The conductive heat transfer through rarefied gases composed by rigid rotators and confined between coaxially placed cylinders maintained at different temperatures is investigated on the basis of the Holway and Rykov kinetic models as well as on the Boltzmann equation via the DSMC scheme supplemented by the Borgnakke–Larsen collision model. The translational and rotational parts as well as the total temperature and heat flux distributions are computed and their behavior in terms of the gas rarefaction, the temperature difference between the cylinders and the ratio of the radii is investigated. The two kinetic models and the DSMC method provide results which are in good agreement for HS and VHS molecules. Furthermore, very good agreement with available experimental data for polyatomic gases has been observed at small and large temperature differences validating the implemented modeling. Qualitatively the behavior of the dimensionless total macroscopic quantities is similar to that of the monatomic ones. Quantitatively however, the heat fluxes of polyatomic gases are significantly higher than the corresponding monatomic ones. Also, as the amount of the elastic compared to the inelastic collisions is increased, the translational heat fluxes are increased and they tend to the monatomic ones, while always the rotational heat fluxes are about 50% and 75% of the translational ones for linear and non-linear rigid rotators, respectively. It is clearly demonstrated that heat transfer simulations through rarefied polyatomic gases in MEMS and other devices cannot rely on typical monatomic modeling. On the contrary, reliable kinetic modeling for polyatomic gases must be implemented.

Conductive heat transfer in a rarefied polyatomic gas confined between coaxial cylinders

FREZZOTTI, ALDO;
2014-01-01

Abstract

The conductive heat transfer through rarefied gases composed by rigid rotators and confined between coaxially placed cylinders maintained at different temperatures is investigated on the basis of the Holway and Rykov kinetic models as well as on the Boltzmann equation via the DSMC scheme supplemented by the Borgnakke–Larsen collision model. The translational and rotational parts as well as the total temperature and heat flux distributions are computed and their behavior in terms of the gas rarefaction, the temperature difference between the cylinders and the ratio of the radii is investigated. The two kinetic models and the DSMC method provide results which are in good agreement for HS and VHS molecules. Furthermore, very good agreement with available experimental data for polyatomic gases has been observed at small and large temperature differences validating the implemented modeling. Qualitatively the behavior of the dimensionless total macroscopic quantities is similar to that of the monatomic ones. Quantitatively however, the heat fluxes of polyatomic gases are significantly higher than the corresponding monatomic ones. Also, as the amount of the elastic compared to the inelastic collisions is increased, the translational heat fluxes are increased and they tend to the monatomic ones, while always the rotational heat fluxes are about 50% and 75% of the translational ones for linear and non-linear rigid rotators, respectively. It is clearly demonstrated that heat transfer simulations through rarefied polyatomic gases in MEMS and other devices cannot rely on typical monatomic modeling. On the contrary, reliable kinetic modeling for polyatomic gases must be implemented.
Kinetic theory, DSMC, Holway model, Rykov model, Micro heat transfer, Micro pirani sensor, Vacuum technology
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11311/844592
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