Abstract: Horizontal flow of supercritical carbon dioxide (S-CO₂) will flow stratification under heating or cooling conditions, resulting in different heat transfer phenomena at the top and bottom of the tube. In order to study the flow heat transfer behavior driven by upward lift in vertical flow direction, the development process of S-CO₂ natural convection and the influence of pressure, pipe diameter and temperature interval on the development process are studied based on a two-dimensional circular cavity physical model. The results show that the development process of flow heat transfer away from the pseudo-critical temperature range is relatively stable compared with the pseudo-critical temperature range. In the pseudo-critical temperature range, the higher the pressure, the faster the heat transfer development process. In the pseudo-critical temperature range, the larger the diameter of the pipe, the longer the time for heat transfer to reach stability, and the more intense the main flow zone is in the initial stage of development.

Key words: supercritical carbon dioxide, flow heat transfer, natural convection, numerical simulation