Heat Transfer in Turbulent Channel Flows of Polyatomic Gases with Variable Physical Properties

Resumo

Universal relationships for boundary layer characteristics are used to derive an equation for the Nusselt number, which describes heat transfer in turbulent gas flows in straight and smooth channels. The equation contains the structural parameter that takes account of the influence of the variability of physical properties of the heat carrier on heat transfer. Analysis of quasi-thermal flow conditions showed that the derived equation agrees well with the Petukhov and Kirillov formula. The influence of the temperature factor T
_w/T
_av in the 0.2–5 variation range on heat transfer of the gas flows is analyzed. The results of calculations of heat transfer of air flow under conditions of variability of its physical properties are compared with theoretical and experimental data of other authors. It was found that, apart from the temperature factor, the Re number and atomicity of the gas affect the Nu/Nu₀ ratio (Nu₀ corresponds to constant properties). The nature of these influences differs for heating and cooling of the gas flow. For gases with atomicity higher than 8, heat transfer becomes self-similar with respect to the number of atoms in the gas molecule.