The effect of density pulsations in the field of a buoyancy force on heat transfer and turbulent fluid flow in a vertical pipe at supercritical pressures

Regimes of deteriorated (with peaks of the wall temperature) heat transfer are calculated for a turbulent buoyant flow and down flow of carbon dioxide under supercritical pressure in a vertical pipe, as well as in a horizontal round pipe. The calculations involve a system of motion, continuity, and energy equations written in the narrow channel approximation. These equations are solved by the finite difference method. A model of turbulent stress and turbulent thermal flow takes into account the influence of density pulsations in the field of the buoyancy force and in the presence of thermal acceleration of the flow. Regimes with a small influence of the buoyancy force are considered. The calculation results for the variation in the wall temperature and resistance coefficients along the pipe agree well with the experimental data. An explanation for the appearance of a peak in the wall temperature distribution along the pipe in the region where the fluid temperature is close to the pseudocritical temperature is presented.