THEORETICAL AND EXPERIMENTAL-STUDY OF NATURAL-CONVECTION PIPE FLOWS AT HIGH RAYLEIGH NUMBER

A combined theoretical and experimental study is performed to investigate natural convection pipe flows at high Rayleigh number. The wall conduction effects and thermal property variations of the fluid and pipe wall are also considered in the analysis. A low-Reynolds-number k-epsilon turbulence model is employed to treat the transitional and turbulent flow regime including buoyancy effects. The predicted and measured distributions of wall temperature and Nusselt number are in good agreement. Empirical correlations for the induced flow rate and average Nusselt number are proposed. Results show that the characteristics of natural convection heat transfer in a vertical pipe approach those along a single vertical plate for large Rayleigh number.