Effect of the variable physical properties on sub- and supercritical CO2 flowing over a stationary spherical particle

Abstract

In industrial applications, the phenomenon of sub- and supercritical fluid flowing over particles is highly common. Like other fluids, when the operating temperature and pressure of CO2 are near the critical point, the thermal conductivity, density, viscosity, and specific heat capacity, which affect the flow and heat transfer of the fluid, vary drastically. To study these phenomena, we use particle-resolved direct numerical simulation without considering the role of gravity and buoyancy to study the drag and heat transfer of subcritical CO2 flowing over a heated spherical particle as well as supercritical CO2 flowing over a cooled spherical particle in the process of crossing critical temperature. We compare the results with those of a fluid with constant physical properties. The study considers Reynolds numbers from 10 to 200. By analyzing the thickness of the velocity boundary layer and temperature boundary layer near the particle surface under different operating conditions and considering the variations in the fluid physical properties, we elucidate how the drag and heat transfer depends on the operating conditions. The results show that increasing the particle-surface temperature increases the drag coefficient under all operating conditions, although the effect on heat transfer differs. In addition, the effect of pressure on drag and heat transfer also depends on the operating conditions. For a given range of operating pressure and temperature, we propose correlations between the drag coefficient and the Nusselt number that are based on well-established correlations and applicable to the processes involving trans-critical temperature dynamics.