The thermal conductivity of the carbon dioxide in porous glass media at the critical point vicinity

G. Guseinov1

1Institute of Physics, Daghestan Scientific Center of the RAS, Makhachkala, Russia

Keywords: thermal conductivity, critical point
property: thermal conductivity
material: carbon dioxide, porous glass

The investigation of nanomaterials possessing unique properties is crucial for the understanding of a nature and mechanism of molecular interactions and phase transformations.

The experimental research of thermal conductivity (λ) of microporous glass saturated by carbon dioxide (CO2) is to answer unsolved problems there. A purpose of this work is to investigate the behavior of CO2 thermal conductivity in the microporous glass, in particular, at the critical region. A microporous glass with a rigid framework and mutually percolating pores has been taken as a model object for our investigation. The microporous media was filled with CO2, which thermal conductivity had been sufficiently studied in a wide range of parameters including the critical region. The CO2 is stable, has low critical parameters and does not decompose in the studied ranges of temperature and pressure. Investigations of the effective thermal conductivity (λ eff.) of microporous glass saturated by CO2 were carried out using a high precision device with inaccuracy of 1.2%. The obtained results for effective thermal conductivity of microporous glass with average pore size 16μm, saturated by CO2 in the temperature range of 290-370K and at the pressure of 7.379 MPa are presented in this work at the first time. The results of investigation are as following: the effective thermal conductivity of the microporous glass saturated by CO2 along the critical isobar curve has been investigated for the first time; and highly pronounced maximum of thermal conductivity in the critical region is observed. Also, as a result of the experiment on the thermal conductivity in the critical region, it is found that amplitude of the thermal conductivity maximum decreases, the maximum shifts towards to lower temperatures, and the maximum appears in the wider temperature range than that for the pure CO2. These effects are explained on the base of the homogeneity media concept, as a result of some nanoscale peculiarities intrinsic to the glass such as a difference between CO2 molecule energies near the pore surface and free CO2; and the formation of two-phase amorphous crystal structures – kind of nanostructures in CO2 phase (with layer thickness about 10-1000nm). The thermal conductivity of CO2 in the porous media has been calculated is found to be greater by 18,64 % than that for  free CO2. To our opinion, it can be explained as an influence of the pore interface which makes CO2 to be more structured, having the greater thermal conductivity, than in free volume. Thus, the new approach to the nanoscale investigation is proposed, that brings the next understanding of the chemistry and physics of the nanostructures.

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