, I would like to know if the Thermal Conductivity of a liquefied gas increases or decreases when becomes a supercritical fluid.

Also, I would like to know how is the relation between the molecular mass and thermal conductivity of a liquefied gas and a supercritical fluid, because in the gaseous phase, as higher the molecular mass, smaller seems to be the thermal conductivity value. Per example in gaseous phase:

Helium
Molecular weight : 4.0026 g/mol
Thermal conductivity (1.013 bar and 0 °C (32 °F)) : 142.64 mW/(m.K)

Methane
Molecular weight : 16.043 g/mol
Thermal conductivity (1.013 bar and 0 °C (32 °F)) : 32.81mW/(m.K)

Hexafluoroethane - R116
Molecular weight : 138.02 g/mol
Thermal conductivity (1.013 bar and 0 °C (32 °F)) : 13.47mW/(m.K)

Is it the same for supercritical fluids?

http://en.wikipedia.org/wiki/Supercritical_fluid

Thanks a lot.

PS - This is not a homework question, is part of a personal and independent research. I hardly tried to find the answer, but I could not. I did not ask about it in the Chemical Forum because I consider it not a formulation problem, but a question about the characteristics of the state of the matter. Thanks.

 

[Aaron Barnard]

The thermal conductivity of supercritical fluids usually increases with increasing temperature, pressure, and molecular mass. Generally, the thermal conductivity of a supercritical fluid is greater than that of its gaseous and liquid phases. The relation between molecular mass and thermal conductivity of a supercritical fluid is generally similar to that of its gaseous phase, in that higher molecular mass will generally result in lower thermal conductivity. However, the magnitude of the difference in thermal conductivity between different molecules can be more pronounced for supercritical fluids than for their gaseous phase.