The significance of the buffer zone of boundary layer on convective heat transfer to a vertical turbulent flow of a supercritical fluid

Abstract

A two-dimensional model is developed to simultaneously solve the momentum and energy equations in order to predict convective heat transfer to an upward turbulent flow of supercritical carbon dioxide in a round tube. It is very important to choose a proper turbulence model. An appropriate turbulence model, based on the previous studies, has been selected. The main focus of the present study is on significance of the buffer zone in the boundary layer. The results of this study indicate that in enhanced regime of heat transfer, the peak of heat transfer coefficient occurs when the pseudo-critical temperature, or the situation of maximum heat capacity, lies within the buffer layer. In deteriorated regime of heat transfer, the extent of the laminar sub-layer appears to be changed so that the buffer zone is experienced at a farther distance from the wall. This causes a delay in the turbulent diffusion near the wall and leading to a jump in the wall temperatures.