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An extended description of the thermal diffusivity singular behavior of difluoromethane near the critical point.

DOI: 10.21047/1606-4313-2017-16-4-59-65
UDC 561.22

An extended description of the thermal diffusivity singular behavior of difluoromethane near the critical point.

Tsvetkov O.B. , Laptev Yu.A. , Kletsky A. V., Mitropov V.V., Galachova N.A.

For citation: Tsvetkov O.B., Laptev Yu.A., Kletskii A.V., Mitropov V.V., Galakhova N.A. An extended description of the thermal diffusivity singular behavior of difluoromethane near the critical point. Vestnik Mezhdunarodnoi akademii kholoda. 2017. No 4. p. 59-65

Abstract
The validity of the available theoretical and empirical descriptions of the asymptotic and nonasymptotic behavior of the transport properties of fluids close to the critical point is examined. A crossover formalism developed by Olchowy and Sengers for the thermal diffusivity near the vapor–liquid point and far away from it is considered for difluoromethane (refrigerant HFC-32). The transport properties were expressed as the sum of two contributions: regular or background in the absence of critical fluctuations and the critical part. Very close to the critical point the critical part of thermal diffusivity satisfies a Stokes–Einstein relation, but to interpret the actual behavior of the thermal diffusivity in the critical region two crossover functions have been used to describe the crossover from the singular behavior to the regular behavior where the critical part is negligible. For the calculation of the densities and the various thermodynamic properties of difluoromethane in the critical region and to make a comparison with theoretical results it was applied an accurate crossover equation of state developed by Rykov et al. describing the thermodynamic surface not only in a regular part and also in the neighborhood of critical point. For the critical temperature, pressure and density of difluoromethane (refrigerant HFC-32) have been adopted the values pc = 5.7847 MPa, Tc = 351.255 K, ρc= 424 kg·m–3.

Keywords: thermal diffusivity, critical region, singularity, refrigerant HFC-32, difluoromethane.

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