Investigation of natural convection flow and heat transfer characteristics of liquid/supercritical CO2 at constant volume

Abstract

In this paper, a CFD model was used to study the natural convection of CO₂ under different initial states in a cylindrical closed high-pressure chamber. Under the premise of constant total power and heat input, the heating methods are central heating, external circumferential heating and bottom heating. The effects of CO₂ properties and heating scheme on the flow field structure, temperature stratification and flow heat transfer of the medium in the closed chamber were analysed by numerical model. It was found that in most cases, with the development of flow in the cavity, the boundary layer velocity is further weakened, the wall heat transfer tends to be stable, and one or more vortices are formed at the bottom of the cavity. The choice of heating scheme leads to significant changes in the structure of natural convection flow field in the cavity. The corresponding heat transfer coefficient of bottom heating is usually 3–5 times that of the other two heating schemes and the field temperature uniformity is better. When the temperature is close to the pseudo-critical point, the wall heat transfer is enhanced, but the fluidity shows different rules under different heating schemes. Overall, it is recommended to use internal heating, and the heating element is placed horizontally near the lower end of the cavity.