An analytical model for decaying swirl flow and heat transfer inside a tube

Decaying swirl flow can enhance the heat transfer inside a tube. For the de caying swirl flow of which maximum tangential velocity is located in the im mediate vicinity of the wall, an analytical model based on the fluid theore m about the moment of momentum is proposed for the local maximum tangential velocity, local friction factor, and local Nusselt number in this paper. T he analytical solutions compare favorably with the experimental data. Influ ences of the Reynolds number, wall roughness and initial tangential-to-axia l velocity ratio on the decaying characteristics of the friction factor and Nusselt number have been analyzed. The analytical results show that the sw irl flow decays more rapidly at the initial segment; for same conditions, t he friction factor decays more severly than the Nusselt number; relative to the values of the nonswirl flow, the friction factor increases more intens ely than the Nusselt number.