Direct numerical simulation of supercritical CO2 near the critical point flowing over a single Stefan flow-affected spherical particle

Abstract

scCO2 (supercritical CO2) is now an efficient, clean, and pollution-free solvent widely used in industrial productions, such as extraction, printing and dyeing, as well as pharmaceutical productions. In general, a radial mass flux will exist on the surface of active component particles or drug particles during the process of particle dissolution or re-forms due to variations in operating condition of scCO2, which is called Stefan flow. Comparing with the conventional fluids (0.744 < Pr(Prandtl number) < 1.5), typical high-Pr characteristic (Pr > 10) of scCO2 near critical point will present a unique heat transfer performance, while the relative variations of density and viscosity near critical point affect the mechanics characteristic of particle and distribution details of flow field near particle surface, especially considering the effect of different intensities and directions of Stefan flow. To this, based on the PR-DNS (Particle Resolve-Direct Numerical Simulation) method, this work investigates the Stefan flow-affected drag of the sphere, the flow and temperature field near sphere surface, as well as the interphase heat transfer on the sphere surface. We pay more attention to the high-Pr characteristic and relative variations of density and viscosity of scCO2 near critical point. Results point out that the correlation of Nu (Nusselt number) vs. Resf (Stefan Reynolds number) is no longer linear compared with the cases of conventional fluids, and variable physical properties lead larger drag coefficient while worse heat transfer performance.